title: S100P is a novel interaction partner and regulator of IQGAP1.
abstract: Ca(2+)-binding proteins of the S100 family participate in intracellular Ca(2+) signaling by binding to and regulating specific cellular targets in their Ca(2+)-loaded conformation. Because the information on specific cellular targets of different S100 proteins is still limited, we developed an affinity approach that selects for protein targets only binding to the physiologically active dimer of an S100 protein. Using this approach, we here identify IQGAP1 as a novel and dimer-specific target of S100P, a member of the S100 family enriched in the cortical cytoskeleton. The interaction between S100P and IQGAP1 is strictly Ca(2+)-dependent and characterized by a dissociation constant of 0.2 μM. Binding occurs primarily through the IQ domain of IQGAP1 and the first EF hand loop of S100P, thus representing a novel structural principle of S100-target protein interactions. Upon cell stimulation, S100P and IQGAP1 co-localize at or in close proximity to the plasma membrane, and complex formation can be linked to altered signal transduction properties of IQGAP1. Specifically, the EGF-induced tyrosine phosphorylation of IQGAP1 that is thought to function in assembling signaling intermediates at IQGAP1 scaffolds in the subplasmalemmal region is markedly reduced in cells overexpressing S100P but not in cells expressing an S100P mutant deficient in IQGAP1 binding. Furthermore, B-Raf binding to IQGAP1 and MEK1/2 activation occurring downstream of IQGAP1 in EGF-triggered signaling cascades are compromised at elevated S100P levels. Thus, S100P is a novel Ca(2+)-dependent regulator of IQGAP1 that can down-regulate the function of IQGAP1 as a signaling intermediate by direct interaction.
authors.affiliation: Institute of Medical Biochemistry, Centre for Molecular Biology of Inflammation, University of Muenster, Von-Esmarch-Strasse 56, D-48149 Muenster, Germany.
authors.forename: Annika
authors.initials: A
authors.lastname: Heil
authors.forename: Ali Reza
authors.initials: AR
authors.lastname: Nazmi
authors.forename: Max
authors.initials: M
authors.lastname: Koltzscher
authors.forename: Michaela
authors.initials: M
authors.lastname: Poeter
authors.forename: Judith
authors.initials: J
authors.lastname: Austermann
authors.forename: Nicole
authors.initials: N
authors.lastname: Assard
authors.forename: Jacques
authors.initials: J
authors.lastname: Baudier
authors.forename: Kozo
authors.initials: K
authors.lastname: Kaibuchi
authors.forename: Volker
authors.initials: V
authors.lastname: Gerke
mesh_terms: D002135:Calcium-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D003599:Cytoskeleton / Q000378:metabolism; D019281:Dimerization; D006367:HeLa Cells; D006801:Humans; D048369:MAP Kinase Kinase 1 / Q000378:metabolism; D048370:MAP Kinase Kinase 2 / Q000378:metabolism; D020935:MAP Kinase Signaling System / Q000502:physiology*; D009363:Neoplasm Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation / Q000502:physiology; D054730:Protein Interaction Domains and Motifs / Q000502:physiology; D017434:Protein Structure, Tertiary; D048493:Proto-Oncogene Proteins B-raf / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D020703:ras GTPase-Activating Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D002135:Calcium-Binding Proteins; D002147:Calmodulin; C101203:IQ motif containing GTPase activating protein 1; D009363:Neoplasm Proteins; D011994:Recombinant Proteins; C103003:S100P protein, human; D020703:ras GTPase-Activating Proteins; C482128:MAP2K2 protein, human; C482119:BRAF protein, human; D048493:Proto-Oncogene Proteins B-raf; D048369:MAP Kinase Kinase 1; D048370:MAP Kinase Kinase 2; C482125:MAP2K1 protein, human