Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P04637 (p53)
 77,613 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Activation of Ca2+ -calmodulin- and cyclic AMP-dependent protein kinases has been suggested to be involved in stimulus-secretion coupling in the pancreatic beta-cell. To study the properties of suc kinases and their endogenous protein substrates homogenates of rat islets of Langerhans were incubated with [gamma-32P]ATP. Phosphorylated proteins were separated by sodium dodecyl sulphate polyacrylamide gel electrophoresis and detected by autoradiography. The phosphorylation of certain proteins could be enhanced by Ca2+ plus calmodulin or by cyclic AMP. The major effect of Ca2+ and calmodulin was to stimulate the phosphorylation of a protein (P53) of molecular weight 53,100 +/- 500 (n = 15). Maximum phosphorylation of protein P53 occurred within 2 min with 2 micrometers free Ca2+ and 0.7 micrometers calmodulin. Incorporation of label into protein P53 was inhibited by trifluoperazine or W7 but not by cyclic AMP-dependent protein kinase inhibitor. Phosphorylation of a proteins of similar molecular weight could be enhanced to a lesser extent in the absence of Ca2+ but in the presence of cyclic AMP and 3-isobutylmethylxanthine: this phosphorylation was blocked by cyclic AMP-dependent protein kinase inhibitor. Cyclic AMP also stimulated incorporation of label into polypeptides of molecular weights 55,000 and 70-80,000. The results are consistent with the hypothesis that protein phosphorylation mechanisms may play a role in the regulation of insulin secretion.
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PMID:Effects of Ca2+, calmodulin and cyclic AMP on the phosphorylation of endogenous proteins by homogenates of rt islets of langerhans. 627 12

2-chloroadenosine induced DNA fragmentation and cell death in human thymocytes primarily by Ca(2+)-dependent mechanisms. Incubation of human thymocytes with 2-chlorodeoxyadenosine (5-1000 nM) also induced cell death (apoptosis) which was dependent on macromolecule synthesis and involved activation of an endonuclease which was inhibited by Zn2+. The effect of 2-chlorodeoxyadenosine was prevented by addition of dipyridamole, a strong nucleoside transport inhibitor, or of deoxycytidine, previously shown to compete for uptake by deoxycytidine kinase. 2-Chlorodeoxyadenosine-induced apoptosis did not involve increases in the cytosolic Ca2+ concentration, but required the presence of intracellular Ca2+. It was not inhibited by activators of protein kinase C previously shown to inhibit Ca(2+)-dependent cell death. Addition of 2-chlorodeoxyadenosine induced an increase in the amount of p53 in human thymocytes, while 2-chloroadenosine had no effect. These data suggest that 2-chloroadenosine and 2-chlorodeoxyadenosine induce cell death in human thymocytes via different signalling pathways.
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PMID:The 2-chlorodeoxyadenosine-induced cell death signalling pathway in human thymocytes is different from that induced by 2-chloroadenosine. 748 99

Aggregation of the high affinity IgE receptors (Fc epsilon RI) on rat basophilic leukemia RBL-2H3 cells results in protein tyrosine phosphorylations. Previously we reported that there is prominent tyrosine phosphorylation of approximately 72-kDa proteins (pp72) and that the tyrosine kinase p72syk is one component of pp72. Here we studied further the relationship of p72syk to pp72. The aggregation of Fc epsilon RI induced the activation of p72syk which was parallel to its tyrosine phosphorylation. By in vitro kinase assay of immune complexes purified with anti-phosphotyrosine antibodies, p72syk was the major pp72 tyrosine kinase. However, by immunoblotting with anti-phosphotyrosine antibodies, p72syk was a minor component of pp72. The heterogeneous nature of pp72 was indicated by different studies. Under optimum conditions of one-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis, pp72 consisted of a heterogeneous group of 69-, 71-, and 72-kDa tyrosine-phosphorylated proteins. There were differences in the tyrosine phosphorylation of these proteins in cells activated in the absence of extracellular calcium or when stimulation was with the calcium ionophore A23187 or with phorbol myristate acetate. One of the proteins migrating at 69 kDa was p72syk. By two-dimensional gel electrophoresis pp72 was found to consist of multiple tyrosine-phosphorylated protens including 71-80-kDa proteins that associate with p53/56lyn. A 75-kDa tyrosine-phosphorylated protein, different from pp72, was identified as p75HS1 (SPY75). These results demonstrate the heterogeneous nature of the pp72 and that p72syk is activated after Fc epsilon RI aggregation.
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PMID:Activation of protein tyrosine kinase p72syk by Fc epsilon RI aggregation in rat basophilic leukemia cells. p72syk is a minor component but the major protein tyrosine kinase of pp72. 751 87

