Ewings Katherine E, Hadfield-Moorhouse Kathryn, Wiggins Ceri M, Wickenden Julie A, Balmanno Kathryn, Gilley Rebecca, Degenhardt Kurt, White Eileen, Cook Simon J
Laboratory of Molecular Signalling, The Babraham Institute, Babraham Research Campus, Cambridge, UK.
EMBO J. 2007 Jun 20;26(12):2856-67. doi: 10.1038/sj.emboj.7601723. Epub 2007 May 24.
The proapoptotic protein Bim is expressed de novo following withdrawal of serum survival factors. Here, we show that Bim-/- fibroblasts and epithelial cells exhibit reduced cell death following serum withdrawal in comparison with their wild-type counterparts. In viable cells, Bax associates with Bcl-2, Bcl-x(L) and Mcl-1. Upon serum withdrawal, newly expressed Bim(EL) associates with Bcl-x(L) and Mcl-1, coinciding with the dissociation of Bax from these proteins. Survival factors can prevent association of Bim with pro-survival proteins by preventing Bim expression. However, we now show that even preformed Bim(EL)/Mcl-1 and Bim(EL)/Bcl-x(L) complexes can be rapidly dissociated following activation of ERK1/2 by survival factors. The dissociation of Bim from Mcl-1 is specific for Bim(EL) and requires ERK1/2-dependent phosphorylation of Bim(EL) at Ser(65). Finally, ERK1/2-dependent dissociation of Bim(EL) from Mcl-1 and Bcl-x(L) may play a role in regulating Bim(EL) degradation, since mutations in the Bim(EL) BH3 domain that disrupt binding to Mcl-1 cause increased turnover of Bim(EL). These results provide new insights into the role of Bim in cell death and its regulation by the ERK1/2 survival pathway.
促凋亡蛋白Bim在血清存活因子撤除后重新表达。在此，我们发现与野生型成纤维细胞和上皮细胞相比，Bim基因敲除的成纤维细胞和上皮细胞在血清撤除后细胞死亡减少。在存活细胞中，Bax与Bcl-2、Bcl-x(L)和Mcl-1结合。血清撤除后，新表达的Bim(EL)与Bcl-x(L)和Mcl-1结合，同时Bax从这些蛋白上解离。存活因子可通过阻止Bim表达来防止Bim与促存活蛋白结合。然而，我们现在发现，即使是预先形成的Bim(EL)/Mcl-1和Bim(EL)/Bcl-x(L)复合物，在存活因子激活ERK1/2后也能迅速解离。Bim从Mcl-1上的解离对Bim(EL)具有特异性，并且需要ERK1/2依赖的Bim(EL)在Ser(65)位点的磷酸化。最后，ERK1/2依赖的Bim(EL)从Mcl-1和Bcl-x(L)上的解离可能在调节Bim(EL)降解中起作用，因为Bim(EL) BH3结构域中破坏与Mcl-1结合的突变会导致Bim(EL)周转增加。这些结果为Bim在细胞死亡中的作用及其受ERK1/2存活途径调控提供了新的见解。
