Abstract
Disruption of the regulatory mechanisms that control cell proliferation and cell migration results in multiple disease states including cancer and leukaemia. The proline-rich homeodomain protein (PRH)/haematopoietically expressed homeobox protein (HHEX) is a transcription factor that controls cell proliferation and cell migration in a variety of tissues in the adult and in the embryo. Phosphorylation of PRH by Protein Kinase CK2 (Casein Kinase II) stops PRH from binding to DNA and regulating the transcription of its direct target genes. In leukaemic cells, phosphorylation also results in the production of a transdominant-negative truncated PRH phosphoprotein by the proteasome. Phosphorylation of PRH is increased in breast and prostate cancer cells and the consequent loss of PRH activity increases cell proliferation and migration. PRH also regulates the proliferation of vascular smooth muscle cells and CK2-dependent phosphorylation of PRH in these cells accompanies increased cell proliferation during intimal thickening. Thus the ability of PRH to regulate cell behaviour and the control of PRH by CK2 is not limited to a specific cell type or tissue. This raises the possibility that the PRH-CK2 axis could be targeted in a variety of disease states ranging from multiple cancers to the intimal thickening that occurs in vein bypass graft failure and restenosis.
Keywords
- cell proliferation
- cell migration
- cell invasion
- tumourigenesis
- tumour growth
- restenosis
- intimal thickening
1. Introduction
The proline-rich homeodomain (PRH) or haematopoietically expressed homeobox (HHEX) protein, is a highly conserved transcription factor belonging to the homeodomain family (reviewed by Soufi et al. [1]). Originally characterised in the haematopoietic compartment [2, 3, 4], PRH has since been found in a wide variety of tissues [1]. PRH is critically important in embryonic development where it regulates anteroposterior axis formation and the development of multiple organ systems including the liver, thyroid, lung, thymus, gallbladder and pancreas [5, 6, 7, 8]. In the adult, PRH is expressed in a variety of tissues including the thyroid, lungs, liver and haematopoietic compartment [4, 9]. In these tissues PRH acts as a master regulator of genes important in cell proliferation, cell migration and invasion, and cell differentiation [1]. Changes in PRH activity therefore have profound effects on cell behaviour. This review focuses on the regulation of PRH activity by Protein Kinase CK2 and the role that this plays in tumourigenesis and in the control of vascular smooth muscle cell (VSMC) proliferation during intimal thickening.
2. The regulation of gene expression by PRH
2.1. The PRH protein
The PRH protein has three functional domains; a central homeodomain that mediates DNA binding, with N-terminal and C-terminal domains that regulate transcription ( Figure 1 ). The PRH homeodomain is a 60 amino acid sequence that forms three α helices. The second and third helices make up a helix-turn-helix motif and together with amino acids in an N-terminal arm of this domain, this mediates sequence-specific DNA binding. The mutation of asparagine to alanine at position 187 within the PRH homeodomain dramatically reduces DNA binding and prevents PRH from repressing the transcription of its direct target genes [10, 11]. The PRH homeodomain also mediates binding to transcription factor AP1 [12]. The PRH N-terminal domain can repress transcription when attached to a heterologous DNA binding domain [10, 13]. Additionally, the N-terminal domain interacts with a variety of proteins including the promyelocytic leukaemic (PML) protein, eukaryotic initiation factor 4E (eIF-4E), proteasome subunit C8, and the regulatory subunit of Protein Kinase CK2 [14, 15, 16, 17]. The C-terminal domain is rich in acidic residues and it also functions in transcriptional regulation since its loss prevents PRH from activating transcription of the sodium-dependent bile acid co-transporter (NTCP) gene [18, 19].
The PRH protein forms oligomeric complexes
2.2. The regulation of gene expression
Like many transcription factors PRH can either repress or activate transcription depending on its target gene (see Soufi et al. [1] and Gaston et al. [40] for lists of PRH target genes) and its partner proteins (shown in Figure 1 ). For example, PRH represses the Goosecoid, ESM-1, VEGFA, VEGFR-1, VEGFR-2, and thyroglobulin promoters [8, 21, 23, 24]. An Eh1 motif in PRH N-terminal domain allows PRH to recruit members the Groucho/transducin-like enhancer of split (TLE) family of co-repressor proteins which in turn recruit histone deacetylases [25]. Similarly, PRH can repress transcription by recruiting the polycomb-repressive complex 2 (PRC2) to target genes to bring about histone methylation [26]. These co-repressor interactions can bring about short- and long-range transcriptional repression through histone modification and consequent chromatin condensation. PRH can also repress transcription by interfering with other transcription factors. Binding of PRH to GATA-2 suppresses GATA-2-mediated activation of vascular endothelial growth factor receptor 2 (VEGFR-2) transcription [27]. Similarly, PRH binds to Jun and cMyc inhibiting Jun- and cMyc-dependent transcription activation, respectively [12, 28]. PRH also activates transcription through multiple mechanisms including direct binding to target promoters as in the case of the NTCP promoter [19]. Moreover, PRH binding to hepatocyte nuclear factor 1α (HNF-1α) and serum-response factor (SRF) increases HNF-1α- and SRF-activated transcription [29, 30]. In addition, PRH can regulate gene expression post-transcriptionally through binding to eIF-4E. PRH binding to eIF-4E in PML nuclear bodies disrupts these structures and blocks eIF-4E-dependent transport of cyclin D1 mRNA down-regulating cyclin D1 protein expression [15].
