Department of Veterans Affairs, Nashville, Tennessee, United States of America.
PLoS One. 2011;6(8):e23813. doi: 10.1371/journal.pone.0023813. Epub 2011 Aug 18.
Chemotaxis is essential for a number of physiological processes including leukocyte recruitment. Chemokines initiate intracellular signaling pathways necessary for chemotaxis through binding seven transmembrane G protein-couple receptors. Little is known about the proteins that interact with the intracellular domains of chemokine receptors to initiate cellular signaling upon ligand binding. CXCR2 is a major chemokine receptor expressed on several cell types, including endothelial cells and neutrophils. We hypothesize that multiple proteins interact with the intracellular domains of CXCR2 upon ligand stimulation and these interactions comprise a "chemosynapse", and play important roles in transducing CXCR2 mediated signaling processes.
METHODOLOGY/PRINCIPAL FINDINGS: In an effort to define the complex of proteins that assemble upon CXCR2 activation to relay signals from activated chemokine receptors, a proteomics approach was employed to identify proteins that co-associate with CXCR2 with or without ligand stimulation. The components of the CXCR2 "chemosynapse" are involved in processes ranging from intracellular trafficking to cytoskeletal modification. IQ motif containing GTPase activating protein 1 (IQGAP1) was among the novel proteins identified to interact directly with CXCR2. Herein, we demonstrate that CXCR2 co-localizes with IQGAP1 at the leading edge of polarized human neutrophils and CXCR2 expressing differentiated HL-60 cells. Moreover, amino acids 1-160 of IQGAP1 directly interact with the carboxyl-terminal domain of CXCR2 and stimulation with CXCL8 enhances IQGAP1 association with Cdc42.
Our studies indicate that IQGAP1 is a novel essential component of the CXCR2 "chemosynapse".
趋化作用对于许多生理过程是必不可少的，包括白细胞募集。趋化因子通过与七个跨膜 G 蛋白偶联受体结合，启动细胞内信号通路，从而引发趋化作用。关于与趋化因子受体细胞内结构域相互作用的蛋白质，在配体结合时启动细胞信号，目前知之甚少。CXCR2 是多种细胞类型（包括内皮细胞和中性粒细胞）表达的主要趋化因子受体。我们假设，配体刺激后，多个蛋白质与 CXCR2 的细胞内结构域相互作用，这些相互作用构成了一个“化学突触”，并在传递 CXCR2 介导的信号转导过程中发挥重要作用。
方法/主要发现：为了确定配体刺激后组装在 CXCR2 上的蛋白质复合物，以传递激活的趋化因子受体信号，我们采用蛋白质组学方法来鉴定与 CXCR2 结合或不结合配体刺激时共结合的蛋白质。CXCR2“化学突触”的组成部分涉及从细胞内运输到细胞骨架修饰的过程。含有 IQ 基序的 GTP 酶激活蛋白 1（IQGAP1）是与 CXCR2 直接相互作用的新蛋白质之一。在此，我们证明 CXCR2 与极化人中性粒细胞和表达 CXCR2 的 HL-60 细胞的极化细胞的前缘中的 IQGAP1 共定位。此外，IQGAP1 的氨基酸 1-160 直接与 CXCR2 的羧基末端结构域相互作用，并且 CXCL8 的刺激增强了 IQGAP1 与 Cdc42 的关联。
我们的研究表明，IQGAP1 是 CXCR2“化学突触”的一个新的必需组成部分。