A variety of genotoxic agents can induce an accumulation of p53 protein in the nuclei of mammalian cells and lead to either growth arrest or apoptosis in a p53-dependent manner. Recently, the induction of the p53 pathway has also been reported for non-genotoxic agents such as heat shock and hypoxia, rendering it likely that p53 activity might be triggered by a wider range of cellular stress factors. Here we report the effect of calcium phosphate-mediated transfection, a technique commonly used in studies of transient gene expression in mammalian cells, on fibroblasts containing wild-type p53. Incubation with a calcium phosphate precipitate results in a transient growth arrest in the presence or absence of plasmid DNA. The effect is accompanied by a rise in p53 protein levels and increased transcription of a p53-dependent reporter construct and is not observed in fibroblasts derived from p53 knockout mice.
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PMID:p53-dependent growth arrest following calcium phosphate-mediated transfection of murine fibroblasts. 775 62

We previously immortalized normal human oral keratinocytes by transfection with recombinant HPV-16 DNA and subsequently exposed the cells to benzo(a)pyrene for 7 days. The exposure to benzo(a)pyrene modified the immortalized cells: the modified cells (HOK-16B-BaP) proliferated in an ordinary culture medium containing physiological calcium level (1.5 mM), but demonstrated only enhanced proliferation capacity without tumor formation in nude mice and failed to show in vitro anchorage-independency. In this study, we further modified the HOK-16B-BaP cells by subculturing the cells in a medium containing benzo(a)pyrene for 6 months. The cells were further modified with a chronic benzo(a)pyrene exposure and were termed HOK-16B-BaP-T cells (1) demonstrated a malignant phenotype in organotypic 'raft' culture, (2) showed in vitro anchorage-independency, (3) developed tumors in nude mice when injected subcutaneously, (4) contained a significantly higher copy number of intact and integrated HPV-16 DNA; (5) contained higher level of HPV-16 E6/E7 messages and E7 protein, (6) were more resistant to transforming growth factor-beta 1 and (7) secreted higher level of vascular endothelial growth factor with molecular weight of 56 kd than parental HOK-16B-BaP cells. However, the levels of p53 and ras proteins and the levels of p53, c-myc and c-fos transcripts in the HOK-16B-BaP-T cells were not different from those in the HOK-16B-BaP cells. The highly conserved coding regions of the p53, c-Ha-ras1, and c-Ki-ras2 genes of the tumor cells were not mutated. These data indicate that the HPV-immortalized human oral keratinocytes can convert to tumorigenic cells by chronic exposure to benzo(a)pyrene. The tumorigenic conversion seems to be associated with (1) the overexpression of viral oncogenes such as E6 and E7 genes, (2) the higher resistance of cells to transforming growth factor-beta 1 and (3) the high secretion of 56 kd vascular endothelial growth factor from the cells.
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PMID:Combined oral carcinogenicity of HPV-16 and benzo(a)pyrene: an in vitro multistep carcinogenesis model. 778 58

The regulation of p53 protein synthesis and p53-mediated gene transactivation were evaluated in cultured mouse keratinocytes maintained as basal cells or induced to differentiate by Ca2+ > 0.1 mM. p53 protein half-life, p53 protein synthesis and the level of p53 mRNA decreased during terminal differentiation, as detected by immunoprecipitation with a panel of p53-specific antibodies and Northern blotting. Thus differentiating keratinocytes have lower levels of p53 protein. This decline is not observed following growth arrest alone, or in papilloma cell lines which do not terminally differentiate in response to Ca2+. In contrast, the ability of endogenous p53 to transactivate transcription from the PG13 CAT plasmid increased during differentiation in vitro. This change in activity cannot be explained by changes in p53 conformation or nuclear localization. Consistent with these findings, mRNA for the p53-mediated genes WAF1 and mdm-2 increased with Ca(2+)-induced differentiation in a time dependent manner, suggesting activation of p53 contributes to the differentiated phenotype. However, p53-null mice exhibit histologically normal skin and epidermal keratinocytes from these mice express the appropriate markers of differentiation and suppression of DNA synthesis in vitro when the [Ca2+] is > 0.1 mM. The observation that proliferating cells have higher levels of p53 protein which is less active for its function than differentiated cell types could have a consequence for the selection of p53 gene mutations during carcinogenesis, depending upon the stage of differentiation of the tumor cell type.
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PMID:p53-mediated transcriptional activity increases in differentiating epidermal keratinocytes in association with decreased p53 protein. 778 75

Male weanling Fischer 344 rats were fed either a semipurified diet deficient in the methyl donors methionine, choline, and folic acid or a supplemented control diet for a period of 9 weeks. At intervals of 2, 5, and 7 days, 3 weeks, and 9 weeks after initiation of the respective diets, the relative level of DNA strand breaks and the degree of cytosine methylation were quantified in high molecular weight DNA and also within the p53 gene in liver samples from these rats. Genome-wide strand break accumulation was associated with progressive genomic hypomethylation and increased DNA methyltransferase activity. With the use of quantitative PCR as a gene-specific DNA strand break assay, unique DNA strand breaks were detected in exon 5 but not in exons 6-8 of the p53 gene, and were accompanied by significant p53 gene hypomethylation. DNA hypomethylation has been shown to alter the conformation and stability of the chromatin structure, rendering affected regions more accessible to DNA-damaging agents. To determine whether methylation status alters the sensitivity of DNA to strand breakage, DNA in isolated nuclei was methylated in vitro and exposed to endogenous calcium/magnesium-dependent endonuclease activated under defined conditions. The incidence of enzyme-induced DNA strand breaks was decreased significantly with increased DNA methylation. In nuclei isolated from livers of methyl-deficient rats, the hypomethylated DNA was found to be more sensitive to enzyme- and oxidant-induced DNA strand break induction. Taken together, these results provide evidence that DNA strand breaks are induced in high molecular weight DNA and also within the p53 gene in liver tissue from methyl-deficient rats. The increased incidence of these strand breaks in DNA from methyl-deficient rats may be related to alterations in chromatin accessibility associated with DNA hypomethylation.
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PMID:Breaks in genomic DNA and within the p53 gene are associated with hypomethylation in livers of folate/methyl-deficient rats. 779 83

