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Query: UNIPROT:P04637 (p53)
 77,613 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Epstein-Barr Virus (EBV) replication and transcription activator (Rta/BRLF1) is an immediate-early transcription factor that controls the conversion of the latent viral genome into one undergoing lytic replication. By using a doxycycline-inducible expression system, the present study demonstrates that EBV Rta efficiently elicits growth arrest in the human epithelial cell line HEK293. In cells arrested by EBV Rta, the expression of p21 (CDKN1A), p27 (CDKN1B) and cyclin E were increased. In contrast, the levels of cyclin D1, CDK4 and CDK6 were sharply decreased. Activation of the host cell DNA damage response (DDR), indicated by the increasing phosphorylation of H2AX and p53 Ser15, was observed on day 3 and day 5 after EBV Rta expression, respectively. Finally, EBV Rta arrested cells exhibited strong senescence-associated beta-galactosidase staining on day 10 after doxycycline induction. Together, these results indicate that, in addition to triggering viral lytic replication in epithelial cells, EBV Rta concurrently initiates a cellular senescence program that was previously undocumented. This finding, showing Rta may be centrally involved in inducing a host cell state amenable to efficient viral reproduction, in addition to its previously characterized regulation of viral transcription, provides new perspectives in understanding EBV pathogenesis.
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PMID:The Epstein-Barr virus replication and transcription activator, Rta/BRLF1, induces cellular senescence in epithelial cells. 1909 30

The tumor suppressor p53 preserves genome integrity by inducing transcription of genes controlling growth arrest or apoptosis. Transcriptional activation involves nucleosomal perturbation by chromatin remodeling enzymes. Mammalian SWI/SNF remodeling complexes incorporate either the Brahma-related gene 1 (BRG1) or Brahma (Brm) as the ATPase subunit. The observation that tumor cell lines harboring wild-type p53 specifically maintain expression of BRG1 and that BRG1 complexes with p53 prompted us to examine the role of BRG1 in regulation of p53. Remarkably, RNAi depletion of BRG1, but not Brm, led to the activation of endogenous wild-type p53 and cell senescence. We found a proline-rich region unique to BRG1 was required for binding to the histone acetyl transferase protein, CBP, as well as to p53. Ectopic expression of a proline-rich region deletion mutant BRG1 that is defective for CBP binding inhibited p53 destabilization. Importantly, RNAi knockdown of BRG1 and CBP reduced p53 poly-ubiquitination in vivo. In support of p53 inactivation by the combined activities of BRG1 and CBP, we show that DNA damage signals promoted disassociation of BRG1 from CBP, thereby allowing p53 accumulation. Our data demonstrate a novel function of the evolutionarily conserved chromatin remodeling subunit BRG1, which cooperates with CBP to constrain p53 activity and permit cancer cell proliferation.
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PMID:The SWI/SNF chromatin remodeling subunit BRG1 is a critical regulator of p53 necessary for proliferation of malignant cells. 1944 67

HIC1, a tumor suppressor gene epigenetically silenced in many human cancers encodes a transcriptional repressor involved in regulatory loops modulating p53-dependent and E2F1-dependent cell survival and stress responses. HIC1 is also implicated in growth control since it recruits BRG1, one of the two alternative ATPases (BRM or BRG1) of SWI/SNF chromatin-remodeling complexes to repress transcription of E2F1 in quiescent fibroblasts. Here, through yeast two-hybrid screening, we identify ARID1A/BAF250A, as a new HIC1 partner. ARID1A/BAF250A is one of the two mutually exclusive ARID1-containing subunits of SWI/SNF complexes which define subsets of complexes endowed with anti-proliferative properties. Co-immunoprecipitation assays in WI38 fibroblasts and in BRG1-/- SW13 cells showed that endogenous HIC1 and ARID1A proteins interact in a BRG1-dependent manner. Furthermore, we demonstrate that HIC1 does not interact with BRM. Finally, sequential chromatin immunoprecipitation (ChIP-reChIP) experiments demonstrated that HIC1 represses E2F1 through the recruitment of anti-proliferative SWI/SNF complexes containing ARID1A.
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PMID:HIC1 interacts with a specific subunit of SWI/SNF complexes, ARID1A/BAF250A. 1948 93

