Cytokine-mediated modulation of the hepatic miRNome: IL-6-mediated up-regulation of miR-146b-5p

IL-6-type cytokines play important roles in the (patho-)biology of the liver. For instance, they induce the important acute phase response to inflammatory signals and they are involved in hepatocarcinogenesis. Much is known about the regulation of protein-coding genes by cytokine whereas their effect on the miRNome is less well understood. Here, we performed a microarray screen to identify microRNAs (miRNAs) in human hepatocytes which are subject to regulation by IL-6-type cytokines. Using samples of two donors, 27 and 68 miRNAs (out of 1,733) were found to be differentially expressed upon incubation with hyper-IL-6 (HIL-6) for up to 72 h, with an overlap of 15 commonly regulated miRNAs. qPCR validation revealed that miR-146b-5p was also consistently up-regulated in hepatocytes derived from two other donors. Interestingly, miR-146b-5p (but not miR-146a-5p) were induced by HIL-6 and the IL-6-type cytokine OSM but also by IFN? in non-transformed liver-derived PH5CH8 and THLE-2 cells and in Huh-7 hepatoma cells. We did not find evidence for a regulation of miR-146b-5p expression by promoter methylation, also when analyzing the TCGA data set on liver cancer samples. Inducible overexpression of miR-146b-5p in PH5CH8 cells followed by RNA-Seq revealed effects on multiple mRNAs. The differentially regulated mRNAs include those encoding IRAK1 and TRAF6 crucial for Toll-like receptor signaling. Indeed, LPS, but not TNF -mediated up-regulation of MCP-1 and IL-6 mRNAs was attenuated upon overexpression of miR-146b-5p, suggesting a possible negative regulatory loop to switch off inflammatory signaling in hepatocytes.