title: Activated AMPK inhibits PPAR-{alpha} and PPAR-{gamma} transcriptional activity in hepatoma cells.
abstract: AMP-activated protein kinase (AMPK) and peroxisome proliferator-activated receptor-α (PPAR-α) are critical regulators of short-term and long-term fatty acid oxidation, respectively. We examined whether the activities of these molecules were coordinately regulated. H4IIEC3 cells were transfected with PPAR-α and PPAR-γ expression plasmids and a peroxisome-proliferator-response element (PPRE) luciferase reporter plasmid. The cells were treated with PPAR agonists (WY-14,643 and rosiglitazone), AMPK activators 5-aminoimidazole-4-carboxamide riboside (AICAR) and metformin, and the AMPK inhibitor compound C. Both AICAR and metformin decreased basal and WY-14,643-stimulated PPAR-α activity; compound C increased agonist-stimulated reporter activity and partially reversed the effect of the AMPK activators. Similar effects on PPAR-γ were seen, with both AICAR and metformin inhibiting PPRE reporter activity. Compound C increased basal PPAR-γ activity and rosiglitazone-stimulated activity. In contrast, retinoic acid receptor-α (RAR-α), another nuclear receptor that dimerizes with retinoid X receptor (RXR), was largely unaffected by the AMPK activators. Compound C modestly increased AM580 (an RAR agonist)-stimulated activity. The AMPK activators did not affect PPAR-α binding to DNA, and there was no consistent correlation between effects of the AMPK activators and inhibitor on PPAR and the nuclear localization of AMPK-α subunits. Expression of either a constitutively active or dominant negative AMPK-α inhibited basal and WY-14,643-stimulated PPAR-α activity and basal and rosiglitazone-stimulated PPAR-γ activity. We concluded that the AMPK activators AICAR and metformin inhibited transcriptional activities of PPAR-α and PPAR-γ, whereas inhibition of AMPK with compound C activated both PPARs. The effects of AMPK do not appear to be mediated through effects on RXR or on PPAR/RXR binding to DNA. These effects are independent of kinase activity and instead appear to rely on the activated conformation of AMPK. AMPK inhibition of PPAR-α and -γ may allow for short-term processes to increase energy generation before the cells devote resources to increasing their capacity for fatty acid oxidation.
authors.affiliation: Indianapolis, IN 46202, USA. msozio@iupui.edu
authors.forename: Margaret S
authors.initials: MS
authors.lastname: Sozio
authors.forename: Changyue
authors.initials: C
authors.lastname: Lu
authors.forename: Yan
authors.initials: Y
authors.lastname: Zeng
authors.forename: Suthat
authors.initials: S
authors.lastname: Liangpunsakul
authors.forename: David W
authors.initials: DW
authors.lastname: Crabb
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000620:Aminoimidazole Carboxamide / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D006528:Carcinoma, Hepatocellular / Q000378:metabolism*; D045744:Cell Line, Tumor; D008113:Liver Neoplasms; D008687:Metformin / Q000494:pharmacology; D047493:PPAR alpha / Q000037:antagonists & inhibitors*; D047495:PPAR gamma / Q000037:antagonists & inhibitors*; D051381:Rats; D012263:Ribonucleosides / Q000494:pharmacology; D000077154:Rosiglitazone; D045162:Thiazolidinediones / Q000494:pharmacology; D015533:Transcriptional Activation / Q000187:drug effects*
chemical_list: D047493:PPAR alpha; D047495:PPAR gamma; D012263:Ribonucleosides; D045162:Thiazolidinediones; D000077154:Rosiglitazone; D000620:Aminoimidazole Carboxamide; C011651:acadesine; D008687:Metformin; D055372:AMP-Activated Protein Kinases