title: The hepatitis B virus X protein abrogates Bcl-2-mediated protection against Fas apoptosis in the liver.
abstract: The role of the hepatitis B virus protein HBx in liver cell proliferation and apoptosis remains controversial. Using a transgenic mouse model, we have recently shown that HBx stimulates the apoptotic turnover of hepatocytes, independently of p53. In this paper, we tested whether the proapoptotic function of HBx can interfere with Bcl-2 during hepatic apoptosis in vivo. HBx transgenic mice were crossed with PK-hBcl-2 mice that are protected against Fas killing by constitutive overexpression of Bcl-2 in hepatocytes. In a lethal challenge with Fas antibodies, HBx expressed at low levels restored sensitivity to Fas-mediated apoptosis and fulminant hepatic failure in mice overexpressing Bcl-2. Furthermore, cytochrome c release from mitochondria and caspase 3 activation were restored to normal levels in HBx/Bcl-2 mice during transduction of the Fas signal. Thus, the proapoptotic activity of HBx overcomes or bypasses the inhibitory effect of Bcl-2 against Fas cytotoxicity. This effect was not apparently mediated through downregulation of the PK-hBcl-2 transgene or via delocalization of the Bcl-2 protein, and a direct interaction of HBx with Bcl-2, Bcl-X(L) or Bax could not be evidenced in yeast two-hybrid assays. We further show that apoptosis induced by ectopic expression of HBx is associated with mitochondrial membrane alterations and caspase 3 activation. Our data indicate that the dominant function of HBx upon Bcl-2-regulated control of apoptosis might play an important role in the pathogenesis of chronic hepatitis B.
authors.affiliation: Unité de Recombinaison et Expression Génétique, Inserm U163, Institut Pasteur, Paris, France.
authors.forename: Olivier
authors.initials: O
authors.lastname: Terradillos
authors.forename: Alix
authors.initials: A
authors.lastname: de La Coste
authors.forename: Teresa
authors.initials: T
authors.lastname: Pollicino
authors.forename: Christine
authors.initials: C
authors.lastname: Neuveut
authors.forename: Delphine
authors.initials: D
authors.lastname: Sitterlin
authors.forename: Hervé
authors.initials: H
authors.lastname: Lecoeur
authors.forename: Marie-Lise
authors.initials: ML
authors.lastname: Gougeon
authors.forename: Axel
authors.initials: A
authors.lastname: Kahn
authors.forename: Marie-Annick
authors.initials: MA
authors.lastname: Buendia
mesh_terms: D000818:Animals; D017209:Apoptosis; D015153:Blotting, Western; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D003574:Cytochrome c Group / Q000378:metabolism; D005434:Flow Cytometry; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D006367:HeLa Cells; D022781:Hepatocytes / Q000166:cytology / Q000378:metabolism / Q000473:pathology; D006801:Humans; D008099:Liver / Q000166:cytology* / Q000378:metabolism* / Q000473:pathology / Q000821:virology; D051379:Mice; D008822:Mice, Transgenic; D008928:Mitochondria / Q000201:enzymology / Q000378:metabolism; D011485:Protein Binding; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D013997:Time Factors; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D014162:Transfection; D020798:Two-Hybrid System Techniques; D054334:Viral Regulatory and Accessory Proteins; D019014:fas Receptor / Q000276:immunology / Q000378:metabolism*
chemical_list: D003574:Cytochrome c Group; D019253:Proto-Oncogene Proteins c-bcl-2; D015534:Trans-Activators; D054334:Viral Regulatory and Accessory Proteins; D019014:fas Receptor; C057628:hepatitis B virus X protein; C505407:CASP3 protein, human; C505409:Casp3 protein, mouse; D053148:Caspase 3; D020169:Caspases