Important research published in late 2010 and 2011 relates to a protein JDP2 that plays a key role in cell-cycle processes. JDP2 is involved with epigenetic modifications to histones relevant to age-related changes in stem cell differentiation and cell senescence. Like the previously-discussed Smurf2 gene, JDP2 is involved in the regulation of the differentiation and proliferation of cells. Its presence or absence affects whether cells differentiate or become senescent. The new research has implications related to organismal aging and for the Programmed Epigenomic Changes theory of aging. I review some of the new publications here and relate new findings to matters I have discussed previously. The subject is highly technical and the actions of JDP2 are complex So, I have framed some of the explanations and interpretations I put forward here in simplified terms.
I start with the abstract of the 2011 electronic publication Jun dimerization protein 2 controls senescence and differentiation via regulating histone modification, and then go on to interpret and amplify certain key points. “Transcription factor, Jun dimerization protein 2 (JDP2), binds directly to histones and DNAs and then inhibits the p300-mediated acetylation both of core histones and of reconstituted nucleosomes that contain JDP2 recognition DNA sequences. JDP2 plays a key role as a repressor of adipocyte differentiation by regulation of the expression of the gene C/EBPÎ´ via inhibition of histone acetylation. Moreover, JDP2-deficient mouse embryonic fibroblasts (JDP2(-/-) MEFs) are resistant to replicative senescence. JDP2 inhibits the recruitment of polycomb repressive complexes (PRC1 and PRC2) to the promoter of the gene encoding p16(Ink4a), resulting from the inhibition of methylation of lysine 27 of histone H3 (H3K27). Therefore, it seems that chromatin-remodeling factors, including the PRC complex controlled by JDP2, may be important players in the senescence program. The novel mechanisms that underline the action of JDP2 in inducing cellular senescence and suppressing adipocyte differentiation are reviewed.”
JDP2 is an epigenetic modifier, a transcription factor that inhibits gene expression
In binding to histones and preventing acetylation of core histones, JDP2 keeps the corresponding chromatin tightly wrapped up inhibiting accessibility of promoter regions of certain genes and therefore inhibiting expression of those genes. “We found that acetylation by p300 is inhibited in a dose-dependent manner by JDP2, when added exogenously. We also found that JDP2 was not acetylated by p300 under our experimental conditions. The inhibitory effect of JDP2 was detected on histone acetylation induced by p300, CREB-binding protein (CBP), p300/CBP-associated protein (PCAF), and general control nonrepressive 5 (GCN5). The overexpression of JDP2 apparently represses the RA-induced acetylation of lysines 8 and 16 of histone H4 and some amino terminal lysine residues of histone H3(ref).”
JDP2 is a repressor of cell differentiation
As stated in the 2010 publication Histone chaperone Jun dimerization protein 2 (JDP2): role in cellular senescence and aging, “Thus JDP2 plays a key role as a repressor of cell differentiation by regulating the expression of genes with an activator protein 1 (AP-1) site via inhibition of histone acetylation and/or assembly and disassembly of nucleosomes.” Going back to the 2007 publication JDP2 suppresses adipocyte differentiation by regulating histone acetylation, “–JDP2 inhibited both the acetylation of histone H3 in the promoter of the gene for C/EBPdelta and transcription from this promoter. Our data indicate that JDP2 plays a key role as a repressor of adipocyte differentiation by regulating the expression of the gene for C/EBPdelta via inhibition of histone acetylation.” Additional insight is provided in the November 2010 publication Suppression of cell-cycle progression by Jun dimerization protein-2 (JDP2) involves downregulation of cyclin-A2. “Fibroblasts derived from embryos of Jdp2KO mice proliferated faster and formed more colonies than fibroblasts from wild-type mice. JDP2 was recruited to the promoter of the gene for cyclin-A2 (ccna2) at the AP-1 site. Cells lacking Jdp2 had elevated levels of cyclin-A2 mRNA. Furthermore, reintroduction of JDP2 resulted in the repression of transcription of ccna2 and of cell-cycle progression. Thus, transcription of the gene for cyclin-A2 appears to be a direct target of JDP2 in the suppression of cell proliferation.” JDP2 is a driver of cell senescence, and does