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First published online 29 July 2008
doi: 10.1242/jcs.021808

Journal of Cell Science 121, 2768-2781 (2008)
Published by The Company of Biologists 2008
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Research Article

Rab18 and Rab43 have key roles in ER-Golgi trafficking

Selma Y. Dejgaard1, Ayesha Murshid1, Aysegül Erman1, Özge Kizilay1, David Verbich1, Robert Lodge2, Kurt Dejgaard3, Thi Bach Nga Ly-Hartig4, Rainer Pepperkok4, Jeremy C. Simpson4,* and John F. Presley1,{ddagger}

1 Department of Anatomy and Cell Biology, McGill University, Montreal, Quebec, Canada, H3A 2B2
2 Laboratoire d'Immunoretrovirologie, Centre de Recherche d'Infectiologie – CHUL, Quebec, Canada, G1V 4G2
3 Department of Biochemistry, McGill University, Montreal, Quebec, Canada, H3G 1Y6
4 Cell Biology and Biophysics Unit, EMBL, 69117 Heidelberg, Germany

{ddagger} Author for correspondence (e-mail: john.presley{at}mcgill.ca)

Accepted 19 May 2008

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 p150Glued 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 β-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.

Key words: ER-Golgi Trafficking, GFP, Golgi, Rab18, Rab43, Endoplasmic reticulum


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