Hepatitis B virus (HBV) encoded x antigen (HBxAg) is a trans-activating protein that contributes to the development of hepatocellular carcinoma (HCC) by the up- or down-regulated expression of selected hepatocellular genes. To identify some of these genes, HBxAg or vector were introduced into the human hepatoblastoma cell line, HepG2. Differentially expressed genes were identified by microarray analysis and by PowerBlot (SDS/PAGE followed by western blotting). Both assays showed decreased E-cadherin and increased expression of b-catenin and several b-catenin target genes in HBxAg [+] compared to [-] cells. In the livers of HBV carriers, there was an inverse relationship between HBxAg staining and E-cadherin and co- staining between HBxAg and b-catenin, suggesting that HBxAg contributes to hepatocellular transformation by altering the b-catenin signaling pathway. Hence, the objective of this work is to elucidate the mechanisms whereby HBxAg stabilizes b-catenin and thereby stimulates signaling, and to determine the contribution of these mechanisms to HBxAg mediated transformation. Accordingly, experiments will test the hypothesis that the accumulation/activation of b-catenin in HBxAg positive cells results from HBxAg trans-activation of the b-catenin gene, from HBxAg inactivation of glycogen synthase kinase 3b (GSKSp), from the HBxAg down-regulation of E-cadherin, and/or from the HBxAg inhibition of b-catenin degradation in the proteasome (Aim 1). Additional experiments will test whether the HBxAg stabilization of b-catenin contributes to the pathogenesis of HCC (Aim 2). These experiments will establish the extent to which up-regulated b-catenin signaling underlies the pleiotropic properties whereby HBxAg contributes to HCC development on the molecular level, and the corresponding mechanism(s) whereby this occurs. Given that wild type b-catenin is up-regulated in the majority of HBV associated HCCs, elucidation of the underlying mechanism(s) will identify critical pathways that will be targeted for chemoprevention of HCC and for therapeutic intervention in tumor bearing patients. The results from this research would also provide therapeutic targets for the application of existing drugs (against b-catenin effectors) in patients with HCC. In doing so, the proposed work is expected to promote the development of multiple public health benefits for HBV infected carriers with chronic liver disease and HCC. ? ?
Showing the most recent 10 out of 18 publications