by activating the gene p16(Ink4a)The 2010 publication Epigenetic regulation of p16Ink4a and Arf by JDP2 in cellular senescence recapitulates the complex mechanisms through which JDP2 is a regulator of cellular senescence. “In response to accumulating cellular stress, cells protect themselves from abnormal growth by entering the senescent stage. Senescence is controlled mainly by gene products from the p16Ink4a/Arf locus. In mouse cells, the expression of p16Ink4a and Arf increases continuously during proliferation in cell culture. Transcription from the locus is under complex control. p16Ink4a and Arf respond independently to positive and negative signals, and the entire locus is epigenetically suppressed by histone methylation that depends on the Polycomb repressive complex-1 and -2 (PRC1 and PRC2). In fact, the PRCs associate with the p16Ink4a/Arf locus in young proliferating cells and dissociate in aged senescent cells. Thus, it seems that chromatin-remodeling factors that regulate association and dissociation of PRCs might be important players in the senescence program. Here, we summarize the molecular mechanisms that mediate cellular aging and introduce the Jun dimerization protein 2 (JDP2) as a factor that regulates replicative senescence by mediating dissociation of PRCs from the p16Ink4a/Arf locus.”
According to the 2009 publication JDP2 (Jun Dimerization Protein 2)-deficient mouse embryonic fibroblasts are resistant to replicative senescence “Senescence protects normal cells from abnormal growth signals and oncogenic transformation by interrupting the cell cycle. Senescence is induced not only by cellular aging but also by the forced activation of the MAPK3 pathway and by genotoxic stressors, such as peroxide and certain DNA-damaging compounds. There is evidence to suggest that, in mice, two inhibitors of progression of the cell cycle, p16Ink4a and p19Arf (Arf and p14ARF in humans), are the main regulators of senescence. These proteins are encoded by overlapping reading frames at the CDKN2A (MTS1) locus (1–3). The expression of both p16Ink4a and p19Arf is enhanced in rodent cells with aging (1, 2). By contrast, in human cells, senescence is generally associated with the increased expression of p16Ink4a but not of Arf (1–3).”
The same publication reports “JDP2 (Jun dimerization protein 2, an AP-1 transcription factor) is involved in the regulation of the differentiation and proliferation of cells. We report here that JDP2-deficient mouse embryonic fibroblasts (Jdp2(-/-) MEF) are resistant to replicative senescence. In the absence of JDP2, the level of expression of p16(Ink4a), which is known to rise as normal fibroblasts age, fell significantly when cells were cultured for more than 2 months. Conversely, the overexpression of JDP2 induced the expression of genes for p16(Ink4a) and p19(Arf). Moreover, at the promoter of the gene for p16(Ink4a) in Jdp2(-/-) MEF, the extent of methylation of lysine 27 of histone H3 (H3K27), which is important for gene silencing, increased. Polycomb-repressive complexes (PRC-1 and PRC-2), which are responsible for histone methylation, bound efficiently to the promoter to repress the expression of the gene for p16(Ink4a). As a result, JDP2-deficient MEF became resistant to replicative senescence. Our results indicate that JDP2 is involved in the signaling pathway for senescence via epigenetic regulation of the expression of the gene for p16(Ink4a).”
The October 2010 publication Histone chaperone Jun dimerization protein 2 (JDP2): role in cellular senescence and aging relates “Senescent cells show a series of alterations, including flatten and enlarged morphology, increase in nonspecific acidic Î²-galactosidase activity, chromatin condensation, and changes in gene expression patterns. The onset and maintenance of senescence are regulated by two tumor suppressors, p53 and retinoblastoma proteins. The expression of p53 and retinoblastoma proteins is regulated by two distinct proteins, p16(Ink4a) and Arf, respectively, which are encoded by cdkn2a. JDP2 inhibits recruitment of the polycomb repressive complexes 1 and 2 (PRC-1 and PRC-2) to the promoter of the gene that encodes p16(Ink4a) and inhibits the methylation of lysine 27 of histone H3 (H3K27). The PRCs associate with the p16(Ink4a)/Arf locus in young proliferating cells and dissociate from it in senescent cells. Therefore, it seems that chromatin-remodeling factors that regulate association and dissociation of PRCs, and are controlled by JDP2, might play an important role in the senescence program.”
