The nuclear receptor coactivator PGC-1alpha exhibits modes of interaction with the estrogen receptor distinct from those of SRC-1.
Estrogen receptor (ER) function is mediated by multi-domain co-regulator proteins. A fluorescently labelled fragment of the human PGC-1alpha co-regulator (residues 91-408) bearing the two motifs most strongly implicated in interactions with nuclear receptors (NR box2 and NR box3), was used to characterize in vitro binding of PGC-1alpha to ER. Anisotropy measurements revealed that the affinity of this PGC-1alpha fragment for human ERalpha and beta was fairly strong in the presence of estradiol (approximately 5 nM), and that unlike a similar fragment of SRC-1 (570-780), PGC-191-408 exhibited ligand-independent interactions with ER, particularly with ERbeta (Kd approximately 30 nM). Competition experiments of the complex between ERalpha and fluorescently labelled PGC-1 91-408 with unlabelled SRC-1 570-780 showed that PGC-1 91-408 was an efficient competitor of SRC-1 570-780, while the inverse was not true, underscoring their distinct modes of binding. The anisotropy data provide strong evidence for a ternary complex between ERalpha, SRC-1 570-780 and PGC-1 91-408. GST-pull-down experiments with deletion mutants of ERalpha revealed that the constitutive binding of PGC-1 91-408 requires the presence of the linker domain between the DNA binding and ligand binding domains (DBD and LBD). Homology modeling studies of the different regions of full length PGC-1alpha confirmed the lack of compact tertiary structure of the N-terminal region bearing the NR box motifs, and suggested a slightly different mode of interaction compared to the NR box motifs of SRC-1. They also provided reasonable structural models for the coiled-coil dimerization motif at residues 633-675, as well as the C-terminal putative RNA binding domain, raising important questions concerning the stoichiometry of its complex with the nuclear receptors.
Bourdoncle
Anne
A
INSERM U554 Centre de Biochimie Structurale, 29 rue de Navacelles 34090, Montpellier Cedex, France. royer@cbs.cnrs.fr
Labesse
Gilles
G
Margueron
Raphaël
R
Castet
Audrey
A
Cavaillès
Vincent
V
Royer
Catherine A
CA
D016880:Anisotropy; D019281:Dimerization; D047628:Estrogen Receptor alpha / Q000235:genetics / Q000378:metabolism*; D047629:Estrogen Receptor beta / Q000235:genetics / Q000378:metabolism*; D006360:Heat-Shock Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D051548:Histone Acetyltransferases; D006801:Humans; D008024:Ligands; D008954:Models, Biological; D008958:Models, Molecular; D009154:Mutation / Q000235:genetics; D056920:Nuclear Receptor Coactivator 1; D000071248:Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D013050:Spectrometry, Fluorescence; D013816:Thermodynamics; D017186:Titrimetry; D014157:Transcription Factors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic / Q000235:genetics
D047628:Estrogen Receptor alpha; D047629:Estrogen Receptor beta; D006360:Heat-Shock Proteins; D008024:Ligands; C486497:PPARGC1A protein, human; D000071248:Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha; D014157:Transcription Factors; D051548:Histone Acetyltransferases; C538859:NCOA1 protein, human; D056920:Nuclear Receptor Coactivator 1