Mechanisms underlying the neuronal calcium sensor-1-evoked enhancement of exocytosis in PC12 cells.
Neuronal calcium sensor-1 (NCS-1) or the originally identified homologue frequenin belongs to a superfamily of EF-hand calcium binding proteins. Although NCS-1 is thought to enhance synaptic efficacy or exocytosis mainly by activating ion channel function, the detailed molecular basis for the enhancement is still a matter of debate. Here, mechanisms underlying the NCS-1-evoked enhancement of exocytosis were investigated using PC12 cells overexpressing NCS-1. NCS-1 was found to have a broad distribution in the cells being partially distributed in the cytosol and associated to vesicles and tubular-like structures. Biochemical and immunohistochemical studies indicated that NCS-1 partially colocalized with the light synaptic vesicle marker synaptophysin. When stimulated with UTP or bradykinin, agonists to phospholipase C-linked receptors, NCS-1 enhanced the agonist-mediated elementary and global Ca2+ signaling and increased the levels of downstream signals of phosphatidylinositol 4-kinase. NCS-1 enhanced the UTP-evoked exocytosis but not the depolarization-evoked Ca2+ responses or exocytosis, suggesting that the enhancement by NCS-1 should involve phospholipase C-linked receptor-mediated signals rather than the Ca2+ channels or exocytotic machinery per se. Taken together, NCS-1 enhances phosphoinositide turnover, resulting in enhancement of Ca2+ signaling and exocytosis. This is a novel regulatory mechanism of exocytosis that might involve the activation of phosphatidylinositol 4-kinase.
Koizumi
Schuichi
S
Section of Neuropharmacology, Division of Pharmacology, National Institute of Health Sciences, 1-18-1 Kamiyoga, Setagaya, Tokyo 158-8501, Japan. skoizumi@nihs.go.jp
Rosa
Patrizia
P
Willars
Gary B
GB
Challiss
R A John
RA
Taverna
Elena
E
Francolini
Maura
M
Bootman
Martin D
MD
Lipp
Peter
P
Inoue
Kazuhide
K
Roder
John
J
Jeromin
Andreas
A
D000818:Animals; D001920:Bradykinin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000378:metabolism / Q000502:physiology*; D005089:Exocytosis / Q000502:physiology*; D005455:Fluorescent Antibody Technique; D051580:Neuronal Calcium-Sensor Proteins; D009479:Neuropeptides / Q000378:metabolism / Q000502:physiology*; D016716:PC12 Cells; D010716:Phosphatidylinositols / Q000378:metabolism; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D015398:Signal Transduction; D013347:Subcellular Fractions / Q000378:metabolism; D014544:Uridine Triphosphate / Q000494:pharmacology
D002135:Calcium-Binding Proteins; D051580:Neuronal Calcium-Sensor Proteins; D009479:Neuropeptides; D010716:Phosphatidylinositols; C101464:frequenin calcium sensor proteins; D011188:Potassium; D001920:Bradykinin; D002118:Calcium; D014544:Uridine Triphosphate