JDP2 contributes to aging via activation of p16(Ink4a)
I have discussed the role of p16(Ink4a) as an epigenetic driver of aging before in this blog and in my treatise as part of the discussion of the Programmed Epigenomic Changes theory of aging. Specifically, levels of p16(Ink4a) increase with aging and p16(Ink4a) inhibits the differentiation of adult stem cells. “Buildup of levels of Ink4a/P16 associated with aging slows down the rate of differentiation of adult stem cells. “Recent evidence shows that loss of Bmi-1, a polycomb transcriptional repressor of the Ink4a-Arf locus, results in progressive loss of HSCs in adult mice with subsequent failure of hematopoiesis.” – “ These results show that either both p16Ink4a and p19Arf can inhibit HSC self-renewal in a serial transplant setting, or that only p16(Ink4a) is necessary(ref).“
The new research suggests that the smoking gun driving p16(Ink4a) expression and therefore cell senescence is JDP2.
The 2009 publication Expression of p16(INK4a) in peripheral blood T-cells is a biomarker of human aging relates “Expression of the p16(INK4a) tumor suppressor sharply increases with age in most mammalian tissues, and contributes to an age-induced functional decline of certain self-renewing compartments. These observations have suggested that p16(INK4a) expression could be a biomarker of mammalian aging. To translate this notion to human use, we determined p16(INK4a) expression in cellular fractions of human whole blood, and found highest expression in peripheral blood T-lymphocytes (PBTL). We then measured INK4/ARF transcript expression in PBTL from two independent cohorts of healthy humans (170 donors total), and analyzed their relationship with donor characteristics. Expression of p16(INK4a), but not other INK4/ARF transcripts, appeared to exponentially increase with donor chronologic age. Importantly, p16(INK4a) expression did not independently correlate with gender or body-mass index, but was significantly associated with tobacco use and physical inactivity. In addition, p16(INK4a) expression was associated with plasma interleukin-6 concentration, a marker of human frailty. These data suggest that p16(INK4a) expression in PBTL is an easily measured, peripheral blood biomarker of molecular age.”
The usefulness of p16(INK4a) as a biomarker of aging is also related in the 2008 publication p16INK4A is a robust in vivo biomarker of cellular aging in human skin. “To determine whether p16INK4A expression in human skin correlates with donor age, p16INK4A expression was analyzed by immunohistochemistry as well as the expression of the p16INK4A repressor BMI1. Samples from the age groups 0-20, 21-70, and 71-95 years were selected from a bank of healthy human skin. We show that the number of p16INK4A positive cells is significantly higher in elderly individuals compared to the younger age groups. The number of p16INK4A positive cells was found to be increased in both epidermis and dermis, compartments with strictly different proliferative activities. BMI1 gene expression was significantly down-regulated with increasing donor age, whereas no striking age differences were observed for Ki67. — In conclusion, we provide for the first time evidence that p16INK4A expression directly correlates with chronological aging of human skin in vivo. p16INK4A therefore is a biomarker for human aging in vivo. The data reported here suggest a model for changes in regulatory gene expression that drive aging in human skin.”
