Hormone-steroid-specific targets

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...

Water-insoluble hormones (steroid, retinoid, and thyroid hormones) readily pass through the plasma membrane of their target cells to reach their receptor proteins in the nucleus (Fig. 23-4). With this class of hormones, the hormone-receptor complex itself carries the message it interacts with DNA to alter the expression of specific genes, changing the enzyme complement of the cell and thereby changing cellular metabolism (see Fig. 12 10). 

Illustration of Some Alternative Approaches by Reagents Directed Towards Steroid— Hormone-Specific Targets... 

The basic mechanism of steroid hormone action on target cells is similar for the various classes of agents. Differences in the actions of adrenocorticoids, estrogens, progestins, and androgens arise from the specificity of... 

By selectively affecting gene transcription and the consequent production of appropriate target mRNAs, the amounts of specific proteins are changed and metabolic processes are influenced. The influence of each of these hormones is quite specific generally, the hormone affects less than 1% of the genes, mRNA, or proteins in a target cell sometimes only a few are affected. The nuclear actions of steroid, thyroid, and retinoid hormones are quite well defined. Most evidence sug-... 

Receptors are proteins or glycoproteins found either on the surface of the target cell or located within the cell interior. The surface receptors engage peptide hormones which, being hydrophilic, do not traverse the fatty plasma membrane intracellular receptors combine specifically with particular steroids or tri-iodothyronine, T3. 

Like all steroids, aldosterone enters the target cell and combines with cytosolic mineralocorticoid receptor. Such receptors are not entirely specific for aldosterone and will also bind cortisol, the principal glucocorticoid hormone. The receptors are protected from cortisol activation by 11 3 hydroxysteroid dehydrogenase which... 

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