Let-7a Inhibits Tumor Metastasis by Regulating TGF-β/Smad Signaling in the Colorectal Adenocarcinoma Cell Line LS-174T.

Abstract

Colorectal adenocarcinoma has a poor prognosis due to its propensity for metastasis. It has been experimentally demonstrated that the microRNA (miRNA) let-7a can effectively inhibit tumor proliferation and metastasis by regulating the transforming growth factor (TGF)-β signaling pathway; however, limited research has been conducted in the area of on colorectal cancer. Herein, we aimed to clarify the role and regulation of let-7a in a colorectal adenocarcinoma cell line (LS-174T). LS-174T cells were transfected to express let-7a. Let-7a miRNA expression was detected by quantitative real-time polymerase chain reaction (RT-qPCR). Cell growth was assessed by methyl thiazolyl tetrazolium (MTT) assay; invasion and migration were examined by Matrigel invasion and wound healing assays. The expression levels of matrix metalloproteinase (MMP)-2, phosphorylated Drosophila mothers against decapentaplegic 2 (p-SMAD2), and TGF-β1 were analyzed by western blotting. The mRNA expression levels of TGFB1 were also analyzed by RT-qPCR. Overexpression of let-7a resulted in significant inhibition of LS-174T cell proliferation in vitro. The invasion and migration abilities of the cells overexpressing let-7a were decreased, compared to the control group and miR-negative control group. Transfection of LS-174T cells with let-7a resulted in down-regulation of MMP-2, as well as of TGF-β1 and p-SMAD2 protein expression. Moreover, TGF-β1 mRNA levels were reduced following let-7a overexpression. Let-7a inhibited the growth and metastasis of colonic mucinous adenocarcinoma cells, at least partially, by regulating the TGF-β/Smad signaling pathway.