Signal Transduction by the Microtubule Destabilizer, Stathmin/Oncoprotein 18

描述（由申请人提供）：控制细胞增殖和存活是维持健康细胞群和消除适当细胞周期控制缺陷细胞的关键因素。调节细胞周期和细胞凋亡的关键蛋白是p53，这种蛋白在50%的人类癌症中发生突变。我们最近发现p53和stathmin（一种微管不稳定蛋白）的联合缺失会导致细胞周期G2期的细胞周期延迟和细胞凋亡死亡。这些数据提供了对控制细胞增殖的控制的见解，并具有确定特异性杀死缺乏功能性p53的肿瘤细胞的目标的潜力。本应用中提出的实验旨在确定连接安定素水平降低和细胞周期G2期延迟进展的信号通路。完成所提出的目标将验证静息素耗竭稳定间期微管细胞骨架的假设，这一假设在下游起作用，限制rho依赖性的Aurora A激活和有丝分裂进入。在整个目标中，还测试了其他模型。在Aim 1中，将确定安定素耗竭的下游信号中继。药物诱导的微管解聚或稳定将用于测试它们消除（解聚）或模拟（稳定）G2中观察到的延迟的能力。其他安定素结合伙伴，p27Kip1和STAT3，将测试其在安定素耗竭后调节细胞周期进程中的潜在作用。stathmin截断的过表达将用于进一步探测微管依赖或独立的间期细胞周期进程调节。在Aim 2中，控制有丝分裂进入的途径将被检查它们在安定素耗竭后传递信号的作用。细胞周期蛋白的水平及其积累速率将被测量，直接控制有丝分裂进入的酶的活性状态将被检查，最后，上游信号级联将被操纵以消除或模拟在G2中由稳定素耗尽引起的延迟。完成这两个目标将确定连接安定素耗竭和有丝分裂进入的信号级联。

DESCRIPTION (provided by applicant): The control of cell proliferation and survival are critical factors in maintaining healthy cell populations and eliminating those cells defective in proper cell cycle control. A key protein regulating the cell cycle and apoptosis is p53, a protein mutated in >50% of human cancers. We recently found that the combined loss of both p53 and stathmin, a microtubule destabilizing protein, results in a cell cycle delay during the G2 phase of the cell cycle and cell death by apoptosis. These data provide insight into controls governing cell proliferation and hold the potential to identify targets to kill specifically those tumor cells lacking functional p53. Experiments proposed in this application look to identify the signal pathway linking reduced stathmin level and delayed progression through the G2 phase of the cell cycle. Completion of the proposed aims will test the hypothesis that stathmin depletion stabilizes the interphase microtubule cytoskeleton, which acts downstream to limit Rho-dependent activation of Aurora A and mitotic entry. Throughout the aims, alternative models are also tested. In Aim 1, the signal relay downstream of stathmin depletion will be identified. Drug-induced microtubule depolymerization or stabilization will be used to test for their ability to abrogate (depolymerization) or mimic (stabilization) the observed delay in G2. The other stathmin binding partners, p27Kip1 and STAT3, will be tested for their potential role(s) in regulating cell cycle progression after stathmin depletion. Over-expression of stathmin truncations will be used to further probe for microtubule- dependent or -independent regulation of interphase cell cycle progression. In Aim 2, pathways controlling mitotic entry will be examined for their role in relaying signals after stathmin depletion. The levels of cyclins and their rate of accumulation will be measured, the activity states of enzymes directly controlling mitotic entry will be examined, and finally, upstream signal cascades will be manipulated to either abrogate or mimic the stathmin depletion-induced delay in G2. Completion of the two aims will identify the signal cascade linking stathmin depletion and mitotic entry. PUBLIC HEALTH RELEVANCE: Controlling cancer cell proliferation requires interventions that can block cell replication, ideally without impacting the non-transformed cells in the body. We have identified the microtubule destabilizing protein, stathmin, as a protein necessary for reproduction and survival of cancer cells lacking the tumor suppressor p53. Since about half of all human cancers harbor mutations in p53, understanding why stathmin is required for cell proliferation in these cells holds great potential for selectively controlling their growth.