The RB pathway in liver cancer

描述（由申请人提供）：全球每年有超过60万人死于肝细胞癌（HCC）。引起HCC的环境因素是众所周知的，包括乙型和丙型肝炎病毒（HBV和HCV）感染、黄曲霉毒素B1暴露和过量饮酒。然而，目前尚无有效的治疗方法，HCC患者预后通常较差，总中位生存期不足一年。RB肿瘤抑制因子及其家族成员的p107和p130在几乎所有人类HCC病例中都是功能性失活的。这种失活是由于CDK4抑制剂p16沉默或CDK4伴侣细胞周期蛋白D1表达增加导致CDK4激酶活性增加。此外，HBV和HCV产生的一些蛋白质可以灭活RB家族成员，包括通过触发它们的降解。我们通过删除成年小鼠肝脏中的RB家族基因来模拟RB家族蛋白的功能失活，从而建立了人类HCC的小鼠模型。RB/p107/p130三敲除（TKO）小鼠的肝脏肿瘤的组织学和基因表达谱与人类hcc相似。通常被RB家族抑制的E2F转录因子活性在TKO HCC细胞中较高。TKO hcc起源于祖细胞而不是肝细胞，由于未知的机制抑制其增殖而不能分裂。TKO HCC模型提供了一个独特的体内系统来查询肝脏肿瘤发生机制，并专门询问RB/E2F转录调节复合物如何控制HCC的发展。我们的一般假设是，RB途径的失活至少在一定程度上驱动了癌症的发生

DESCRIPTION (provided by applicant): More than 600,000 people die from Hepatocellular carcinoma (HCC) worldwide annually. The environmental factors that cause HCC are well known and include infection by hepatitis B and C viruses (HBV and HCV), exposure to Aflatoxin B1, and excessive alcohol intake. However, no effective treatments exist for HCC and the prognosis of HCC patients is usually poor, with an overall median survival of less than one year. The RB tumor suppressor and its family member's p107 and p130 are functionally inactivated in nearly all cases of human HCC. This inactivation is due to increased CDK4 kinase activity resulting from the silencing of the CDK4 inhibitor p16 or from increased expression of the CDK4 partner Cyclin D1. In addition, some proteins produced by HBV and HCV can inactivate RB family members, including by triggering their degradation. We generated a mouse model for human HCC by deleting RB family genes in the liver of adult mice to model this functional inactivation of RB family proteins. RB/p107/p130 triple knockout (TKO) mice develop liver tumors whose histology and gene expression profiles resemble human HCCs. The activity of E2F transcription factors, which are normally inhibited by the RB family, is high in TKO HCC cells. TKO HCCs initiate from progenitor cells and not hepatocytes, which do not divide due to unknown mechanisms that suppress their proliferation. The TKO HCC model provides a unique in vivo system to query the mechanisms of tumorigenesis in the liver and to specifically interrogate how RB/E2F transcriptional regulatory complexes control HCC development. Our general hypothesis is that inactivation of the RB pathway drives cancer initiation at least in part by deregulating E2F activity and compromising the balance between regulatory networks in acutely sensitive cell populations. Specifically, we propose that increased E2F activity engages pathways that promote the expansion of mutant cells, including liver progenitors, but also triggers negative feedback loops preventing cancer initiation from mature hepatocytes and limiting the growth of HCC cells. We will first test the specific hypothesis that activation of p21 by E2F in the TKO model blocks the proliferation of hepatocytes, thereby preventing HCC initiation from these mature cells. Next, we will test the idea that activation of Notch signaling y E2F limits the expansion of HCC cells during tumorigenesis. Finally, we will examine the possibility that activation of the EZH2 methyltransferase by E2F promotes the growth of both liver progenitors and HCC cells. To test these hypotheses, we will manipulate the activity of RB and E2F family members, p21 and CDK2, Notch pathway members, and EZH2 in adult liver progenitor cells, mature hepatocytes, and HCC cells in vivo. These experiments in mutant mice will be complemented by analyses of human liver cells ex vivo. Our studies will identify novel means to diagnose, detect, and treat HCC. In addition, because genetic, epigenetic, and/or viral inactivation of the RB pathway is a nearly universal event in human cancer cells, these studies are generally relevant to a broad cross-section of cancer patients.