关键词： IQGAP1   ovarian carcinoma   cell adhesion   cytoskeleton   tumor invasion   metastasis  

摘要： IQGAP1 is a multifunctional protein involved in actin cytoskeleton assembly and E-cadherin-mediated cell adhesion. To determine the role of IQGAP1 in ovarian tumors, we evaluated IQGAP1 expression by immunohistochemistry in 17 adenomas, 30 borderline tumors and 80 adenocarcinomas and its relation with patient survival. IQGAP1 was overexpressed in adenocarcinomas compared with adenomas and borderline tumors. Enhanced immunostaining in invasive tumor fronts was categorized as focal or diffuse. The diffuse expression pattern correlated with high histological grade and clinicopathological stages. IQGAP1 overexpression and diffuse invasion pattern were significantly associated with poor prognosis by multivariate analysis. Our findings suggest the involvement of IQGAP1 in the progression and spread of ovarian adenocarcinomas. Overexpression and diffuse expression pattern of IQGAP1 are potentially useful independent molecular predictors of highly aggressive ovarian carcinomas. (c) 2005 Elsevier Ireland Ltd. All rights reserved.

关键词： growth factor   IQGAP1   kinase suppressor of Ras (KSR)   mitogen-activated protein kinase (MAPK)   mitogen-activated protein kinase/extracellular-signal-regulated kinase kinase (MEK)   scaffold  

摘要： Signal transduction networks allow cells to recognize and respond to changes in the extracellular environment. All eukaryotic cells have MAPK (mitogen-activated protein kinase) pathways that participate in diverse cellular functions, including differentiation, survival, transformation and movement. Five distinct groups of MAPKs have been characterized in mammals, the most extensively studied of which is the Ras/Raf/MEK [MAPK/ERK (extracellular-signal-regulated kinase) kinase]/ERK cascade. Numerous stimuli, including growth factors and phorbol esters, activate MEK/ERK signalling. How disparate extracellular signals are translated by MEK/ERK into different cellular functions remains obscure. originally identified in yeast, scaffold proteins are now recognized to contribute to the specificity of MEK/ERK pathways in mammalian cells. These scaffolds include KSR (kinase suppressor of Ras), beta-arrestin, MEK partner-1, Sef and IQGAP1. Scaffolds organize multiprotein signalling complexes. This targets MEK/ERK to specific substrates and facilitates communication with other pathways, thereby mediating diverse functions. The adaptor proteins regulate the kinetics, amplitude and localization of MEK/ERK signalling, providing an efficient mechanism that enables an individual extracellular stimulus to promote a specific biological response.

摘要： The accurate identification and thorough characterization of tumorigenic cells in glioblastomas are essential to enhance our understanding of their malignant behavior and for the design of strategies that target this important cell population. We report here that, in rat brain, the scaffolding protein IQGAP1 is a marker of brain nestin(+) amplifying neural progenitor cells. In a rat model of glioma, IQGAP1 also characterizes a subpopulation of nestin(+) amplifying tumor cells in glioblastoma-like tumors but not in tumors with oligodendroglioma features. We next confirmed that IQGAP1 represents a new marker that may help to discriminate human glioblastoma from oligodendrogliomas. In human glioblastoma exclusively, IQGAP1 specifies a subpopulation of amplifying nestin(+) cancer cells. Neoplastic IQGAP1(+) cells from glioblastoma can be expanded in culture and possess all the characteristics of cancer stem-like progenitors. The similarities between amplifying neural progenitors and glioblastoma amplifying cancer cells may have significant implications for understanding the biology of glioblastoma.

关键词： angiogenesis   cell-cell adherions   IQGAP1   reactive oxygen species   vascular endothelial growth factor   VE-cadherin  

摘要： Objective - Vascular endothelial growth factor ( VEGF) induces angiogenesis by stimulating reactive oxygen species ( ROS) production primarily through the VEGF receptor-2 ( VEGFR2). One of the initial responses in established vessels to stimulate angiogenesis is loss of vascular endothelial ( VE)- cadherin - based cell - cell adhesions;however, little is known about the underlying mechanisms. IQGAP1 is a novel VEGFR2 binding protein, and it interacts directly with actin, cadherin, and beta- catenin, thereby regulating cell motility and morphogenesis. Methods and Results - Confocal microscopy analysis shows that IQGAP1 colocalizes with VE-cadherin at cell - cell contacts in unstimulated human endothelial cells (ECs). VEGF stimulation reduces staining of IQGAP1 and VE-cadherin at the adherens junction without affecting interaction of these proteins. Knockdown of IQGAP1 using siRNA inhibits localization of VE-cadherin at cell - cell contacts, VEGF-stimulated recruitment of VEGFR2 to the VE- cadherin/ beta- catenin complex, ROS- dependent tyrosine phosphorylation of VE- cadherin, which is required for loss of cell - cell contacts and capillary tube formation. IQGAP1 expression is increased in a mouse hindlimb ischemia model of angiogenesis. Conclusions - IQGAP1 is required for establishment of cell - cell contacts in quiescent ECs. To induce angiogenesis, it may function to link VEGFR2 to the VE- cadherin containing adherens junctions, thereby promoting VEGF-stimulated, ROS- dependent tyrosine phosphorylation of VE- cadherin and loss of cell - cell contacts.

