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

The normal functioning of p53 is thought to involve p53 target proteins. We have previously identified a cellular 35 kd protein associated with p53 and now report evidence identifying this 35 kd protein as p34cdc2, product of the cell cycle control cdc2 gene. The association between p53 and p34cdc2 was detected in SV3T3 and T3T3 cell lines, both expressing the wild-type p53 phenotype, and in 3T3tx cells, expressing 'mutant' p53 phenotype. Binding of the mutant p53 phenotype with p34cdc2 was greatly reduced relative to wild-type. Complexes of p53-p34cdc2 may represent inactivation or activation of either component. The p34cdc2 kinase functions at cell cycle control points and is necessary for entry and passage through mitosis. It also operates in G1 and is involved in the commitment of cells into the proliferative cycle. Since we were unable to detect p53-p34cdc2 complexes in mitotic cells we propose that the interaction between p53 and p34cdc2 may be functional in cell growth control, possibly to promote or to suppress cell proliferation.
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PMID:p53 is associated with p34cdc2 in transformed cells. 216 34

The p53 tumor suppressor is a transcription factor frequently mutated in human malignancies. Tumor-derived p53 missense mutants are defective in sequence-specific DNA binding and fail to activate p53 target genes. mAb PAb421 was shown previously to restore DNA binding to selected p53 mutants in vitro. Here we show that mAb PAb421 when microinjected into human SW480 colorectal carcinoma cells restores the transcription activation function to the resident mutant p53 (arg to his 273, pro to ser 309). Codon 273 is the second most frequent p53 missense mutant found in human tumors. Our results lend support to the concept of restoring wild-type function to mutant p53 as a strategy for cancer therapy.
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PMID:Microinjection of monoclonal antibody PAb421 into human SW480 colorectal carcinoma cells restores the transcription activation function to mutant p53. 762 52

The p53 protein is a multifunctional transcription factor which orchestrates cellular responses to DNA damage, so helping to conserve genomic stability. It may also regulate genes involved in intercellular signalling, such as thrombospondin, a negative regulator of angiogenesis and metastatic spread. Activation of p53 target genes requires sequence-specific DNA binding, a function which maps to the central core of the protein. Missense point mutations within this domain inactivate p53 tumour suppressor function and involve either (i) DNA contact residues, or (ii) residues important for conformational structure. Using in vitro techniques we have analysed seven DNA contact mutants and 17 structural mutants known to occur in cancer. We show that DNA contact mutants can be carried into specific DNA interaction when co-expressed with wild type protein. For structural mutants, 9/17 retained DNA binding capacity and, with one exception, DNA binding correlated with conformational flexibility of the mutant protein. The exception was Asp281, which appeared essential for DNA interaction, probably due to its ability to form salt bridges with DNA contact residues Arg273 and Arg280. We suggest that different classes of p53 mutant may prove amenable to different strategies for restoration of wild type tumour suppressor function as means of anti-cancer therapy.
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PMID:Specific DNA binding by different classes of human p53 mutants. 765 40

The p53 tumor suppressor protein is a transcriptional activator, which can mediate apoptotic cell death in a variety of cell types. To determine whether sequence-specific trans-activation is a prerequisite for the induction of apoptosis by p53, the apoptotic effects of various p53 deletion mutants were monitored in an assay based on the transient transfection of HeLa cells. A truncated protein (p53dl214), containing only the first 214 amino-terminal residues of murine p53, induced extensive apoptosis, albeit at a slower rate than trans-activation-competent wild-type p53. p53dl214 also suppressed the transformation of rat fibroblasts by several oncogene combinations and particularly by myc plus ras and HPV E7 plus ras. p53dl214 lacks a major portion of the DNA-binding domain and cannot activate p53-responsive promoters. Moreover, a human p53 protein carrying mutations in residues 22 and 23 also triggered HeLa cell apoptosis, despite failing to induce significant activation of relevant p53 target promoters. These data suggest the existence of two p53-dependent apoptotic pathways--one requiring activation of specific target genes, and the other independent of sequence-specific trans-activation. The latter pathway may actually be totally uncoupled from the binding of p53 to its consensus DNA sites. The relative contribution of trans-activation-independent apoptosis to tumor suppression by p53 may be dictated by the specific genetic lesions present in the particular tumor.
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PMID:Induction of apoptosis in HeLa cells by trans-activation-deficient p53. 765 68

