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A more recent version of this article appeared on October 1, 2007
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Submitted on February 2, 2007
Revised on July 24, 2007
Accepted on July 26, 2007
*Laboratory of Epithelial Cell Biology/Renal Electrolyte Division of the Department of Medicine and
Department of Cell Biology and Physiology, University of Pittsburgh, Pittsburgh, PA 15261;
Department of Physiology and Biophysics, Chicago Medical School, Chicago, IL 60064;
Department of Cell Biology and Neuroscience, Rutgers University, Piscataway, NJ 08854; ||Department of Surgery and Cell and Developmental Biology, Vanderbilt University and the Nashville Veterans Affairs Medical Center, Nashville, TN 37212; ¶Department of Anatomy and Cell Biology, University of Iowa, Iowa City, IA 52242
Monitoring Editor: Keith Mostov
The octameric exocyst complex is associated with the junctional complex and recycling endosomes, and is proposed to selectively tether cargo vesicles directed toward the basolateral surface of polarized Madin-Darby canine kidney (MDCK) cells. We observed that the exocyst subunits Sec6, Sec8, and Exo70 were localized to early endosomes, transferrin-positive common recycling endosomes, and Rab11a-positive apical recycling endosomes of polarized MDCK cells. Consistent with its localization to multiple populations of endosomes, addition of function-blocking Sec8 antibodies to streptolysin-O permeabilized cells revealed exocyst requirements for several endocytic pathways including basolateral recycling, apical recycling, and basolateral-to-apical transcytosis. The latter was selectively dependent on interactions between the small GTPase Rab11a and Sec15A and was inhibited by expression of the C-terminus of Sec15A or down-regulation of Sec15A expression using shRNA. These results indicate that the exocyst complex may be a multi-purpose regulator of endocytic traffic directed toward both poles of polarized epithelial cells, and that transcytotic traffic is likely to require Rab11a-dependent recruitment and modulation of exocyst function, likely through interactions with Sec15A.
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