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Regulation of Apical Membrane Traffic

 

Polarized epithelial cells have the remarkable capacity to generate and maintain differentiated apical and basolateral plasma membrane domains with distinct protein and lipid compositions. This is accomplished in part by the selective delivery of newly synthesized membrane proteins to these domains. In cells of renal origin, these proteins traffic together through the Golgi, and emerge from the trans -Golgi network (TGN) in distinct populations of carriers. Little is known about how apically-destined proteins are selected and packaged in the TGN, although association with glycolipid-enriched lipid microdomains is thought to be important for the delivery of a subset of apical proteins. In addition, both N- and O-glycans can function as apical targeting motifs on some proteins.

We and others have found that apically destined proteins traffic to the membrane in distinct carriers whose formation is independently regulated. Moreover, these carriers appear to fuse with endocytic compartments prior to reaching the apical membrane. Our current studies are directed towards dissecting the mechanisms by which proteins are sorted into transport carriers, identifying the cytoplasmic proteins that facilitate the formation and budding of these carriers, and determining the routes that apical proteins take to the cell surface. Using the combined approaches of in vitro reconstitution assays and live-cell imaging, we hope to generate a more comprehensive view of how apical protein export from the TGN is regulated.

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