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

In normal cells, p53 is maintained at a low level by ubiquitin-mediated proteolysis, but after genotoxic insult this process is inhibited and p53 levels rise dramatically. Ubiquitination of p53 requires the ubiquitin-activating enzyme Ubc5 as a ubiquitin conjugation enzyme and Mdm2, which acts as a ubiquitin protein ligase. In addition to the N-terminal region, which is required for interaction with Mdm2, the C-terminal domain of p53 modulates the susceptibility of p53 to Mdm2-mediated degradation. To analyze the role of the C-terminal domain in p53 ubiquitination, we have generated p53 molecules containing single and multiple lysine-to-arginine changes between residues 370 and 386. Although wild-type (WT) and mutant molecules show similar subcellular distributions, the mutants display a higher transcriptional activity than WT p53. Simultaneous mutation of lysine residues 370, 372, 373, 381, 382, and 386 to arginine residues (6KR p53 mutant) generates a p53 molecule with potent transcriptional activity that is resistant to Mdm2-induced degradation and is refractory to Mdm2-mediated ubiquitination. In contrast to WT p53, transcriptional activity directed by the 6KR p53 mutant fails to be negatively regulated by Mdm2. Those differences are also manifest in HeLa cells which express the human papillomavirus E6 protein, suggesting that p53 C-terminal lysine residues are also implicated in E6-AP-mediated ubiquitination. These data suggest that p53 C-terminal lysine residues are the main sites of ubiquitin ligation, which target p53 for proteasome-mediated degradation.
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PMID:Multiple C-terminal lysine residues target p53 for ubiquitin-proteasome-mediated degradation. 1104 42

The c-myb proto-oncogene product (c-Myb) is a sequence-specific DNA-binding protein that functions as a transcriptional activator. The transcriptional coactivator CREB-binding protein (CBP) binds via its KIX domain to the activation domain of c-Myb and mediates c-Myb-dependent transcriptional activation. CBP possesses intrinsic histone acetyltransferase activity, and can acetylate not only histones but also certain transcriptional factors such as GATA1 and p53. Here we demonstrate that the C/H2 domain of CBP, which is critical for the acetyltransferase activity, also directly interacts with the negative regulatory domain (NRD) of c-Myb. Consistent with this observation, CBP acetylated c-Myb in vitro at Lys(438) and Lys(441) within the NRD. In addition, CBP acetylated c-Myb in vivo not only at the sites found in this study but also at the p300-induced acetylation sites reported recently. Replacement of lysine by arginine at all of these sites dramatically decreased the trans-activating capacity of c-Myb. The results of transcriptional activation assays with c-Myb acetylation site mutants suggested that acetylation of c-Myb at each of these five sites synergistically enhances c-Myb activity. Mutations of these acetylation sites reduced the strength of the interaction between c-Myb and CBP. Thus, acetylation of c-Myb by CBP increases the trans-activating capacity of c-Myb by enhancing its association with CBP. These results demonstrate a novel molecular mechanism of regulation of c-Myb activity.
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PMID:Increased affinity of c-Myb for CREB-binding protein (CBP) after CBP-induced acetylation. 1107 48

To investigate the effect of mutations in the p53 C-terminal domain on MDM2-mediated degradation, we introduced single and multiple point mutations into a human p53 cDNA at four putative acetylation sites (amino acid residues 372, 373, 381, and 382). Substitution of all four lysine residues by alanines (the A4 mutant) and single lysine-to-alanine substitutions were functional in sequence-specific DNA binding and transactivation; however, the A4 mutant protein was resistant to MDM2-mediated degradation, whereas the single lysine substitutions were not. Although the A4 mutant protein and the single lysine substitutions both bound MDM2 reasonably well, the single lysine substitutions underwent normal MDM2-dependent ubiquitination, whereas the A4 protein was inefficiently ubiquitinated. In addition, the A4 mutant protein was found in the cytoplasm as well as in the nucleus of a subpopulation of cells, unlike wild-type p53, which is mostly nuclear. The partially cytoplasmic distribution of A4 mutant protein was not due to a defect in nuclear import because inhibition of nuclear export by leptomycin B resulted in nuclear accumulation of the protein. Taken together, the data suggest that mutations in the putative acetylation sites of the p53 C-terminal domain interfere with ubiquitination, thereby regulating p53 degradation.
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PMID:Multiple lysine mutations in the C-terminal domain of p53 interfere with MDM2-dependent protein degradation and ubiquitination. 1109 89

