title: Fatty acids induce L-CPT I gene expression through a PPARalpha-independent mechanism in rat hepatoma cells.
abstract: Liver carnitine palmitoyl transferase (L-CPT) I is a key regulatory enzyme of long-chain fatty acid (LCFA) oxidation that ensures the first step of LCFA import into the mitochondrial matrix. In rat hepatocytes, we showed previously that L-CPT I gene expression was induced by LCFAs as well as by fibrates. The aim of this study was to determine whether LCFA-induced L-CPT I gene expression was mediated by PPARalpha. For this purpose, we constructed a PPARalpha-dominant negative receptor to inhibit endogenous PPARalpha signaling. Highly conserved hydrophobic and charged residues (Leu459 and Glu462) in helix 12 of the ligand-binding domain were mutated to alanine. These mutations led to a total loss of transcriptional activity due to impaired coactivator recruitment. Furthermore, competition studies confirmed that the mutated PPARalpha receptor abolished the wild-type PPARalpha receptor action and thus acted as a powerful dominant negative receptor. When overexpressed in rat hepatoma cells (H4IIE) using a recombinant adenovirus, the mutated PPARalpha receptor antagonized the clofibrate-induced L-CPT I gene expression, whereas it did not affect LCFA-induced L-CPT I. These results provide the first direct demonstration that LCFAs regulate L-CPT I transcription through a PPARalpha-independent pathway, at least in hepatoma cells.
authors.affiliation: Institut Cochin, INSERM U567, CNRS UMR 8104, Université PARIS V, Département d'Endocrinologie, Paris.
authors.forename: Cédric
authors.initials: C
authors.lastname: Le May
authors.forename: Michèle
authors.initials: M
authors.lastname: Caüzac
authors.forename: Claire
authors.initials: C
authors.lastname: Diradourian
authors.forename: Dominique
authors.initials: D
authors.lastname: Perdereau
authors.forename: Jean
authors.initials: J
authors.lastname: Girard
authors.forename: Anne-Françoise
authors.initials: AF
authors.lastname: Burnol
authors.forename: Jean-Paul
authors.initials: JP
authors.lastname: Pégorier
mesh_terms: D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D019556:COS Cells; D006528:Carcinoma, Hepatocellular; D002334:Carnitine O-Palmitoyltransferase / Q000235:genetics* / Q000378:metabolism*; D045744:Cell Line, Tumor; D002522:Chlorocebus aethiops; D002994:Clofibrate / Q000494:pharmacology; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D000960:Hypolipidemic Agents / Q000494:pharmacology; D019787:Linoleic Acid / Q000494:pharmacology*; D008113:Liver Neoplasms; D047493:PPAR alpha / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D015533:Transcriptional Activation / Q000187:drug effects
chemical_list: D000960:Hypolipidemic Agents; D047493:PPAR alpha; D011994:Recombinant Proteins; D019787:Linoleic Acid; D002334:Carnitine O-Palmitoyltransferase; D002994:Clofibrate