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Effect of dexamethasone on prostaglandin synthesis and on lipocortin status in human endothelial cells. Inhibition of prostaglandin I2 synthesis occurring without alteration of arachidonic acid liberation and of lipocortin synthesis
Glucocorticoids have been shown to decrease prostaglandin I2 synthesis in human endothelial cells, suggesting the possible involvement of lipocortin in the inhibition of arachidonic acid liberation achieved by phospholipase A2 (De Caterina, R., and Weksler, B. B. (1986) Thromb. Haemostasis 55, 369-3...
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Published in: | The Journal of biological chemistry 1989-02, Vol.264 (6), p.3506-3513 |
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Main Authors: | , , , , |
Format: | Article |
Language: | English |
Subjects: | |
Online Access: | Get full text |
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Summary: | Glucocorticoids have been shown to decrease prostaglandin I2 synthesis in human endothelial cells, suggesting the possible
involvement of lipocortin in the inhibition of arachidonic acid liberation achieved by phospholipase A2 (De Caterina, R.,
and Weksler, B. B. (1986) Thromb. Haemostasis 55, 369-374). To test this hypothesis, human endothelial cells labeled with
[14C]arachidonic acid were stimulated with thrombin (2 units/ml, 10 min), resulting in the secretion of free arachidonic acid
together with various 14C-labeled metabolites, mainly 6-keto-prostaglandin F1 alpha, the stable derivative of prostaglandin
I2. Under conditions where prior incubation of cells with dexamethasone reduced by 51% 6-keto-prostaglandin F1 alpha production,
phospholipid hydrolysis induced by thrombin remained unaffected. Using three rabbit polyclonal antibodies directed against
endonexin I, lipocortin I, and lipocortin II, evidence was obtained for the presence in human endothelial cells of equivalent
amounts of lipocortin I and an immunologically unrelated 33-kDa protein, together with lower quantities of 67-kDa calelectrin/calcimedin.
These Ca2+- and phospholipid-binding proteins were selectively extracted with [ethylene-bis(oxyethylene-nitrilo)]tetraacetic
acid (EGTA) from cell membranes precipitated in the presence of Ca2+, and they displayed an inhibitory activity against pig
pancreas phospholipase A2. However, the amounts of the three proteins were not changed by cell treatment with 2.5 microM dexamethasone,
as detected upon polyacrylamide gel electrophoresis by silver staining, immunoblotting, or autoradiography following [35S]methionine
in vivo labeling. Since the antiphospholipase A2 activity of EGTA extracts was hardly modified, it was concluded that an increased
synthesis of lipocortin cannot account for the inhibition of prostaglandin synthesis brought about by dexamethasone, suggesting
other biological functions for these proteins. |
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ISSN: | 0021-9258 1083-351X |