title: Characterization of the Rab8-specific membrane traffic route linked to protrusion formation.
abstract: Rab8 has a drastic effect on cell shape, but the membrane trafficking route it regulates is poorly defined. Here, we show that endogenous and ectopically expressed Rab8 is associated with macropinosomes generated at ruffling membrane domains. These macropinosomes fuse or transform into tubules that move toward the cell center, from where they are recycled back to the leading edge. The biogenesis of these tubules is dependent on actin and microtubular dynamics. Expression of dominant-negative Rab8 mutants or depletion of Rab8 by RNA interference inhibit protrusion formation, but promote cell-cell adhesion and actin stress fiber formation, whereas expression of the constitutively active Rab8-Q67L has the opposite effect. Rab8 localization overlaps with both Rab11 and Arf6, and is functionally linked to Arf6. We also demonstrate that Rab8 activity is needed for the transport of transferrin and the transferrin receptor to the pericentriolar region and to cell protrusions, and that Rab8 controls the traffic of cholera toxin B to the Golgi compartment. Finally, Rab8 colocalizes and binds specifically to a synaptotagmin-like protein (Slp1/JFC1), which is involved in controlling Rab8 membrane dynamics. We propose that Rab8 regulates a membrane-recycling pathway that mediates protrusion formation.
authors.affiliation: Institute of Biotechnology, PO Box 56 (Viikinkaari 9), FIN-00014 University of Helsinki, Finland.
authors.forename: Katarina
authors.initials: K
authors.lastname: Hattula
authors.forename: Johanna
authors.initials: J
authors.lastname: Furuhjelm
authors.forename: Jaana
authors.initials: J
authors.lastname: Tikkanen
authors.forename: Kimmo
authors.initials: K
authors.lastname: Tanhuanpää
authors.forename: Pirjo
authors.initials: P
authors.lastname: Laakkonen
authors.forename: Johan
authors.initials: J
authors.lastname: Peränen
mesh_terms: D000089982:ADP-Ribosylation Factor 6; D020727:ADP-Ribosylation Factors / Q000502:physiology; D000199:Actins / Q000502:physiology; D000818:Animals; D002451:Cell Compartmentation; D022081:Cell Surface Extensions / Q000378:metabolism*; D002772:Cholera Toxin / Q000493:pharmacokinetics; D006367:HeLa Cells; D006801:Humans; D008565:Membrane Proteins / Q000502:physiology; D051379:Mice; D008870:Microtubules / Q000502:physiology; D041681:NIH 3T3 Cells; D021381:Protein Transport; D034622:RNA Interference; D015398:Signal Transduction; D014168:Transferrin / Q000378:metabolism; D014407:Tumor Cells, Cultured; D020691:rab GTP-Binding Proteins / Q000378:metabolism* / Q000502:physiology; D000075745:rab27 GTP-Binding Proteins
chemical_list: D000089982:ADP-Ribosylation Factor 6; D000199:Actins; D008565:Membrane Proteins; C431146:SYTL1 protein, human; D014168:Transferrin; D000075745:rab27 GTP-Binding Proteins; D002772:Cholera Toxin; C066694:RAB27A protein, human; C082377:RAB8A protein, human; D020727:ADP-Ribosylation Factors; C000715348:ARF6 protein, human; C000715727:Arf6 protein, mouse; D020691:rab GTP-Binding Proteins