Differential effects on apoptosis induction in hepatocyte lines by stable expression of hepatitis B virus X protein.
OBJECTIVE
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 p21(waf/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, p21(waf/cip/sdi)-protein expression and p21(waf/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.


CONCLUSIONS
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.
Fiedler
Nicola
N
Abt. Virologie, Institut fur Medizinische Mikrobiologie, Schillingallee 70, Universitat Rostock, D-18055 Rostock, Germany.
Quant
Ellen
E
Fink
Ludger
L
Sun
Jianguang
J
Schuster
Ralph
R
Gerlich
Wolfram H
WH
Schaefer
Stephan
S
D000818:Animals; D017209:Apoptosis / Q000235:genetics / Q000502:physiology* / Q000528:radiation effects; D002460:Cell Line; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000235:genetics / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic / Q000502:physiology / Q000528:radiation effects; D015967:Gene Expression Regulation, Viral / Q000502:physiology* / Q000528:radiation effects; D006509:Hepatitis B / Q000150:complications; D018197:Hepatoblastoma / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D022781:Hepatocytes / Q000378:metabolism / Q000473:pathology*; D006801:Humans; D008113:Liver Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D051379:Mice; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism; D014466:Ultraviolet Rays; D054334:Viral Regulatory and Accessory Proteins
D050759:Cyclin-Dependent Kinase Inhibitor p21; D015534:Trans-Activators; D016159:Tumor Suppressor Protein p53; D054334:Viral Regulatory and Accessory Proteins; C057628:hepatitis B virus X protein