JDP2 affects responses of cells to stress and growth signals by repressing ATF3
The 2009 publication The ubiquitously expressed bZIP inhibitor, JDP2, suppresses the transcription of its homologue immediate early gene counterpart, ATF3 reports “JDP2 is a ubiquitously expressed bZIP repressor protein. JDP2 binds TPA response element and cyclic AMP response element located within various promoters. JDP2 displays a high degree of homology to the immediate early gene ATF3. ATF3 plays a crucial role in the cellular adaptive response to multiple stress insults as well as growth stimuli. We have identified ATF3 as a potential target gene for JDP2 repression. JDP2 regulates the ATF3 promoter potentially through binding to both the consensus ATF/CRE site and a non-consensus ATF3 auto-repression DNA-binding element. Expression of ATF3 protein in wild-type mouse embryo fibroblast (MEF) cells is below the detectable levels, whereas, JDP2 disrupted MEF cells display noticeable level of ATF3 protein. Following either serum or ER stress stimulation, ATF3 expression is potentiated in JDP2-KO fibroblast cells as compared with wild-type cells. Mice with either JDP2 over-expression or JDP2 disruption display undetectable level of ATF3 protein. However, ATF3 induction in response to either growth or stress signals is dependent on JDP2 expression level. ATF3 induction is attenuated in JDP2 over-expressing mice whereas is potentiated in JDP2-KO mice as compared with the corresponding wild-type mice. Collectively, the data presented strongly suggest that JDP2 plays a role in the determination of the ATF3 adaptive cellular threshold response to different stress insults and growth stimuli.”
JDP2 may play mixed roles in cancer processes.
“It is also interesting that JDP2 is one of the candidate oncoproteins that collaborate in the oncogenesis associated with the loss of p27 as the result of insertional mutations . Recent study of tumor cells demonstrated that JDP2 was a tumor suppressor (ref).” The 2002 publication Identification of oncogenes collaborating with p27Kip1 loss by insertional mutagenesis and high-throughput insertion site analysis reported “This analysis identified a remarkable number of putative protooncogenes in these lymphomas, which included loci that were novel as well as those that were overrepresented in p27-/- tumors. We found that Myc activations occurred more frequently in p27-/- lymphomas than in p27+/+ tumors. We also characterized insertions within two novel loci: (i) the Jun dimerization protein 2 gene (Jundp2), and (ii) an X-linked locus termed Xpcl1. Each of the loci that we found to be frequently involved in p27-/- lymphomas represents a candidate oncogene collaborating with p27 loss.” The 2004 publication The c-Jun dimerization protein 2 inhibits cell transformation and acts as a tumor suppressor gene reported “we show for the first time the potential role of JDP2 in inhibition of cell transformation and tumor suppression. The mechanism of tumor suppressor action of JDP2 can be partially explained by the generation of inhibitory AP-1 complexes via the increase of JunB, JunD, and Fra2 expression and decrease of c-Jun expression.”
The 2010 publication The AP-1 repressor protein, JDP2, potentiates hepatocellular carcinoma in mice provides a later take: “RESULTS: JDP2-transgenic mice display normal liver function. JDP2-transgenic mice displayed potentiation of liver cancer, higher mortality and increased number and size of tumors. The expression of JDP2 at the promotion stage was found to be the most critical for enhancing liver cancer severity.– CONCLUSIONS: This study suggests that JDP2 expression may play a critical role in liver cancer development by potentiating the compensatory proliferative response and increased inflammation in the DEN liver cancer model.”
There is much more to the literature of JDP2 than I have been able to cover. However, it is clear that JDP2 is an important actor in the epigenetic cell-cycle regulatory system that relaters to stem cell differentiation capability, cell senescence and aging. I believe this literature tends to support the Programmed Epigenomic Changes theory of aging. According to this theory, aging involves progressive and somewhat systematic changes in the chromatin. JDP2 is a key player in the program as are the polycomb repressive complexes, P16(INK4a), Arf, P53 and a number of other regulatory proteins. Yet, the extent and exact functioning of the program remains far from clear. Most of the literature I have reviewed was focused on what JDP2 does and I saw little if any discussion of what promotes or inhibits JDP2 itself in-vivo. Do any of the sirtuins impact on JDP2 expression? Is JDP2 expression conditioned by exercise, by diet, by phytochemicals? I saw no answers to these questions or a host of others I can think of. So, I expect there will be much more to report as time progresses.