The clathrin adaptor AP-1A mediates basolateral polarity

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Clathrin and adaptor protein 1B (AP-1B) are known to mediate basolateral trafficking in epithelial cells.
• The absence of AP-1B in some epithelia and the viability of AP-1B knockout mice suggest alternative mechanisms for basolateral polarity control.

Purpose of the Study:

• To investigate the role of the ubiquitous clathrin adaptor AP-1A in basolateral protein sorting.
• To elucidate the complementary functions of AP-1A and AP-1B in maintaining epithelial polarity.

Main Methods:

• RNA interference (RNAi) to knockdown AP-1A and AP-1B in MDCK cells.
• Analysis of basolateral protein missorting.
• Localization studies of AP-1A at the trans-Golgi network (TGN).
• Yeast two-hybrid assays to detect protein interactions.

Main Results:

• Knockdown of AP-1A leads to basolateral protein missorting, particularly after AP-1B knockdown, indicating functional compensation.
• AP-1A knockdown causes basolateral proteins to spill into recycling endosomes, the functional site of AP-1B.
• Interactions between the transferrin receptor's basolateral signal and both AP-1A and AP-1B were confirmed.

Conclusions:

• AP-1A has a distinct and significant role in basolateral protein sorting, independent of AP-1B.
• AP-1A and AP-1B exhibit complementary roles in regulating epithelial basolateral polarity.
• AP-1 adaptors are established as major regulators of epithelial polarity.