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

Wild-type and mutant p53 proteins exhibit opposing activities in respectively suppressing and promoting tumour development. In a rat embryo fibroblast cell line transformed with a murine temperature-sensitive p53 gene, p53 functions as a oncogene at 37 degrees C and as a tumour suppressor at 32 degrees C [Michalovitz, D., Halevy, O. & Oren, M. (1990). Cell, 62, 671-680]. We have used this cell line to investigate whether this temperature-dependent switching of function involves changes in the phosphorylation of p53 protein. Monoclonal antibodies PAb246 and PAb240 were used to immunoprecipitate metabolically 32P-labelled p53 protein in the 'wild-type' or mutant conformation from cells grown at 32 degrees C or 37 degrees C. Tryptic phosphopeptide maps were prepared from the isolated 'wild-type' and mutant p53 proteins. At 32 degrees C and 37 degrees C phosphopeptide maps of the 'wild-type' and mutant protein were identical. This demonstrates that the temperature-dependent conformation change, and associated functional change, in the p53 protein does not involve a change in the state of phosphorylation.
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PMID:The conformational change of a murine temperature-sensitive p53 protein is independent of a change in phosphorylation status. 163 Aug 25

To facilitate the purification of wild type p53 protein, we established a recombinant p53 vaccinia viral expression system. Using this efficient eukaryotic expression vector, we found that the expressed p53 proteins retained their specific structural characteristics. A comparison between wild type and mutant p53 proteins showed the conservation of the typical subcellular localization and the expression of specific antigenic determinants. Furthermore, wild type p53 exhibited a typical binding with large T antigen, whereas no binding was detected with mutant p53. Both wild type and mutant p53 proteins were highly stable and constituted 5-7% of total protein expressed in the infected cells. These expression recombinant viruses offer a simple, valuable system for the purification of wild type and mutant p53 proteins that are expressed abundantly in eukaryotic cells.
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PMID:Expression of wild-type and mutant p53 proteins by recombinant vaccinia viruses. 163 Sep 14

Germ-line mutations in the p53 tumor suppressor gene have been observed in patients with Li-Fraumeni syndrome, brain tumors, second malignancies, and breast cancers. It is unclear whether all of these mutations have inactivated p53 and thereby provide an increased risk for cancer. Therefore, it is necessary to establish the biological significance of these germ-line mutations by the functional and structural analysis of the resulting mutant p53 proteins. We analyzed the ability of seven germ-line mutant proteins observed in patients with Li-Fraumeni syndrome, second primary neoplasms, or familial breast cancer to block the growth of malignant cells and compared the structural properties of the mutant proteins to that of the wild-type protein. Six of seven missense mutations disrupted the growth inhibitory properties and structure of the wild-type protein. One germ-line mutation retained the features of the wild-type p53. Genetic analysis of the breast cancer family in which this mutation was observed indicated that this germ-line mutation was not associated with the development of cancer. These results demonstrate that germ-line p53 mutations observed in patients with Li-Fraumeni syndrome and with second malignancies have inactivated the p53 tumor suppressor gene. The inability of the germ-line p53 mutants to block the growth of malignant cells can explain why patients with these germ-line mutations have an increased risk for cancer. The observation of a functionally silent germ-line mutation indicates that, before associating a germ-line tumor suppressor gene mutation with cancer risk, it is prudent to consider its functional significance.
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PMID:Germ-line mutations of the p53 tumor suppressor gene in patients with high risk for cancer inactivate the p53 protein. 163 Nov 37

Basal cell carcinoma (BCC) of the skin is the most common human cancer, but its molecular-genetic pathogenesis is unclear. In many other types of cancer, mutations of the tumor-suppressor gene p53 occur frequently and may lead to overexpression of a long-lived mutant form of p53 protein. In this study, overexpression of p53 protein was detected immunohistochemically in 30 (83%) of 36 specimens of BCC of the head and neck. The same regions of tumor typically were reactive both with a monoclonal antibody (PAb240) specific for the mutant protein and with one (PAb1801) directed against an epitope common to both wild-type and mutant p53 protein. Keratinocytes of chronically sun-exposed epidermis adjacent to BCCs also focally overexpressed p53 protein in the majority of cases, whereas those of sun-protected buttock skin did not. Mutation of p53 may form an important part of the pathogenetic sequence in a majority of cases of BCC.
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PMID:Overexpression of p53 protein in basal cell carcinomas of human skin. 163 67

