Plk1 in Chemo-resistance of Cancer

描述(申请人提供)：PLK1在癌症的化疗耐药中。摘要：紫杉醇和阿霉素已被广泛用于治疗多种癌症。然而，化疗失败的一个主要问题是，在长期暴露后，对药物介导的细胞死亡逐渐产生抗药性。P21CIP1/WAF1最初被认为是导致细胞周期停滞的一个因素，它可以由P53依赖和非依赖的机制诱导。P21作为一种细胞增殖抑制因子，在药物诱导的肿瘤抑制中发挥着重要作用。然而，现在公认的是，根据细胞环境的不同，药物治疗后，p21可以同时承担促凋亡和抗凋亡的功能。对于野生型p53的肿瘤，阿霉素治疗会导致p53/p21通路的激活，导致细胞周期停滞和细胞凋亡。P53/p21通路失活是阿霉素引起的细胞周期停滞恢复所必需的。相反，对紫杉醇介导的细胞死亡的抵抗与p21水平的升高有关，而p21的下调恢复了紫杉醇的敏感性。因此，控制肿瘤细胞中的p21水平对于紫杉醇和阿霉素，以及可能的其他药物的疗效至关重要。由于p21是一种短命和高度非结构化的蛋白质，对其降解速度的调节对其细胞内水平的调节具有重要意义。P21与G2期的GTSE1/Hsp90/WISp39复合体和G1期的SGT1/Hsp90复合体结合，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APCCDc20依赖的途径降解，在S期通过SCFSkp2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存在。Polo-like kinase1(Plk1)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度表达。因为我们已经确定GTSE1和SGT1是两种Plk1底物，所以我们假设Plk1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。我们的工作模型如下：PLK1的GTSE1磷酸化阻止APCCDC20介导的有丝分裂中p21的降解，Plk1的SGT1磷酸化在S期抑制SCFSkp2相关的p21的降解。这两个磷酸化事件都导致p21稳定，导致癌细胞对紫杉醇介导的细胞死亡产生抵抗力。对于携带WTP53的癌细胞，阿霉素治疗会导致细胞周期停滞。在随后的恢复过程中，Sgt1和GTSE1的Plk1磷酸化导致P53途径失活，使细胞周期重新进入，从而导致肿瘤细胞对阿霉素介导的凋亡产生抵抗。为了验证我们的假设，我们将首先验证Plk1在癌细胞对紫杉醇/阿霉素介导的凋亡耐药中发挥关键作用。从机制上，我们将确定GTSE1和SGT1的Plk1磷酸化如何调节培养细胞和异种移植瘤的化疗。如果成功，预测结果将确定Plk1是一个新的靶点，抑制Plk1将防止化疗耐药，从而提高化疗的疗效。

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.