Inhibition of hepatic phosphatidylcholine synthesis by 5-aminoimidazole-4-carboxamide-1-beta-4-ribofuranoside is independent of AMP-activated protein kinase activation.
5-Aminoimidazole-4-carboxamide-1-beta-d-ribofuranoside (AICAr), a commonly used indirect activator of AMP-activated protein kinase (AMPK), inhibits phosphatidylcholine (PC) biosynthesis in freshly isolated hepatocytes. In all nucleated mammalian cells, PC is synthesized from choline via the Kennedy (CDP-choline) pathway. The purpose of our study was to provide direct evidence that AMPK regulates phospholipid biosynthesis and to elucidate the mechanism(s) by which AMPK inhibits hepatic PC synthesis. Incubations of hepatocytes with AICAr resulted in a dose-dependent activation of AMPK and inhibition of PC biosynthesis. Surprisingly, adenoviral delivery of constitutively active AMPK did not alter PC biosynthesis. In addition, expression of dominant negative mutants of AMPK was unable to block the AICAr-dependent inhibition of PC biosynthesis, indicating that AICAr was acting independently of AMPK activation. Determination of aqueous intermediates of the CDP-choline pathway indicated that choline kinase, the first enzyme in the pathway, was inhibited by AICAr administration. Flux through the CDP-choline pathway was directly correlated to the level of intracellular ATP concentrations. Therefore, it is possible that inhibition of PC biosynthesis is another process by which the cell can reduce ATP consumption in times of energetic stress. However, unlike cholesterol and triacylglycerol biosynthesis, PC production is not regulated by AMPK.
Jacobs
René L
RL
Canadian Institutes of Health Research Group on the Molecular and Cell Biology of Lipids and Department of Biochemistry and the University of Alberta, Edmonton, Alberta T6G 2S2, Canada.
Lingrell
Susanne
S
Canadian Institutes of Health Research Group on the Molecular and Cell Biology of Lipids and Department of Biochemistry and the University of Alberta, Edmonton, Alberta T6G 2S2, Canada.
Dyck
Jason R B
JRB
Cardiovascular Research Group, Departments of Pediatrics and Pharmacology, University of Alberta, Edmonton, Alberta T6G 2S2, Canada.
Vance
Dennis E
DE
Canadian Institutes of Health Research Group on the Molecular and Cell Biology of Lipids and Department of Biochemistry and the University of Alberta, Edmonton, Alberta T6G 2S2, Canada. Electronic address: dennis.vance@ualberta.ca.
D055372:AMP-Activated Protein Kinases; D000255:Adenosine Triphosphate / Q000378:metabolism; D000620:Aminoimidazole Carboxamide / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D002478:Cells, Cultured; D019916:Choline-Phosphate Cytidylyltransferase / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004734:Energy Metabolism / Q000187:drug effects / Q000235:genetics; D004789:Enzyme Activation / Q000187:drug effects / Q000235:genetics; D022781:Hepatocytes / Q000166:cytology / Q000201:enzymology*; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D050356:Lipid Metabolism / Q000235:genetics; D008297:Male; D051379:Mice; D009097:Multienzyme Complexes / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D010713:Phosphatidylcholines / Q000096:biosynthesis*; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D012265:Ribonucleotides / Q000494:pharmacology*; D014280:Triglycerides / Q000096:biosynthesis
D007004:Hypoglycemic Agents; D009097:Multienzyme Complexes; D010713:Phosphatidylcholines; D012265:Ribonucleotides; D014280:Triglycerides; D000620:Aminoimidazole Carboxamide; D000255:Adenosine Triphosphate; D017346:Protein Serine-Threonine Kinases; D055372:AMP-Activated Protein Kinases; D019916:Choline-Phosphate Cytidylyltransferase; C031143:AICA ribonucleotide