Two distinct secretory vesicle-priming steps in adrenal chromaffin cells.
Priming of large dense-core vesicles (LDCVs) is a Ca(2+)-dependent step by which LDCVs enter a release-ready pool, involving the formation of the soluble N-ethyl-maleimide sensitive fusion protein attachment protein (SNAP) receptor complex consisting of syntaxin, SNAP-25, and synaptobrevin. Using mice lacking both isoforms of the calcium-dependent activator protein for secretion (CAPS), we show that LDCV priming in adrenal chromaffin cells entails two distinct steps. CAPS is required for priming of the readily releasable LDCV pool and sustained secretion in the continued presence of high Ca(2+) concentrations. Either CAPS1 or CAPS2 can rescue secretion in cells lacking both CAPS isoforms. Furthermore, the deficit in the readily releasable LDCV pool resulting from CAPS deletion is reversed by a constitutively open form of syntaxin but not by Munc13-1, a priming protein that facilitates the conversion of syntaxin to the open conformation. Our data indicate that CAPS functions downstream of Munc13s but also interacts functionally with Munc13s in the LDCV-priming process.
Liu
Yuanyuan
Y
Institut für Physiologie, Universität des Saarlandes, 66421 Homburg, Germany.
Schirra
Claudia
C
Edelmann
Ludwig
L
Matti
Ulf
U
Rhee
JeongSeop
J
Hof
Detlef
D
Bruns
Dieter
D
Brose
Nils
N
Rieger
Heiko
H
Stevens
David R
DR
Rettig
Jens
J
D000311:Adrenal Glands / Q000166:cytology*; D000818:Animals; D002135:Calcium-Binding Proteins / Q000378:metabolism; D019439:Chromaffin Cells / Q000378:metabolism* / Q000648:ultrastructure; D003198:Computer Simulation; D051379:Mice; D018345:Mice, Knockout; D009419:Nerve Tissue Proteins / Q000378:metabolism; D009716:Numerical Analysis, Computer-Assisted; D050765:Qa-SNARE Proteins / Q000378:metabolism; D055571:Secretory Pathway; D022142:Secretory Vesicles / Q000378:metabolism* / Q000648:ultrastructure
C480975:CAPS2 protein, mouse; C510820:Cadps protein, mouse; D002135:Calcium-Binding Proteins; D009419:Nerve Tissue Proteins; D050765:Qa-SNARE Proteins; C503321:Unc13a protein, mouse