title: AP-1A controls secretory granule biogenesis and trafficking of membrane secretory granule proteins.
abstract: The adaptor protein 1A complex (AP-1A) transports cargo between the trans-Golgi network (TGN) and endosomes. In professional secretory cells, AP-1A also retrieves material from immature secretory granules (SGs). The role of AP-1A in SG biogenesis was explored using AtT-20 corticotrope tumor cells expressing reduced levels of the AP-1A μ1A subunit. A twofold reduction in μ1A resulted in a decrease in TGN cisternae and immature SGs and the appearance of regulated secretory pathway components in non-condensing SGs. Although basal secretion of endogenous SG proteins was unaffected, secretagogue-stimulated release was halved. The reduced μ1A levels interfered with the normal trafficking of carboxypeptidase D (CPD) and peptidylglycine α-amidating monooxygenase-1 (PAM-1), integral membrane enzymes that enter immature SGs. The non-condensing SGs contained POMC products and PAM-1, but not CPD. Based on metabolic labeling and secretion experiments, the cleavage of newly synthesized PAM-1 into PHM was unaltered, but PHM basal secretion was increased in sh-μ1A PAM-1 cells. Despite lacking a canonical AP-1A binding motif, yeast two-hybrid studies demonstrated an interaction between the PAM-1 cytosolic domain and AP-1A. Coimmunoprecipitation experiments with PAM-1 mutants revealed an influence of the luminal domains of PAM-1 on this interaction. Thus, AP-1A is crucial for normal SG biogenesis, function and composition.
authors.affiliation: Department of Molecular Biology and Biophysics, University of Connecticut Health Center, Farmington, CT, 06030, USA.
authors.forename: Mathilde
authors.initials: M
authors.lastname: Bonnemaison
authors.forename: Nils
authors.initials: N
authors.lastname: Bäck
authors.forename: Yimo
authors.initials: Y
authors.lastname: Lin
authors.forename: Juan S
authors.initials: JS
authors.lastname: Bonifacino
authors.forename: Richard
authors.initials: R
authors.lastname: Mains
authors.forename: Betty
authors.initials: B
authors.lastname: Eipper
mesh_terms: D033961:Adaptor Protein Complex 1 / Q000378:metabolism*; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D002268:Carboxypeptidases / Q000378:metabolism; D045744:Cell Line, Tumor; D057809:HEK293 Cells; D006801:Humans; D051379:Mice; D006899:Mixed Function Oxygenases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011333:Pro-Opiomelanocortin / Q000378:metabolism; D011485:Protein Binding; D055571:Secretory Pathway; D022142:Secretory Vesicles / Q000378:metabolism*; D021601:trans-Golgi Network / Q000378:metabolism
chemical_list: D033961:Adaptor Protein Complex 1; D009097:Multienzyme Complexes; D011333:Pro-Opiomelanocortin; D006899:Mixed Function Oxygenases; C035189:peptidylglycine monooxygenase; D002268:Carboxypeptidases; C078874:carboxypeptidase D
keywords: PAM; TGN; carboxypeptidase D; peptide hormone; regulated secretion