Regulation of phosphatidylcholine and phosphatidylethanolamine synthesis in rat hepatocytes by 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR).
The present study was undertaken to study the role of AMP-activated kinase (AMPK) in the biosynthesis of two major membrane phospholipids, phosphatidylcholine (PC) and phosphatidylethanolamine (PE). Incubation of rat hepatocytes with 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR), an activator of AMPK, produced dose-dependent inhibition of the incorporation of [(3)H]choline and [(3)H]ethanolamine into PC and PE, respectively. Determination of the cellular uptake of choline and ethanolamine showed that the reduced synthesis of PC and PE did not result from impaired uptake of these two precursors. The decreased synthesis of PC was not mirrored by a reduction in the activities of the enzymes of the CDP-choline pathway. The diminution of PE biosynthesis, however, was paralleled by a depressed activity of CTP:phosphoethanolamine cytidylyltransferase (ET), the pace-setting enzyme of the CDP-ethanolamine pathway. AICAR treatment of hepatocytes stimulated the conversion of choline into betaine, indicating that reduced PC synthesis most probably resulted from a decrease in the availability of choline. In addition, AICAR induced a 50% reduction in the cellular level of diacylglycerols, which may further impair the synthesis of PC and PE. The results thus indicate that AICAR inhibits the biosynthesis of PC and PE and that the effect is exerted at different sites in the two pathways. Increased oxidation of choline to betaine is the main target of AICAR in the PC pathway, whereas inhibition of ET activity is the locus of AICAR action in the PE pathway.
Houweling
Martin
M
Department of Biochemistry and Cell Biology, Faculty of Veterinary Medicine, University of Utrecht, P.O. Box 80176, 3508 TD Utrecht, The Netherlands. m.houweling@vet.uu.nl
Klein
Wil
W
Geelen
Math J H
MJ
D055372:AMP-Activated Protein Kinases; D000620:Aminoimidazole Carboxamide / Q000031:analogs & derivatives* / Q000494:pharmacology*; D000818:Animals; D022781:Hepatocytes / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D009097:Multienzyme Complexes / Q000378:metabolism*; D010713:Phosphatidylcholines / Q000096:biosynthesis*; D010714:Phosphatidylethanolamines / Q000096:biosynthesis*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D012265:Ribonucleotides / Q000494:pharmacology*
D009097:Multienzyme Complexes; D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines; D012265:Ribonucleotides; D000620:Aminoimidazole Carboxamide; D017346:Protein Serine-Threonine Kinases; D055372:AMP-Activated Protein Kinases; C031143:AICA ribonucleotide