title: Endocytic turnover of Rab8 controls cell polarization.
abstract: Adaptation of cell shape and polarization through the formation and retraction of cellular protrusions requires balancing of endocytosis and exocytosis combined with fine-tuning of the local activity of small GTPases like Rab8. Here, we show that endocytic turnover of the plasma membrane at protrusions is directly coupled to surface removal and inactivation of Rab8. Removal is induced by reduced membrane tension and mediated by the GTPase regulator associated with focal adhesion kinase-1 (GRAF1, also known as ARHGAP26), a regulator of clathrin-independent endocytosis. GRAF1-depleted cells were deficient in multi-directional spreading and displayed elevated levels of GTP-loaded Rab8, which was accumulated at the tips of static protrusions. Furthermore, GRAF1 depletion impaired lumen formation and spindle orientation in a 3D cell culture system, indicating that GRAF1 activity regulates polarity establishment. Our data suggest that GRAF1-mediated removal of Rab8 from the cell surface restricts its activity during protrusion formation, thereby facilitating dynamic adjustment of the polarity axis.
authors.affiliation: Integrative Medical Biology, Umeå University, Umeå 901 87, Sweden.
authors.forename: Maite
authors.initials: M
authors.lastname: Vidal-Quadras
authors.affiliation: Integrative Medical Biology, Umeå University, Umeå 901 87, Sweden.
authors.forename: Mikkel R
authors.initials: MR
authors.lastname: Holst
authors.affiliation: Integrative Medical Biology, Umeå University, Umeå 901 87, Sweden.|Medical Biochemistry and Biophysics, Laboratory for Molecular Infection Medicine Sweden, Umeå University, Umeå 901 87, Sweden.
authors.forename: Monika K
authors.identifier: 0000-0002-6806-0515
authors.initials: MK
authors.lastname: Francis
authors.affiliation: Integrative Medical Biology, Umeå University, Umeå 901 87, Sweden.|Medical Biochemistry and Biophysics, Laboratory for Molecular Infection Medicine Sweden, Umeå University, Umeå 901 87, Sweden.
authors.forename: Elin
authors.initials: E
authors.lastname: Larsson
authors.affiliation: Centro de Biología Molecular Severo Ochoa, Consejo Superior de Investigaciones Científicas-UAM, Madrid 28049, Spain.
authors.forename: Mariam
authors.initials: M
authors.lastname: Hachimi
authors.affiliation: Medical Biochemistry and Biophysics, Laboratory for Molecular Infection Medicine Sweden, Umeå University, Umeå 901 87, Sweden.
authors.forename: Wai-Lok
authors.initials: WL
authors.lastname: Yau
authors.affiliation: Department of Anatomy, Faculty of Medicine, University of Helsinki, Helsinki FIN-00014, Finland.
authors.forename: Johan
authors.initials: J
authors.lastname: Peränen
authors.affiliation: Centro de Biología Molecular Severo Ochoa, Consejo Superior de Investigaciones Científicas-UAM, Madrid 28049, Spain.
authors.forename: Fernando
authors.initials: F
authors.lastname: Martín-Belmonte
authors.affiliation: Integrative Medical Biology, Umeå University, Umeå 901 87, Sweden richard.lundmark@umu.se.|Medical Biochemistry and Biophysics, Laboratory for Molecular Infection Medicine Sweden, Umeå University, Umeå 901 87, Sweden.
authors.forename: Richard
authors.identifier: 0000-0001-9104-724X
authors.initials: R
authors.lastname: Lundmark
mesh_terms: D000818:Animals; D016764:Cell Polarity; D022081:Cell Surface Extensions / Q000378:metabolism; D004285:Dogs; D004705:Endocytosis; D020690:GTPase-Activating Proteins / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D061985:Madin Darby Canine Kidney Cells; D053511:Matrix Metalloproteinase 14 / Q000378:metabolism; D011485:Protein Binding; D021381:Protein Transport; D008941:Spindle Apparatus / Q000378:metabolism; D020691:rab GTP-Binding Proteins / Q000378:metabolism*
chemical_list: D020690:GTPase-Activating Proteins; D006160:Guanosine Triphosphate; D053511:Matrix Metalloproteinase 14; C082377:RAB8A protein, human; D020691:rab GTP-Binding Proteins
keywords: Cell polarization; Endocytosis; GRAF1; Rab8