Open access peer-reviewed chapter

Cellular-Defined Microenvironmental Internalization of Exosomes

Written By

Amber Gonda, Ron Moyron, Janviere Kabagwira, Paul A. Vallejos and Nathan R. Wall

Submitted: 03 December 2018 Reviewed: 25 March 2019 Published: 20 April 2019

DOI: 10.5772/intechopen.86020

From the Edited Volume

Extracellular Vesicles and Their Importance in Human Health

Edited by Ana Gil De Bona and Jose Antonio Reales Calderon

Chapter metrics overview

1,906 Chapter Downloads

View Full Metrics


The extracellular environment exhibits a potent effect on cellular growth and development. Exosomes secreted into this milieu carry functional proteins and nucleic acids from the cell of origin to recipient cells, facilitating intercellular communication. This interaction is particularly influential in the tumor microenvironment, transporting oncogenes and oncoproteins within a tumor and to distant sites. The mechanisms by which cells internalize exosomes vary greatly and the factors dictating this process are still unknown. Most cancers show evidence of exosomal transfer of material, but differences in cell type can dictate the effectiveness and extent of the process. Improving therapeutics requires addressing specific cellular functions, illustrating the need to better understand the forces involved in exosome-cell interactions. This review summarizes what is known about the different types of cells that play a role in exosome internalization.


  • exosome
  • endocytosis
  • receptors
  • internalization
  • uptake

1. Introduction

Intercellular communication is essential to homeostasis and is largely dependent on the cellular secretome [1]. An emerging awareness of the role that the extracellular environment plays is evident in the field of secreted vesicles. The vesicular contribution to the tumor microenvironment (TME) has furthered our understanding of the communication between cells and the surrounding stroma [2]. This relationship has also elucidated many potential therapeutic targets and possible transporters of chemotherapeutics [3, 4]. There are multiple extracellular vesicle types, characterized by biogenesis, size, and common protein markers [5, 6]. Of these, exosomes are the smallest, with sizes ranging from 30 to 150 nm [6]. These vesicles have the most complex synthesis, emerging from the endocytic pathway. They arise from intraluminal invaginations into a multivesicular body (MVB) and are released from the cell when the MVB fuses with the plasma membrane. Exosomes consist of intracellular material surrounded by a lipid membrane that reflects the cellular membrane of the host cell [7]. These specific vesicles have demonstrated promise in several fields of research, including rheumatoid arthritis [8, 9] and neurodegenerative disease [10], but primarily in cancer [11, 12]. Tumor-derived exosomes (TEX) contain oncoproteins and oncogenes from the cell of origin and thus are very influential in intercellular communication. Numerous studies have used these luminal proteins and genes to better understand tumor growth and metastasis, as well as for improving diagnostic, prognostic, and therapeutic methods [13, 14].

While there has been an exponential growth in research focused on exosome biology, clarification on the mechanisms of transport between the cell of origin and the recipient cell is essential to maximizing on exosome potential in treating and diagnosing disease. The methods by which exosomes influence the cells with which they interact are still under review. Some exosomes have been shown to fuse to the recipient cell [15, 16], while others are internalized by specific receptor-ligand interactions [17, 18] or by stimulating an indirect uptake by macropinocytosis [19]. Exosome binding to cells has been seen both as a mechanism of transferring luminal contents [15, 16] and as an initial step in the endocytosis process [17, 20]. The significance of the effects of cell-exosome binding in comparison to internalization is still unknown. Most types of endocytosis have been described in the process of exosome uptake [21], but which factors determine the specific mechanism used, are still unclear. Previous reviews have clearly identified a number of ligands and receptors involved in exosome trafficking [21, 22, 23], but little is known about the dependence of uptake mechanism on cell-type. This review presents the current understanding of the endocytosis process utilized by specific cells involved in exosomal internalization.


2. Endocytosis pathways

Endocytosis is a basic cellular function that is performed by all cell types in the process of maintaining homeostasis. Many of the molecules essential for cellular function are small enough to cross the cell membrane either passively or actively, however, other structures, such as exosomes, are too large and require a more complicated process. This general process of internalization is called endocytosis and is separated into various types based on the shape [24] and the size of particles internalized [25]. There are many well-written reviews covering the specifics of the endocytic pathways [25, 26], but here we will address them only superficially. Classification under the umbrella of endocytosis varies, but the major methods include phagocytosis, macropinocytosis, clathrin-mediated endocytosis, caveolin-mediated endocytosis, and clathrin/caveolin-independent or lipid raft-mediated endocytosis [25, 26]. Receptor-mediated endocytosis (RME) is an additional type that is often considered to be a subcategory under several of those previously mentioned (Figure 1).

Figure 1.

Endocytosis pathways involved in exosome uptake: (A) Phagocytosis, (B) Macropinocytosis, (C) Clathrin-mediated endocytosis, (D) Caveolin-mediated endocytosis, (E) Lipid Raft-dependent or clathrin−/caveolin-independent endocytosis, (F) Receptor-mediated endocytosis.

2.1 Phagocytosis

Phagocytosis is the mechanism by which specialized cells (such as macrophages and monocytes) engulf large particles (>0.5 μm) by way of receptor/ligand interactions [25, 27] (Figure 1A). Promiscuous receptors allow for a broad range of ligand recognition and binding, facilitating a key role phagocytes play in clearing apoptotic cells [27]. Exosomes, derived from a diverse population of cells, present a vast array of available ligands that make phagocytes ideal recipient cells. This process of phagocytosis is designed to not only internalize extracellular material by enveloping it, but also to regulate the immune response by presenting degraded proteins as antigens on the phagocyte surface [25]. Tumor-derived exosomes influence immune involvement in the tumor [28, 29] which may be facilitated by this mechanism of endocytosis. Other non-phagocytic cells, such as epithelial cells, Sertoli, liver endothelial, astrocytes, and cancer cells have also been shown to perform phagocytosis [27], potentially expanding the impact of exosomal communication. It is therefore important to define how the process of phagocytosis influences exosome function and if that influence is cell type dependent.

2.2 Macropinocytosis

While phagocytosis or “cell eating” involves ingestion of large molecules, macropinocytosis (“cell drinking”) internalizes slightly smaller particles (>1 μm) [25] (Figure 1B). This method is a way for cells to sample the external environment without specific receptors or ligands. It is a constitutive process in specialized antigen presenting cells, but is stimulated by growth factors in most others [30]. Macropinocytosis has a unique membrane ruffling process caused by projections from the cell surface encircling extracellular fluid and fusing to the membrane [25], resulting in an increased membrane surface area and volume of engulfed material. Nakase et al., showed that stimulation of the epidermal growth factor (EGF) receptor, either by soluble EGF or exosome-bound, increased exosome internalization 27-fold through the activation of macropinocytosis [19].

2.3 Clathrin-dependent endocytosis

The next three mechanisms, clathrin-dependent, caveolae-dependent, and clathrin/caveolae-independent, are facilitated by specific membrane proteins/structures: clathrin, caveolae, and lipid rafts. Clathrin is an intracellular protein that forms a coat around an invaginating vesicle facilitating formation and internalization [31] (Figure 1C). These vesicles internalize material around 120 nm [25], which is within the exosome size range. Stimulation can occur through receptor/ligand mediation or can be constitutive, depending on cell-type and receptor presence, but clathrin-mediated endocytosis (CME) occurs in all cell types [31]. Data continues to show that the extracellular cargo of these clathrin-coated vesicles can drive the specific mechanisms and protein interactions of internalization [32], giving way for exosome surface proteins to influence uptake. Two proteins used extensively to describe the details of CME are transferrin (Tf) and low density lipoprotein (LDL) and their respective receptors [25], which are all (except LDL) found on the surface of exosomes [33, 34]. Overexpression of transferrin receptors on cancer cells [35] may also contribute to increased exosomal uptake and clathrin-mediated endocytosis in tumors, as there have been shown to be 50–80 percent more receptors on the cancer cell compared to the non-cancer cell [36].

2.4 Caveolin-dependent endocytosis

Caveolin is similar to clathrin, as it forms a coat around membrane invaginations called caveolae and facilitates the entry of extracellular material (Figure 1D). These are particularly prevalent on endothelial cells but have been found on a wide distribution of cell types [25]. Caveolae are about half the size of clathrin-coated vesicles, limiting their cargo to smaller structures [25] but still covering some of the exosome size range. This type of endocytosis as well as lipid raft-dependent uptake, plays a key role in lipid transport and homeostasis [25]. One of the defining factors of the exosome membrane is its slightly altered lipid profile, which has been shown to influence internalization [37]. Two proteins commonly active in caveolae-dependent endocytosis, which have also been identified on the surface of exosomes, are the insulin receptor and albumin [34, 38, 39]. The cellular insulin receptor itself has also recently been found to influence exosome uptake [18].

2.5 Lipid raft dependent or clathrin-/caveolin-independent endocytosis

Lipid dependence is not only characteristic of caveolae-dependent endocytosis, but also clathrin/caveolae-independent processes. Lipid raft-dependent (or clathrin/caveolae-independent) endocytosis is similar to caveolae-dependent, except for the absence of the protein cav-1. Lipid rafts are 40-50 nm sections of the membrane with a high percentage of glycosphingolipids and cholesterol, and are anchoring points for many membrane proteins [40]. Lipid rafts are involved in exosome biogenesis and trafficking [41, 42, 43] and exosome uptake has been reduced by blocking lipid raft endocytosis [44] (Figure 1E).

2.6 Receptor mediated endocytosis

As mentioned previously, RME is an endocytosis pathway that can fit under several of the other categories (Figure 1F). The term and pathway were originally considered to be interchangeable with CME, but it is now understood that not all RME is dependent on clathrin [25]. Receptor-ligand interactions play a role in phagocytosis [25, 27], macropinocytosis [19], and lipid raft-dependent endocytosis [40]. Exosome internalization has been linked to multiple receptor-ligand interactions in each of these pathways [19, 20]. Each subtype of endocytosis has been identified in the exosome internalization process (Table 1) but additional research is needed to determine the driving factors behind the specific mechanisms. One hypothesized factor is that the recipient cell type may determine the specific type of internalization.

