Estradiol regulates miR-135b and mismatch repair gene expressions via estrogen receptor-β in colorectal cells

Estrogen has anti-colorectal cancer effects which are thought to be mediated by mismatch repair gene (MMR) activity. Estrogen receptor (ER) expression is associated with microRNA (miRNA) expression in ER-positive tumors. However, studies of direct link between estrogen (especially estradiol E(2)), miRNA expression, and MMR in colorectal cancer (CRC) have not been done. In this study, we first evaluated the effects of estradiol (E(2)) and its antagonist ICI182,780 on the expression of miRNAs (miR-31, miR-155 and miR-135b) using COLO205, SW480 and MCF-7 cell lines, followed by examining the association of tissue miRNA expression and serum E(2) levels using samples collected from 18 colorectal cancer patients. E(2) inhibited the expressions of miRNAs in COLO205 cells, which could be reversed by E(2) antagonist ICI 182.780. The expression of miR-135b was inversely correlated with serum E(2) level and ER-β mRNA expression in CRC patients' cancer tissues. There were significant correlations between serum E(2) level and expression of ER-β, miR-135b, and MMR in colon cancer tissue. This study suggests that the effects of estrogen on MMR function may be related to regulating miRNA expression via ER-β, which may be the basis for the anti-cancer effect in colorectal cells.