Nuclear translocation of YAP drives BMI‐associated hepatocarcinogenesis in hepatitis B virus infection

Abstract

Background and AimsHepatitis B virus (HBV) infection is a major cause of hepatocellular carcinoma (HCC) development and progression. The aim of this study was to mechanistically investigate the involvement of Hippo signalling in HBV surface antigen (HBsAg)‐dependent neoplastic transformation.MethodsLiver tissue and hepatocytes from HBsAg‐transgenic mice were examined for the Hippo cascade and proliferative events. Functional experiments in mouse hepatoma cells included knockdown, overexpression, luciferase reporter assays and chromatin immunoprecipitation. Results were validated in HBV‐related HCC biopsies.ResultsHepatic expression signatures in HBsAg‐transgenic mice correlated with YAP responses, cell cycle control, DNA damage and spindle events. Polyploidy and aneuploidy occurred in HBsAg‐transgenic hepatocytes. Suppression and inactivation of MST1/2 led to the loss of YAP phosphorylation and the induction of BMI1 expression in vivo and in vitro. Increased BMI1 directly mediated cell proliferation associated with decreased level of p16INK4a, p19ARF, p53 and Caspase 3 as well as increased Cyclin D1 and γ‐H2AX expression. Chromatin immunoprecipitation and the analysis of mutated binding sites in dual‐luciferase reporter assays confirmed that the YAP/TEAD4 transcription factor complex bound and activated the Bmi1 promoter. In chronic hepatitis B patients, paired liver biopsies of non‐tumour and tumour tissue indicated a correlation between YAP expression and the abundance of BMI1. In a proof‐of‐concept, treatment of HBsAg‐transgenic mice with YAP inhibitor verteporfin directly suppressed the BMI1‐related cell cycle.ConclusionHBV‐associated proliferative HCC might be related to the HBsAg‐YAP‐BMI1 axis and offer a potential target for the development of new therapeutic approaches.

Role of Hippo pathway dysregulation from gastrointestinal premalignant lesions to cancer

“…In HBV surface antigen (HBsAg)-transgenic mice, Hippo signaling disruption by MST1/2 inactivation caused the nuclear translocation of YAP and upregulation of BMI1 proto-oncogene resulting in sustained hepatocarcinogenesis. Treatment with the YAP inhibitor verteporfin decreased both YAP and BMI1 levels controlling HCC progression [ 61 ]. Also, in HBV-positive HCC cases, the preS2 domain of C-terminal truncated middle surface protein, another transactivator encoded by HBV, upregulated TAZ by suppressing miR338-3p fueling HCC proliferation [ 62 ].…”

Hepatitis B surface antigen expression impairs endoplasmic reticulum stress-related autophagic flux by decreasing LAMP2

“…These events were investigated in 2-, 8- and 12-month-old HBsAg-transgenic male mice (Tg(Alb1HBV)44Bri/J, Alb-HBs), representing non-HCC, early HCC and HCC stages, respectively. 15 , 16 Immunohistochemical staining showed that large amounts of HBsAg already accumulated in hepatocytes of at least 2-month-old HBsAg-transgenic mice ( Fig. 1 C).…”

Large HBV Surface Protein-Induced Unfolded Protein Response Dynamically Regulates p27 Degradation in Hepatocellular Carcinoma Progression

“…HBV particles derived from cell culture can promote the proliferation and colony formation of hepatoma cell lines [ 26 ]. A recent study showed that in HBsAg transgenic mice, the accumulation of HBsAg induces inactivation of Hippo signaling and upregulation of BMI1, and increased BMI1 directly mediates cell proliferation related to the decrease in levels of p16, p19 and p53 [ 27 ]. Moreover, HBV X protein is related to the cell cycle progression and hepatocarcinogenesis of HCC, and the mitochondrial protein SIRT4 has been demonstrated to upregulate the expression of p16 and p21 proteins, suppress cyclin B1/Cdc2 and Cdc25c, and suppress survivin to induce cell apoptosis [ 28 ].…”

“…HBV particles derived from cell culture can promote the proliferation and colony formation of hepatoma cell lines [26]. A recent study showed that in HBsAg transgenic mice, the accumulation of HBsAg induces inactivation of Hippo signaling and upregulation of BMI1, and increased BMI1 directly mediates cell proliferation related to the decrease in levels of p16, p19 and p53 [27]. Moreover, HBV X protein is related…”