Endocytosis pathway Recipient cell type Recipient cell line Exosome cell of origin References
Phagocytosis Macrophage RAW264.7 Leukemia cell (K562 or MT4) [20]
Macrophage J774 Rat reticulocyte [52]
Macrophage Primary Trophoblast (Sw71) [58]
Monocytes Primary Activated T cell [50]
Macrophage Peritoneal Mouse melanoma cell (B16BL6) [51]
Macrophage Mouse bone marrow-derived Mouse CRC (CT-26) [54]
Microglia MG6 Pheochromocytoma (PC12) [117]
Microglia BV-2 Neuron (N2a) [49]
Dendritic cell Mouse primary Mouse dendritic cell [15]
Epithelial Ovarian cancer (SKOV3) Ovarian cancer cell (SKOV3) [97]
Epithelial Alveolar cells (A549) Dendritic cell [66]
Macropinocytosis Epithelial Cervical cancer (HeLa) Epidermoid carcinoma (A431) [90]
Epithelial Epidermoid carcinoma (A431), Pancreatic carcinoma (MIA PaCa-2) Cervical cancer cell (HeLa) [19]
Epithelial Ovarian cancer (SKOV3) Ovarian cancer cell (SKOV3) [97]
Epithelial Breast cancer (MCF7) Normal breast epithelial cell (MCF-10A)—exosome mimetics [96]
Endothelial Cerebral vascular (hCMEC D3) Macrophage (RAW264.7) [89]
Microglia Primary mouse Mouse oligodendrocyte (Oli-neu) [56]
Neuron precursor cell Pheochromocytoma (PC12) Pheochromocytoma (PC12) [114]
Clathrin-mediated endocytosis Epithelial Ovarian cancer (SKOV3) Ovarian cancer cell (SKOV3) [97]
Epithelial Alveolar cells (A549) Dendritic cell [66]
Epithelial Gastric cancer (AGS, MKN1) Gastric cancer cell (AGS, MKN1) [94]
Epithelial Breast cancer (MCF7) Normal breast epithelial cell (MCF-10A)—exosome mimetics [96]
Endothelial Cerebral vascular endothelial (hCMEC D3) Macrophage (RAW264.7) [89]
Endothelial Brain microvascular endothelial Embryonic kidney cell (Hek293T) [87]
Neuron Cortical mouse neuron Oligodendrocyte (Oli-neu) [115]
Neuron precursor cell Pheochromocytoma (PC12) Pheochromocytoma (PC12) [114]
Caveolin-dependent endocytosis Epithelial Cervical cancer (HeLa) Epidermoid carcinoma (A431) [90]
Epithelial (CNE1, HONE1, NU-GC-3, A549) EBV-infected B cells [95]
Epithelial Breast cancer (MCF7) Normal breast epithelial cell (MCF-10A)—exosome mimetics [96]
Endothelial Cerebral vascular endothelial (hCMEC D3) Macrophage (RAW264.7) [89]
Endothelial Brain microvascular endothelial Embryonic kidney cell (Hek293T) [87]
Lipid raft-dependent endocytosis Dendritic cell Mouse primary Mouse dendritic cell [15]
Dendritic cell (DC), T cell Monocyte derived primary DC, T cell (Jurkat) T cell (Jurkat) [75]
Epithelial, endothelial Glioblastoma (U87), umbilical vein endothelial (HUVEC) Glioblastoma (U87) [43]
Epithelial Ovarian cancer (SKOV3) Ovarian cancer cell (SKOV3) [97]
Epithelial Breast carcinoma (BT549) Breast carcinoma (BT549) [44]
Epithelial, macrophage, endothelial Melanoma (A375), (RAW264.7), dermal microvascular endothelial (HMVEC) Melanoma (A375) [46]
Endothelial Brain microvascular endothelial Embryonic kidney cell (Hek293T) [87]
B cell Mantle cell lymphoma (Jeko1) Mantle cell lymphoma (Jeko1) [61]

Table 1.

Endocytosis pathways involved in exosome internalization in various cell types.


3. Cell type-specific internalization of exosomes

3.1 Phagocytes

As introduced previously, some cells are uniquely designed to internalize extracellular material through phagocytosis. Those cells generally considered “professional” phagocytes are monocytes, macrophages, and neutrophils [25] with dendritic cells, osteoclasts, and eosinophils occasionally included [27]. Phagocytosis is dependent on receptor/ligand interactions, relying on a vast array of different receptors and ligands. Some of the established receptors include Fc receptors, integrins, pattern-recognition receptors, phosphatidylserine (PS) receptors, and scavenger receptors [45]. Macrophage uptake of exosomes has been shown to involve many of these receptors including scavenger receptors [46, 47, 48], PS/PS receptors [20, 48, 49, 50, 51], lectins [17, 52, 53] and Fc receptors [54].

However, internalization of extracellular material by phagocytes does not always fit perfectly with the hallmarks of phagocytosis. Some phagocytic receptors, such as integrins (αvβ3), scavenger receptors (CD68 and CD36), and CD14, facilitate the tethering of apoptotic cells to the phagocyte surface, but then are unable to initiate internalization without other means, such as PS and PS receptor binding [55]. The PS/PS receptor interaction also stimulates membrane ruffling and vacuole appearance—classic hallmarks of macropinocytosis [55]. Phagocytes are primarily involved in phagocytosis, but this evidence supports the idea that multiple modes of endocytosis are operational in the same cell. This is not unique to apoptotic cell uptake, but has been seen with exosome internalization by microglia (phagocytic cells in the brain) exhibiting a dependence on PS in a macropinocytic manner [49, 56]. Cooperation between multiple receptors appears to be an important characteristic of endocytosis in phagocytic cells. Plebenak et al., showed that the scavenger receptor SR-B1 on macrophages, when blocked, reduces exosome uptake, but with further testing on melanoma cells this blocking was dependent both on the receptor as well as on cholesterol flux in the lipid rafts [46], broadening the endocytosis landscape of phagocytes to include lipid raft-dependent endocytosis.

The dependence of phagocytosis on extracellular- facing PS, which on healthy cells is expressed only on the cytosolic side of the membrane, is evidence that the material to be ingested influences the endocytic pathway of phagocytes. Further support of this interaction is found in the hypothesis that exosomes “target” specific recipient cells [48, 57]. Macrophage uptake (Figure 2A) of TEX is dependent on the presence of cellular scavenger receptors or exosomal PS [20, 46, 48, 51, 56], while non-tumor cell-derived exosomes require the presence of a heterogeneity of receptors. When internalized by macrophages and monocytes, hepatic stellate cell-derived exosomes require Fc receptors [54]; B cell, dendritic cell and reticulocyte-derived exosomes use lectins [52, 53]; trophoblast-derived exosomes bind to integrins [58]; and T cell-derived exosomes need scavenger receptors [50] (Table 2). Costa-Silva et al., showed that when comparing TEX to normal cell-derived exosomes, Kupffer cells, liver-specific macrophages, preferentially internalized TEX [57]. The significance of the exosome surface topography is therefore influential in directing a specific endocytosis pathway. Phagocytes are responsible for internalization of extracellular material and are so named based on the primary use of phagocytosis, but as seen above, other endocytic pathways are utilized, especially in the context of exosomal internalization.

Figure 2.

Cell-specific internalization of exosomes by antigen presenting cells: (A) macrophage, (B) B cell and (C) Dendritic cells each employ multiple endocytic pathways in the uptake of exosomes. Macrophages utilize multiple endocytic pathways in the uptake of exosomes. B Cells and dendritic cells (DC) both employ multiple endocytic pathways in the uptake of exsomes. Lipid rafts, integrins and adhesion molecules are used by B cells while tetraspanins and adhesion molecules are the more common receptors found in DC-exosome interactions. Intercellular adhesion molecule 1 (ICAM-1), Dendritic Cell-Specific Intercellular adhesion molecule-3-Grabbing Non-integrin (DC-SIGN).

Protein Cell type Exosome origin References
Scavenger receptor Macrophage Hek293 (embryonic kidney cells) [47]
Phosphatidylserine (PS) Macrophage, microglia Neuron, melanoma, oligodendrocytes [49, 50, 51, 56]
PS receptor Macrophage Activated T cells [50]
TIM4 Macrophage K562, MT4 (leukemia cell lines) [20]
Lectins Lymph node cells, splenic cells, pancreatic adenocarcinoma, lung fibroblast, macrophage, dendritic cell, hCMEC/D3(brain endothelial cells), platelet, HeLa Pancreatic adenocarcinoma, reticulocyte, B cell, macrophage, mesenchymal stem cell [17, 48, 52, 53, 65, 89, 72, 103]
Fc receptors Macrophage CT26 (colon carcinoma cells) [54]
Integrins Macrophage, B cell Trophoblast, pancreatic adenocarcinoma cells [17, 58]
Tetraspanins B cell, pancreatic adenocarcinoma, endothelial cell Pancreatic adenocarcinoma cells [17, 48, 106]
EGFR A431 (epidermoid carcinoma cells) HeLa cells [19]
CD11c Lymph node cells/splenic cells Pancreatic adenocarcinoma cells [17]
CD11b Lymph node cells/splenic cells Pancreatic adenocarcinoma cells [17]
CD44 Lymph node cells/splenic cells Pancreatic adenocarcinoma cells [17]
CD49d/CD106 Lymph node cells/splenic cells Pancreatic adenocarcinoma cells [17]
Tspan8 Endothelial cell Pancreatic adenocarcinoma cells [48, 106]
ICAM-1/LFA-1 Dendritic cell, hCMEC/D3 (brain endothelial cells), aortic endothelium, HUVEC Dendritic cells, pancreatic adenocarcinoma cells, T cells, macrophage [16, 17, 37, 65, 69, 89]
DC-SIGN Dendritic cell Breast milk [70]
HSPG U87 (glioblastoma cells), CAG (myeloma), HUVEC, SW780 (bladder cancer cells) U-87 cells, myeloma cells, SW780 cells [63, 99, 100, 101]
Cad-11 PC3-mm2 (prostate cancer cells) Osteoblasts [104]
Syncytin Choriocarcinoma cells Trophoblasts [105]
SNAP 25 Neuron Mesenchymal stromal cells [116]
CD62L Lymph node cells, splenic cells, pancreatic adenocarcinoma, lung fibroblasts Pancreatic adenocarcinoma [17, 48]
Galectin 5 Macrophage Reticulocyte [52]
CD169/ α2,3-linked sialic acid Lymph node cells, splenic cells B cell [53]
C-type lectin/C-type lectin receptor Dendritic cell, brain endothelial cell (hCMEC/D3) Macrophage [65, 89]
P-selectin/PSGL-1 Platelet Macrophage [72]

Table 2.

Proteins involved in exosomal uptake.

3.2 Antigen presenting cells

The antigen presenting cells (APCs) include primary phagocytes such as macrophages, but also B cells and dendritic cells [59]. The immune response is heavily dependent on the recognition of foreign structures, such as peptides, for activation. These APCs sample the extracellular environment, digest and display peptides on their surface, and then present these peptides to immune cells that can execute the response. The intercellular trafficking of immune regulating proteins, such as the major histocompatibility complexes (MHC) [28], by exosomes has the potential to either stimulate or block the immune response, dependent on the exosomal contents [17]. Uptake of exosomes plays an important role in B cell and DC cell proliferation, protein presentation, and interactions with other immune cells [17].