Transcription factor activating enhancer-binding protein 4 (AP-4) is a basic helix-loop-helix protein that binds to E-box elements. AP-4 has received increasing attention for its regulatory role in cell growth and development, including transcriptional repression of the human homolog of murine double minute 2 (HDM2), an important oncoprotein controlling cell growth and survival, by an unknown mechanism. Here we demonstrate that AP-4 binds to an E-box located in the HDM2-P2 promoter and represses HDM2 transcription in a p53-independent manner. Incremental truncations of AP-4 revealed that the C-terminal Gln/Pro-rich domain was essential for transcriptional repression of HDM2. To further delineate the molecular mechanism(s) of AP-4 transcriptional control and its potential implications, we used DNA-affinity purification followed by complementary quantitative proteomics, cICAT and iTRAQ labeling methods, to identify a previously unknown E-box-bound AP-4 protein complex containing 75 putative components. The two labeling methods complementarily quantified differentially AP-4-enriched proteins, including the most significant recruitment of DNA damage response proteins, followed by transcription factors, transcriptional repressors/corepressors, and histone-modifying proteins. Specific interaction of AP-4 with CCCTC binding factor, stimulatory protein 1, and histone deacetylase 1 (an AP-4 corepressor) was validated using AP-4 truncation mutants. Importantly, inclusion of trichostatin A did not alleviate AP-4-mediated repression of HDM2 transcription, suggesting a previously unidentified histone deacetylase-independent repression mechanism. In contrast, the complementary quantitative proteomics study suggested that transcription repression occurs via coordination of AP-4 with other transcription factors, histone methyltransferases, and/or a nucleosome remodeling SWI.SNF complex. In addition to previously known functions of AP-4, our data suggest that AP-4 participates in a transcriptional-regulating complex at the HDM2-P2 promoter in response to DNA damage.
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PMID:Complementary quantitative proteomics reveals that transcription factor AP-4 mediates E-box-dependent complex formation for transcriptional repression of HDM2. 1950 73

Malignant rhabdoid tumors (MRTs) are poorly differentiated pediatric cancers that arise in various anatomical locations and have a very poor outcome. The large majority of these malignancies are caused by loss of function of the SNF5/INI1 component of the SWI/SNF chromatin remodeling complex. However, the mechanism of tumor development associated with SNF5 loss remains unclear. Multiple studies have demonstrated a role for SNF5 in the regulation of cyclin D1, p16(INK4A), and pRb(f) activities suggesting it functions through the SWI/SNF complex to affect transcription of genes involved in cell cycle control. Previous studies in genetically engineered mouse models (GEMM) have shown that loss of SNF5 on a p53-null background significantly accelerates tumor development. Here, we use established GEMM to further define the relationship between the SNF5 and p53 tumor suppressor pathways. Combined haploinsufficiency of p53 and Snf5 leads to decreased latency for MRTs arising in alternate anatomical locations but not for the standard facial MRTs. We also observed acceleration in the appearance of T-cell lymphomas in the p53(+/-);Snf5(+/-) mice. Our studies suggest that loss of SNF5 activity does not bestow a selective advantage on the p53 spectrum of tumors in the p53(+/-);Snf5(+/-) mice. However, reduced p53 expression specifically accelerated the growth of a subset of MRTs in these mice.
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PMID:Inactivation of SNF5 cooperates with p53 loss to accelerate tumor formation in Snf5(+/-);p53(+/-) mice. 1967

