miR-126 downregulates CXCL12 expression in intestinal epithelial cells to suppress the recruitment and function of macrophages and tumorigenesis in a murine model of colitis-associated colorectal cancer.

Inflammatory bowel disease, characterised by chronic relapsing-remitting colitis, is a significant risk factor for colorectal cancer (CRC). Previously, we showed that miR-126 functions as a tumour suppressor in CRC and is inversely correlated with tumour proliferation, metastasis and patient prognosis. In the current study, we documented a protective role for miR-126 in colitis-associated CRC (CAC) and its underlying mechanism. We detected downregulated miR-126 expression during colorectal tumorigenesis in the mouse CAC model and in specimens from patients with CRC. The deficiency of miR-126 in intestinal epithelial cells (IECs) exacerbated tumorigenesis in mice. We identified CXCL12 as a direct target of miR-126 in inhibiting the development of colitis and CAC. Moreover, miR-126 regulated the recruitment of macrophages via CXCL12 and decreased the levels of proinflammatory cytokines (IL-6, IL-12 and IL-23). In addition, IL-6 secreted by macrophages, which were regulated by cocultured transfected CRC cells, altered the proliferation and migration of colon cells. Our data suggest that miR-126 exerts an antitumour effect on CAC by regulating the crosstalk between IECs and macrophages via CXCL12-IL-6 signalling. Our study contributes to the understanding of cancer progression and suggests miR-126 as a potential therapy for CRC.