B cells perform multiple functions as an immune cell, including presenting antigens to T cells in order to stimulate additional immune responses. B cells traditionally operate though clathrin-mediated endocytosis, relying heavily on the B-cell receptor [60]. However, when it comes to exosome internalization, B cells have shown a greater dependence on lipid rafts and various receptors, such as adhesion molecules and tetraspanins [17] than on clathrin, indicating a preference for clathrin-independent and receptor-mediated endocytosis (Figure 2B). In analyzing B cell uptake of exosomes, using the mantle cell lymphoma (mutated immature B cell) cell line, Jeko-1, Hazan-Halevy et al., found dynamin, epidermal growth factor receptor (EGFR), and cholesterol to be involved in exosome internalization instead of clathrin [61]. EGFR is a well-established target in cancer therapy, particularly with lung cancer [62] and its role in exosome internalization may lend clarity and power to multiple existing and future chemotherapeutics. Additional exosomal surface proteins, with receptor functions, have been identified as participants in B cell internalization of TEX, including integrins (CD49) and cell adhesion molecules (intercellular adhesion molecule 1—ICAM-1/CD54 and CD62L) [17].

These protein interactions between the cell and the exosomal membranes are essential steps in the influence the exosome has on the recipient cell. Exosomes derived from myeloma cells, cancerous plasma (mature B) cells, are dependent on the interaction between exosomal fibronectin and cellular heparan sulfate in order to form a bond between cell and exosome, resulting in modification of intracellular signaling [63]. As seen with these cells, the effects caused by the exosomes are not entirely dependent on uptake, even though the standard operation of APCs requires internalization. Some exosome-cell binding (as opposed to internalization) may be sufficient, or specifically designed, to alter intracellular processes, including signaling, as is also seen with dendritic cell-derived exosomes and T cell function [16]. While the influence of heparan sulfate on internalization in B cells is still unclear, there is evidence linking heparan sulfate proteoglycans to exosomal internalization which indicates that while it wasn’t assessed in these cells, the uptake may still be present [21, 22, 23]. Whether these differing mechanisms and protein participants of uptake in the B cell population are dependent on normal versus oncologic physiology of recipient cells, or on the origin of the exosome population (tumor-derived versus non-tumor derived) is yet to be determined.

These heterogeneous protein profiles are specific to each cell type and contribute to the comparative ability of each cell to internalize exosomes. In line with the role of B cells, it was found that they readily take in exosomes, in contrast to other immune cells such as T cells and natural killer cells [61, 64]. This suggests that certain immune cells are more effective at endocytosing exosomes than others, consistent with the primary functions of these specific cell types. Additional groups have shown that while B cells internalize exosomes, the uptake is significantly less than that of macrophages and dendritic cells, but similar to T cells [17]. This was shown in non-mutated mouse cells and may also illustrate important differences between cancer cell and normal cell internalization mechanisms.

Dendritic cells (DC) can be classified as both APCs and as phagocytes since internalization of extracellular material is a crucial part of their role in the immune system. Endocytosis pathways involved in exosome uptake in these cells have been tested with various endocytic blockers, including cytochalasin D (inhibits actin polymerization), EDTA (chelates calcium), and decreased temperature (reducing active cellular processes) [15, 37, 65, 66]. As dendritic cells mature, their mode of endocytosis changes; starting first with macropinocytosis, and then in the mature cell, receptor-mediated endocytosis and phagocytosis prevails [67] (Figure 2C). Despite the evidence of phagocytosis in mature DCs, it was demonstrated that immature DCs are more adept at exosomal uptake [37, 68]. Developmental preference for exosome uptake may shed light on why cancer cells, which often have similar profiles to developing cells and are subject to continuous proliferation, are so responsive to modification by exosomes. Also, immature DCs play a role in immunologic tolerance and so are less likely to activate T cells, while mature DCs activate T cell immunity [15]. This down-regulation of the adaptive immune response by immature DCs would be advantageous for tumors and so TEX may specifically target immature DCs, explaining the increase in uptake. While the mechanism is still unknown, dendritic cells are also more likely to take up TEX or DC-derived exosomes than B and T cells, as seen with fluorescent staining in vitro and in vivo in a rat model of pancreatic adenocarcinoma [17] and flow cytometry analysis of mouse bone marrow derived cells [15]. The CD11c membrane protein present on the DC and not on the other cells, was found to be involved in the internalization of TEX, as uptake decreased in the presence of an antibody to CD11c. The expression of this protein unique to DCs may contribute to the disparity in uptake among the immune cell types [17]. Recipient cell specificity in exosome uptake and DC interconnection with immune effector cells is another potential area of immune-therapeutic manipulation.

Many of the studies of exosome internalization by DCs have revealed dependence on various adhesion molecules. The ubiquity of these proteins on exosomes, leukocytes, and endothelial cells promotes the non-specific internalization characteristic of DCs. The involvement of ICAM-1 and/or its ligand, lymphocyte function-associated antigen (LFA-1), in DC-exosome interaction has been shown both in vitro and in vivo [16, 17, 37, 65, 69]. These interactions are not unique to exosome uptake as DCs regularly depend on a wide range of adhesion molecules, including a dendritic cell-specific intercellular adhesion molecule-3 grabbing non-integrin (DC-SIGN) [70]. This particular adhesion molecule has been shown to be more effective at exosome uptake by DCs, when looking at breast milk-derived exosomes, than the ICAM-1/LFA-1 binding [71]. In addition to adhesion molecules, C-type lectin and its receptor have also been identified in DC-exosome binding [65]. These glycan binding proteins have also been identified as exosome uptake mediators in other cell types, including macrophages [52] and platelets [72].

In addition to binding to membrane receptors, dendritic cell endocytosis is dependent on lipid rafts and the lipid components of the cell membrane, particularly with viral or bacterial uptake [73, 74]. As viruses and exosomes are similar in size, endocytosis mechanisms are often common between these two structures [22]. Lipid-dependent endocytosis is evident in exosome uptake by DCs as illustrated with DC- and T-cell derived exosomes [15, 75]. While proteins have been the most common structure analyzed in connection with exosomal uptake, the membrane cholesterol concentration of recipient cells [15] as well as the lipid profile of the exosomal membrane [75] both play a role in uptake of exosomes by dendritic cells and need further clarification.

3.3 Circulating cells

In addition to the previously mentioned cells, two other circulating cells/structures have also been found to endocytose exosomes, platelets and T cells. Platelets are cell fragments involved in blood coagulation that are unique in their formation as they are devoid of a nucleus and some organelles. Despite a reduced intracellular load, they are involved in binding extracellular vesicles. They do so through the interaction of cellular P-selectin and vesicular P-selectin glycoprotein ligand-1 (PSGL-1) as well as PS [72]. Data suggests that binding facilitates fusion of the exosomes to the platelets, transferring of material and enhancing platelet coagulation activity [72]. This speaks to the impact of these exosomes on intracellular communication, both in the variability and specificity of recipient cells, since binding and fusion occurred preferentially in the activated platelets [72] (Figure 3A). The exosomes in this study came from monocytes, suggesting this interaction could be a key player in coagulation at a site of injury.

Figure 3.

Cell-specific internalization of exosomes: (A) Platelet-exosome interactions have been linked to fusion as well as the binding to PSGL-1 and phosphatidylserine, (B) T cell are influenced through their surface interactions with exosomes.

T cells are the effector cells of the immune system and intercellular communication is essential for activation. Endocytosis, while not a primary function of T cells, is important to T cell receptor signaling [76] as well as other functions. Dynamin-dependent endocytosis [76], phagocytosis [77], and RME [78] are some of the mechanisms involved in T cell interaction with its surrounding environment. In relation to exosomes, T cells operate through RME [17, 79, 80] and lipid raft-dependent endocytosis [75]. However, T cells do not always readily uptake exosomes as was found in a comparison with other blood cell types. In a peripheral blood mononuclear cell culture, when uptake by monocytes was blocked, internalization by T-cells increased [47], suggesting that T cell uptake may be an adaptive response to increased exosome concentration. When exosome uptake was compared to multiple splenic leukocytes [15] or peripheral blood leukocytes [64], T cells showed minimal internalization. T cell activity is often regulated by surface interactions with other cells, such as with the T cell receptor and the MHC II/antigen interaction with APCs. Exosomal influence on T cells may therefore operate similarly with surface interaction instead of exosome internalization (Figure 3B). When cultured with DC or DC-derived exosomes, T cells acquired functional surface molecules including MHC II from exosomes through direct exosome interaction with the T cell membrane, while still showing little evidence of internalization [81]. Mouse T cells do not express MHC II and after incubation with these exosomes, this protein was identified on the surface of the T cell, suggesting the binding of exosomes to cellular membranes is sufficient to transfer material, without internalization [81]. Further research into the transfer of material between exosomes and immune cells may elucidate the role exosomes play in immune regulation in the tumor microenvironment. Depending on the cell type involved, exosome-mediated communication and manipulation may not be entirely dependent on endocytosis.

3.4 Epithelial and endothelial cells

Epithelial and endothelial cells are responsible for lining most of the organs, spaces, and blood vessels in the body. They are in a prime position to be exposed to and actively endocytose a wide variety of extracellular material. Due to this broad selection, the specific mechanisms utilized are dependent on the cell subtype as well as the character of the endocytosed material [82, 83, 84]. With such variability, it is no surprise that exosome uptake by epithelial and endothelial cells is just as diverse (Figure 4). Cellular location of these cells is crucial in cancer biology as most of the TEX will be in close proximity to epithelial and endothelial cells either in the circulatory system or during paracrine spread in solid tumors. While there have been many studies on cell-exosome interaction in these cells, there is still much work needed to clearly understand all of the factors that dictate the endocytic mechanism of epithelial and endothelial cells from different tissues.

Figure 4.

Cell-specific internalization of exosomes: (A) epithelial and (B) endothelial cells. Epithelial cells and endothelial cells show the most diversity in exosome uptake of all the cell types. Multiple receptor involved in the internalization process are expressed on both cell types, including tetraspanins, adhesion molecules, and heparan sulfate peptidoglycans (HSPG). Intercellular adhesion molecule 1 (ICAM-1).

A unique finding in exosome studies with epithelial and endothelial cells is the dependence of uptake on intracellular signaling. Svensson et al., discovered that exosome internalization is dependent on the proper functioning of the signaling pathway, ERK1/2-HSP27 [43]. The promotion of endocytosis through intracellular signaling has been shown previously with EGFR-cSrc-ERK1/2 pathways in epithelial cells [85] and the Ras-PI3K pathway with virus uptake by fibroblasts [86]. However, little is known about how these pathways facilitate exosome internalization. The ability of exosomes to cross the blood–brain barrier and be endocytosed by the microvascular endothelial cells in the brain is also dependent on signaling. Tumor necrosis factor (TNFα) signaling, as is seen in stroke models, enhances exosome uptake [87]. Intracellular signaling may provide a regulatory mechanism to control exosome internalization. Some studies described previously have shown that fusion of exosomes to the cell membrane, without endocytosis, can influence intracellular signaling [63], but these are the first to show how intracellular signaling specifically impacts the endocytosis mechanism of exosomes. These results illustrate the complexity of exosome-cell interactions and where additional research is needed. The interdependence of exosome-cell interactions and intracellular signaling are unexplored areas with vast therapeutic potential and are necessary to better understand how extracellular vesicles influence their environment.

