Widespread Dysregulation of Peptide Hormone Release in Mice Lacking Adaptor Protein AP-3

Abstract

The regulated secretion of peptide hormones, neural peptides and many growth factors depends on their sorting into large dense core vesicles (LDCVs) capable of regulated exocytosis. LDCVs form at the trans-Golgi network, but the mechanisms that sort proteins to this regulated secretory pathway and the cytosolic machinery that produces LDCVs remain poorly understood. Recently, we used an RNAi screen to identify a role for heterotetrameric adaptor protein AP-3 in regulated secretion and in particular, LDCV formation. Indeed, mocha mice lacking AP-3 have a severe neurological and behavioral phenotype, but this has been attributed to a role for AP-3 in the endolysosomal rather than biosynthetic pathway. We therefore used mocha mice to determine whether loss of AP-3 also dysregulates peptide release in vivo. We find that adrenal chromaffin cells from mocha animals show increased constitutive exocytosis of both soluble cargo and LDCV membrane proteins, reducing the response to stimulation. We also observe increased basal release of both insulin and glucagon from pancreatic islet cells of mocha mice, suggesting a global disturbance in the release of peptide hormones. AP-3 exists as both ubiquitous and neuronal isoforms, but the analysis of mice lacking each of these isoforms individually and together shows that loss of both is required to reproduce the effect of the mocha mutation on the regulated pathway. In addition, we show that loss of the related adaptor protein AP-1 has a similar effect on regulated secretion but exacerbates the effect of AP-3 RNAi, suggesting distinct roles for the two adaptors in the regulated secretory pathway.

Upregulation of μ3A Drives Homeostatic Plasticity by Rerouting AMPAR into the Recycling Endosomal Pathway

“…Systemic loss of functional AP-3 causes endosomal trafficking defects, Hermansky-Pudlak syndrome, and neurological symptoms (Kantheti et al, 1998; Lane and Deol, 1974; Peden et al, 2002; Seong et al, 2005; Sirkis et al, 2013; Swank et al, 2000; Yang et al, 2000). These have mainly been ascribed to defects in lysosomal trafficking and/or biogenesis of LROs.…”

SORCS1 is necessary for normal insulin secretory granule biogenesis in metabolically stressed β cells

“…Sor4 expression is induced in coordination with SG proteins upon discharge of the mucocyst. One of these proteins, AP3, has recently been shown to be essential for the regulated secretion of insulin in β cells; β cells deficient in AP3 secreted insulin through the constitutive pathway (59,60). In Toxoplasma, deletion of the Vps10 homolog sortilin-like receptor (TgSORTLR) abolished the formation of its secretory organelles, rhoptries and micronemes.…”

Two Dipolar α-Helices within Hormone-encoding Regions of Proglucagon Are Sorting Signals to the Regulated Secretory Pathway

“…PC12 and ␣TC1-6 cells express chromogranin A, and human ␣ cells additionally express chromogranin B and secretogranins III (34,45,46), whereas L cells express CgB and secretogranins II, III, and V (47), thus showing similarities in sorting machinery. The exocytosis machinery is also similar, with both PC12 and ␣TC1-6 cells expressing the SNARE proteins syntaxin-1a, VAMP2, SNAP25 (34,48), and the SNARE-associated proteins Munc13-1 and Munc18-1 (49, 50), whereas AP-1 and AP-3 are expressed by PC12 and mouse ␣ cells (51). More recently, it has been shown that the GLUTag L cell model also expresses SNAP25, VAMP-1, -2 and -3, syntaxin-1a, and Munc18-1 (52).…”