Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0027651 (tumor)
 685,946 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The relationship between the grade of astrocytic tumor and the expression of deoxyribonucleic acid methyltransferase (DNA-MTase) gene was examined. The levels of DNA-MTase messenger ribonucleic acid (mRNA) were measured by semiquantitative reverse transcriptase-polymerase chain reaction in surgical specimens from 12 astrocytic tumors (4 astrocytomas, 6 anaplastic astrocytomas, and 2 glioblastomas) and two normal brain tissues, and in four glioma cell lines. Compared to normal brain tissues, the levels of DNA-MTase mRNA were increased by 16- to 55-fold in low grade astrocytomas, and significantly increased by 200- to 4500-fold in high grade astrocytomas (anaplastic astrocytomas and glioblastomas) and more than 4500-fold in glioma cell lines. In situ hybridization with paraffin-embedded surgical specimens of human astrocytic tumors showed DNA-MTase mRNA was abundantly expressed in high grade astrocytomas. The detection of increased DNA-MTase expression in astrocytic tumor indicates involvement in the tumorigenesis and suggests that blocking of this change with specific inhibitors may offer new therapeutic strategies for malignant astrocytic tumors.
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PMID:Increased expression of deoxyribonucleic acid methyltransferase gene in human astrocytic tumors. 1110 93

We evaluated the significance of aberrant DNA methyltransferase expression in human carcinogenesis by examining 32 colorectal and 34 stomach cancers. Levels of mRNAs encoding DNA methyltransferases were measured by reverse transcription, followed by real-time quantitative detection of PCR products. The DNA methylation state of CpG islands and peri-centromeric satellite regions was examined by bisulfite modification and Southern blotting, respectively. The average level of mRNA for DNMT1 and DNMT3b in colorectal and stomach cancers was significantly higher than in corresponding non-cancerous mucosae, whereas the average level of mRNA for DNMT2 was significantly lower in colorectal and stomach cancers than in non-cancerous tissue. Over-expression of DNMT3b in stomach cancer was significantly higher in cases with lymph node metastasis than in cases without. DNA hypermethylation on the p16, human Mut L homologue-1 and thrombospondin-1 genes and the methylated in tumor (MINT) 1, 2, 12, 25 and 31 clones was found in 23%, 27%, 9%, 23%, 20%, 23%, 20% and 10% of the colon cancers and in 9%, 19%, 30%, 25%, 34%, 19%, 81% and 3% of the stomach cancers, respectively. Criteria for identification of the CpG island methylator phenotype (CIMP) were met in 23% of colorectal cancers and 31% of stomach cancers. DNA hypomethylation on satellites 2 and 3 was detected in 0% and 8% of colorectal and stomach cancers, respectively. Over-expression of DNMT1 mRNA was significantly associated with CIMP, whereas the level of DNMT3b mRNA was not associated with CIMP or DNA hypomethylation of peri-centromeric satellite regions. These data suggest that both over-expression of the maintenance DNA methyltransferase DNMT1 and over-expression of a newly identified de novo DNA methyltransferase, DNMT3b, are involved in human carcinogenesis, probably at different stages and through different mechanisms.
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PMID:DNA methyltransferase expression and DNA methylation of CPG islands and peri-centromeric satellite regions in human colorectal and stomach cancers. 1114 46

