The Leader Proteinase of Foot-and-Mouth Disease Virus Negatively Regulates the Type I Interferon Pathway by Acting as a Viral Deubiquitinase

摘要

The leader proteinase (L^pro) of foot-and-mouth disease virus (FMDV) is a papain-like proteinase that plays an important role in FMDV pathogenesis. Previously, it has been shown that L^pro is involved in the inhibition of the type I interferon (IFN) response by FMDV. However, the underlying mechanisms remain unclear. Here we demonstrate that FMDV Lb^pro, a shorter form of L^pro, has deubiquitinating activity. Sequence alignment and structural bioinformatics analyses revealed that the catalytic residues (Cys51 and His148) are highly conserved in FMDV Lb^pro of all seven serotypes and that the topology of FMDV Lb^pro is remarkably similar to that of ubiquitin-specific protease 14 (USP14), a cellular deubiquitylation enzyme (DUB), and to that of severe acute respiratory syndrome coronavirus (SARS-CoV) papain-like protease (PLpro), a coronaviral DUB. Both purified Lb^pro protein and in vivo ectopically expressed Lb^pro removed ubiquitin (Ub) moieties from cellular substrates, acting on both lysine-48- and lysine-63-linked polyubiquitin chains. Furthermore, Lb^pro significantly inhibited ubiquitination of retinoic acid-inducible gene I (RIG-I), TANK-binding kinase 1 (TBK1), TNF receptor-associated factor 6 (TRAF6), and TRAF3, key signaling molecules in activation of type I IFN response. Mutations in Lb^pro that ablate the catalytic activity (C51A or D163N/D164N) or disrupt the SAP (for SAF-A/B, Acinus, and PIAS) domain (I83A/L86A) abrogated the DUB activity of Lb^pro as well as its ability to block signaling to the IFN-β promoter. Collectively, these results demonstrate that FMDV Lb^pro possesses DUB activity in addition to serving as a viral proteinase and describe a novel mechanism evolved by FMDV to counteract host innate antiviral responses.