DNMT1 and EZH2 mediated methylation silences the microRNA-200b/a/429 gene and promotes tumor progression

Abstract

Aberrant expression of the microRNA-200 (miR-200) family has been linked to the occurrence and development of various types of malignant tumors, including hepatocellular carcinoma (HCC), colon cancer and breast cancer. However, little is known about the precise mechanism by which miR-200 expression is downregulated. The intricate relationship between DNA methylation and histone modifications has become a subject of increasing interest. The expression of miR-200 family members is modified by similar or complementary epigenetic mechanisms in MGC-803 and BGC-823 gastric cancer cells and U87 MG glioma cells. Chromatin immunoprecipitation assays revealed that DNA methyltransferase 1 (DNMT1) bound to miR-200b/a/429 promoter regions, indicating an interaction between DNMT1 and the miR-200b/a/429 promoter. Furthermore, Co-Immunoprecipitation (Co-IP) detection showed that DNMT1, together with the PcG protein Enhancer of Zeste homolog 2 (EZH2), a histone methyltransferase, contributed to the transcriptional repression of microRNA-200 family members. Knockdown of EZH2 not only impacted H3K27 trimethylation but also reduced DNMT1 presence on the miR-200b/a/429 promoter. EZH2 appeared to be essential for DNMT1 recruitment to the promoter region. Silencing EZH2 and DNMT1 using drugs or RNA interference dramatically reduced the levels of miR-200b/a/429 expression. Collectively, these results indicated that EZH2 and DNMT1-mediated epigenetic silencing contributed to the progression of gastric cancer and glioblastoma, and therefore represents a novel therapeutic target for malignant tumors.