Other characteristics are influential in directing endocytosis in epithelial cells including vesicle size, lipid profile, and protein profile (Figure 4A). In epithelial cells, particle size dictates entry mechanism with macropinocytosis as one of the pathways operative at a size range that corresponds with exosomes [88]. This pattern is supported by multiple studies where exosome internalization was decreased when key aspects of macropinocytosis were targeted. Macropinocytosis was blocked with an inhibitor of Na+/H+ exchange (which affects Rac1 activation and actin reorganization) in human cerebral microvascular endothelial cells (hCMEC/D3) [89] and HeLa cells, as well as with an inhibitor of phosphoinositide 3-kinase (PI3K) (influences membrane ruffling and macropinosome formation) [19, 90] with concomitant decreases in exosome internalization. Assessing the same pathway but from an activating instead of inhibiting direction, exosome internalization was stimulated by activation of epidermal growth factor receptor (which activates Rac family members) in HeLa cells [19]. Membrane extensions, or filopodia, that facilitate the formation of the macropinosome and are regulated by Rac1 activation have also been shown to influence exosome internalization in hepatocyte (Huh7) and kidney (Hek293) cells [91], furthering the support that exosomes utilize macropinocytosis in multiple epithelial cell lines.

The lipid profile of the exosomes and membrane integrity of the cell are also important contributors to vesicle uptake in several different types of epithelial and endothelial cells. While macrophages readily recognize external-facing PS, these cells can also utilize exosomal PS in the process of internalization, as was shown when pre-incubating exosomes with Annexin V inhibited uptake by HeLa cells (cervical cancer epithelial cells), A375 and A431 cells (squamous skin cancer cells) [92] and in human umbilical vein endothelial cells (HUVEC) [93]. Disruption of cellular lipid raft integrity through cholesterol depletion or sequestration reduced exosome uptake in U87 human glioblastoma epithelial cells [43], hCME/D3 human cerebral microvascular cells [89], HeLa cells [43, 90], HUVECs [43, 46], and A375 cells [46]. Lipid rafts play a key role in many of the functions of epithelial cells, including the protein binding interactions between cell and extracellular environment. Also, some of the most central components to epithelial cell function are proteins that interact closely with the environment such as integrins and adhesion molecules, and are anchored into lipid rafts.

Protein interactions are essential to epithelial and endothelial function and are closely tied to several of the most common endocytosis pathways used by these cells. Clathrin-dependent endocytosis has been shown in gastric [94], nasopharyngeal [95], breast [96], ovarian cancer epithelial cells [97] and HUVECs [98]. Caveolin-dependence was seen in breast [96] and nasopharyngeal cancer [95], however, caveolin-1 showed negative regulation in glioblastoma cell lines [43] (Figure 4B). General receptor-mediated uptake has been shown with several proteins including heparan sulfate peptidoglycan (HSPG) in glioblastoma cells and HUVECs [99, 100] and in the transitional epithelial cells of the bladder [101]; intercellular adhesion molecule (ICAM1) in hCMEC/D3 cells [89], rat aortic endothelial cells [48], and HUVECs [102]; lectins in cervical cancer [103], HUVECs [102], rat aortic endothelial cells [48] and hCMEC/D3 cells [89]; cad-11 in prostate cancer [104]; syncytin proteins in choriocarcinoma [105] and tetraspanins in an in vivo rat model of pancreatic cancer [48, 106]. The nature of cellular research has limited most of the epithelial endocytosis studies to cell lines, which consist entirely of transformed cells, and it is still unknown whether these trends are translatable to normal healthy epithelial and endothelial cells. While the mechanisms remain unknown, cultured primary normal epithelial cells take up TEX [107] highlighting a role for exosome intercellular communication in normal cell physiology.

3.5 Fibroblasts

The extracellular matrix (ECM) and stroma are important contributors to cellular homeostasis and function. This is particularly evident in tumors when evaluating the role of the tumor microenvironment (TME) on the survival and progression of the tumor cells. Fibroblasts are the major component of this extracellular environment. In normal physiology, they promote stromal stability, while in cancer, they contribute to altered ECM, increased angiogenesis, and metastasis [108]. These cells are in a pivotal position to interact with circulating exosomes and their internalization can have a compounding effect on the surrounding environment. Fibroblasts have been shown to participate primarily in clathrin-mediated endocytosis [109, 110] and occasionally receptor-mediated endocytosis [111]. Interestingly, RME [48, 106] and macropinocytosis [91] are the mechanisms by which fibroblasts have been shown to internalize exosomes (Figure 5). Tetraspanins are important proteins in fibroblast function and migration [112]. This protein family is well represented on the exosomal surface and is key to the uptake in many different cell types [48]. Additionally, evidence shows that the smaller the size of the vesicle, the more likely the fibroblast is to use receptors to internalize particles [111]. These three qualities lend support to the evidence of RME as a key pathway for fibroblasts to endocytose exosomes.

Figure 5.

Cell-specific internalization of exosomes: fibroblasts. Fibroblasts take up exosomes with tetraspanins and utilize multiple endocytic pathways.

3.6 Neurons and glial cells

The nervous system is a uniquely isolated environment with limited connection to the systemic circulation. This characteristic has long impeded therapeutic delivery for brain pathologies. The potential of exosome transport, however, is particularly poignant, as exosomes have been observed selectively targeting neurons and glial cells, successfully crossing the blood brain barrier [113]. Improving our understanding of endocytosis mechanisms involved in these particular cells is essential to therapeutic progression. Clathrin-mediated endocytosis is the most commonly observed pathway with exosomal trafficking between neurons and glial cells [114, 115]. However, some neurons also utilize macropinocytosis [114] and specific receptors, such as SNAP25 (a SNARE family protein) [116], to take up exosomes (Figure 6). Microglia performs phagocytosis similar to their counterparts in the extra-neuronal environment [117]. Using exosomes from two different sources, Chivet et al., illustrated the specificity of exosome targeting seen elsewhere in the body, is also evident in the nervous system. Exosomes from a neuroblastoma cell line (N2a) were preferentially internalized by astrocytes and oligodendrocytes, whereas exosomes from cortical neurons were primarily taken up by hippocampal neurons [118]. It was also shown that pre-synaptic regions were the primary site of internalization of these exosomes [118]. Endocytosis is an important process in the pre-synaptic membrane to recycle released synaptic vesicles [119], indicating that the exosomes may capitalize on this constitutive process for entrance to the neuron. Whether exosomes primarily utilize the specific clathrin-mediated endocytosis in this region [119] or are simply taken by chance with the constant bulk endocytosis [120] still remains unclear. Exosome uptake is a developing area of neuro-research, but with significant potential for therapeutics, it is growing rapidly.

Figure 6.

Cell-specific internalization of exosomes: neurons. Neurons use similar pathways but receptor/ligand binding has less variability. Synaptosomal associated protein 25 (SNAP25).


4. Conclusion

Exosomes are internalized by a multitude of cell types and play an important role in cellular physiology. Our grasp of the mechanisms of this internalization is growing as we are better able to identify characteristics of the cell and the vesicles that facilitate uptake. Pathologic states, such as cancer, have played an integral role in our understanding of how the cellular-exosomal interaction proceeds. Clarity is still needed to better understand the mechanisms by which exosome internalization is so varied from cell to cell and within the same cell. As we have seen with fibroblasts, the vesicle size can dictate mechanism of uptake [111]. The presence or abundance of specific proteins such as scavenger receptors on macrophages [46, 47, 48] and lipid profiles in several types of cells, such as external-facing phosphatidylserine [20, 48, 49, 56] all contribute to the specificity of uptake. As has been discussed, cell type can dictate uptake mechanism, particularly with phagocytic cells and professional antigen presenting cells, but even within these specialized cells, differing mechanisms occur regularly and further evaluation is needed to parse the primary determinants.

Various types of endocytosis have been identified as possible mechanisms of intercellular transport of exosomal contents to include macropinocytosis [19, 56, 114], phagocytosis [20], clathrin-mediated [52, 114], caveolin-dependent [95], lipid raft-dependent [43, 46], and clathrin- /caveolin-independent [61] endocytosis. Though much about these processes is unique, there are some aspects where functional overlap exists between them. Macropinocytosis is a form of endocytosis that consists of membrane ruffles forming intracellular vesicles to internalize large amounts of extracellular fluid [30]. This varies from other forms of endocytosis in its formation of separate and distinct intracellular vesicles (macropinosomes) and the internalization of material that is considered non-specific exosomal has been recorded in microglia [56], human epidermoid carcinoma-derived A431 cells stimulated by endothelial growth factor receptor (EGFR) and by the pancreatic cancer MiaPaCa-2 cell line [19]. Macropinocytosis is not selective in which molecules are internalized from the extracellular environment, and so uptake may be dictated simply by proximity to the cells and not targeted by the exosome specifically [121]. However, it has been shown that some exosomes naturally induce macropinocytosis internalization [90] and others, through manipulation of exosomal content, can selectively activate this mechanism in order to increase uptake [122]. Phagocytosis is a much more common method of taking up exosomes, especially with phagocytic cells of the immune system. Feng et al., showed that two leukemia cell lines, K562 and MT4, solely utilized phagocytosis for exosome internalization [20, 121].