Employing the myeloblastic leukemia M1 cell line, which does not express endogenous p53, and genetically engineered variants, it was recently shown that activation of p53, using a p53 temperature-sensitive mutant transgene (p53ts), resulted in rapid apoptosis that was delayed by high level ectopic expression of bcl-2. In this report, advantage has been taken of these M1 variants to investigate the relationship between p53-mediated G1 arrest and apoptosis. Flow cytometric cell cycle analysis has provided evidence that activation of wild-type (wt) p53 function in M1 cells resulted in the induction of G1 growth arrest; this was clearly seen in the M1p53/bcl-2 cells because of the delay in apoptosis that unmasked p53-induced G1 growth arrest. This finding was further corroborated at the molecular level by analysis of the expression and function of key cell cycle regulatory genes in M1p53 versus M1p53/bcl-2 cells after the activation of wt p53 function; events that take place at early times during the p53-induced G1 arrest occur in both the M1p53 and the M1p53/bcl-2 cells, whereas later events occur only in the M1p53/bcl-2 cells, which undergo delayed apoptosis, thereby allowing the cells to complete G1 arrest. Finally, it was observed that a spectrum of p53 target genes implicated in p53-induced growth suppression and apoptosis were similarly regulated, either induced (gadd45, waf1, mdm2, and bax) or suppressed (c-myc and bcl-2), after activation of wt p53 function in M1p53 and M1p53/bcl-2 cells. Taken together, these findings show that wt p53 can simultaneously induce the genetic programs of both G1 growth arrest and apoptosis within the same cell type, in which the genetic program of cell death can proceed in either G1-arrested (M1p53/bcl-2) or cycling (M1p53) cells. These findings increase our understanding of the functions of p53 as a tumor suppressor and how alterations in these functions could contribute to malignancy.
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PMID:Dissection of the genetic programs of p53-mediated G1 growth arrest and apoptosis: blocking p53-induced apoptosis unmasks G1 arrest. 774 28

Over the past year, insights have been made into the biochemistry and biological effects of p53. The high-resolution three-dimensional structure has been determined for the central core and carboxy-terminal domain of the protein, important p53 target genes (such as WAF1) have been identified, and insight has been gained into the relationship between p53-mediated growth arrest and apoptosis.
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PMID:Biochemical properties and biological effects of p53. 774 31

Mutation of the p53 gene is one of the most common genetic lesions observed in human cancer. The p53 protein functions as a transcription factor, however it is still unresolved to what extend this property is related to its tumour suppressor activity. Since there is evidence that protein modifications as well as protein-protein interactions may regulate p53 function, we have studied p53 protein-DNA complex formation in nuclear extracts prepared from human tumour cell lines. In 13 different cell lines PAb421-induced DNA binding activity was compared to the level and conformation of the endogenous p53 protein. Surprisingly, sequence-specific p53 DNA binding activity was detected not only in cell lines that express wild-type p53, but also in seven cell lines which contain only mutant protein. Oligonucleotide competition analyses with various p53 target sequences and methylation interference experiments establish that wild-type and mutant p53 differ significantly in their sequence-specific interactions. Our analysis also provides evidence that the PAb1620 conformation is neither sufficient nor essential for DNA binding of endogenous p53 and that the cellular environment in addition to the specific point mutation may influence p53 DNA binding activity.
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PMID:p53 derived from human tumour cell lines and containing distinct point mutations can be activated to bind its consensus target sequence. 789 29

