关键词： Chemotaxis   Chemokines   Intracellular receptors   Motor proteins   Cell differentiation   Co-immunoprecipitation   Immunoprecipitation   Actins  

摘要： Background: 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. Conclusions: Our studies indicate that IQGAP1 is a novel essential component of the CXCR2 "chemosynapse".

关键词： IQGAP1   MAPKs   AKT   Heart hypertrophy   Pressure overload  

摘要： Aims The Raf-MEK1/2-ERK1/2 (ERK1/2-extracellular signal-regulated kinases 1/2) signalling cascade is crucial in triggering cardiac responses to different stress stimuli. Scaffold proteins are key elements in coordinating signalling molecules for their appropriate spatiotemporal activation. Here, we investigated the role of IQ motif-containing GTPase-activating protein 1 (IQGAP1), a scaffold for the ERK1/2 cascade, in heart function and remodelling in response to pressure overload. Methods and results IQGAP1-null mice have unaltered basal heart function. When subjected to pressure overload, IQGAP1-null mice initially develop a compensatory hypertrophy indistinguishable from that of wild-type (WT) mice. However, upon a prolonged stimulus, the hypertrophic response develops towards a thinning of left ventricular walls, chamber dilation, and a decrease in contractility, in an accelerated fashion compared with WT mice. This unfavourable cardiac remodelling is characterized by blunted reactivation of the foetal gene programme, impaired cardiomyocyte hypertrophy, and increased cardiomyocyte apoptosis. Analysis of signalling pathways revealed two temporally distinct waves of both ERK1/2 and AKT phosphorylation peaking, respectively, at 10 min and 4 days after aortic banding in WT hearts. IQGAP1-null mice show strongly impaired phosphorylation of MEK1/2-ERK1/2 and AKT following 4 days of pressure overload, but normal activation of these kinases after 10 min. Pull-down experiments indicated that IQGAP1 is able to bind the three components of the ERK cascade, namely c-Raf, MEK1/2, and ERK1/2, as well as AKT in the heart. Conclusion These data demonstrate, for the first time, a key role for the scaffold protein IQGAP1 in integrating hypertrophy and survival signals in the heart and regulating long-term left ventricle remodelling upon pressure overload.

关键词： Protein 4.1R   IQGAP1   Cell migration  

摘要： In red blood cells, multifunctional protein 4.1R stabilizes the spectrin-actin network and anchors it to the plasma membrane. To contribute to the characterization of functional roles of 4.1R in nonerythroid cells, we have analyzed the participation of protein 4.1R in cell migration. The distribution of endogenous 4.1R is polarized towards the leading edge of migrating cells. Exogenous 4.1R isoforms containing a complete membrane-binding domain consistently localized to plasma membrane extensions enriched in F-actin. Silencing of 4.1R caused the loss of persistence of migration in subconfluent cells and of directional migration in cells moving into a wound. Coimmunoprecipitation and pull-down assays identified the scaffold protein IQGAP1 as a partner for protein 4.1R and showed that the 4.1R membrane-binding domain is involved in binding IQGAP1. Importantly, we show that protein 4.1R is necessary for the localization of IQGAP1 to the leading edge of cells migrating into a wound, whereas IQGAP1 is not required for protein 4.1R localization. Collectively, our results indicate a crucial role for protein 4.1R in cell migration and in the recruitment of the scaffold protein IQGAP1 to the cell front.

摘要： Studies in patient samples and in cell culture suggest inhibiting IQGAP1 could help treat Herceptin trastuzumab–resistant, HER2-positive breast cancer.

关键词： Ventral body wall defects   IQGAP1   Rac1   Cdc42   Chick embryo  

摘要： Cadmium (Cd) induces ventral body wall defects (VBWD) in the chick embryo, with adherens junctions (AJs) breakdown at 4h post treatment (4H). Signalling by which Cd disrupts AJs in this model remains unclear. IQGAP1 regulates AJs via binding to Cdc42 and Rac1, Rho-family GTPases. Activation of IQGAP1-Cdc42 interaction regulates AJs positively, whereas Rac1 activation inhibits AJs. We hypothesised that IQGAP1 and Cdc42 are downregulated and Rac1 is upregulated during embryogenesis in the Cd chick model. Chick embryos were explanted and treated with saline or Cd after 60 h incubation. Chicks were harvested at 1H, 4H and 8H post treatment and RT-PCR and immunohistochemistry were performed. Gene expression levels of IQGAP1 and Cdc42 were significantly downregulated and Rac1 was upregulated in Cd group compared to controls only at 4H. Immunoreactivity of IQGAP1 and Cdc42 was also markedly decreased, whereas Rac1 was increased in Cd group compared to controls at 4H. Alteration of IQGAP and Rho-family GTPases may cause VBWD in Cd chick model by inducing the dissociation of cadherin-mediated AJs. (C) 2011 Elsevier Inc. All rights reserved.

