1] Institut für Biochemie, Westfälische-Wilhelms-Universität Münster, Münster, Germany [2] Graduate School of Chemistry (GSC-MS), Westfälische-Wilhelms-Universität Münster, Germany.
Oncogenesis. 2013 Jan 14;2(1):e37. doi: 10.1038/oncsis.2012.37.
The tumor suppressor protein Pdcd4 is a nuclear/cytoplasmic shuttling protein that has been implicated in the development of several types of human cancer. In the nucleus, Pdcd4 affects the transcription of specific genes by modulating the activity of several transcription factors. We have identified the Daxx protein as a novel interaction partner of Pdcd4. Daxx is a scaffold protein with roles in diverse processes, including transcriptional regulation, DNA-damage signaling, apoptosis and chromatin remodeling. We show that the interaction of both proteins is mediated by the N-terminal domain of Pdcd4 and the central part of Daxx, and that binding to Pdcd4 stimulates the degradation of Daxx, presumably by disrupting the interaction of Daxx with the de-ubiquitinylating enzyme Hausp. Daxx has previously been shown to serve as a scaffold for protein kinase Hipk2 and tumor suppressor protein p53 and to stimulate the phosphorylation of p53 at serine 46 (Ser-46) in response to genotoxic stress. We show that Pdcd4 also disrupts the Daxx-Hipk2 interaction and inhibits the phosphorylation of p53. We also show that ultraviolet irradiation decreases the expression of Pdcd4. Taken together, our results support a model in which Pdcd4 serves to suppress the phosphorylation of p53 in the absence of DNA damage, while the suppressive effect of Pdcd4 is abrogated after DNA damage owing to the decrease of Pdcd4. Overall, our data demonstrate that Pdcd4 is a novel modulator of Daxx function and provide evidence for a role of Pdcd4 in restraining p53 activity in unstressed cells.
肿瘤抑制蛋白 Pdcd4 是一种核质穿梭蛋白，与多种人类癌症的发生有关。在核内，Pdcd4 通过调节几种转录因子的活性来影响特定基因的转录。我们已经确定 Daxx 蛋白是 Pdcd4 的一种新的相互作用伙伴。Daxx 是一种支架蛋白，在多种过程中发挥作用，包括转录调控、DNA 损伤信号转导、细胞凋亡和染色质重塑。我们表明，两种蛋白质的相互作用是由 Pdcd4 的 N 端结构域和 Daxx 的中心部分介导的，并且与 Pdcd4 的结合刺激了 Daxx 的降解，可能是通过破坏 Daxx 与去泛素化酶 Hausp 的相互作用。先前已经表明，Daxx 作为蛋白激酶 Hipk2 和肿瘤抑制蛋白 p53 的支架，并在应对遗传毒性应激时刺激 p53 在丝氨酸 46（Ser-46）的磷酸化。我们表明，Pdcd4 还破坏了 Daxx-Hipk2 相互作用并抑制了 p53 的磷酸化。我们还表明，紫外线照射会降低 Pdcd4 的表达。总之，我们的结果支持了这样一种模型，即 Pdcd4 在没有 DNA 损伤的情况下抑制 p53 的磷酸化，而在 DNA 损伤后，由于 Pdcd4 的减少，Pdcd4 的抑制作用被消除。总的来说，我们的数据表明 Pdcd4 是 Daxx 功能的一种新型调节剂，并为 Pdcd4 在未受应激的细胞中抑制 p53 活性提供了证据。
