P135 Defining the intracellular innate immune synapse

Abstract

Introduction Innate immunity to RNA virus infection is triggered when the cytosolic pathogen recognition receptor RIG-I engages viral RNA in infected cells. RIG-I pathway signaling is transmitted by the RIG-I adaptor protein MAVS, which resides on mitochondria, peroxisomes, and the mitochondrial-associated membrane (MAM), a distinct membrane that links ER to mitochondria. During RNA virus infection, RIG-I is recruited into the MAM where it binds MAVS and drives the actions of a signalosome that mediates downstream induction of antiviral, proinflammatory, and immunomodulatory genes that impart control of infection and immunity. MAM-tethering to mitochondria and peroxisomes coordinates MAVS localization to form a signaling synapse between membranes. The importance of the MAM within this “innate immune synapse” is highlighted by the fact that the hepatitis C virus (HCV) NS3/4A protease cleaves MAVS on the MAM, but not the mitochondria, to evade immunity. Methods To identify the components that regulate formation and function of the innate immune synapse and the MAVS signalosome, we characterized the proteome of MAM, ER, and cytosol subcellular fractions from uninfected cells and from cells with either chronic (HCV) or acute (Sendai) RNA virus infections. Results Comparative analysis of protein trafficking dynamics during both chronic and acute infection reveals differential protein profiles in the MAM compartment under RIG-I pathway activation. We also identified molecules recruited to the MAM in both chronic and acute RNA viral infections representing proteins that drive immunity and/or regulate viral replication. Conclusion Our proteomic analysis reveals dynamic cross-talk between subcellular compartments during both acute and chronic RNA virus infection, and demonstrates the importance of the MAM as a central platform that coordinates innate immune signaling to initiate immunity against RNA virus infection.