C-terminal truncated hepatitis B virus X protein regulates tumorigenicity, self-renewal and drug resistance via STAT3/Nanog signaling pathway.

Rachel Hiu Ha Ching,Irene Oi Lin Ng,Yung-Tuen Chiu,Karen Man Fong Sze,Eunice Yuen Ting Lau,Terence Kin Wah Lee,Joyce Man Fong Lee

doi:10.18632/oncotarget.15183

Rachel Hiu Ha Ching, Irene Oi Lin Ng + Show 5 more

Open Access

https://doi.org/10.18632/oncotarget.15183

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Abstract

Hepatitis B virus (HBV) is a major risk factor of chronic liver disease and hepatocellular carcinoma (HCC). Random integration of HBV DNA into the host genome is frequent in HCC leading to truncation of the HBV DNA, particularly at the C-terminal end of the HBV X protein (HBx). C-terminally truncated HBx (HBx-ΔC) has been implicated in playing a pro-oncogenic role in hepatocarcinogenesis. However, the mechanism whereby HBx-ΔC1 contributes to hepatocarcinogenesis remains unclear. In this study, we investigated the functional role of HBx-ΔC1 in regulating liver cancer stem cell (CSC) properties. Using Tet-on inducible system, we found that HBx-ΔC1 enhanced CSC properties including self-renewal, tumorigenicity, chemoresistance, migration and expression of liver CSC markers, when compared with the full-length HBx counterpart and vector control. Interestingly, HBx-ΔC1 conferred resistance in HCC cells towards sorafenib treatment through suppression of apoptotic cascade. In addition, HBx-ΔC1 upregulated a panel of stemness genes, in which Nanog was found to be among the most significant one in both trasnfected cell lines. Consistently, Nanog was upregulated in human HCC samples which had HBx-ΔC1 expression. Furthermore, the induction of CSC properties by HBx-ΔC1 was via the Stat3/Nanog pathway, as administration of Stat3 inhibitor abolished the HBx-ΔC1-induced self-renewing capacity. In conclusion, our data suggest that HBx-ΔC1 enhances liver CSCs properties through Stat3/Nanog cascade, and provide a new insight for the therapeutic intervention for HBV-related HCC.

Highlights

Hepatocellular carcinoma (HCC) is the fifth most prevalent cancer and a highly lethal cancer with increasing worldwide incidence [1]
To determine the optimal time of gene induction, we examined the effect of Hepatitis B virus (HBV) X protein (HBx)-FL and HBx-ΔC1 on the induction of stemness-related genes ranging from Day 5 to Day 27 and Day 6 to Day 9 in Bel-7402 and SMMC-7721 transfectants, respectively (Supplementary Figure 1)
We found a stepwise increase in expression of stemness-related genes including Nanog and Sox2 from Empty vector (EV), HBx-FL to HBx-ΔC1 transfectants derived from Bel-7402 from Day 23 onwards (Figure 1B and Supplementary Figure 1)

Summary

Introduction

Hepatocellular carcinoma (HCC) is the fifth most prevalent cancer and a highly lethal cancer with increasing worldwide incidence [1]. Accumulating evidence shows that random integration of HBV is detected in 80% to 90% of the host genome from HBV-infected HCC cases, frequently leading to truncation of HBV genome, especially on the HBx gene locus at the C-terminus [5, 6]. HBx (a major C-terminal truncated form reported with a breakpoint at 130aa) (HBx-ΔC1) may contribute to more aggressive behavior of HCC, which includes enhancing metastasis and tumorigenicity [7,8,9,10]. The molecular mechanism underlying HBx-ΔC1 contributes to HCC remains largely unknown. This lack of knowledge presents a hurdle to the identification of novel targeted therapeutic strategies for this fatal disease

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