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)

We examined 28 cases of surgically resected gastric cancer, excluding the diffuse type, for loss of heterozygosity (LOH) on 12 chromosomal arms using polymorphic DNA markers. LOH on chromosome 18q was detected in 61% (14 of 23) of the cases by the probes OLVIIA8, OLVIIE10, p15-65, SAM 1.1, and OS-4, and a putative common region showing LOH included the locus of the DCC tumor suppressor gene. LOH on chromosome 17p was also frequently found (8 of 19 or 42% of the cases) by the probes p10-3 and pHF12-1, and in 5 of these 6 cases the LOH on chromosome 17p was accompanied by LOH on chromosome 18q. On the other hand, the incidence of LOH was 30% or less using probes pHRnES, pHF12-65, p-c-mybE2.6, NJ3 3.2, pHF12-8, pHINS6.0, p9D11, hp2-alpha, pCMM6, and P1A5 on chromosomes 1q, 5, 6q, 7q, 9, 11p, 13q, 16q, 20, and 22q, respectively. LOH on chromosome 18q was frequent irrespective of the depth of tumor invasion, whereas the incidence of LOH on chromosome 17p was higher in the cases in which the tumor invaded beyond the muscularis propria than in those in which tumor invasion was limited to the submucosa and muscularis propria. These results suggest that LOH on chromosome 18q occurs at an earlier stage than LOH on chromosome 17p and that the inactivation of tumor suppressor genes located on chromosome 17p and 18q (e.g., the p53 and DCC genes) is critically involved in the development of the majority of gastric cancers. While alteration of the p53 gene is observed in various human cancers, that of the DCC gene is considered to occur more selectively in gastrointestinal cancers.
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PMID:Frequent loss of heterozygosity at the DCC locus in gastric cancer. 159 22

Sites of cytosine methylation are known to be hot spots for C.G to T.A mutations in a number of systems, including human cells. Traditionally, spontaneous hydrolytic deamination of 5-methylcytosine to thymine has been invoked as the cause of this phenomenon. We show here that a bacterial cytosine methyltransferase can convert 5-methylcytosine in DNA to thymine and that this reaction creates a mutational hot spot at a site of DNA methylation. The reaction is fairly insensitive to the methyl donor in the reaction, S-adenosylmethionine. In many cancers, the most frequent class of mutations is C to T changes within CG dinucleotides of the tumor suppressor gene p53. Because of the similarities of the reaction mechanisms of mammalian and bacterial enzymes and the physiology of the cancer cells, this reaction is expected to contribute to mutations at CG dinucleotides in precancerous cells.
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PMID:A cytosine methyltransferase converts 5-methylcytosine in DNA to thymine. 757 83

Dietary folate/methyl deficiency provides a unique model of endogenous hepatocarcinogenesis in which to study progressive alterations in DNA methylation patterns during tumor progression in vivo. Weanling male F344 rats were given a semi-purified diet deficient in the methyl donors choline, methionine and folic acid for a period of 9 weeks. Using a genomic sequencing procedure based on the PCR amplification of bisulfite-modified DNA, the methylation status of individual CpG sites within exons 6 and 7 of the p53 gene in liver samples from control and deficient rats was determined. Treatment of denatured nuclear DNA with sodium bisulfite quantitatively converts all cytosine residues to uracil which are then amplified as thymine in the PCR reaction. In contrast, 5-methylcytosine is resistant to bisulfite deamination under the reaction conditions and is amplified as cytosine. Automated sequencing of bisulfite-modified DNA will then elucidate the methylation status of each cytosine residue within a defined gene sequence. In addition to evaluation of the methylation status of the p53 gene, the relative activity of the DNA methyltransferase was also quantified in nuclear extracts from control and folate/methyl deficient rats. The results indicate that specific 5-methyl cytosines within the hepatic p53 gene from methyl deficient rats are resistant to demethylation despite the diet-induced decrease in S-adenosylmethionine and the increase in cell proliferation associated with this dietary intervention. Progressive demethylation was observed at other methylated cytosine residues in folate/methyl deficient rats after 9 weeks despite a paradoxical increase in DNA methyltransferase activity. The application of this sequence-specific technology will allow the definition of the methylation status of every CpG site within a coding sequence or promoter region and should provide new insights into mechanisms and consequences of methylation dysregulation during progressive multistage carcinogenesis.
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PMID:Differential sensitivity to loss of cytosine methyl groups within the hepatic p53 gene of folate/methyl deficient rats. 758 11

