Glucocorticoid receptor defects

A large number of glucocorticoid-resistant subclones of the lymphoid cell lines S49.1, WEHI-7 and CEM-7 have been isolated in the way described above. Receptor defects of different types were found to be the prevailing cause for resistance. For classifying the receptor abnormalities a whole-cell hormone-binding assay followed by crude cell fractionation has been employed [20,57],... 

The selectivity of hydrocortisone for the glucocorticoid receptor is not due to a different binding affinity of hydrocortisone to the two receptors but to the protection of the mineralocorticoid receptor by locally high concentrations of the enzyme 11 J-hydroxysteroid dehydrogenase, which converts cortisol (hydrocortisone) to the inactive cortisone. This enzyme is inhibited by one of the components of liquorice, and can occasionally harbour a genetic defect. Therefore both acquired (in liquorice addicts) and inherited syndromes of pseudohyperaldo-steronism can occasionally occur. 

Impaired glucocorticoid signaling due to defects in the glucocorticoid receptor-mediated response. 

Most current assays use immunofluorescence or GFP fluorescence to evaluate the nucleocytoplasmic distribution of endogenous nuclear proteins (Corbett et al., 1995 Lim et al, 1995 Schlenstedt et al, 1995) or NLS-containing reporter proteins (Nehrbass et al, 1993 Schlaich and Hurt, 1995) in the steady state. These methods are usually sensitive only to defects that severely impair the transport apparatus (see example below). Even the use of inducible promoters to express reporter proteins after shifting cells to nonpermissive conditions (Corbett et al, 1995 Schlenstedt et al, 1995) requires at least 30-60 min to produce an adequate signal and is, therefore, often too slow. A clever assay was recently described to measure defects in nuclear export signal-mediated protein export in yeast (Lee et al, 1996). An attractive in vivo approach now in use in tissue culture cells is the application of hormone-stimulated GFP-glucocorticoid receptor import to study import kinetics (Htun et al, 1996 Carey et al, 1996). 

Glucocorticoid resistance is characterized by high levels of cortisol (without stigmata of Cushing syndrome), resistance of the hypothalamic-pituitary-adrenal axis to dexamethasone, and an affinity defect of the glucocorticoid receptor. Some of the affected patients presented with hypertension and hypokalemia due to illegal activation of the mineralocorticoid receptor by cortisol [16]. 

Therefore, the inability of glucocorticoids alone to stimulate System A activity in long-term cultures may result from a post-receptor defect. 

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