2.3. PRH activity in tumourigenesis
Inappropriate expression and/or aberrant subcellular localization of PRH has been observed in a variety of disease states including acute myelogenous leukaemia (AML) [31, 32], chronic myelogenous leukaemia (CML) [32], breast, thyroid, and prostate cancer [33, 34, 35, 36], liver disease, and cardiovascular disease [37, 38]. In normal haematopoietic cells PRH protein is clearly discernable in distinct foci within the nucleus, co-localising with PML and translation factor eIF-4E [14, 25], whereas in AML and CML PRH appears to be mislocalised to the cytoplasm [32]. Comparably, in thyroid cancer and breast cancer cells, PRH appears to be mislocalised from the nuclear compartment to the cytoplasm and often shows down-regulation in expression [33, 34, 35]. In breast and prostate cells loss of PRH activity results in increase cell proliferation and increased cell migration and invasion [35, 36]. Moreover, PRH over-expression in mouse mammary tumour cells inhibits tumour growth
In contrast, PRH has been shown to function as an oncoprotein in T-cell lineages and in AML subtypes (reviewed by Gaston et al. [40]). In retroviral insertion experiments in mice (Lvis1)-elevated PRH expression is associated with B-cell- and T-cell-derived leukaemias and lymphomas [41, 42]. Transgenic mice with ectopic PRH expression in T cell progenitors showed increased numbers of progenitors but this did not result in leukaemia [43]. However mice transplanted with bone marrow cells transduced with a retrovirus expressing PRH exhibit aggressive neoplastic transformation within T-cell populations [44] and in mouse models of early T-cell precursor-like acute lymphoblastic leukaemia (ETP-ALL), PRH is important in Lmo2-driven T-cell self-renewal [45, 46]. Furthermore, in a mouse model of AML elevated PRH is essential for the initiation and maintenance of the leukaemia [26]. Interestingly a human AML has been identified where alteration of the Nup98 and PRH genes to form a fusion gene is the only identified cytogenetic abnormality [31].
2.4. PRH in vascular compartments
PRH is expressed in the developing vascular system in haematopoietic and endothelial progenitor cells [9]. PRH over-expression inhibits haematopoietic and vascular development in embryoid bodies [47] while PRH loss leads to abnormal vasculogenesis and cardiac morphogenesis [5]. PRH can inhibit the proliferation of leukaemic cells by repressing the transcription of VEGFA and other genes involved in VEGF signalling and haematopoietic and vascular biology [48]. PRH is also important in neo-angiogenesis; in endothelial cells PRH represses transcription of multiple genes that control blood vessel formation including VEGFR-1, VEGFR-2, tyrosine kinase with Ig and EGF homology domains (TIE)-1, TIE-2, and neuropilin-1 [27, 49]. PRH is also targeted by urokinase-type plasminogen activator (uPA). uPA regulates angiogenesis and vascular permeability by proteolytic degradation of the extracellular matrix and through intracellular signalling. Single chain uPA is transported from the cell surface receptors to the nucleus where it modulates gene transcription by binding to transcription factors including PRH. The binding of uPA to PRH derepresses VEGFR-1 and VEGFR-2 thereby promoting their expression [50].
Importantly, PRH is up-regulated in VSMCs after balloon injury of the rat aorta [37]. During the period of cell dedifferentiation and cell proliferation following injury, PRH activates transcription of SMemb/NMHC-B, a marker for dedifferentiated cells [37]. Moreover, over-expression of PRH in embryonic fibroblasts results in the expression of early, but not late, markers of VSMC differentiation [29]. It has also been reported that in VSMCs infected with Human Cytomegalovirus (HCMV) PRH up-regulation promotes cell proliferation and inhibits apoptosis [51]. Our recent work has shown that PRH inhibits the proliferation of human and rat VSMCs (see Section 6.2 [38]). This suggests that HCMV infection may switch PRH from being an inhibitor of VSMC proliferation to an activator.
3. Protein kinase CK2
3.1. CK2 structure
Protein Kinase CK2 (formerly known as Casein Kinase II) is a ubiquitously expressed enzyme important in a range of cellular functions and processes including cell cycle progression and cell migration and invasion [52]. CK2 is a Ser/Thr kinase with the minimal consensus target sequence Ser/Thr– X – X – Asp/Glu/pSer (where X indicates any non-basic amino acid). However, CK2 can phosphorylate wide variety of target sequences. CK2 exists as a hetero-tetrameric enzyme consisting of two catalytic α subunits and two regulatory β subunits. In humans, two isoenzymic forms of the catalytic subunit, designated α and α′, are well-characterised while a more recently discovered α″ subunit is less well understood [53, 54, 55].
3.2. CK2 function
CK2 is important in the control of cell migration and cell proliferation and in many other cell functions. To this end CK2 is pleiotropic, in that it has multiple effects via the phosphorylation of numerous cytoplasmic and nuclear proteins. For example, phosphorylation of inhibitor of kappa B (IκB) by CK2 causes disassembly of the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB)-IκB complex [56]. This allows NF-κB to regulate the transcription of genes involved in cell cycle progression and cell survival. CK2 is also important in the control of extracellular proteins. For example, phosphorylation of the extracellular matrix protein vitronectin by CK2 is important for the adhesion of VSMCs [57]. CK2 itself is regulated by multiple signalling cascades and can cross talk to co-ordinate cell survival and cell proliferation. The ABL, Src and ERK kinase families all act as upstream regulators of CK2 and inhibitors that target these kinases can be used to inhibit CK2 indirectly [58, 59, 60].
3.3. CK2 in tumourigenesis
Aberrant CK2 activity has been demonstrated to be oncogenic and elevated CK2 expression is seen in multiple cancers including breast [61], prostate [62], lung [63], head and neck [64], and kidney cancers [65]. CK2-mediated abrogation of tumour suppressor activity or stimulation of oncogenic proteins has been demonstrated to play a significant role in tumourigenesis. The tumour suppressors promyelocytic leukaemia protein (PML), connexin, and phosphatase and tensin homology protein (PTEN) are all CK2 substrates that are inactivated by phosphorylation [66]. CK2 has additionally been shown to potentiate aberrant activation of oncoproteins including NF-κB [56], and AKT [67]. Drugs that inhibit CK2 have proven to be well-tolerated in a number of clinical trials and systemic or local delivery of these inhibitors is therefore a potential treatment for multiple disease states [68, 69].
4. The regulation of PRH by CK2
4.1. CK2 binds to PRH and phosphorylates the homeodomain
To identify PRH binding proteins we performed a yeast two hybrid screen using PRH as bait. This showed that the regulatory β subunit of CK2 can bind to the PRH N terminal domain [17]. The interaction was confirmed in human chronic myeloid leukaemia K562 cells using pull-down experiments and co-immunoprecipitation [17]. Importantly, PRH is a phosphoprotein in these cells and pharmacological inhibition of CK2 with DMAT (2-dimethylamino-4,5,6,7-tetrabromo-1H-benzimidazole) or TBB (4,5,6,7-tetrabromo-1H-benzotriazole) significantly reduces the amount of phosphorylated PRH (pPRH) indicating that PRH is also a CK2 substrate [17]. CK2β controls substrate specificity and therefore the interaction with PRH is potentially of importance for the control of CK2 activity on other specific substrates as well as in the phosphorylation of PRH.
