Phosphatidylinositol 4-OH kinase is a downstream target of neuronal calcium sensor-1 in enhancing exocytosis in neuroendocrine cells.
Neuronal calcium sensor-1 (NCS-1), the mammalian orthologue of frequenin, belongs to a family of EF-hand-containing Ca(2+) sensors. NCS-1/frequenin has been shown to enhance synaptic transmission in PC12 cells and Drosophila and Xenopus, respectively. However, the precise molecular mechanism for the enhancement of exocytosis is largely unknown. In PC12 cells, NCS-1 potentiated exocytosis evoked by ATP, an agonist to phospholipase C-linked receptors, but had no effect on depolarization-evoked release. NCS-1 also enhanced exocytosis triggered by ionomycin, a Ca(2+) ionophore that bypasses K(+) and Ca(2+) channels. Overexpression of NCS-1 caused a shift in the dose-response curve of inhibition of ATP-evoked secretion using phenylarsine oxide, an inhibitor of phosphatidylinositol 4-OH kinase (PI4K). Plasma membrane phosphatidylinositol 4,5-bisphosphate pools were increased upon NCS-1 transfection as visualized using a phospholipase C-delta pleckstrin homology domain-green fluorescent protein construct. NCS-1-transfected cell extracts displayed increased phosphatidylinositol-4-phosphate biosynthesis, indicating an increase in PI4K activity. Mutations in NCS-1 equivalent to those that abolish the interaction of recoverin, another EF-hand-containing Ca(2+) sensor, with its downstream target rhodopsin kinase, lost their ability to enhance exocytosis. Taken together, the present data indicate that NCS-1 modulates the activity of PI4K, leading to increased levels of phosphoinositides and concomitant enhancement of exocytosis.
Rajebhosale
Manisha
M
University of Manchester, School of Biological Sciences, Oxford Road, Manchester M13 9PT, United Kingdom.
Greenwood
Sam
S
Vidugiriene
Jolanta
J
Jeromin
Andreas
A
Hilfiker
Sabine
S
D019870:1-Phosphatidylinositol 4-Kinase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001152:Arsenicals / Q000494:pharmacology; D020013:Calcium Signaling / Q000502:physiology; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D004330:Drosophila; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005089:Exocytosis / Q000187:drug effects / Q000502:physiology*; D015759:Ionomycin / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D051580:Neuronal Calcium-Sensor Proteins; D009479:Neuropeptides / Q000378:metabolism*; D009490:Neurosecretory Systems / Q000187:drug effects / Q000502:physiology; D016716:PC12 Cells; D010673:Pheochromocytoma; D051381:Rats; D010738:Type C Phospholipases / Q000378:metabolism; D014981:Xenopus
D001152:Arsenicals; D002135:Calcium-Binding Proteins; D004791:Enzyme Inhibitors; D051580:Neuronal Calcium-Sensor Proteins; D009479:Neuropeptides; C101464:frequenin calcium sensor proteins; C029341:oxophenylarsine; D015759:Ionomycin; D000255:Adenosine Triphosphate; D019870:1-Phosphatidylinositol 4-Kinase; D010738:Type C Phospholipases