MicroRNA‐124‐3p suppresses PD‐L1 expression and inhibits tumorigenesis of colorectal cancer cells via modulating STAT3 signaling

Abstract Programmed death ligand 1 ( PD‐L1 ) plays a significant role in colorectal tumorigenesis through induction of regulatory T cells (Tregs) and suppression of antitumor immunity. Furthermore, microRNAs (miRNAs) as the posttranscriptional regulators of gene expression show considerable promise as a therapeutic target for colorectal cancer (CRC) treatment. Considering this, in vitro effects of miRNA‐124 (miR‐124‐3p) on CRC cell tumorigenesis and Tregs differentiation via targeting PD‐L1 were investigated in the current study. Functional analysis showed that miR‐124 is significantly downregulated in CRC tissues as compared with marginal normal samples ( p < .0001), and its downregulation was negatively correlated with PD‐L1 expression. Moreover, a specific region in PD‐L1 3′‐untranslated region was predicted as the miR‐124 target and validated using the luciferase assay. Further investigation showed that transfection of HT29 and SW480 cells with miR‐124 mimics significantly reduced PD‐L1 mRNA, protein, and cell surface expression, and inhibited Tregs in coculture models via modulating interleukin [ IL ] ‐10, IL‐2, tumor necrosis factor α, transforming growth factor beta , and interferon gamma expression levels. Besides, miR‐124 overexpression decreased CRC cell proliferation and arrested cell cycle at the G1 phase through downregulation of c‐Myc and induced apoptosis in CRC cells via upregulation of both intrinsic and extrinsic pathways. Also, miR‐124 exogenous overexpression could reduce colony and spheroid formation ability of CRC cells via downregulating CD44 mRNA expression. miR‐124 also diminished MMP‐9 expression and subsequently suppressed cell migration and invasion. We also illustrated that STAT3 signaling was repressed by miR‐124 in CRC cells. Taken together, our findings imply that considering the involvement of miR‐124 in the regulation of PD‐L1 through colorectal tumorigenesis and its remarkable antitumor effects, this miRNA could be regarded as the promising target for the development of therapeutic approaches for colorectal cancer.