To map CK2 phosphorylation sites within PRH, purified, human PRH protein was incubated with CK2 and ATP and subjected to surface-enhancer laser desorption/ionisation time-of-flight mass spectrophotometry (SELDI-TOF-MS) analysis. This showed that S163 and S177 located within the PRH homeodomain can be phosphorylated by CK2 [17]. S163 is located within a CK2 target consensus site while S177 is within a non-consensus site. Subsequently further phosphorylation sites have been identified within PRH but these sites have not been associated with a specific kinase.
4.2. Phosphorylation of PRH blocks DNA binding
Phosphorylation of the PRH homeodomain by CK2 abrogates PRH DNA-binding activity
4.3. Phosphorylation of PRH induces protein processing
Hypo-phosphorylated PRH is stable in K562 cells treated with the translation inhibitor anisomycin [48]. However, pPRH is rapidly degraded in these cells. The half-life of pPRH is extended by treatment with proteasome inhibitors showing that phosphorylation targets PRH for proteasome-mediated protein cleavage. Interestingly, pPRH is cleaved to produce is a stable truncated protein that lacks the C-terminal domain (PRHδC). Over-expression of CK2 increases the production of this cleavage product and the truncated protein can act as transdominant negative regulator of full-length PRH by sequestering TLE co-repressor proteins and possibly other PRH interacting proteins [48]. This suggests that phosphorylation of PRH not only blocks DNA binding but also acts to prevent unphosphorylated PRH from regulating transcription ( Figure 2 ). As might be expected, PRH S163C,S177C cannot be phosphorylated at these residues and this protein is not processed by the proteasome. In contrast, the phosphomimetic PRH S163E,S177E is more readily processed to produce PRHδC than wild type PRH [48].
4.4. pPRH in tumourigenesis
Pre-clinical studies have shown that pPRH is elevated in benign prostatic hyperplasias and in breast ductal carcinoma
5. PRH and CK2 in tumourigenesis
5.1. pPRH and PRH as potential biomarkers
The identification of protein modifications that contribute to increased cancer cell proliferation and increased cell migration and invasion is likely to result in new therapeutic approaches that could be of great benefit to patients. Moreover such cancer biomarkers could be useful as prognostic indicators and as indicators of pharmacologic responses to a therapeutic intervention. Prognostic biomarkers that can flag a tumour as potentially benign or requiring further treatment are urgently required. Many breast and prostate tumours for example do not need intervention and are currently over-treated by surgery because of a lack of biomarkers for prognosis. In pre-clinical studies the levels and localization of pPRH and PRH appear to be altered in breast and prostate tumours compared to controls [35, 36]. However, additional studies with large numbers of patients will be required to determine whether pPRH and PRH or the pPRH/PRH ratio is a good prognostic indicator.
5.2. The restoration of PRH function
Since PRH appears to be inactivated in breast and prostate cancer cells by CK2-dependent phosphorylation resulting in increased cell proliferation and cell migration, the inhibition of CK2 in these tissues would be expected to restore PRH function. This would be expected to inhibit cell proliferation and it could inhibit tumour growth. CK2 inhibitors have been proposed as novel treatments for multiple cancers including prostate cancer. In normal immortalised prostate epithelial cells the inhibition of proliferation brought about by the inhibition of CK2 requires the presence of PRH [35]. It is likely that CK2 inhibitors will have similar effects in other cancer cell types through the prevention of PRH phosphorylation and the restoration of PRH function. Indirect inhibition of CK2 activity can also restore PRH function and re-establish the control of cell proliferation. Our previous work showed that in chronic myeloid leukaemia cells Dasatinib decreases CK2 activity and decreases the phosphorylation of PRH [58]. Dasatinib inhibits membrane bound tyrosine kinases and Src family kinases and is an efficacious therapeutic for leukaemias expressing BCR-ABL fusion proteins and those with activated Src [70]. Importantly, Src-kinases are known to stimulate CK2 activity [59]. It is possible that other Abl/Src kinase inhibitors will also restore PRH activity via the indirect inhibition of CK2. However, since PRH can act as oncoprotein in some cell types it is possible that the reduction of PRH phosphorylation in these cell types might be counterproductive.
6. Saphenous vein graft failure
6.1. Intimal thickening in saphenous vein grafts
Atherosclerotic plaque development within coronary arteries is a major precursor for myocardial infarction (commonly known as heart attack). Coronary artery bypass graft (CABG) surgery is an effective treatment for occlusive or ruptured coronary artery atherosclerotic plaques; surgery most often involves harvesting and grafting of healthy, autologous saphenous vein to bypass the occluded artery and facilitate revascularisation of the cardiac tissue [71, 72]. Arteriovenous grafts are however predisposed to reblocking (restenosis), and despite extensive research, 10–15% of CABG patients suffer early vein graft failure within the first year after surgery, and as many as 50% suffer graft failure within 10 years [71, 72, 73]. Thrombosis, intimal thickening, and accelerated atherosclerosis are the underlying causes of saphenous vein graft failure. Intimal thickening, which serves as a foundation for superimposed atherosclerosis, is often the cause of late vein graft failure ( Figure 3 ), while thrombosis is the cause of early graft failure. Intimal thickening is a product of aberrant VSMC migration into the intima where they proliferate and deposit extracellular matrix.
