title: The epsilon hinge-ear region regulates membrane localization of the AP-4 complex.
abstract: Adaptor protein (AP) complexes are key factors for the spatial and temporal regulation of intracellular trafficking events. Four complexes (AP-1, -2, -3, -4) are known, among which AP-4 is only poorly characterized. Recent work suggests a role for AP-4 in the intracellular trafficking of the β-amyloid precursor protein and molecular genetics showed that the loss of functional AP-4 is associated with congenital neuronal disorders of severe cognitive dysfunction. To unravel the molecular mechanisms controlling AP-4 functions, we established the intracellular expression of recombinant AP-4 complex. This approach combined with the analysis of mutant complexes allowed us to discover that the epsilon adaptin hinge-ear region has a function in membrane recruitment of AP-4. We further show that this process is phosphorylation dependent and involves PP2A-like protein phosphatases and a staurosporine-sensitive kinase. Deletion of the residues 839-871 in the carboxy-terminal region of the hinge of epsilon adaptin abrogated the membrane/cytosol recycling of AP-4. As targets of phosphorylation, we identified three serine residues: S847, S868 and S871. We conclude that the terminal hinge region and the appendage of the AP-4 epsilon subunit are involved in membrane association in a process that is controlled by phosphorylation and dephosphorylation events.
authors.affiliation: Department of Biomedical Sciences and Biotechnologies, Faculty of Medicine, University of Brescia, Viale Europa 11, 25123 Brescia, Italy.
authors.forename: Lucia
authors.initials: L
authors.lastname: Paolini
authors.forename: Annalisa
authors.initials: A
authors.lastname: Radeghieri
authors.forename: Sara
authors.initials: S
authors.lastname: Civini
authors.forename: Luigi
authors.initials: L
authors.lastname: Caimi
authors.forename: Doris
authors.initials: D
authors.lastname: Ricotta
mesh_terms: D033964:Adaptor Protein Complex 4 / Q000235:genetics / Q000378:metabolism*; D034001:Adaptor Protein Complex Subunits / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D054648:Protein Phosphatase 2 / Q000378:metabolism; D021381:Protein Transport; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D012694:Serine / Q000378:metabolism; D014407:Tumor Cells, Cultured
chemical_list: D033964:Adaptor Protein Complex 4; D034001:Adaptor Protein Complex Subunits; D008565:Membrane Proteins; D011994:Recombinant Proteins; D012694:Serine; D054648:Protein Phosphatase 2