Selective autophagy receptor SQSTM1/ p62 inhibits Seneca Valley virus replication by targeting viral VP1 and VP3

Macroautophagy/autophagy plays a critical role in antiviral immunity through targeting viruses and initiating host immune responses. The receptor protein, SQSTM1/p62 (sequestosome 1), plays a vital role in selective autophagy. It serves as a receptor targeting ubiquitinated proteins or pathogens to phagophores for degradation. In this study, we explored the reciprocal regulation between selective autophagy receptor SQSTM1 and Seneca Valley virus (SVV). SVV infection induced autophagy. Autophagy promoted SVV infection in pig cells but played opposite functions in human cells. Overexpression of SQSTM1 decreased viral protein production and reduced viral titers. Further study showed that SQSTM1 interacted with SVV VP1 and VP3 independent of its UBA domain. SQSTM1 targeted SVV VP1 and VP3 to phagophores for degradation to inhibit viral replication. To counteract this, SVV evolved strategies to circumvent the host autophagic machinery to promote viral replication. SVV 3Cpro targeted the receptor SQSTM1 for cleavage at glutamic acid 355, glutamine 392, and glutamine 395 and abolished its capacity to mediate selective autophagy. At the same time, the 3Cpro-mediated SQSTM1 cleavage products lost the ability to inhibit viral propagation. Collectively, our results provide evidence for selective autophagy in host against viruses and reveal potential viral strategies to evade autophagic machinery for successful pathogenesis. Abbreviations: Baf.A1: bafilomycin A1; Co-IP: co-immunoprecipitation; hpi: h post-infection; LIR: LC3-interacting region; MAP1LC3B/LC3B: microtubule-associated protein 1 light chain 3 beta; MOI: multiplicity of infection; PB1: N-terminal Phox/Bem1p; Rap.: rapamycin; Seneca Valley virus: SVV; SQSTM1/p62: sequestosome 1; SQSTM1-N355: residues 1 to 355 of SQSTM1; SQSTM1-C355: residues 355 to 478 of SQSTM1; SQSTM1-N392: residues 1 to 392 of SQSTM1; SQSTM1-C392: residues 392 to 478 of SQSTM1; SQSTM1-N388: residues 1 to 388 of SQSTM1; SQSTM1-N397: residues 1 to 397 of SQSTM1; UBA: ubiquitin association; Ubi: ubiquitin.

巨自噬（Macroautophagy，又称自噬）通过靶向病毒并启动宿主免疫应答，在抗病毒免疫中发挥关键作用。受体蛋白SQSTM1/p62（sequestosome 1，泛素结合蛋白p62）在选择性自噬中具有核心功能，其作为受体可将泛素化蛋白或病原体靶向递送至自噬前体膜以进行降解。本研究探究了选择性自噬受体SQSTM1与塞内卡谷病毒（Seneca Valley Virus, SVV）之间的相互调控机制。SVV感染可诱导自噬发生；自噬在猪源细胞中可促进SVV感染，但在人源细胞中则发挥相反功能。过表达SQSTM1可降低病毒蛋白生成量并减少病毒滴度。进一步研究显示，SQSTM1可独立于其泛素相关（UBA）结构域与SVV衣壳蛋白VP1及VP3相互作用，并将SVV VP1、VP3靶向递送至自噬前体膜进行降解，从而抑制病毒复制。为对抗这一宿主防御过程，SVV进化出多种策略以逃逸宿主自噬系统，进而促进病毒复制。SVV 3C蛋白酶（3Cpro）可在谷氨酸355、谷氨酰胺392及谷氨酰胺395位点切割SQSTM1受体，使其丧失介导选择性自噬的能力；同时，3Cpro介导产生的SQSTM1切割片段也失去了抑制病毒增殖的功能。综上，本研究结果为宿主通过选择性自噬抵御病毒提供了实验证据，并揭示了病毒逃逸自噬系统以完成致病过程的潜在策略。

缩写说明：Baf.A1：巴弗洛霉素A1（bafilomycin A1）；Co-IP：免疫共沉淀（co-immunoprecipitation）；hpi：感染后小时数（hours post-infection）；LIR：LC3互作区域（LC3-interacting region）；MAP1LC3B/LC3B：微管相关蛋白1轻链3β（microtubule-associated protein 1 light chain 3 beta）；MOI：感染复数（multiplicity of infection）；PB1：N端Phox/Bem1p结构域（N-terminal Phox/Bem1p）；Rap.：雷帕霉素（rapamycin）；Seneca Valley virus：塞内卡谷病毒（SVV）；SQSTM1/p62：泛素结合蛋白p62（sequestosome 1）；SQSTM1-N355：SQSTM1的1~355位氨基酸残基；SQSTM1-C355：SQSTM1的355~478位氨基酸残基；SQSTM1-N392：SQSTM1的1~392位氨基酸残基；SQSTM1-C392：SQSTM1的392~478位氨基酸残基；SQSTM1-N388：SQSTM1的1~388位氨基酸残基；SQSTM1-N397：SQSTM1的1~397位氨基酸残基；UBA：泛素相关结构域（ubiquitin association）；Ubi：泛素（ubiquitin）。