6.2. PRH is up-regulated in neointimal cells
PRH expression is up-regulated in the intimal compartment of rat thoracic aortas injured with a balloon embolectomy catheter – a robust model for neointimal hyperplasia [37]. However, PRH mRNA and protein expression is absent in healthy aorta. Moreover PRH activates transcription of SMemb/NMHC-B, a marker of dedifferentiated VSMCs with a synthetic, proliferative phenotype, and not of differentiated VSMCs with a quiescent, contractile phenotype [37]. Together these findings could indicate that PRH promotes VSMC de-differentiation and accumulation in the intima, thereby accelerating disease progression. However, ectopic overexpression of wild-type PRH in primary cultures of rat aortic VSMCs inhibits cell cycle progression, whereas siRNA-mediated knockdown of PRH promotes cell proliferation [38]. These data clearly indicate an anti-proliferative role for PRH in VSMCs. Transfection of isolated rat aortic VSMCs with a vector expressing PRH F32E, a mutant that does not bind TLE, did not block cell proliferation suggesting that in these cells, PRH inhibits cell cycle progression in a TLE-independent manner (KSW unpublished observations). Interestingly, PRH S163C,S177C exhibited a prolonged anti-mitotic effect with respect to wild-type PRH [38]. This indicates that phosphorylation of PRH at Ser163 and Ser177 prevents PRH from inhibiting VSMC proliferation. Moreover, adenovirus-mediated gene transfer of PRH S163C,S177C retarded intimal thickening in an
6.3. CK2 activity during intimal thickening
Multiple studies have implicated the involvement of CK2 in the regulation of VSMC proliferation and pathophysiological intimal thickening. For example, treatment of cultured human aortic smooth muscle cells with emodin (1,3,8-trihydroxy-6-methylanthraquinone) – a naturally occurring CK2 inhibitor used in traditional Chinese medicine – blocked platelet-derived growth factor (PDGF)- and tumour necrosis factor α (TNF-α)-induced cell proliferation in a dose-dependent manner [74]. Also, in the rat aortic VSMC line A10, inhibition of CK2 with the synthetic compounds DDZ (daidzein) and DRB (5,6-dichlorobenzimidazole riboside) antagonised lysophosphatidic acid-induced cell division [75]. However, emodin, DDZ and DRB show high promiscuity as inhibitors [76]. PDGF, basic fibroblast growth factor (bFGF), and Wnt proteins are well-recognised atherogenic mitogens that are up-regulated in atherosclerotic and restenotic lesions ([38] and references therein). Interestingly, pharmacological inhibition of CK2 with the highly selective compounds TBB and K66 suppresses PDGF-, bFGF- and Wnt-4-induced cell replication in primary cultures of rat aortic VSMCs [38]. Silencing of CK2 using exogenous siRNAs also inhibited VSMC proliferation further suggesting that CK2 promotes the proliferation of these cells. Furthermore, treatment of human saphenous vein organ cultures with the CK2 inhibitor K66 disrupted neointima formation [38].
6.4. CK2 acts via PRH to modulate VSMC proliferation
One mechanism through which CK2 may facilitate VSMC proliferation could be via blocking PRH activity. Treatment with the K66 failed to arrest PDGF- and bFGF-stimulated cell cycle progression in VSMCs with depleted levels of PRH [38]. Thus CK2-dependent mitogenic signal transduction at least in part requires the presence of PRH ( Figure 4 ). Similarly, treatment of human immortalised myelogenous K562 cells with the CK2 inhibitor DMAT inhibits cell proliferation but has no significant effect on the proliferation of K562 cells in which PRH has been knocked down using shRNA [58]. In K562 cells PRH controls cell proliferation via the inhibition of VEGF signalling [24, 58]. Further work is required to determine whether PRH controls VSMC proliferation via the inhibition of VEGF signalling or whether other signalling pathways targeted by PRH are important in this context. For instance, another potential mechanism by which PRH might control VSMC proliferation involves urokinase-type plasminogen activator (uPA)-mediated signalling [77]. uPA is a serine protease that is up-regulated in atheromas and restenotic lesions of human arteries [77, 78, 79]. In uPA deficient mice, subsequent to either electrical or mechanical arterial injury, intimal thickening and cell accumulation is significantly reduced compared to wild-type mice [80]. In human umbilical vein VSMCs, endogenous uPA has been shown to be involved in the induction of a mitogenic response by either PDGF or bFGF [77]. Furthermore, in PDGF- or bFGF-stimulated cells, pharmacological inhibition of uPA and CK2 with p-aminobenzamidine and 4 μM TBB, respectively, markedly enhances the anti-proliferative effects of 4 μM TBB alone in an additive manner [77]. Intracellular uPA has recently been shown to bind to PRH in endothelial cells and to prevent PRH from repressing VEGF signalling genes [50]. Therefore it is possible that the effects of uPA inhibition on endothelial proliferation and CK2 inhibition on VSMC proliferation during intimal thickening are both mediated by PRH.
6.5. Implications for saphenous vein grafts
As protein kinase CK2 is ubiquitously expressed, systemic delivery of a CK2 inhibitor for the treatment of saphenous vein graft degeneration may cause unwanted side effects. However, perivascular drug delivery systems could be employed for localised, sustained release of a CK2 inhibitor to a grafted vein. Such a system has been used to deliver sunitinib in a biocompatible hyaluronic acid-based hydrogel within a polyactide-co-glycolide perivascular wrap [81]. Other approaches for delivery include drug-eluting nanoparticles and drug-linked antibodies [82].
Gene therapy also has therapeutic potential in alleviating saphenous vein graft stenosis, and could be used for the introduction of PRH, particularly PRH S163C,S177C, to grafted vein. Genetic manipulation of a venous graft must however occur peri-operatively, meaning there is only a single opportunity to complete gene transfer. Therefore, helper-dependent adenovirus technology may be necessary to provide prolonged expression of PRH or PRH S163C,S177C within the grafted conduit [83, 84]. In a similar instance, delivery of tissue inhibitor of metalloproteinase 3 (TIMP-3) has been shown to block neointima formation in autologous porcine arteriovenous interposition grafts for up to 3 months [85].
7. Conclusion
The regulation of cell proliferation and cell migration/invasion by PRH is not limited to a particular cell type. Similarly, the control of PRH by CK2-dependent phosphorylation is also seen in multiple cell types. The PRH-CK2 axis is likely to be important for the regulation of cell proliferation and cell behaviour across a broad spectrum of cell types and in a variety of disease states. Further work in this area is therefore likely to be of great clinical relevance.
Acknowledgments
We are grateful to the British Heart Foundation (FS/10/58/28515) and the Medical Research Council for supporting this work. We apologise to the many authors whose papers we have not cited here due to space constraints.
Abbreviations
ATP | adenosine triphosphate |
bFGF | basic fibroblast growth factor |
CABG | coronary artery bypass graft |
CK2 | protein kinase CK2 (Casein Kinase II) |
DDZ | daidzein |
DMAT | 2-dimethylamino-4,5,6,7-tetrabromo-1H-benzimidazole) |
DRB | 5,6-dichlorobenzimidazole riboside |
K66 | 1-carboxymethyl-2-dimethylamino-4,5,6,7-tetrabromo-benzimidazole |
PDGF | platelet-derived growth factor |
SDS | sodium dodecyl sulphate |
SELDI-TOF-MS | surface-enhancer laser desorption/ionisation time-of-flight mass spectrophotometry |
TBB | 4,5,6,7-tetrabromo-1H-benzotriazole |
VSMC | vascular smooth muscle cell |
References
- 1.
