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Vol. 18, Issue 7, 2687-2697, July 2007

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Recycling Endosomes of Polarized Epithelial Cells Actively Sort Apical and Basolateral Cargos into Separate Subdomains

Anthony Thompson^*, Randy Nessler, Dolora Wisco, Eric Anderson, Bettina Winckler, and David Sheff^*

*Department of Pharmacology and Imaging Core Facility, University of Iowa Carver College of Medicine, Iowa City, IA 52242; Department of Neuroscience, University of Virginia Medical School, Charlottesville, VA 22908; and Department of Cell Biology, Yale School of Medicine and Ludwig Institute for Cancer Research, New Haven, CT 06520

Submitted September 20, 2005; Revised April 25, 2007; Accepted April 26, 2007
Monitoring Editor: Keith Mostov

The plasma membranes of epithelial cells plasma membranes contain distinct apical and basolateral domains that are critical for their polarized functions. However, both domains are continuously internalized, with proteins and lipids from each intermixing in supranuclear recycling endosomes (REs). To maintain polarity, REs must faithfully recycle membrane proteins back to the correct plasma membrane domains. We examined sorting within REs and found that apical and basolateral proteins were laterally segregated into subdomains of individual REs. Subdomains were absent in unpolarized cells and developed along with polarization. Subdomains were formed by an active sorting process within REs, which precedes the formation of AP-1B–dependent basolateral transport vesicles. Both the formation of subdomains and the fidelity of basolateral trafficking were dependent on PI3 kinase activity. This suggests that subdomain and transport vesicle formation occur as separate sorting steps and that both processes may contribute to sorting fidelity.

The online version of this article contains supplemental material at MBC Online (http://www.molbiolcell.org).

Address correspondence to: David Sheff (david-sheff{at}uiowa.edu)

Abbreviations used: Tfn, transferrin; TfnR, transferrin receptor; FcLR, Fc ectodomain fused to low-density-lipoprotein receptor cytoplasmic domain; EE, early endosome; RE, recycling endosome; MDCKT, MDCK cells stably transfected with human transferrin receptor; CHOT, Chinese hamster ovary (CHO) cells stably expressing human Tfn receptor.

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