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Published 27 October 2003. doi:10.1083/jcb.200309020
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© The Rockefeller University Press, 0021-9525/2003/10/351 $8.00
The Journal of Cell Biology, Volume 163, Number 2, 351-362


Article

The AP-1A and AP-1B clathrin adaptor complexes define biochemically and functionally distinct membrane domains

Heike Fölsch2, Marc Pypaert1, Sandra Maday1, Laurence Pelletier1 and Ira Mellman1

1 Department of Cell Biology, Ludwig Institute for Cancer Research, Yale University School of Medicine, New Haven, CT 06520
2 Department of Biochemistry, Molecular Biology, and Cell Biology, Northwestern University, Evanston, IL 60208

Address correspondence to Heike Fölsch, Department of Biochemistry, Molecular Biology, and Cell Biology, Northwestern University, 2205 Tech Drive, Evanston, IL 60208-3500. Tel.: (847) 491-5089. Fax: (847) 467-1380. email: h-folsch{at}northwestern.edu

Most epithelial cells contain two AP-1 clathrin adaptor complexes. AP-1A is ubiquitously expressed and involved in transport between the TGN and endosomes. AP-1B is expressed only in epithelia and mediates the polarized targeting of membrane proteins to the basolateral surface. Both AP-1 complexes are heterotetramers and differ only in their 50-kD µ1A or µ1B subunits. Here, we show that AP-1A and AP-1B, together with their respective cargoes, define physically and functionally distinct membrane domains in the perinuclear region. Expression of AP-1B (but not AP-1A) enhanced the recruitment of at least two subunits of the exocyst complex (Sec8 and Exo70) required for basolateral transport. By immunofluorescence and cell fractionation, the exocyst subunits were found to selectively associate with AP-1B–containing membranes that were both distinct from AP-1A–positive TGN elements and more closely apposed to transferrin receptor–positive recycling endosomes. Thus, despite the similarity of the two AP-1 complexes, AP-1A and AP-1B exhibit great specificity for endosomal transport versus cell polarity.

Key Words: epithelial cells; basolateral sorting; exocytosis; TGN; exocyst


The online version of this article includes supplemental material.

Abbreviations used in this paper: CHC, clathrin heavy chain; CI-MPR, cation-independent mannose 6-phosphate receptor; Tfn, transferrin; VSVG, vesicular stomatitis virus G protein.


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