Gene expression, androgens steroid hormones

The steroid receptor superfamily comprises the glucocorticoid (GR), progesterone (PR), mineralocorticoid (MR), androgen (AR), thyroid hormone (TR),and vitamin Dg (VDR) receptors (60). These receptors bind to steroid hormones and are translocated to the nucleus where they bind to hormone responsive elements on DNA promoter regions to alter gene expression. While steroids are very effective anti-inflammatory agents, they have a multiplicity of serious side effects that limit their full use. 

Fig. 1.1. General mechanism of action of steroid hormones. Steroid hormones cross through the plasmatic membrane without apparent difficulty favored by gradient. Some, which can be considered prohormones, are metabolized and transformed into more active products. This is the case with testosterone, which becomes dihydrotestosterone (DHT) in the target tissues of androgens, through the 5-alfa-reductase enzyme. The hormone binds to the receptor, a soluble protein of the cellular cytosol that, in the absence of hormone, is found associated with other proteins (hsp90 and others) that maintain the receptor in an inactive state. The hormone-receptor bond causes the other proteins to separate and a homodimer to be formed. The homodimer is the activated form of the receptor since it is capable of recognizing the genes that depend on that steroid hormone as well as of activating its expression, which leads to the synthesis of specific proteins...

An example of gene expression can be illustrated by consideration of the action of steroid hormones, and in the control of sterol biosynthesis. Steroid hormones enter the cell by diffusion through the plasma membrane and bind to their steroid hormone receptor. These receptors are part of a large related family that includes those for glucocorticoids, oestrogens, androgens, thyroid hormone, calcitriol and the retinoids. All steroid hormone receptors are zinc finger transcription factors. The receptor must ... 

A. Mechanism of Action Like other steroid hormones, androgens enter cells and bind to cytosolic receptors (Figure 39-2). The hormone-receptor complex enters the nucleus and modulates the expression of certain genes. 

Slow-acting hormones, including the steroid hormones such as cortisol and the sex steroids (androgens, oestrogens and progesterone), vitamin A (section 11.2.3.2), vitamin D (section 11.3.3) and the thyroid hormones (section 11.15.3.3) act by changing the rate at which the genes for individual enzymes are expressed. 

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