Changes in the pattern of DNA methylation have been a consistent finding in cancer cells. The mostly descriptive nature of these studies and the fact that both hypo- and hypermethylation have been observed at various loci have made it difficult to assess whether these changes are causally involved in the transformation process or whether they reflect the altered physiology of rapidly dividing cancer cells. It is clear, however, that DNA methylation plays an important role in the generation of mutations in human tumors. The high incidence of C-to-T transitions found in the p53 tumor-suppressor gene is attributed to the spontaneous deamination of 5-methylcytosine residues. The multiple observations linking DNA methylation to cancer can be resolved in a model proposing that the high rate of mutation at CpG dinucleotides is due in part to methyltransferase-facilitated deamination. Support for a role of DNA methyltransferase as a mutator enzyme is provided by work with a prokaryotic DNA methyltransferase under S-adenosyl-methionine methyl-donor limiting conditions. Methyl-donor limiting conditions might arise in early stages of tumor development, leading to high rates of methyltransferase-mediated CpG mutagenesis, as seen in human tumors. Such a mechanism is consistent with the frequently reported methionine auxotrophy of cancer cells and with the tumorigenic effects of methyl-deficient diets. Methyl deficiency in tumor cells is also consistent with the commonly observed global hypomethylation of tumor cell DNA, despite normal or even high levels of DNA methyltransferase expression.
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PMID:DNA methylation and cancer. 784 43

Carcinogenesis is a complex process characterized by the cumulative activation of various oncogenes and the inactivation of suppressor genes. Epigenetic mechanisms are also involved. Mutational activation of ras family genes occurs in most spontaneous or carcinogen-induced liver tumors, in susceptible mice, and less frequently in preneoplastic lesions. This suggests a pathogenetic role of these changes in hepatic carcinogenesis, in the mouse. Overexpression of various growth-related genes occurs in preneoplastic tissue during rat liver carcinogenesis, but mutational activation of protooncogenes, notably of ras family genes, seems to be a late and rare event, while c-myc amplification is a late but frequent event in both rodent and human carcinogenesis. However, mutation of the suppressor p53 gene has been found in relatively early preneoplastic lesions in rat liver, and it may be frequently seen in human hepatocellular carcinomas. The possibility that this mutation is involved in the initiation stage of liver carcinogenesis is an attractive hypothesis which needs further evaluation. DNA hypomethylation is involved in carcinogenesis, but the mechanisms underlying this effect are still elusive. Hypomethylation of growth-related genes is associated with their overexpression and this could favor overgrowth of preneoplastic liver tissue. Decrease in S-adenosyl methionine/S-adenosylhomocysteine (SAM/SAH) ratio occurs in the liver of rats fed a methyl deficient diet, which is a carcinogenic treatment, and in preneoplastic liver tissue, developing in initiated/promoted rats fed an adequate diet. The role of low SAM/SAH ratio in carcinogenesis is substantiated by the tumor chemopreventive effect of lipotropic compounds. Treatment with exogenous SAM prevents the development of preneoplastic and neoplastic lesions in rat liver. This is associated with recovery of SAM/SAH ratio, DNA methylation and inhibition of growth-related gene expression. SAM effect on prenoplastic cell growth is abolished by 5-azacytidine, a hypomethylating agent, indicating the involvement of DNA methylation. The possibility that in SAM-treated rats, methylation and inhibition of the expression of growth-related genes is implicated in growth restraint is attractive and should be further evaluated. Modulation of rat liver carcinogenesis by influencing gene expression through DNA methylation or other epigenetic mechanisms could be a new approach to chemoprevention of these tumors.
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PMID:Genomic abnormalities in hepatocarcinogenesis. Implications for a chemopreventive strategy. 823 5

