title: Ligand-induced heterodimerization between the ligand binding domains of the Drosophila ecdysteroid receptor and ultraspiracle.
abstract: The insect ecdysteroid receptor consists of a heterodimer between EcR and the RXR-orthologue, USP. We addressed the question of whether this heterodimer, like all other RXR heterodimers, may be formed in the absence of ligand and whether ligand promotes dimerization. We found that C-terminal protein fragments that comprised the ligand binding, but not the DNA binding domain of EcR and USP and which were equipped with the activation or DNA binding region of GAL4, respectively, exhibit a weak ability to interact spontaneously with each other. Moreover, the heterodimer formation is greatly enhanced upon administration of active ecdysteroids in a dose-dependent manner. This was shown in vivo by a yeast two-hybrid system and in vitro by a modified electromobility shift assay. Furthermore, the EcR fragment expressed in yeast was functional and bound radioactively labelled ecdysteroid specifically. Ligand binding was greatly enhanced by the presence of a USP ligand binding domain. Therefore, ecdysteroids are capable of inducing heterodimer formation between EcR and USP, even when the binding of these receptor proteins to cognate DNA response elements does not occur. This capability may be a regulated aspect of ecdysteroid action during insect development.
authors.affiliation: Institute for Cell Biology, ETH-Hönggerberg, CH-8093 Zürich, Switzerland. lezzi@cell.biol.ethz.ch
authors.forename: Markus
authors.initials: M
authors.lastname: Lezzi
authors.forename: Thomas
authors.initials: T
authors.lastname: Bergman
authors.forename: Vincent C
authors.initials: VC
authors.lastname: Henrich
authors.forename: Martin
authors.initials: M
authors.lastname: Vögtli
authors.forename: Christina
authors.initials: C
authors.lastname: Frömel
authors.forename: Marco
authors.initials: M
authors.lastname: Grebe
authors.forename: Sabina
authors.initials: S
authors.lastname: Przibilla
authors.forename: Margarethe
authors.initials: M
authors.lastname: Spindler-Barth
mesh_terms: D000818:Animals; D001665:Binding Sites; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D019281:Dimerization; D004305:Dose-Response Relationship, Drug; D004330:Drosophila; D029721:Drosophila Proteins; D026461:Ecdysteroids / Q000378:metabolism / Q000494:pharmacology; D004441:Ecdysterone / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D008024:Ligands; D011987:Receptors, Steroid / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D020218:Response Elements; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D020798:Two-Hybrid System Techniques; D015003:Yeasts / Q000235:genetics
chemical_list: D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D026461:Ecdysteroids; D008024:Ligands; D011987:Receptors, Steroid; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; C066030:USP protein, Drosophila; C034808:ecdysteroid receptor; C055348:muristerone A; D004441:Ecdysterone