Association with Ets-1 causes ligand- and AF2-independent activation of nuclear receptors.
The vitamin D receptor (VDR) normally functions as a ligand-dependent transcriptional activator. Here we show that, in the presence of Ets-1, VDR stimulates the prolactin promoter in a ligand-independent manner, behaving as a constitutive activator. Mutations in the AF2 domain abolish vitamin D-dependent transactivation but do not affect constitutive activation by Ets-1. Therefore, in contrast with the actions of vitamin D, activation by Ets-1 is independent of the AF2 domain. Ets-1 also conferred a ligand-independent activation to the estrogen receptor and to peroxisome proliferator-activated receptor alpha. In addition, Ets-1 cooperated with the unliganded receptors to stimulate the activity of reporter constructs containing consensus response elements fused to the thymidine kinase promoter. There is a direct interaction of the receptors with Ets-1 which requires the DNA binding domains of both proteins. Interaction with Ets-1 induces a conformational change in VDR which can be detected by an increased resistance to proteolytic digestion. Furthermore, a retinoid X receptor-VDR heterodimer in which both receptors lack the core C-terminal AF2 domain can recruit coactivators in the presence, but not in the absence, of Ets-1. This suggests that Ets-1 induces a conformational change in the receptor which creates an active interaction surface with coactivators even in the AF2-defective mutants. These results demonstrate the existence of a novel mechanism, alternative to ligand binding, which can convert an unliganded receptor from an inactive state into a competent transcriptional activator.
Tolón
R M
RM
Instituto de Investigaciones Biomédicas "Alberto Sols," Consejo Superior de Investigaciones Científicas and Universidad Autónoma de Madrid, 28029 Madrid, Spain.
Castillo
A I
AI
Jiménez-Lara
A M
AM
Aranda
A
A
D050882:CREB-Binding Protein; D004967:Estrogens / Q000378:metabolism; D017930:Genes, Reporter; D051548:Histone Acetyltransferases; D008024:Ligands; D009687:Nuclear Proteins / Q000378:metabolism; D056920:Nuclear Receptor Coactivator 1; D011388:Prolactin / Q000235:genetics; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D050784:Proto-Oncogene Protein c-ets-1; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D050783:Proto-Oncogene Proteins c-ets; D018167:Receptors, Calcitriol / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D011960:Receptors, Estrogen / Q000378:metabolism; D020218:Response Elements; D015534:Trans-Activators / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism*; D015533:Transcriptional Activation; D014807:Vitamin D / Q000378:metabolism
D004967:Estrogens; D008024:Ligands; D009687:Nuclear Proteins; D050784:Proto-Oncogene Protein c-ets-1; D011518:Proto-Oncogene Proteins; D050783:Proto-Oncogene Proteins c-ets; D018167:Receptors, Calcitriol; D018160:Receptors, Cytoplasmic and Nuclear; D011960:Receptors, Estrogen; D015534:Trans-Activators; D014157:Transcription Factors; D014807:Vitamin D; D011388:Prolactin; D050882:CREB-Binding Protein; D051548:Histone Acetyltransferases; D056920:Nuclear Receptor Coactivator 1