C --> T transitions at CpG sites are the most prevalent mutations found in the p53 tumor suppressor gene in human colon tumors and in the germline (Li-Fraumeni syndrome). All of the mutational hot spots are methylated to 5-methylcytosine, and it has been hypothesized that the majority of these mutations are caused by spontaneous hydrolytic deamination of this base to thymine. We have previously reported that bacterial methyltransferases induce transition mutations at CpG sites by increasing the deamination rate of C --> U when the concentration of the methyl group donor S-adenosylmethionine (AdoMet) drops below its Km, suggesting an alternative mechanism to create these mutations. Unrepaired uracil pairs with adenine during replication, completing the C --> T transition mutation. To determine whether this mechanism could contribute to the development of human colon cancer, we examined the level of DNA (cytosine-5)-methyltransferase (MTase) expression, the concentration of AdoMet, and the activity of uracil-DNA glycosylase in human colon tissues, and searched for the presence of mutations in the MTase gene. Using reverse transcription-PCR methods, we found that average MTase mRNA expression levels were only 3.7-fold elevated in tumor tissues compared with surrounding normal mucosa from the same patient. Also, no mutations were found in conserved regions of the gene in 10 tumors sequenced. High-performance liquid chromatographic analysis of extracts from the same tissues showed that AdoMet concentrations were not reduced below the Km value for the mammalian enzyme, and the concentration ratio of AdoMet:S-adenosylhomocysteine, the breakdown product of AdoMet and the competitive MTase inhibitor, did not differ significantly. Finally, extracts from the tumor tissue efficiently removed uracil from DNA. Therefore, biochemical conditions favoring a mutagenic pathway of C --> U --> T were not found in a target tissue known to undergo a high rate of C --> T transitions at CpG sites.
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PMID:Mechanisms for the involvement of DNA methylation in colon carcinogenesis. 862 14

More than 60 previously undetected SAM domain-containing proteins have been identified using profile searching methods. Among these are over 40 EPH-related receptor tyrosine kinases (RPTK), Drosophila bicaudal-C, a p53 from Loligo forbesi, and diacyglycerol-kinase isoform delta. This extended dataset suggests that SAM is an evolutionary conserved protein binding domain that is involved in the regulation of numerous developmental processes among diverse eukaryotes. A conserved tyrosine in the SAM sequences of the EPH related RPTKs is likely to mediate cell-cell initiated signal transduction via the binding of SH2 containing proteins to phosphotyrosine.
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PMID:SAM as a protein interaction domain involved in developmental regulation. 900 98

Arsenic is a potent human carcinogen to which there is significant worldwide exposure through natural contamination of food and drinking water sources. Because arsenic is detoxified via methylation using a methyltransferase (MTase) and S-adenosylmethionine (SAM) as the methyl donor, we hypothesized that a mechanism of carcinogenesis of arsenic could involve alterations of MTase/SAM-dependent DNA methylation of a tumor suppressor gene. We found that exposure of human lung adenocarcinoma A549 cells to sodium arsenite (0.08-2 microM) or sodium arsenate (30-300 microM), but not dimethylarsenic acid (2-2000 microM), produced significant dose-responsive hypermethylation within a 341-base pair fragment of the promoter of p53. This was determined by quantitative PCR/HpaII restriction site analysis to analyze methylation status of two CCGG sites. In experiments with arsenite, DNA sequencing using bisulfite to visualize 5-methylcytosine (5-MeC) over the entire promoter region confirmed data obtained by restriction analysis. Limited data using SssI methylase also suggested that over-methylation of CpG sequences may exist over the entire genome in response to arsenite exposure. We propose that alteration of DNA methylation by arsenic offers a plausible, unified hypothesis for the carcinogenic mechanism of action of arsenic, and we present a model for arsenic carcinogenesis that utilizes perturbations of DNA methylation as the basis for the carcinogenic effects of arsenic.
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PMID:Arsenic alters cytosine methylation patterns of the promoter of the tumor suppressor gene p53 in human lung cells: a model for a mechanism of carcinogenesis. 921 64

