Tegument protein UL16 of herpes simplex virus 1 suppresses the innate immune response by downregulating MAVS abundance via mitophagy.

Publication date: Jul 02, 2026

Herpes simplex virus 1 (HSV-1) is a globally prevalent pathogen that poses a significant health threat due to its lifelong latency. This persistence is driven by intricate immune evasion mechanisms, the deciphering of which remains a challenge. Here, we identified the HSV-1 tegument protein UL16 as a novel viral immunosuppressive factor, which significantly suppresses the RIGI-like receptor (RLR)-mediated antiviral immunity. We found that UL16 can interact with MAVS (mitochondrial antiviral signaling protein) and induce its degradation, thereby inhibiting type I interferon (IFN-I) production. Further investigation revealed that UL16-induced MAVS degradation was facilitated via mitophagy involving the mitochondrial cargo receptor FUNDC1 (FUN14 domain containing 1). Knockout of FUNDC1 expression completely disrupted UL16-induced MAVS degradation and restricted HSV-1 replication. In contrast, overexpression of FUNDC1 augmented the suppressive effect of UL16 on MAVS-triggered IFN-I signaling and consequently benefited viral replication. Notably, the C-terminal domain (CTD) of UL16 primarily accounted for its immunosuppressive function, which was also demonstrated to be essential for UL16 engagement with MAVS, FUNDC1 and MAP1LC3/LC3 (microtubule associated protein 1 light chain 3). A conserved LC3-interacting region (LIR) motif within the UL16 CTD was identified to play a critical role in LC3 recruitment enhancement. Furthermore, the UL16-deficient HSV-1 exhibited markedly attenuated viral infectivity and pathogenicity in vivo. In summary, our findings uncover a previously uncharacterized pathway through which HSV-1 UL16 subverts host immunity by inducing mitophagy. This study provides critical insights into host-pathogen interactions and establishes a rational foundation for developing novel therapeutics against HSV-1 infection. Abbreviations:3-MA: 3-methyladenine; BNIP3L/NIX: BCL2 interacting protein 3 like; BSA: bovine serum albumin; CALCOCO2/NDP52: calcium binding and coiled-coil domain 2; CARD: caspase recruitment domain; Cas9: CRISPR-associated system 9; CGAS: cyclic GMP-AMP synthase; co-IP: co-immunoprecipitation; COX8: cytochrome c oxidase subunit 8; CQ: chloroquine; CRISPR: clustered regulatory interspaced short palindromic repeat; CTD: C-terminal domain; Ctrl: control; CXCL10: C-X-C motif chemokine ligand 10; DAPI: 4,’6-diamidino-2-phenylindole; DMEM: Dulbecco’s modified Eagle’s medium; DMSO: dimethyl sulfoxide; ds: double-stranded; FBS: fetal bovine serum; FUNDC1: FUN14 domain containing 1; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GFP: green fluorescent protein; HEK: human embryonic kidney; HSV-1: herpes simplex virus 1; IAV: influenza A virus; IFIH1/MDA5: interferon induced with helicase C domain 1; IFIT1/ISG56: interferon induced protein with tetratricopeptide repeats 1; IFN-I: type I interferon; IgG: Immunoglobulin G; IRF3: interferon regulatory factor 3; ISGs: IFN-stimulated genes; kDa: kilodalton; KO: knockout; KSHV: Kaposi sarcoma-associated herpesvirus; LIR: LC3-interacting region; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MAVS: mitochondrial antiviral signaling protein; Mdivi-1: mitochondrial division inhibitor 1; MG132: cbz-leu-leu-leucinal; MOI: multiplicity of infection; NanoBiT: NanoLuc Binary Technology; NC: negative control; NTD: N-terminal domain; OPTN: optineurin; p-: phosphorylated; PFU: plaque-forming unit; PINK1: PTEN induced kinase 1; poly(I:C): polyinosinic-polycytidylic acid; PRKN/parkin: parkin RBR E3 ubiquitin protein ligase; qPCR: quantitative polymerase chain reaction; RIGI/RIG-I: RNA sensor RIG-I; RLR: RIGI-like receptor; SARS-CoV-2: severe acute respiratory syndrome coronavirus 2; SeV: Sendai virus; sgRNA: single guide RNA; shRNA: short hairpin RNA; SQSTM1/p62: sequestosome 1; STING1: stimulator of interferon response cGAMP interactor 1; TBK1: TANK binding kinase 1; TM: transmembrane; TOMM20: translocase of outer mitochondrial membrane 20; TRAF: TNF receptor associated factor; TUFM: Tu translation elongation factor, mitochondrial; UL16: unique long region 16; VSV: vesicular stomatitis virus; VZV: varicella zoster virus; WCL: whole-cell lysate; WT: wild-type; Z-VAD-FMK: carbobenzoxy-valyl-alanyl-aspartyl-[O-methyl]-fluoromethylketone.

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