Serine/arginine-rich splicing factor 7 (SRSF7) promotes the type I interferon response by activating Irf7 transcription

Tight regulation of macrophage immune gene expression is required to fight infection without risking harmful inflammation. The contribution of RNA binding proteins (RBPs) to shaping the macrophage response to pathogens remains poorly understood. Transcriptomic analysis revealed that a member of the serine/arginine-rich (SR) family of mRNA processing factors, SRSF7, is required for optimal expression of a cohort of interferon stimulated genes (ISGs) in macrophages. Using genetic and biochemical assays, we discovered that in addition to its canonical role in regulating alternative splicing, SRSF7 drives transcription of interferon regulatory transcription factor 7 (IRF7) to promote antiviral immunity. At the Irf7 promoter, SRSF7 maximizes STAT1 transcription factor binding and RNA polymerase II elongation via cooperation with the H4K20me1 histone methyltransferase KMT5a (SET8). These studies define an unorthodox role for an SR protein in activating transcription and reveal an unappreciated RNA binding protein-chromatin network that orchestrates macrophage antiviral gene expression. Overall design: The goal of the experiment was to determine the contribution of IRF7 to basal and induced type I IFN expression in RAW 264.7 macrophages. RAW 264.7 macrophages expressing Cas9 were transduced with lentivirus expressing either a GFP gRNA (untargeted, control) or a gRNA targeted to exon 3 of Irf7 (KO1 and KO2). Knockout of IRF7 was confirmed by immunoblot. RNA was isolated from GFP gRNA and Irf7 KO cell lines at baseline (UN) and after 4h LPS (100ng/ml) using the Zymo Direct-Zol RNA purification kit and eluted in nuclease-free water.