The major observation of this investigation is that a single intraperitoneal injection of butylated hydroxytoluene (BHT, 60 mg/kg body mass) results within a few hours in a strong increase in nuclear DNA(cytosine-5)-methyl transferase (methyl transferase) activity in the liver, kidneys, heart, spleen, brain and lungs of male rats. In most organs, the rise in methyl transferase activity is observed as early as 4 h after BHT injection, it reaches a maximum at 8 h and then, except for lungs and brain, gradually decreases to its initial level at 16 h. At the maximum induction times, the methyl transferase activity in liver, kidney and spleen increases by about 16-, 3- and 5-fold, respectively. A second BHT injection at 96 h results in a secondary rise in hepatic methyl transferase activity. Isoelectric focusing electrophoresis of control rat liver nuclear extracts showed methyl transferase activity in the pI 4.7 and 7.4 protein fractions. Both fractions methylate calf thymus DNA better than they do Drosophila melanogaster DNA. In similar extracts from BHT-treated rats, the methyl transferase activity is found in three protein fractions with pI values equal to 4.0, 6.2 and 9.5, respectively. Most of the methyl transferase fractions from the livers of BHT-treated rats methylate the completely unmethylated D. melanogaster DNA better than they do calf thymus DNA. Thus, BHT induces methyl transferase activity that preferably provides de novo DNA methylation. BHT injection had no significant effect on the hepatic contents of S-adenosylmethionine (AdoMet), S-adenosylhomocysteine (AdoHcy) and AdoMet/AdoHcy ratios. While BHT injection did not alter the 5-methyldeoxycytidine content in liver DNA, it did appear to alter such content in other organs. BHT appears to cause the reversible changes in the methylation status of an internal cytosine residue in some CCGG sites of the rat liver cytosine DNA-methyl transferase gene. BHT induces also hypomethylation of the renal methyl transferase gene and the hepatic c-Ha-ras gene. While BHT also increases the hepatic mRNA transcripts for the S-adenosylmethionine synthetase and the p53 genes, it had no detectable effects on the corresponding mRNA transcripts for methyl transferase homologous to murine methyl transferase. Thus, BHT induces tissue-specific reversible changes in methyl transferase activity and methylation of total DNA and various genes in rats. A strong increase in methyl transferase activity in rat liver is accompanied with BHT-induced change in the methyl transferase set observed in this organ.
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PMID:Butylated hydroxytoluene modulates DNA methylation in rats. 978 Feb 27

p73 and p63 are two recently cloned genes with homology to the tumor suppressor p53, whose protein product is a key transcriptional regulator of genes involved in cell cycle arrest and apoptosis. While all three proteins share conserved transcriptional activation, DNA-binding and oligomerization domains, p73 and p63 have an additional conserved C-terminal region. We have determined the three-dimensional solution structure of this conserved C-terminal domain of human p73. The structure reveals a small five-helix bundle with striking similarity to the SAM (sterile alpha motif) domains of two ephrin receptor tyrosine kinases. The SAM domain is a putative protein-protein interaction domain found in a variety of cytoplasmic signaling proteins and has been shown to form both homo- and hetero-oligomers. However, the SAM-like C-terminal domains of p73 and p63 are monomeric and do not interact with one another, suggesting that this domain may interact with additional, as yet uncharacterized proteins in a signaling and/or regulatory role.
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PMID:Solution structure of a conserved C-terminal domain of p73 with structural homology to the SAM domain. 1044 9


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