A genetic screen to identify deubiquitinases as regulators of IRF7

Virus infection rapidly induces the production and secretion of interferons (IFNs), amplifying antiviral responses in infected and neighboring uninfected cells. IFN regulatory factor 7 (IRF7), the ‘master transcription factor,’ is pivotal in IFN induction, particularly in myeloid cells. Ubiquitination of IRF7 is essential for its transcriptional activation; however, the underlying molecular mechanisms remain poorly understood. We hypothesized that deubiquitinases (DUBs) act as endogenous regulators of IRF7 activity and conducted a genetic screen using a human DUB-targeted siRNA library. This screen identified USP2 as a positive regulator and OTUD5 as a negative regulator of IRF7 activity. OTUD5, an inducible DUB, physically interacted with IRF7 and inhibited its K63-linked ubiquitination, thereby suppressing IRF7 activation. Conversely, USP2 promoted IRF7 activity by binding to IRF7 and removing K27-linked ubiquitin chains, which we found to be inhibitory. Specifically, K27-linked ubiquitination impeded phosphorylation of IRF7, a critical step for its activation. Collectively, our genetic screen and mechanistic studies uncovered USP2 and OTUD5 as novel modulators of IRF7 function, providing new insights into the regulation of antiviral immunity.