Four other general categories of endocytosis focus on specific cellular proteins that facilitate the uptake of particles. Clathrin and caveolin are both cytosolic proteins that form specific pits with which to internalize various substances [25]. The exact reasons why and when a cell uses clathrin, caveolin, or neither, is still incompletely understood but particle size and cell type seem to play a role [43, 115, 121]. Caveolin-dependent endocytosis is important in albumin uptake, cholesterol transport, and intracellular signaling. Due to the small size of the caveolae, its endocytosed material tends to be smaller than 60 nm [25]. Clathrin-dependent mechanisms however can internalize particles up to 120 nm. The size restrictions may indicate, with further investigation into which uptake mechanism is utilized by which cells, a possible functional difference between vesicle sizes within the current exosome size range [121]. The clathrin-dependent process is involved in many different cell types and functions ranging from vesicle recycling in the neuronal synapse to organ development and ion homeostasis [25]. Many of the common, well-known endocytosis receptors utilize clathrin coated pits, such as low-density lipoprotein receptor (LDLR) and transferrin receptor (TfR). One of the most commonly used ways to determine which of these mechanisms is in operation is through inhibitory drugs or knocking down certain key players [121]. Dynamin, a GTPase, facilitates the fission of the intracellular clathrin coated vesicle [25, 123]. Dynasore, an inhibitor of dynamin, has been utilized to effectively block endocytosis of extracellular vesicles and establish clathrin-mediated endocytosis as a mechanism of uptake for these vesicles [21, 52, 56]. Following siRNA downregulation of caveolin-1 (the primary protein involved in caveolae-dependent endocytosis), exosome internalization was significantly reduced in B cells [95, 121]. Inhibitory drugs have also been useful in the determination of a third mechanism, lipid-raft mediated endocytosis. The lipid raft is a small portion of the plasma membrane, rich in sphingolipids and sterols, that facilitates various cellular processes [124]. Use of methyl-β-cyclodextrin (MβCD), which alters the cholesterol content of the membrane and disrupts lipid rafts, has been seen by several groups to impair exosomal internalization [43, 44, 97]. While lipid raft-dependent endocytosis is the primary clathrin- and caveolae-independent mechanism, other pathways and independent interactions have been described in the internalization of exosomes [61, 124]. Endocytosis is the primary method of exosomal delivery of its contents but research is still needed to understand what determines the specific mechanism whether it is cell type, exosome type, or condition specific [121].

Exosome stability, ubiquitous presence, and influential contents make them ideal candidates for therapeutic modalities in a wide variety of pathologies. The significance of exosomal contribution to the cellular network throughout the body still carries untapped potential for conquering some of the most pressing current health challenges including cancer and neurodegeneration. Understanding how these exosomes interact with and enter the myriad of cells in the body will empower our ability to capitalize on this natural social network.


