title: The cytohesin paralog Sec7 of Dictyostelium discoideum is required for phagocytosis and cell motility.
abstract: BACKGROUND
  Dictyostelium harbors several paralogous Sec7 genes that encode members of three subfamilies of the Sec7 superfamily of guanine nucleotide exchange factors. One of them is the cytohesin family represented by three members in D. discoideum, SecG, Sec7 and a further protein distinguished by several transmembrane domains. Cytohesins are characterized by a Sec7-PH tandem domain and have roles in cell adhesion and migration.
  
  
  RESULTS
  We study here Sec7. In vitro its PH domain bound preferentially to phosphatidylinositol 3,4-bisphosphate (PI(3,4)P2), phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) and phosphatidylinositol 3,4,5-trisphosphate (PI(3,4,5)P3). When following the distribution of GFP-Sec7 in vivo we observed the protein in the cytosol and at the plasma membrane. Strikingly, when cells formed pseudopods, macropinosomes or phagosomes, GFP-Sec7 was conspicuously absent from areas of the plasma membrane which were involved in these processes. Mutant cells lacking Sec7 exhibited an impaired phagocytosis and showed significantly reduced speed and less persistence during migration. Cellular properties associated with mammalian cytohesins like cell-cell and cell-substratum adhesion were not altered. Proteins with roles in membrane trafficking and signal transduction have been identified as putative interaction partners consistent with the data obtained from mutant analysis.
  
  
  CONCLUSIONS
  Sec7 is a cytosolic component and is associated with the plasma membrane in a pattern distinctly different from the accumulation of PI(3,4,5)P3. Mutant analysis reveals that loss of the protein affects cellular processes that involve membrane flow and the actin cytoskeleton.
authors.affiliation: Institute of Biochemistry I, Medical Faculty, Center for Molecular Medicine Cologne and Cologne Excellence Cluster on Cellular Stress Responses in Aging-Associated Diseases, University of Cologne, 50931 Köln, Germany.
authors.forename: Rolf
authors.initials: R
authors.lastname: Müller
authors.forename: Claudia
authors.initials: C
authors.lastname: Herr
authors.forename: Salil K
authors.initials: SK
authors.lastname: Sukumaran
authors.forename: Napoleon Nosa
authors.initials: NN
authors.lastname: Omosigho
authors.forename: Markus
authors.initials: M
authors.lastname: Plomann
authors.forename: Tanja Y
authors.initials: TY
authors.lastname: Riyahi
authors.forename: Maria
authors.initials: M
authors.lastname: Stumpf
authors.forename: Karthic
authors.initials: K
authors.lastname: Swaminathan
authors.forename: Marios
authors.initials: M
authors.lastname: Tsangarides
authors.forename: Kyriacos
authors.initials: K
authors.lastname: Yiannakou
authors.forename: Rosemarie
authors.initials: R
authors.lastname: Blau-Wasser
authors.forename: Christoph
authors.initials: C
authors.lastname: Gallinger
authors.forename: Michael
authors.initials: M
authors.lastname: Schleicher
authors.forename: Waldemar
authors.initials: W
authors.lastname: Kolanus
authors.forename: Angelika A
authors.initials: AA
authors.lastname: Noegel
mesh_terms: D000595:Amino Acid Sequence; D002448:Cell Adhesion / Q000502:physiology; D002633:Chemotaxis; D004023:Dictyostelium / Q000502:physiology*; D020662:Guanine Nucleotide Exchange Factors / Q000737:chemistry / Q000502:physiology*; D008969:Molecular Sequence Data; D010587:Phagocytosis; D017434:Protein Structure, Tertiary; D015800:Protozoan Proteins / Q000737:chemistry / Q000502:physiology*; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism
chemical_list: D020662:Guanine Nucleotide Exchange Factors; D015800:Protozoan Proteins; D011994:Recombinant Proteins
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