摘要： Maintenance of 01 integrin-mediated cell adhesion in quiescent human mammary epithelial (HME) cells requires protein phosphatase (PP) 2A for not only dephosphorylation of beta 1 integrin but also recruitment of IQGAP1 to Rac-bound beta 1 integrin. However, how PP2A-dependent regulatory machinery of cell adhesion responds to EGF remains to be elucidated. We report here that phosphorylated Ca2+/calmodulin-dependent protein kinase II(CaMKII) at threonine 286 was involved in the beta 1 integrin complex that consisted of PP2A, Rac, and IQGAP1 in quiescent HME cells. Stimulation of the cells with EGF concomitantly induced an increase in intracellular Ca2+, activation of CaMKII, and dissociation of PP2A-IQGAP1-CaMKII from beta 1 integrin-Rac. Because the activation of CaMKII and dissociation of PP2A-IQGAP1-CaMKII were blocked by either Ca2+-chelator or CaMKII inhibitor, we therefore propose that EGF has the ability to abrogate the PP2A function in the maintenance of P1 integrin-mediated cell adhesion by dissociation of PP2A-IQGAP1-CaMKII from beta 1 integrin-Rac through activation of CaMKII.

摘要： Ischemia-reperfusion injury (IRI) represents a major determinant of liver transplantation. IRI-induced graft dysfunction is related to biliary damage, partly due to a loss of bile canaliculi (BC) integrity associated with a dramatic remodeling of actin cytoskeleton. However, the molecular mechanisms associated with these events remain poorly characterized. Using liver biopsies collected during the early phases of organ procurement (ischemia) and transplantation (reperfusion), we characterized the global patterns of expression and phosphorylation of cytoskeleton-related proteins during hepatic IRI. This targeted functional proteomic approach, which combined protein expression pattern profiling and phosphoprotein enrichment followed by mass spectrometry analysis, allowed us to identify IQGAP1, a Cdc42/Rac1 effector, as a potential regulator of actin cytoskeleton remodeling and maintenance of BC integrity. Cell fractionation and immunohistochemistry revealed that IQGAP1 expression and localization were affected upon IRI and related to actin reorganization. Furthermore using an IRI model in human hepatoma cells, we demonstrated that IQGAP1 silencing decreased the basal level of actin polymerization at BC periphery, reflecting a defect in BC structure coincident with reduced cellular resistance to IRI. In summary, this study uncovered new mechanistic insights into the global regulation of IRI-induced cytoskeleton remodeling and led to the identification of IQGAP1 as a regulator of BC structure. IQGAP1 therefore represents a potential target for the design of new organ preservation strategies to improve transplantation outcome.

摘要： IQGAP1 was identified in 1994 as a widely expressed IQ domain-containing protein with a region containing sequence similarity to the Ras GTPase-activating proteins. IQGAP1 has roles in many different aspects of cell physiology and interacts with numerous proteins. It modulates the actin cytoskeleton through Rac1 and Cdc42, and cell-cell adhesion through E-cadherin and beta-catenin. It also regulates the mitogen activated protein kinase pathway, which influences cell proliferation and differentiation. Evidence suggests that IQGAP1 is a scaffold protein that links components of signaling cascades. Here, we evaluate recent data that identify the participation of IQGAP1 in signaling networks and we illustrate how this influences diverse cellular functions. These findings suggest that IQGAP1 integrates signaling pathways and coordinates several fundamental cellular activities.

摘要： Serine/threonine protein phosphatase (PP) 2A regulates many biological processes, however it remains unclear whether PP2A participates in cadherin-mediated cell-cell adhesion. We show here that the core enzyme of PP2A (PP2A-AC) is localized in the cell-cell adhesion sites between adjacent cells and associated with the E-cadherin-catenins complex in non-malignant human mammary epithelial (HME) cells at confluence. Treatment of the cells with either okadaic acid (OA), an inhibitor of PP2A, or siRNA for the regulatory subunit A of PP2A (PP2A-A) caused disruption of cell-cell adhesion and F-actin assembly, without affecting the complex formation of E-cadherin with beta- and alpha-catenins. While a small GTPase Rac and its effector IQGAP1 were associated with the E-cadherin-catenins complex, either OA or PP2A-A siRNA concomitantly induced the dissociation of IQGAP1, but not Rac, from the complex and the internalization of E-cadherin from the cell surface. We, therefore, propose that PP2A plays a crucial role in the maintenance of cell-cell adhesion through recruitment of IQGAP1 to the Rac-bound E-cadherin-catenins complex. (C) 2005 Wiley-Liss, Inc.

关键词： Enzyme kinetics  

摘要： The receptor protein-tyrosine phosphatase PTP mu is a member of the Ig superfamily of cell adhesion molecules. The extracellular domain of PTP mu contains motifs commonly found in cell adhesion molecules. The intracellular domain of PTP mu contains two conserved catalytic domains, only the membrane-proximal domain has catalytic activity. The unique features of PTP mu make it an attractive molecule to transduce signals upon cell-cell contact. PTP mu has been shown to regulate cadherin-mediated cell adhesion, neurite outgrowth, and axon guidance. Protein kinase C is a component of the PTP mu signaling pathway utilized to regulate these events. To aid in the further characterization of PTP mu signaling pathways, we used a series of GST-PTP mu fusion proteins, including catalytically inactive and substrate trapping mutants, to identify PTP mu-interacting proteins. We identified IQGAP1, a known regulator of the Rho GTPases, Cdc42 and Rac1, as a novel PTP mu-interacting protein. We show that this interaction is due to direct binding. In addition, we demonstrate that amino acid residues 765-958 of PTP mu, which include the juxtamembrane domain and 35 residues of the first phosphatase domain, mediate the binding to IQGAP1. Furthermore, we demonstrate that constitutively active Cdc42, and to a lesser extent Rac1, enhances the interaction of PTP mu and IQGAP1. These data indicate PTP mu may regulate Rho-GTPase-dependent functions of IQGAP1 and suggest that IQGAP1 is a component of the PTP mu signaling pathway. In support of this, we show that a peptide that competes IQGAP1 binding to Rho GTPases blocks PTP mu-mediated neurite outgrowth.