Signal Transduction by the Microtubule Destabilizer, Stathmin/Oncoprotein 18

描述(申请人提供)：细胞增殖和存活的控制是维持健康细胞群体和消除那些在适当的细胞周期控制中有缺陷的细胞的关键因素。调控细胞周期和细胞凋亡的关键蛋白质是P53，这是一种在50%的人类癌症中发生突变的蛋白质。我们最近发现，P53和微管不稳定蛋白stathmin的共同缺失导致细胞周期延迟在细胞周期的G2期，并导致细胞死亡。这些数据提供了对控制细胞增殖的控制的洞察，并具有识别靶点以特定地杀死那些缺乏功能性p53的肿瘤细胞的潜力。本申请中提出的实验旨在确定连接Stathmin水平降低和细胞周期G2期延迟进展的信号通路。拟议的目标的完成将检验这样的假设，即stathmin的耗尽稳定了间期微管细胞骨架，后者向下游作用，限制Rho依赖的Aurora A的激活和有丝分裂的进入。在整个AIMS中，还对替代模式进行了测试。在目标1中，将确定Stathmin耗尽下游的信号继电器。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Stathmin结合伙伴，p27Kip1和STAT3，将被测试它们在Stathmin耗尽后调节细胞周期进程中的潜在作用(S)。Stathmin截断的过表达将被用来进一步探索间期细胞周期进程的微管依赖或独立调控。在目标2中，将检查控制有丝分裂进入的通路在Stathmin耗尽后在信号传递中的作用。我们将测量细胞周期蛋白的水平及其积累速度，检测直接控制有丝分裂进入的酶的活性状态，最后，上游信号级联将被操纵以消除或模拟Stathmin耗尽诱导的G2延迟。完成这两个目标将确定连接stathmin耗尽和有丝分裂进入的信号级联。 公共卫生相关性：控制癌细胞增殖需要能够阻止细胞复制的干预措施，理想情况下不会影响体内未转化的细胞。我们已经确定微管不稳定蛋白stathmin是缺乏肿瘤抑制因子p53的癌细胞繁殖和存活所必需的蛋白质。由于大约一半的人类癌症含有p53突变，理解为什么stathmin是这些细胞增殖所必需的，对于选择性地控制它们的生长具有巨大的潜力。

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.