Mechanism of viral hepatitis-mediated hepatocarcinogenesis

我们先前的结果表明，HBx含有一个功能性的核输出信号基序，该基序利用了RAN/CRM1复合体，这是许多细胞和病毒蛋白核质运输中必不可少的成分。我们证明HBX不仅使用并破坏依赖RAN/CRM1的活动，可能是为了防止宿主的抗病毒反应。这一发现表明RAN/CRM1复合体参与了乙肝病毒的分子发病机制。最近，我们发现了RAN/CRM1复合体在调控细胞蛋白中的一个新角色，该蛋白控制中心体复制和有丝分裂纺锤体组装。我们发现核磷蛋白是RAN/CRM1的一种新的底物，可以负向调节不必要的中心体复制。此外，我们还证明了乙肝病毒/HBX依赖的RanBP1的激活，RanBP1是一种已知的破坏RAN/CRM1复合体稳定的RAN结合蛋白。在阳性的肝组织和肝细胞癌中也可以观察到RanBP1的升高。RanBP1的表达增加导致多极纺锤体和异常有丝分裂。因此，乙肝病毒/HBx的联合作用导致了染色体的不稳定。这些发现导致我们产生了一个新的假说，即RAN/CRM1复合体通过提供控制细胞内稳态的加载对接机制作为中心体复制检查点，而该复合体的破坏可能导致基因组不稳定，这可能是病毒性肝炎介导的肝癌发生的早期步骤。除了HBx，我们最近还完成了一项初步研究，通过测定B淋巴细胞中丙型肝炎病毒核心相关基因的表达谱。我们发现，丙型肝炎病毒核心可能通过选择性地抑制与抗原呈递有关的基因来驱逐免疫。这些研究有助于剖析在肝癌发生过程中必不可少的病毒活动。此外，我们还进行了分子图谱研究，以比较携带HBx或丙型肝炎病毒结构基因或非结构基因(p21CORE、NS3或NS5A)的腺病毒感染原代人类肝细胞后基因表达的变化。我们还将这些基因表达谱与从慢性肝病患者和丙型肝炎病毒相关性肝细胞癌患者的丙型肝炎病毒感染的肝脏样本中获得的基因表达谱进行比较。我们发现，与HBx相比，丙型肝炎病毒相关蛋白在很大程度上诱导了独特的基因。尤其是干扰素诱导基因27在丙型肝炎病毒或核心感染的肝细胞和丙型肝炎病毒相关的慢性肝病或肝细胞癌中高表达，而在HBx感染的肝细胞或乙肝病毒相关的慢性肝病或肝细胞癌中表达较弱，提示干扰素诱导基因27可能在丙型肝炎病毒介导的肝细胞癌中发挥作用。综上所述，我们的结果提示，乙肝病毒和丙型肝炎病毒促进肝细胞癌的发生主要是通过不同的机制。

Our previous results indicate that HBx contains a functional nuclear export signal motif that utilizes the Ran/Crm1 complex, a component essential in nucleocytoplasmic transport of many cellular and viral proteins. We demonstrated that HBx not only uses but also disrupts Ran/Crm1-dependent activities, presumably to prevent a host antiviral response. This finding implicates the Ran/Crm1 complex in the molecular pathogenesis of hepatitis B virus. Recently, we uncovered a new role of the Ran/Crm1 complex in regulating cellular proteins that control centrosome duplication and mitotic spindle assembly. We revealed nucleophosmin as a novel substrate for Ran/Crm1 to negatively regulate unnecessary centrosome duplication. In addition, we demonstrated a hepatitis B virus / HBx -dependent activation of RanBP1, a Ran-binding protein that is known to destabilize the Ran/Crm1 complex. Elevated RanBP1 is also observed in positive liver tissues and in hepatocellular carcinoma. Increased expression of RanBP1 leads to multipolar spindles and abnormal mitoses. Thus, the combined effects of hepatitis B virus / HBx contribute to chromosome instability. These findings led us to generate a new hypothesis in which the Ran/Crm1 complex serves as the centrosome duplication checkpoint by providing a loading dock mechanism that controls cellular homeostasis, and the disruption of this complex may result in genomic instability, which may be an early step in viral hepatitis-mediated hepatocarcinogenesis. In addition to HBx, recently we have completed a pilot study by determining hepatitis C virus core-related gene expression profiles in B lymphocytes. We found that hepatitis C virus core may evict immunity by selectively suppressing genes involved in antigen presentation. These studies are useful in dissecting viral activities that are essential in hepatocarcinogenesis. Furthermore, we have conducted molecular profiling studies to compare the gene expression changes in primary human hepatocytes infected with adenoviruses harboring HBx or hepatitis C virus structural or non-structural genes (p21CORE, NS3 or NS5A). We also compared these gene expression profiles to those obtained from hepatitis C virus -infected liver samples from chronic liver disease patients and hepatitis C virus -related hepatocellular carcinoma. We found that hepatitis C virus -related proteins largely induce unique genes when compared to HBx. In particular, interferon-inducible gene 27 was highly expressed in hepatitis C virus or core infected hepatocytes and hepatitis C virus -related chronic liver disease or hepatocellular carcinoma, but was less significantly expressed in HBx infected hepatocytes or hepatitis B virus-related chronic liver disease or hepatocellular carcinoma, indicating that interferon-inducible gene 27 may play a role in hepatitis C virus -mediated hepatocellular carcinoma. In conclusion, our results suggest that hepatitis B virus and hepatitis C virus promote hepatocellular carcinoma development mainly through different mechanisms.