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Published online 5 February 2001. doi:10.1083/jcb.152.3.595
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© The Rockefeller University Press, 0021-9525/2001//595 $5.00
The Journal of Cell Biology, Volume 152, Number 3, , 2001 595-606

Original Article

Distribution and Function of Ap-1 Clathrin Adaptor Complexes in Polarized Epithelial Cells



Heike Fölscha, Marc Pypaerta, Peter Schub, and Ira Mellmana

a Department of Cell Biology and Ludwig Institute for Cancer Research, Yale University School of Medicine, New Haven, Connecticut 06520
b Center for Biochemistry and Molecular Cell Biology, Biochemistry Department II, University of Göttingen, D-37073 Göttingen, Germany
Department of Cell Biology, Yale University School of Medicine, 333 Cedar St., New Haven, CT 06510.(203) 785-4301(203) 785-4303

ira.mellman{at}yale.edu

Expression of the epithelial cell–specific heterotetrameric adaptor complex AP-1B is required for the polarized distribution of many membrane proteins to the basolateral surface of LLC-PK1 kidney cells. AP-1B is distinguished from the ubiquitously expressed AP-1A by exchange of its single 50-kD µ subunit, µ1A, being replaced by the closely related µ1B. Here we show that this substitution is sufficient to couple basolateral plasma membrane proteins, such as a low-density lipoprotein receptor (LDLR), to the AP-1B complex and to clathrin. The interaction between LDLR and AP-1B is likely to occur in the trans-Golgi network (TGN), as was suggested by the localization of functional, epitope-tagged µ1 by immunofluorescence and immunoelectron microscopy. Tagged AP-1A and AP-1B complexes were found in the perinuclear region close to the Golgi complex and recycling endosomes, often in clathrin-coated buds and vesicles. Yet, AP-1A and AP-1B localized to different subdomains of the TGN, with only AP-1A colocalizing with furin, a membrane protein that uses AP-1 to recycle between the TGN and endosomes. We conclude that AP-1B functions by interacting with its cargo molecules and clathrin in the TGN, where it acts to sort basolateral proteins from proteins destined for the apical surface and from those selected by AP-1A for transport to endosomes and lysosomes.

Key Words: cell polarity • Golgi complex • furin • trans-Golgi network • endosomes

© 2001 The Rockefeller University Press

Abbreviations used in this paper: FSG; fish skin gelatin; HA, hemagglutinin; LDLR, low-density lipoprotein receptor; pfu, plaque forming unit; Tfn, transferrin; TfnR, Tfn receptor.


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