Soufi A, Jayaraman PS. PRH/Hex: An oligomeric transcription factor and multifunctional regulator of cell fate. Biochemical Journal. 2008; 412 (3):399-413 - 2.
Crompton MR, Bartlett TJ, MacGregor AD, Manfioletti G, Buratti E, Giancotti V, Goodwin GH. Identification of a novel vertebrate homeobox gene expressed in haematopoietic cells. Nucleic Acids Research. 1992; 20 (21):5661-5667 - 3.
Hromas R, Radich J, Collins S. PCR cloning of an orphan homeobox gene (PRH) preferentially expressed in myeloid and liver cells 30. Biochemical and Biophysical Research Communications. 1993; 195 (2):976-983 - 4.
Bedford FK, Ashworth A, Enver T, Wiedemann LM. HEX: A novel homeobox gene expressed during haematopoiesis and conserved between mouse and human. Nucleic Acids Research. 1993; 21 (5):1245-1249 - 5.
Hallaq H, Pinter E, Enciso J, McGrath J, Zeiss C, Brueckner M, Madri J, Jacobs HC, Wilson CM, Vasavada H, et al. A null mutation of Hhex results in abnormal cardiac development, defective vasculogenesis and elevated Vegfa levels. Development. 2004; 131 (20):5197-5209 - 6.
Martinez Barbera JP, Clements M, Thomas P, Rodriguez T, Meloy D, Kioussis D, Beddington RS. The homeobox gene Hex is required in definitive endodermal tissues for normal forebrain, liver and thyroid formation. Development. 2000; 127 (11):2433-2445 - 7.
Keng VW, Yagi H, Ikawa M, Nagano T, Myint Z, Yamada K, Tanaka T, Sato A, Muramatsu I, Okabe M, et al. Homeobox gene Hex is essential for onset of mouse embryonic liver development and differentiation of the monocyte lineage. Biochemical and Biophysical Research Communications. 2000; 276 (3):1155-1161 - 8.
Brickman JM, Jones CM, Clements M, Smith JC, Beddington RS. Hex is a transcriptional repressor that contributes to anterior identity and suppresses Spemann organiser function. Development. 2000; 127 (11):2303-2315 - 9.
Manfioletti G, Gattei V, Buratti E, Rustighi A, De IA, Aldinucci D, Goodwin GH, Pinto A. Differential expression of a novel proline-rich homeobox gene (Prh) in human hematolymphopoietic cells. Blood. 1995; 85 (5):1237-1245 - 10.
Guiral M, Bess K, Goodwin G, Jayaraman PS. PRH represses transcription in hematopoietic cells by at least two independent mechanisms. The Journal of Biological Chemistry. 2001; 276 (4):2961-2970 - 11.
Desjobert C, Noy P, Swingler T, Williams H, Gaston K, Jayaraman PS. The PRH/Hex repressor protein causes nuclear retention of Groucho/TLE co-repressors. Biochemical Journal. 2009; 417 (1):121-132 - 12.
Schaefer LK, Shuguang W, Schaefer TS. Functional interaction of Jun and homeodomain proteins. The Journal of Biological Chemistry. 2001; 276 :43074-43082 - 13.
Tanaka T, Inazu T, Yamada K, Myint Z, Keng VW, Inoue Y, Taniguchi N, Noguchi T. cDNA cloning and expression of rat homeobox gene, Hex, and functional characterization of the protein. Biochemical Journal. 1999; 339 (1):111-117 - 14.
Topcu Z, Mack DL, Hromas RA, Borden KL. The promyelocytic leukemia protein PML interacts with the proline-rich homeodomain protein PRH: A RING may link hematopoiesis and growth control. Oncogene. 1999; 18 (50):7091-7100 - 15.
Topisirovic I, Culjkovic B, Cohen N, Perez JM, Skrabanek L, Borden KL. The proline-rich homeodomain protein, PRH, is a tissue-specific inhibitor of eIF4E-dependent cyclin D1 mRNA transport and growth. The EMBO Journal. 2003; 22 (3):689-703 - 16.
Bess KL, Swingler TE, Rivett AJ, Gaston K, Jayaraman PS. The transcriptional repressor protein PRH interacts with the proteasome. Biochemical Journal. 2003; 374 (3):667-675 - 17.
Soufi A, Noy P, Buckle M, Sawasdichai A, Gaston K, Jayaraman PS. CK2 phosphorylation of the PRH/Hex homeodomain functions as a reversible switch for DNA binding. Nucleic Acids Research. 2009; 37 :3288-3300 - 18.
Kasamatsu S, Sato A, Yamamoto T, Keng VW, Yoshida H, Yamazaki Y, Shimoda M, Miyazaki J, Noguchi T. Identification of the transactivating region of the homeodomain protein, hex. Journal of Biochemistry (Tokyo). 2004; 135 (2):217-223 - 19.
Denson LA, Karpen SJ, Bogue CW, Jacobs HC. Divergent homeobox gene hex regulates promoter of the Na(+)-dependent bile acid cotransporter 5. American Journal of Physiology-Gastrointestinal and Liver Physiology. 2000; 279 (2):G347-G355 - 20.
Soufi A, Smith C, Clarke AR, Gaston K, Jayaraman PS. Oligomerisation of the developmental regulator proline rich homeodomain (PRH/Hex) is mediated by a novel proline-rich dimerisation domain. Journal of Molecular Biology. 2006; 358 (4):943-962 - 21.
Williams H, Jayaraman PS, Gaston K. DNA wrapping and distortion by an oligomeric homeodomain protein. Journal of Molecular Biology. 2008; 383 (1):10-23 - 22.
Cong R, Jiang X, Wilson CM, Hunter MP, Vasavada H, Bogue CW. Hhex is a direct repressor of endothelial cell-specific molecule 1 (ESM-1). Biochemical and Biophysical Research Communications. 2006; 346 (2):535-545 - 23.
Zamparini AL, Watts T, Gardner CE, Tomlinson SR, Johnston GI, Brickman JM. Hex acts with beta-catenin to regulate anteroposterior patterning via a Groucho-related co-repressor and nodal. Development. 2006; 133 (18):3709-3722 - 24.
