DIRECT INTERACTION OF HEPATITIS-C VIRUS CORE PROTEIN WITH THE CELLULAR LYMPHOTOXIN-BETA RECEPTOR MODULATES THE SIGNAL PATHWAY OF THE LYMPHOTOXIN-BETA RECEPTOR

Previous studies suggest that the core protein of hepatitis C virus (H CV) has a pleiotropic function in the replication cycle of the virus. To understand the role of this protein in HCV pathogenesis, we used a yeast two-hybrid protein interaction cloning system to search for cell ular proteins physically interacting with the HCV core protein. One su ch cellular gene was isolated and characterized as the gene encoding t he lymphotoxin-beta receptor (LT-beta R). In vitro binding analysis de monstrated that the HCV core protein binds to the C-terminal 98 amino acids within the intracellular domain of the LT-beta R that is involve d in signal transduction, although the binding affinity of the full-le ngth HCV core protein was weaker than that of its C-terminally truncat ed form. Our results also indicated that the N-terminal 40-amino-acid segment of the HCV core protein was sufficient for interaction with LT -beta R and that the core protein could form complexes with the oligom eric form of the intracellular domain of LT-beta R, which is a prerequ isite for downstream signaling of this receptor. Similar to other memb ers of the tumor necrosis factor (TNF) receptor superfamily, LT-beta R is involved in the cytotoxic effect of the signaling pathway and thus we have elucidated the biological consequence of interaction between the HCV core protein and LT-beta R. Our results indicated that in the presence of the synergizing agent gamma interferon, tbe HCV core prote in enhances the cytotoxic effects of recombinant forms of LT-beta R li gand in HeLa cells but not in hepatoma cells. Furthermore, this enhanc ement of the cytolytic activity was cytokine specific, since in the pr esence of cycloheximide, the expression of the HCV core protein did no t elicit an increase in the cytolytic activity of TNF in both HeLa and hepatoma cells. In summary, the HCV core protein can associate with L T-beta R, and this protein-protein interaction has a modulatory effect on the signaling pathway of LT-beta R in certain cell types. Given th e known roles of LT-beta R/LT-alpha(1) beta(2) receptor-ligand interac tions in the normal development of peripheral lymphoid organs and in t riggering cytolytic activity and NF-kappa B activation in certain cell types, our finding implies that the HCV core protein may aggravate th ese biological functions of LT-beta R, resulting in pathogenesis in HC V-infected cells.