关键词： RhoC   IQGAP1   gastric cancer cell   migration  

摘要： The scaffold protein IQGAP1 is closely related to certain Rho GTPases. Research has revealed that IQGAP1 acts as an effector of Cdc42 and Rac1 in the regulation of cell activity such as proliferation and migration. However, whether IQGAP1 is associated with RhoC, another important Rho GTPase, is unclear. Previous results from our laboratory indicated that IQGAP1 and RhoC are highly expressed in gastric cancer tissues and cells. This study was designed to investigate the possible interaction between IQGAP1 and RhoC in the regulation of the migration of cancer cells. The expression of IQGAP1 and RhoC in gastric cancer tissues and cell lines was detected by Western blotting. siRNAs targeting IQGAP1 or RhoC were transfected into gastric cancer cells to knock down the expression of the proteins. Adenoviral constructs encoding full length IQGAP1, the C-terminal fragment of IQGAP1, and the constitutively active RhoC gene were used to infect gastric cancer cells to increase the expression of the proteins. The migratory activity of a gastric cancer cell line was measured by a transwell migration assay. Western blotting revealed that the IQGAP1 and RhoC proteins were highly expressed in gastric cancer tissues and cells. Spearman's rank correlation analysis indicated that the increases in the expression of IQGAP1 and RhoC were closely correlated. The transwell migration assay revealed that both IQGAP1 and RhoC stimulated the migration activity of the gastric cancer cell line AGS. The knockdown of IQGAP1 expression by siRNA blocked the migration-stimulating activity of RhoC, while the knockdown of RhoC expression had no effect on the migration-stimulatory activity of IQGAP1. Co-IP results showed that RhoC and IQGAP1 bound to each other. These results reveal a previously unrecognized interaction between IQGAP1. and RhoC, and demonstrate that IQGAP1 is a downstream effector of RhoC in the regulation of the migration activity of gastric cancer cells.

摘要： General or brain-region-specific decreases in spine number or morphology accompany major neuropsychiatric disorders. It is unclear, however, whether changes in spine density are specific for an individual mental process or disorder and, if so, which molecules confer such specificity. Here we identify the scaffolding protein IQGAP1 as a key regulator of dendritic spine number with a specific role in cognitive but not emotional or motivational processes. We show that IQGAP1 is an important component of NMDAR multiprotein complexes and functionally interacts with the NR2A subunits and the extracellular signal-regulated kinase 1 (ERK1) and ERK2 signaling pathway. Mice lacking the IQGAP1 gene exhibited significantly lower levels of surface NR2A and impaired ERK activity compared to their wild-type littermates. Accordingly, primary hippocampal cultures of IQGAP1(-/-) neurons exhibited reduced surface expression of NR2A and disrupted ERK signaling in response to NR2A-dependent NMDAR stimulation. These molecular changes were accompanied by region-specific reductions of dendritic spine density in key brain areas involved in cognition, emotion, and motivation. IQGAP1 knockouts exhibited marked long-term memory deficits accompanied by impaired hippocampal long-term potentiation (LTP) in a weak cellular learning model;in contrast, LTP was unaffected when induced with stronger stimulation paradigms. Anxiety-and depression-like behavior remained intact. On the basis of these findings, we propose that a dysfunctional IQGAP1 gene contributes to the cognitive deficits in brain disorders characterized by fewer dendritic spines.

关键词： Aurora-A   骨架蛋白   稳定性   酶蛋白   GTPase  

摘要： 目的：IQGAP1是IQGAPs（IQ motif containing GTPase activating proteins）家族中的一员，

关键词： IQGAP1蛋白   肿瘤  

摘要： IQGAP1是一种能结合多种信号分子及结构分子的骨架蛋白。通过与目的蛋白相互作用，参与信号通路的整合和细胞功能的调节。越来越多的研究发现，IQGAP1可通过促进细胞增殖和转化，降低细胞黏附性以及刺激细胞活动性和侵袭性而在肿瘤的发生发展中扮演重要角色。

关键词： MAP Kinases (MAPKs)   Mass Spectrometry (MS)   Protein Phosphorylation   Receptor Regulation   Receptor Tyrosine Kinase  

摘要： Cellular responses produced by EGF are mediated through the receptor (EGFR) and by various enzymes and scaffolds. Recent studies document IQGAP1 as a scaffold for the MAPK cascade, binding directly to B-Raf, MEK, and ERK and regulating their activation in response to EGF. We previously showed that EGF is unable to activate B-Raf in cells lacking IQGAP1. However, the mechanism by which IQGAP1 links B-Raf to EGFR was unknown. Here we report that endogenous EGFR and IQGAP1 co-localize and co-immunoprecipitate in cells. EGF has no effect on the association, but Ca2+ attenuates binding. In vitro analysis demonstrated a direct association mediated through the IQ and kinase domains of IQGAP1 and EGFR, respectively. Calmodulin disrupts this interaction. Using a mass spectrometry-based assay, we show that EGF induces phosphorylation of IQGAP1 Ser(1443), a residue known to be phosphorylated by PKC. This phosphorylation is eliminated by pharmacological inhibition of either EGFR or PKC and transfection with small interfering RNA directed against the PKC alpha isoform. In IQGAP1-null cells, EGF-stimulated tyrosine phosphorylation of EGFR is severely attenuated. Normal levels of autophosphorylation are restored by reconstituting wild type IQGAP1 and enhanced by an IQGAP1 S1443D mutant. Collectively, these data demonstrate a functional interaction between IQGAP1 and EGFR and suggest that IQGAP1 modulates EGFR activation.