DNMT1 promotes cell proliferation via methylating hMLH1 and hMSH2 promoters in EGFR-mutated non-small cell lung cancer

Aberrant DNA methylation is a common form of epigenetic alterations and it has been proved to be closely related to many cancers, while its role in epidermal growth factor receptor (EGFR)-mutated non-small cell lung cancer (NSCLC) is not clear. This study focuses on the role of DNA methyltransferase 1 (DNMT1) in EGFR-mutated NSCLC pathogenesis. First, the expression of DNMT1 was up-regulated, while the expressions of human mutL homolog 1(hMLH1) and human mutS homolog 2 (hMSH2) were down-regulated in EGFR-mutated NSCLC patients and cell line HCC827. The results of the correlation analysis showed that DNMT1 expression was inversely correlated with the expressions of hMLH1 and hMSH2. Then, we found that DNMT1 enhanced the promoter methylation levels of hMLH1 and hMSH2, thus suppressing their expressions. DNMT1 knockdown inhibited the proliferation of HCC827 cells, while both hMLH1 knockdown and hMSH2 knockdown could eliminate its inhibitory effect on cell proliferation. In xenograft mouse models, lentiviral vector-sh-DNMT1 could significantly reduce tumor volumes, confirmed that DNMT1 inhibited tumor cell proliferation in vivo. In conclusion, DNMT1 suppressed the expressions of hMLH1 and hMSH2 via elevating their promoter methylation, thus promoting cell proliferation in EGFR-mutated NSCLC.