title: Transcriptional activity of ecdysone receptor isoforms is regulated by modulation of receptor stability and interaction with Ab- and C-domains of the heterodimerization partner ultraspiracle.
abstract: The stability of ecdysone receptor (EcR) expressed in a heterologous system is regulated in an isoform-specific manner and modified by ligand and heterodimerization partner. Transcriptional activities of various receptor complexes with Usp and ligand as determined by reporter assays are the result of two effects: change in receptor concentration and altered transcriptional capability. Transcriptional activity of EcR-A is low when compared to EcR-B1 independent of the absence or presence of Ultraspiracle (Usp). Ligand increased the concentration of EcR-A, but had no effect on the transcriptional capability, in contrast to EcR-B1, which is not stabilized by hormone or Usp, but the transcriptional capability is enhanced by heterodimerization and ligand. Exchange of the AB-domain of Usp by the activation domain (AD) of Vp16 revealed that the N-terminus of Usp inhibited transcriptional activity only with EcR-B isoforms, whereas the hexapeptide in the AB-domain of wild type Usp adjacent to the C-domain of Usp harbours an activating function. Deletion of the C-domain of Usp did not affect the stability of the receptor complex, but reduced the transcriptional capability of heterodimers with all EcR-isoforms, indicating that the stability of the receptor, which is important for termination of the hormone signal transduction, is regulated in a cooperative manner by the AB-domains of EcR and Usp, and ligand. We show the active role of Usp in modulation of the transcriptional activity of the heterodimer in an isoform-specific manner by the inhibitory N-terminus, the activating hexapeptide in the AB-domain, and the C-domain of Usp.
authors.affiliation: Institute of General Zoology and Endocrinology, University of Ulm, Ulm, Germany.
authors.forename: Heike
authors.initials: H
authors.lastname: Ruff
authors.forename: Christian
authors.initials: C
authors.lastname: Tremmel
authors.forename: Margarethe
authors.initials: M
authors.lastname: Spindler-Barth
mesh_terms: D000818:Animals; D004268:DNA-Binding Proteins / Q000378:metabolism*; D019281:Dimerization; D029721:Drosophila Proteins / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000378:metabolism*; D005786:Gene Expression Regulation; D020033:Protein Isoforms / Q000378:metabolism; D055550:Protein Stability; D017434:Protein Structure, Tertiary; D011987:Receptors, Steroid / Q000737:chemistry / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism*
chemical_list: D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D020033:Protein Isoforms; D011987:Receptors, Steroid; D014157:Transcription Factors; C066030:USP protein, Drosophila; C055469:ecdysone receptor