Background: Hepatitis B virus (HBV) X protein (HBx) and pre-S2 deletion mutant large surface antigens have been recognized as oncoproteins that induce hepatocellular carcinoma (HCC). The interaction of these two oncoproteins in the hepatocytes and its significance in tumorigenesis remains to be elucidated. Methods: In this study, a newly developed monoclonal antibody designed specifically against HBx was used for immunohistochemical and double-labeled immunofluorescence studies and the expression of HBx and surface antigens were evaluated. In vitro studies and transgenic mice models were used to evaluate the interaction and oncogenic effects of these two viral oncoproteins. Results: We observed the co-expression of HBx with surface antigens in ground glass hepatocytes in 5 of 20 hepatitis B surface antigen positive livers. In vitro, hepatocytes co-expressing HBx and pre-S2 mutant showed an enhanced expression of vascular endothelial growth factor-A (VEGF-A), phosphorylated Akt1/2/3 (p-Akt1/2/3), phosphorylated extracellular signal-regulated kinase 1/2 (p-ERK1/2) and phosphorylated mammalian target of rapamycin (p-mTOR) signals. Transgenic mice harboring the double HBx and pre-S2 mutant construct plasmids developed HCCs at an average of 15.1 months, earlier than that of HBx (16.9 months) or pre-S2 mutant (24.5 months) alone. Interestingly, the oncogenic signals of VEGF-A, p-Akt1/2/3, p-ERK1/2, and p-mTOR were sequentially and differentially activated at different stages in the progression of tumorigenesis. Phosphorylated mTOR was consistently activated in transgenic and human HCCs. Conclusions: We conclude that ground glass hepatocytes co-expressing HBx and surface antigens may exhibit enhanced oncogenic effects and tumorigenesis in chronic HBV infections. The mTOR signal cascade may represent the key regulator in HBV tumorigenesis and is implicated for the design of HCC therapy.
Date:
2014-05
Relation:
Journal of Clinical Oncology. 2014 May;32(15, Suppl.):e15115.
