MgATP has different inhibitory effects on the use of 1-acyl-lysophosphatidylcholine and lyso platelet-activating factor acceptors by neuronal nuclear acetyltransferase activities

The inhibitory effects of MgATP on neuronal nuclear acetyltransferase activities were studied using lyse platelet-activating factor (lyso-PAF, 1-alkyl-sn-glycero-3-phosphocholine) and lysophosphatidylcholine (lyso-PC, 1-acyl-sn-glycero-3-phosphocholine). The nuclear (N-1) acetylation of lyse-PC was more profoundly inhibited by MgATP. MgATP did not alter the apparent K-m for acetyl-CoA in either acetylation reaction. The inhibitory effects of MgATP were not seen for other nucleotides or MgAMP-PCP. Kinase inhibitors such as staurosporine (1 mu M), chelerythrine, and R59022 (diglyceride kinase inhibitor I) did not block the MgATP inhibition of either acetylation. However, the addition of phospholipids to the assays indicated a selective inhibitory effect for PIP (25-50 mu M) in the nuclear acetylation of lyso-PAF. When N-1 was incubated with [gamma-P-33]ATP, phosphatidic acid and PIP were the principal radioactive lipid products. While the extent of MgATP inhibition of lyso-PAF acetylation was similar at different concentrations of lyso-PAF, increasing lyse-PC concentrations greatly decreased the MgATP inhibition seen in lyse-PC acetylations. Nuclear envelopes prepared in the presence of PMSF, and fraction N-1 exposed to PMSF, did not show the inhibitory effect of MgATP on lyse-PC acetylation. PMSF (an inhibitor of certain phospholipase and lysophospholipase activities) did not reduce the MgATP inhibition of lyso-PAF acetylation. Arachidonoyl trifluoromethylketone, an inhibitor of cytosolic phospholipases A(2) and of lysophospholipase activity associated with cPLA(2), also blocked the inhibitory effect of MgATP on lyse-PC acetylation. Using radioactive lyse-PC substrate, fraction N-1 produced labeled free fatty acid and phosphatidylcholine. In the presence of acetyl-CoA, the production of radioactive phosphatidylcholine increased almost 6-fold when MgATP was also included in these incubations. In the presence of MgATP and acetyl-CoA, PMSF reduced the levels of radioactive free fatty acid and phosphatidylcholine derived from lyse-PC, while Triacsin C, an inhibitor of acyl CoA synthetase, decreased phosphatidylcholine labeling. These findings suggest that MgATP inhibition of lyse-PC acetylation results from a loss of lyse-PC substrate that is largely mediated by nuclear lysophospholipase, acyl-CoA synthetase and lyse-PC acylation. Thus the neuronal nuclear production of Acyl PAF may be regulated by paths that compete for the lyse-PC substrate. In contrast, the acetylation of lyso-PAF is inhibited by PIP, a product of nuclear PI kinase reactions. (C) 1998 Elsevier Science B.V.