Rapid regulated dense-core vesicle exocytosis requires the CAPS protein

Abstract

Although many proteins essential for regulated neurotransmitter and peptide hormone secretion have been identified, little is understood about their precise roles at specific stages of the multistep pathway of exocytosis. To study the function of CAPS (Ca 2؉ -dependent activator protein for secretion), a protein required for Ca 2؉ -dependent exocytosis of dense-core vesicles, secretory responses in single rat melanotrophs were monitored by patch-clamp membrane capacitance measurements. Flash photolysis of caged Ca 2؉ elicited biphasic capacitance increases consisting of rapid and slow components with distinct Ca 2؉ dependencies. A threshold of Ϸ10 M Ca 2؉ was required to trigger the slow component, while the rapid capacitance increase was recorded already at a intracellular Ca 2؉ activity < 10 M. Both kinetic membrane capacitance components were abolished by botulinum neurotoxin B or E treatment, suggesting involvement of SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor)-dependent vesicle fusion. The rapid but not the slow component was inhibited by CAPS antibody. These results were further clarified by immunocytochemical studies that revealed that CAPS was present on only a subset of dense-core vesicles. Overall, the results indicate that dense-core vesicle exocytosis in melanotrophs occurs by two parallel pathways. The faster pathway exhibits high sensitivity to Ca 2؉ and requires the presence of CAPS, which appears to act at a late stage in the secretory pathway.capacitance ͉ pituitary cells ͉ rat melanotrophs

Important Contribution of α-Neurexins to Ca2+-Triggered Exocytosis of Secretory Granules

“…The vesicle protein synaptotagmin 1 is essential as the Ca 2ϩ sensor of fast release, as demonstrated in hippocampal neurons (Geppert et al, 1994;Fernandez-Chacon et al, 2001) and endocrine cells (Voets et al, 2001b;Kreft et al, 2003). In the fusion complex the essential contribution of the soluble N-ethylmaleimide-sensitive factor attachment protein (SNAP) receptor (SNARE) proteins syntaxin, SNAP25, and synaptobrevin has been demonstrated in neurons by cleavage studies (Sakaba et al, 2005) and also in endocrine cells (Rupnik et al, 2000;Sorensen et al, 2003). Deletion of Munc18 protein silenced neurotransmission (Verhage et al, 2000) and reduced large dense-core vesicle release (Voets et al, 2001a).…”

UNC-73/Trio RhoGEF-2 Activity Modulates Caenorhabditis elegans Motility Through Changes in Neurotransmitter Signaling Upstream of the GSA-1/Gαs Pathway

“…UNC-31 is the C. elegans homolog of mammalian CAPS, a component of the DCV release machinery required for hormone and neuropeptide release from neuroendocrine cells (Walent et al 1992;Rupnik et al 2000). Although CAPS and its paralog CAPS-2 may have additional functions, including synaptic vesicle priming and catecholamine uptake into DCVs, the role of the only C. elegans CAPS homolog, UNC-31, specifically involves DCV docking in the process of exocytosis from neurons (Speidel et al 2005;Gracheva et al 2007;Jockusch et al 2007;Speese et al 2007;Zhou et al 2007;Hammarlund et al 2008).…”

Neuronal calcium sensor-1 potentiates glucose-dependent exocytosis in pancreatic β cells through activation of phosphatidylinositol 4-kinase β

“…PI(4,5)P 2 binds specifically to the Ca 2ϩ -dependent activator protein for secretion (CAPS), which is required for Ca 2ϩ -triggered exocytosis once ATP-dependent priming has been completed (20)(21)(22)(23). In the present study, we have explored the signaling mechanisms by which glucose stimulates PI4K activity in the pancreatic ␤ cell.…”