Chang Y-C, Lee H-H, Chen Y-J, Bokoch G M, Chang Z-F
Institute of Biochemistry and Molecular Biology, College of Medicine, National Taiwan University, No. 1 Section 1 Jen-Ai Road, Taipei, Taiwan, ROC.
Cell Death Differ. 2006 Dec;13(12):2023-32. doi: 10.1038/sj.cdd.4401901. Epub 2006 Apr 7.
Phorbol-12-myristate-13-acetate (PMA) treatment induces erythroblastoma D2 cells kept in suspension to undergo RhoA-dependent contraction and to become proapoptotic, while attached cells are induced to differentiate accompanied by the reduction of RhoA activity. In this study, we found that guanine exchange factor H1 (GEF-H1) is highly expressed in D2 cells. Depletion of GEF-H1 expression in D2 cells decreased RhoA activity and prevented PMA-induced contraction and apoptosis. Upon PMA stimulation, GEF-H1 became associated with microtubules in cells that were induced to differentiate. As a contrast, in the proapoptotic population of cells GEF-H1 stayed in the cytoplasm without showing PMA-responsive microtubule translocation. Given that GEF-H1 is inactivated when associated with microtubules and its release into cytosol due to depolymerization of microtubules activates RhoA, our results demonstrated that nonmicrotubule-associated GEF-H1 in D2 cells contributes to the sustained activation of RhoA/ROCK signaling in suspension cells, making cells susceptible to PMA-induced apoptosis.
佛波醇-12-肉豆蔻酸酯-13-乙酸酯（PMA）处理可诱导悬浮培养的成红细胞瘤D2细胞发生RhoA依赖性收缩并变得促凋亡，而贴壁细胞则被诱导分化，同时RhoA活性降低。在本研究中，我们发现鸟嘌呤交换因子H1（GEF-H1）在D2细胞中高表达。D2细胞中GEF-H1表达的缺失降低了RhoA活性，并阻止了PMA诱导的收缩和凋亡。在PMA刺激下，GEF-H1与被诱导分化的细胞中的微管相关。相反，在促凋亡细胞群体中，GEF-H1停留在细胞质中，未显示出对PMA有反应的微管易位。鉴于GEF-H1与微管结合时会失活，并且由于微管解聚而释放到细胞质中会激活RhoA，我们的结果表明，D2细胞中与微管不相关的GEF-H1有助于悬浮细胞中RhoA/ROCK信号的持续激活，使细胞易受PMA诱导的凋亡影响。
