Control of hepatic fatty acid oxidation by 5'-AMP-activated protein kinase involves a malonyl-CoA-dependent and a malonyl-CoA-independent mechanism.
Incubation of rat hepatocytes with 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR), an activator of the 5'-AMP-activated protein kinase (AMPK), produced a twofold stimulation of palmitate oxidation and of the activity of carnitine palmitoyltransferase I (CPT-I), together with a profound decrease of the activity of acetyl-CoA carboxylase and of the intracellular level of malonyl-CoA. AICAR-induced CPT-I stimulation progressively blunted with time after cell permeabilization, pointing to reversal of conformational constraints of the enzyme in control cells due to the permeabilization-triggered dilution of intracellular malonyl-CoA. The stimulation stabilized at a steady 20-25%. This 20-25% increase in CPT-I activity survived upon complete removal of malonyl-CoA from the permeabilized cells, indicating that it was not dependent on the malonyl-CoA concentration of the cell. This malonyl-CoA-independent activation of CPT-I was not evident when mitochondria were isolated for assay of enzyme activity or when cells were disrupted by vigorous sonication. In addition, the microtubule stabilizer taxol prevented the malonyl-CoA-independent stimulation of CPT-I induced by AICAR. Hence, stimulation of hepatic fatty acid oxidation by AMPK seems to rely on the activation of CPT-I by two different mechanisms: deinhibition of CPT-I induced by depletion of intracellular malonyl-CoA levels and malonyl-CoA-independent stimulation of CPT-I, which might involve modulation of interactions between CPT-I and cytoskeletal components.
Velasco
G
G
Department of Biochemistry and Molecular Biology I, Faculty of Biology, Complutense University, Madrid, Spain.
Geelen
M J
MJ
Guzmán
M
M
D055372:AMP-Activated Protein Kinases; D000103:Acetyl-CoA Carboxylase / Q000378:metabolism; D000620:Aminoimidazole Carboxamide / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D002210:Caprylates / Q000378:metabolism; D002334:Carnitine O-Palmitoyltransferase / Q000378:metabolism*; D004789:Enzyme Activation; D005227:Fatty Acids / Q000378:metabolism*; D066298:In Vitro Techniques; D008099:Liver / Q000166:cytology / Q000378:metabolism*; D008297:Male; D008316:Malonyl Coenzyme A / Q000378:metabolism*; D008870:Microtubules / Q000187:drug effects / Q000502:physiology; D008930:Mitochondria, Liver / Q000201:enzymology; D009097:Multienzyme Complexes / Q000378:metabolism*; D019319:Okadaic Acid / Q000494:pharmacology; D010084:Oxidation-Reduction; D017239:Paclitaxel / Q000494:pharmacology; D010168:Palmitates / Q000378:metabolism; D011494:Protein Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases; D051381:Rats; D017208:Rats, Wistar; D012265:Ribonucleotides / Q000378:metabolism / Q000494:pharmacology
D002210:Caprylates; D005227:Fatty Acids; D009097:Multienzyme Complexes; D010168:Palmitates; D012265:Ribonucleotides; D019319:Okadaic Acid; D000620:Aminoimidazole Carboxamide; D008316:Malonyl Coenzyme A; D002334:Carnitine O-Palmitoyltransferase; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; D055372:AMP-Activated Protein Kinases; D000103:Acetyl-CoA Carboxylase; C031143:AICA ribonucleotide; D017239:Paclitaxel