CAPS acts at a prefusion step in dense-core vesicle exocytosis as a PIP2 binding protein.
CAPS-1 is required for Ca2+-triggered fusion of dense-core vesicles with the plasma membrane, but its site of action and mechanism are unknown. We analyzed the kinetics of Ca2+-triggered exocytosis reconstituted in permeable PC12 cells. CAPS-1 increased the initial rate of Ca2+-triggered vesicle exocytosis by acting at a rate-limiting, Ca2+-dependent prefusion step. CAPS-1 activity depended upon prior ATP-dependent priming during which PIP2 synthesis occurs. CAPS-1 activity and binding to the plasma membrane depended upon PIP2. Ca2+ was ineffective in triggering vesicle fusion in the absence of CAPS-1 but instead promoted desensitization to CAPS-1 resulting from decreased plasma membrane PIP2. We conclude that CAPS-1 functions following ATP-dependent priming as a PIP2 binding protein to enhance Ca2+-dependent DCV exocytosis. Essential prefusion steps in dense-core vesicle exocytosis involve sequential ATP-dependent synthesis of PIP2 and the subsequent PIP2-dependent action of CAPS-1. Regulation of PIP2 levels and CAPS-1 activity would control the secretion of neuropeptides and monoaminergic transmitters.
Department of Biochemistry, University of Wisconsin, Madison, Wisconsin 53706, USA.
Ruslan N
RN
Grishanin
Judith A
JA
Kowalchyk
Vadim A
VA
Klenchin
Kyougsook
K
Ann
Cynthia A
CA
Earles
Edwin R
ER
Chapman
Roy R L
RR
Gerona
Thomas F J
TF
Martin
D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000502:physiology; D002135:Calcium-Binding Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D005089:Exocytosis / Q000502:physiology*; D016716:PC12 Cells; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011485:Protein Binding / Q000502:physiology; D051381:Rats; D011919:Rats, Inbred Strains; D022142:Secretory Vesicles / Q000378:metabolism*; D033921:Vesicular Transport Proteins
C409027:CADPS protein, human; D002135:Calcium-Binding Proteins; D019269:Phosphatidylinositol 4,5-Diphosphate; D033921:Vesicular Transport Proteins; D002118:Calcium