Noy P, Williams H, Sawasdichai A, Gaston K, Jayaraman P-S. PRH/Hhex controls cell survival through coordinate transcriptional regulation of vascular endothelial growth factor signaling. Molecular and Cellular Biology. 2010; 30 (9):2120-2134 - 25.
Swingler TE, Bess KL, Yao J, Stifani S, Jayaraman PS. The proline-rich homeodomain protein recruits members of the Groucho/Transducin-like enhancer of split protein family to co-repress transcription in hematopoietic cells. Journal of Biological Chemistry. 2004; 279 (33):34938-34947 - 26.
Shields BJ, Jackson JT, Metcalf D, Shi W, Huang Q, Garnham AL, Glaser SP, Beck D, Pimanda JE, Bogue CW, et al. Acute myeloid leukemia requires Hhex to enable PRC2-mediated epigenetic repression of Cdkn2a. Genes & Development. 2016; 30 (1):78-91 - 27.
Minami T, Murakami T, Horiuchi K, Miura M, Noguchi T, Miyazaki J, Hamakubo T, Aird WC, Kodama T. Interaction between hex and GATA transcription factors in vascular endothelial cells inhibits flk-1/KDR-mediated vascular endothelial growth factor signaling. Journal of Biological Chemistry. 2004; 279 (20):20626-20635 - 28.
Marfil V, Blazquez M, Serrano F, Castell JV, Bort R. Growth-promoting and tumourigenic activity of c-Myc is suppressed by Hhex. Oncogene. 2014; 34 (23):3011-3022 - 29.
Oyama Y, Kawai-Kowase K, Sekiguchi K, Sato M, Sato H, Yamazaki M, Ohyama Y, Aihara Y, Iso T, Okamaoto E, et al. Homeobox protein Hex facilitates serum responsive factor-mediated activation of the SM22alpha gene transcription in embryonic fibroblasts. Arteriosclerosis, Thrombosis, and Vascular Biology. 2004; 24 (9):1602-1607 - 30.
Tanaka H, Yamamoto T, Ban T, Satoh S, Tanaka T, Shimoda M, Miyazaki J, Noguchi T. Hex stimulates the hepatocyte nuclear factor 1alpha-mediated activation of transcription. Archives of Biochemistry and Biophysics. 2005; 442 (1):117-124 - 31.
Jankovic D, Gorello P, Liu T, Ehret S, La SR, Desjobert C, Baty F, Brutsche M, Jayaraman PS, Santoro A, et al. Leukemogenic mechanisms and targets of a NUP98/HHEX fusion in acute myeloid leukemia. Blood. 2008; 111 (12):5672-5682 - 32.
Topisirovic I, Guzman ML, McConnell MJ, Licht JD, Culjkovic B, Neering SJ, Jordan CT, Borden KL. Aberrant eukaryotic translation initiation factor 4E-dependent mRNA transport impedes hematopoietic differentiation and contributes to leukemogenesis. Molecular and Cellular Biology. 2003; 23 (24):8992-9002 - 33.
D'Elia AV, Tell G, Russo D, Arturi F, Puglisi F, Manfioletti G, Gattei V, Mack DL, Cataldi P, Filetti S, et al. Expression and localization of the homeodomain-containing protein HEX in human thyroid tumors. The Journal of Clinical Endocrinology and Metabolism. 2002; 87 (3):1376-1383 - 34.
Puppin C, Puglisi F, Pellizzari L, Manfioletti G, Pestrin M, Pandolfi M, Piga A, Di LC, Damante G. HEX expression and localization in normal mammary gland and breast carcinoma. BMC Cancer. 2006; 6 :e192 - 35.
Siddiqui YH, Kershaw RM, Humphreys EH, Assis Junior EM, Chaudhri S, Jayaraman PS, Gaston K. CK2 abrogates the inhibitory effects of PRH/HHEX on prostate cancer cell migration and invasion and acts through PRH to control cell proliferation. Oncogene. 2017; 6 (1):e293 - 36.
Kershaw RM, Roberts D, Wragg J, Shaaban AM, Humphreys E, Halsall J, Price L, Bicknell R, Gaston K, Jayaraman PS. Proline-rich homeodomain protein (PRH/HHEX) is a suppressor of breast tumour growth. Oncogene. 2017; 6 (6):e346 - 37.
Sekiguchi K, Kurabayashi M, Oyama Y, Aihara Y, Tanaka T, Sakamoto H, Hoshino Y, Kanda T, Yokoyama T, Shimomura Y, et al. Homeobox protein hex induces SMemb/nonmuscle myosin heavy chain-B gene expression through the cAMP-responsive element. Circulation Research. 2001; 88 (1):52-58 - 38.
Wadey KS, Brown BA, Sala-Newby GB, Jayaraman PS, Gaston K, George SJ. Protein kinase CK2 inhibition suppresses neointima formation via a proline-rich homeodomain-dependent mechanism. Vascular Pharmacology. 2017; 99 :34-44 - 39.
Su J, You P, Zhao JP, Zhang SL, Song SH, ZR F, Ye LW, Zi XY, Xie DF, Zhu MH, et al. A potential role for the homeoprotein Hhex in hepatocellular carcinoma progression. Medical Oncology. 2012; 29 (2):1059-1067 - 40.
Gaston K, Tsitsilianos MA, Wadey K, Jayaraman PS. Misregulation of the proline rich homeodomain (PRH/HHEX) protein in cancer cells and its consequences for tumour growth and invasion. Cell & Bioscience. 2016; 6 :e12 - 41.
Hansen GM, Justice MJ. Activation of Hex and mEg5 by retroviral insertion may contribute to mouse B-cell leukemia. Oncogene. 1999; 18 (47):6531-6539 - 42.
Li J, Shen H, Himmel KL, Dupuy AJ, Largaespada DA, Nakamura T, Shaughnessy JD Jr, Jenkins NA, Copeland NG. Leukaemia disease genes: Large-scale cloning and pathway predictions. Nature Genetics. 1999; 23 (3):348-353 - 43.
Mack DL, Leibowitz DS, Cooper S, Ramsey H, Broxmeyer HE, Hromas R. Down-regulation of the myeloid homeobox protein Hex is essential for normal T-cell development. Immunology. 2002; 107 (4):444-451 - 44.
George A, Morse HC III, Justice MJ. The homeobox gene Hex induces T-cell-derived lymphomas when overexpressed in hematopoietic precursor cells. Oncogene. 2003; 22 (43):6764-6773 - 45.
