In Vivo RNAi Screening Identifies MDA5 as a Significant Contributor to the Cellular Defense against Influenza A Virus

Abstract

SUMMARY Responding to an influenza A virus (IAV) infection demands an effective intrinsic cellular defense strategy to slow replication. To identify contributing host factors to this defense, we exploited the host microRNA pathway to perform an in vivo RNAi screen. To this end, IAV, lacking a functional NS1 antagonist, was engineered to encode individual siRNAs against antiviral host genes in an effort to rescue attenuation. This screening platform resulted in the enrichment of strains targeting virus-activated transcription factors, specific antiviral effectors, and intracellular pattern recognition receptors (PRRs). Interestingly, in addition to RIG-I, the PRR for IAV, a virus with the capacity to silence MDA5 also emerged as a dominant strain in wild type, but not in MDA5-deficient mice. Transcriptional profiling of infected knockout cells confirmed RIG-I to be the primary PRR for IAV but implicated MDA5 as a significant contributor to the cellular defense against influenza A virus.

Standing on three legs: antiviral activities of RIG-I against influenza viruses

“…For host responses against FLUAV, the dominant cytoplasmic PRR is RIG-I, whereas MDA5 and the dsRNAactivate kinase PKR are amplifying the antiviral signal [9][10][11]. RNA transfection studies helped to pin down the critical viral RNA structures involved in RIG-I activation.…”

Specific induction of endogenous viral restriction factors using CRISPR/Cas-derived transcriptional activators

“…Moreover, many restriction factors are not constitutively expressed but are instead induced upon viral infection, including numerous IFN-stimulated genes (ISGs). Whereas the identification of restriction factors therefore remains challenging, screens for factors whose knockdown using siRNAs enhances viral replication have had some success (41).…”

Checks and Balances between Autophagy and Inflammasomes during Infection

“…This allows RIG-I interaction with mitochondrial antiviral signaling protein (MAVS) at the mitochondria and subsequent signaling that activates specific transcription factors required for induction of IFNs [191–194]. In addition, a minor role for the RNA sensor Melanoma Differentiation-Associated protein 5 (MDA5), which also signals through MAVS, has been reported recently [195], and TLR7 is the primary sensor for influenza virus leading to IFN production specifically in plasmacytoid DCs [190,196]. Double knockout of MAVS and TLR7 thus results in increased mortality during infection due to loss of type I IFN production [197].…”