The Role Of MiRNAs In Colitis-associated Colonic Carcinogenesis

As a chronic recurrent gastrointestinal inflammation, colitis or inflammatory bowel disease (IBD) is one of risk factors for colon cancer. MicroRNAs (miRNAs), single-stranded small non-coding RNAs, are dysregulated in a wide variety of tumors and function as oncogene or tumor suppressor by targeting the downstream mRNA. Increasing evidence shows that miRNAs are involved in the carcinogenesis, development and metastasis of cancer. However, it is unclear what the role of miRNAs is in colitis-associated carcinogenesis. In the current study, miR-155and some apoptosis-related miRNAs were studied.(The first part) The role of miR-155in inflammation and cancer has been well demonstrated but its role in colitis and colitis-associated carcinogenesis is absent. To study it, colitis-associated colon cancer was induced by azoxymethane (AOM) and dextran sulfate sodium (DSS) in mice. Expression of miR-155in colon tissue was gradually elevated with the formation of colitis-associated colon cancer which was measured by real-time PCR. However, there was no change on miR-155expression in chronic inflammation only group. And then target genes of miR-155were screened out with the gene expression microarray and the miRNA target genes prediction software. It showed that Tle4, Kcna1, Itk, Bcorl1, Cacnalc, Rspo2and Foxo3were potential target genes of miR-155. Changes of Kcnal and Cacnalc in AOM-DSS mouse model were validated to be consistent with the changes in the gene expression microarray.(The second part) High level of nitric oxide (NO) in chronic inflammation plays important role in colony selection during the carcinogenesis. However, little is known about the involvement of miRNAs in NO-induced apoptosis. Since previous study inplied that NO induced apoptosis through the downregulation of bcl-xL, five miRNAs were chosen according to their potential to target bcl-xL. In colon cancer cell line, NO donor induced apoptosis through a dose and time-dependent manner which was measured by flow cytometry and western blot. Deficiency of p53dramatically blocked NO-induced apoptosis. The levels of miR-34c-5p, miR-122, miR-149-3p, miR-203and miR-1301were significantly elevated after the NO treatment. Further study showed that NO-related upregulation of miR-34c-5p, miR-203and miR-1301was mediated by wild type p53. And inhibition of these miRNAs respectively could significantly block NO-induced apoptosis in colon cancer cell. Moreover, we found that expression of miR-34c-5p was significantly negatively correlated with the expression of inducible NO synthase (iNOS) in human colon cancer samples. But it is not significant for miR-203and miR-1301.In summary, our data suggested that miRNAs play important roles in colitis-associated colonic carcinogenesis. The up-regulation of miR-155might be related to colitis-associated carcinogenesis. Low level of miR-34c-5p which mediated NO-induced apoptosis, may contribute to carcinogenesis through the inhibition of cell death induced by chronic inflammation related stress.