McCormack MP, Young LF, Vasudevan S, de Graaf CA, Codrington R, Rabbitts TH, Jane SM, Curtis DJ. The Lmo2 oncogene initiates leukemia in mice by inducing thymocyte self-renewal. Science. 2010; 327 (5967):879-883 - 46.
Smith S, Tripathi R, Goodings C, Cleveland S, Mathias E, Hardaway JA, Elliott N, Yi Y, Chen X, Downing J, et al. LIM domain only-2 (LMO2) induces T-cell leukemia by two distinct pathways. PLoS One. 2014; 9 (1):e85883 - 47.
Kubo A, Chen V, Kennedy M, Zahradka E, Daley GQ, Keller G. The homeobox gene HEX regulates proliferation and differentiation of hemangioblasts and endothelial cells during ES cell differentiation. Blood. 2005; 105 (12):4590-4597 - 48.
Noy P, Sawasdichai A, Jayaraman PS, Gaston K. Protein kinase CK2 inactivates PRH/Hhex using multiple mechanisms to de-repress VEGF-signalling genes and promote cell survival. Nucleic Acids Research. 2012; 40 (18):9008-9020 - 49.
Nakagawa T, Abe M, Yamazaki T, Miyashita H, Niwa H, Kokubun S, Sato Y. HEX acts as a negative regulator of angiogenesis by modulating the expression of angiogenesis-related gene in endothelial cells in vitro. Arteriosclerosis, Thrombosis, and Vascular Biology. 2003; 23 (2):231-237 - 50.
Stepanova V, Jayaraman PS, Zaitsev SV, Lebedeva T, Bdeir K, Kershaw R, Holman KR, Parfyonova YV, Semina EV, Beloglazova IB, et al. Urokinase-type plasminogen activator (uPA) promotes angiogenesis by attenuating proline-rich homeodomain protein (PRH) transcription factor activity and de-repressing vascular endothelial growth factor (VEGF) receptor expression. The Journal of Biological Chemistry. 2016; 291 (29):15029-15045 - 51.
Li L, Liu M, Kang L, Li Y, Dai Z, Wang B, Liu S, Chen L, Tan Y, Wu G. HHEX: A crosstalker between HCMV infection and proliferation of VSMCs. Frontiers in Cellular and Infection Microbiology. 2016; 6 :e169 - 52.
Litchfield DW. Protein kinase CK2: Structure, regulation and role in cellular decisions of life and death. Biochemical Journal. 2003; 369 (1):1-15 - 53.
Wirkner U, Voss H, Lichter P, Ansorge W, Pyerin W. The human gene (CSNK2A1) coding for the casein kinase II subunit alpha is located on chromosome 20 and contains tandemly arranged Alu repeats. Genomics. 1994; 19 (2):257-265 - 54.
Bodenbach L, Fauss J, Robitzki A, Krehan A, Lorenz P, Lozeman FJ, Pyerin W. Recombinant human casein kinase II. A study with the complete set of subunits (alpha, alpha' and beta), site-directed autophosphorylation mutants and a bicistronically expressed holoenzyme. European Journal of Biochemistry. 1994; 220 (1):263-273 - 55.
Yang-Feng TL, Naiman T, Kopatz I, Eli D, Dafni N, Canaani D. Assignment of the human casein kinase II alpha' subunit gene (CSNK2A1) to chromosome 16p13.2-p13.3. Genomics. 1994; 19 (1):173 - 56.
Wang D, Westerheide SD, Hanson JL, Baldwin AS Jr. Tumor necrosis factor alpha-induced phosphorylation of RelA/p65 on Ser529 is controlled by casein kinase II. The Journal of Biological Chemistry. 2000; 275 (42):32592-32597 - 57.
Stepanova V, Jerke U, Sagach V, Lindschau C, Dietz R, Haller H, Dumler I. Urokinase-dependent human vascular smooth muscle cell adhesion requires selective vitronectin phosphorylation by ectoprotein kinase CK2. The Journal of Biological Chemistry. 2002; 277 (12):10265-10272 - 58.
Noy P, Gaston K, Jayaraman PS. Dasatinib inhibits leukaemic cell survival by decreasing PRH/Hhex phosphorylation resulting in increased repression of VEGF signalling genes. Leukemia Research. 2012; 36 (11):1434-1437 - 59.
Donella-Deana A, Cesaro L, Sarno S, Ruzzene M, Brunati AM, Marin O, Vilk G, Doherty-Kirby A, Lajoie G, Litchfield DW, et al. Tyrosine phosphorylation of protein kinase CK2 by Src-related tyrosine kinases correlates with increased catalytic activity. Biochemical Journal. 2003; 372 (3):841-849 - 60.
Mishra S, Reichert A, Cunnick J, Senadheera D, Hemmeryckx B, Heisterkamp N, Groffen J. Protein kinase CKIIalpha interacts with the Bcr moiety of Bcr/Abl and mediates proliferation of Bcr/Abl-expressing cells. Oncogene. 2003; 22 (51):8255-8262 - 61.
Landesman-Bollag E, Song DH, Romieu-Mourez R, Sussman DJ, Cardiff RD, Sonenshein GE, Seldin DC. Protein kinase CK2: Signaling and tumorigenesis in the mammary gland. Molecular and Cellular Biochemistry. 2001; 227 (1-2):153-165 - 62.
Yenice S, Davis AT, Goueli SA, Akdas A, Limas C, Ahmed K. Nuclear casein kinase 2 (CK-2) activity in human normal, benign hyperplastic, and cancerous prostate. Prostate. 1994; 24 (1):11-16 - 63.
Daya-Makin M, Sanghera JS, Mogentale TL, Lipp M, Parchomchuk J, Hogg JC, Pelech SL. Activation of a tumor-associated protein kinase (p40TAK) and casein kinase 2 in human squamous cell carcinomas and adenocarcinomas of the lung. Cancer Research. 1994; 54 (8):2262-2268 - 64.
Faust RA, Gapany M, Tristani P, Davis A, Adams GL, Ahmed K. Elevated protein kinase CK2 activity in chromatin of head and neck tumors: Association with malignant transformation. Cancer Letters. 1996; 101 (1):31-35 - 65.
