Alphaherpesvirus UL48 homologs degrade STING1 by selective autophagy

Alpha-herpesviruses have evolved strategies to break through immune defenses and cause severe host damage. Here, we demonstrate that the tegument protein UL48 in pseudorabies virus (PRV) inhibits type I interferon signaling by triggering STING1 degradation via a selective macroautophagy/autophagy pathway. Mechanistically, UL48 recruits the E3 ligase TRIM21 (tripartite motif containing 21), which catalyzes the ubiquitination of STING1 to form a K33/K63 linkage and is captured by the cargo receptor CALCOCO2/NDP52 for lysosomal degradation. In addition, multiple α-herpesvirus tegument protein UL48 homologs also target STING1 for degradation. Importantly, this phenotype was also observed in other herpesviruses driven by PRV UL48 homologs (herpes simplex virus-1 [HSV-1] and cercopithecine alphaherpesvirus 2 [CHV-2]). In addition, UL48-deficient PRV and HSV-1 mutant viruses attenuated pathogenicity in mice. In conclusion, this study describes a novel mechanism by which α-herpesviruses utilize UL48 proteins to promote viral escape from the host immune response.
Abbreviations: 3-MA: 3-methyladenine; B-DNA: poly (dA:dT); BNIP3L/Nix: BCL2 interacting protein 3 like; CALCOCO2/NDP52: calcium binding and coiled-coil domain 2; cGAMP: cyclic GMP-AMPP; CGAS: cyclic GMP-AMP synthase; CHX: cyclohexane; CHV-2: cercopithecine herpesvirus 2; CQ: chloroquine; DAPI: 4’,6-diamidino-2-phenylindole; DMSO: dimethyl sulfoxide; ER: endoplasmic reticulum; GFP: green fluorescent protein; H&E: hematoxylin and eosin; HSV-1: herpes simplex virus 1; IRF3: interferon regulatory factor 3; LIR: LC3-interacting region; MAP1LC3A/LC3: microtubule associated protein 1 light chain 3 alpha; MG132: cbz-leu-leu-leucinal; NBR1: NBR1 autophagy cargo receptor; OPTN: optineurin; PRV: pseudorabies virus; sgRNA: single guide RNA; siRNA: small interfering RNA; SQSTM1/p62: sequestosome 1; STING1/STING: stimulator of interferon response cGAMP interactor 1; TBK1: TANK binding kinase 1; TOLLIP: toll interacting protein