Complexin II plays a positive role in Ca2+-triggered exocytosis by facilitating vesicle priming

TY - JOUR

T1 - Complexin II plays a positive role in Ca2+-triggered exocytosis by facilitating vesicle priming

AU - Cai, Haijiang

AU - Reim, Kerstin

AU - Varoqueaux, Frederique

AU - Tapechum, Sompol

AU - Hill, Kerstin

AU - Sørensen, Jakob B

AU - Brose, Nils

AU - Chow, Robert H

PY - 2008/12

Y1 - 2008/12

N2 - SNARE-mediated exocytosis is a multistage process central to synaptic transmission and hormone release. Complexins (CPXs) are small proteins that bind very rapidly and with a high affinity to the SNARE core complex, where they have been proposed recently to inhibit exocytosis by clamping the complex and inhibiting membrane fusion. However, several other studies also suggest that CPXs are positive regulators of neurotransmitter release. Thus, whether CPXs are positive or negative regulators of exocytosis is not known, much less the stage in the vesicle life cycle at which they function. Here, we systematically dissect the vesicle stages leading up to exocytosis using a knockout-rescue strategy in a mammalian model system. We show that adrenal chromaffin cells from CPX II knockout mice exhibit markedly diminished releasable vesicle pools (comprising the readily and slowly releasable pools), while showing no change in the kinetics of fusion pore dilation or morphological vesicle docking. Overexpression of WT CPX II-but not of SNARE-binding-deficient mutants-restores the size of the the releasable pools in knockout cells, and in WT cells it markedly enlarges them. Our results show that CPXs regulate the size of the primed vesicle pools and have a positive role in Ca(2+)-triggered exocytosis.

AB - SNARE-mediated exocytosis is a multistage process central to synaptic transmission and hormone release. Complexins (CPXs) are small proteins that bind very rapidly and with a high affinity to the SNARE core complex, where they have been proposed recently to inhibit exocytosis by clamping the complex and inhibiting membrane fusion. However, several other studies also suggest that CPXs are positive regulators of neurotransmitter release. Thus, whether CPXs are positive or negative regulators of exocytosis is not known, much less the stage in the vesicle life cycle at which they function. Here, we systematically dissect the vesicle stages leading up to exocytosis using a knockout-rescue strategy in a mammalian model system. We show that adrenal chromaffin cells from CPX II knockout mice exhibit markedly diminished releasable vesicle pools (comprising the readily and slowly releasable pools), while showing no change in the kinetics of fusion pore dilation or morphological vesicle docking. Overexpression of WT CPX II-but not of SNARE-binding-deficient mutants-restores the size of the the releasable pools in knockout cells, and in WT cells it markedly enlarges them. Our results show that CPXs regulate the size of the primed vesicle pools and have a positive role in Ca(2+)-triggered exocytosis.

KW - Adaptor Proteins, Vesicular Transport

KW - Animals

KW - Calcium

KW - Catecholamines

KW - Chromaffin Cells

KW - Exocytosis

KW - Female

KW - Male

KW - Membrane Potentials

KW - Mice

KW - Mice, Mutant Strains

KW - Microscopy, Electron

KW - Nerve Tissue Proteins

KW - Patch-Clamp Techniques

KW - SNARE Proteins

KW - Secretory Vesicles

U2 - 10.1073/pnas.0810232105

DO - 10.1073/pnas.0810232105

M3 - Journal article

C2 - 19033464

SN - 0027-8424

VL - 105

SP - 19538

EP - 19543

JO - Proceedings of the National Academy of Sciences of the United States of America

JF - Proceedings of the National Academy of Sciences of the United States of America

IS - 49

ER -