  1. 1. Zullo J, Matsumoto K, Xavier S, Ratliff B, Goligorsky MS. The cell secretome, a mediator of cell-to-cell communication. Prostaglandins & Other Lipid Mediators. 2015;120:17-20 [Epub May 6, 2015]. DOI: 10.1016/j.prostaglandins.2015.03.012
  2. 2. Quail DF, Joyce JA. Microenvironmental regulation of tumor progression and metastasis. Nature Medicine. 2013;19(11):1423-1437 [Epub Oct 11, 2013]. DOI: 10.1038/nm.3394
  3. 3. Osterman CJ, Lynch JC, Leaf P, Gonda A, Ferguson Bennit HR, Griffiths D, et al. Curcumin modulates pancreatic adenocarcinoma cell-derived exosomal function. PloS One. 2015;10(7):e0132845 [Epub Jul 16, 2015]. DOI: 10.1371/journal.pone.0132845
  4. 4. Marleau AM, Chen CS, Joyce JA, Tullis RH. Exosome removal as a therapeutic adjuvant in cancer. Journal of Translational Medicine. 2012;10:134 [Epub Jun 29, 2012]. DOI: 10.1186/1479-5876-10-134
  5. 5. Lotvall J, Hill AF, Hochberg F, Buzas EI, Di Vizio D, Gardiner C, et al. Minimal experimental requirements for definition of extracellular vesicles and their functions: A position statement from the International Society for Extracellular Vesicles. Journal of Extracellular Vesicles. 2014;3:26913 [Epub Dec 30, 2014]. DOI: 10.3402/jev.v3.26913
  6. 6. Kalra H, Drummen GP, Mathivanan S. Focus on extracellular vesicles: Introducing the next small big thing. International journal of Molecular Sciences. 2016;17(2) [Epub Feb 11, 2016]. DOI: 10.3390/ijms17020170
  7. 7. Li SP, Lin ZX, Jiang XY, Yu XY. Exosomal cargo-loading and synthetic exosome-mimics as potential therapeutic tools. Acta Pharmacologica Sinica. 2018;39(4):542-551 [Epub Feb 29, 2018]. DOI: 10.1038/aps.2017.178
  8. 8. Ahn JK, Oh JM, Lee J, Bae EK, Ahn KS, Cha HS, et al. Increased extracellular survivin in the synovial fluid of rheumatoid arthritis patients: Fibroblast-like synoviocytes as a potential source of extracellular survivin. Inflammation. 2010;33(6):381-388. [Epub Mar 3, 2010]. DOI: 10.1007/s10753-010-9196-1
  9. 9. Bokarewa M, Lindblad S, Bokarew D, Tarkowski A. Balance between survivin, a key member of the apoptosis inhibitor family, and its specific antibodies determines erosivity in rheumatoid arthritis. Arthritis Research & Therapy. 2005;7(2):R349-R358 [Epub Mar 4, 2005]. DOI: 10.1186/ar1498
  10. 10. De Toro J, Herschlik L, Waldner C, Mongini C. Emerging roles of exosomes in normal and pathological conditions: New insights for diagnosis and therapeutic applications. Frontiers in Immunology. 2015;6:203 [Epub May 23, 2015]. DOI: 10.3389/fimmu.2015.00203
  11. 11. Rak J. Extracellular vesicles—Biomarkers and effectors of the cellular interactome in cancer. Frontiers in Pharmacology. 2013;4:21 [Epub Mar 20, 2013]. DOI: 10.3389/fphar.2013.00021
  12. 12. Kahlert C, Kalluri R. Exosomes in tumor microenvironment influence cancer progression and metastasis. Journal of Molecular Medicine (Berlin, Germany). 2013;91(4):431-437 [Epub Mar 23, 2013]. DOI: 10.1007/s00109-013-1020-6
  13. 13. Couto N, Caja S, Maia J, Strano Moraes MC, Costa-Silva B. Exosomes as emerging players in cancer biology. Biochimie. 2018 (in press). [Epub Mar 21, 2018]. DOI: 10.1016/j.biochi.2018.03.006
  14. 14. Turay D, Khan S, Diaz Osterman CJ, Curtis MP, Khaira B, Neidigh JW, et al. Proteomic profiling of serum-derived exosomes from ethnically diverse prostate cancer patients. Cancer Investigation. 2016;34(1):1-11 [Epub Nov 5, 2015]. DOI: 10.3109/07357907.2015.1081921
  15. 15. Montecalvo A, Larregina AT, Shufesky WJ, Stolz DB, Sullivan ML, Karlsson JM, et al. Mechanism of transfer of functional microRNAs between mouse dendritic cells via exosomes. Blood. 2012;119(3):756-766 [Epub Oct 28, 2011]. DOI: 10.1182/blood-2011-02-338004
  16. 16. Segura E, Guerin C, Hogg N, Amigorena S, Thery C. CD8+ dendritic cells use LFA-1 to capture MHC-peptide complexes from exosomes in vivo. Journal of Immunology (Baltimore, MD: 1950). 2007;179(3):1489-1496. [Epub Jul 21, 2007]
  17. 17. Zech D, Rana S, Buchler MW, Zoller M. Tumor-exosomes and leukocyte activation: An ambivalent crosstalk. Cell Communication and Signaling: CCS. 2012;10(1):37 [Epub Nov 30, 2012]. DOI: 10.1186/1478-811x-10-37
  18. 18. Gonda AKJ, Senthil GN, Ferguson Bennit HR, Neidigh J, Khan S, Wall NR. Exosomal survivin facilitates vesicle internalization. Oncotarget. 9 Oct 2018;9(79):34919-34934. DOI: 10.18632/oncotarget.26182. eCollection 9 Oct 2018. PMID:30405884
  19. 19. Nakase I, Kobayashi NB, Takatani-Nakase T, Yoshida T. Active macropinocytosis induction by stimulation of epidermal growth factor receptor and oncogenic Ras expression potentiates cellular uptake efficacy of exosomes. Scientific Reports. 2015;5:10300 [Epub Jun 4, 2015]. DOI: 10.1038/srep10300
  20. 20. Feng D, Zhao WL, Ye YY, Bai XC, Liu RQ , Chang LF, et al. Cellular internalization of exosomes occurs through phagocytosis. Traffic (Copenhagen, Denmark). 2010;11(5):675-687. [Epub Feb 9, 2010]. DOI: 10.1111/j.1600-0854.2010.01041.x
  21. 21. Mulcahy LA, Pink RC, Carter DR. Routes and mechanisms of extracellular vesicle uptake. Journal of Extracellular Vesicles. 4 Aug 2014. DOI: 10.3402/jev.v3.24641. eCollection 2014. Review.PMID: 25143819
  22. 22. van Dongen HM, Masoumi N, Witwer KW, Pegtel DM. Extracellular vesicles exploit viral entry routes for cargo delivery. Microbiology and Molecular Biology Reviews. 2016;80(2):369-386 [Epub Mar 5, 2016]. DOI: 10.1128/mmbr.00063-15
  23. 23. French KC, Antonyak MA, Cerione RA. Extracellular vesicle docking at the cellular port: Extracellular vesicle binding and uptake. Seminars in Cell & Developmental Biology. 2017;67:48-55. [Epub 2017/01/21. DOI: 10.1016/j.semcdb.2017.01.002
  24. 24. Richards DM, Endres RG. Target shape dependence in a simple model of receptor-mediated endocytosis and phagocytosis. Proceedings of the National Academy of Sciences of the United States of America. 2016;113(22):6113-6118 [Epub May 8, 2016]. DOI: 10.1073/pnas.1521974113
  25. 25. Conner SD, Schmid SL. Regulated portals of entry into the cell. Nature. 2003;422(6927):37-44 [Epub Mar 7, 2003]. DOI: 10.1038/nature01451
  26. 26. Schmid SL, Sorkin A, Zerial M. Endocytosis: Past, present, and future. Cold Spring Harbor Perspectives in Biology. 2014;6(12):a022509 [Epub Nov 2, 2014]. DOI: 10.1101/cshperspect.a022509
  27. 27. Gordon S. Phagocytosis: An immunobiologic process. Immunity. 2016;44(3):463-475. [Epub Mar 18, 2016]. DOI: 10.1016/j.immuni.2016.02.026
  28. 28. Whiteside TL. Immune modulation of T-cell and NK (natural killer) cell activities by TEXs (tumour-derived exosomes). Biochemical Society Transactions. 2013;41(1):245-251 [Epub Jan 30, 2013]. DOI: 10.1042/bst20120265
  29. 29. Ferguson Bennit HR, Gonda A, McMullen JRW, Kabagwira J, Wall NR. Peripheral blood cell interactions of cancer-derived exosomes affect immune function. Cancer Microenvironment: Official Journal of the International Cancer Microenvironment Society. 30 Mar 2018. [Epub ahead of print] DOI: 10.1007/s12307-018-0209-1. PMID:29603062
  30. 30. Lim JP, Gleeson PA. Macropinocytosis: An endocytic pathway for internalising large gulps. Immunology and Cell Biology. 2011;89(8):836-843
  31. 31. McMahon HT, Boucrot E. Molecular mechanism and physiological functions of clathrin-mediated endocytosis. Nature reviews Molecular cell biology. 2011;12(8):517-533. [Epub Jul 23, 2011]. DOI: 10.1038/nrm3151
  32. 32. Benmerah A, Lamaze C. Clathrin-coated pits: Vive la difference? Traffic (Copenhagen, Denmark). 2007;8(8):970-982 [Epub Jun 6, 2007]. DOI: 10.1111/j.1600-0854.2007.00585.x
  33. 33. He M, Qin H, Poon TC, Sze SC, Ding X, Co NN, et al. Hepatocellular carcinoma-derived exosomes promote motility of immortalized hepatocyte through transfer of oncogenic proteins and RNAs. Carcinogenesis. 2015;36(9):1008-1018. [Epub Jun 10, 2015]. DOI: 10.1093/carcin/bgv081
  34. 34. Xu R, Greening DW, Rai A, Ji H, Simpson RJ. Highly-purified exosomes and shed microvesicles isolated from the human colon cancer cell line LIM1863 by sequential centrifugal ultrafiltration are biochemically and functionally distinct. Methods (San Diego, CA). 2015;87:11-25 [Epub Apr 19, 2015]. DOI: 10.1016/j.ymeth.2015.04.008
  35. 35. Daniels-Wells TR, Penichet ML. Transferrin receptor 1: A target for antibody-mediated cancer therapy. Immunotherapy. 2016;8(9):991-994. [Epub Jul 5, 2016]. DOI: 10.2217/imt-2016-0050
  36. 36. Singh M, Mugler K, Hailoo DW, Burke S, Nemesure B, Torkko K, et al. Differential expression of transferrin receptor (TfR) in a spectrum of normal to malignant breast tissues: Implications for in situ and invasive carcinoma. Applied Immunohistochemistry & Molecular Morphology. 2011;19(5):417-423. [Epub Feb 8, 2011]. DOI: 10.1097/PAI.0b013e318209716e
  37. 37. Morelli AE, Larregina AT, Shufesky WJ, Sullivan ML, Stolz DB, Papworth GD, et al. Endocytosis, intracellular sorting, and processing of exosomes by dendritic cells. Blood. 2004;104(10):3257-3266. [Epub Jul 31, 2004]. DOI: 10.1182/blood-2004-03-0824
  38. 38. Lajoie P, Nabi IR. Lipid rafts, caveolae, and their endocytosis. International Review of Cell and Molecular Biology. 2010;282:135-163. [Epub Jul 16, 2010]. DOI: 10.1016/s1937-6448(10)82003-9
  39. 39. Buschow SI, van Balkom BW, Aalberts M, Heck AJ, Wauben M, Stoorvogel W. MHC class II-associated proteins in B-cell exosomes and potential functional implications for exosome biogenesis. Immunology and Cell Biology. 2010;88(8):851-856. [Epub May 12, 2010]. DOI: 10.1038/icb.2010.64
  40. 40. Ewers H, Helenius A. Lipid-mediated endocytosis. Cold Spring Harbor Perspectives in Biology. 2011;3(8):a004721 [Epub May 18, 2011]. DOI: 10.1101/cshperspect.a004721
  41. 41. Pienimaeki-Roemer A, Kuhlmann K, Bottcher A, Konovalova T, Black A, Orso E, et al. Lipidomic and proteomic characterization of platelet extracellular vesicle subfractions from senescent platelets. Transfusion. 2015;55(3):507-521. [Epub Oct 22, 2014]. DOI: 10.1111/trf.12874
  42. 42. Phuyal S, Hessvik NP, Skotland T, Sandvig K, Llorente A. Regulation of exosome release by glycosphingolipids and flotillins. The FEBS Journal. 2014;281(9):2214-2227. [Epub Mar 13, 2014]. DOI: 10.1111/febs.12775
  43. 43. Svensson KJ, Christianson HC, Wittrup A, Bourseau-Guilmain E, Lindqvist E, Svensson LM, et al. Exosome uptake depends on ERK1/2-heat shock protein 27 signaling and lipid Raft-mediated endocytosis negatively regulated by caveolin-1. The Journal of Biological Chemistry. 2013;288(24):17713-17724 [Epub May 9, 2013]. DOI: 10.1074/jbc.M112.445403
  44. 44. Koumangoye RB, Sakwe AM, Goodwin JS, Patel T, Ochieng J. Detachment of breast tumor cells induces rapid secretion of exosomes which subsequently mediate cellular adhesion and spreading. PloS One. 2011;6(9):e24234 [Epub Sep 15, 2011]. DOI: 10.1371/journal.pone.0024234
  45. 45. Freeman GJ, Casasnovas JM, Umetsu DT, DeKruyff RH. TIM genes: A family of cell surface phosphatidylserine receptors that regulate innate and adaptive immunity. Immunological Reviews. 2010;235(1):172-189 [Epub Jun 12, 2010]. DOI: 10.1111/j.0105-2896.2010.00903.x
