Department of Pathophysiology, Beijing Institute of Basic Medical Sciences, 27 Taiping Road, Beijing 100850, PR China.
Nucleic Acids Res. 2013 May 1;41(10):5210-22. doi: 10.1093/nar/gkt223. Epub 2013 Apr 5.
The stress-responding protein, GADD45α, plays important roles in cell cycle checkpoint, DNA repair and apoptosis. In our recent study, we demonstrate that GADD45α undergoes a dynamic ubiquitination and degradation in vivo, which process can be blocked by the cytotoxic reagent, arsenite, resulting in GADD45α accumulation to activate JNKs cell death pathway, thereby revealing a novel mechanism for the cellular GADD45α functional regulation. But the factors involved in GADD45α stability modulations are unidentified. Here, we demonstrated that MDM2 was an E3 ubiquitin ligase for GADD45α. One of MDM2-binding partner, ribosomal protein S7, interacted with and stabilized GADD45α through preventing the ubiquitination and degradation of GADD45α mediated by MDM2. This novel function of S7 is unrelated to p53 but seems to depend on S7/MDM2 interaction, for the S7 mutant lacking MDM2-binding ability lost its function to stabilize GADD45α. Further investigations indicated that arsenite treatment enhanced S7-MDM2 interaction, resulting in attenuation of MDM2-dependent GADD45α ubiquitination and degradation, thereby leading to GADD45α-dependent cell death pathway activation. Silencing S7 expression suppressed GADD45α-dependent cytotoxicity induced by arsenite. Our findings thus identify a novel function of S7 in control of GADD45α stabilization under both basal and stress conditions and its significance in mediating arsenite-induced cellular stress.
应激反应蛋白 GADD45α 在细胞周期检测点、DNA 修复和细胞凋亡中发挥重要作用。在我们最近的研究中，我们证明 GADD45α 在体内经历动态泛素化和降解，该过程可被细胞毒性试剂亚砷酸盐阻断，导致 GADD45α 积累并激活 JNKs 细胞死亡途径，从而揭示了细胞 GADD45α 功能调节的新机制。但是，参与 GADD45α 稳定性调节的因素尚不清楚。在这里，我们证明了 MDM2 是 GADD45α 的 E3 泛素连接酶。MDM2 的一个结合伙伴核糖体蛋白 S7 通过防止 GADD45α 被 MDM2 介导的泛素化和降解，与 GADD45α 相互作用并稳定 GADD45α。S7 的这种新功能与 p53 无关，但似乎依赖于 S7/MDM2 相互作用，因为缺乏 MDM2 结合能力的 S7 突变体丧失了稳定 GADD45α 的功能。进一步的研究表明，亚砷酸盐处理增强了 S7-MDM2 相互作用，导致 MDM2 依赖性 GADD45α 泛素化和降解减弱，从而导致 GADD45α 依赖性细胞死亡途径激活。沉默 S7 表达可抑制亚砷酸盐诱导的 GADD45α 依赖性细胞毒性。我们的研究结果因此确定了 S7 在控制基础和应激条件下 GADD45α 稳定方面的新功能，以及其在介导亚砷酸盐诱导的细胞应激中的重要性。
