Viral Hepatitis
Copyright ©2006 Baishideng Publishing Group Co., Limited. All rights reserved.
World J Gastroenterol. Aug 7, 2006; 12(29): 4673-4682
Published online Aug 7, 2006. doi: 10.3748/wjg.v12.i29.4673
Differential effects on apoptosis induction in hepatocyte lines by stable expression of hepatitis B virus X protein
Nicola Fiedler, Ellen Quant, Ludger Fink, Jianguang Sun, Ralph Schuster, Wolfram H Gerlich, Stephan Schaefer
Nicola Fiedler, Ralph Schuster, Wolfram H Gerlich, Stephan Schaefer, Institut für Medizinische Virologie, Justus-Liebig-Universität, Frankfurter Str. 107, D-35392 Gießen, Germany
Ellen Quant, Abteilung für Innere Medizin, Christian Albrecht Universität, Kiel, Germany
Ludger Fink, Zentrum für Innere Medizin, Justus-Liebig-Universität, Gießen, Germany
Jianguang Sun, Stephan Schaefer, Abteilung Virologie, Universität Rostock, Schillingallee 70, 18055 Rostock, Germany
Jianguang Sun, Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agricultural Sciences, Beijing 100081, China
Supported by grant 01 KI 9552 of the Bundesministerium für Forschung und Technologie and grant 01 KI 98589 of the Bundesministerium für Bildung und Forschung to S.S. and W.H.G and grant 10-1854-Scha I from Deutsche Krebshilfe to SS
Correspondence to: Stephan Schaefer, Abt. Virologie, Institut für Medizinische Mikrobiologie, Schillingallee 70, Universität Rostock, D-18055 Rostock, Germany. stephan.schaefer@med.uni-rostock.de
Telephone: +49-381-4945947 Fax: +49-381-4945925
Received: September 28, 2005
Revised: September 28, 2005
Accepted: January 15, 2006
Published online: August 7, 2006
Abstract

AIM: Hepatitis B virus protein X (HBx) has been shown to be weakly oncogenic in vitro. The transforming activities of HBx have been linked with the inhibition of several functions of the tumor suppressor p53. We have studied whether HBx may have different effects on p53 depending on the cell type.

METHODS: We used the human hepatoma cell line HepG2 and the immortalized murine hepatocyte line AML12 and analyzed stably transfected clones which expressed physiological amounts of HBx. P53 was induced by UV irradiation.

RESULTS: The p53 induction by UV irradiation was unaffected by stable expression of HBx. However, the expression of the cyclin kinase inhibitor p21waf/cip/sdi which gets activated by p53 was affected in the HBx transformed cell line AML12-HBx9, but not in HepG2. In AML-HBx9 cells, p21waf/cip/sdi-protein expression and p21waf/cip/sdi transcription were deregulated. Furthermore, the process of apoptosis was affected in opposite ways in the two cell lines investigated. While stable expression of HBx enhanced apoptosis induced by UV irradiation in HepG2-cells, apoptosis was decreased in HBx transformed AML12-HBx9. P53 repressed transcription from the HBV enhancer I, when expressed from expression vectors or after induction of endogenous p53 by UV irradiation. Repression by endogenous p53 was partially reversible by stably expressed HBx in both cell lines.

CONCLUSION: Stable expression of HBx leads to deregulation of apoptosis induced by UV irradiation depending on the cell line used. In an immortalized hepatocyte line HBx acted anti-apoptotic whereas expression in a carcinoma derived hepatocyte line HBx enhanced apoptosis.

Keywords: Apoptosis, Hepatitis B virus, Hepatocyte lines