AP-1A Controls Secretory Granule Biogenesis and Trafficking of Membrane Secretory Granule Proteins

作者：Bonnemaison Mathilde; Back Nils; Lin Yimo; Bonifacino Juan S; Mains Richard; Eipper Betty^*

来源：Traffic, 2014, 15(10): 1099-1121.

DOI：10.1111/tra.12194

• carboxypeptidase D
• PAM
• peptide hormone
• regulated secretion
• TGN

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 1A subunit. A twofold reduction in 1A 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 1A levels interfered with the normal trafficking of carboxypeptidase D (CPD) and peptidylglycine -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-1A 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.

• 出版日期2014-10