title: Deducing the temporal order of cofactor function in ligand-regulated gene transcription: theory and experimental verification.
abstract: Cofactors are intimately involved in steroid-regulated gene expression. Two critical questions are (1) the steps at which cofactors exert their biological activities and (2) the nature of that activity. Here we show that a new mathematical theory of steroid hormone action can be used to deduce the kinetic properties and reaction sequence position for the functioning of any two cofactors relative to a concentration limiting step (CLS) and to each other. The predictions of the theory, which can be applied using graphical methods similar to those of enzyme kinetics, are validated by obtaining internally consistent data for pair-wise analyses of three cofactors (TIF2, sSMRT, and NCoR) in U2OS cells. The analysis of TIF2 and sSMRT actions on GR-induction of an endogenous gene gave results identical to those with an exogenous reporter. Thus new tools to determine previously unobtainable information about the nature and position of cofactor action in any process displaying first-order Hill plot kinetics are now available.
authors.affiliation: Steroid Hormones Section, Clinical Endocrinology Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland, United States of America.
authors.forename: Edward J
authors.initials: EJ
authors.lastname: Dougherty
authors.forename: Chunhua
authors.initials: C
authors.lastname: Guo
authors.forename: S Stoney
authors.initials: SS
authors.lastname: Simons
authors.forename: Carson C
authors.initials: CC
authors.lastname: Chow
mesh_terms: D000465:Algorithms; D015153:Blotting, Western; D045744:Cell Line, Tumor; D003907:Dexamethasone / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D005786:Gene Expression Regulation / Q000187:drug effects*; D005938:Glucocorticoids / Q000494:pharmacology; D006801:Humans; D018970:Insulin-Like Growth Factor Binding Protein 1 / Q000235:genetics / Q000378:metabolism; D007700:Kinetics; D008024:Ligands; D008957:Models, Genetic; D056971:Nuclear Receptor Co-Repressor 1 / Q000235:genetics / Q000378:metabolism*; D056985:Nuclear Receptor Co-Repressor 2 / Q000235:genetics / Q000378:metabolism*; D051958:Nuclear Receptor Coactivator 2 / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D011965:Receptors, Glucocorticoid / Q000819:agonists / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013997:Time Factors
chemical_list: D005938:Glucocorticoids; C032231:IGFBP1 protein, human; D018970:Insulin-Like Growth Factor Binding Protein 1; D008024:Ligands; C498001:NCOA2 protein, human; C539127:NCOR1 protein, human; C539130:NCOR2 protein, human; D056971:Nuclear Receptor Co-Repressor 1; D056985:Nuclear Receptor Co-Repressor 2; D051958:Nuclear Receptor Coactivator 2; D011965:Receptors, Glucocorticoid; D003907:Dexamethasone