IQGAP1 binds Rap1 and modulates its activity
IQGAP1 binds Rap1 and modulates its activity
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DOI：
10.1074/jbc.m700487200
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发表时间：
2007-07-13
影响因子：
4.8
通讯作者：
Sacks, David B.
中科院分区：
文献类型：
--
作者：
Jeong, Ha-Won;Li, Zhigang;Sacks, David B.
IQGAP1是一种参与多种基本细胞活动的支架蛋白，包括转录、细胞-细胞附着和细胞骨架调控。为了在这些途径中发挥作用，IQGAP1与许多蛋白质相关，如肌动蛋白、钙调蛋白、E-cadherin、β -连环蛋白、CLIP-170和丝裂原活化蛋白激酶途径的成分。此外，IQGAP1与活性Cdc42和Rac1结合，而不与RhoA或Ras结合。这里我们发现IQGAP1也与小GTPase Rap1结合。体外分析表明，Rap1与IQGAP1之间存在直接相互作用，并通过Rap1的激活（GTP加载）增强了这种相互作用。Cdc42不调节Rap1和IQGAP1之间的相互作用。相反，在Ca2+存在和不存在的情况下，这种关联被钙调素消除。Rap1与不能与钙调素相互作用的点突变型IQGAP1的结合量是野生型IQGAP1的2.5倍。与这些发现一致，Rap1结合到IQGAP1的IQ区域。共聚焦显微镜显示，Rap1和IQGAP1共定位于人上皮细胞的外周，而不在细胞质中。这种相互作用具有功能性后遗症。过表达IQGAP1可显著降低Rap1粘附介导的激活。此外，在过表达IQGAP1的细胞中，cAMP对Rap1的激活减弱，而在缺乏IQGAP1的细胞中，cAMP对Rap1的激活增强。这些发现表明，IQGAP1与Rap1的相互作用在几个方面不同于它与其他小GTPases的相互作用。此外，我们的数据表明IQGAP1可能连接钙调素和Rap1信号通路。
IQGAP1 is a scaffolding protein involved in multiple fundamental cellular activities, including transcription, cell-cell attachment, and regulation of the cytoskeleton. To function in these pathways, IQGAP1 associates with numerous proteins such as actin, calmodulin, E-cadherin, beta-catenin, CLIP-170, and components of the mitogen-activated protein kinase pathway. Moreover, IQGAP1 binds to active Cdc42 and Rac1 but not RhoA or Ras. Here we show that IQGAP1 also binds to the small GTPase Rap1. In vitro analysis demonstrates a direct interaction between Rap1 and IQGAP1, which is augmented by activation (GTP loading) of Rap1. Cdc42 does not modulate the interaction between Rap1 and IQGAP1. In contrast, the association is eliminated by calmodulin both in the absence and presence of Ca2+. The binding of Rap1 to a point mutant IQGAP1 construct that is unable to interact with calmodulin is 2.5-fold more than to wild type IQGAP1. Consistent with these findings, Rap1 binds to the IQ region of IQGAP1. Confocal microscopy demonstrates that Rap1 and IQGAP1 co-localize at the periphery of human epithelial cells but not in the cytoplasm. The interaction has functional sequelae. Overexpression of IQGAP1 substantially reduces adhesion-mediated activation of Rap1. In addition, Rap1 activation by cAMP is attenuated in cells that overexpress IQGAP1 and enhanced in cells lacking IQGAP1. These findings reveal that the interaction of IQGAP1 with Rap1 differs in several respects from its interaction with other small GTPases. Furthermore, our data suggest that IQGAP1 may link the calmodulin and Rap1 signaling pathways.