We have been studying (i) the regulation of microRNAs by cytokines, (ii) their impact on cytokine signaling.
(i) To analyse the contribution of IL-6-regulated miRNAs to the effects of this cytokine on liver cells, we investigated its impact on the miRNome of hepatoma cells and non-transformed hepatocytes. Surprisingly, only few miRNAs were significantly differentially expressed in two hepatoma cell lines (Huh-7 and HepG2) stimulated with hyper-IL-6. A stronger effect could be observed in primary human hepatocytes (68 or 27 significantly differentially expressed microRNAs in samples from 2 different patients). To address cytokine-mediated changes of the miRNome in a broader setting, we performed a comparative analysis including, next to liver-derived cells, also melanoma, colon cancer and corresponding non-transformed cells. The effects of IL-6-type cytokines (activating mainly STAT3) were compared to the ones of the STAT1-activating cytokines IFN-g and IL-27. Our results reveal that the amplitude of the signaling outputs critically depends on the cell type and on the stimulus, both regarding the regulated mRNA transcriptomes and miRNomes.
(ii) In an independent approach, we aim at identifying miRNAs regulating key players of IL-6 signal transduction. To this end, we set up two screening systems based on STAT3-regulated luciferase read-outs. A first screen of 538 mimics in HEK293T reporter cells was followed by a second screen, re-testing 129 mimics in Hep3B reporter cells. Several candidate miRNAs are subject of an ongoing in-depth analysis (effects on IL-6-induced STAT3 phosphorylation, on the activity of a reporter gene fused to the 3’ UTR of STAT3, SOCS3, Jak1, gp130, or gp80, on corresponding protein levels, etc.) to elucidate their molecular targets.
These complementary approaches are also expected to allow for the identification of regulatory circuits regarding IL-6 signal transduction, its effect on and regulation by miRNAs.