Hepatitis C virus core protein enhances FADD-mediated apoptosis and suppresses TRADD signaling of tumor necrosis factor receptor.
Hepatitis C virus (HCV) core protein has been shown to interact with the death domain (DD) of tumor necrosis factor receptor-1 (TNFR1). In this study, we further examined the interaction of the core protein with the signaling molecules of TNFR1, including FADD, TRADD, and TRAF2, in a human embryonic kidney cell line, HEK-293, that overexpresses the HCV core protein. This core protein-expressing cell line exhibited enhanced sensitivity to TNF-induced apoptosis. By in vitro binding and in vivo coimmunoprecipitation assays, we showed that the HCV core protein interacted with the DD of FADD and enhanced apoptosis induced by FADD overexpression. This enhancement could be blocked by a dominant-negative mutant of FADD. In contrast, the core protein did not directly interact with the DD of TRADD, but could disrupt the binding of TRADD to TNFR1. TRAF2 recruitment to the TNFR1 signaling complex was also disrupted by the core protein. Correspondingly, TRAF2-dependent activation of the protein kinase JNK was suppressed in the core protein-expressing cells. However, NF kappa B activation by TNF was not significantly altered by the HCV core protein, suggesting the existence of TRAF2-independent pathways for NF kappa B activation. These results combined indicate that the HCV core protein sensitizes cells to TNF-induced apoptosis primarily by facilitating FADD recruitment to TNFR1. The inhibition of JNK activation by the HCV core protein may also contribute to the increased propensity of cells for apoptosis. These results, in comparison with other published studies, suggest that the effects of the HCV core protein and their underlying mechanisms vary significantly among cells of different origins.
Zhu
N
N
Howard Hughes Medical Institute, University of Southern California Keck School of Medicine, Los Angeles, California 90033, USA.
Ware
C F
CF
Lai
M M
MM
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D053200:Fas-Associated Death Domain Protein; D005786:Gene Expression Regulation; D016174:Hepacivirus; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases; D048670:MAP Kinase Kinase 4; D051379:Mice; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D018124:Receptors, Tumor Necrosis Factor / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D053199:TNF Receptor-Associated Death Domain Protein; D047990:TNF Receptor-Associated Factor 1; D047992:TNF Receptor-Associated Factor 2; D014162:Transfection; D047988:Tumor Necrosis Factor Receptor-Associated Peptides and Proteins; D014758:Viral Core Proteins / Q000235:genetics / Q000378:metabolism*
D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; C505533:FADD protein, human; C505534:Fadd protein, mouse; D053200:Fas-Associated Death Domain Protein; D011506:Proteins; D018124:Receptors, Tumor Necrosis Factor; D053199:TNF Receptor-Associated Death Domain Protein; D047990:TNF Receptor-Associated Factor 1; D047992:TNF Receptor-Associated Factor 2; C481226:Tradd protein, mouse; D047988:Tumor Necrosis Factor Receptor-Associated Peptides and Proteins; D014758:Viral Core Proteins; C069130:nucleocapsid protein, Hepatitis C virus; D048031:JNK Mitogen-Activated Protein Kinases; D048670:MAP Kinase Kinase 4; D020929:Mitogen-Activated Protein Kinase Kinases