Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.1.1.37 (DNA methyltransferase)
4,983 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

O6-Methylguanine DNA methyltransferase (MGMT) repairs the mutagenic and cytotoxic O6-alkylguanine lesions produced by environmental carcinogens and the chemotherapeutic nitrosoureas. As such, MGMT-mediated repair of O6-alkylguanine lesions constitutes a major form of resistance to nitrosourea chemotherapy and makes control of MGMT expression of clinical interest. The variability of expression in cell lines and tissues, along with the ease with which the MGMT phenotype reverts under various conditions, suggests that MGMT is under epigenetic control. One such epigenetic mechanism, 5-methylation of cytosines, has been linked to MGMT expression. We have used an isogenic human multiple myeloma tumor cell line model composed of an MGMT-positive parent cell line, RPMI 8226/S, and its MGMT-negative variant, termed 8226/V, to study the control of MGMT expression. The loss of MGMT activity in 8226/V was found to be due to the loss of detectable MGMT gene expression. Bisulfite sequencing of the MGMT CpG island promoter revealed large increases in the levels of CpG methylation within discrete regions of the 8226/V MGMT CpG island compared to those in 8226/S. These changes in CpG methylation are associated with local heterochromatinization of the 8226/V MGMT transcription start site and provide a likely mechanism for the loss of MGMT transcription in 8226/V.
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PMID:Methylation of discrete regions of the O6-methylguanine DNA methyltransferase (MGMT) CpG island is associated with heterochromatinization of the MGMT transcription start site and silencing of the gene. 927 36

We previously reported loss of expression of p27Kip1 (p27) protein in rat GH3 and mouse GHRH-CL1 pituitary tumor cells compared with normal pituitary (NP). The molecular basis for the loss of expression of p27 protein in GH3 and GHRH-CL1 cells is unknown. To determine the role of p27 gene methylation in the regulation of the expression of this cell cycle protein, the methylation patterns of p27 in normal and neoplastic pituitary cells was analyzed. Inhibition of DNA methyltransferase (DNA-MTase) with 5-aza-2'-deoxycytidine (AZAdC) induced expression of both p27 protein and mRNA when GH3 and GHRH-CL1 cells were treated for 7 days in vitro. DNA methylation correlated inversely with the expression of p27 gene products in NP and pituitary tumor cell lines. Bisulfite genomic sequencing analysis showed that the normally unmethylated cytosines in exon 1 in NP and AtT20 cells were extensively methylated in GH3 and GHRH-CL1 cells. After treatment of GH3 and GHRH-CL1 cells with 10 micromol/L AZAdC, there were decreased numbers of methylated cytosines (by 60% to 90%/o) with variable methylation patterns observed by bisulfite genomic sequencing. Analysis of genomic DNA with methylation-sensitive enzymes showed that all SmaI, HhaI, and AvaI enzyme sites of the p27 gene in exon 1 were methylated in GH3 cells but not in NP, confirming the bisulfite genomic sequencing results. AtT20 cells and a human pituitary null cell adenoma cell line (HP75), which expressed abundant p27, had a methylation pattern similar to the NP. DNA-MTase activity was elevated fourfold in GH3 cells and twofold in GHRH-CL1 cells compared with DNA-MTase activity in NP and AtT20 cells. These results suggest that increased DNA methylation is another mechanism of silencing of the p27 gene in some pituitary tumors and possibly in other types of neoplasms.
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PMID:DNA methylation regulates p27kip1 expression in rodent pituitary cell lines. 981 39

