IQGAP1 Binds ERK2 and Modulates Its Activity

Abstract

IQGAP1 binds several proteins including actin, calmodulin, E-cadherin, ␤-catenin, Cdc42, Rac1, and CLIP-170. The interaction with these targets enables IQGAP1 to participate in many cellular functions varying from regulation of the cytoskeleton to gene transcription. Here we show that extracellular signal-regulated kinase (ERK) 2 binds to IQGAP1. In vitro analysis with purified proteins demonstrated a direct interaction between ERK2 and IQGAP1. Moreover, binding occurred in cells as endogenous ERK2 co-immunoprecipitated with IQGAP1 from human breast epithelial cell lysates. The association between ERK2 and IQGAP1 was independent of epidermal growth factor. The in vivo interaction has functional significance. Manipulation of intracellular IQGAP1 levels significantly reduced growth factorstimulated ERK1 and ERK2 activity. Similarly, stimulation of ERK1 and ERK2 activity by insulin-like growth factor I was reduced when IQGAP1 levels were changed. In contrast, overexpression of an IQGAP1 construct lacking the ERK2 binding region did not interfere with activation of ERK1 and ERK2 by epidermal growth factor. Our data disclose a previously unidentified communication between IQGAP1 and the ERK pathway and imply that IQGAP1 modulates the Ras/mitogen-activated protein kinase signaling cascade.Extracellular signals are converted into cellular responses via a complex network of intersecting signaling pathways (1). A prominent component of intracellular signaling is the family of mitogen-activated protein (MAP) 1 kinases. The archetypal MAP kinase pathway consists of a three-kinase cascade, a MAP kinase kinase kinase (MAPKKK or MEKK) that activates the downstream MAP/ERK kinase (MAPKK or MEK) by phosphorylation, which in turn elicits a phosphorylation-dependent increase in the activity of the MAP kinase (2, 3). The MAP kinase then induces phosphorylation of a variety of cytosolic or nuclear targets, transcription factors, transcriptional adaptor proteins, and other protein kinases. Of the various mammalian MAP kinase pathways, the Ras/Raf/MEK/ERK is the most studied. This cascade, triggered by a diverse range of stimuli acting through cell surface receptors, is under the control of the small G protein Ras (4). When GTP-bound, Ras binds to Raf and recruits it to the cell membrane where Raf is activated (5-7). Raf phosphorylates and activates the dual specificity protein kinases MEK1 and MEK2, which in turn stimulate ERK1 and ERK2 by catalyzing their phosphorylation (3). The Ras/Raf/MEK/ERK cascade is conserved in all eukaryotes, and ERK plays a vital role in several biological processes, particularly those involving cellular proliferation, differentiation, survival, and apoptosis (8).IQGAP1 is a scaffolding protein with multiple protein-interacting domains (for reviews, see Refs. 9 -11). These motifs include a calponin homology domain (CHD), four IQ motifs, and a RasGAP-related domain. Targets for IQGAP1 include calmodulin (12-14), Cdc42 (12, 13), Rac1 (13), actin (14, 15), ␤-catenin (16, 17), E-cadherin (16, 18), S100B (19) ...

Multiple proteins mediate IQGAP1-stimulated cell migration

“…To determine the effect on migration stimulated by IQGAP1, we used cells that stably overexpress IQGAP1. Termed MCF/I, these cells have 3-fold more IQGAP1 than the control, vector-transfected MCF/V cells [11,17,33,34]. As previously documented [11], the motility of MCF/I cells is greater than that of MCF/ V cells (Fig.…”

“…The anti-IQGAP1 polyclonal and monoclonal antibodies [4,17] and anti-calmodulin monoclonal antibody [20] have been previously characterized. Anti-Myc monoclonal antibody (9E10.2) was manufactured by Maine Biotechnology.…”

“…IQGAP1 binds to multiple proteins, including calmodulin, actin, Cdc42, Rac1, E-cadherin, β-catenin, adenomatous polyposis coli (APC) and components of the mitogen-activated protein (MAP) kinase pathway (specifically MEK and ERK) [15][16][17][18]. Initial investigation revealed that the interaction of IQGAP1 with Cdc42 and Rac1 contributes to its effects on cell migration [11].…”

Hyaluronan-mediated CD44 activation of RhoGTPase signaling and cytoskeleton function promotes tumor progression

“…These structural domains include four putative calmodulin-binding (IQ) motifs, a calponin homology (CHD) domain, a poly-proline binding (WW) domain and a Ras-GAP-related (GRD) domain [97]. Some of these motifs are involved in IQGAP1 interaction with specific proteins, such as Cdc42, Rac, actin, calmodulin ERK2, E-cadherin and β-catenin [97][98][99]. The establishment of a physical linkage between IQGAP1 and its binding partners has been shown to generate several important biological activities.…”

Scaffold mediated regulation of MAPK signaling and cytoskeletal dynamics: A perspective

“…IQGAP may also serve to localize MEK and ERK [161,162] to dynamic microtubules. IQGAP is a calmodulin regulated actin binding protein with a GAP-like domain that while lacking GAP activity toward Rho facilitates retention of Cdc42 and Rac in their GTP bound states [163].…”