UC San Diego

MicroRNAs are small (̃22 nt) noncoding RNAs which function is to regulate mRNA levels in multicellular organisms. Several host-derived miRNAs have been shown to play an important role during viral infections by regulating the expression of genes encoding key immune mediators. We sought to investigate the ability of miRNA to regulate the intestinal epithelial cell (IEC) innate immune response. Using siRNA we downregulated the expression of the 2 key microRNA processing enzymes Drosha and Dicer-1 in HCT116 and HT29 and then infected with Sendai virus, Rotavirus, or stimulated the cells with the synthetic dsRNA mimic polyinosinic-polycytidylic acid (poly(I:C)). We observed that Drosha-silenced, but not Dicer-silenced cells, induced a significant increase in IFN-[Beta] expression and secretion, and also up-regulated the expression of ISG -15, which caused reduced viral load in infected cells. The cells showed also an increased expression of inflammatory cytokines TNF-[alpha] and IL-6. These responses were not due to changes in levels of phosphorylated IRF3 or phosphorylated I[kappa]B[alpha]. Top candidate miRNAs endogenous to IECs and predicted to target IFN-[Beta], TNF-[alpha], and IL-6 were found