Sidney & Joan Pestka Graduate Award
Type-I interferon mediated degradation of microRNAs is sequence and length dependent, Charlotte Nejad1, 2, Michael Paul Gantier1, 2; 1Centre for Innate Immunity and Infectious Diseases, Hudson Institute of Medical Research, Clayton, Australia, 2Department of Molecular and Translational Science, Monash University, Clayton, Australia
Innate immune activation by pathogens promotes global transcriptional changes in infected cells, promptly affecting the levels of messenger RNAs (mRNAs) and non-coding RNAs such as microRNAs (miRNAs). As such, induced miRNAs cause rapid down regulation of mRNA targets, thereby controlling the duration and intensity of the immune response. Interestingly, there is evidence that upon type-I interferon (IFN) stimulation select miRNAs can be actively degraded, including the pro-inflammatory miR-221 and miR-222. However, the impact of these decreased miRNAs on IFN responses is currently not known.
In this work, we initially observed by RT-qPCR that the levels of miR-221, and not that of the co-expressed miR-222, were decrease by >80% following Toll-like receptor (TLR) 3/4 stimulation, but not that of other TLRs. This specific decrease of miR-221 was type-I IFN dependent, and ablated in IFN-α/β receptor 1 deficient bone marrow-derived macrophages (BMDMs). Unexpectedly, miR-221 decrease was restricted to its longer isoforms, a phenomenon also observed for miR-222. RNA sequencing (RNAseq) carried out on human fibroblasts treated with type-I IFN confirmed these observations, identifying a group of other miRNAs for which the longer isoforms were similarly impacted. Significantly, we identified a core motif in these miRNAs directly regulating their stability, upon IFN-β stimulation, which can be attributed to the exoribonuclease Pnpt1. In addition, the RNAseq data revealed an overall decrease >70% of miR-222 molecules with IFN-β.
Collectively, these findings suggest that sequence and length-dependent miRNA degradation helps control the overall abundance of miR-221/222, and their pro-inflammatory function during type-I IFN responses.