MicroRNA Profiling in Muc2 Knockout Mice of Colitis-Associated Cancer Model Reveals Epigenetic Alterations during Chronic Colitis Malignant Transformation

Our previous studies have demonstrated that genetic deletion of the Muc2 gene causes colorectal cancers in mice. The current study further showed that at the early stage (<3 months) the Muc2 knockout mice spontaneously developed chronic inflammation in colon and rectum, similar pathological features as human colitis; and at the late stage (>3 months) the mice exhibited colorectal cancer, including a unique phenotype of rectal prolapsed (rectal severe inflammation and adenocarcinoma). Thus, the age of 3 months might be the key point of the transition from chronic inflammation to cancer. To determine the mechanisms of the malignant transformation, we conducted miRNA array on the colonic epithelial cells from the 3-month Muc2(-/-) and (+/+) mice. MicroRNA profiling showed differential expression of miRNAs (i.e. lower or higher expression enrichments) in Muc2(-/-) mice. 15 of them were validated by quantitative PCR. Based on relevance to cytokine and cancer, 4 miRNAs (miR-138, miR-145, miR-146a, and miR-150) were validate and were found significantly downregulated in human colitis and colorectal cancer tissues. The network of the targets of these miRNAs was characterized, and interestedly, miRNA-associated cytokines were significantly increased in Muc2(-/-) mice. This is the first to reveal the importance of aberrant expression of miRNAs in dynamically transformation from chronic colitis to colitis-associated cancer. These findings shed light on revealing the mechanisms of chronic colitis malignant transformation.