HEPATITIS-C VIRUS CORE PROTEIN BINDS TO THE CYTOPLASMIC DOMAIN OF TUMOR-NECROSIS-FACTOR (TNF) RECEPTOR-1 AND ENHANCES TNF-INDUCED APOPTOSIS

The hepatitis C virus (HCV) core protein is known to be a multifunctio nal protein, besides being a component of viral nucleocapsids, Previou sly, we have shown that the core protein binds to the cytoplasmic doma in of lymphotoxin beta receptor, which is a member of tumor necrosis f actor receptor (TNFR) family. In this study, we demonstrated that the core protein also binds to the cytoplasmic domain of TNFR 1, The inter action was demonstrated both by glutathione S-transferase fusion prote in pull-down assay in vitro and membrane flotation method in vivo. Bot h 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 rece ptor. We have further shown that stable expression of the core protein in a mouse cell line (BC10ME) or human cell Hines (HepG2 and HeLa cel ls) sensitized them to TNF-induced apoptosis, as determined by the TNF cytotoxicity or annexin V apoptosis assay. The presence of the core p rotein did not alter the level of TNFR 1 mRNA in the cells or expressi on 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 o f TNFR 1. Furthermore, we observed that the core protein blocked the T NF-induced activation of RelA/NF-kappa B in murine BC10ME cells, thus at least partially accounting for the increased sensitivity of BC10ME cells to TNF, However, NF-kappa B activation was not blocked in core p rotein-expressing HeLa or HepG2 cells, implying another mechanism of T NF sensitization by core protein. These results together suggest that the core protein can promote cell death during HCV infection via TNF s ignaling pathways possibly as a result of its interaction with the cyt oplasmic tail of TNFR 1, Therefore, TNF may play a role in HCV pathoge nesis.