Intracellular antibody targeting HBx suppresses invasion and metastasis in hepatitis B virus-related hepatocarcinogenesis via protein phosphatase 2A-B56γ-mediated dephosphorylation of protein kinase B

Abstract

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 (B56γ), as a tumour suppressor, plays a critical role in regulating cellular phosphorylation signals via dephosphorylation of signalling proteins. However, the underlying mechanism that B56γ 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 B56γ 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 B56γ 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 B56γ overexpression, and intracellular anti-HBx antibody inhibited cell growth, migration, and invasion in HBx-expressing HCC cells.

Conclusions: Our results demonstrated that B56γ 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 B56γ may provide a multipattern chemopreventive strategy against HBV-related HCC.