Nongenomic Action of Steroid Hormones in Vertebrates

Steroid honnones regulate diverse biological functions by binding to intracellular receptors, which in turn alter the expression of genes. According to the common theory of steroid action, steroids modulate gene transcription by interacting with intracellular receptors, which act as ligand dependent transcription factors. Steroids regulate various genes either by positive or negative expression (1,2). Most of the steroid receptors are located in side the cell and hence the steroids need to get into the ceils and alter gene expression. The receptors for glucocorticoid, mineralocorticoid, progesterone and androgen are cytoplasmic and that of estrogen is nuclear (3). These receptors exist in inactive state in the cytoplasm or nucleus. The inactive state is maintained by their interaction with a group of receptor associated proteins called the chaperones and cochaperones (4,5). The mode of action of steroids requires intracellular localization of the steroid receptor and typically takes at least 30 to 60 min for the response. These cellular responses of steroids are known as the classical genomic action of steroids, which are characterized by a specific delay and sensitivity towards inhibitors of transcription and translation. The detailed description of steroid actions was the result of intensive long term research on steroid hormones.