Erickson J W, Cerione R A, Hart M J
Department of Pharmacology, College of Veterinary Medicine, Cornell University, Ithaca, New York 14853-6401, USA.
J Biol Chem. 1997 Sep 26;272(39):24443-7. doi: 10.1074/jbc.272.39.24443.
The Rho subfamily of low molecular weight GTPases have been implicated in a variety of cellular functions that include reorganization of the actin cytoskeleton and stress-induced activation of the c-Jun kinase. The downstream targets that mediate the effects of Cdc42 on the actin cytoskeleton have yet to be fully identified. We have used the transient transfection of COS-7 cells with epitope-tagged Cdc42 to identify candidate signaling partners for this GTPase and identified the IQGAP protein as a major in vivo target for activated Cdc42. Epidermal growth factor stimulation of serum-starved COS-7 cells promoted the formation of a Cdc42-IQGAP complex, indicating that growth factors can increase the pool of activated Cdc42. Activated HA-Cdc42 co-localized with IQGAP or F-actin in vivo, whereas cells transfected with dominant-negative forms of Cdc42 (Cdc42(T17N)) showed predominantly dispersed distributions for both HA-Cdc42 and endogenous IQGAP. In detergent lysates from COS-7 cells transiently transfected with different forms of Cdc42, or from stably transfected CHO cells, the induction of actin polymerization by phalloidin resulted in the incorporation of both IQGAP and Cdc42 into actin-containing complexes. Taken together, these findings are consistent with a model whereby IQGAP serves as a target for GTP-bound Cdc42 providing a direct link between the activated GTPase and the actin cytoskeleton.
低分子量GTP酶的Rho亚家族与多种细胞功能有关，包括肌动蛋白细胞骨架的重组以及应激诱导的c-Jun激酶激活。介导Cdc42对肌动蛋白细胞骨架作用的下游靶点尚未完全确定。我们通过用表位标记的Cdc42瞬时转染COS-7细胞来鉴定该GTP酶的候选信号转导伙伴，并确定IQGAP蛋白是活化Cdc42在体内的主要靶点。对血清饥饿的COS-7细胞进行表皮生长因子刺激促进了Cdc42-IQGAP复合物的形成，表明生长因子可增加活化Cdc42的数量。活化的HA-Cdc42在体内与IQGAP或F-肌动蛋白共定位，而用显性负性形式的Cdc42（Cdc42(T17N)）转染的细胞中，HA-Cdc42和内源性IQGAP均主要呈分散分布。在用不同形式的Cdc42瞬时转染的COS-7细胞的去污剂裂解物中，或在稳定转染的CHO细胞的去污剂裂解物中，鬼笔环肽诱导的肌动蛋白聚合导致IQGAP和Cdc42均掺入含肌动蛋白的复合物中。综上所述，这些发现与一种模型一致，即IQGAP作为GTP结合的Cdc42的靶点，在活化的GTP酶和肌动蛋白细胞骨架之间提供了直接联系。
