Dissecting E2f3's role in tumorigenesis

描述（由申请人提供）：肿瘤的发展依赖于两个关键肿瘤抑制通路的失活，p16- cycD/cdk4-pRB-E2F和p19Arf-mdm2-p53，它们共同调节细胞增殖和肿瘤监测反应。该建议关注E2f家族的一个成员E2f3，它是pRB和p53网络的一个组成部分，其扩增与人类膀胱和前列腺肿瘤的发展有关。E2f3编码两种不同的蛋白质，分别是E2F3A和E2F3B，它们的不同之处在于它们的N端序列。现有的研究没有解决在人类肿瘤中观察到的E2F3上调是否反映了E2F3A、E2F3B或两种亚型水平的增加。因此，目前尚不清楚这些蛋白中是否有一种或两者都有助于肿瘤的发展。突变小鼠模型分析明确证明E2f3在体内以剂量依赖的方式促进肿瘤形成。这验证了小鼠作为研究E2f3致癌活性的模型系统。初步研究表明，E2F3A和E2F3B蛋白在体内具有不同的生物学特性。E2F3A被认为通过激活编码细胞周期控制机制关键成分的基因转录来促进细胞增殖。相反，E2F3B有助于Art肿瘤抑制因子的转录抑制，从而阻碍p53肿瘤监测应答的诱导。本提案的目的是验证E2F3A和E2F3B在体内具有不同作用的假设，并确定这些亚型如何促进E2f3在细胞增殖、正常发育和致瘤性中的作用。本提案有三个目的：(1)确定E2F3A和E2F3B在细胞过程中的相对作用；(2)利用突变小鼠品系确定E2F3A和E2F3B在肿瘤发生中的作用；(3)通过阐明E2F3抑制因子复合物的组成和鉴定其特异性下游靶基因，研究E2F3抑制因子的作用机制。

DESCRIPTION (provided by applicant): Tumor development is dependent upon the inactivation of two key tumor suppressor pathways, p16- cycD/cdk4-pRB-E2F and p19Arf-mdm2-p53, that together regulate cellular proliferation and the tumor surveillance response. This proposal focuses on one member of the E2f family, E2f3, which is a component of both the pRB and p53 networks and whose amplification has been linked to the development of human bladder and prostate tumors. E2f3 encodes two distinct proteins, called E2F3A and E2F3B that differ only in their N terminal sequences. Existing studies do not address whether the observed up-regulation of E2F3 in human tumors reflects an increase in the levels of E2F3A, E2F3B or both isoforms. Thus, it is currently unclear whether either, or both, of these proteins contribute to tumor development. The analysis of mutant mouse models has provided unequivocal proof that E2f3 acts in dose-dependent manner to promote tumor formation in vivo. This validates the mouse as model system to investigate E2f3's oncogenic activity. Preliminary studies suggest that the E2F3A and E2F3B proteins have distinct biological properties in vivo. E2F3A is believed to promote cellular proliferation by activating the transcription of genes that encode key components of the cell cycle control machinery. In contrast, E2F3B contributes to the transcriptional repression of the Art tumor suppressor and thereby impedes induction of the p53 tumor surveillance response. The goal of this proposal is to test the hypothesis that E2F3A and E2F3B have differential roles in vivo and to determine how each of these isoforms contribute to E2f3's roles in cellular proliferation, normal development and tumorigenicity. This proposal has three aims: (1) To identify the relative roles of E2F3A and E2F3B in cellular processes; (2) To use mutant mouse strains to determine the role of E2F3A and E2F3B in tumorigenesis; and (3) To investigate the mechanism of action of the E2F3 repressor by elucidating the components of the E2F3 repressor complex and identifying its specific downstream target genes.