The tetraspanin CD63 enhances the internalization of the H,K-ATPase β-subunit

Abstract

The tetraspanin CD63 resides in late endosomes, lysosomes, secretory vesicles, and at the plasma membrane, and it moves among these compartments. We find that CD63 is present also in tubulovesicular elements, the intracellular compartments that contain the H,K-ATPase in unstimulated gastric parietal cells. The H,K-ATPase β-subunit and CD63 colocalize in parietal cells and form a complex that can be coprecipitated. The β-subunit and CD63 also interact when they are coexpressed in COS-7 cells. Furthermore, expression with CD63 induces the redistribution of the β-subunit from the cell surface to CD63+ intracellular compartments. Immunofluorescence and biochemical experiments reveal that this redistribution occurs by enhanced endocytosis of H,K-ATPase β-subunit complexed with CD63. Coexpression of the β-subunit with mutant CD63 polypeptides demonstrates that the enhanced internalization of the β-subunit depends on the capacity of CD63 to interact with adaptor protein complexes 2 and 3. These data indicate that CD63 serves as an adaptor protein that links its interaction partners to the endocytic machinery of the cell and suggest a previously uncharacterized protein-trafficking role for the tetraspanins.