Negative feedback of IFN-I signaling through IFN-competent RIG-I-like receptor-induced HSPA6

The RIG-I-like receptors (RLRs) form filaments to activate type-I interferon (IFN-I) and NF-KB signaling through their adaptor protein MAVS and downstream cascades. These filaments are recognized and regulated by cell-encoded machinery for correct activation. Here, we identified the stress-sensitive heat shock protein, HSPA6, was induced to express upon RLR-MAVS activation to act as a negative regulator of IFN-I signaling. Interestingly, by using MAVS-KO cells, we showed that HSPA6 was upregulated dependent on the presence of IFN-competent RLRs but not MAVS. Gene knockout (KO) tests indicated that the E3 ligases, stress granules (SGs), and transcription factors IRF1 and AP1 were all shared to induce HSPA6 and the canonical IFNb. Kinetic analysis showed that HSPA6 upregulated slower than IFNb, implicating these two genes competed machinery for transcription activation. Further tests suggested the induced HSPA6 bound to IFN-competent MDA5 to dissolve the filaments and downregulated IFN induction. Thus, our study uncovered a new gene activation mechanism by the IFN-competent RLRs to serve as negative feedback, arguing for a gene regulatory role of functional filaments of innate immunity. Overall design: We performed an RNA-seq to compare gene expression in WT and GOF MDA5 (G495R) expressing cells. And exclude the gene expression after IFN treatment stimulation.