The importance of being varied in steroid receptor transactivation.
A major response of steroid receptors to steroid hormones is the induction of gene transcription. Two relevant, albeit less studied, properties of these receptors are the EC(50) values of the receptor-agonist complexes and the partial agonist activity of the receptor-antagonist complexes. Contrary to earlier expectations, neither the EC(50) value nor the partial agonist activity is constant for a given receptor-steroid complex. This variation is, however, beneficial to cells and organisms because it provides a mechanism both for differential control of gene expression by a single concentration of circulating hormone and for limiting side-effects during endocrine therapies. In this article, the factors and proposed mechanisms for the modulation of the EC(50) value and partial agonist activity of receptor-steroid complexes are discussed.
Stoney Simons
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Steroid Hormones Section, Building 8, Room B2A-07, NIDDK/LMCB, National Institutes of Health, Bethesda, MD 20892, USA. steroids@helix.nih.gov
D000818:Animals; D006801:Humans; D011987:Receptors, Steroid / Q000819:agonists / Q000037:antagonists & inhibitors / Q000096:biosynthesis* / Q000235:genetics*; D015533:Transcriptional Activation / Q000502:physiology*
D011987:Receptors, Steroid