title: Hepatitis C virus core protein binds to the cytoplasmic domain of tumor necrosis factor (TNF) receptor 1 and enhances TNF-induced apoptosis.
abstract: The hepatitis C virus (HCV) core protein is known to be a multifunctional protein, besides being a component of viral nucleocapsids. Previously, we have shown that the core protein binds to the cytoplasmic domain of lymphotoxin beta receptor, which is a member of tumor necrosis factor receptor (TNFR) family. In this study, we demonstrated that the core protein also binds to the cytoplasmic domain of TNFR 1. The interaction was demonstrated both by glutathione S-transferase fusion protein pull-down assay in vitro and membrane flotation method in vivo. Both the in vivo and in vitro binding required amino acid residues 345 to 407 of TNFR 1, which corresponds to the "death domain" of this receptor. We have further shown that stable expression of the core protein in a mouse cell line (BC10ME) or human cell lines (HepG2 and HeLa cells) sensitized them to TNF-induced apoptosis, as determined by the TNF cytotoxicity or annexin V apoptosis assay. The presence of the core protein did not alter the level of TNFR 1 mRNA in the cells or expression of TNFR 1 on the cell surface, suggesting that the sensitization of cells to TNF by the viral core protein was not due to up-regulation of TNFR 1. Furthermore, we observed that the core protein blocked the TNF-induced activation of RelA/NF-kappaB in murine BC10ME cells, thus at least partially accounting for the increased sensitivity of BC10ME cells to TNF. However, NF-kappaB activation was not blocked in core protein-expressing HeLa or HepG2 cells, implying another mechanism of TNF sensitization by core protein. These results together suggest that the core protein can promote cell death during HCV infection via TNF signaling pathways possibly as a result of its interaction with the cytoplasmic tail of TNFR 1. Therefore, TNF may play a role in HCV pathogenesis.
authors.affiliation: Department of Molecular Microbiology and Immunology, University of Southern California School of Medicine, Los Angeles 90033, USA.
authors.forename: N
authors.initials: N
authors.lastname: Zhu
authors.forename: A
authors.initials: A
authors.lastname: Khoshnan
authors.forename: R
authors.initials: R
authors.lastname: Schneider
authors.forename: M
authors.initials: M
authors.lastname: Matsumoto
authors.forename: G
authors.initials: G
authors.lastname: Dennert
authors.forename: C
authors.initials: C
authors.lastname: Ware
authors.forename: M M
authors.initials: MM
authors.lastname: Lai
mesh_terms: D000818:Animals; D015703:Antigens, CD / Q000235:genetics / Q000378:metabolism*; D017209:Apoptosis; D001665:Binding Sites; D001692:Biological Transport; D019556:COS Cells; D002467:Cell Nucleus / Q000378:metabolism; D003593:Cytoplasm; D003603:Cytotoxins / Q000633:toxicity*; D006367:HeLa Cells; D016174:Hepacivirus / Q000378:metabolism*; D006801:Humans; D008322:Mammals; D051379:Mice; D016328:NF-kappa B / Q000378:metabolism; D018124:Receptors, Tumor Necrosis Factor / Q000235:genetics / Q000378:metabolism*; D047888:Receptors, Tumor Necrosis Factor, Type I; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D051996:Transcription Factor RelA; D014407:Tumor Cells, Cultured; D014409:Tumor Necrosis Factor-alpha / Q000633:toxicity*; D015854:Up-Regulation; D014758:Viral Core Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D015703:Antigens, CD; D003603:Cytotoxins; D016328:NF-kappa B; D018124:Receptors, Tumor Necrosis Factor; D047888:Receptors, Tumor Necrosis Factor, Type I; D011993:Recombinant Fusion Proteins; D051996:Transcription Factor RelA; D014409:Tumor Necrosis Factor-alpha; D014758:Viral Core Proteins; C069130:nucleocapsid protein, Hepatitis C virus