A novel role for a YXXPhi motif in directing the caveolin-dependent sorting of membrane-spanning proteins.

Previous studies showed that the sequence between amino acids 38 and 63 of the chicken AE1-4 anion exchanger is sufficient to direct basolateral sorting and recycling to the Golgi when fused to a cytoplasmic tailless F(c)RII B2 receptor. Further characterization of the recycling pathway has indicated that the chimera F(c)38-63 colocalizes with caveolin 1 in the basolateral membrane of MDCK cells, and in early endosomes following its internalization from the cell surface. Studies using small interfering RNA (siRNA) and dominant-negative mutants revealed that F(c)38-63 endocytosis is primarily caveolin-dependent and clathrin-independent. The endocytosis of the chimera is also dependent upon cholesterol and dynamin. Co-precipitation studies indicated that caveolin 1 associates with F(c)38-63. Mutation of the tyrosine or leucine residues in the cytoplasmic sequence Y(47)VEL of F(c)38-63 disrupts this interaction and inhibits the endocytosis of the chimera. Additional analyses revealed that AE1-4 also associates with caveolin 1. Mutation of the leucine in the Y(47)VEL sequence of AE1-4 disrupts this interaction, and blocks the recycling of this transporter from the basolateral membrane to the Golgi. The Y(47)VEL tetrapeptide matches the sequence of a YXXPhi motif, and our results indicate a novel role for this motif in directing caveolin-dependent sorting.