Plk1 in Chemo-resistance of Cancer

说明（申请人提供）：Plk 1在癌症的化学抗性中摘要：紫杉醇和阿霉素已被广泛用于治疗各种癌症。然而，化疗失败的一个主要问题是在长期暴露后逐渐发展对药物介导的细胞死亡的抗性。p21 CIP 1/WAF 1最初被认为是导致细胞周期停滞的因子，可通过p53依赖性和非依赖性机制诱导。p21作为一种细胞增殖抑制剂，在药物诱导的肿瘤抑制中发挥重要作用。然而，现在公认的是，p21可以在药物治疗后根据细胞环境承担促凋亡和抗凋亡功能。对于具有野生型p53的肿瘤，多柔比星治疗引起p53/p21途径的激活，导致细胞周期停滞和细胞凋亡。p53/p21通路的失活是随后从阿霉素诱导的细胞周期停滞中恢复所必需的。相反，对紫杉醇介导的细胞死亡的抗性与p21水平升高相关，p21的敲低恢复了紫杉醇的敏感性。因此，控制肿瘤细胞中的p21水平对于紫杉醇和多柔比星以及可能的其他药物的疗效至关重要。由于p21是一种短寿命和高度非结构化的蛋白质，其降解速率的调节显着有助于其细胞内水平的调节。p21与G2期的GTSE 1/Hsp 90/WISp 39复合物和G1期的Sgt 1/Hsp 90复合物的结合保护其免受蛋白酶体的降解。在正常细胞中，p21在有丝分裂中通过APCCdc 20依赖性途径降解，在S期通过SCFSkp 2介导的途径降解。然而，p21在整个细胞周期中在癌细胞中稳定。Polo样激酶1（Plk 1）是许多细胞周期相关事件的关键调节因子，在几种类型的癌症中过表达。因为我们已经确定GTSE 1和Sgt 1作为Plk 1的两个底物，我们假设Plk 1在癌症中的水平升高促进了p21的稳定性，从而导致了化疗耐药性。我们的工作模型如下：GTSE 1的Plk 1磷酸化阻止APCCdc 20介导的有丝分裂中p21的降解，Sgt 1的Plk 1磷酸化抑制SCFSkp 2相关的S期p21的降解。两种磷酸化事件都导致p21稳定化，导致癌细胞对紫杉醇介导的细胞死亡产生抗性。对于携带WT p53的癌细胞，多柔比星处理导致细胞周期停滞。在随后的恢复过程中，Sgt 1和GTSE 1的Plk 1磷酸化导致p53通路失活，从而允许细胞周期重新进入，从而有助于癌细胞对阿霉素介导的细胞凋亡的抗性。为了验证我们的假设，我们将首先验证Plk 1在癌细胞对紫杉醇/阿霉素介导的凋亡的抗性中起关键作用。从机制上讲，我们将确定GTSE 1和Sgt 1的Plk 1磷酸化如何调节培养细胞和异种移植肿瘤中的化疗。如果成功的话，预测的结果将确定Plk 1作为一个新的目标，抑制它将防止化疗耐药性，从而提高化疗的疗效。 公共卫生相关性：Plk 1在癌症的化疗耐药性叙述这些研究将有助于我们了解Plk 1及其相互作用的蛋白质在抵抗两种广泛使用的化疗药物：阿霉素和紫杉醇的癌细胞的作用。由于Plk 1水平升高与几种癌症患者的低生存率相关，我们研究的长期目标是应用我们的知识和技术来提高化疗的疗效。

DESCRIPTION (provided by applicant): Plk1 in chemoresistance of cancer Abstract: Paclitaxel and doxorubicin have been widely used to treat various cancers. However, one major problem for the failure of the chemotherapy is gradual development of resistance to drug-mediated cell death after prolonged exposure. Initially identified as a factor that leads to cell cycle arrest, p21CIP1/WAF1 can be induced by both p53-dependent and -independent mechanisms. As an inhibitor of cell proliferation, p21 plays an important role in drug-induced tumor suppression. However, it is now accepted that p21 can assume both pro- and anti- apoptotic functions after drug treatment depending on cellular context. For tumors with wild type p53, doxorubicin treatment causes activation of the p53/p21 pathway, resulting in cell cycle arrest and apoptosis. Inactivation of the p53/p21 pathway is required for subsequent recovery from doxorubicin-induced cell cycle arrest. In contrast, resistance to paclitaxel-mediated cell death has been correlated to elevated levels of p21 and knock-down of p21 restores paclitaxel sensitivity. Therefore, controlling p21 levels in tumor cells is critical for the efficacy of paclitaxel and doxorubicin, and possibly, other drugs. Because p21 is a short-lived and highly unstructured protein, modulation of its degradation rate significantly contributes to the regulation of its intracellular level. Association of p21 with the GTSE1/Hsp90/WISp39 complex in G2 phase and the Sgt1/Hsp90 complex in G1 phase protects it from degradation by the proteasome. In normal cells, p21 is degraded via the APCCdc20-dependent pathway in mitosis and the SCFSkp2-mediated pathway in S phase. However, p21 is stabilized in cancer cells throughout the cell cycle. Polo-like kinase 1 (Plk1), a critical regulator of many cell cycle-related events, is overexpressed in several types of cancers. Because we have identified GTSE1 and Sgt1 as two Plk1 substrates, we hypothesize that elevated levels of Plk1 in cancers promote p21 stability, thus contributing to chemoresistance. Our working model is as follows: Plk1 phosphorylation of GTSE1 prevents APCCdc20-mediated degradation of p21 in mitosis, and Plk1 phosphorylation of Sgt1 inhibits SCFSkp2-associated degradation of p21 in S phase. Both phosphorylation events lead to p21 stabilization, resulting in resistance of cancer cells to paclitaxel-mediated cell death. For cancer cells harboring WT p53, doxorubicin treatment results in cell cycle arrest. During the subsequent recovery, Plk1 phosphorylation of both Sgt1 and GTSE1 leads to inactivation of the p53 pathway to allow cell cycle re-entry, thus contributing to resistance of cancer cells to doxorubicin-mediated apoptosis. To test our hypothesis, we will first validate that Plk1 plays a critical role in resistance of cancer cells to paclitaxel/doxorubicin-mediated apoptosis. Mechanistically, we will determine how Plk1 phosphorylation of GTSE1 and Sgt1 regulates chemotherapy in both cultured cells and xenograft tumors. If successful, the predicted results will identify Plk1 as a novel target, inhibition of which will prevent chemoresistance, thus increasing the efficacy of chemotherapy. PUBLIC HEALTH RELEVANCE: Plk1 in chemoresistance of cancer Narrative These studies will contribute to our understanding of the roles of Plk1 and its interacting proteins in resistance of cancer cells to two widely used chemotherapeutic agents: doxorubicin and paclitaxel. Since elevated Plk1 levels correlate with low survival rates of patients with several types of cancers, the long-term goal of our studies is to apply our knowledge and techniques to enhance the efficacy of chemotherapy.