Hepatitis B virus pre‐S₂ mutant large surface protein inhibits DNA double‐strand break repair and leads to genome instability in hepatocarcinogenesis

Abstract

Although hepatitis B virus (HBV) has been established to cause hepatocellular carcinoma (HCC), the exact mechanism remains to be clarified. Type II ground glass hepatocytes (GGHs) harbouring the HBV pre-S2 mutant large surface protein (LHBS) have been recognized as a morphologically distinct hallmark of HCC in the advanced stages of chronic HBV infection. Considering its preneoplastic nature, we hypothesized that type II GGH may exhibit high genomic instability, which is important for the carcinogenic process in chronic HBV carriers. In this study we found that pre-S2 mutant LHBS directly interacted with importin α1, the key factor that recognizes cargos undergoing nuclear transportation mediated by the importin α/β-associated nuclear pore complex (NPC). By interacting with importin α1, which inhibits its function as an NPC factor, pre-S2 mutant LHBS blocked nuclear transport of an essential DNA repair and recombination factor, Nijmegen breakage syndrome 1 (NBS1), upon DNA damage, thereby delaying the formation of nuclear foci at the sites of DNA double-strand breaks (DSBs). Pre-S2 mutant LHBS was also found to block NBS1-mediated homologous recombination repair and induce multi-nucleation of cells. In addition, pre-S2 mutant LHBS transgenic mice showed genomic instability, indicated by increased global gene copy number variations (CNVs), which were significantly higher than those in hepatitis B virus X mice, indicating that pre-S2 mutant LHBS is the major viral oncoprotein inducing genomic instability in HBV-infected hepatocytes. Consistently, the human type II GGHs in HCC patients exhibited increased DNA DSBs representing significant genomic instability. In conclusion, type II GGHs harbouring HBV pre-S2 mutant oncoprotein represent a high-risk marker for the loss of genome integrity in chronic HBV carriers and explain the complex chromosome changes in HCCs. Mouse array CGH raw data: GEO Accession No. GSE61378 (http://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE61378).

Hepatitis B virus surface gene pre‐S2 mutant as a high‐risk serum marker for hepatoma recurrence after curative hepatic resection

“…Snap-frozen protein lysates of the surgically resected tumorous and peritumorous HCC tissues of patients (n 5 22) at NCKUH were analyzed for LHBS expression by western blotting, following the protocol described. (29) The wild-type (n 5 10) and pre-S 2 mutant (n 5 12) cases were preidentified by pre-S gene chip analysis. (30) LHBS was detected using an in-house-developed mouse monoclonal antibody (clone 7-21-5) recognizing the pre-S 1 region.…”

“…Pre‐S 2 mutant LHBS protein also directly interacts with c‐Jun activation domain‐binding protein 1, which degrades cyclin‐dependent kinase inhibitor p27 Kip1 and, consequently, G 1 –S‐phase cell‐cycle progression, even in the presence of DNA damage . We also recently reported that pre‐S 2 mutant LHBS transgenic mice were genomically unstable, which was indicated by global gene copy number variations significantly higher than those in age‐matched HBx mice. This indicates that the pre‐S 2 mutant LHBS is the main viral oncoprotein which induces host genomic instability and triggers carcinogenesis.…”

Hepatitis B virus PreS2-mutant large surface antigen activates store-operated calcium entry and promotes chromosome instability

“…Independent of the ER stress pathways, preS2-LHBS directly interacted with c-Jun activation domain-binding protein 1 (JAB1), which led to the degradation of p27 and thereby promoted the hyperphosphorylation of retinoblastoma [ 18 ]. In addition, preS2-LHBS directly interacted with importin α1, thereby blocked the nuclear transport of an essential DNA repair and recombinant factor, Nijmegen breakage syndrome 1 (NBS1), upon DNA damage, and subsequently impeded DNA double-stranded break repair [ 19 ]. Notably, transgenic mice carrying preS2-LHBS displayed higher genomic instability than transgenic mice carrying HBV X protein using array-based comparative genomic hybridization.…”

Review article: the prevention of hepatitis B‐related hepatocellular carcinoma

“…These deletion mutations may induce defective immunity against HBV . The accumulation of in‐frame pre‐S2 mutant large surface protein inhibits hepatocyte DNA double‐strand break repair and is associated with HCC tumourigenesis . On the other hand, the presence of truncated pre‐S/S protein has the function of transcriptional transactivator .…”