  46. 46. Plebanek MP, Mutharasan RK, Volpert O, Matov A, Gatlin JC, Thaxton CS. Nanoparticle targeting and cholesterol flux through scavenger receptor type B-1 inhibits cellular exosome uptake. Scientific Reports. 2015;5:15724 [Epub Oct 30, 2015]. DOI: 10.1038/srep15724
  47. 47. Watson DC, Bayik D, Srivatsan A, Bergamaschi C, Valentin A, Niu G, et al. Efficient production and enhanced tumor delivery of engineered extracellular vesicles. Biomaterials. 2016;105:195-205. [Epub Aug 16, 2016]. DOI: 10.1016/j.biomaterials.2016.07.003
  48. 48. Rana S, Yue S, Stadel D, Zoller M. Toward tailored exosomes: The exosomal tetraspanin web contributes to target cell selection. The international Journal of Biochemistry & Cell Biology. 2012;44(9):1574-1584. [Epub Jun 26, 2012]. DOI: 10.1016/j.biocel.2012.06.018
  49. 49. Yuyama K, Sun H, Mitsutake S, Igarashi Y. Sphingolipid-modulated exosome secretion promotes clearance of amyloid-beta by microglia. The Journal of Biological Chemistry. 2012;287(14):10977-10989 [Epub Feb 4, 2012]. DOI: 10.1074/jbc.M111.324616
  50. 50. Zakharova L, Svetlova M, Fomina AF. T cell exosomes induce cholesterol accumulation in human monocytes via phosphatidylserine receptor. Journal of Cellular Physiology. 2007;212(1):174-181. [Epub Feb 15, 2007]. DOI: 10.1002/jcp.21013
  51. 51. Matsumoto A, Takahashi Y, Nishikawa M, Sano K, Morishita M, Charoenviriyakul C, et al. Role of phosphatidylserine-derived negative surface charges in the recognition and uptake of intravenously injected B16BL6-derived exosomes by macrophages. Journal of Pharmaceutical Sciences. 2017;106(1):168-175. DOI: 10.1016/j.xphs.2016.07.022
  52. 52. Barres C, Blanc L, Bette-Bobillo P, Andre S, Mamoun R, Gabius HJ, et al. Galectin-5 is bound onto the surface of rat reticulocyte exosomes and modulates vesicle uptake by macrophages. Blood. 2010;115(3):696-705. [Epub Nov 12, 2009]. DOI: 10.1182/blood-2009-07-231449
  53. 53. Saunderson SC, Dunn AC, Crocker PR, McLellan AD. CD169 mediates the capture of exosomes in spleen and lymph node. Blood. 2014;123(2):208-216 [Epub Nov 21, 2013]. DOI: 10.1182/blood-2013-03-489732
  54. 54. Chen Z, Yang L, Cui Y, Zhou Y, Yin X, Guo J, et al. Cytoskeleton-centric protein transportation by exosomes transforms tumor-favorable macrophages. Oncotarget. 2016;7(41):67387-67402 [Epub Sep 8, 2016]. DOI: 10.18632/oncotarget.11794
  55. 55. Hoffmann PR, de Cathelineau AM, Ogden CA, Leverrier Y, Bratton DL, Daleke DL, et al. Phosphatidylserine (PS) induces PS receptor-mediated macropinocytosis and promotes clearance of apoptotic cells. The Journal of Cell Biology. 2001;155(4):649-659 [Epub Nov 14, 2001]. DOI: 10.1083/jcb.200108080
  56. 56. Fitzner D, Schnaars M, van Rossum D, Krishnamoorthy G, Dibaj P, Bakhti M, et al. Selective transfer of exosomes from oligodendrocytes to microglia by macropinocytosis. Journal of Cell Science. 2011;124(Pt 3):447-458. [Epub Jan 19, 2011]. DOI: 10.1242/jcs.074088
  57. 57. Costa-Silva B, Aiello NM, Ocean AJ, Singh S, Zhang H, Thakur BK, et al. Pancreatic cancer exosomes initiate pre-metastatic niche formation in the liver. Nature Cell Biology. 2015;17(6):816-826. [Epub May 20, 2015]. DOI: 10.1038/ncb3169
  58. 58. Atay S, Gercel-Taylor C, Taylor DD. Human trophoblast-derived exosomal fibronectin induces pro-inflammatory IL-1beta production by macrophages. American Journal of Reproductive Immunology (New York, NY: 1989). 2011;66(4):259-269 [Epub Mar 18, 2011]. DOI: 10.1111/j.1600-0897.2011.00995.x
  59. 59. Wilke CM, Kryczek I, Zou W. Antigen-presenting cell (APC) subsets in ovarian cancer. International Reviews of Immunology. 2011;30(2-3):120-126. [Epub May 12, 2011]. DOI: 10.3109/08830185.2011.567362
  60. 60. Hoogeboom R, Tolar P. Molecular mechanisms of B cell antigen gathering and endocytosis. Current Topics in Microbiology and Immunology. 2016;393:45-63. [Epub Sep 5, 2015]. DOI: 10.1007/82_2015_476
  61. 61. Hazan-Halevy I, Rosenblum D, Weinstein S, Bairey O, Raanani P, Peer D. Cell-specific uptake of mantle cell lymphoma-derived exosomes by malignant and non-malignant B-lymphocytes. Cancer Letters. 2015;364(1):59-69 [Epub May 3, 2015]. DOI: 10.1016/j.canlet.2015.04.026
  62. 62. Suda K, Mitsudomi T. Role of EGFR mutations in lung cancers: Prognosis and tumor chemosensitivity. Archives of Toxicology. 2015;89(8):1227-1240. [Epub May 20, 2015]. DOI: 10.1007/s00204-015-1524-7
  63. 63. Purushothaman A, Bandari SK, Liu J, Mobley JA, Brown EE, Sanderson RD. Fibronectin on the surface of myeloma cell-derived exosomes mediates exosome-cell interactions. The Journal of Biological Chemistry. 2016;291(4):1652-1663 [Epub Nov 26, 2015]. DOI: 10.1074/jbc.M115.686295
  64. 64. Ferguson Bennit HR GA, Oppegard LJ, Chi DP, Khan S, Wall NR. Uptake of lymphoma-derived exosomes by peripheral blood leukocytes. Blood and Lymphatic Cancer: Targets and Therapy. 2017;7:9-23. DOI: 10.2147/BLCTT.S130826
  65. 65. Hao S, Bai O, Li F, Yuan J, Laferte S, Xiang J. Mature dendritic cells pulsed with exosomes stimulate efficient cytotoxic T-lymphocyte responses and antitumour immunity. Immunology. 2007;120(1):90-102 [Epub Nov 1, 2006]. DOI: 10.1111/j.1365-2567.2006.02483.x
  66. 66. Obregon C, Rothen-Rutishauser B, Gerber P, Gehr P, Nicod LP. Active uptake of dendritic cell-derived exovesicles by epithelial cells induces the release of inflammatory mediators through a TNF-alpha-mediated pathway. The American Journal of Pathology. 2009;175(2):696-705 [Epub Jul 25, 2009]. DOI: 10.2353/ajpath.2009.080716
  67. 67. Platt CD, Ma JK, Chalouni C, Ebersold M, Bou-Reslan H, Carano RA, et al. Mature dendritic cells use endocytic receptors to capture and present antigens. Proceedings of the National Academy of Sciences of the United States of America. 2010;107(9):4287-4292 [Epub Feb 10, 2010]. DOI: 10.1073/pnas.0910609107
  68. 68. Pegtel DM, Cosmopoulos K, Thorley-Lawson DA, van Eijndhoven MA, Hopmans ES, Lindenberg JL, et al. Functional delivery of viral miRNAs via exosomes. Proceedings of the National Academy of Sciences of the United States of America. 2010;107(14):6328-6333 [Epub Mar 23, 2010]. DOI: 10.1073/pnas.0914843107
  69. 69. Xie Y, Zhang H, Li W, Deng Y, Munegowda MA, Chibbar R, et al. Dendritic cells recruit T cell exosomes via exosomal LFA-1 leading to inhibition of CD8+ CTL responses through downregulation of peptide/MHC class I and Fas ligand-mediated cytotoxicity. Journal of Immunology (Baltimore, MD: 1950). 2010;185(9):5268-5278 [Epub Oct 1, 2010]. DOI: 10.4049/jimmunol.1000386
  70. 70. Garcia-Vallejo JJ, van Kooyk Y. The physiological role of DC-SIGN: A tale of mice and men. Trends in Immunology. 2013;34(10):482-486. [Epub Apr 24, 2013]. DOI: 10.1016/
  71. 71. Naslund TI, Paquin-Proulx D, Paredes PT, Vallhov H, Sandberg JK, Gabrielsson S. Exosomes from breast milk inhibit HIV-1 infection of dendritic cells and subsequent viral transfer to CD4+ T cells. AIDS (London, England). 2014;28(2):171-180 [Epub Jan 15, 2014]. DOI: 10.1097/qad.0000000000000159
  72. 72. Del Conde I, Shrimpton CN, Thiagarajan P, Lopez JA. Tissue-factor-bearing microvesicles arise from lipid rafts and fuse with activated platelets to initiate coagulation. Blood. 2005;106(5):1604-1611. [Epub Mar 3, 2005]. DOI: 10.1182/blood-2004-03-1095
  73. 73. Lemire P, Houde M, Segura M. Encapsulated group B Streptococcus modulates dendritic cell functions via lipid rafts and clathrin-mediated endocytosis. Cellular Microbiology. 2012;14(11):1707-1719. [Epub Jun 28, 2012]. DOI: 10.1111/j.1462-5822.2012.01830.x
  74. 74. Sharma R, Ghasparian A, Robinson JA, McCullough KC. Synthetic virus-like particles target dendritic cell lipid rafts for rapid endocytosis primarily but not exclusively by macropinocytosis. PloS One. 2012;7(8):e43248 [Epub Aug 21, 2012]. DOI: 10.1371/journal.pone.0043248
  75. 75. Izquierdo-Useros N, Naranjo-Gomez M, Archer J, Hatch SC, Erkizia I, Blanco J, et al. Capture and transfer of HIV-1 particles by mature dendritic cells converges with the exosome-dissemination pathway. Blood. 2009;113(12):2732-2741 [Epub Oct 24, 2008]. DOI: 10.1182/blood-2008-05-158642
  76. 76. Willinger T, Staron M, Ferguson SM, De Camilli P, Flavell RA. Dynamin 2-dependent endocytosis sustains T-cell receptor signaling and drives metabolic reprogramming in T lymphocytes. Proceedings of the National Academy of Sciences of the United States of America. 2015;112(14):4423-4428 [Epub Apr 2, 2015]. DOI: 10.1073/pnas.1504279112
  77. 77. Alarcon B, Martinez-Martin N. RRas2, RhoG and T-cell phagocytosis. Small GTPases. 2012;3(2):97-101 [Epub Jul 14, 2012]. DOI: 10.4161/sgtp.19138
  78. 78. Shah DK, Zuniga-Pflucker JC. Notch receptor-ligand interactions during T cell development, a ligand endocytosis-driven mechanism. Current Topics in Microbiology and Immunology. 2012;360:19-46. [Epub May 15, 2012]. DOI: 10.1007/82_2012_225
  79. 79. Nanjundappa RH, Wang R, Xie Y, Umeshappa CS, Chibbar R, Wei Y, et al. GP120-specific exosome-targeted T cell-based vaccine capable of stimulating DC- and CD4(+) T-independent CTL responses. Vaccine. 2011;29(19):3538-3547. [Epub Mar 17, 2011]. DOI: 10.1016/j.vaccine.2011.02.095
  80. 80. Nolte-‘t Hoen EN, Buschow SI, Anderton SM, Stoorvogel W, Wauben MH. Activated T cells recruit exosomes secreted by dendritic cells via LFA-1. Blood. 2009;113(9):1977-1981. [Epub Dec 10, 2008]. DOI: 10.1182/blood-2008-08-174094
  81. 81. Buschow SI, Nolte-‘t Hoen EN, van Niel G, Pols MS, ten Broeke T, Lauwen M, et al. MHC II in dendritic cells is targeted to lysosomes or T cell-induced exosomes via distinct multivesicular body pathways. Traffic (Copenhagen, Denmark). 2009;10(10):1528-1542 [Epub Aug 18, 2009]. DOI: 10.1111/j.1600-0854.2009.00963.x
  82. 82. Asmat TM, Agarwal V, Saleh M, Hammerschmidt S. Endocytosis of Streptococcus pneumoniae via the polymeric immunoglobulin receptor of epithelial cells relies on clathrin and caveolin dependent mechanisms. International Journal of Medical Microbiology. 2014;304(8):1233-1246. [Epub Dec 3, 2014]. DOI: 10.1016/j.ijmm.2014.10.001
  83. 83. Devadas D, Koithan T, Diestel R, Prank U, Sodeik B, Dohner K. Herpes simplex virus internalization into epithelial cells requires Na+/H+ exchangers and p21-activated kinases but neither clathrin- nor caveolin-mediated endocytosis. Journal of Virology. 2014;88(22):13378-13395 [Epub Sep 12, 2014]. DOI: 10.1128/jvi.03631-13
  84. 84. Takano M, Kawami M, Aoki A, Yumoto R. Receptor-mediated endocytosis of macromolecules and strategy to enhance their transport in alveolar epithelial cells. Expert Opinion on Drug Delivery. 2015;12(5):813-825. [Epub Dec 17, 2014]. DOI: 10.1517/17425247.2015.992778
  85. 85. Rincon-Heredia R, Flores-Benitez D, Flores-Maldonado C, Bonilla-Delgado J, Garcia-Hernandez V, Verdejo-Torres O, et al. Ouabain induces endocytosis and degradation of tight junction proteins through ERK1/2-dependent pathways. Experimental Cell Research. 2014;320(1):108-118. [Epub Oct 22, 2013]. DOI: 10.1016/j.yexcr.2013.10.008
