The function of cyclin C in tumorigenesis

 描述(申请人提供)：本项目的目标是阐明细胞周期蛋白C在肿瘤发生中的作用。在拟议的工作中，我们将重点放在T淋巴细胞白血病(T-ALL，目标1和2中的T-ALL)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。20多年前，在哺乳动物和果蝇的筛选中，细胞周期蛋白C与细胞周期蛋白D1和E一起被克隆出来，这些基因可以补充酿酒酵母CLN1-3基因的突变。随后，人们对细胞周期蛋白D1和E进行了广泛的研究，它们与癌症的关系也得到了很好的证明。相比之下，细胞周期蛋白C在人类癌症中的作用却鲜为人知。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中的基因打靶技术，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，急性去除造血细胞中的细胞周期蛋白C导致细胞内Notch1(ICN1)水平强烈上调。我们观察到，周期蛋白C-CDK8激酶使ICN1磷酸化，进而允许ICN1与F-box蛋白Fbw7结合，并触发ICN1的多泛素化和随后的蛋白酶体降解。细胞周期蛋白C的消融破坏了这一过程，导致ICN1水平的强烈上调。对条件细胞周期蛋白C基因敲除小鼠的分析表明，这些动物对T-ALL的易感性增加。重要的是，细胞周期蛋白C杂合子也显示出肿瘤易感性增加。此外，我们观察到，在人类T-ALL的相当一部分中，细胞周期蛋白C基因杂合性缺失，并且这些肿瘤表现为细胞周期蛋白C水平降低。总而言之，这些观察表明，细胞周期蛋白C在体内可能作为单倍体不足的肿瘤抑制因子发挥作用。在拟议的工作中，我们将扩展这些观察结果。在具体目标1中，我们将利用人类肿瘤细胞系来研究细胞周期蛋白C在T-ALL中的确切分子功能。在特定的目标2中，我们将利用来自患者的原代人类T-ALL样本来搜索编码细胞周期蛋白C激酶伙伴(细胞周期蛋白依赖蛋白激酶CDK8、CDK19和CDK3)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.