Epidermal keratinocyte cultures were established from newborn mice expressing a null mutation in the p53 gene to explore the contribution of p53 to epidermal growth regulation and neoplasia. Keratinocytes were initiated by transduction with a replication-defective retrovirus encoding the v-rasHa oncogene and grafted onto nude mouse hosts. Tumors arising from keratinocytes heterozygous or null for functional p53 in the presence of v-rasHa have growth rates approximately 5-fold higher than those derived from p53(+/+) controls and rapidly form carcinomas, in contrast to the benign phenotype observed in p53(+/+)/v-rasHa grafts. In vitro, p53-deficient keratinocytes with and without v-rasHa expression display decreased responsiveness to the negative growth regulators transforming growth factors beta 1 and beta 2. In combination with v-rasHa, p53-deficient keratinocytes also exhibit decreased responsiveness to elevated Ca2+. These differences between genotypes cannot be attributed to changes in transforming growth factor beta receptor types present or altered levels of epidermal growth factor receptor and are independent of c-myc transcript levels. mRNA expression for the p-53 inducible protein WAF1 correlates with p53 gene dosage, but low levels are still detectable in p53(-/-) keratinocytes. The altered responsiveness of p53 deficient keratinocytes to negative growth regulators may provide a growth advantage to such cells in vivo and render them more susceptible to genetic alterations and malignant conversion.
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PMID:p53 gene dosage modifies growth and malignant progression of keratinocytes expressing the v-rasHa oncogene. 792 1

The surface immunoglobulin M (sIgM)-associated src family protein tyrosine kinases (PTKs) p55blk, p59fyn, and p53/56lyn become activated in B cells within seconds following sIgM cross-linking. Studies using protein tyrosine kinase (PTK) inhibitors have demonstrated that PTK activity is crucial for downstream events such as calcium flux, inositol phospholipid hydrolysis, and cell cycle entry. The roles that the individual src family PTKs play in sIgM signaling are largely unknown, however. In order to determine whether p59fyn plays a distinct role in sIgM signal transduction, the signaling capabilities of B cells isolated from fyn "knockout" mice were evaluated. We observed that in the absence of p59fyn, there was no demonstrable compromise of the sIgM-coupled signaling events measured (tyrosine phosphorylation, inositol phospholipid hydrolysis, and Ca2+ flux). We propose that either p59fyn is not involved in coupling sIgM to these specific signaling pathways or that other PTKs are able to compensate for the absence of p59fyn, indicating redundancy in the sIgM signaling pathways.
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PMID:Surface IgM-stimulated proliferation, inositol phospholipid hydrolysis, Ca2+ flux, and tyrosine phosphorylation are not altered in B cells from p59fyn-1- mice. 799 57

Apoptosis, or programmed cell death, is defined by morphologic change resulting in nonpathologic cell loss and is relevant to a wide spectrum of biology. The process is best characterized in the nematode Caenorhabditis elegans where ced genes mediate the death of specific cells during development. Some corresponding genes have been identified in mammalian cells. Expression of the mammalian bcl-2 gene (homologous to ced-9) suppresses apoptosis in many systems. The ced-3 gene is homologous to a mammalian protease. Increased levels of the tumor suppressor p53 due to DNA damage may result in either blockage of the cell cycle at G1 or apoptosis. Mutation of p53 is associated with decreased cell death from radiation and cytotoxic drugs. Initiation of the apoptotic pathway may occur as a consequence of conflicting growth signals. Hierarchical relationships variously between bcl-2, p53, myc, and other genes indicate a complex pattern of regulation. Stimuli resulting in apoptosis may cause production of free radicals and increased intracellular calcium concentration. The relationship of these changes to the hallmark of apoptosis, internucleosomal fragmentation of DNA, is unclear, and "laddering" of DNA is not always evident. Apoptotic DNA degradation probably occurs sequentially, initially involving breakage into 50 kilobases or larger fragments. The nuclease(s) responsible have not been identified, but deoxyribonuclease I is implicated. The association between nuclease activation and chromatin condensation is complex, and programmed cell death may be subject to cytoplasmic regulation. Available data suggest that clearer understanding of apoptosis will result in better cancer therapy.
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PMID:Mechanisms of apoptosis: integration of genetic, biochemical, and cellular indicators. 806 87


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