Disease relevance of DNMT1

• Expression of DNA methyltransferases DNMT1, 3A, and 3B in normal hematopoiesis and in acute and chronic myelogenous leukemia [1].
• 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) [1].
• Chromatin immunoprecipitation analysis detected the presence of MBD2 and DNMT1 at the GSTP1 promoter in MCF-7 breast cancer cells but not in MCF-7/ADR breast cancer cells [2].
• These results indicate that human colorectal carcinogenesis is accompanied by a progressive dysregulation of DNMT1 expression and suggest that abnormalities in DNMT1 expression may contribute to the abnormal CpG dinucleotide methylation changes characteristic of human colorectal carcinoma cell DNA [3].
• 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 [4].

Psychiatry related information on DNMT1

• In BA9 of SZ and bipolar disorder patients with psychosis, DNMT1 mRNA and protein expression preferentially increases in layer I, II, and IV interneurons, and this increase is paralleled by a decreased number of GAD67 mRNA-positive neurons [5].
• Body temperature, locomotor activity, skilled paw-reaching ability and performance of the delayed non-match to place (DNMTP) procedure was assessed daily during this period and on an intermittent schedule over the following 16 days [6].
• (a) The operant delayed non-matching-to-position (DNMTP) test was used to study short-term memory function [7].

High impact information on DNMT1

• CpG island hypermethylation is maintained in human colorectal cancer cells after RNAi-mediated depletion of DNMT1 [8].
• In human bladder cancer cells, selective depletion of DNMT1 with antisense inhibitors has been shown to induce demethylation and reactivation of the silenced tumor-suppressor gene CDKN2A [9].
• DNMT1 is required to maintain CpG methylation and aberrant gene silencing in human cancer cells [9].
• Selective depletion of DNMT1 using either antisense or siRNA resulted in lower cellular maintenance methyltransferase activity, global and gene-specific demethylation and re-expression of tumor-suppressor genes in human cancer cells [9].
• We show here that the chief enzyme that maintains mammalian DNA methylation, DNMT1, can also establish a repressive transcription complex [10].

Chemical compound and disease context of DNMT1

• METHODS: CALU-6 and A549 lung cancer, SKGT5 and BIC esophageal adenocarcinoma, and H2373 and H2052 malignant pleural mesothelioma (MPM) cells, as well as normal human bronchial epithelial (NHBE) cells, were transfected with phosphorothioate-modified antisense oligos targeting DNMT1, DNMT3b, or both, or mismatch oligos [11].
• OBJECTIVE: The aim of this study was to investigate whether expression of the enzymes that catalyze cytosine CpG island methylation, DNA methyltransferases, DNMT1, DNMT3a, and DNMT3b is altered in human ovarian cancer [12].
• Our previous studies showed that treatment of estrogen receptor (ER)-alpha-negative human breast cancer cells with the DNMT inhibitor 5-aza-2'-deoxycytidine (5-aza-dC) led to ER mRNA and protein re-expression [13].
• In this paper, we investigated the impact of methylation levels in the cell on mitoxantrone-induced cytotoxicity using the colon cancer cell line HCT116 and its derived DNA methyltransferase (DNMT) 1 and DNMT 3a knockout (DKO8) cell line [14].
• Azacitidine (Vidaza, Pharmion Corp., Boulder, CO, USA) and decitabine (Dacogentrade mark, SuperGen, Inc., Dublin, CA, USA, and MGI Pharma, Inc., Bloomington, MN, USA) are DNA methyltransferase (DNMT) inhibitors that have clinical activity in patients with myelodysplastic syndromes [15].

Biological context of DNMT1

• Thus, DNMT1 not only maintains DNA methylation, but also may directly target, in a heritable manner, transcriptionally repressive chromatin to the genome during DNA replication [10].
• 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 [4].
• The synergistic activation of ER occurs concomitantly with markedly reduced soluble DNMT1 expression and activity, partial demethylation of the ER CpG island, and increased acetylation of histones H(3) and H(4) [13].
• In adenomatous polyps, although DNMT1 expression coincided with the expression of other cell proliferation markers, many DNMT1-expressing cells also expressed p21 [3].
• DNMT1 overexpression correlated significantly with poorer tumor differentiation (P < 0.001), but not with the phenotype (gastric type versus intestinal type) of the cancer cells [16].

Anatomical context of DNMT1

• Treatment with pharmacologic grade DNMT1 anti-sense oligonucleotides and STAT3 small-interfering RNA induces in the malignant T cells DNA demethylation and expression of SHP-1 gene [17].
• 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 [1].
• The rDNA primary transcript level was significantly elevated in DNMT1-/- or DNMT3B-/- human colon carcinoma (HCT116) cells [18].
• Therefore, DNMT1 expression relative to proliferation was investigated in TCC cell lines and tissue as well as in renal carcinoma (RCC) cell lines, which also display hypomethylation, as indicated by decreased LINE-1 methylation [19].
• DNA methylation of multiple tumor-related genes in association with overexpression of DNA methyltransferase 1 (DNMT1) during multistage carcinogenesis of the pancreas [20].