SNF2L, a chromatin remodeling gene expressed in diverse tissues, cancers, and derived cell lines, contributes to the chromatin remodeling complex that facilitates transcription. Because of this wide expression, it has not been exploited as a cancer therapeutic target. However, based on our present studies, we find that cancer cells, although expressing SNF2L at similar levels as their normal counterparts, are sensitive to its knockdown. This is not observed when its imitation SWI ortholog, SNF2H, is inhibited. SNF2L siRNA inhibition using two different siRNAs separately reduced SNF2L transcript levels and protein in both normal and cancer lines, but only the cancer lines showed significant growth inhibition, DNA damage, a DNA damage response, and phosphorylation of checkpoint proteins and marked apoptosis. DNA damage and the damage response preceded apoptosis rather than being consequences of it. The damage response consisted of increased phosphorylation of multiple substrates including ATR, BRCA1, CHK1, CHK2, and H2AX. Both the total and phosphorylated levels of p53 increased. The downstream targets of p53, p21, GADD45A, and 14-3-3sigma, were also upregulated. The alterations in checkpoint proteins included increased phosphorylated cdc2 but not Rb, which resulted in a modest G(2)-M arrest. Although apoptosis may be mediated by Apaf-1/caspase 9, other caspases could be involved. Other members of the chromatin remodeling or SWI/SNF gene families exhibited overall reduced levels of expression in the cancer lines compared with the normal lines. This raised the hypothesis that cancers are sensitive to SNF2L knockdown because, unlike their normal counterparts, they lack sufficient compensation from other family members.
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PMID:Inhibition of expression of the chromatin remodeling gene, SNF2L, selectively leads to DNA damage, growth inhibition, and cancer cell death. 1999 4

SNF5, a core component of the SWI/SNF chromatin remodeling complex, is expressed as two isoforms, SNF5a and SNF5b. SNF5 is a tumor suppressor, as mutation of SNF5 leads to tumor formation and cooperates with p53 deficiency to enhance cancer susceptibility. Interestingly, lack of SNF5 inhibits cell survival and embryonic development, potentially through abnormal activation of p53. To further examine this, we generated cell lines in which SNF5a, SNF5b or both can be inducibly knocked down. We found that SNF5 knockdown leads to cell-cycle arrest in G(1), and SNF5a and SNF5b are functionally redundant. We also showed that SNF5 knockdown impairs p53-dependent transcription of p21 and murine double minute 2. However, contrary to earlier reports that p53 is activated by SNF5 knockout in murine cells, SNF5 knockdown leads to decreased, but not increased, expression of both basal and stress-induced p53 in multiple human cell lines. In addition, we showed that SNF5 knockdown induces adenosine monophosphate-activated protein kinase activation and inhibits eIF4E expression. Finally, we showed that SNF5 knockdown inhibits p53 translation by eIF4E and replacement of eIF4E in SNF5 knockdown cells restores p53 expression and cell survival. Together, our study results suggest that the p53 pathway is regulated by, and mediates the activity of, SNF5 in tumor suppression and prosurvival.
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PMID:SNF5, a core component of the SWI/SNF complex, is necessary for p53 expression and cell survival, in part through eIF4E. 2047 26

The ability of oncogenes to engage tumor suppressor pathways represents a key regulatory mechanism that can limit the outgrowth of incipient tumor cells. For example, in a number of settings oncogenic Ras strongly activates the Ink4a/Arf locus, resulting in cell cycle arrest or senescence. The capacity of different cell types to execute tumor suppressor programs following expression of endogenous K-ras(G12D) in vivo has not been examined. Using compound mutant mice containing the Arf(GFP) reporter and the spontaneously activating K-ras(LA2) allele, we have uncovered dramatic tissue specificity of K-ras(G12D)-dependent p19(Arf) up-regulation. Lung tumors, which can arise in the presence of functional p19(Arf), rarely display p19(Arf) induction. In contrast, sarcomas always show robust activation, which correlates with genetic evidence, suggesting that loss of the p19(Arf)-p53 pathway is a requisite event for sarcomagenesis. Using constitutive and inducible RNAi systems in vivo, we highlight cell type-specific chromatin regulation of Ink4a/Arf as a critical determinant of cellular responses to oncogenic K-ras. Polycomb-group complexes repress the locus in lung tumors, whereas the SWI/SNF family member Snf5 acts as an important mediator of p19(Arf) induction in sarcomas. This variation in tumor suppressor induction might explain the inherent differences between tissues in their sensitivity to Ras-mediated transformation.
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PMID:Tissue-specific p19Arf regulation dictates the response to oncogenic K-ras. 2047 39

