Molecular Genetics of Liver Cancers

描述（由申请人提供）：肝细胞癌（HCC），也称为肝癌，是全球癌症死亡的主要原因之一。肝癌发生的分子遗传学仍然知之甚少。与HCC发展相关的信号通路之一是Ras/MAPK通路，因为已经证明该通路在几乎所有人类HCC中都被激活。然而，Ras或B-Raf突变在这种恶性肿瘤中极为罕见。那么Ras/MAPK信号是如何在人类HCC中被激活的呢？在我们之前的全基因组表达研究中，我们发现了大量在人类HCC样本中表达水平失调控的基因。通过生物信息学分析，我们确定了Spry2和EphA2，这两种Ras/MAPK信号的反馈负抑制剂在人类HCC样本中同时下调。为了研究Spry2和EphA2在HCC发病过程中的潜在作用，我们为这两个基因建立了新的小鼠模型。我们发现，Spry2显性阴性形式（Spry2Y55F）对Spry活性的抑制与活化的2-连环蛋白协同诱导肝癌的形成，EphA2的缺失使DENA诱导的小鼠肝癌增敏。这些新的小鼠模型提供了令人信服的证据，证明Spry2和EphA2确实可以直接参与体内HCC的发病，并作为肿瘤抑制基因发挥作用。基于这些初步研究，我们假设Spry2和/或EphA2的缺失导致Ras/MAPK信号通路的异常激活，并与其他遗传改变共同促进HCC的发病。这些假设将在三个方面得到检验。在第一部分中，我们将定义Spry2在HCC发病机制中的调控和作用；在第二阶段，我们将确定EphA2表达缺失对HCC发展的影响；在第三部分中，我们将研究Spry2和EphA2在肝癌发生过程中同时下调的功能。总之，本应用的目的是表征Spry2和EphA2在HCC中的功能意义，并阐明在HCC发病过程中Ras或B-Raf基因突变缺失时Ras/MAPK通路激活的新机制。这些小鼠模型可用于药物筛选，以识别和测试靶向Ras/MAPK途径的小分子或抗体的功效。这些项目代表了来自描述性基因组分析的令人兴奋和重要的功能基因组研究，并可能揭示HCC发病机制的新分子机制。公共卫生相关性：肝癌是一种致命的疾病，缺乏任何有效的治疗选择。肝癌在美国的发病率正在上升。我们实验室主要研究肝癌发展过程中的基因改变。在这个应用中，我们将描述Spry2和EphA2两个基因的功能，它们的表达水平在人类肝癌中被去调控。这些研究可能会为我们提供诊断和治疗这种恶性肿瘤的新靶点。

DESCRIPTION (provided by applicant): Hepatocellular carcinoma (HCC), also known as liver cancer, is one of the leading causes of cancer death world wide. Molecular genetics underlying hepatocarcinogenesis are still poorly understood. One of the signaling pathways that have been implicated in HCC development is the Ras/MAPK pathway, as it has been shown that this pathway is activated in virtually all human HCC. However, Ras or B-Raf mutations are extremely rare in this malignancy. So how does Ras/MAPK signaling get activated in human HCC? In our previous genome-wide expression studies, we identified a large list of genes whose expression levels are de- regulated in human HCC samples. Using bioinformatics analysis, we identified Spry2 and EphA2, both feedback negative inhibitors of the Ras/MAPK signaling to be down-regulated in human HCC samples in a concomitant manner. To address the potential roles of Spry2 and EphA2 during HCC pathogenesis, we developed novel mouse models for these two genes. We show that inhibition of Spry activity by a dominant negative form of Spry2 (Spry2Y55F) cooperates with activated 2-catenin to induce liver cancer formation, and loss of EphA2 sensitizes DENA induced hepatic carcinogenesis in mice. These novel mouse models provide compelling evidence that Spry2 and EphA2 can indeed directly contribute to HCC pathogenesis in vivo and function as tumor suppressor genes. Based on these preliminary studies, we hypothesize that the loss of Spry2 and/or EphA2 leads to aberrant activation of the Ras/MAPK signaling pathway and cooperates with other genetic alterations to promote HCC pathogenesis. The hypotheses will be tested in three aims. In Aim one, we will define the regulation and roles of Spry2 in HCC pathogenesis; In Aim two, we will determine the effects of loss of EphA2 expression in HCC development; and in Aim three, we will investigate the functions of concomitant downregulation of Spry2 and EphA2 during hepatic carcinogenesis. Altogether, the goal of this application is to characterize the functional significance of Spry2 and EphA2 in HCC, and to elucidate novel mechanisms of activation of the Ras/MAPK pathway in the absence of Ras or B-Raf gene mutations during HCC pathogenesis. These mouse models can be used in drug screens to identify and test the efficacy of small molecules or antibodies that target Ras/MAPK pathway. These projects represent exciting and important functional genomic studies stemmed from a descriptive genomic analysis and will likely unveil novel molecular mechanisms for HCC pathogenesis. PUBLIC HEALTH RELEVANCE: Liver cancer is a deadly disease, lacking any effective treatment options. Liver cancer incidence is increasing in the US. Our lab focuses on studying the genetic alternations during liver cancer development. In this application we will characterize the functions of two genes, Spry2 and EphA2, whose expression levels are de- regulated in human liver cancers. These studies will likely provide us novel targets for the diagnosis and treatment of this malignancy.