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)

Wild-type mouse p53, expressed in Escherichia coli, was phosphorylated by highly purified casein kinase I (CKI) from rabbit muscle. The major site of phosphorylation in the p53 was identified as serine 6, which is known to be phosphorylated in vivo. Serines 4 and 9 were also phosphorylated. To determine whether CKI is likely to be a physiological p53 kinase, SV3T3 cell lysates were fractionated on a Mono Q column and assayed for p53 kinase and casein kinase activities. Four p53 kinase activities were detected, one of which co-purified with CKI activity. This p53 kinase (designated PK270) further co-purified with CKI on sucrose gradients and had a native molecular weight, like CKI, in the range of 35,000-45,000. However, PK270 was separated from the bulk of CKI activity on a phosvitin-Sepharose affinity column, and was therefore likely to be a CKI-related kinase. In support of these conclusions, phosphorylation of p53, by both CKI and PK270, was inhibited by a peptide corresponding to a consensus CKI target sequence, but not by a non-specific peptide. Moreover, phosphopeptide analyses of p53 phosphorylated by CKI or by PK270 gave similar results, indicating that these two kinases phosphorylate the same sites in p53.
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PMID:Phosphorylation of the p53 tumour-suppressor protein at three N-terminal sites by a novel casein kinase I-like enzyme. 162 May 49

Recent studies have suggested that the p53 oncoprotein might function normally as a tumor suppressor. Mutations in highly conserved regions of the p53 gene have been observed in numerous types of tumors and tumor cell lines. To detect in a more sensitive manner p53 gene mutations in small cell lung cancer (SCLC) we utilized the single strand conformation polymorphism (SSCP) technique of Orita et al., (1989). Using PCR primers for the most highly conserved regions of the p53 gene, including exons 4-9, we have identified p53 mutations in 5 of 9 small cell lung cancer (SCLC) tumor DNA samples and in 1 SCLC cell line. None of the mutations seen in tumor DNA samples were present in normal DNA from the same patients, indicating that mutation of the p53 gene in these tumors was a somatic event. Of the six mutations observed, two were found in exon 7, three were found in the region encompassing exons 8 and 9, and one was found in the region encompassing exons 5 and 6. Nucleotide sequencing of one of the exon 7 mutations and one of the exon 8-9 mutations indicated that each was a C to T transition. In SCLC-6 the mutation resulted in substitution of serine for proline at amino acid 278 and in SCLC-4 substitution of tryptophan for arginine at amino acid 248, both nonconservative amino acid substitutions. Both of these changes are in regions of the p53 gene where mutations have been observed in other tumors. Two additional mutations were observed in SCLC cell lines using conventional PCR techniques. One of these is a mutation which results in altered splicing of the p53 pre-mRNA.
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PMID:Use of the single strand conformation polymorphism technique and PCR to detect p53 gene mutations in small cell lung cancer. 164 2

In this study, we analyzed 10 human squamous cell carcinomas (SCCs) for alterations in the p53 tumor suppressor gene in exons 4 through 9 by single-strand conformation polymorphism (SSCP) analysis. We found that 2 of 10 SCCs displayed unusual SSCP alleles at exon 7 of the p53 gene. Subsequent cloning and sequencing of PCR-amplified exon 7 DNA from these two tumors revealed that one had a G----A transition at the first position of codon 244, predicting a glycine-to-serine amino acid change, while the other tumor exhibited a G----T base change at the second nucleotide of codon 248, predicting an arginine-to-leucine substitution. Because the mutations in the p53 tumor suppressor gene in both tumors were located opposite potential pyrimidine dimer sites (C-C), it is consistent with these mutations having been induced by the ultraviolet radiation present in sunlight. These studies demonstrate that inactivation of the p53 tumor suppressor gene, as well as activation of ras oncogenes, may be involved in the pathogenesis of some human skin cancers.
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PMID:Mutations in the p53 tumor suppressor gene in human cutaneous squamous cell carcinomas. 179 82

