The function of cyclin C in tumorigenesis

 描述（由申请人提供）：本项目的目的是阐明细胞周期蛋白C在肿瘤发生中的功能。在拟议的工作中，我们将重点关注细胞周期蛋白C在T细胞淋巴细胞白血病（T-ALL，在目标1和2）中的作用，而在目标3中，我们将把我们的分析扩展到前列腺癌和肺癌。 细胞周期蛋白C在20多年前与细胞周期蛋白D1和E一起被克隆，用于筛选哺乳动物和果蝇的cDNA，这些cDNA可以补充酿酒酵母CLN 1 -3基因的突变。随后，细胞周期蛋白D1和E已被广泛研究，它们在癌症中的作用已得到很好的证明。相比之下，细胞周期蛋白C在人类癌症中的作用则知之甚少。 为了分析细胞周期蛋白C在肿瘤发生中的作用，我们利用胚胎干细胞基因打靶技术建立了条件性细胞周期蛋白C基因敲除小鼠。出乎意料的是，我们发现造血细胞中细胞周期蛋白C的急性消融导致细胞内Notch 1（ICN 1）水平的强烈上调。我们观察到细胞周期蛋白C-CDK 8激酶磷酸化ICN 1，这反过来又允许ICN 1与F-box蛋白Fbw 7结合，并触发ICN 1多聚泛素化和随后的蛋白体降解。细胞周期蛋白C的消融破坏了这一过程，导致ICN 1水平的强烈上调。对条件性细胞周期蛋白C基因敲除小鼠的分析显示，这些动物对T-ALL的易感性增加。重要的是，细胞周期蛋白C杂合子也显示出增加的肿瘤易感性。此外，我们观察到细胞周期蛋白C基因在相当一部分人T-ALL中异源缺失，这些肿瘤显示细胞周期蛋白C水平降低。总的来说，这些观察结果表明，细胞周期蛋白C可能在体内作为一个单倍不足的肿瘤抑制剂的功能。 在本书中，我们将扩展这些观察。在具体目标1中，我们将使用人类肿瘤细胞系研究细胞周期蛋白C在T-ALL中的确切分子功能。在特定目标2中，我们将利用原发性、患者来源的人T-ALL样本来搜索编码细胞周期蛋白C激酶伴侣（细胞周期蛋白依赖性激酶CDK 8、CDK 19和CDK 3）的基因的突变或缺失。在目标3中，我们将把研究扩展到前列腺癌和肺癌。

 DESCRIPTION (provided by applicant): The goal of this project is to elucidate the function of cyclin C in tumorigenesis. In the proposed work we will focus on the role for cyclin C in T-cell lymphoblastic leukemia (T-ALL, in Aims 1 and 2), while in Aim 3 we will extend our analyses to prostate and lung cancers. Cyclin C was cloned over 20 years ago, together with cyclins D1 and E, in a screen for mammalian and Drosophila cDNAs that can complement mutations in Saccharomyces cerevisiae CLN1-3 genes. Subsequently, cyclins D1 and E have been extensively studied, and their involvement in cancer has been extremely well documented. In contrast, the role of cyclin C in human cancer is much less understood. In order to analyze the function of cyclin C in tumorigenesis, we generated conditional cyclin C knockout mice, using gene targeting in embryonic stem cells. Unexpectedly, we found that an acute ablation of cyclin C in hematopoietic cells led to a strong upregulation of intracellular Notch1 (ICN1) levels. We observed that cyclin C-CDK8 kinase phosphorylates ICN1, which in turn allows binding of ICN1 to an F-box protein Fbw7, and triggers ICN1 poly-ubiquitination and subsequent proteosomal degradation. Ablation of cyclin C disrupts this process, leading to strong upregulation of ICN1 levels. Analyses of conditional cyclin C knockout mice revealed that these animals display increased susceptibility to T-ALL. Importantly, cyclin C heterozygotes also display increased tumor susceptibility. Moreover, we observed that the cyclin C gene is heterozygously deleted in a substantial fraction of human T-ALL, and these tumors display reduced cyclin C levels. Collectively, these observations suggest that cyclin C likely functions in vivo as a haploinsufficient tumor-suppressor. In the proposed work we will extend these observations. In Specific Aim 1, we will study the exact molecular function of cyclin C in T-ALL using human tumor cell lines. In Specific Aim 2, we will utilize primary, patient-derived human T-ALL samples to search for mutations or deletions in genes encoding cyclin C kinase partners (cyclin-dependent kinases CDK8, CDK19 and CDK3). In Aim 3, we will extend our studies to prostate and lung cancers.