The development of Friend virus induced murine erythroleukaemia is associated with specific genetic events. One of these events is loss of wild type p53 expression, which can occur by internal deletion or proviral insertion in the p53 gene and by single point mutations in the coding sequence. In all cases, the corresponding wild type allele is absent. The high frequency of observed p53 mutations strongly suggests that inactivation of p53 may be an obligatory step in the development of Friend disease. Further evidence that abrogation of normal p53 expression contributes to the development of malignant clones was provided by in vitro reconstitution experiments in Friend cell lines: whereas exogenous mutant p53 was stably expressed in p53 negative FCLs, long term wild type p53 expression was not detected. Friend erythroleukaemia arises as a late consequence of infection of susceptible mice with Friend virus. In addition to p53 gene mutations, proviral insertions occur frequently adjacent to one of two cellular genes, Spi-1/PU.1 or Fli-1. Aberrant expression of these genes may therefore be involved in virus induced erythroleukaemia. Interaction of SFFV env gp55 with the EPO-R also appears to be important in providing a mitogenic signal to infected cells. The order in which these events occur and whether the order is relevant to the progression of the disease are not known. Investigation of the stepwise appearance of these events could provide information on the possible interactions of the gene products involved. Abrogation of normal p53 expression is not restricted to Friend erythroleukaemia: the observation of p53 mutations and allele loss in human breast, lung, colon and hepatocellular carcinomas and in leukaemia suggests that mutation of p53 may be the most common genetic abnormality detected in human cancer (reviewed in this issue). Studies of p53 expression in FCLs provided an early indication that p53 was a tumour suppressor gene. Further studies of the mechanisms by which wild type and mutant p53 affect the growth of p53 negative FCLs may reveal important biochemical properties of p53 in relation to cell cycle control and differentiation of erythroid cells.
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PMID:Friend virus induced murine erythroleukaemia: the p53 locus. 163 45

The DNA from a wide variety of human tumors has sustained mutations within the conserved p53 coding regions. We have purified wild-type and tumor-derived mutant p53 proteins expressed from baculovirus vectors and examined their interactions with SV40 DNA. Using DNAase I footprinting assays, we observed that both human and murine wild-type p53 proteins bind specifically to sequences adjacent to the late border of the viral replication origin. By contrast, mutant p53 proteins failed to bind specifically to these sequences. SV40 T antigen prevented wild-type p53 from interacting with this region. These data show that normal but not oncogenic forms of p53 are capable of sequence-specific interactions with viral DNA. Furthermore, they provide insights into the mechanisms by which viral proteins might regulate the control of viral growth and cell division.
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PMID:Wild-type but not mutant p53 immunopurified proteins bind to sequences adjacent to the SV40 origin of replication. 164 78

Clinical and experimental evidence is consistent with a key role for transforming human papilloma viruses (HPVs) in the aetiology of anogenital carcinoma. Cervical carcinoma does, however, occasionally occur in the absence of HPV sequences (Riou et al., 1990). We have used a direct cDNA/PCR sequencing protocol to analyse the sequence of p53 mRNA expressed by HPV positive and negative cervical carcinoma cell lines. Six cell lines which contain HPV sequences express p53 mRNA which has wild-type sequence throughout conserved boxes 2, 3, 4 and 5. The two HPV negative cell lines (C33a and HT3) express mutant p53 mRNA. In each case the mutation occurs in an evolutionarily conserved amino acid. Our data suggest that loss of wild-type p53 function is important in development of cervical carcinoma, and that this might be achieved either by mutation within the p53 gene or the presence of a virally encoded p53 binding protein.
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PMID:p53 point mutation in HPV negative human cervical carcinoma cell lines. 164 90

