Dai Mu-Shui, Lu Hua
Department of Biochemistry and Molecular Biology, School of Medicine, Oregon Health & Science University, Portland, Oregon 97201, USA.
J Biol Chem. 2004 Oct 22;279(43):44475-82. doi: 10.1074/jbc.M403722200. Epub 2004 Aug 11.
The oncoprotein MDM2 associates with ribosomal proteins L5, L11, and L23. Both L11 and L23 have been shown to activate p53 by inhibiting MDM2-mediated p53 suppression. Here we have shown that L5 also activates p53. Overexpression of L5 stabilized ectopic p53 in H1299 cells and endogenous p53 in U2OS cells. Consequently, L5 enhanced p53 transcriptional activity and induced p53-dependent G1 cell cycle arrest. Furthermore, like L11 and L23, L5 also remarkably inhibited MDM2-mediated p53 ubiquitination. The interaction of L5 with MDM2 was also enhanced by treatment with a low dose of actinomycin D. Actinomycin D-induced p53 was inhibited by small interference RNA against L5. By reciprocal co-immunoprecipitation, we further showed that there were at least two MDM2-ribosomal protein complexes in cells: MDM2-L5-L11-L23 and p53-MDM2-L5-L11-L23. We propose that the MDM2-L5-L11-L23 complex functions to inhibit MDM2-mediated p53 ubiquitination and thus activates p53.
癌蛋白MDM2与核糖体蛋白L5、L11和L23相关联。L11和L23均已被证明可通过抑制MDM2介导的p53抑制作用来激活p53。在此我们证明L5也能激活p53。L5的过表达使H1299细胞中的异位p53以及U2OS细胞中的内源性p53稳定。因此，L5增强了p53转录活性并诱导p53依赖的G1期细胞周期停滞。此外，与L11和L23一样，L5也显著抑制MDM2介导的p53泛素化。低剂量放线菌素D处理也增强了L5与MDM2的相互作用。针对L5的小干扰RNA可抑制放线菌素D诱导的p53。通过相互免疫共沉淀，我们进一步表明细胞中至少存在两种MDM2-核糖体蛋白复合物：MDM2-L5-L11-L23和p53-MDM2-L5-L11-L23。我们提出MDM2-L5-L11-L23复合物的功能是抑制MDM2介导的p53泛素化，从而激活p53。
