Abstract：
Inhibitors of polo-like kinase (PLK) are currently being evaluated as anticancer drugs. However, the molecular mechanism of PLK inhibitor-induced cell death is not fully understood. In this study, we found that GW843682X and BI2536, two inhibitors of PLK1, significantly induced cell death in multiple type cells. The induction of cell death was related to the preferring expression of PLK1. However, in human umbilical vascular endothelial cells (HUVEC) and human colorectal carcinoma cells, which expressed higher levels of both PLK1 and PLK2, PLK1 inhibitors induced very low levels of cell death. Clinical analysis reveals PLK1 presence in 26 of 30 NPC tumor tissues. In in vivo NPC lung metastasis nude mouse models, PLK1 inhibitors decreased NPC progress. Mechanistically, the PLK1 inhibitor did not activate p53, and the cell death was not reversed by p53 inhibition. Moreover, PLK1 inhibitor-induced cell death was PARP- and caspase-independent. Although PLK1 inhibitors induced down-regulation of calpain inhibitor calpastatin and calpain was activated by PLK1 inhibition, calpain blocking did not reverse cell death induced by PLK1 inhibitors, suggesting the non-involvement of calpain. Surprisingly, we found that PLK1 inhibitors induced the activation of proteasome, and the treatment of cells with PLK1 inhibitors reduced the levels of ubiquitinated proteins. And proteasome inhibitors reversed cell death induced by PLK1 inhibitors in various cell types in which PLK1 was preferentially expressed. Moreover, PLK1 inhibition reversed the degradation of proteins including p53, caspase 8, PARP and calpastatin. These results suggest that the activation of proteasome is critical for cell death induced by PLK1 inhibition.
摘要：
目前正在评估polo样激酶（PLK）的抑制剂作为抗癌药物。然而,PLK抑制剂诱导细胞死亡的分子机制尚不完全清楚。在这项研究中,我们发现PLK1的两种抑制剂GW843682X和BI2536显著诱导多种类型细胞的细胞死亡。细胞死亡的诱导与PLK1的优选表达有关。然而,在人脐血管内皮细胞（HUVEC）和人大肠癌细胞中，PLK1和PLK2的表达水平较高，PLK1抑制剂诱导的细胞死亡水平非常低。临床分析显示在30个NPC肿瘤组织中的26个中存在PLK1。在体内NPC肺转移裸鼠模型中，PLK1抑制剂下降了NPC的进展。机械上,PLK1抑制剂不能激活p53,p53抑制也不能逆转细胞死亡.此外，PLK1抑制剂诱导的细胞死亡是不依赖PARP和caspase的。尽管PLK1抑制剂诱导了钙蛋白酶抑制剂calpastatin的下调，但PLK1抑制激活了钙蛋白酶，钙蛋白酶阻断不能逆转PLK1抑制剂诱导的细胞死亡，提示钙蛋白酶不受累。令人惊讶的是,我们发现PLK1抑制剂能诱导蛋白酶体的激活，用PLK1抑制剂处理细胞降低了泛素化蛋白的水平。蛋白酶体抑制剂逆转了PLK1抑制剂在PLK1优先表达的各种细胞类型中诱导的细胞死亡。此外，PLK1抑制逆转了包括p53、半胱天冬酶8、PARP和calpastatin在内的蛋白质的降解。这些结果表明，蛋白酶体的激活对于PLK1抑制诱导的细胞死亡至关重要。