Inherited susceptibility to a wide variety of neoplasias (Li-Fraumeni syndrome), has been shown in studies of one cancer-prone family, to have an intriguing association with an aberrant c-raf-1 gene and inheritance of a radioresistant phenotype in their non-cancerous skin fibroblasts. This association together with observations that DNA topoisomerases, when defective, can introduce errors into DNA and that these enzymes are perturbed in vitro by serine/threonine kinases similar to raf encoded proteins, prompted investigation of DNA topoisomerase activity of the family's fibroblasts. Since radioresistance was transferred to murine cells (NIH-3T3) when the aberrant c-raf-1 gene from this family was transfected, we also examined transformants containing this and other oncogenes. V-raf/c-myc and EJ-ras transformants were examined, the former because the family's skin fibroblasts also have 3-8-fold elevated myc expression (not apparently relevant to radioresistance) and the latter because ras, like raf, conveys radioresistance. The family members' fibroblasts and the three transfected murine lines, showed a similar perturbation of a spermidine and ATP-dependent DNA catenation activity (typical of DNA topoisomerase II). There was a significant positive correlation (r = 0.93; P = 0.0026) between the degree of activation of topoisomerase II and one measure of radioresistance (the Dq value). Relaxation of DNA supercoiling (topoisomerase I activity and other DNA nicking enzymes) was not abnormal. Cytotoxicity assays and evaluation of the influence of topoisomerase II inhibitors on DNA/protein complex formation, corroborated the existence of a qualitative topoisomerase II defect in the family's cells and transfectants. Although the contention that the qualitative topoisomerase II abnormalities observed here may be associated with malfunction is highly speculative, these findings may be relevant to the mechanism of oncogenesis, not only in this family, but with raf and ras type oncogenes.
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PMID:Aberrant DNA topoisomerase II activity, radioresistance and inherited susceptibility to cancer. 184 52

The Rev2 cell line is a cellular revertant of the SV40 wild-type transformed rat cell line SV-52 [Bauer, M., Guhl, E., Graessmann, M. & Graessmann, A. (1987). J. Virol., 61, 1821-1827]. To characterize the level of cellular interference with the SV40 large T antigen (large T)-induced transformation pathway in Rev2 cells, we analysed the biological and biochemical properties of large T expressed in Rev2 cells. We found that Rev2 cells encoded an authentic wild-type large T, with regard to its sequence and its transforming functions. No differences were found in the metabolic stability of large T, or in complex formation with the cellular p53 protein, or in p53 metabolic stabilization. In contrast to SV-52 cells, Rev2 cells showed no association of large T with the chromatin fraction of isolated nuclei. This difference correlated with a reduced affinity of the Rev2 large T to SV40 DNA in vitro. The T proteins from both cell lines were phosphorylated at the same multiple sites. However, in Rev2 cells the phosphorylation of large T at specific serine -residues was significantly reduced. Thus the revertant phenotype of Rev2 cells may be due to an altered phosphorylation state of its large T protein, leading to altered nuclear localization and reduced transforming activity. The alterations of Rev2 large T properties and phosphorylation were very similar to the changes observed with mutant large T in FR(tsA58)A cells, an SV40 tsA58 N-type transformant, when the cells had reverted to the normal phenotype at the non-permissive growth temperature. Thus altered phosphorylation might provide a common structural basis for the biological inactivation of the large T proteins in these cells.
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PMID:Altered phosphorylation at specific sites confers a mutant phenotype to SV40 wild-type large T antigen in a flat revertant of SV40-transformed cells. 192 16

Heterogeneity of p53 protein expression is seen in blast cells of patients with acute myelogenous leukemia (AML). p53 protein is detected in the blasts of certain AML patients but not in others. We have identified p53 protein variants with abnormal mobility on gel electrophoresis and/or prolonged half-life (t 1/2). We have sequenced the p53 coding sequence from primary blast cells of five AML patients and from the AML cell line (OCIM2). In OCIM2, a point mutation in codon 274 was identified that changes a valine residue to aspartic acid. A wild type p53 allele was not detected in these cells. Two point mutations (codon 135, cysteine to serine; codon 246, methionine to valine) were identified in cDNA from blasts of one AML patient. Both mutations were present in blast colonies grown from single blast progenitor cells, indicating that individual leukemia cells had sustained mutation of both p53 alleles. The cDNAs sequenced from blast samples of four other patients, including one with prolonged p53 protein t 1/2 and one with no detectable p53 protein, were fully wild type. Thus, the heterogeneity of p53 expression cannot be explained in all cases by genetic change in the p53 coding sequence. The prolonged t 1/2 of p53 protein seen in some AML blasts may therefore reflect changes not inherent to p53. A model is proposed in which mutational inactivation of p53, although not required for the evolution of neoplasia, would confer a selective advantage, favoring clonal outgrowth during disease progression.
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PMID:Mutation of the p53 gene in human acute myelogenous leukemia. 200 69

