Intracellular antibody targeting HBx suppresses invasion and metastasis in hepatitis B virus-related hepatocarcinogenesis via protein phosphatase 2A-B56 gamma-mediated dephosphorylation of protein kinase B

Objectives Hepatitis B virus X (HBx) is closely associated with HBV-related hepatocarcinogenesis via the inactivation of tumour suppressors. Protein phosphatase 2A (PP2A) regulatory subunit B56 gamma (B56 gamma), as a tumour suppressor, plays a critical role in regulating cellular phosphorylation signals via dephosphorylation of signalling proteins. However, the underlying mechanism that B56 gamma involved in regulating HBx-associated hepatocarcinogenesis phenotypes and mediating anti-HBx antibody-mediated tumour suppression remains unknown. Materials and Methods We used bioinformatics analysis, paired HCC patient specimens, HBx transgenic (HBx-Tg) mice, xenograft nude mice, HBV stable replication in the HepG2.2.15 cells, and anti-HBx antibody intervention to systematically evaluate the biological function of protein kinase B (AKT) dephosphorylation through B56 gamma in HBx-associated hepatocarcinogenesis. Results Bioinformatics analysis revealed that AKT, matrix metalloproteinase 2 (MMP2), and MMP9 were markedly upregulated, while cell migration and viral carcinogenesis pathways were activated in HBV-infected liver tissues and HBV-associated HCC tissues. Our results demonstrated that HBx-expression promotes AKT phosphorylation (p-AKT(Thr308/Ser473)), mediating the migration and invasion phenotypes in vivo and in vitro. Importantly, in clinical samples, HBx and B56 gamma were downregulated in HBV-associated HCC tumour tissues compared with peritumor tissues. Moreover, intervention with site-directed mutagenesis (AKT(T308A), AKT(S473A)) of p-AKT(Thr308/Ser473) mimics dephosphorylation, genetics-based B56 gamma overexpression, and intracellular anti-HBx antibody inhibited cell growth, migration, and invasion in HBx-expressing HCC cells. Conclusions Our results demonstrated that B56 gamma inhibited HBV/HBx-dependent hepatocarcinogenesis by regulating the dephosphorylation of p-AKT(Thr308/Ser473) in HCC cells. The intracellular anti-HBx antibody and the activator of B56 gamma may provide a multipattern chemopreventive strategy against HBV-related HCC.