Inactivation of the transforming growth factor beta (TGFbeta)-signaling pathway and gene silencing through hypermethylation of promoter CpG islands are two frequent alterations in human and experimental cancers. Here we report that nonneoplastic TGFbeta1-/- keratinocyte cell lines exhibit increased sensitivity to cell killing by alkylating agents, and this is due to lack of expression of the DNA repair enzyme O(6)-methylguanine DNA methyltransferase (MGMT). In TGFbeta1-/- but not TGFbeta1+/- cell lines, the CpG dinucleotides in the MGMT promoter are hypermethylated, as measured by restriction enzyme analysis and methylation specific polymerase chain reaction. In one unstable TGFbeta1+/- cell line, loss of the wild type TGFbeta1 allele correlates with the appearance of methylation in the MGMT promoter. Bisulfite sequencing shows that in the KO3 TGFbeta1-/- cell line nearly all of the 28 CpG sites in the MGMT promoter 475 base pairs upstream of the start site of transcription are methylated, whereas most are unmethylated in the H1 TGFbeta1+/- line. Treatment of the TGFbeta1-/- cell lines with 5-azacytidine causes reexpression of MGMT mRNA and demethylation of CpG islands in the promoter. Analysis of the time course of methylation using methylation-specific polymerase chain reaction shows a lack of methylation in primary TGFbeta1-/- keratinocytes and increasing methylation with passage number of immortalized clones. Subcloning of early passage clones reveals a remarkable heterogeneity and instability of the methylation state in the TGFbeta1-/- keratinocytes. Thus, the TGFbeta1-/- genotype does not directly regulate MGMT methylation but predisposes cells to immortalization-associated MGMT hypermethylation.
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PMID:Increased sensitivity of transforming growth factor (TGF) beta 1 null cells to alkylating agents reveals a novel link between TGFbeta signaling and O(6)-methylguanine methyltransferase promoter hypermethylation. 1126 4

Complementary sets of genes are epigenetically silenced in male and female gametes in a process termed genomic imprinting. The Dnmt3L gene is expressed during gametogenesis at stages where genomic imprints are established. Targeted disruption of Dnmt3L caused azoospermia in homozygous males, and heterozygous progeny of homozygous females died before midgestation. Bisulfite genomic sequencing of DNA from oocytes and embryos showed that removal of Dnmt3L prevented methylation of sequences that are normally maternally methylated. The defect was specific to imprinted regions, and global genome methylation levels were not affected. Lack of maternal methylation imprints in heterozygous embryos derived from homozygous mutant oocytes caused biallelic expression of genes that are normally expressed only from the allele of paternal origin. The key catalytic motifs characteristic of DNA cytosine methyltransferases have been lost from Dnmt3L, and the protein is more likely to act as a regulator of imprint establishment than as a DNA methyltransferase.
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PMID:Dnmt3L and the establishment of maternal genomic imprints. 1171 92

CDX1 is a homeobox protein that inhibits proliferation of intestinal epithelial cells and regulates intestine-specific genes involved in differentiation. CDX1 expression is developmentally and spatially regulated, and its expression is aberrantly down-regulated in colorectal cancers and colon cancer-derived cell lines. However, very little is known about the molecular mechanism underlying the regulation of CDX1 gene expression. In this study, we characterized the CDX1 gene structure and identified that its gene promoter contained a typical CpG island with a CpG observed/expected ratio of 0.80, suggesting that the CDX1 gene is a target of aberrant methylation. Alterations of DNA methylation in the CDX1 gene promoter were investigated in a series of colorectal cancer cell lines. Combined Bisulfite Restriction Analysis (COBRA) and bisulfite sequencing analysis revealed that the CDX1 promoter is methylated in CDX1 non-expressing colorectal cancer cell lines but not in human normal colon tissue and T84 cells, which express CDX1. Treatment with 5'-aza-2'-deoxycytidine (5-azaC), a DNA methyltransferase inhibitor, induced CDX1 expression in the colorectal cancer cell lines. Furthermore, de novo methylation was determined by establishing stably transfected clones of the CDX1 promoter in SW480 cells and demethylation by 5-azaC-activated reporter gene expression. These results indicate that aberrant methylation of the CpG island in the CDX1 promoter is one of the mechanisms that mediate CDX1 down-regulation in colorectal cancer cell lines.
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PMID:DNA methylation down-regulates CDX1 gene expression in colorectal cancer cell lines. 1212 93