Histone N-acetyltransferases (HATs) are a group of enzymes which acetylate specific lysine residues in the N-terminal tails of nucleosomal histones to promote transcriptional activation. Recent structural and enzymatic work on the GCN5/PCAF HAT family has elucidated the structure of their catalytic domain and mechanism of histone acetylation. However, the substrate specificity of these enzymes has not been quantitatively investigated. Utilizing a novel microplate fluorescent HAT assay which detects the enzymatic production of coenzyme A (CoA), we have compared the activities of the HAT domains of human PCAF and its GCN5 homologue from yeast and Tetrahymena and found that they have similar kinetic parameters. PCAF was further assayed with a series of different length histone H3 peptide substrates, which revealed that the determinants for substrate recognition lie within a 19-residue sequence. Finally, we evaluated the acetylation of three putative PCAF substrates, histones H3 and H4 and the transcription factor p53, and have determined that histone H3 is significantly preferred over the histone H4 and p53 substrates. Taken together, the fluorescent acetyltransferase assay presented here should be widely applicable to other HAT enzymes, and the results obtained with PCAF demonstrate a strong substrate preference for the N-terminal residues of histone H3.
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PMID:Application of a fluorescent histone acetyltransferase assay to probe the substrate specificity of the human p300/CBP-associated factor. 1111 80

Histone acetylation has long been associated with transcriptional activation, whereas conversely, deacetylation of histones is associated with gene silencing and transcriptional repression. Here we report that inhibitors of histone deacetylase (HDAC), depsipeptide and trichostatin A, induce apoptotic cell death in human lung cancer cells as demonstrated by DNA flow cytometry and Western immunoblot to detect cleavage of poly(ADP-ribose) polymerase. This HDAC inhibitorinduced apoptosis is greatly enhanced in the presence of the DNA methyltransferase inhibitor, 5-aza-2'-deoxycytidine (DAC). The HDAC inhibitor-induced apoptosis appears to be p53 independent, because no change in apoptotic cell death was observed in H1299 cells that expressed exogenous wild-type p53 (H1299 cells express no endogenous p53 protein). To further investigate the mechanism of DAC-enhanced, HDAC inhibitor-induced apoptosis, we analyzed histone H3 and H4 acetylation by Western immunoblotting. Results showed that depsipeptide induced a dose-dependent acetylation of histones H3 and H4, which was greatly increased in DAC-pretreated cells. By analyzing the acetylation of specific lysine residues at the amino terminus of histone H4 (Ac-5, Ac-8, Ac-12, and Ac-16), we found that the enhancement of HDAC inhibitor-induced acetylation of histones in the DAC-pretreated cells was not lysine site specific. These results demonstrate that DNA methylation status is an important determinant of apoptotic susceptibility to HDAC inhibitors.
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PMID:DNA methyltransferase inhibition enhances apoptosis induced by histone deacetylase inhibitors. 1124 29

The p53 tumor suppressor gene is one of the most frequently altered genes in human malignancies. To explore the implication of p53 alteration in Ewing's sarcoma, we analyzed the deletion and sequence alterations of p53 and abnormal amplification of MDM2, which acts as a functional inhibitor of p53, in 35 tissue specimens. Quantitative genomic PCR analysis showed that 2 of 35 tumors have extremely low levels of the p53 gene, indicating a homozygous deletion of the gene. Mutational analysis of exons 4 to 9 of p53 by PCR-SSCP revealed that 3 of 35 tumors carry sequence alterations in exons 5 or 8, and DNA sequencing analysis identified missense point mutations at codon 132 (AAG-->ATG, lysine-->methionine) and codon 135 (TGC-->TCC, cystein-->serine) in exon 5, and codon 287 (GAG-->GTG, glutamic acid-->valine) in exon 8 from these tumors. No abnormal amplification of the MDM2 gene was recognized. Taken together, our data demonstrate that p53 is genetically altered in a small fraction of Ewing's sarcoma.
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PMID:P53 mutations in Ewing's sarcoma. 1129 75

