Pro-apoptotic function of HBV X protein is mediated by interaction with c-FLIP and enhancement of death-inducing signal.
Despite its implication in the progression of hepatitis B virus (HBV)-associated liver disease, the pro-apoptotic function of HBx protein remains poorly understood. We show that the expression of HBx leads to hyperactivation of caspase-8 and caspase-3 upon treatment with tumor necrosis factor-alpha (TNF-alpha) or anti-Fas antibody, and this activation is correlated with the sensitivity to apoptosis. We demonstrate cytoplasmic co-localization and direct interaction between HBx and the cellular FLICE inhibitory protein (c-FLIP), a key regulator of the death-inducing signaling complex (DISC). Deletion analysis shows that the death effector domain 1 (DED1) of c-FLIP is important for the observed interaction. Overexpression of c-FLIP rescued the cells from HBx-mediated apoptosis, with both the full-length HBV genome and HBx expression vectors. Moreover, c-FLIP and caspase-8 inhibitor considerably protected cells from HBx-mediated apoptosis. These data suggest that HBx abrogates the apoptosis-inhibitory function of c-FLIP and renders the cell hypersensitive towards the TNF-alpha apoptotic signal even below threshold concentration. This provides a novel mechanism for deregulation of hepatic cell growth in HBV patients and a new target for intervention in HBV-associated liver cancer and disease.
Kim
Kyun-Hwan
KH
Department of Biotechnology, College of Engineering and Bioproducts Research Center, Yonsei University, Seoul 120-749, Korea.
Seong
Baik L
BL
D017209:Apoptosis / Q000502:physiology*; D001483:Base Sequence; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D002352:Carrier Proteins / Q000378:metabolism*; D053148:Caspase 3; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism; D002460:Cell Line; D017931:DNA Primers; D004789:Enzyme Activation; D016679:Genome, Viral; D006509:Hepatitis B / Q000235:genetics; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D011485:Protein Binding; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D015534:Trans-Activators / Q000378:metabolism / Q000502:physiology*; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D054334:Viral Regulatory and Accessory Proteins
D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; C506386:CFLAR protein, human; D002352:Carrier Proteins; D017931:DNA Primers; D047908:Intracellular Signaling Peptides and Proteins; D011993:Recombinant Fusion Proteins; D015534:Trans-Activators; D014409:Tumor Necrosis Factor-alpha; D054334:Viral Regulatory and Accessory Proteins; C057628:hepatitis B virus X protein; C505407:CASP3 protein, human; C505530:CASP8 protein, human; C506433:CASP9 protein, human; D053148:Caspase 3; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases