Activators of protein kinase A decrease the levels of free arachidonic acid in osteoblasts via stimulation of phosphatidylcholine and phosphatidylethanolamine synthesis.
In order to examine the role of protein kinase A (PKA) in the regulation of arachidonic acid availability, the interaction between cAMP agonists and the G protein activator AIF4- in their effects on phospholipid metabolism were measured in MC3T3-E1 osteoblasts. We show that forskolin and 8-brcAMP, activators of PKA, amplify the AIF4(-)-induced stimulation of phosphatidylinositol-specific phospholipase C (phosphatidylinositol inositolphosphohydrolase; EC 3.1.4.3), measured by the formation of [3H]inositol phosphates in prelabeled cells. However, the AIF4(-)-stimulated production of 1,2-diacylglycerols and the release of [3H]arachidonic acid ([3H]AA) were inhibited 50-75% by forskolin and 8-bromocAMP. Furthermore, pretreatment with PKA activators prevented much of the AIF4(-)-induced loss of [3H]AA from phosphatidylcholine and phosphatidylethanolamine in prelabeled osteoblasts. In addition, in the absence of AIF4-, forskolin was found to stimulate the incorporation of [3H]AA and [32P]orthophosphoric acid selectively into these two major phospholipids and selectively increased their mass. The effects of forskolin and 8-BrcAMP on the levels of free [3H]AA were completely reversed by pretreatment with the PKA inhibitor H-89. Therefore, our findings suggest that the activation of cAMP-dependent protein kinase can reduce the availability of free arachidonic acid for prostaglandin synthesis in osteoblast cells by stimulating its reesterification via phospholipid resynthesis.
Rapuano
B E
BE
Division of Research, The Hospital for Special Surgery, NY, NY 10021, USA.
Bockman
R S
RS
D017607:Aluminum Compounds / Q000008:administration & dosage / Q000494:pharmacology; D000818:Animals; D016718:Arachidonic Acid / Q000037:antagonists & inhibitors* / Q000378:metabolism; D002460:Cell Line; D017868:Cyclic AMP-Dependent Protein Kinases / Q000187:drug effects* / Q000378:metabolism*; D004075:Diglycerides / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D005227:Fatty Acids / Q000378:metabolism; D005459:Fluorides / Q000008:administration & dosage / Q000494:pharmacology; D010006:Osteoblasts / Q000187:drug effects* / Q000378:metabolism; D010713:Phosphatidylcholines / Q000096:biosynthesis*; D010714:Phosphatidylethanolamines / Q000096:biosynthesis*; D010743:Phospholipids / Q000378:metabolism; D010756:Phosphoric Acids / Q000378:metabolism; D010761:Phosphorus Radioisotopes; D014316:Tritium
D017607:Aluminum Compounds; D004075:Diglycerides; D005227:Fatty Acids; D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines; D010743:Phospholipids; D010756:Phosphoric Acids; D010761:Phosphorus Radioisotopes; D014316:Tritium; C050992:tetrafluoroaluminate; D016718:Arachidonic Acid; C030242:phosphoric acid; D017868:Cyclic AMP-Dependent Protein Kinases; D005459:Fluorides