ABSTRACT
It has been now well established that steroid hormones act by regulating gene expression. This action of steroids is a classic mechanism of inducing cellular processes such as growth and differentiation in steroid-sensitive tissues. The genomic effects of steroids are mediated through proteins that are members of the superfamily of steroid hormone receptors, a group of intracellular transcription factors (Beato, 1989). These receptors reside within the cell in an inactive form until binding to their steroid ligand, which causes a conformation change in the receptor, allowing it to bind to DNA (Figure 8.1). At this point, the steroid-receptor complex is translocated to the nucleus where it binds to various steroid response elements on the promoters of a number of genes, and alters gene expression (reviewed in Miesfield, 1989). These genomic actions of steroids are characterized by occurring over a long period of time, ranging from many hours to days to years. The steroid hormone receptor superfamily includes the glucocorticoid and mineralocorticoid receptors for stress steroids, progesterone, estrogen and androgen receptors for the sex steroids, thyroid hormone, vitamin D and retinoic acid receptors.