The aberrant overexpression of interleukin 6 (IL-6) is implicated as an autocrine mechanism in the enhanced proliferation of the neoplastic cell elements in various B- and T-cell malignancies and in some carcinomas and sarcomas; many of these neoplasms have been shown to be associated with a mutated p53 gene. The possibility that wild-type (wt) p53, a nuclear tumor-suppressor protein, but not its transforming mutants might serve to repress IL-6 gene expression was investigated in HeLa cells. We transiently cotransfected these cells with constitutive cytomegalovirus (CMV) enhancer/promoter expression plasmids overproducing wt or mutant human or murine p53 and with appropriate chloramphenicol acetyltransferase (CAT) reporter plasmids containing the promoter elements of human IL-6, c-fos, or beta-actin genes or of porcine major histocompatibility complex (MHC) class I gene in pN-38 to evaluate the effect of the various p53 species on these promoters. Murine and human wt p53 derived from pCMVNc9 and pC53-SN3, respectively, strongly repressed the IL-6 (promoter position -225 to +13), c-fos (-711 to +42), beta-actin (-3400 to +912), and MHC (-528 to -38) promoters in serum-induced HeLa cells; additionally, IL-6 promoter/CAT transcription unit constructs induced by IL-1, phorbol ester, or pseudorabies virus were also repressed by wt human and murine p53. The murine transforming mutant p53 (pCMVc5) was less active in repressing the IL-6, c-fos, beta-actin, and MHC promoter constructs. The human p53 mutant derived from pC53-SCX3 was also less active than the wt protein in repressing the IL-6, c-fos, beta-actin, and MHC promoters, except that serum-induced IL-6/CAT expression was equally repressed by both human wt and mutant p53. In similar transient transfection experiments in HeLa cells, overexpression of the wt human retinoblastoma susceptibility gene product, RB, was found to repress the serum-induced IL-6 (-225 to +13), c-fos (-711 to +42), and beta-actin (-3400 to +912) promoters but not the PRV-induced IL-6 (-110 to +13) or the serum-induced MHC (-528 to -38) promoters. These observations identify transcriptional repression as a property of p53 and suggest that p53 and RB may be involved as transcriptional repressors in modulating IL-6 gene expression during cellular differentiation and oncogenesis.
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PMID:Repression of the interleukin 6 gene promoter by p53 and the retinoblastoma susceptibility gene product. 165 55

We examined samples of tumors of human breast, ovary, and colon of various degrees of malignancy for the expression of p53 protein, using a panel of anti-p53 antibodies and peroxidase immunohistochemistry. Of 66 tumor cases (24 cases of ovarian carcinoma, 23 cases of colon adenocarcinoma, and 19 cases of breast carcinoma), 36 (53%) showed high levels of expression of p53 using a human-specific antibody, and 16 (24%) showed high expression of a mutant form of p53. In the mutant p53-positive breast tumor samples, six (86%) were positive for HER-2/neu reactivity, compared with colon (0/4) and ovarian tumors (1/5). The pattern of p53 intracellular localization and tissue distribution, and the relationship between the expression of mutant p53 and cell differentiation, were also examined; poorly differentiated cells showed either overexpression of p53 or higher levels of mutant p53 in comparison with more normal cells.
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PMID:Immunohistochemical analysis of p53 and HER-2/neu proteins in human tumors. 168 Aug 97

Cancer is a genetic disease caused by defective control of cell proliferation. As cancer cells divide, the genetic defect is inherited by each daughter cell, leading to tumour development with possible progression to malignancy. The identification of those genes linked with cancer is essential for our understanding of the regulation of cell proliferation and for the therapeutic management of cancer cell growth. Recent studies have revealed that p53 is the most commonly affected gene in human cancer. It is a single copy gene and functions in the regulation of cell proliferation. Mutation of p53 is linked with tumour development, and this may involve abnormal functioning of mutant p53 protein. A mutant allele of p53 is functionally temperature-sensitive and can promote or suppress cell proliferation. The tertiary structure of the mutant protein is also sensitive to temperature and adopts promoter and suppressor forms of p53. A conformation model for the functioning of p53 proposes that wild-type p53 is induced to change from suppressor to promoter form during the cell growth response. This model predicts that any mutation that deregulates the normal control of p53 conformation may lead to cancer.
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PMID:A conformation hypothesis for the suppressor and promoter functions of p53 in cell growth control and in cancer. 168 37


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