title: IQGAP1 modulates activation of B-Raf.
abstract: IQGAP1 modulates several cellular functions, including cell-cell adhesion, transcription, cytoskeletal architecture, and selected signaling pathways. We previously documented that IQGAP1 binds ERK and MAPK kinase (MEK) and regulates EGF-stimulated MEK and ERK activity. Here we characterize the interaction between IQGAP1 and B-Raf, the molecule immediately upstream of MEK in the Ras/MAPK signaling cascade. B-Raf binds directly to IQGAP1 in vitro and coimmunoprecipitates with IQGAP1 from cell lysates. Importantly, IQGAP1 modulates B-Raf function. EGF is unable to stimulate B-Raf activity in IQGAP1-null cells and in cells transfected with an IQGAP1 mutant construct that is unable to bind B-Raf. Interestingly, binding to IQGAP1 significantly enhances B-Raf activity in vitro. Our data identify a previously unrecognized interaction between IQGAP1 and B-Raf and suggest that IQGAP1 is a scaffold necessary for activation of B-Raf by EGF.
authors.affiliation: Department of Pathology, Brigham and Women's Hospital and Harvard Medical School, Boston, MA 02115, USA.
authors.forename: Jian-Guo
authors.initials: JG
authors.lastname: Ren
authors.forename: Zhigang
authors.initials: Z
authors.lastname: Li
authors.forename: David B
authors.initials: DB
authors.lastname: Sacks
mesh_terms: D000818:Animals; D002461:Cell Line, Transformed; D002478:Cells, Cultured; D016895:Culture Media, Serum-Free; D004622:Embryo, Mammalian; D004789:Enzyme Activation; D004815:Epidermal Growth Factor / Q000494:pharmacology; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism; D005982:Glutathione Transferase / Q000378:metabolism; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D009154:Mutation; D010957:Plasmids / Q000378:metabolism; D011233:Precipitin Tests; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D048493:Proto-Oncogene Proteins B-raf / Q000032:analysis / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D013997:Time Factors; D014162:Transfection; D020703:ras GTPase-Activating Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D016895:Culture Media, Serum-Free; C101203:IQ motif containing GTPase activating protein 1; D011993:Recombinant Fusion Proteins; D020703:ras GTPase-Activating Proteins; D004815:Epidermal Growth Factor; D005982:Glutathione Transferase; D048493:Proto-Oncogene Proteins B-raf