title: Induction of rac-guanine nucleotide exchange activity of Ras-GRF1/CDC25(Mm) following phosphorylation by the nonreceptor tyrosine kinase Src.
abstract: Ras-GRF1/CDC25(Mm) has been implicated as a Ras-guanine nucleotide exchange factor (GEF) expressed in brain. Ras-GEF activity of Ras-GRF1 is augmented in response to Ca(2+) influx and G protein betagamma subunit (Gbetagamma) stimulation. Ras-GRF1 also acts as a GEF toward Rac, but not Rho and Cdc42, when activated by Gbetagamma-mediated signals. Tyrosine phosphorylation of Ras-GRF1 is critical for the induction of Rac-GEF activity as evidenced by inhibition by tyrosine kinase inhibitors. Herein, we show that the nonreceptor tyrosine kinase Src phosphorylates Ras-GRF1, thereby inducing Rac-GEF activity. Ras-GRF1 transiently expressed with v-Src was tyrosine-phosphorylated and showed significant GEF activity toward Rac, but not Rho and Cdc42, which was comparable with that induced by Gbetagamma. In contrast, Ras-GEF activity remained unchanged. The recombinant c-Src protein phosphorylated affinity-purified glutathione S-transferase-tagged Ras-GRF1 in vitro and thereby elicited Rac-GEF activity. Taken together, tyrosine phosphorylation by Src is sufficient for the induction of Rac-GEF activity of Ras-GRF1, which may imply the involvement of Src downstream of Gbetagamma to regulate Ras-GRF1.
authors.affiliation: Faculty of Bioscience, Tokyo Institute of Technology, Yokohama 226-8501, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Kiyono
authors.forename: Y
authors.initials: Y
authors.lastname: Kaziro
authors.forename: T
authors.initials: T
authors.lastname: Satoh
mesh_terms: D002460:Cell Line; D002474:Cell-Free System; D019204:GTP-Binding Proteins / Q000378:metabolism; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism*; D006801:Humans; D010766:Phosphorylation; D010957:Plasmids; D010982:Platelet-Derived Growth Factor / Q000378:metabolism; D011233:Precipitin Tests; D016392:Proto-Oncogene Proteins pp60(c-src) / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D013997:Time Factors; D014162:Transfection; D014443:Tyrosine / Q000378:metabolism; D020666:ras-GRF1 / Q000378:metabolism*; D019061:src-Family Kinases / Q000378:metabolism*
chemical_list: D020662:Guanine Nucleotide Exchange Factors; D010982:Platelet-Derived Growth Factor; D011993:Recombinant Fusion Proteins; D020666:ras-GRF1; D014443:Tyrosine; D016392:Proto-Oncogene Proteins pp60(c-src); D019061:src-Family Kinases; D019204:GTP-Binding Proteins