Genetic and epigenetic regulation of Hepatitis B contributes to liver cancer

描述（由申请人提供）：本提案研究先天免疫系统的某些元素如何通过病毒DNA的遗传和表观遗传修饰来调节肝组织中的B型肝炎病毒（HBV）DNA水平，以及先天免疫系统的这些相同元素如何促成致癌作用。这一建议直接关系到扩大我们对慢性HBV感染如何导致肝细胞癌的理解。对HBV感染认识的最新进展表明，发生HCC的风险与血清HBV DNA水平成正比，降低血清HBV DNA水平是治疗HBV的主要治疗靶点。宿主控制肝内乙型肝炎病毒复制的生物学机制仍不完全清楚，但更好的了解可能会带来更有效的治疗方法，从而预防肝细胞癌的发展。我们假设肝内HBV水平部分受先天免疫系统的部分调节，先天免疫系统通过激活APOBEC蛋白家族导致HBV基因组突变，宿主甲基转移酶使HBV基因组甲基化，导致HBV基因表达降低。我们进一步假设这些机制通过导致肿瘤抑制基因的甲基化增加（对应于肝细胞癌中的甲基化表型）而促成癌变。在目的一中，我们将确定慢性HBV感染肝脏中APOBEC诱导HBV基因组超突变的频率，并检验超突变程度预测HBV DNA水平的假设。目的二：利用甲基化特异性PCR定性和定量检测非整合HBV的甲基化频率和甲基化水平，并验证HBV DNA甲基化水平可预测肝内HBV水平的假设。我们还检验了人类细胞可以直接甲基化HBV DNA的假设，并调查了负责甲基转移酶。在目的三，我们研究HBV相关的肝癌，以探讨这一假设，他们将证明肿瘤抑制基因甲基化水平的增加。这些研究将大大提高我们对HCC的认识，并可能提高我们治疗HCC的能力。该提案研究先天免疫系统的某些元素如何通过病毒DNA的遗传和表观遗传修饰来调节肝组织中的B型肝炎病毒（HBV）DNA水平，以及先天免疫系统的这些相同元素如何促成致癌作用。

DESCRIPTION (provided by applicant): This proposal studies how certain elements of the innate immune system regulate levels of hepatitis B viral (HBV) DNA in liver tissues through genetic and epigenetic modification of viral DNA and how these same elements of the innate immune system contribute to carcinogenesis. This proposal is directly relevant to expanding our understanding of how chronic HBV infection leads to hepatocellular carcinoma. Recent advances in the understanding of HBV infection have shown that the risk for developing HCC is directly proportional to the serum levels of HBV DNA and reducing serum levels of HBV DNA are a major therapeutic target in the treatment of HBV. The biological mechanisms by which the host controls intrahepatic HBV replication remain incompletely understood, but better understanding may lead to more effective treatments that will prevent the development of HCC. We hypothesize that intrahepatic HBV levels are partly regulated by portions of the innate immune system that lead to mutations in the HBV genome through activation of the APOBEC family of proteins and that host methyltransferases methylate the HBV genome, leading to decreased HBV gene expression. We further hypothesize that these mechanisms contribute to carcinogenesis by leading to increased methylation of tumor suppressor genes (corresponding to the methylator phenotype in hepatocellular carcinoma). In Aim One, we will determine the frequency of APOBEC induced hypermutations of the HBV genome in livers with chronic HBV infection and test the hypothesis that the extent of hypermutations predictes levels of HBV DNA. In Aim Two, we will determine the frequency of methylation and the quantitative levels of methylation of non-integrated HBV using qualitative and quantitative methylation specific PCR and test the hypothesis that methylation levels of HBV DNA is predicitive of the levels of intrahepatic HBV. We also test the hypothesis that human cells can directly methylate HBV DNA and investigate the methyltransferases responsible. In Aim Three, we study HBV associated HCCs to explore the hypothesis that they will demonstrate increased levels of tumor suppressor gene methylation. These studies will significantly advance our understanding and potentially our ability to treat HCC. This proposal studies how certain elements of the innate immune system regulate levels of hepatitis B viral (HBV) DNA in liver tissues through genetic and epigenetic modification of viral DNA and how these same elements of the innate immune system contribute to carcinogenesis.