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Hepatitis B x protein inhibits p53-dependent DNA repair in primary mouse hepatocytes
1Department of Pathology, University Medical School, Teviot Place, Edinburgh EH8 9AG, Scotland. s.prost@ed.ac.uk
Abstract:
The mechanisms by which the hepatitis B x protein (HBx) contributes to hepatocarcinogenesis remain unclear. However, interaction with the tumor suppressor gene p53 and inhibition of p53-dependent cellular functions, including nucleotide excision repair, could be central to this process. We studied the levels of global repair (removal of cyclobutane pyrimidine dimers (CPDs) and 6-4 photoproducts) and transcription-coupled repair (removal of CPDs in both strands of the dihydrofolate reductase gene) in primary wild-type and p53-null mouse hepatocytes. We show that global repair of CPDs appears to be more efficient in mouse hepatocytes than in other commonly studied rodent cells and approaches the levels of human cells and that p53 is required for global genomic DNA repair of CPDs but not for transcription-coupled repair. We then investigated the effect of HBx expression on hepatocyte nucleotide excision repair. We demonstrate that HBx expression affects DNA repair in a p53-dependent manner. Transient HBx expression reduces global DNA repair in wild-type cells to the level of p53-null hepatocytes and has no effect on the repair of a transfected damaged plasmid. Therefore, in viral hepatitis, the hepatitis B virus could inhibit the p53-dependent component of global repair leading, over time, to accumulation of genetic defects and fostering carcinogenesis.
Insights
Hepatitis B virus X protein (HBx) impairs DNA repair in liver cells. This impairment is p53-dependent, potentially contributing to liver cancer development by accumulating genetic damage.
Area of Science:
- Hepatology
- Molecular Biology
- Cancer Research
Background:
- Hepatitis B virus X protein (HBx) is implicated in liver cancer (hepatocarcinogenesis).
- HBx may contribute to cancer by interfering with the tumor suppressor p53 and its DNA repair functions.
- The precise mechanisms of HBx-induced DNA repair inhibition are not fully understood.
Purpose of the Study:
- To investigate the role of p53 in DNA repair in hepatocytes.
- To determine how HBx affects nucleotide excision repair (NER) in liver cells.
- To elucidate the p53-dependent mechanisms by which HBx may promote hepatocarcinogenesis.
Main Methods:
- Assessed global genomic repair and transcription-coupled repair of DNA damage (cyclobutane pyrimidine dimers and 6-4 photoproducts) in wild-type and p53-null mouse hepatocytes.
- Expressed HBx in hepatocytes to evaluate its impact on DNA repair.
- Compared DNA repair efficiency in different cell types and under various experimental conditions.
Main Results:
- Mouse hepatocytes exhibit efficient global repair of cyclobutane pyrimidine dimers, comparable to human cells.
- p53 is essential for global genomic DNA repair of cyclobutane pyrimidine dimers but not for transcription-coupled repair.
- HBx expression reduces global DNA repair in a p53-dependent manner, lowering repair levels in wild-type cells to those of p53-null cells.
Conclusions:
- Hepatitis B virus X protein inhibits the p53-dependent component of global DNA repair in hepatocytes.
- This inhibition can lead to the accumulation of genetic defects over time, potentially fostering liver cancer development.
- Targeting HBx-mediated DNA repair inhibition could be a strategy for preventing hepatitis B virus-associated liver cancer.