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A Pleckstrin Homology Domain Specific for Phosphatidylinositol 4,5-Bisphosphate (PtdIns-4,5-P2) and Fused to Green Fluorescent Protein Identifies Plasma Membrane PtdIns-4,5-P2 as Being Important in Exocytosis

Kinetically distinct steps can be distinguished in the secretory response from neuroendocrine cells with slow ATP-dependent priming steps preceding the triggering of exocytosis by Ca2+. One of these priming steps involves the maintenance of phosphatidylinositol 4,5-bisphosphate (PtdIns-4,5-P2) throu...

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Bibliographic Details
Published in:The Journal of biological chemistry 2000-06, Vol.275 (23), p.17878-17885
Main Authors: Holz, Ronald W., Hlubek, Michael D., Sorensen, Scott D., Fisher, Stephen K., Balla, Tamas, Ozaki, Shoichiro, Prestwich, Glenn D., Stuenkel, Edward L., Bittner, Mary A.
Format: Article
Language:English
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Summary:Kinetically distinct steps can be distinguished in the secretory response from neuroendocrine cells with slow ATP-dependent priming steps preceding the triggering of exocytosis by Ca2+. One of these priming steps involves the maintenance of phosphatidylinositol 4,5-bisphosphate (PtdIns-4,5-P2) through lipid kinases and is responsible for at least 70% of the ATP-dependent secretion observed in digitonin-permeabilized chromaffin cells. PtdIns-4,5-P2is usually thought to reside on the plasma membrane. However, because phosphatidylinositol 4-kinase is an integral chromaffin granule membrane protein, PtdIns-4,5-P2 important in exocytosis may reside on the chromaffin granule membrane. In the present study we have investigated the localization of PtdIns-4,5-P2 that is involved in exocytosis by transiently expressing in chromaffin cells a pleckstrin homology (PH) domain that specifically binds PtdIns-4,5-P2 and is fused to green fluorescent protein (GFP). The PH-GFP protein predominantly associated with the plasma membrane in chromaffin cells without any detectable association with chromaffin granules. Rhodamine-neomycin, which also binds to PtdIns-4,5-P2, showed a similar subcellular localization. The transiently expressed PH-GFP inhibited exocytosis as measured by both biochemical and electrophysiological techniques. The results indicate that the inhibition was at a step after Ca2+ entry and suggest that plasma membrane PtdIns-4,5-P2 is important for exocytosis. Expression of PH-GFP also reduced calcium currents, raising the possibility that PtdIns-4,5-P2 in some manner alters calcium channel function in chromaffin cells.
ISSN:0021-9258
1083-351X
DOI:10.1074/jbc.M000925200