Aberrant hypermethylation of tumor suppressor genes plays an important role in the development of many tumors. Recently identified new DNA methyltransferase (DNMT) genes, DNMT3A and DNMT3B, code for de novo methyltransferases. To determine the roles of DNMT3A, DNMT3B, as well as DNMT1, in the development of leukemia, competitive polymerase chain reaction (PCR) assays were performed and the expression levels of DNMTs were measured in normal hematopoiesis, 33 cases of acute myelogenous leukemia (AML), and 17 cases of chronic myelogenous leukemia (CML). All genes were constitutively expressed, although at different levels, in T lymphocytes, monocytes, neutrophils, and normal bone marrow cells. Interestingly, DNMT3B was expressed at high levels in CD34(+) bone marrow cells but down-regulated in differentiated cells. In AML, 5.3-, 4.4-, and 11.7-fold mean increases were seen in the levels of DNMT1, 3A, and 3B, respectively, compared with the control bone marrow cells. Although CML cells in the chronic phase did not show significant changes, cells in the acute phase showed 3.2-, 4.5-, and 3.4-fold mean increases in the levels of DNMT1, 3A, and 3B, respectively. Using methylation-specific PCR, it was observed that the p15(INAK4B) gene, a cell cycle regulator, was methylated in 24 of 33 (72%) cases of AML. Furthermore, AML cells with methylated p15(INAK4B) tended to express higher levels of DNMT1 and 3B. In conclusion, DNMTs were substantially overexpressed in leukemia cells in a leukemia type- and stage-specific manner. Up-regulated DNMTs may contribute to the pathogenesis of leukemia by inducing aberrant regional hypermethylation. (Blood. 2001;97:1172-1179)
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PMID:Expression of DNA methyltransferases DNMT1, 3A, and 3B in normal hematopoiesis and in acute and chronic myelogenous leukemia. 1122 58

To evaluate the significance of alterations in DNA methylation during human hepatocarcinogenesis, we examined levels of mRNA for DNA methyltransferases and methyl-CpG-binding proteins and the DNA methylation status in 67 hepatocellular carcinomas (HCCs). The average level of mRNA for DNMT1 and DNMT3a was significantly higher in noncancerous liver tissues showing chronic hepatitis or cirrhosis than in histologically normal liver tissues, and was even higher in HCCs. Significant overexpression of DNMT3b and reduced expression of DNMT2 were observed in HCCs compared with the corresponding noncancerous liver tissues. DNA hypermethylation on CpG islands of the p16 (8% and 66%) and hMLH1 (0% and 0%) genes and methylated in tumor (MINT) 1 (6% and 34%), 2 (24% and 58%), 12 (21% and 33%), 25 (0% and 5%), and 31 (0% and 23%) clones, and DNA hypomethylation on satellites 2 and 3 (18% and 67%), were detected in noncancerous liver tissues and HCCs, respectively. There was no significant correlation between the expression level of any DNA methyltransferase and DNA methylation status. Reduced expression of DNA repair protein, MBD4, was significantly correlated with poorer tumor differentiation and involvement of portal vein. Slightly reduced expression of MBD2 was detected in HCCs, and the expression of MeCP2 was particularly reduced in HCCs with portal vein involvement. These data suggest that overexpression of DNMT1 and DNMT3a, DNA hypermethylation on CpG islands, and DNA hypomethylation on pericentromeric satellite regions are early events during hepatocarcinogenesis, and that reduced expression of MBD4 may play a role in malignant progression of HCC.
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PMID:Expression of mRNA for DNA methyltransferases and methyl-CpG-binding proteins and DNA methylation status on CpG islands and pericentromeric satellite regions during human hepatocarcinogenesis. 1123 Jul 35

The hamster ornithine decarboxylase antizyme (ODC-Az) cDNA was transfected into the hamster malignant oral keratinocyte cell line, HCPC-1. Ectopic expression of ODC-Az resulted in the reversion of malignant phenotypes and alteration of DNA methylation status of CCGG sites. The phenotypes examined include ODC enzymatic activity, doubling time, morphological change, anchorage dependent growth, tumorigenicity in nude mice, induction of epithelial differentiation marker protein (involucrin), and change of cell cycle position. Comparison of CCGG DNA methylation status of the ODC-Az and control vector transfectants revealed a significant increase in demethylation of 5-methyl cytosines (m5C) of CCGG sites in the ODC-Az transfectants. Ectopic expression of ODC-Az gene in hamster malignant oral keratinocytes led to reduce ODC activity and the subsequent demethylation of 5-methyl cytosines, presumably via the ODC/ polyamines/ decarboxylated S-adenosylmethionine (dc-AdoMet) pathways. Our data suggest that ODC-Az shared the same pathway of polyamines/ dc-AdoMet/DNA methyltransferase (DNA MTase). We propose that ODC-Az mediates a novel mechanism in tumor suppression by DNA demethylation and presumably re-activation of key cellular genes silenced by DNA hypermethylation during cancer development. Oncogene (2001) 20, 24 - 33.
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PMID:Induction of epithelial differentiation and DNA demethylation in hamster malignant oral keratinocyte by ornithine decarboxylase antizyme. 1124 2

