Chronic infection with hepatitis B virus (HBV) is an important risk factor in the development of hepatocellular carcinoma (HCC). We present a model for the role of HBV in HCC, derived from our demonstration that the HBV transactivator X protein (HBx) interacts with XAP-1/UV-DDB, a cellular protein involved in nucleotide excision repair (NER), and that HBx expression inhibits normal NER. We hypothesize that HBx binds XAP-1 to provide a function to the HBV life cycle, and that the protein interaction cripples DNA repair and inadvertently contributes to the development of HCC. We will test the model utilizing several approaches and the following specific aims: (1) Effect of HBx on cellular DNA repair. The domains of HBx responsible for inhibition of NER will be mapped using mutant HBx proteins. Fibroblasts from Xeroderma pigmentosum (XP) patients will be used to determine whether HBx inhibits DNA synthesis through a pathway involving XAP-1. The effect of HBx on mutation frequency will be tested utilizing our HBV X transgenic mice. The possibility that HBx interference of DNA repair requires alteration of a p53-mediated pathway will be examined. (2) Investigation of functional interactions between cellular XAP-1 and HBx proteins in the liver using a mouse model. Murine XAP-1 will be cloned. Cellular DNA repair assays will measure functional effects of HBx-XAP-1 protein interactions within the livers of HBV X transgenic mice. The effect of HBx expression during liver regeneration will be tested. (3) Determination of a role for DNA repair protein XAP-1 in the HBV life cycle. A role for XAP-1 in the repair of the HBV partial double-stranded DNA genome will be tested. A panel of HBx mutant proteins will be used to investigate the requirement for XAP-1 in HBx transactivation. The proposed program builds on our model of HBV-related HCC and suggests a novel mechanism of action for indirect-acting human tumor viruses such as HBV. The experiments will provide new insights into HBV effects on hepatocytes, viral replication, and the development of HCC.

Agency
National Institute of Health (NIH)
Institute
National Cancer Institute (NCI)
Type
Research Project (R01)
Project #
5R01CA054557-07
Application #
2894883
Study Section
Metabolic Pathology Study Section (MEP)
Program Officer
Cole, John S
Project Start
1991-03-15
Project End
2001-03-31
Budget Start
1999-04-01
Budget End
2001-03-31
Support Year
7
Fiscal Year
1999
Total Cost
Indirect Cost
Name
Baylor College of Medicine
Department
Biochemistry
Type
Schools of Medicine
DUNS #
074615394
City
Houston
State
TX
Country
United States
Zip Code
77030
Madden, Charles R; Finegold, Milton J; Slagle, Betty L (2002) Altered DNA mutation spectrum in aflatoxin b1-treated transgenic mice that express the hepatitis B virus x protein. J Virol 76:11770-4
Madden, C R; Slagle, B L (2001) Stimulation of cellular proliferation by hepatitis B virus X protein. Dis Markers 17:153-7
Madden, C R; Finegold, M J; Slagle, B L (2001) Hepatitis B virus X protein acts as a tumor promoter in development of diethylnitrosamine-induced preneoplastic lesions. J Virol 75:3851-8
Wentz, M J; Becker, S A; Slagle, B L (2000) Dissociation of DDB1-binding and transactivation properties of the hepatitis B virus X protein. Virus Res 68:87-92
Madden, C R; Finegold, M J; Slagle, B L (2000) Expression of hepatitis B virus X protein does not alter the accumulation of spontaneous mutations in transgenic mice. J Virol 74:5266-72
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Krishnamoorthy, R R; Lee, T H; Butel, J S et al. (1997) Apolipoprotein B gene regulatory factor-2 (BRF-2) is structurally and immunologically highly related to hepatitis B virus X associated protein-1 (XAP-1). Biochemistry 36:960-9
Butel, J S; Lee, T H; Slagle, B L (1996) Is the DNA repair system involved in hepatitis-B-virus-mediated hepatocellular carcinogenesis? Trends Microbiol 4:119-24

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