Protein synthesis inhibition and GADD34 control IFN‐β heterogeneous expression in response to dsRNA. (18th January 2017) - Dalet, Alexandre
Abstract: In innate immune responses, induction of type‐I interferons (IFNs) prevents virus spreading while viral replication is delayed by protein synthesis inhibition. We asked how cells perform these apparently contradictory activities. Using single fibroblast monitoring by flow cytometry and mathematical modeling, we demonstrate that type‐I IFN production is linked to cell's ability to enter dsRNA‐activated PKR‐dependent translational arrest and then overcome this inhibition by decreasing eIF2α phosphorylation through phosphatase 1c cofactor GADD34 (Ppp1r15a) expression. GADD34 expression, shown here to be dependent on the IRF3 transcription factor, is responsible for a biochemical cycle permitting pulse of IFN synthesis to occur in cells undergoing protein synthesis inhibition. Translation arrest is further demonstrated to be key for anti‐viral response by acting synergistically with MAVS activation to amplify TBK1 signaling and IFN‐β mRNA transcription, while GADD34‐dependent protein synthesis recovery contributes to the heterogeneous expression of IFN observed in dsRNA‐activated cells. Synopsis: Double‐stranded ribonucleic acid (dsRNA) recognition triggers type‐I interferon (IFN) expression, while causing PKR‐dependent translation initiation factor‐2 phosphorylation (eIF2) and protein synthesis inhibition. Expression of the phosphatase 1 cofactor GADD34 is required to overcome translation inhibition and enable infected cells to secrete IFNs by displaying an undulating protein synthesis dynamics that also modulates the magnitude of the anti‐viral response. Translation recovery upon PKR activation is dependent on GADD34 and is essential to produce IFN‐β. Upon dsRNA recognition, GADD34 transcription is IRF3 dependent. Translation arrest strongly enhances the activation of the IRFs and NF‐κB pathways upon viral sensor activation. The intensity of translational arrest, IRF signaling, and GADD34‐dependent translation recovery is coordinated to minimize viral translation and maximize interferon secretion by adopting an oscillatory dynamic at the single‐cell level, which can account for apparent IFN‐β stochastic expression. Abstract : GADD34 coordinates transcriptional and translational responses to viral dsRNA to optimize type‐I IFN production.