title: Characterization of the GbpD-activated Rap1 pathway regulating adhesion and cell polarity in Dictyostelium discoideum.
abstract: The regulation of cell polarity plays an important role in chemotaxis. GbpD, a putative nucleotide exchange factor for small G-proteins of the Ras family, has been implicated in adhesion, cell polarity, and chemotaxis in Dictyostelium. Cells overexpressing GbpD are flat, exhibit strongly increased cell-substrate attachment, and extend many bifurcated and lateral pseudopodia. These cells overexpressing GbpD are severely impaired in chemotaxis, most likely due to the induction of many protrusions rather than an enhanced adhesion. The GbpD-overexpression phenotype is similar to that of cells overexpressing Rap1. Here we demonstrate that GbpD activates Rap1 both in vivo and in vitro but not any of the five other characterized Ras proteins. In a screen for Rap1 effectors, we overexpressed GbpD in several mutants defective in adhesion or cell polarity and identified Phg2 as Rap1 effector necessary for adhesion, but not cell polarity. Phg2, a serine/threonine-specific kinase, directly interacts with Rap1 via its Ras association domain.
authors.affiliation: Department of Molecular Cell Biology, University of Groningen, Kerklaan 30, 9751 NN Haren, The Netherlands.
authors.forename: Arjan
authors.initials: A
authors.lastname: Kortholt
authors.forename: Holger
authors.initials: H
authors.lastname: Rehmann
authors.forename: Helmut
authors.initials: H
authors.lastname: Kae
authors.forename: Leonard
authors.initials: L
authors.lastname: Bosgraaf
authors.forename: Ineke
authors.initials: I
authors.lastname: Keizer-Gunnink
authors.forename: Gerald
authors.initials: G
authors.lastname: Weeks
authors.forename: Alfred
authors.initials: A
authors.lastname: Wittinghofer
authors.forename: Peter J M
authors.initials: PJ
authors.lastname: Van Haastert
mesh_terms: D000818:Animals; D002448:Cell Adhesion / Q000235:genetics / Q000502:physiology; D002460:Cell Line; D016764:Cell Polarity / Q000235:genetics / Q000502:physiology*; D002633:Chemotaxis / Q000235:genetics / Q000502:physiology; D004023:Dictyostelium / Q000737:chemistry* / Q000235:genetics / Q000502:physiology; D011554:Pseudopodia / Q000378:metabolism / Q000502:physiology; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology*; D020827:rap1 GTP-Binding Proteins / Q000737:chemistry* / Q000235:genetics / Q000502:physiology*; D020663:ras Guanine Nucleotide Exchange Factors / Q000737:chemistry* / Q000235:genetics / Q000502:physiology
chemical_list: D020663:ras Guanine Nucleotide Exchange Factors; D020827:rap1 GTP-Binding Proteins