[show abstract][hide abstract] ABSTRACT: Fe65 is characterized as an adaptor precursor (APP) through its PID2 element, as well as with the other members of the APP protein family. With the serum- and glucocorticoid-induced kinase 1 (SGK1) substrate specificity information, we found that the putative site of phosphorylation in Fe65 by SGK1 is present on its Ser(566) residue in (560)CRVRFLSFLA(569)(X60469). Thus, we demonstrated that Fe65 and the fluorescein-labeled Fe65 peptide FITC-(560)CRVRFLSFLA(569) are phosphorylated in vitro by SGK1. Phosphorylation of the Ser(566) residue was also demonstrated using a Ser566 phospho-specific antibody. The phospho Fe65 was found mainly in the nucleus, while Fe65 S556A mutant was localized primarily to the cytoplasm. Therefore, these data suggest that SGK1 phosphorylates the Ser(566) residue of Fe65 and that this phosphorylation promotes the migration of Fe65 to the nucleus of the cell.