Protein kinase C-independent activation of a novel nonspecific phospholipase C pathway by phorbol myristate acetate releases arachidonic acid for prostaglandin synthesis in MC3T3-E1 osteoblasts.
The effects of phorbol myristate acetate, an activator of protein kinase C, on the release of [3H]arachidonic acid and prostaglandin synthesis were studied in an osteoblast cell line (MC3T3-E1). Phorbol myristate acetate (20 uM) liberated 16 and 55% of the [3H]arachidonate in prelabeled phosphatidylinositol and phosphatidylethanolamine, respectively; and evoked a 19-fold stimulation in the synthesis of prostaglandin E2. Phorbol myristate acetate doubled the cellular mass of 1,2-diacylglycerol and stimulated the liberation of [3H]arachidonate from the diacylglycerol pool in prelabeled cells. The diacylglycerol lipase inhibitor RHC 80267 blocked 75-80% of the phorbol ester-promoted (total) cellular liberation of [3H]arachidonic acid and production of prostaglandin E2. In comparison, the release of [3H]arachidonate from phosphatidylethanolamine (but not phosphatidylinositol) was only partially antagonized (to the same degree) by the PLA2 inhibitor p-bromophenacylbromide and the protein kinase C inhibitor Et-18-OMe, PMA-induced formation of diacylglycerol or synthesis of PGE2 was not affected by the prior inhibition of protein kinase C. Therefore, we have shown a novel pathway for the liberation of arachidonic acid in osteoblasts involving the nonspecific hydrolysis of phosphatidylinositol and phosphatidylethanolamine by phospholipase C followed by the deesterification of diacylglycerol. This pathway can be activated by a phorbol ester through a protein kinase C-independent mechanism.
Rapuano
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BE
Division of Endocrinology, Cornell University Medical College, Hospital for Special Surgery, N.Y., N.Y. 10021, USA.
Bockman
R S
RS
D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism*; D002273:Carcinogens / Q000494:pharmacology; D002460:Cell Line; D003512:Cyclohexanones / Q000494:pharmacology; D004075:Diglycerides / Q000378:metabolism; D015232:Dinoprostone / Q000096:biosynthesis; D015536:Down-Regulation; D015777:Eicosanoids / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D008071:Lipoprotein Lipase / Q000037:antagonists & inhibitors / Q000378:metabolism; D008563:Membrane Lipids / Q000378:metabolism; D051379:Mice; D010006:Osteoblasts / Q000187:drug effects / Q000378:metabolism*; D010714:Phosphatidylethanolamines / Q000378:metabolism; D010716:Phosphatidylinositols / Q000378:metabolism; D010741:Phospholipases A / Q000037:antagonists & inhibitors / Q000378:metabolism; D054467:Phospholipases A2; D010742:Phospholipid Ethers / Q000494:pharmacology; D010743:Phospholipids / Q000378:metabolism; D011453:Prostaglandins / Q000096:biosynthesis*; D011480:Protease Inhibitors / Q000494:pharmacology; D011493:Protein Kinase C / Q000187:drug effects / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors / Q000378:metabolism*
D002273:Carcinogens; D003512:Cyclohexanones; D004075:Diglycerides; D015777:Eicosanoids; D008563:Membrane Lipids; D010714:Phosphatidylethanolamines; D010716:Phosphatidylinositols; D010742:Phospholipid Ethers; D010743:Phospholipids; D011453:Prostaglandins; D011480:Protease Inhibitors; D014409:Tumor Necrosis Factor-alpha; C026659:edelfosine; D016718:Arachidonic Acid; C036535:1,6-bis(cyclohexyloximinocarbonyl)hexane; D011493:Protein Kinase C; D010741:Phospholipases A; D008071:Lipoprotein Lipase; D054467:Phospholipases A2; D010738:Type C Phospholipases; D015232:Dinoprostone; D013755:Tetradecanoylphorbol Acetate