title: N- and C-terminal degradation of ecdysteroid receptor isoforms, when transiently expressed in mammalian CHO cells, is regulated by the proteasome and cysteine and threonine proteases.
abstract: Transcriptional activity of nuclear receptors is the result of transactivation capability and the concentration of the receptor protein. The concentration of ecdysteroid receptor (EcR) isoforms, constitutively expressed in mammalian CHO cells, is dependent on a number of factors. As shown previously, ligand binding stabilizes receptor protein concentration. In this paper, we investigate the degradation of EcR isoforms and provide evidence that N-terminal degradation is modulated by isoform-specific ubiquitination sites present in the A/B domains of EcR-A and -B1. This was demonstrated by the increase in EcR concentration by treatment with carbobenzoxy-L-leucyl-L-leucyl-L-leucinal (MG132), an inhibitor of ubiquitin-mediated proteasomal degradation and by deletion of ubiquitination sites. In addition, EcR is degraded by the peptidyl-dipeptidase cathepsin B (CatB) and the endopeptidase cathepsin S (CatS) at the C-terminus in an isoform-specific manner, despite identical C-termini. Ubiquitin-proteasome-mediated degradation and the proteolytic action are modulated by heterodimerization with Ultraspiracle (USP). The complex regulation of receptor protein concentration offers an additional opportunity to regulate transcriptional activity in an isoform- and target cell-specific way and allows the temporal limitation of hormone action.
authors.affiliation: Institute of General Zoology and Endocrinology, Ulm University, Ulm, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Schauer
authors.forename: T
authors.initials: T
authors.lastname: Burster
authors.forename: M
authors.initials: M
authors.lastname: Spindler-Barth
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D015153:Blotting, Western; D016466:CHO Cells; D002154:Calpain / Q000037:antagonists & inhibitors / Q000378:metabolism; D002403:Cathepsins / Q000037:antagonists & inhibitors / Q000378:metabolism; D006224:Cricetinae; D057056:Cysteine Proteases / Q000378:metabolism*; D029721:Drosophila Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D004331:Drosophila melanogaster / Q000378:metabolism; D007976:Leupeptins / Q000494:pharmacology; D008322:Mammals / Q000378:metabolism*; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000494:pharmacology; D011480:Protease Inhibitors / Q000494:pharmacology; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D061988:Proteasome Inhibitors; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D055503:Protein Multimerization / Q000187:drug effects; D055550:Protein Stability / Q000187:drug effects; D017434:Protein Structure, Tertiary; D059748:Proteolysis / Q000187:drug effects; D011987:Receptors, Steroid / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D013912:Threonine / Q000037:antagonists & inhibitors / Q000378:metabolism*; D014158:Transcription, Genetic / Q000187:drug effects; D054875:Ubiquitination / Q000187:drug effects
chemical_list: D029721:Drosophila Proteins; D007976:Leupeptins; D009842:Oligopeptides; D011480:Protease Inhibitors; D061988:Proteasome Inhibitors; D020033:Protein Isoforms; D011987:Receptors, Steroid; C542812:benzyloxycarbonyl-arginyl-leucyl-arginyl-alpha-azaglycyl-isoleucyl-valine methyl ester; C034808:ecdysteroid receptor; D013912:Threonine; D002403:Cathepsins; D057056:Cysteine Proteases; D002154:Calpain; D046988:Proteasome Endopeptidase Complex; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde