Increased DNA Methyltransferase 1 (DNMT1) Protein Expression Correlates Significantly with Poorer Tumor Differentiation and Frequent DNA Hypermethylation of Multiple CpG Islands in Gastric Cancers

Abstract

We evaluated the significance of aberrant DNA methyltransferase 1 (DNMT1) protein expression during gastric carcinogenesis. The protein expression of DNMT1, Muc2, human gastric mucin, E-cadherin, and proliferating cell nuclear antigen was examined immunohistochemically in gastric cancers and corresponding noncancerous mucosae from 134 patients. The DNA methylation status of the CpG islands of the p16, human MutL homologue 1 (hMLH1), E-cadherin, and thrombospondin-1 (THBS-1) genes and the methylated in tumor (MINT)-1, -2, -12, and -31 clones was examined by methylation-specific polymerase chain reaction and combined bisulfite restriction enzyme analysis. Epstein-Barr virus (EBV) infection was detected by in situ hybridization. Nuclear immunoreactivity for DNMT1 was not detected in any of the noncancerous epithelia, except in proliferative zones (positive internal control), but was found in 97 (72%) of the gastric cancers. 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. It also correlated significantly with DNA hypermethylation of the CpG islands of the hMLH1 (P ‫؍‬ 0.024) and THBS-1 genes (P ‫؍‬ 0.043), and with the CpG island methylator phenotype in the gastric cancers (P ‫؍‬ 0.007). 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). DNMT1 overexpression was also associated with EBV infection (a potential etiological factor in gastric car- DNA methylation plays an important role in transcriptional regulation and chromatin remodeling in mammalian cells.1 Both overall DNA hypomethylation and more regional DNA hypermethylation have been well documented in various cancers.1-8 Aberrant DNA methylation may be involved in carcinogenesis as a result of 1) increased gene mutagenicity because of deamination of 5-methylcytosine to thymine; 2) a possible association of aberrant DNA methylation with allelic loss; and 3) repression of gene transcription through methylation of CpG islands in regulatory regions of specific genes, including tumor-suppressor genes.

DNA methyltransferase 1 expression and promoter methylation of E‐cadherin in mucoepidermoid carcinoma

“…To discriminate definitively positive samples from samples with background staining, if Ͼ 30% of the cells in a tissue sample exhibited nuclear staining, then the sample was categorized with positive immunoreactivity. 16 Among the 46 MEC samples, 29 samples (63%) were positive for DNMT1. Correlations between the incidence of nuclear immunoreactivity for DNMT1 and the clinicopathologic features of patients with MEC are shown in Table 1.…”

MicroRNA-148a Can Regulate Runt-Related Transcription Factor 3 Gene Expression via Modulation of DNA Methyltransferase 1 in Gastric Cancer

“…The most abundant of these is DNMT1, which is primarily responsible for maintenance and regulation of DNA methylation patterns, while DNMT3A and DNMT3B establish de novo methylation patterns which are then maintained by DNMT1 (Jones and Baylin, 2002;Okano et al, 1999). Previous studies have shown that significant increased expression of DNMT1 protein positively correlates with the hypermethylation status of CpG islands of several genes in gastric cancers, including p16, human MutL homologue 1 (hMLH1), CDH1, and thrombospondin-1 (THBS1) (Etoh et al, 2004).…”

RUNX3-mediated transcriptional inhibition of Akt suppresses tumorigenesis of human gastric cancer cells

“…The gene instability in gastric cancer including gene amplification, loss of heterozygosity (Sano et al, 1991) or microsatellite instability (Fang et al, 2003) may cause the inactivation of some tumor-suppressor genes, such as p53, and deregulation of some signaling molecules so as to enhance some signaling pathways, such as Wnt or Ras-dependent mitogen-activated protein kinase (MAPK) pathway, which may promote the tumorigenesis (Kim et al, 1991;Clements et al, 2002;Stock and Otto, 2005). In another way, the gene silencing in gastric cancer frequently results from promoter hypermethylation caused by overexpression of DNA methyltransferase 1 and involves many genes expression such as hMLH1, E-cadherin, transforming growth factor (TGF)-b receptor type I and RUNX3 that loss of them may exacerbate the gastric cancer progression (Etoh et al, 2004;Stock and Otto, 2005;Sato and Meltzer, 2006). The more comprehensive investigations of molecular mechanisms related to gastric carcinogenesis will provide more evidences for developing novel diagnostic and therapeutic strategies against gastric cancer.…”