The p53 tumor suppressor is activated in response to various stresses driving the cells into growth arrest or apoptosis. We have addressed the question of how disintegration of microtubule system induces activation of p53. Depolymerization of microtubules by colcemid in rat and human quiescent fibroblasts resulted in accumulation of transcriptionally active p53 that caused cell-cycle arrest at the G1/S boundary. The p53 activation correlated with prominent activation of Erk1/2 MAP kinases that resulted from colcemid-stimulated development of focal adhesions. Inhibition of focal contacts development by plating of cells onto poly-L-lysine abrogated both Erk1/2 and p53 activations in colcemid-treated cells, while plating of cells onto fibronectin caused transient up-regulation of p53 even in the absence of colcemid. Pre-treatment of cells with the specific MEK1 inhibitor PD098059 also attenuated colcemid-induced p53 activation and G1 cell cycle arrest. Cell types which either failed to develop focal adhesions in response to colcemid treatment (human MCF-7 epithelial cells), or lacked colcemid-induced sustained Erk activation (primary mouse embryo fibroblasts and 12(1) cells) showed virtually no p53 up-regulation in response to disruption of microtubules during G0/G1. Our results indicate that p53 activation is not triggered by disintegration of microtubule system by itself, but rather originates from some of the consequences of such disintegration, in particular, from the development of focal adhesions leading to activation of Erk signaling pathway.
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PMID:p53 activation in response to microtubule disruption is mediated by integrin-Erk signaling. 1131 25

p53 tumor suppressor is a subject of several post-translational modifications, including phosphorylation, ubiquitination and acetylation, which regulate p53 function. A new covalent modification of p53 at lysine 386 by SUMO-1 was recently identified. To elucidate the function of sumoylated p53, we compared the properties of wild type p53 and sumoylation-deficient p53 mutant, K386R. No differences were found between wild type p53 and K386R mutant of p53 in transactivation or growth suppression assays. Moreover, overexpression of SUMO-1 has no effect on p53-regulated transcription. Biochemical fractionation showed that sumoylated p53 is localized in the nucleus and is tightly bound to chromatin structures. p53 and SUMO-1 co-localized in PML nuclear bodies in 293 cells and the nucleoli in MCF7 and HT1080 cells. However, sumoylation-deficient p53 mutant showed a similar pattern of intranuclear localization, suggesting that SUMO-1 does not target p53 to subnuclear structures. These data indicate that SUMO-1 modification of p53 at lysine 386 may not be essential for p53's cellular localization, transcriptional activation, or growth regulation.
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PMID:Functional analysis and intracellular localization of p53 modified by SUMO-1. 1142 Jun 69

We cloned a novel ankyrin repeat protein, Arpp, by immunoscreening a cDNA library constructed from a human esophageal carcinoma cell line, TE1, with an antibody directed to a hypothetical protein encoded by antisense p53 mRNA. Arpp protein is composed of 333 amino acids and contains four ankyrin-like repeat motifs in the middle portion of the protein, a PEST-like sequence and a lysine-rich sequence similar to a nuclear localization signal in the N-terminal region, and a proline-rich region containing consensus phosphorylation sites in the C-terminal region. Protein sequence analysis revealed that Arpp is homologous (52.7% identity) to Carp which is shown to be involved in the regulation of the transcription of the cardiac ventricular myosin light chain 2 gene. Arpp mRNA was found to be expressed in normal skeletal and cardiac muscle. Interestingly, Arpp expression was detectable in bilateral ventricles, but undetectable in bilateral atria and large vessels, suggesting that Arpp may play a specific function in cardiac ventricles as well as skeletal muscles.
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PMID:Identification of a novel human ankyrin-repeated protein homologous to CARP. 1145 52

The p33ING1 protein is a regulator of cell cycle, senescence, and apoptosis. Three alternatively spliced transcripts of p33ING1 encode p47ING1a, p33ING1b, and p24ING1c. We cloned an additional ING family member, p33ING2/ING1L. Unlike p33ING1b, p33ING2 is induced by the DNA-damaging agents etoposide and neocarzinostatin. p33ING1b and p33ING2 negatively regulate cell growth and survival in a p53-dependent manner through induction of G(1)-phase cell-cycle arrest and apoptosis. p33ING2 strongly enhances the transcriptional-transactivation activity of p53. Furthermore, p33ING2 expression increases the acetylation of p53 at Lys-382. Taken together, p33ING2 is a DNA damage-inducible gene that negatively regulates cell proliferation through activation of p53 by enhancing its acetylation.
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PMID:DNA damage-inducible gene p33ING2 negatively regulates cell proliferation through acetylation of p53. 1148 24


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