Steroid Hormones Mechanism

Each steroid hormone diffuses across the plasma membrane of its target cell and binds to a specific cytosolic or nuclear receptor. These receptor–ligand complexes accumulate in the nucleus, dimerize, and bind to specific regulatory DNA sequences (hormone response elements [HRE]) in association with co-activator proteins, thereby causing increased transcription of targeted genes (Fig. 1). An HRE is found in the promoter or an enhancer element  for genes that respond to a specific steroid hormone, thus insuring coordinated regulation of these genes. Hormone–receptor complexes can also inhibit transcription in association with corepressors. [Note: The binding of a hormone to its receptor causes a conformational change in the receptor that uncovers its DNA-binding domain, allowing the complex to interact through a zinc finger motif with the appropriate DNA sequence. Receptors for the steroid hormones, plus those for thyroid hormone, retinoic acid, and 1,25-dihydroxycholecalciferol (vitamin D), are members of a superfamily of structurally related gene regulators that function in a similar way.]

Figure 1:  Activation of transcription by interaction of steroid hormone–receptor complex with hormone response element (HRE). The receptor contains domains that bind the hormone, DNA, and coactivating proteins. mRNA = messenger RNA.