AP-3 complex sorts preferential cargo to govern dense core vesicle function in neuroendocrine cells

This study reveals new insights into the role of the Adaptor protein (AP-3) complex in dense core vesicle function. Despite numerous studies, an existing knowledge lacuna in the role of AP-3 in DCV function prompted us to delve deeper. Advanced microscopy and biochemical analysis revealed compromised DCV exocytosis in AP-3-depleted PC12 cells and C. elegans. AP-3 depletion altered the size and positioning of DCVs. Golgi defects and RUSH (Retention under Selective Hook) substantiated the role of AP-3 in trans-Golgi DCV budding. Proteomics revealed the loss of specific known and putative novel DCV proteins, which were mislocalized and rerouted to lysosomes in AP-3-depleted cells. Bioinformatics, Proximity ligation assays and Co-immunoprecipitation identified interactions of mislocalized proteins with AP-3 subunit. These findings corroborated with functional defects in granule maturation, release modes, Zinc and neurotransmitter mobilisation. Our study highlights the complexity of the AP-3 complex in regulating DCV function and its importance in vesicle transport in neurons and neuroendocrine cells. SummaryThis work reveals the critical role of AP-3 complex in DCV function, highlighting its impact on DCV exocytosis, positioning, and trans-Golgi budding. This study identifies Dlk1 as a novel DCV cargo.