Pocket protein dependent and pocket protein independent effects of the Merkel cell polyomavirus Large T antigen on proliferation and survival

默克尔细胞癌（MCC）是一种高度侵袭性的皮肤癌。在大约80%的病例中，肿瘤是由默克尔细胞多瘤病毒（MCPyV）引起的。病毒编码的T抗原（小抗原和大抗原）是肿瘤发生和发展所必需的，而MCC细胞基因组中很少发生的体细胞突变是否也有助于癌变尚不清楚。在mcpyv阳性mcc中，大T抗原（LT）是肿瘤细胞增殖的关键。阻止诱导增殖的中心细胞抑制剂是三种口袋蛋白（p107， p130和RB1）。它们共同调节G1/S转变，但它们在其他细胞周期阶段的重要性尚不清楚。第一个资助期的一个关键发现是观察到MCPyV-LT有效地结合和灭活RB1，同时不干扰p107和p130，这两种物质也在MCC细胞中表达。此外，我们可以证明-独立于RB1相互作用- MCPyV-LT能够抑制脱落，从而诱导多倍体。为了进一步加深我们对MCPyV T抗原驱动的癌变所涉及的分子事件的理解，我们将1)…建立一个实验系统，可以分析不同细胞周期阶段的蛋白质功能。利用该系统，我们将评估RB1功能和MCPyV-LT/RB1在周期过程中的相互作用。2)…分析mcc细胞p107和p130失活的机制。特别是，周期蛋白依赖性激酶4和6的作用将在这种情况下进行评估；两者都是众所周知的口袋蛋白失活激酶，在MCC细胞中表现出非常不同的表达。3)……鉴定MCPyV-LT的细胞靶分子，这些分子介导rb1不依赖的分离抑制和多倍体的诱导。4)……评估在病毒阳性mcc中发现的罕见体细胞突变是否有助于MCPyV T抗原驱动的癌变。

Merkel cell carcinoma (MCC) is a highly aggressive skin cancer. In about 80% of cases the tumor is caused by the Merkel cell polyomavirus (MCPyV). The virus-encoded T antigens (small and Large) are required for tumor development and progression, while it is unknown whether rarely occurring somatic mutations in the genome of the MCC cells also contribute to carcinogenesis. In MCPyV-positive MCCs Large T antigen (LT) is pivotal for proliferation of the tumor cells. The central cellular inhibitors preventing the induction of proliferation are the three pocket proteins (p107, p130 and RB1). They jointly regulate the G1/S transition, but their importance in other cell cycle phases is less clear. A key finding of the first funding period was the observation that MCPyV-LT efficiently binds and inactivates RB1 while it does not interfere with p107 and p130, which are also expressed in MCC cells. Moreover, we could demonstrate that - independently of the RB1 interaction - MCPyV-LT is capable of repressing abscission and thereby inducing polyploidy. To further increase our understanding of the molecular events involved in MCPyV T antigen driven carcinogenesis we will .…1) ….. establish an experimental system allowing analysis of protein function in the different cell cycle phases. Utilizing this system we will evaluate RB1 function and MCPyV-LT/RB1 interaction in the course of the cycle.2) ….. analyze mechanisms of p107 und p130 inactivation in MCC-cells. In particular, the role of the cyclin dependent kinases 4 and 6 will be evaluated in this context; both are well known as pocket protein inactivating kinases and display a very diverging expression in MCC cells.3) ….. identify cellular target molecules of MCPyV-LT, which are mediating the RB1-independent suppression of abscission and induction of polyploidy. 4) .…. evaluate whether the rare somatic mutations found in virus-positive MCCs contribute to MCPyV T antigen driven carcinogenesis.