Hsa-Mirna-26b Regulates Spak Expression During Intestinal Epithelial Cell Differentiation

The Ste20-like proline/alanine rich kinase (SPAK) is involved in variety of physiological cellular processes such as cellular volume regulation and epithelial barrier integrity, as well as some abnormal conditions such as intestinal inflammation, but the underlying mechanisms remain largely unknown. MicroRNAs also plays important roles in numerous cellular functions like apoptosis and proliferation by post-transcriptionally regulating the production of target gene expression. Here, we studied if microRNAs are involved in the regulation of SPAK-mediated cellular differentiation and inflammation. We demonstrated that miRNA-26b can directly bind to the 3'-untranslated region (UTR) of SPAK mRNA, by which negatively regulates its expression in Caco2-BBE cells. The expression of SPAK is always inversely related to the production of miRNA-26b, in both well-differentiated and poor-differentiated Caco2-BBE cells and mouse jejunum villus/crypt cells. Further, miRNA-26b can reverse SPAK overexpression-mediated epithelial cell barrier dysfunction in Caco2-BBE cell, suggesting that miRNA-26b modulates the integrity of epithelial cell and expression of junction proteins (such as occludin) by regulating SPAK expression, which in turn could affect differentiation. In a pathological context, the pro-inflammatory cytokine interferon-gamma (IFN-gamma) increases SPAK expression in Caco2-BBE cells by decreasing miRNA-26b levels. Consis-tent with these in vitro data, miRNA-26b levels were decreased in actively inflamed colonic tissues in ulcerative colitis, where SPAK expression was up-regulated, compared with normal tissues. Taken together, these results reveal a novel mecha-nism underlying the regulation of SPAK expression by miRNA-26b during the differentiation of epithelial cells, and in inflammatory conditions, which raises miRNA-26b as promising therapeutic targets for intestinal inflammation.