title: 1,2-Diacylglycerols and phorbol esters stimulate phosphatidylcholine metabolism in GH3 pituitary cells. Evidence for separate mechanisms of action.
abstract: Phorbol esters have been shown to cause degradation and synthesis of phosphatidylcholine. The present studies measure effects of another class of protein kinase C activators, the 1,2-diacylglycerols, on phosphatidylcholine metabolism using GH3 rat pituitary cells. 1,2-Dioctanoylglycerol (diC8, 200 micrograms/ml) reduced phosphatidylcholine levels to 95 and 70% of control by 5 min and 1 h, respectively, in cells labeled to equilibrium with [3H]choline. Concomitantly, lysophosphatidylcholine increased 3.5-fold by 15 min and remained elevated for 1 h. Glycerol 3-phosphocholine, the product of sequential deacylation of phosphatidylcholine, increased 5-fold in the medium over 1 h. DiC8 also increased the levels of unesterified arachidonic and stearic acids. Arachidonic acid was preferentially released from the 2-position of phosphatidylcholine to form lysophosphatidylcholine. These results suggest that diC8 stimulates a phospholipase A2. 1-Oleoyl-2-acetylglycerol produced similar effects. In contrast, phorbol esters failed to enhance degradation in these cells. 1,2-Diacylglycerols and phorbol esters, however, stimulated phosphatidylcholine synthesis via the CDP-choline pathway. This was measured as concentration-dependent incorporation of 32Pi and [3H]choline into phosphatidylcholine in short-term labeling studies. The effects of maximal concentrations of diC8 and the phorbol ester, 12-O-tetradecanoylphorbol-13-acetate, were additive. Furthermore, in cells down-modulated for phorbol ester action, diC8-induced degradation and synthesis were unchanged. These studies demonstrate that phorbol esters and 1,2-diacylglycerols have different effects on phosphatidylcholine metabolism and suggest that 1,2-diacylglycerols may stimulate phosphatidylcholine metabolism via a pathway independent of the protein kinase C which mediates phorbol ester action. This represents the first description of a biochemical pathway activated by 1,2-diacylglycerols and not by phorbol esters.
mesh_terms: D000818:Animals; D003566:Cytidine Diphosphate Choline / Q000378:metabolism; D004075:Diglycerides / Q000494:pharmacology*; D005989:Glycerides / Q000494:pharmacology*; D010703:Phorbol Esters / Q000494:pharmacology*; D010713:Phosphatidylcholines / Q000378:metabolism*; D010911:Pituitary Neoplasms / Q000378:metabolism*; D051381:Rats; D013229:Stearic Acids / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
chemical_list: D004075:Diglycerides; D005989:Glycerides; D010703:Phorbol Esters; D010713:Phosphatidylcholines; D013229:Stearic Acids; C044295:1,2-dioctanoylglycerol; C031183:stearic acid; D003566:Cytidine Diphosphate Choline; D013755:Tetradecanoylphorbol Acetate