Retinoic acid (RA) receptor (RAR) beta2 has been shown to be underexpressed in human breast cancer cells, including MCF-7 cells, and recent reports have suggested that hypermethylation of the RAR beta2 promoter and 5'-UTR is the underlying cause. Here we show that RAR alpha2 is also underexpressed in MCF-7 breast cancer cells, at both the message and the protein level, relative to normal or nontumorigenic breast epithelial cells. Bisulfite sequencing of the CpG island in the RAR alpha2 promoter revealed highly penetrant and uniform cytosine methylation in MCF-7 cells. Pretreatment with the DNA methyltransferase inhibitor, azacytidine, followed by treatment with RA and a histone deacetylase inhibitor, trichostatin A, resulted in partial promoter demethylation and RAR alpha2 induction, which strongly suggested that promoter hypermethylation is responsible for RAR alpha2 underexpression. We compared the outcome of ectopic expression in MCF-7 cells of matched levels of RAR alpha2 and RAR beta2. On the basis of a clonogenic assay, RAR alpha2 displayed ligand-dependent growth-suppressive activity similar to that of RARb eta2; thus, 10 and 20 nM RA inhibited clonogenic growth by 52 and 80%, respectively, in RAR alpha2-transfected cells compared with 75 and 77%, respectively, in RAR beta2-transfected cells. We conclude that the silencing of the RAR alpha2 promoter by hypermethylation may play a contributory role in the dysregulation of RA signaling in mammary tumorigenesis.
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PMID:Retinoic acid receptor alpha2 is a growth suppressor epigenetically silenced in MCF-7 human breast cancer cells. 1219 72

Defects in the AIRE gene cause a monogenic autoimmune syndrome APECED (autoimmune polyendocrinopathy candidiasis ectodermal dystrophy), which is characterized by loss of self-tolerance to multiple organs. In concordance with its role in immune tolerance, AIRE is most strongly expressed in thymic epithelial cells and in cells of monocytic-dendritic lineage. The AIRE protein has been shown to function as a transcriptional regulator, however, the mechanisms regulating AIRE gene expression are not known. Here we have characterized the AIRE promoter region by identifying a minimal promoter region within 350 bp of the translation initiation codon. Electrophoretic mobility shift assays and transient transfections with mutated promoter constructs revealed a functional TATA box (-163 to -153) and binding sites for transcription complexes AP-1 (-307 to -296), NF-Y (-213 to -202), and Sp1 (-202 to -189). The presence of a 390-bp CpG island within the proximal promoter suggested that cytosine methylation has a role in transcriptional regulation of AIRE, which was supported by in vitro methylation experiments of promoter constructs. Sodium bisulfite sequencing showed a less methylated status of AIRE promoter in the thymic epithelial cell line TEC1A3 compared with HeLa and monocytic cells U937 and THP-1. Real-time PCR analysis showed that treatment with 5-aza-2'-deoxycytidine (5-azaCdR), a DNA methyltransferase inhibitor, up-regulated AIRE transcript levels in TEC1A3, U937, and HeLa cells and that even greater activations in TEC1A3 and U937 cells were observed using combined treatments with deacetylase inhibitor trichostatin A. These results suggest that AIRE gene expression is modulated through modifications in chromatin methylation and acetylation.
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PMID:Characterization of regulatory elements and methylation pattern of the autoimmune regulator (AIRE) promoter. 1265 56

Expression of cyclin D2 is absent in 30-70% of gastric cancers. We investigated the role of promoter hypermethylation in the transcriptional silencing of cyclin D2 in five gastric cell lines and 47 primary gastric carcinomas. CpG island methylation status of the cyclin D2 gene was studied by methylation-specific polymerase chain reaction and bisulphite sequencing. RNA and protein expression was analysed by reverse transcription-PCR and Western blot, respectively. Dense methylation of cyclin D2 was detected in three cell lines (KATOIII, AGS and NCI-N87), which also lacked cyclin D2 mRNA and protein expression. Bisulphite DNA sequencing revealed that loss of cyclin D2 expression was closely associated with the density of methylation in the promoter region. Treatment with DNA methyltransferase inhibitor, 5-aza-2'-deoxycytidine, restored the cyclin D2 expression level in methylated gastric cells. Among the 47 primary gastric cancers, cyclin D2 hypermethylation was detected in 23 (48.9%) cases. None of the 23 normal gastric biopsies from noncancer patients showed hypermethylation. Hypermethylation was associated with loss of mRNA (P&<0.001) and protein (P=0.006) expressions. Our study showed that cyclin D2 hypermethylation is associated with loss of cyclin D2 expression in a subset of gastric cancers, which may suggest an alternative gastric carcinogenesis pathway in the absence of cyclin D2 expression.
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PMID:Absence of cyclin D2 expression is associated with promoter hypermethylation in gastric cancer. 1277 22