  86. 86. Fujioka Y, Tsuda M, Hattori T, Sasaki J, Sasaki T, Miyazaki T, et al. The Ras-PI3K signaling pathway is involved in clathrin-independent endocytosis and the internalization of influenza viruses. PloS One. 2011;6(1):e16324 [Epub Feb 2, 2011]. DOI: 10.1371/journal.pone.0016324
  87. 87. Chen CC, Liu L, Ma F, Wong CW, Guo XE, Chacko JV, et al. Elucidation of exosome migration across the blood-brain barrier model in vitro. Cellular and Molecular Bioengineering. 2016;9(4):509-529 [Epub Apr 11, 2017]. DOI: 10.1007/s12195-016-0458-3
  88. 88. Turner L, Bitto NJ, Steer DL, Lo C, D’Costa K, Ramm G, et al. Helicobacter pylori outer membrane vesicle size determines their mechanisms of host cell entry and protein content. Frontiers in Immunology. 2018;9:1466 [Epub Jul 18, 2018]. DOI: 10.3389/fimmu.2018.01466
  89. 89. Yuan D, Zhao Y, Banks WA, Bullock KM, Haney M, Batrakova E, et al. Macrophage exosomes as natural nanocarriers for protein delivery to inflamed brain. Biomaterials. 2017;142:1-12. [Epub Jul 18, 2017]. DOI: 10.1016/j.biomaterials.2017.07.011
  90. 90. Costa Verdera H, Gitz-Francois JJ, Schiffelers RM, Vader P. Cellular uptake of extracellular vesicles is mediated by clathrin-independent endocytosis and macropinocytosis. Journal of Controlled Release: Official Journal of the Controlled Release Society. 2017;266:100-108. [Epub Sep 19, 2017]. DOI: 10.1016/j.jconrel.2017.09.019
  91. 91. Heusermann W, Hean J, Trojer D, Steib E, von Bueren S, Graff-Meyer A, et al. Exosomes surf on filopodia to enter cells at endocytic hot spots, traffic within endosomes, and are targeted to the ER. The Journal of Cell Biology. 2016;213(2):173-184 [Epub Apr 27, 2016]. DOI: 10.1083/jcb.201506084
  92. 92. Al-Nedawi K, Meehan B, Kerbel RS, Allison AC, Rak J. Endothelial expression of autocrine VEGF upon the uptake of tumor-derived microvesicles containing oncogenic EGFR. Proceedings of the National Academy of Sciences of the United States of America. 2009;106(10):3794-3799 [Epub Feb 24, 2009]. DOI: 10.1073/pnas.0804543106
  93. 93. Wei X, Liu C, Wang H, Wang L, Xiao F, Guo Z, et al. Surface phosphatidylserine is responsible for the internalization on microvesicles derived from hypoxia-induced human bone marrow mesenchymal stem cells into human endothelial cells. PloS One. 2016;11(1):e0147360 [Epub Jan 26, 2016]. DOI: 10.1371/journal.pone.0147360
  94. 94. Yoon JH, Ham IH, Kim O, Ashktorab H, Smoot DT, Nam SW, et al. Gastrokine 1 protein is a potential theragnostic target for gastric cancer. Gastric Cancer: Official Journal of the International Gastric Cancer Association and the Japanese Gastric Cancer Association. 2018. [Epub Apr 29, 2018]. DOI: 10.1007/s10120-018-0828-8
  95. 95. Nanbo A, Kawanishi E, Yoshida R, Yoshiyama H. Exosomes derived from Epstein-Barr virus-infected cells are internalized via caveola-dependent endocytosis and promote phenotypic modulation in target cells. Journal of Virology. 2013;87(18):10334-10347 [Epub Jul 19, 2013]. DOI: 10.1128/jvi.01310-13
  96. 96. Yang Z, Xie J, Zhu J, Kang C, Chiang C, Wang X, et al. Functional exosome-mimic for delivery of siRNA to cancer: In vitro and in vivo evaluation. Journal of Controlled Release: Official Journal of the Controlled Release Society. 2016;243:160-171. [Epub Nov 5, 2016]. DOI: 10.1016/j.jconrel.2016.10.008
  97. 97. Escrevente C, Keller S, Altevogt P, Costa J. Interaction and uptake of exosomes by ovarian cancer cells. BMC Cancer. 2011;11:108 [Epub Mar 29, 2011]. DOI: 10.1186/1471-2407-11-108
  98. 98. Chiba M, Kubota S, Sato K, Monzen S. Exosomes released from pancreatic cancer cells enhance angiogenic activities via dynamin-dependent endocytosis in endothelial cells in vitro. Scientific Reports. 2018;8(1):11972 [Epub Aug 12, 2018]. DOI: 10.1038/s41598-018-30446-1
  99. 99. Christianson HC, Belting M. Heparan sulfate proteoglycan as a cell-surface endocytosis receptor. Matrix Biology: Journal of the International Society for Matrix Biology. 2014;35:51-55. [Epub Oct 23, 2013]. DOI: 10.1016/j.matbio.2013.10.004
  100. 100. Atai NA, Balaj L, van Veen H, Breakefield XO, Jarzyna PA, Van Noorden CJ, et al. Heparin blocks transfer of extracellular vesicles between donor and recipient cells. Journal of Neuro-Oncology. 2013;115(3):343-351 [Epub Sep 5, 2013]. DOI: 10.1007/s11060-013-1235-y
  101. 101. Franzen CA, Simms PE, Van Huis AF, Foreman KE, Kuo PC, Gupta GN. Characterization of uptake and internalization of exosomes by bladder cancer cells. BioMed Research International. 2014;2014:619829 [Epub Feb 28, 2014]. DOI: 10.1155/2014/619829
  102. 102. Jang SC, Kim OY, Yoon CM, Choi DS, Roh TY, Park J, et al. Bioinspired exosome-mimetic nanovesicles for targeted delivery of chemotherapeutics to malignant tumors. ACS Nano. 2013;7(9):7698-7710. [Epub Sep 6, 2013]. DOI: 10.1021/nn402232g
  103. 103. Shimoda A, Tahara Y, Sawada SI, Sasaki Y, Akiyoshi K. Glycan profiling analysis using evanescent-field fluorescence-assisted lectin array: Importance of sugar recognition for cellular uptake of exosomes from mesenchymal stem cells. Biochemical and Biophysical Research Communications. 2017;491(3):701-707. [Epub Jul 29, 2017]. DOI: 10.1016/j.bbrc.2017.07.126
  104. 104. Bilen MA, Pan T, Lee YC, Lin SC, Yu G, Pan J, et al. Proteomics profiling of exosomes from primary mouse osteoblasts under proliferation versus mineralization conditions and characterization of their uptake into prostate cancer cells. Journal of Proteome Research. 2017;16(8):2709-2728. [Epub Jul 5, 2017]. DOI: 10.1021/acs.jproteome.6b00981
  105. 105. Vargas A, Zhou S, Ethier-Chiasson M, Flipo D, Lafond J, Gilbert C, et al. Syncytin proteins incorporated in placenta exosomes are important for cell uptake and show variation in abundance in serum exosomes from patients with preeclampsia. FASEB Journal: Official Publication of the Federation of American Societies for Experimental Biology. 2014;28(8):3703-3719. [Epub May 9, 2014]. DOI: 10.1096/fj.13-239053
  106. 106. Nazarenko I, Rana S, Baumann A, McAlear J, Hellwig A, Trendelenburg M, et al. Cell surface tetraspanin Tspan8 contributes to molecular pathways of exosome-induced endothelial cell activation. Cancer Research. 2010;70(4):1668-1678. [Epub Feb 4, 2010]. DOI: 10.1158/0008-5472.can-09-2470
  107. 107. Dutta S, Warshall C, Bandyopadhyay C, Dutta D, Chandran B. Interactions between exosomes from breast cancer cells and primary mammary epithelial cells leads to generation of reactive oxygen species which induce DNA damage response, stabilization of p53 and autophagy in epithelial cells. PloS One. 2014;9(5):e97580 [Epub May 17, 2014]. DOI: 10.1371/journal.pone.0097580
  108. 108. Bhome R, Bullock MD, Al Saihati HA, Goh RW, Primrose JN, Sayan AE, et al. A top-down view of the tumor microenvironment: Structure, cells and signaling. Frontiers in Cell and Developmental Biology. 2015;3:33 [Epub Jun 16, 2015]. DOI: 10.3389/fcell.2015.00033
  109. 109. Ng CT, Tang FM, Li JJ, Ong C, Yung LL, Bay BH. Clathrin-mediated endocytosis of gold nanoparticles in vitro. Anatomical record (Hoboken, NJ: 2007). 2015;298(2):418-427 [Epub Sep 23, 2014]. DOI: 10.1002/ar.23051
  110. 110. Veettil MV, Bandyopadhyay C, Dutta D, Chandran B. Interaction of KSHV with host cell surface receptors and cell entry. Viruses. 2014;6(10):4024-4046 [Epub Oct 25, 2014]. DOI: 10.3390/v6104024
  111. 111. Bozavikov P, Rajshankar D, Lee W, McCulloch CA. Particle size influences fibronectin internalization and degradation by fibroblasts. Experimental Cell Research. 2014;328(1):172-185. [Epub Jul 6, 2014]. DOI: 10.1016/j.yexcr.2014.06.018
  112. 112. Geary SM, Cowin AJ, Copeland B, Baleato RM, Miyazaki K, Ashman LK. The role of the tetraspanin CD151 in primary keratinocyte and fibroblast functions: Implications for wound healing. Experimental Cell Research. 2008;314(11-12):2165-2175. [Epub Jun 7, 2008]. DOI: 10.1016/j.yexcr.2008.04.011
  113. 113. Alvarez-Erviti L, Seow Y, Yin H, Betts C, Lakhal S, Wood MJ. Delivery of siRNA to the mouse brain by systemic injection of targeted exosomes. Nature Biotechnology. 2011;29(4):341-345. [Epub Mar 23, 2011]. DOI: 10.1038/nbt.1807
  114. 114. Tian T, Zhu YL, Zhou YY, Liang GF, Wang YY, Hu FH, et al. Exosome uptake through clathrin-mediated endocytosis and macropinocytosis and mediating miR-21 delivery. The Journal of Biological Chemistry. 2014;289(32):22258-22267 [Epub Jun 22, 2014]. DOI: 10.1074/jbc.M114.588046
  115. 115. Fruhbeis C, Frohlich D, Kuo WP, Amphornrat J, Thilemann S, Saab AS, et al. Neurotransmitter-triggered transfer of exosomes mediates oligodendrocyte-neuron communication. PLoS Biology. 2013;11(7):e1001604 [Epub Jul 23, 2013]. DOI: 10.1371/journal.pbio.1001604
  116. 116. Zhang Y, Chopp M, Liu XS, Katakowski M, Wang X, Tian X, et al. Exosomes derived from mesenchymal stromal cells promote axonal growth of cortical neurons. Molecular Neurobiology. 2017;54(4):2659-2673 [Epub Mar 20, 2016]. DOI: 10.1007/s12035-016-9851-0
  117. 117. Bahrini I, Song JH, Diez D, Hanayama R. Neuronal exosomes facilitate synaptic pruning by up-regulating complement factors in microglia. Scientific Reports. 2015;5:7989 [Epub Jan 24, 2015]. DOI: 10.1038/srep07989
  118. 118. Chivet M, Javalet C, Laulagnier K, Blot B, Hemming FJ, Sadoul R. Exosomes secreted by cortical neurons upon glutamatergic synapse activation specifically interact with neurons. Journal of Extracellular Vesicles. 2014;3:24722. DOI: 10.3402/jev.v3.24722
  119. 119. Granseth B, Odermatt B, Royle SJ, Lagnado L. Clathrin-mediated endocytosis is the dominant mechanism of vesicle retrieval at hippocampal synapses. Neuron. 2006;51(6):773-786. [Epub Sep 20, 2006]. DOI: 10.1016/j.neuron.2006.08.029
  120. 120. Cousin MA. Synaptic vesicle endocytosis and endosomal recycling in central nerve terminals: Discrete trafficking routes? The Neuroscientist: A Review Journal Bringing Neurobiology, Neurology and Psychiatry. 2015;21(4):413-423. [Epub Jul 17, 2014]. DOI: 10.1177/1073858414542251
  121. 121. Gonda A, Kabagwira J, Senthil GN, Wall NR. Internalization of exosomes through receptor-mediated endocytosis. Molecular Cancer Research. 2019;17(2):337-347. [Epub Nov 30, 2018]. DOI: 10.1158/1541-7786.MCR-18-0891
  122. 122. Nakase I, Noguchi K, Fujii I, Futaki S. Vectorization of biomacromolecules into cells using extracellular vesicles with enhanced internalization induced by macropinocytosis. Scientific Reports. 2016;6:34937 [Epub Oct 18, 2016]. DOI: 10.1038/srep34937
  123. 123. Lanzetti L, Di Fiore PP. Endocytosis and cancer: An ‘insider’ network with dangerous liaisons. Traffic (Copenhagen, Denmark). 2008;9(12):2011-2021. DOI: 10.1111/j.1600-0854.2008.00816.x
  124. 124. El-Sayed A, Harashima H. Endocytosis of gene delivery vectors: From clathrin-dependent to lipid raft-mediated endocytosis. Molecular Therapy. 2013;21(6):1118-1130. DOI: 10.1038/mt.2013.54

Written By

Amber Gonda, Ron Moyron, Janviere Kabagwira, Paul A. Vallejos and Nathan R. Wall

Submitted: 03 December 2018 Reviewed: 25 March 2019 Published: 20 April 2019