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

Area of Science:

• Cell biology
• Molecular biology
• Membrane trafficking

Background:

• Epithelial cells utilize two AP-1 clathrin adaptor complexes, AP-1A and AP-1B, for intracellular transport.
• AP-1A mediates general transport between the TGN and endosomes, while AP-1B directs polarized protein targeting to the basolateral surface in epithelia.
• Both complexes are heterotetramers, differing only in their mu1A or mu1B subunits.

Purpose of the Study:

• To investigate the distinct membrane domains and functions of AP-1A and AP-1B complexes.
• To determine if AP-1B plays a specific role in recruiting components for basolateral transport.

Main Methods:

• Immunofluorescence microscopy to visualize AP-1 complexes and exocyst subunits.
• Cell fractionation to biochemically separate membrane compartments.
• Analysis of exocyst subunit recruitment in response to AP-1 complex expression.

Main Results:

• AP-1A and AP-1B define physically and functionally distinct membrane domains.
• AP-1B expression, but not AP-1A, enhanced the recruitment of exocyst subunits (Sec8, Exo70) essential for basolateral transport.
• Exocyst subunits selectively associated with AP-1B-containing membranes, distinct from AP-1A-positive TGN and near recycling endosomes.

Conclusions:

• AP-1A and AP-1B, despite structural similarities, exhibit specific roles in membrane trafficking.
• AP-1B is crucial for establishing cell polarity by mediating the recruitment of the exocyst complex for basolateral protein delivery.
• This study elucidates the specialized functions of AP-1 complexes in regulating endosomal transport and epithelial cell polarity.