WAF1/Cip1 was recently identified as the wild-type p53 target that appears to mediate the tumor suppressing effects of p53. We investigated the mechanisms of regulation of WAF1/Cip1 gene expression in human breast carcinoma (HBC) cells. Our results demonstrate that the HBC cells harboring wild-type p53 express 26-33-fold higher WAF1/Cip1 mRNA levels than the cells harboring mutant p53. The DNA damaging agent etoposide induced p53 accumulation only in cells harboring wild-type p53 yet it induced WAF1/Cip1 gene expression in cells carrying wild-type or mutant p53, suggesting the involvement of p53-dependent and independent signaling pathways in the regulation of WAF1/Cip1 gene expression. Serum starvation-induced growth arrest although not altering the endogenous p53 levels or its ability to transactivate the reporter gene, induced WAF1/Cip1 gene expression in cells carrying wild-type as well as mutant p53. These results further implicated the involvement of p53-independent signal transduction pathways in WAF1/Cip1 gene regulation. Our data also suggest that WAF1/Cip1 gene expression is tightly associated with cell cycle progression in cells containing either wild-type or mutant p53. WAF1/Cip1 expression was transiently induced in response to serum treatment and declined as the cells passed through the S-phase of the cell cycle. We thus provide evidence that the mechanisms of WAF1/Cip1 gene regulation involve p53-dependent and independent signaling pathways in HBC.
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PMID:Mechanisms of regulation of WAF1/Cip1 gene expression in human breast carcinoma: role of p53-dependent and independent signal transduction pathways. 797 Jun 99

DNA-damaging agents such as ionizing radiation (IR) activate the tumor suppressor p53 and in some cases can cause apoptosis. M1 cells, which do not express the endogenous tumor suppressor gene p53, undergo apoptosis following activation of a temperature sensitive p53 transgene, where it has been shown that bax, an important mediator of apoptosis, is a p53 target gene (Selvakumaran et al, Oncogene 9, 1791-8, 1994). Since p53 can function as a transcription factor after activation by IR, the genetic response to this stress was examined in a panel of human cells with defined p53 status. Like the p53-regulated gene gadd45, bax was rapidly induced, as measured by increased mRNA levels, in the p53 wt (wild type) human myeloid line ML-1, and it was not induced in cells lacking functional p53. However, unlike other p53-regulated genes, bax was only induced in p53 wt cells in which IR also triggered apoptosis. In the case of bcl2, which opposes bax function, mRNA levels were reduced in ML-1 cells after IR. Thus, bax appears to be an unique p53-regulated gene in that its induction by IR not only requires functional p53 but also requires that the cells be apoptosis "proficient."
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PMID:Induction of bax by genotoxic stress in human cells correlates with normal p53 status and apoptosis. 797 Jul 35

Deregulated expression of the c-myc proto-oncogene can lead to apoptosis under certain physiological conditions. By introducing a conditionally active Myc allele into primary embryo fibroblasts null for p53, and into fibroblasts without endogenous p53 expression but ectopically expressing a temperature-sensitive p53 allele, we show that expression of wild-type p53 is required for susceptibility to Myc-mediated apoptosis. Although ectopic expression of wild-type p53 blocked cells in the G1 phase of the cell cycle, G1 arrest by isoleucine starvation, in a manner independent of p53, did not confer susceptibility to apoptosis. Thus, growth arrest per se is not sufficient to induce Myc-mediated apoptosis; instead, a property intrinsic to p53 is specifically required. Moreover, apoptosis did not require induction of p53 target proteins, including the cyclin-dependent kinase inhibitor p21waf1/cip1. Therefore, the role of p53 in apoptosis may be distinct from its role in cell cycle arrest.
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PMID:Myc-mediated apoptosis requires wild-type p53 in a manner independent of cell cycle arrest and the ability of p53 to induce p21waf1/cip1. 799 20


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