title: Peroxisomal bifunctional enzyme binds and activates the activation function-1 region of the peroxisome proliferator-activated receptor alpha.
abstract: The transcriptional activity of peroxisome proliferator-activated receptors (PPARs), and of nuclear hormone receptors in general, is subject to modulation by cofactors. However, most currently known co-activating proteins interact in a ligand-dependent manner with the C-terminal ligand-regulated activation function (AF)-2 domain of nuclear receptors. Since PPARalpha exhibits a strong constitutive transactivating function contained within an N-terminal AF-1 region, it can be speculated that a different set of cofactors might interact with this region of PPARs. An affinity purification approach was used to identify the peroxisomal enoyl-CoA hydratase/3-hydroxyacyl-CoA dehydrogenase (bifunctional enzyme, BFE) as a protein which strongly and specifically interacted with the N-terminal 92 amino acids of PPARalpha. Protein-protein interaction assays with the cloned BFE confirmed this interaction, which could be mapped to amino acids 307-514 of the BFE and the N-terminal 70 amino acids of PPARalpha. Moreover, transient transfection experiments in hepatoma cells revealed a 2.2-fold increase in the basal and ligand-stimulated transcriptional activity of PPARalpha in the presence of BFE. This stimulatory effect is preferentially observed for the PPARalpha isoform and it is significantly stronger (4.8-fold) in non-hepatic cells, which presumably express lower levels of endogenous BFE. Hence, the BFE represents the first known cofactor capable of activating the AF-1 domain of PPAR without requiring additional regions of this receptor. These data are compatible with a model whereby the PPAR-regulated BFE is able to modulate its own expression through an enhancement of the activity of PPARalpha, representing a novel peroxisomal-nuclear feed-forward regulatory loop.
authors.affiliation: Division of Endocrinology and Diabetes, Department of Medicine, University Hospital Geneva, 24 rue Micheli-du-Crest, CH-1211 Geneva 14, Switzerland.
authors.forename: C E
authors.initials: CE
authors.lastname: Juge-Aubry
authors.forename: S
authors.initials: S
authors.lastname: Kuenzli
authors.forename: J C
authors.initials: JC
authors.lastname: Sanchez
authors.forename: D
authors.initials: D
authors.lastname: Hochstrasser
authors.forename: C A
authors.initials: CA
authors.lastname: Meier
mesh_terms: D015094:3-Hydroxyacyl CoA Dehydrogenases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D016475:3T3 Cells; D000818:Animals; D002374:Catalase / Q000378:metabolism; D002458:Cell Fractionation; D004746:Enoyl-CoA Hydratase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004789:Enzyme Activation; D007535:Isomerases; D008099:Liver / Q000201:enzymology; D051379:Mice; D009097:Multienzyme Complexes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010088:Oxidoreductases / Q000737:chemistry / Q000378:metabolism; D063994:Peroxisomal Bifunctional Enzyme; D020675:Peroxisomes / Q000201:enzymology; D010957:Plasmids; D018160:Receptors, Cytoplasmic and Nuclear / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D014162:Transfection
chemical_list: D009097:Multienzyme Complexes; D018160:Receptors, Cytoplasmic and Nuclear; D014157:Transcription Factors; D010088:Oxidoreductases; D015094:3-Hydroxyacyl CoA Dehydrogenases; D002374:Catalase; C063427:trihydroxycoprostanoyl-CoA oxidase; C576254:Ehhadh protein, mouse; D004746:Enoyl-CoA Hydratase; D063994:Peroxisomal Bifunctional Enzyme; D007535:Isomerases