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MBC in Press, published online ahead of print September 19, 2007
Mol. Biol. Cell 10.1091/mbc.E06-11-0991

A more recent version of this article appeared on December 1, 2007
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Submitted on November 6, 2006
Revised on September 5, 2007
Accepted on September 11, 2007

Golgi-bound Rab34 Is a Novel Member of the Secretory Pathway

Neil M. Goldenberg,* Sergio Grinstein,{dagger} and Mel Silverman{ddagger}

*Institute of Medical Science and {ddagger}Department of Medicine, University of Toronto, Toronto, ON, Canada, M5S 1A8; {dagger}Program in Cell Biology, Hospital for Sick Children, Toronto, ON, Canada, M5G 2C4

Monitoring Editor: Jennifer Lippincott-Schwartz

Golgi-localized Rab34 has been implicated in repositioning lysosomes and activation of macropinocytosis. Using HeLa cells we undertook a detailed investigation of Rab34 involvement in intracellular vesicle transport. Immunoelectron microscopy and immunocytochemistry confirmed that Rab34 is localized to the Golgi stack and that active Rab34 shifts lysosomes to the cell center. Contrary to a previous report, we found that Rab34 is not concentrated at membrane ruffles and is not involved in fluid-phase uptake. Also, Rab34 induced repositioning of lysosomes does not affect mannose 6-phosphate receptor trafficking. Most strikingly, HeLa cells depleted of Rab34 by transfection with dominant-negative Rab34, or following RNA interference, failed to transport the temperature-sensitive Vesicular Stomatitis Virus G-protein fused to GFP (VSVG-GFP) from the Golgi to the plasma membrane. Transfection with mouse Rab34 rescued this defect. Using endogenous MHC class I (MHC) as a marker, an endoglycosidase H resistance assay showed that ER to medial Golgi traffic remains intact in knock-down cells indicating that Rab34 specifically functions downstream of the ER. Further, brefeldin A treatment revealed that Rab34 effects intraGolgi transport, not exit from the trans-Golgi network. Collectively, these results define Rab34 as a novel member of the secretory pathway acting at the Golgi.

Address correspondence to: Mel Silverman (melvin.silverman{at}utoronto.ca)






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