Associations of DNMT1 with chemical compounds

• Treatment of cells with other nucleoside analogs modified at C-5, 5-fluorodeoxyuridine and 5-fluorocytidine, did not induce the degradation of DNMT1 [21].
• Furthermore, zebularine, a drug that selectively traps and depletes nuclear DNMT1 and DNMT3b, relieved p53-mediated repression of endogenous Cdc25C and Cdc2 [22].
• The DNMT1-mediated repression of MT-I promoter was relieved by trichostatin A, an HDAC inhibitor [23].
• Gene expression profiles after DNMT1, DNMT3b, or combined DNMT1/3b depletion were remarkably similar, yet distinctly different from expression profiles mediated by 5 aza 2' deoxycytidine [11].
• We used a combination of genetic (antisense and siRNA) and pharmacologic (5-aza-2'-deoxycytidine) inhibitors of DNA methyl transferases to study the contribution of the DNMT isotypes to cancer-cell methylation [9].

Physical interactions of DNMT1

• Moreover, by a co-immunoprecipitation experiment, DNMT1 was shown to form a complex with MBD2 and MBD3 [24].
• Both Daxx and DMAP1 formed a complex with DNMT1 and colocalized in the nucleus [25].
• Here, DNMT1 is shown to bind p53 and colocalize in the nucleus [26].
• CONCLUSIONS: Elevated mRNA expression of DNMT1 may be an independent prognostic factor in NSCLC and CpG island hypermethylation in NSCLC may be maintained by a complex interaction of several factors rather than by a simple transcriptional up-regulation of DNMT1 [27].
• We find that SUV39H1 also binds to Dnmt1 and, consistent with these interactions, SUV39H1 can purify DNA methyltransferase activity from nuclear extracts [28].

Enzymatic interactions of DNMT1

• The activity of DNMT1 against unmethylated CpG rich DNA was further tested by introducing CpG island substrates and DNMT1 into Drosophila melanogaster cells [29].

Regulatory relationships of DNMT1

• We hypothesize that MBD2 enzyme activity is repressed and that DNMT1 enzyme activity is elevated in human prostate cancer [30].
• These results demonstrate that the methylated and unmethylated MT-I promoter are differentially regulated by DNA methyltransferase and methyl-CpG binding proteins, and DNMT1 could suppress MT promoter by a transcriptional mechanism independent of its enzymatic function [23].
• DNMT1-mediated methylation is stimulated by p53 in vitro [26].
• Human DNA methyltransferase gene DNMT1 is regulated by the APC pathway [31].
• DNMT1 levels are regulated with the cell cycle and are induced upon entry into the S phase of the cell cycle [32].

Other interactions of DNMT1

• Immunofluorescence analysis and biochemical fractionation showed that all three DNMTs (DNMT1, DNMT3A, and DNMT3B) are associated with the inactive rDNA in the nucleolus [18].
• Treatment of HCT116 cells with Decitabine (a DNMT inhibitor) or trichostatin A (a histone deacetylase inhibitor) up-regulated endogenous rDNA expression [18].
• DNMT1-mediated suppression of the unmethylated promoter involves de novo methylation of the promoter, whereas histone deacetylase 2 cooperates with DNMT1 to inhibit the methylated rDNA promoter [18].
• Reduced E-cadherin expression correlated significantly with poorer tumor differentiation (P = 0.002), DNA hypermethylation of the E-cadherin gene (P < 0.001) and DNMT1 overexpression (P = 0.014) [16].
• DNMT1 overexpression was also associated with EBV infection (a potential etiological factor in gastric carcinogenesis) but not with the proliferative activity of the cancer cells as indicated by the proliferating cell nuclear antigen-labeling index [16].

Analytical, diagnostic and therapeutic context of DNMT1

• Southern blot analysis demonstrated a moderate level of rDNA promoter hypomethylation in DNMT1-/- cells and a dramatic loss of rDNA promoter methylation in double knockout cells [18].
• Western blot analysis confirmed opposite expression patterns of DNMT1 and DNMT3B protein in endometrioid and serous cancers [33].
• Reverse Northern blot analyses demonstrated sex-specific differences in mRNA expression for the maintenance DNMT1 and the de novo DNMT3A in developing testis and ovary [34].
• Immunohistochemistry showed normal nuclear localization of DNMT1 and DNMT3B in Type I and Type II cancer specimens as well as cell cultures [33].
• We examined levels of DNA methyltransferase (DNMT1, DNMT3a, DNMT3b) and DNA demethylase (MBD2) mRNA expression by semi-quantitative RT-PCR [35].

References