Synthetic peptide substrates for the cell division cycle regulated protein kinase, p34cdc2, have been developed and characterized. These peptides are based on the sequences of two known substrates of the enzyme, Simian Virus 40 Large T antigen and the human cellular recessive oncogene product, p53. The peptide sequences are H-A-D-A-Q-H-A-T-P-P-K-K-K-R-K-V-E-D-P-K-D-F-OH (T antigen) and H-K-R-A-L-P-N-N-T-S-S-S-P-Q-P-K-K-K-P-L-D-G-E-Y-NH2 (p53), and they have been employed in a rapid assay of phosphorylation in vitro. Both peptides show linear kinetics and an apparent Km of 74 and 120 microM, respectively, for the purified human enzyme. The T antigen peptide is specifically phosphorylated by p34cdc2 and not by seven other protein serine/threonine kinases, chosen because they represent major classes of such enzymes. The peptides have been used in whole cell lysates to detect protein kinase activity, and the cell cycle variation of this activity is comparable to that measured with specific immune and affinity complexes of p34cdc2. In addition, the peptide phosphorylation detected in mitotic cells is depleted by affinity adsorption of p34cdc2 using either antibodies to p34cdc2 or by immobilized p13, a p34cdc2-binding protein. Purification of peptide kinase activity from mitotic HeLa cells yields an enzyme indistinguishable from p34cdc2. These peptides should be useful in the investigation of p34cdc2 protein kinase and their regulation throughout the cell division cycle.
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PMID:Characterization of synthetic peptide substrates for p34cdc2 protein kinase. 204 31

The human anti-oncoprotein p53 is shown to be a substrate of cdc2. The primary site of phosphorylation is serine-315. Serine-315 is phosphorylated by both p60-cdc2 and cyclin B-cdc2 enzymes. The phosphorylation of p53 is cell cycle-dependent. The abundance of p53 also oscillates during the cell cycle. The protein is largely absent from cells that have just completed division but accumulates in cells during G1 phase. Phosphorylation by cdc2 might regulate the antiproliferative activity of p53.
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PMID:Human p53 is phosphorylated by p60-cdc2 and cyclin B-cdc2. 214 Nov 71

Enhanced protein phosphorylation seems to be characteristic for cell transformation. Viral or cellular oncogene products which are functionally implicated in cell transformation sometimes activate protein kinases, or they are protein kinases themselves. In the present paper we have shown that a protein kinase activity is tightly associated with immunopurified oncoprotein p53, either uncomplexed or in complex with SV40 large T antigen. Furthermore, we could demonstrate that the protein kinase associated with immunopurified p53 was independent of SV40 large T antigen. p53 in the immunocomplexes served as a substrate for this protein kinase. Phosphoamino acid analysis of in vitro phosphorylated p53 revealed a phosphorylation predominantly on serine residues similar to p53 phosphorylated in vivo. The use of different monoclonal antibodies did not reveal a total inhibition of the protein kinase activity. However, p53 precipitated with monoclonal antibodies which recognize a C-terminal domain, was phosphorylated in vitro to a lesser extent than p53 which was precipitated with monoclonal antibodies that recognize an N-terminal epitope. All subclasses of immunopurified p53 separable by sucrose density gradients or by sequential immunoprecipitation exhibited a protein kinase activity and served as substrates for this protein kinase. Moreover, a protein kinase activity was found to be associated with baculovirus expressed p53 which allows us to attribute this enzymatic activity more directly to p53.
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PMID:Protein kinase activity associated with immunopurified p53 protein. 214 85

The entire coding sequence of wild-type mouse p53 was expressed in Escherichia coli under control of the PL promoter of bacteriophage lambda. The bacterial p53 protein had identical mobility to p53 from SV3T3 cells on SDS polyacrylamide gels and was recognized in bacterial lysates by three p53-specific monoclonal antibodies, including PAb246 which is specific for wild-type mouse p53. Immunoprecipitates of the bacterial p53 were phosphorylated by a highly purified preparation of rat casein kinase II; the stoichiometry of incorporation was approximately 1 mol of phosphate per mol of p53. The phosphorylated residue was identified by phosphopeptide mapping as serine 389, which is a major site of p53 phosphorylation in vivo. p53 (serine 389) kinase activity was detected on lysates of SV3T3 cells; this activity co-purified with casein kinase II on phosphocellulose and Mono Q columns and was inhibited by heparin. Immunoprecipitates of the p53-T antigen complex from SV3T3 cells also had associated serine 389 kinase activity. Phosphorylation of serine 389 by this kinase was potently inhibited by heparin and quenched by excess unlabelled GTP. The data indicate that p53 is a physiological substrate of casein kinase II, which is stimulated in response to mitogens, phosphorylates nuclear oncoproteins, and may play a role in the transduction of extracellular signals to the nucleus.
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PMID:The p53 tumour suppressor protein is phosphorylated at serine 389 by casein kinase II. 214 48


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