title: Signaling of hepatocyte growth factor/scatter factor (HGF) to the small GTPase Rap1 via the large docking protein Gab1 and the adapter protein CRKL.
abstract: Hepatocyte growth factor (HGF; scatter factor) is a multipotent protein with mitogenic, motogenic, and developmental functions. Upon activation, the HGF-receptor c-Met binds and phosphorylates the multisite docking protein Gab1. Besides binding motifs for phosphatidylinositol 3-kinase and Grb2, Gab 1 contains multiple Tyr-X-X-Pro (YXXP) motifs which, when phosphorylated, are potential binding sites for the adapter proteins c-Crk and Crk-like (CRKL). Stimulation of human embryonic kidney cells (HEK293) with HGF leads to Gab1 association with CRKL. The Gab1-CRKL interaction requires both, the SH2 domain of CRKL and the region containing the YXXP motifs in Gab1. CRKL binds via its first SH3 domain to several downstream signal transducers, including C3G an activator of the small GTPase Rap1. Indeed, Rap1 was rapidly activated after HGF stimulation of HEK293 cells. Rap1 activation through HGF was suppressed through transfection of a truncated C3G protein which only contains the SH3-binding motifs of C3G. Transfection of nonmutated Gab1 led to a strong increase of Rap1.GTP in the absence of HGF. In contrast, transfection of the GabDeltaYXXP mutant abolished the elevation of Rap1.GTP by HGF. A replating assay indicated that HGF decreases the adhesion of HEK293 cells. The results presented here delineate a novel signaling pathway from HGF to the GTPase Rap1 which depends on the interaction of the adapter protein CRKL with the exchange factor C3G and could be linked to cell migration.
authors.affiliation: Laboratory of Molecular Oncology, MSZ-Institut für Medizinische Strahlenkunde und Zellforschung, Universität Würzburg, D-97078 Würzburg, Germany.
authors.forename: D
authors.initials: D
authors.lastname: Sakkab
authors.forename: M
authors.initials: M
authors.lastname: Lewitzky
authors.forename: G
authors.initials: G
authors.lastname: Posern
authors.forename: U
authors.initials: U
authors.lastname: Schaeper
authors.forename: M
authors.initials: M
authors.lastname: Sachs
authors.forename: W
authors.initials: W
authors.lastname: Birchmeier
authors.forename: S M
authors.initials: SM
authors.lastname: Feller
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D002478:Cells, Cultured; D004789:Enzyme Activation / Q000187:drug effects; D017228:Hepatocyte Growth Factor / Q000494:pharmacology*; D006801:Humans; D009687:Nuclear Proteins / Q000502:physiology*; D010750:Phosphoproteins / Q000502:physiology; D010766:Phosphorylation; D014443:Tyrosine / Q000378:metabolism; D020827:rap1 GTP-Binding Proteins / Q000502:physiology*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C082869:CRKL protein; C098587:GAB1 protein, human; D009687:Nuclear Proteins; D010750:Phosphoproteins; D014443:Tyrosine; D017228:Hepatocyte Growth Factor; D020827:rap1 GTP-Binding Proteins