Bunyavirus SFTSV nucleoprotein exploits TUFM-mediated mitophagy to impair antiviral innate immunity

Abstract

Severe fever with thrombocytopenia syndrome is an emerging viral hemorrhagic fever caused by a tick-borne bunyavirus, severe fever with thrombocytopenia syndrome virus (SFTSV), with a high case fatality. We previously found that SFTSV nucleoprotein (NP) induces macroautophagy/autophagy to facilitate virus replication. However, the role of NP in antagonizing host innate immunity remains unclear. Mitophagy, a selected form of autophagy, eliminates damaged mitochondria to maintain mitochondrial homeostasis. Here, we demonstrate that SFTSV NP triggers mitophagy to degrade MAVS (mitochondrial antiviral signaling protein), thereby blocking MAVS-mediated antiviral signaling to escape the host immune response. Mechanistically, SFTSV NP translocates to mitochondria by interacting with TUFM (Tu translation elongation factor, mitochondrial), and mediates mitochondrial sequestration into phagophores through interacting with LC3, thus inducing mitophagy. Notably, the N-terminal LC3-interacting region (LIR) motif of NP is essential for mitophagy induction. Collectively, our results demonstrated that SFTSV NP serves as a novel virulence factor, inducing TUFM-mediated mitophagy to degrade MAVS and evade the host immune response.<b>Abbreviation:</b> 3-MA: 3-methyladenine; ACTB: actin beta; co-IP: co-immunoprecipitation; CQ: chloroquine; DAPI: 4',6-diamidino-2-phenylindole, dihydrochloride; DMSO: dimethyl sulfoxide; FCCP: carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone; GFP: green fluorescent protein; HTNV: Hantan virus; IAV: influenza A virus; IFN: interferon; LAMP1: lysosomal associated membraneprotein 1; LIR: LC3-interacting region; MAP1LC3B/LC3B: microtubule associatedprotein 1 light chain 3 beta; MAVS: mitochondrial antiviral signaling protein; Mdivi-1: mitochondrial division inhibitor 1; MOI: multiplicity of infection; MT-CO2/COXII: mitochondrially encoded cytochrome C oxidase II; NP: nucleoprotein; NSs: nonstructural proteins; poly(I:C): polyinosinic:polycytidylic acid; RIGI: RNA sensor RIG-I; RLR: RIGI-like receptor; SFTSV: severe fever withthrombocytopenia syndrome virus; TCID50: 50% tissue culture infectiousdose; TIMM23: translocase of inner mitochondrial membrane 23; TOMM20:translocase of outer mitochondrial membrane 20; TUFM: Tu translation elongationfactor, mitochondrial.