Pivotal role for the non-receptor tyrosine kinase SRMS in IRF3-dependent innate antiviral immune response in murine cells

Abstract Upon viral infections, RIG-I-like receptors (RLRs) sense cytosolic viral RNAs and initiate signaling pathways culminating in the activation of IRF3 and subsequent type I interferon (IFN) antiviral response. This intrinsic protective mechanism is orchestrated by a host of positive and negative regulators, which collectively govern the magnitude and duration of antiviral signaling. SRMS is an understudied non-receptor tyrosine kinase frequently overexpressed in breast cancers. SRMS restrains autophagy and promotes tumor growth, although its physiological function is unclear. We report here that SRMS is critical for IRF3-dependent innate antiviral response in murine cells. Depletion of SRMS impaired virus- or dsRNA-induced expression of type I and III IFNs and ISGs in mouse embryonic fibroblasts (MEFs), mouse hepatoma hepa1–6 cells, and primary mouse lung fibroblasts, concomitant with heightened viral replication. Mechanistically, SRMS loss led to diminished phosphorylations of TBK1 and IRF3, IRF3 dimerization and nuclear translocation. The kinase activity of SRMS, however, was dispensable. Reconstituting the expression of SRMS of mouse or human origin, be it wild-type or kinase-dead protein, in SRMS-null MEFs restored antiviral signaling. Autophagy regulation was not involved, either. Interestingly, antiviral gene expression via the RLRs in human U2OS and MDA-MB-231 cells was not impacted by SRMS deletion, suggesting signaling redundancy in human cells. Altogether, our data uncover a novel role of SRMS in controlling IRF3-dependent innate antiviral responses and describe a non-canonical, kinase- and autophagy-independent regulatory mechanism that operates differentially between mouse and human species. R21 AI142044