Hybridon is conducting studies of the DNA methyltransferase gene and has identified specific sequences on mRNA as targets for chemically-modified antisense oligonucleotides. Hybridon has synthesized compounds that alter methylation of cultured human cancer cells and inhibit their ability to grow in cell culture and inhibit tumor formation in mice [191303]. The work is being carried out in collaboration with McGill University in Montreal and as part of a joint venture called MethylGene, set up by Hybridon and private investors. GEM-231 (a mixed backbone oligonucleotide) is a strand of synthetic DNA, which has been modified with 2'-O-methyl ribose at both ends in order to resemble RNA. It has the ability to inhibit expression of the R1-alpha subunit of protein kinase A, a gene whose expression has been associated with many types of cancer [273331,275860].
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PMID:Technology evaluation: GEM-231, Hybridon Inc. 1124 79

Transcriptional silencing of tumor suppressor genes by DNA methylation occurs in cancer cell lines and in human tumors. This has led to the pursuit of DNA methyltransferase inhibition as a drug target. 5-Aza-2'-deoxycytidine [5-aza-CdR (decitabine)], a potent inhibitor of DNA methyltransferase, is a drug currently in clinical trials for the treatment of solid tumors and leukemia. The efficacy of 5-aza-CdR may be related to the induction of methylation-silenced tumor suppressor genes, genomic hypomethylation, and/or enzyme-DNA adduct formation. Here, we test the hypothesis that 5-aza-CdR treatment is perceived as DNA damage, as assessed by the activation of the tumor suppressor p53. We show that 1) colon tumor cell lines expressing wild-type p53 are more sensitive to 5-aza-CdR mediated growth arrest and cytotoxicity; 2) the response to 5-aza-CdR treatment includes the induction and activation of wild-type but not mutant p53 protein; and 3) the induction of the downstream p53 target gene p21 is partially p53-dependent. The induction of p53 protein after 5-aza-CdR treatment did not correlate with an increase in p53 transcripts, indicating that hypomethylation at the p53 promoter does not account for the p53 response. It is relevant that 5-aza-CdR has shown the greatest promise in clinical trials for the treatment of chronic myelogenous leukemia, a malignancy in which functional p53 is often retained. Our data raise the hypothesis that p53 activation may contribute to the clinical efficacy and/or toxicity of 5-aza-CdR.
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PMID:Activation of the p53 DNA damage response pathway after inhibition of DNA methyltransferase by 5-aza-2'-deoxycytidine. 1125 19

