HTLV-1 Tax induces PINK1-PRKN/parkin-dependent mitophagy to mitigate activation of the CGAS-STING1 pathway

Human T-cell leukemia virus type 1 (HTLV-1) is the causative agent of adult T-cell leukemia/lymphoma (ATLL) and the neuroinflammatory disease, HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). The HTLV-1 Tax regulatory protein plays a critical role in HTLV-1 persistence and pathogenesis; however, the underlying mechanisms are poorly understood. Here we show that Tax dynamically regulates mitochondrial reactive oxygen species (ROS) and membrane potential to trigger mitochondrial dysfunction. Tax is recruited to damaged mitochondria through its interaction with the IKK regulatory subunit IKBKG/NEMO and directly engages the ubiquitin-dependent PINK1-PRKN/parkin pathway to induce mitophagy. Tax also recruits autophagy receptors CALCOCO2/NDP52 and SQSTM1/p62 to damaged mitochondria to induce mitophagy. Furthermore, Tax requires PRKN to limit the extent of CGAS-STING1 activation and suppress type I interferon (IFN) induction. HTLV-1-transformed T-cell lines and PBMCs from HAM/TSP patients exhibit hallmarks of chronic mitophagy, and inhibition of PRKN in HTLV-1-transformed cell lines downregulates p19 Gag expression and induces cell death. Collectively, our findings suggest that Tax manipulation of the PINK1-PRKN mitophagy pathway represents a new HTLV-1 immune evasion strategy important for maintaining viral gene expression and cell survival.Abbreviations: 3-MA: 3-methyladenine; ACTB: actin beta; ATLL: adult T-cell leukemia/lymphoma; BafA1: bafilomycin A1; BECN1: beclin 1; CALCOCO2: calcium binding and coiled-coil domain 2; CCCP: carbonyl cyanide m-chlorophenylhydrazone; CGAS: cyclic GMP-AMP synthase; co-IP: co-immunoprecipitation; DOX: doxycycline; GFP: green fluorescent protein; DNM1L/DRP1: dynamin 1 like; HAM/TSP: HTLV-1-associated myelopathy/tropical spastic paraparesis; HSPD1/HSP60: heat shock protein family D (Hsp60) member 1; HTLV-1: Human T-cell leukemia virus type 1; IFN: interferon; IkB: inhibitor of nuclear factor kappa B; IKBKG/NEMO: inhibitor of nuclear factor kappa B kinase regulatory subunit gamma; IKK: IkB kinase; IRF3: interferon regulatory factor 3; KO: knockout; LAMP2: lysosome associated membrane protein 2; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MT-CO2: mitochondrially encoded cytochrome c oxidase II; mtDNA: mitochondrial DNA; mtROS: mitochondrial reactive oxygen species; NAC: N-acetylcysteine; NBR1: NBR1 autophagy cargo receptor; NFKB: nuclear factor kappa B; OPTN: optineurin; PBMCs: peripheral blood mononuclear cells; PINK1: PTEN induced kinase 1; PRKN: parkin RBR E3 ubiquitin protein ligase; qRT-PCR: quantitative reverse transcription polymerase chain reaction; RFP: red fluorescence protein; ROS: reactive oxygen species; SAR: selective autophagy receptor; SQSTM1: sequestosome 1; STING1: stimulator of interferon response cGAMP interactor 1; TAX1BP1: Tax1 binding protein 1; TEM: transmission electron microscopy; TMRM: tetramethylrhodamine methyl ester; TOMM20: translocase of outer mitochondrial membrane 20; Ub: ubiquitin; VCL: vinculin; WT: wild-type.