Molecular Genetics of Liver Cancers

摘要： 肝细胞癌又称肝癌，是癌症死亡的主要原因之一 世界各地。肝癌发生的分子遗传学基础仍然知之甚少。之一 与HCC发展有关的信号通路是Ras/MAPK通路，因为它已经被 显示该途径在几乎所有人HCC中被激活。然而，Ras或B-Raf突变是 在这种恶性肿瘤中极为罕见。那么Ras/MAPK信号是如何在人HCC中被激活的呢？在我们 以前的全基因组表达研究，我们确定了一个大的基因，其表达水平下降， 在人HCC样品中调节。利用生物信息学分析，我们鉴定了Spry 2和EphA 2，两者均 Ras/MAPK信号传导的负反馈抑制剂在人HCC样品中下调， 伴随的方式。为了阐明Spry 2和EphA 2在HCC发病机制中的潜在作用，我们 为这两个基因开发了新的小鼠模型。我们发现，抑制Spry活动的显性 Spry 2的阴性形式（Spry 2 Y55 F）与活化的连环蛋白协同诱导肝癌形成， EphA 2的缺失使DENA诱导的小鼠肝癌发生增敏。这些新的小鼠模型提供了 令人信服的证据表明，Spry 2和EphA 2确实可以直接促进体内HCC发病机制， 作为肿瘤抑制基因发挥作用。基于这些初步研究，我们假设， Spry 2和/或EphA 2导致Ras/MAPK信号通路的异常激活，并与Ras/MAPK信号通路的激活协同作用。 其他基因改变促进HCC发病机制。这些假设将在三个目标中进行检验。在Aim中 目的一是明确Spry 2在肝癌发病机制中的调控和作用，目的二是明确Spry 2在肝癌发病机制中的作用，目的三是明确Spry 2在肝癌发病机制中的作用。 EphA 2表达缺失在HCC发展中的作用;在第三个目标中，我们将研究EphA 2表达缺失的功能。 在肝癌发生过程中，Spry 2和EphA 2同时下调。总的来说， 本申请的目的是表征Spry 2和EphA 2在HCC中的功能意义，并阐明新的 在Ras或B-Raf基因突变不存在的情况下， HCC发病机制。这些小鼠模型可用于药物筛选，以鉴定和测试小分子药物的功效。 靶向Ras/MAPK通路的分子或抗体。这些项目代表了令人兴奋和重要的 功能基因组研究源于描述性基因组分析， HCC发病机制。

ABSTRACT: 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 ¿-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.