title: Identification and characterization of RA-GEF-2, a Rap guanine nucleotide exchange factor that serves as a downstream target of M-Ras.
abstract: The Ras family small GTPase Rap is regulated by an array of specific guanine nucleotide exchange factors (GEFs) in response to upstream stimuli. RA-GEF-1 was identified as a novel Rap GEF, which possesses a Ras/Rap1-associating (RA) domain. Here we report a protein closely related to RA-GEF-1, named RA-GEF-2. Like RA-GEF-1, a putative cyclic nucleotide monophosphate-binding domain, a Ras exchanger motif, a PSD-95/DlgA/ZO-1 domain, and an RA domain in addition to the GEF catalytic domain are found in RA-GEF-2. However, RA-GEF-2 displays a different tissue distribution profile from that of RA-GEF-1. RA-GEF-2 stimulates guanine nucleotide exchange of both Rap1 and Rap2, but not Ha-Ras. The RA domain of RA-GEF-2 binds to M-Ras in a GTP-dependent manner, but not to other Ras family GTPases tested, including Ha-Ras, N-Ras, Rap1A, Rap2A, R-Ras, RalA, Rin, Rit, and Rheb, in contrast to the RA domain of RA-GEF-1, which specifically binds to Rap1. In accordance with this, RA-GEF-2 colocalizes with activated M-Ras in the plasma membrane in COS-7 cells, suggesting a role of RA-GEF-2 in the regulation of Rap1 and Rap2, particularly in the plasma membrane. In fact, an increase in the level of the GTP-bound form of plasma membrane-located Rap1 was observed when coexpressed with RA-GEF-2 and activated M-Ras. Thus, RA-GEF-2 acts as a GEF for Rap1 and Rap2 downstream of M-Ras in the plasma membrane, whereas RA-GEF-1 exerts Rap GEF function in perinuclear compartments including the Golgi apparatus.
authors.affiliation: Division of Molecular Biology, Department of Molecular and Cellular Biology, Kobe University Graduate School of Medicine, 7-5-1 Kusunoki-cho, Chuo-ku, Japan.
authors.forename: X
authors.initials: X
authors.lastname: Gao
authors.forename: T
authors.initials: T
authors.lastname: Satoh
authors.forename: Y
authors.initials: Y
authors.lastname: Liao
authors.forename: C
authors.initials: C
authors.lastname: Song
authors.forename: C D
authors.initials: CD
authors.lastname: Hu
authors.forename: K
authors.initials: K
authors.lastname: Kariya Ki
authors.forename: T
authors.initials: T
authors.lastname: Kataoka
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001692:Biological Transport; D019556:COS Cells; D002462:Cell Membrane / Q000378:metabolism; D003001:Cloning, Molecular; D020662:Guanine Nucleotide Exchange Factors / Q000032:analysis / Q000235:genetics / Q000502:physiology*; D008969:Molecular Sequence Data; D020559:Monomeric GTP-Binding Proteins / Q000378:metabolism*; D015800:Protozoan Proteins / Q000378:metabolism
chemical_list: D020662:Guanine Nucleotide Exchange Factors; D015800:Protozoan Proteins; C485746:RAPGEF6 protein, human; C065352:rhoptry associated protein, Plasmodium; D020559:Monomeric GTP-Binding Proteins