Previous studies have demonstrated that optimal reversal of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) resistance requires complete inactivation of the DNA repair protein O(6)-methylguanine DNA methyltransferase (MGMT) for at least 24 h following BCNU administration. In preparation for clinical trials at this institution, this study was undertaken to compare the efficacy of a conventional single-bolus dose versus double-bolus dose treatments with O(6)-benzylguanine (BG) in depleting MGMT activity in vivo. In xenograft human glioma SF767 tumors, a single 30-mg/kg bolus dose of BG completely inhibited MGMT activity for at least 8 h, but approximately 50% of the basal MGMT activity recovered within 24 h. To sustain the MGMT depletion for 24 h, a second bolus injection of BG at escalating doses was administered 8 h after the first dose. Second bolus doses of 5, 10, and 15 mg/kg BG attenuated the MGMT recovery in a dose-dependent manner compared with the single 30-mg/kg BG dose alone. When the 15-mg/kg BG dose was administered 8 h after the 30-mg/kg initial dose, MGMT activity was completely inactivated in the tumor xenografts for 24 h. This double-bolus BG treatment also depleted MGMT activity in normal murine tissues, including the liver, kidney, lung, brain, spleen, and bone marrow; and the kinetics of MGMT recovery varied among these tissues. When combined with BCNU treatment, the double-bolus BG treatment would be expected to produce greater antitumor activity in future trials than the conventional single-bolus BG treatment.
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PMID:Comparison of single- versus double-bolus treatments of O(6)-benzylguanine for depletion of O(6)-methylguanine DNA methyltransferase (MGMT) activity in vivo: development of a novel fluorometric oligonucleotide assay for measurement of MGMT activity. 1130 39

Aberrant genome-wide hypomethylation has been thought to be related to tumorigenesis. However, its mechanism and implications in hepatocellular carcinogenesis remain to be elucidated. Samples of hepatoma (hepatocellular carcinoma, HCC) and paired non-HCC liver tissues were obtained from 17 HCC patients. Normal liver tissues obtained from three individuals were used as controls. Compared with the paired non-HCC liver tissues, genome-wide 5-methylcytosine content in HCC was reduced in all of the tested HCC samples (P < 0.001). Conversely, genome-wide 5-methylcytosine content did not significantly differ among normal, noncirrhotic, and cirrhotic liver tissues. Moreover, the degree of reduced DNA methylation was related to late histopathological HCC grade (P = 0.005) and large tumor size (P = 0.079). Compared with the paired non-HCC liver tissues, expression of DNA methyltransferases DNMT-1, DNMT-3A, and DNMT-3B and the DNA methyltransferase-like gene, DNMT-2, was up-regulated in 53, 41, 59, and 47% of the HCC samples, respectively. Surprisingly, small amounts of LINE-1 retrotransposon transcripts were detected in HCC and non-HCC as well as normal liver tissues, and the expression levels were not significantly different in HCC compared with the paired non-HCC or normal liver tissues. Of interest, the 3' ends of these LINE-1 transcripts were truncated. Our findings suggest that genome-wide hypomethylation in HCC is a continuing process that persists throughout the lifetime of the tumor cells rather than a historical event occurring in precancer stages or in cell origins for HCC. Up-regulation of DNA methyltransferases might simply be a result of increased cell proliferation in cancer. In addition, our results did not support the hypothesis of activation of transposable elements in HCC via genome-wide hypomethylation.
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PMID:Genome-wide hypomethylation in hepatocellular carcinogenesis. 1135 50

DNA methylation, chromatin structure, transcription, and cancer have traditionally been studied as separate phenomena. Recent data provide now direct physical and functional links between these processes revealing a complex network of interactions and mutual dependences. Methylated DNA is bound by methyl-CpG binding protein (MeCP) complexes that include histone deacetylases (HDACs). This recruitment of HDACs is suggested to promote local chromatin condensation and thereby repress gene expression. Most recently, also complexes of DNA methyltransferase (Dnmt1) with transcriptional repressors, DMAP1 and pRB, have been described providing a direct link to transcriptional regulation and tumor suppression. Inactivation of the DNA methyltransferase genes (Dnmt1, 3a, and 3b) was found to be lethal in mice and several human diseases (ICF and Rett syndrome) turned out to be linked to DNA methylation. In particular, global hypomethylation has been found in tumor samples together with cancer-type-specific, local hypermethylation. Taken together, these lines of evidence clearly underscore the central role of DNA methylation in the regulation of gene expression and chromatin structure during normal development and diseases like cancer. J. Cell. Biochem. Suppl. 35:78-83, 2000.
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PMID:DNA methylation, nuclear structure, gene expression and cancer. 1138 35


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