Monoamine oxidase (MAO) A and B catalyze the oxidative deamination of neuroactive and dietary monoamines such as serotonin, tyramine, and phenylethylamine. Here we show that MAO B, but not MAO A, gene expression was induced during Caco-2 cell differentiation; thus this cell line was used as a model system to study the gene regulation unique for MAO B. Luciferase and gel shift assays showed that transcription factors Sp1 and Sp3 binding to -246 and -99 bp were responsible for the observed gene activation. Overexpression of Sp3 inhibited the induction of MAO B gene by Sp1, and the expression of Sp3 was decreased during Caco-2 cell differentiation. Computer analysis revealed a putative CpG island containing 22 potential CpG methylation sites between -261 and -58 bp. In vitro methylation of MAO B promoter with 5-aza-2'-deoxycytidine, a DNA methyltransferase inhibitor, up-regulated MAO B gene expression in both HeLa and Caco-2 cells. Sodium bisulfite sequencing showed a gradually reduced methylation of the CpG sites during Caco-2 cell differentiation. These results suggested that MAO B gene expression is selectively induced by a decreased Sp3/Sp1 ratio and reduced DNA methylation. This new information may provide insights on the tissue-specific expression of these two isoenzymes.
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PMID:Decreased methylation and transcription repressor Sp3 up-regulated human monoamine oxidase (MAO) B expression during Caco-2 differentiation. 1285 85

Resistance to the cytotoxic actions of antineoplastic drugs, whether intrinsic or acquired, remains a barrier to the establishment of curative chemotherapy regimens for advanced breast cancer. Over-expression of P-glycoprotein (P-gp), encoded by the MDR1 gene and known to mediate resistance to many antineoplastic drugs, may contribute to poor breast cancer treatment outcome. Nonetheless, the precise molecular mechanisms responsible for high or low level P-gp expression in breast cancer cells have not been established. We assessed the role of DNA hypermethylation near the MDR1 transcriptional regulatory region in MDR1 expression in MCF-7 breast cancer cells, which fail to express MDR1 mRNA, and MCF-7/ADR cells, known to express high MDR1 mRNA levels. When compared to MCF-7/ADR cells, MCF-7 cells manifested markedly diminished MDR1 transcription rates by nuclear run-off assay, but equivalent MDR1 promoter trans-activation activity in transient transfection experiments, indicating that cis factors were most likely responsible for the differences in MDR1 transcription between MCF-7/ADR cells and MCF-7 cells. Bisulfite genomic sequencing analyses revealed substantially less extensive MDR1 promoter methylation in MCF-7/ADR cells than in MCF-7 cells, suggesting that CpG dinucleotide methylation might contribute to the observed MDR1 transcription differences. Chromatin immunoprecipitation analyses indicated an inactive MDR1 chromatin conformation in MCF-7 cells, with a paucity of acetylated histones and the presence of 5-mC-binding proteins MeCP2 and MBD2, and an active MDR1 chromatin conformation in MCF-7/ADR cells, with an abundance of acetylated histones and the presence of the transcriptional trans-activator YB-1. Stable MCF-7 sublines which had been treated with the DNA methyltransferase inhibitor 5-azacytidine, exhibited a reduction in MDR1 promoter methylation and a complex MDR1 chromatin configuration, characterized by the simultaneous presence of transcriptional activators and repressors. In this state, MDR1 expression was markedly sensitive to treatment with the histone deacetylase inhibitor trichostatin A.
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PMID:MDR1 promoter hypermethylation in MCF-7 human breast cancer cells: changes in chromatin structure induced by treatment with 5-Aza-cytidine. 1525 26


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