Aberrant DNA Methylation of MicroRNA Genes in Hepatocellular Carcinoma (HCC)

描述(由申请人提供)：由启动子DNA甲基化导致的肿瘤抑制基因沉默是包括肝细胞癌在内的肿瘤发生的重要机制。MicroRNAs(MiRNAs)作为基因表达的关键调控因子，在细胞的增殖、分化和凋亡过程中起着至关重要的作用。在启动子区域含有CpG岛的肿瘤抑制miRNAs也可能对甲基化介导的沉默敏感。以往的研究发现，抑制肿瘤的miRNAs(miR-1-1、miR-124和miR-203)的表达异常可能是由于DNA甲基化异常所致。这些有限的数据来自不同的动物模型、癌细胞系或从少量冰冻肿瘤组织的研究中获得。许多具有肿瘤抑制功能的miRNAs的甲基化状态在很大程度上是未知的，特别是那些在肝组织中特异表达的miR-122、miR-152、miR-194、miR-199和miR-215。我们的假设是，抑癌miRNA基因中的DNA甲基化是影响相关成熟miRNA表达的常见事件，并有助于区分肝癌组织和非肿瘤组织。两个特定的目的是：(1)检测一组抑癌miRNA基因在肝癌肿瘤组织中的DNA甲基化水平是否显著高于邻近非肿瘤组织，并测试在与乙肝病毒(HBV)和丙型肝炎病毒(HCV)相关的肝癌组织中，miRNA甲基化水平是否不同；(2)检测出现显著甲基化变化的一组miRNA基因亚群是否与相关成熟miRNA表达下调有关。一项仅针对病例的研究将使用哥伦比亚大学医学中心建立的美国肝癌患者的福尔马林固定石蜡包埋(FFPE)组织库进行。本研究共收集120例经组织学证实的肝细胞癌患者的肿瘤及癌旁非肿瘤组织和乙肝病毒/丙型肝炎病毒感染资料。这项初步研究将为了解miRNA基因甲基化在区分肝癌恶性组织和非肿瘤组织中的作用提供有价值的初步数据。这些甲基化标志物有潜在的临床应用，以改善风险评估、早期诊断和预后预测，甚至可能改善治疗，因为表观遗传变化的可逆性。PHS 398/2590(06/09版)页面续格式页面 公共卫生相关性：DNA甲基化异常是肝细胞癌肿瘤发生早期的常见事件。这项初步研究将为肿瘤抑制miRNA基因的甲基化和表达在识别肝癌恶性组织中的关键作用提供初步证据。它将提供初步数据，以支持扩大流行病学研究，这些研究应导致在肝癌风险评估、早期诊断和有效治疗方面的长期改善。

DESCRIPTION (provided by applicant): Tumor suppressor gene silencing by promoter DNA methylation is an important mechanism of tumorigenesis, including in hepatocellular carcinoma (HCC). MicroRNAs (miRNAs), as key regulators of gene expression, play a critical role in cell proliferation, differentiation and apoptosis. Tumor suppressive miRNAs harboring CpG-islands in their promoter regions may also be sensitive to methylation-mediated silencing. Previous studies found that the deregulated expression of tumor suppressive miRNAs (miR-1-1, miR-124, and miR-203) might be due to aberrant DNA methylation. These limited data were obtained from different animal models, cancer cell lines or from a study of a small number of frozen tumor tissues. The methylation status of many miRNAs with tumor suppressive functions is largely unknown, especially for those specifically expressed in liver tissues (miR-122, miR-152, miR-194, miR-199 and miR-215). Our hypothesis is that DNA methylation in tumor suppressive miRNA genes is a common event influencing relevant mature miRNA expression, and contributes to differentiate HCC tumor and non-tumor tissues. The two specific aims are: (1) To examine whether a panel of tumor suppressive miRNA genes have significantly higher levels of DNA methylation in HCC tumor tissues compared with adjacent non-tumor tissues, and test whether the miRNA methylation levels are different for hepatitis B virus (HBV) and hepatitis C virus (HCV)-related HCC; (2) To examine whether a subgroup of miRNA genes showing significant methylation alterations are associated with the down-regulation of relevant mature miRNA expression. A case-only study will be conducted using a well-established, formalin- fixed, paraffin-embedded (FFPE) tissue bank of US HCC patients at Columbia University Medical Center. Totally, 120 histologically confirmed HCC cases with tumor and adjacent non-tumor tissues and HBV/HCV infection data are available for the current study. This pilot study will provide valuable preliminary data to understand the role of miRNA gene methylation in distinguishing HCC malignant tissue from non-tumor tissues. These methylation markers have potential clinical applications to improve risk assessment, early diagnosis and prognostic prediction, and may even possibly improve treatment because of the reversible nature of epigenetic changes. PHS 398/2590 (Rev. 06/09) Page Continuation Format Page PUBLIC HEALTH RELEVANCE: Aberrant DNA methylation is a frequent event occurring early in HCC tumorigenesis. This pilot study will provide initial evidence on the critical role of tumor suppressive miRNA genes' methylation and expression in identifying HCC malignant tissue. It will provide preliminary data to support expanded epidemiological studies that should lead to long term improvements in HCC risk assessment, early diagnosis and efficient treatment.