Overexpression of DNA 5'-cytosine-methyltransferases (DNMT), which are enzymes that methylate the cytosine residue of CpGs, is involved in many cancers. However, the mechanism of DNMT overexpression remains unclear. Here, we showed that wild-type p53 negatively regulated DNMT1 expression by forming a complex with specificity protein 1 (Sp1) protein and chromatin modifiers on the DNMT1 promoter. However, the stoichiometry between p53 and Sp1 determined whether Sp1 acts as a transcription activator or corepressor. Low level of exogenous Sp1 enhanced the repressive activity of endogenous p53 on the DNMT1 promoter whereas high level of Sp1 upregulated DNMT1 gene expression level in A549 (p53 wild-type) cells. In H1299 (p53 null) cells, exogenous Sp1 induced DNMT1 expression in a dose-dependent manner. We also discovered a new mechanism whereby high level of Sp1, via its COOH-terminal domain, induced interaction between p53 and MDM2, resulting in degradation of p53 by MDM2-mediated ubiquitination. Clinical data from 102 lung cancer patients indicated that overexpression of DNMT1 was associated with p53 mutation (P = 0.014) and high expression of Sp1 protein (P = 0.006). In addition, patients with overexpression of both DNMT1 and Sp1 proteins showed poor prognosis (P = 0.037). Our cell and clinical data provided compelling evidence that deregulation of DNMT1 is associated with gain of transcriptional activation of Sp1 and/or loss of repression of p53. DNMT1 overexpression results in epigenetic alteration of multiple tumor suppressor genes and ultimately leads to lung tumorigenesis and poor prognosis.
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PMID:Dysregulation of p53/Sp1 control leads to DNA methyltransferase-1 overexpression in lung cancer. 2057 Aug 96

We focused our attention on brahma-related gene 1 (BRG1), the ATPase subunit of the SWItch/Sucrose NonFermentable (SWI/SNF) chromatin remodeling complex, and analyzed its role in mesenchymal stem cell (MSC) biology. We hypothesized that deviation from the correct concentration of these proteins, which act at the highest level of gene regulation, may be deleterious for cells. We wanted to know what would happen if a cell had to cope with altered regulation of gene expression, either by upregulation or downregulation of BRG1. We assumed that cells would try to restore homeostasis or, alternatively, that the event could trigger senescence/apoptosis phenomena. To this end, in MSCs, we silenced BRG1gene. Knockdown of BRG1 expression induced a significant increase in senescent cells and decrease in apoptotic cells. It is interesting that BRG1 downregulation also induced an increase in heterochromatin. At the molecular level, these phenomena were associated with activation of retinoblastoma-like protein 2 (RB2)/P130- and P53-related pathways. Senescence was accompanied by reduced expression of some stemness-related genes. This is consistent with our previous research, which showed that BRG1 upregulation by ectopic expression also induced senescence processes. Together, these data suggest that BRG1 belongs to a class of genes whose expression is tightly regulated; hence, subtle alterations in BRG1 activity seem to negatively affect mechanisms regulating chromatin status and, in turn, impair cellular physiology.
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PMID:The BRG1 ATPase of chromatin remodeling complexes is involved in modulation of mesenchymal stem cell senescence through RB-P53 pathways. 2069 55


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