title: Disruption of TLR3 signaling due to cleavage of TRIF by the hepatitis A virus protease-polymerase processing intermediate, 3CD.
abstract: Toll-like receptor 3 (TLR3) and cytosolic RIG-I-like helicases (RIG-I and MDA5) sense viral RNAs and activate innate immune signaling pathways that induce expression of interferon (IFN) through specific adaptor proteins, TIR domain-containing adaptor inducing interferon-β (TRIF), and mitochondrial antiviral signaling protein (MAVS), respectively. Previously, we demonstrated that hepatitis A virus (HAV), a unique hepatotropic human picornavirus, disrupts RIG-I/MDA5 signaling by targeting MAVS for cleavage by 3ABC, a precursor of the sole HAV protease, 3C(pro), that is derived by auto-processing of the P3 (3ABCD) segment of the viral polyprotein. Here, we show that HAV also disrupts TLR3 signaling, inhibiting poly(I:C)-stimulated dimerization of IFN regulatory factor 3 (IRF-3), IRF-3 translocation to the nucleus, and IFN-β promoter activation, by targeting TRIF for degradation by a distinct 3ABCD processing intermediate, the 3CD protease-polymerase precursor. TRIF is proteolytically cleaved by 3CD, but not by the mature 3C(pro) protease or the 3ABC precursor that degrades MAVS. 3CD-mediated degradation of TRIF depends on both the cysteine protease activity of 3C(pro) and downstream 3D(pol) sequence, but not 3D(pol) polymerase activity. Cleavage occurs at two non-canonical 3C(pro) recognition sequences in TRIF, and involves a hierarchical process in which primary cleavage at Gln-554 is a prerequisite for scission at Gln-190. The results of mutational studies indicate that 3D(pol) sequence modulates the substrate specificity of the upstream 3C(pro) protease when fused to it in cis in 3CD, allowing 3CD to target cleavage sites not normally recognized by 3C(pro). HAV thus disrupts both RIG-I/MDA5 and TLR3 signaling pathways through cleavage of essential adaptor proteins by two distinct protease precursors derived from the common 3ABCD polyprotein processing intermediate.
authors.affiliation: Lineberger Comprehensive Cancer Center and the Division of Infectious Diseases, Department of Medicine, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.
authors.forename: Lin
authors.initials: L
authors.lastname: Qu
authors.forename: Zongdi
authors.initials: Z
authors.lastname: Feng
authors.forename: Daisuke
authors.initials: D
authors.lastname: Yamane
authors.forename: Yuqiong
authors.initials: Y
authors.lastname: Liang
authors.forename: Robert E
authors.initials: RE
authors.lastname: Lanford
authors.forename: Kui
authors.initials: K
authors.lastname: Li
authors.forename: Stanley M
authors.initials: SM
authors.lastname: Lemon
mesh_terms: D000086042:3C Viral Proteases; D033942:Adaptor Proteins, Vesicular Transport / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D003546:Cysteine Endopeptidases / Q000235:genetics / Q000378:metabolism*; D030041:Hepatitis A virus / Q000201:enzymology* / Q000302:isolation & purification; D006801:Humans; D007113:Immunity, Innate; D050838:Interferon Regulatory Factor-3 / Q000037:antagonists & inhibitors / Q000378:metabolism; D016899:Interferon-beta / Q000378:metabolism; D008156:Luciferases / Q000378:metabolism; D010957:Plasmids / Q000235:genetics; D012367:RNA, Viral / Q000235:genetics*; D015398:Signal Transduction; D013379:Substrate Specificity; D051196:Toll-Like Receptor 3 / Q000235:genetics / Q000378:metabolism*; D014162:Transfection / Q000379:methods; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D033942:Adaptor Proteins, Vesicular Transport; C494232:IRF3 protein, human; D050838:Interferon Regulatory Factor-3; D012367:RNA, Viral; C470409:TICAM1 protein, human; C495344:TLR3 protein, human; D051196:Toll-Like Receptor 3; D014764:Viral Proteins; D016899:Interferon-beta; D008156:Luciferases; D003546:Cysteine Endopeptidases; D000086042:3C Viral Proteases