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Vol. 19, Issue 10, 4167-4176, October 2008

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Regulation of Early Endosomal Entry by the Drosophila Tumor Suppressors Rabenosyn and Vps45

Holly A. Morrison^*, Heather Dionne^*, Tor Erik Rusten, Andreas Brech, William W. Fisher, Barret D. Pfeiffer, Susan E. Celniker, Harald Stenmark, and David Bilder^*

*Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720; Centre for Cancer Biomedicine, University of Oslo, and Department of Biochemistry, The Norwegian Radium Hospital, Montebello, N-0310 Oslo, Norway; and Berkeley Drosophila Genome Project, Lawrence Berkeley National Laboratory, Berkeley, CA 94720

Submitted July 14, 2008; Revised July 24, 2008; Accepted July 29, 2008
Monitoring Editor: Sandra L. Schmid

The small GTPase Rab5 has emerged as an important regulator of animal development, and it is essential for endocytic trafficking. However, the mechanisms that link Rab5 activation to cargo entry into early endosomes remain unclear. We show here that Drosophila Rabenosyn (Rbsn) is a Rab5 effector that bridges an interaction between Rab5 and the Sec1/Munc18-family protein Vps45, and we further identify the syntaxin Avalanche (Avl) as a target for Vps45 activity. Rbsn and Vps45, like Avl and Rab5, are specifically localized to early endosomes and are required for endocytosis. Ultrastructural analysis of rbsn, Vps45, avl, and Rab5 null mutant cells, which show identical defects, demonstrates that all four proteins are required for vesicle fusion to form early endosomes. These defects lead to loss of epithelial polarity in mutant tissues, which overproliferate to form neoplastic tumors. This work represents the first characterization of a Rab5 effector as a tumor suppressor, and it provides in vivo evidence for a Rbsn–Vps45 complex on early endosomes that links Rab5 to the SNARE fusion machinery.

Address correspondence to: David Bilder (bilder{at}berkeley.edu)

Abbreviations used: Avl, Avalanche; Crb, Crumbs; Rbsn, Rabenosyn

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