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MBC in Press, published online ahead of print September 29, 2004
Mol. Biol. Cell 10.1091/mbc.E04-08-0747

A more recent version of this article appeared on December 1, 2004
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Submitted on August 27, 2004
Revised on September 15, 2004
Accepted on September 16, 2004

Rab9 GTPase Regulates Late Endosome Size and Requires Effector Interaction for Its Stability

Ian G. Ganley, Kate Carroll, Lenka Bittova, and Suzanne Pfeffer*

Department of Biochemistry, Stanford University School of Medicine, Stanford, CA 94305-5307

Monitoring Editor: Jennifer Lippincott-Schwartz

Rab9 GTPase resides in a late endosome microdomain together with mannose 6-phosphate receptors (MPRs) and the protein, TIP47. To explore the importance of Rab9 for microdomain establishment, we depleted the protein from cultured cells. Rab9 depletion decreased late endosome size and reduced the numbers of multi-lamellar and dense-tubule containing late endosomes/lysosomes, but not multi-vesicular endosomes. The remaining late endosomes and lysosomes were more tightly clustered near the nucleus, implicating Rab9 in endosome localization. Cells displayed increased surface MPRs and LAMP1 protein. In addition, cells showed increased MPR synthesis in conjunction with MPR mis-sorting to the lysosome. Surprisingly, Rab9 stability on late endosomes required interaction with TIP47. Rabs are thought of as independent, prenylated entities that reside either on membranes or in cytosol, bound to GDP dissociation inhibitor. These data show that Rab9 stability is strongly influenced by a specific effector interaction. Moreover, Rab9 and the proteins with which it interacts seem critical for the maintenance of specific late endocytic compartments and endosome/lysosome localization.

*Corresponding author. E-mail: pfeffer{at}stanford.edu






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