title: Rab18 and Rab43 have key roles in ER-Golgi trafficking.
abstract: Rabs and Arfs/Arls are Ras-related small GTPases of particular relevance to membrane trafficking. It is thought that these proteins regulate specific pathways through interactions with coat, motor, tether and SNARE proteins. We screened a comprehensive list of Arf/Arl/Rab proteins, previously identified on purified Golgi membranes by a proteomics approach (37 in total), for Golgi or intra-Golgi localization, dominant-negative and overexpression phenotypes. Further analysis of two of these proteins, Rab18 and Rab43, strongly indicated roles in ER-Golgi trafficking. Rab43-T32N redistributed Golgi elements to ER exit sites without blocking trafficking of the secretory marker VSVG-GFP from ER to cell surface. Wild-type Rab43 redistributes the p150(Glued) subunit of dynactin, consistent with a specific role in regulating association of pre-Golgi intermediates with microtubules. Overexpression of wild-type GFP-Rab18 or incubation with any of three siRNAs directed against Rab18 severely disrupts the Golgi complex and reduces secretion of VSVG. Rab18 mutants specifically enhance retrograde Golgi-ER transport of the COPI-independent cargo beta-1,4-galactosyltransferase (Galtase)-YFP but not the COPI-dependent cargo p58-YFP from the Golgi to ER in a photobleach assay. Rab18-S22N also potentiated brefeldin-A-induced ER-Golgi fusion. This study is the first comprehensive application of large-scale proteomics to the cell biology of small GTPases of the secretory pathway.
authors.affiliation: Department of Anatomy and Cell Biology, McGill University, Montreal, Quebec, Canada H3A2B2.
authors.forename: Selma Y
authors.initials: SY
authors.lastname: Dejgaard
authors.forename: Ayesha
authors.initials: A
authors.lastname: Murshid
authors.forename: Aysegül
authors.initials: A
authors.lastname: Erman
authors.forename: Ozge
authors.initials: O
authors.lastname: Kizilay
authors.forename: David
authors.initials: D
authors.lastname: Verbich
authors.forename: Robert
authors.initials: R
authors.lastname: Lodge
authors.forename: Kurt
authors.initials: K
authors.lastname: Dejgaard
authors.forename: Thi Bach Nga
authors.initials: TB
authors.lastname: Ly-Hartig
authors.forename: Rainer
authors.initials: R
authors.lastname: Pepperkok
authors.forename: Jeremy C
authors.initials: JC
authors.lastname: Simpson
authors.forename: John F
authors.initials: JF
authors.lastname: Presley
mesh_terms: D000818:Animals; D019556:COS Cells; D002478:Cells, Cultured; D002522:Chlorocebus aethiops; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D006056:Golgi Apparatus / Q000378:metabolism*; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D008954:Models, Biological; D050505:Mutant Proteins / Q000502:physiology; D021381:Protein Transport / Q000502:physiology; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D014709:Vero Cells; D020691:rab GTP-Binding Proteins / Q000502:physiology*; D000099193:rab11 GTP-Binding Proteins
chemical_list: D049452:Green Fluorescent Proteins; D050505:Mutant Proteins; D011993:Recombinant Fusion Proteins; D020691:rab GTP-Binding Proteins; D000099193:rab11 GTP-Binding Proteins; C484168:RAB18 protein, human