Cotransfection Assays and Steroid Receptor Biology

The glucocorticoid, mineralocorticoid, progesterone, androgen, estrogen α and estrogen β receptors (GR, MR, PR, AR, ERα, and ERβ, respectively) form the steroid receptor family, part of the nuclear receptor superfamily (1 ). Like other nuclear receptors, steroid receptors have a conserved domain structure that consists of a C-terminal hormone-binding domain, a central DNA-binding domain, and an N-terminal transcriptional modulatory domain (2 ). However, unlike other nuclear receptors, in the absence of hormone they are associated with chaperone proteins such as HSP90 (3 ). Upon binding of steroid, these receptors undergo a conformational change that brings about dissociation of the receptor-chaperone complex, which in turn allows the receptor to bind to DNA, interact with transcriptional coactivators, and activate transcription (4 ).