title: Regulation of phagocytosis in Dictyostelium by the inositol 5-phosphatase OCRL homolog Dd5P4.
abstract: Phosphoinositides are involved in endocytosis in both mammalian cells and the amoeba Dictyostelium discoideum. Dd5P4 is the Dictyostelium homolog of human OCRL (oculocerebrorenal syndrome of Lowe); both have a RhoGAP domain and a 5-phosphatase domain that acts on phosphatidylinositol 4,5-bisphosphate/phosphatidylinositol 3,4,5-trisphosphate (PI(3,4,5)P3). Inactivation of Dd5P4 inhibits growth on liquid medium and on bacteria. Dd5p4-null cells are impaired in phagocytosis of yeast cells. In wild-type cells, PI(3,4,5)P3 is formed and converted to PI(3,4)P2 just before closure of the phagocytic cup. In dd5p4-null cells, a phagocytic cup is formed upon contact with the yeast cell, and PI(3,4,5)P3 is still produced, but the phagocytic cup does not close. We suggest that Dd5P4 regulates the conversion of PI(3,4,5)P3 to PI(3,4)P2 and that this conversion is essential for closure of the phagocytic cup. Phylogenetic analysis of OCRL-like 5-phosphatases with RhoGAP domains reveal that D. discoideum Dd5P4 is a surprisingly close homolog of human OCRL, the protein responsible for Lowe syndrome. We expressed human OCRL in dd5p4-null cells. Growth on bacteria and axenic medium is largely restored, whereas the rate of phagocytosis of yeast cells is partly restored, indicating that human OCRL can functionally replace Dictyostelium Dd5P4.
authors.affiliation: Department of Molecular Cell Biology, University of Groningen, Kerklaan 30, 9751NN Haren, The Netherlands.
authors.forename: Harriët M
authors.initials: HM
authors.lastname: Loovers
authors.forename: Arjan
authors.initials: A
authors.lastname: Kortholt
authors.forename: Hendrie
authors.initials: H
authors.lastname: de Groote
authors.forename: Leslie
authors.initials: L
authors.lastname: Whitty
authors.forename: Robert L
authors.initials: RL
authors.lastname: Nussbaum
authors.forename: Peter J M
authors.initials: PJ
authors.lastname: van Haastert
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D004023:Dictyostelium / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D020690:GTPase-Activating Proteins / Q000235:genetics; D020868:Gene Silencing; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D000072181:Inositol Polyphosphate 5-Phosphatases; D018613:Microscopy, Confocal; D008969:Molecular Sequence Data; D009154:Mutation; D010587:Phagocytosis / Q000502:physiology*; D010744:Phosphoric Monoester Hydrolases / Q000235:genetics / Q000378:metabolism*; D010802:Phylogeny; D010873:Pinocytosis / Q000502:physiology; D015800:Protozoan Proteins / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D014162:Transfection
chemical_list: D020690:GTPase-Activating Proteins; D015800:Protozoan Proteins; D011993:Recombinant Fusion Proteins; C089420:dagA protein, Dictyostelium; C085379:rho GTPase-activating protein; D049452:Green Fluorescent Proteins; D010744:Phosphoric Monoester Hydrolases; D000072181:Inositol Polyphosphate 5-Phosphatases