Stalter G, Siemer S, Becht E, Ziegler M, Remberger K, Issinger OG. Asymmetric expression of protein kinase CK2 subunits in human kidney tumors. Biochemical and Biophysical Research Communications. 1994; 202 (1):141-147 - 66.
Scaglioni PP, Yung TM, Cai LF, Erdjument-Bromage H, Kaufman AJ, Singh B, Teruya-Feldstein J, Tempst P, Pandolfi PP. A CK2-dependent mechanism for degradation of the PML tumor suppressor. Cell. 2006; 126 (2):269-283 - 67.
Di Maira G, Salvi M, Arrigoni G, Marin O, Sarno S, Brustolon F, Pinna LA, Ruzzene M. Protein kinase CK2 phosphorylates and upregulates Akt/PKB. Cell Death and Differentiation. 2005; 12 (6):668-677 - 68.
Battistutta R, Cozza G, Pierre F, Papinutto E, Lolli G, Sarno S, O'Brien SE, Siddiqui-Jain A, Haddach M, Anderes K, et al. Unprecedented selectivity and structural determinants of a new class of protein kinase CK2 inhibitors in clinical trials for the treatment of cancer. Biochemistry. 2011; 50 (39):8478-8488 - 69.
Martins LR, Lucio P, Melao A, Antunes I, Cardoso BA, Stansfield R, Bertilaccio MT, Ghia P, Drygin D, Silva MG, et al. Activity of the clinical-stage CK2-specific inhibitor CX-4945 against chronic lymphocytic leukemia. Leukemia. 2014; 28 (1):179-182 - 70.
Steinberg M. Dasatinib: A tyrosine kinase inhibitor for the treatment of chronic myelogenous leukemia and philadelphia chromosome-positive acute lymphoblastic leukemia. Clinical Therapeutics. 2007; 29 (11):2289-2308 - 71.
Yusuf S, Zucker D, Peduzzi P, Fisher LD, Takaro T, Kennedy JW, Davis K, Killip T, Passamani E, Norris R, et al. Effect of coronary artery bypass graft surgery on survival: Overview of 10-year results from randomised trials by the coronary artery bypass graft surgery trialists collaboration. Lancet. 1994; 344 (8922):563-570 - 72.
Eagle KA, Guyton RA, Davidoff R, Edwards FH, Ewy GA, Gardner TJ, Hart JC, Herrmann HC, Hillis LD, Hutter AM Jr, et al. ACC/AHA 2004 guideline update for coronary artery bypass graft surgery: A report of the American College of Cardiology/American Heart Association task force on practice guidelines (committee to update the 1999 guidelines for coronary artery bypass graft surgery). Circulation. 2004; 110 (14):e340-e437 - 73.
Harskamp RE, Lopes RD, Baisden CE, de Winter RJ, Alexander JH. Saphenous vein graft failure after coronary artery bypass surgery: Pathophysiology, management, and future directions. Annals of Surgery. 2013; 257 (5):824-833 - 74.
Heo SK, Yun HJ, Park WH, Park SD. Emodin inhibits TNF-alpha-induced human aortic smooth-muscle cell proliferation via caspase- and mitochondrial-dependent apoptosis. Journal of Cellular Biochemistry. 2008; 105 (1):70-80 - 75.
YJ X, Rathi SS, Chapman DC, Arneja AS, Dhalla NS. Mechanisms of lysophosphatidic acid-induced DNA synthesis in vascular smooth muscle cells. Journal of Cardiovascular Pharmacology. 2003; 41 (3):381-387 - 76.
Pagano MA, Bain J, Kazimierczuk Z, Sarno S, Ruzzene M, Di Maira G, Elliott M, Orzeszko A, Cozza G, Meggio F, et al. The selectivity of inhibitors of protein kinase CK2: An update. The Biochemical Journal. 2008; 415 (3):353-365 - 77.
Padro T, Mesters RM, Dankbar B, Hintelmann H, Bieker R, Kiehl M, Berdel WE, Kienast J. The catalytic domain of endogenous urokinase-type plasminogen activator is required for the mitogenic activity of platelet-derived and basic fibroblast growth factors in human vascular smooth muscle cells. Journal of Cell Science. 2002; 115 (9):1961-1971 - 78.
Lupu F, Heim DA, Bachmann F, Hurni M, Kakkar VV, Kruithof EKO. Plasminogen activator expression in human atherosclerotic lesions. Arteriosclerosis, Thrombosis, and Vascular Biology. 1995; 15 (9):1444-1455 - 79.
Raghunath PN, Tomaszewski JE, Brady ST, Caron RJ, Okada SS, Barnathan ES. Plasminogen activator system in human coronary atherosclerosis. Arteriosclerosis, Thrombosis, and Vascular Biology. 1995; 15 (9):1432-1443 - 80.
Carmeliet P, Moons L, Herbert J-M, Crawley J, Lupu F, Lijnen R, Collen D. Urokinase but not tissue plasminogen activator mediates arterial neointima formation in mice. Circulation Research. 1997; 81 (5):829-839 - 81.
Sanders WG, Hogrebe PC, Grainger DW, Cheung AK, Terry CM. A biodegradable perivascular wrap for controlled, local and directed drug delivery. Journal of Controlled Release: Official Journal of the Controlled Release Society. 2012; 161 (1):81-89 - 82.
Thomas AC. Targeted treatments for restenosis and vein graft disease. ISRN Vascular Medicine. 2012; 2012 :23 - 83.
Oka K, Pastore L, Kim IH, Merched A, Nomura S, Lee HJ, Merched-Sauvage M, Arden-Riley C, Lee B, Finegold M, et al. Long-term stable correction of low-density lipoprotein receptor-deficient mice with a helper-dependent adenoviral vector expressing the very low-density lipoprotein receptor. Circulation. 2001; 103 (9):1274-1281 - 84.
Belalcazar LM, Merched A, Carr B, Oka K, Chen KH, Pastore L, Beaudet A, Chan L. Long-term stable expression of human apolipoprotein A-I mediated by helper-dependent adenovirus gene transfer inhibits atherosclerosis progression and remodels atherosclerotic plaques in a mouse model of familial hypercholesterolemia. Circulation. 2003; 107 (21):2726-2732 - 85.
George SJ, Wan S, Hu J, MacDonald R, Johnson JL, Baker AH. Sustained reduction of vein graft neointima formation by ex vivo TIMP-3 gene therapy. Circulation. 2011; 124 (11 Suppl):S135-S142