College of Biological Sciences and Biotechnology, Chungnam National University, Daejeon, Korea.
Oncogene. 2011 Jan 27;30(4):471-81. doi: 10.1038/onc.2010.423. Epub 2010 Oct 4.
Phosphorylation of the Fas-associated death domain (FADD) protein sensitizes cancer cells to various chemotherapeutics. However, the molecular mechanism underlying chemosensitization by phosphorylated FADD (P-FADD) is poorly understood. In this study, we describe the physical interactions and functional interplay between Polo-like kinase 1 (Plk1) and FADD. Plk1 phosphorylates FADD at Ser-194 in response to treatment with taxol. Overexpression of a phosphorylation-mimicking mutant, FADD S194D, caused degradation of Plk1 in an ubiquitin-independent manner, and delayed cytokinesis, consistent with the expected cellular phenotype of Plk1 deficiency. This demonstrates that Plk1 is regulated via a negative feedback loop by its substrate, FADD. Overexpression of FADD S194D sensitized HeLa cells to a low dose of taxol independently of caspase activation, whereas overexpression of FADD S194D resulted in caspase activation in response to a high dose of taxol. Therefore, we examined whether the death potential of P-FADD affected Plk1-mediated tumorigenesis. Transfection of FADD S194D inhibited colony formation by Plk1-overexpressing HeLa cells (HeLa-Plk1). Moreover, overexpression of FADD S194D suppressed tumorigenesis in nude mice xenografted with HeLa-Plk1. Therefore, this study reports the first in vivo validation of tumor-suppressing activity of P-FADD. Collectively, our data demonstrate that in response to taxol, Plk1 endows death-promoting and tumor-suppressor functions to its substrate, FADD.
磷酸化 Fas 相关死亡结构域（FADD）蛋白使癌细胞对各种化疗药物敏感。然而，磷酸化 FADD（P-FADD）引起化学增敏的分子机制尚未完全阐明。在这项研究中，我们描述了 Polo 样激酶 1（Plk1）和 FADD 之间的物理相互作用和功能相互作用。紫杉醇处理后，Plk1 将 FADD 的丝氨酸 194 磷酸化。表达磷酸化模拟突变体 FADD S194D 会导致 Plk1 在非泛素依赖的方式下降解，并且延迟胞质分裂，与 Plk1 缺陷的预期细胞表型一致。这表明 Plk1 通过其底物 FADD 进行负反馈调节。FADD S194D 的过表达使 HeLa 细胞对低剂量紫杉醇敏感，而与半胱天冬酶激活无关，而高剂量紫杉醇会导致 FADD S194D 的过表达激活半胱天冬酶。因此，我们检查了 P-FADD 的死亡潜能是否影响 Plk1 介导的肿瘤发生。FADD S194D 的转染抑制了 Plk1 过表达的 HeLa 细胞（HeLa-Plk1）的集落形成。此外，FADD S194D 的过表达抑制了 HeLa-Plk1 裸鼠异种移植的肿瘤发生。因此，本研究首次在体内验证了 P-FADD 的肿瘤抑制活性。总之，我们的数据表明，紫杉醇处理后，Plk1 将促死亡和肿瘤抑制功能赋予其底物 FADD。
