The AP-1A and AP-1B clathrin adaptor complexes define biochemically and functionally distinct membrane domains.
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 mu1A or mu1B 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.
Department of Cell Biology, Ludwig Institute for Cancer Research, Yale University School of Medicine, New Haven, CT 06520, USA. h-folsch@northwestern.edu
Heike
H
Fölsch
Marc
M
Pypaert
Sandra
S
Maday
Laurence
L
Pelletier
Ira
I
Mellman
D033961:Adaptor Protein Complex 1 / Q000737:chemistry* / Q000378:metabolism*; D033983:Adaptor Protein Complex mu Subunits; D000256:Adenoviridae / Q000235:genetics / Q000378:metabolism; D000818:Animals; D018938:Caco-2 Cells; D002352:Carrier Proteins / Q000378:metabolism; D002451:Cell Compartmentation; D002461:Cell Line, Transformed; D016764:Cell Polarity; D002966:Clathrin / Q000378:metabolism*; D003034:Coated Pits, Cell-Membrane / Q000378:metabolism / Q000648:ultrastructure; D011992:Endosomes / Q000378:metabolism / Q000648:ultrastructure; D004847:Epithelial Cells / Q000502:physiology / Q000648:ultrastructure; D005089:Exocytosis; D005656:Fungal Proteins / Q000378:metabolism; D006801:Humans; D018374:LLC-PK1 Cells; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D021381:Protein Transport / Q000502:physiology*; D011990:Receptors, Transferrin / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D013552:Swine; D022161:Transport Vesicles / Q000378:metabolism / Q000648:ultrastructure; D033921:Vesicular Transport Proteins; D021601:trans-Golgi Network / Q000378:metabolism / Q000648:ultrastructure
C438883:AP1M1 protein, human; D033961:Adaptor Protein Complex 1; D033983:Adaptor Protein Complex mu Subunits; D002352:Carrier Proteins; D002966:Clathrin; C103132:EXO70 protein, S cerevisiae; C489607:EXOC4 protein, human; D005656:Fungal Proteins; D008565:Membrane Proteins; D011990:Receptors, Transferrin; D029701:Saccharomyces cerevisiae Proteins; D033921:Vesicular Transport Proteins; C499066:adaptor protein complex 1, mu 1 subunit