A novel caveolar pathway is involved in directing AE1 anion exchanger trafficking in epithelial cells.

摘要

Analysis of the sorting signals within the chicken kidney AE1-4 anion exchanger has begun to reveal a complex sorting pathway that seems to be independent of the clathrin-based machinery. Using chimeras, we identified two independent endocytic motifs in the N-terminal 63 amino acids of AE1-4. One of these signals is tyrosine-based, whereas the other is serine-based. Interestingly, when these signals are present together, either in the full-length molecule or the chimera, they stabilize these molecules to the basolateral membrane. Our studies have shown that the endocytosis of AE1-4 from the basolateral membrane is inhibited, at least in part, by the actin cytoskeleton. In this way, actin regulates the surface localization of the AE1-4 anion exchanger in polarized epithelial cells.;The tyrosine-based signal in our chimeric analyses indicated that this signal is a strong endocytic signal, which is similar to other clathrin-based internalization signals. Surprisingly, we found that this endocytic signal was not dependent on the clathrin-based endocytic machinery. We found, in fact, that these molecules are tightly associated with the caveolar membrane system and suggest that both AE1 and the chimeras are sorted in a caveolar-dependent manner. In agreement, these molecules are trafficked in a cholesterol dependent manner similar to other caveolar cargo, which includes GPI-linked proteins, and lipids. The dependence of the chimeras and AE1-4 on the actin and microtubules closely resembles the requirements of known caveolar cargo. Our data are the first to link a protein-based sorting signal to the caveolar membrane system and represents the first known transmembrane cargo for caveolae.