C-terminal truncated HBx initiates hepatocarcinogenesis by down-regulating TXNIP and reprogramming glucose metabolism

Abstract

Chronic hepatitis B virus (HBV) infection is the leading causative factor for hepatocellular carcinoma (HCC) , accounting for more than 60% HCC cases in east Asian countries including China. HBV integration into the host genome has been proven strongly associated with the initiation and progression of HCC. However, a substantial amount of virus-induced mechanisms that cause the malignant transformation of HCC cells remains largely unknown, especially for the HBV-induced glucose metabolic reprogramming in HCC.

In the present study, we firstly analyzed the distribution of integration breakpoints in the virus genome from the whole genome sequencing of HBV-related HCC in public databases. We found that HBV integration breakpoints clustered around the 3′-end of HBV X gene in HCC samples, thus we hypothesized that the integration associated C-terminal truncated HBx (Ct-HBx) protein is oncogenic in tumorigenesis. In vitro and in vivo functional assays were applied to study the role of Ct-HBx in HCC cells. Transcriptome sequencing was performed to characterize the molecular basis of the Ct-HBx induced HCC progression.

Ct-HBx is more frequently expressed in HCC samples than the full-length HBx. The oncogenic properties of Ct-HBx were validated in both vitro and vivo functional assays. RNA-sequencing suggested that Ct-HBx mediated the glucose metabolic alteration from oxidative phosphorylation to glycolysis, which is the hallmark of cancer progression. RNA-sequencing also identified TXNIP as the potential target of Ct-HBx, which may mediate metabolic reprogramming. Bioinformatic data from HCC samples in both TCGA database and our own cohort exhibited that TXNIP is significantly downregulated in HCC patients with Ct-HBx expression, compared to those with full-length HBx expression and HBV-negative samples. Lower expression of TXNIP is associated with poor prognosis. We also showed that Ct-HBx transcriptionally downregulates TXNIP through transactivation. Additionally, re-introduction of TXNIP inhibited the metabolic alterations induced by Ct-HBx, thus resulting in tumor growth arrest in HCC.

Our data demonstrated that the generation of C-terminal truncated HBx upon HBV integration has an oncogenic role in HCC development. Ct-HBx promotes glycolysis metabolism through downregulating the expression of TXNIP. Taken together, our finding proposes a promising diagnostic and therapeutic target for HBV-induced HCC.