title: A Rap/phosphatidylinositol 3-kinase pathway controls pseudopod formation [corrected].
abstract: GbpD, a Dictyostelium discoideum guanine exchange factor specific for Rap1, has been implicated in adhesion, cell polarity, and chemotaxis. Cells overexpressing GbpD are flat, exhibit strongly increased cell-substrate attachment, and extend many bifurcated and lateral pseudopodia. Phg2, a serine/threonine-specific kinase, mediates Rap1-regulated cell-substrate adhesion, but not cell polarity or chemotaxis. In this study we demonstrate that overexpression of GbpD in pi3k1/2-null cells does not induce the adhesion and cell morphology phenotype. Furthermore we show that Rap1 directly binds to the Ras binding domain of PI3K, and overexpression of GbpD leads to strongly enhanced PIP3 levels. Consistently, upon overexpression of the PIP3-degradating enzyme PTEN in GbpD-overexpressing cells, the strong adhesion and cell morphology phenotype is largely lost. These results indicate that a GbpD/Rap/PI3K pathway helps control pseudopod formation and cell polarity. As in Rap-regulated pseudopod formation in Dictyostelium, mammalian Rap and PI3K are essential for determining neuronal polarity, suggesting that the Rap/PI3K pathway is a conserved module regulating the establishment of cell polarity.
authors.affiliation: Department of Molecular Cell Biology, University of Groningen, 9751 NN Haren, The Netherlands.
authors.forename: Arjan
authors.initials: A
authors.lastname: Kortholt
authors.forename: Parvin
authors.initials: P
authors.lastname: Bolourani
authors.forename: Holger
authors.initials: H
authors.lastname: Rehmann
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; D002478:Cells, Cultured; D002633:Chemotaxis / Q000502:physiology; D004023:Dictyostelium / Q000166:cytology* / Q000235:genetics / Q000378:metabolism*; D004789:Enzyme Activation; D055785:Gene Knockdown Techniques; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics / Q000378:metabolism; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism*; D015800:Protozoan Proteins / Q000235:genetics / Q000378:metabolism*; D011554:Pseudopodia / Q000378:metabolism* / Q000648:ultrastructure; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D020827:rap1 GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D018631:ras Proteins / Q000378:metabolism
chemical_list: D020662:Guanine Nucleotide Exchange Factors; D015800:Protozoan Proteins; D011993:Recombinant Fusion Proteins; C424065:rasG protein, Dictyostelium; D015544:Inositol 1,4,5-Trisphosphate; D019869:Phosphatidylinositol 3-Kinases; D020827:rap1 GTP-Binding Proteins; D018631:ras Proteins