Regulation of the Rac1-specific exchange factor Tiam1 involves both phosphoinositide 3-kinase-dependent and -independent components
Regulation of the Rac1-specific exchange factor Tiam1 involves both phosphoinositide 3-kinase-dependent and -independent components
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DOI：
10.1042/0264-6021:3510173
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发表时间：
2000-10-01
影响因子：
4.1
通讯作者：
Downes, CP
中科院分区：
文献类型：
--
作者：
Fleming, IN;Gray, A;Downes, CP
小 GTP 酶 Rac1 参与调节膜褶皱、基因转录、细胞周期进程和细胞转化，其中一些事件可被磷酸肌醇 3-激酶 (PI 3-激酶) 抑制剂阻断。此外，Rac1可以被几种鸟嘌呤核苷酸交换因子激活，从而促进GDP的释放。因此，我们研究了 PI 3-激酶脂质产品调节 Rac1 特异性交换因子 Tiam1 的能力。 Tiam1 与多磷酸化肌醇脂质的结合顺序为 PtdIns(3,4,5)P-3 > PtdIns-(3,4)P-2 远大于 PtdIns(4,5)P-2，这种结合可归因于 N 末端普莱克斯特林同源 (N-PH) 结构域。 PtdIns(3,4,5)P-3 和 PtdIns(3,4)P-2 均增强 Tiam1 鸟嘌呤核苷酸交换活性，但 PtdIns(4,5)P 没有作用。组成型活性 PI 3 激酶与 Tiam1 的共表达增加了体内 GTP 结合的 Rac1 的量，这一反应需要 Tiam1 的 N-PH 结构域。 Tiam1 的异位表达引起了 Swiss 3T3 细胞的膜波纹，该细胞的特征是渥曼青霉素敏感和不敏感成分，分别需要 Tiam1 的 N-PH 结构域和 C 端 PH 结构域。这些结果揭示了 Tiam1 依赖性 Racl 功能调节的新方面。
The small GTPase Rac1 is involved in regulating membrane ruffling, gene transcription,cell-cycle progression and cell transformation, and some of these events are blocked by inhibitors of phosphoinositide 3-kinase (PI 3-kinase). Moreover, Rac1 can be activated by several guanine nucleotide exchange factors, which facilitate the release of GDP. We therefore investigated the ability of PI 3-kinase lipid products to regulate Tiam1, a Rac1-specific exchange factor. Tiam1 bound to polyphosphorylated inositol lipids in the rank order PtdIns(3,4,5)P-3 > PtdIns-(3,4)P-2 much greater than PtdIns(4,5)P-2, and this binding could be attributed to the N-terminal pleckstrin-homology (N-PH) domain. Both PtdIns(3,4,5)P-3 and PtdIns(3,4)P-2 enhanced Tiam1 guanine nucleotide exchange activity in vitro, but PtdIns(4,5)P, had no effect. Co-expression of a constitutively active PI 3-kinase with Tiam1 increased the amount of GTP-bound Rac1 in vivo, a response which required the N-PH domain of Tiam1. Ectopic expression of Tiam1 caused membrane ruffling in Swiss 3T3 cells that was characterized by wortmannin-sensitive and -insensitive components, which required the N-PH domain and the C-terminal PH domain of Tiam1 respectively. These results reveal novel facets of Tiam1-dependent regulation of Racl function.