title: Coupling of Ras and Rac guanosine triphosphatases through the Ras exchanger Sos.
abstract: The Son of Sevenless (Sos) proteins control receptor-mediated activation of Ras by catalyzing the exchange of guanosine diphosphate for guanosine triphosphate on Ras. The NH2-terminal region of Sos contains a Dbl homology (DH) domain in tandem with a pleckstrin homology (PH) domain. In COS-1 cells, the DH domain of Sos stimulated guanine nucleotide exchange on Rac but not Cdc42 in vitro and in vivo. The tandem DH-PH domain of Sos (DH-PH-Sos) was defective in Rac activation but regained Rac stimulating activity when it was coexpressed with activated Ras. Ras-mediated activation of DH-PH-Sos did not require activation of mitogen-activated protein kinase but it was dependent on activation of phosphoinositide 3-kinase. These results reveal a potential mechanism for coupling of Ras and Rac signaling pathways.
authors.affiliation: Department of Molecular Genetics and Microbiology, State University of New York at Stony Brook, Stony Brook, NY 11794, USA.
authors.forename: A S
authors.initials: AS
authors.lastname: Nimnual
authors.forename: B A
authors.initials: BA
authors.lastname: Yatsula
authors.forename: D
authors.initials: D
authors.lastname: Bar-Sagi
mesh_terms: D000199:Actins / Q000378:metabolism; D000818:Animals; D019556:COS Cells; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000378:metabolism; D002460:Cell Line; D002462:Cell Membrane / Q000648:ultrastructure; D004789:Enzyme Activation; D020558:GTP Phosphohydrolases / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000378:metabolism*; D020662:Guanine Nucleotide Exchange Factors; D006153:Guanosine Diphosphate / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism*; D020928:Mitogen-Activated Protein Kinases; D011506:Proteins / Q000378:metabolism; D011518:Proto-Oncogene Proteins; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D015682:Retroviridae Proteins, Oncogenic / Q000737:chemistry; D015398:Signal Transduction; D020664:Son of Sevenless Proteins; D014162:Transfection; D020764:cdc42 GTP-Binding Protein; D020744:rac GTP-Binding Proteins; D020663:ras Guanine Nucleotide Exchange Factors; D018631:ras Proteins / Q000378:metabolism*
chemical_list: D000199:Actins; D018797:Cell Cycle Proteins; D020662:Guanine Nucleotide Exchange Factors; C057811:MCF2 protein, human; D008565:Membrane Proteins; D011506:Proteins; D011518:Proto-Oncogene Proteins; D011993:Recombinant Fusion Proteins; D015682:Retroviridae Proteins, Oncogenic; D020664:Son of Sevenless Proteins; D020663:ras Guanine Nucleotide Exchange Factors; D006153:Guanosine Diphosphate; D006160:Guanosine Triphosphate; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins; D020764:cdc42 GTP-Binding Protein; D020744:rac GTP-Binding Proteins; D018631:ras Proteins