Abnormal glucocorticoid receptor gene and mRNA in primary cortisol resistance

Mechanisms of glucocorticoid-resistant asthma

The term "steroid- or glucocorticoid-resistant (GR) asthma" has been used to describe a group of asthmatics who demonstrate persistent airway obstruction and inflammation despite treatment with high doses of systemic glucocorticoids (GCs). There are at least two forms of GR asthma. The first group of patients has an acquired form of GC resistance. Analysis of their bronchoalveolar lavage (BAL) cells indicates an extremely high level of IL-2 and IL-4 gene expression as compared to BAL cells from GC-sensitive asthmatics. The incubation of T cells from normal individuals with the combination of IL-2 and IL-4 induces GC receptor binding defects, and concomitant GC receptor beta expression, in their cells. Similar abnormalities in GC receptor binding defects can be detected in freshly isolated cells from type 1 GR asthmatics, but this defect is reversible when their cells are cultured in the absence of IL-2 and IL-4. The second group involves patients with primary GC resistance who do not develop side effects on high-dose GCs and have very low numbers of GC receptors in their mononuclear cells. This defect is irreversible in culture and affects their T cells as well as non-T cells. The current studies provide new insights into mechanisms by which inflammation induces GC resistance and how defects in the GC receptor may contribute to chronic inflammation, creating the vicious cycle leading to chronic inflammatory diseases.

New insights into steroid resistant asthma

The term "steroid resistant (SR) asthma" refers to a group of asthmatics who have persistent airway obstruction and immune activation despite treatment with high doses of systemic glucocorticoids. There are at least two forms of SR asthma, i.e. primary and acquired types. Type I SR asthma is acquired and is associated with abnormally reduced glucocorticoid receptor (GCR) ligand and DNA binding affinity. Type II SR asthma appears to be due to a constitutive defect and is associated with low numbers of GCRs. An important distinction between these two types of SR asthma is that the GCR defect in Type I, but not Type II, SR asthma is reversible in culture and is sustained by incubation with combination IL-2 and IL-4. Recent studies suggest that the abnormal GCR binding in Type I SR asthma may be due to cytokine-driven alternative splicing of the GCR pre-mRNA to a novel isoform called GCRbeta which does not bind glucocorticoids but antagonizes the transactivating activity of the classic GCR. These GCR changes along with recent evidence for increased transcription factor activation in SR asthma which may inhibit GCR/DNA interactions as well as the selective recruitment of neutrophils into the airways of certain patients with severe asthma contribute to the heterogeneity of mechanisms underlying steroid resistance.

Diagnosis and management of steroid-resistant asthma

The term "steroid-resistant (SR) asthma" has been used to describe a group of asthmatics who demonstrate persistent airway obstruction and inflammation despite treatment with high doses of systemic glucocorticoids. There are at least two forms of SR asthma, that is, primary and acquired types. Type I SR asthma is acquired and is associated with abnormally reduced glucocorticoid receptor (GR) ligand and DNA binding affinity. Type II SR asthma is due to a primary GR binding abnormality. An important distinction between these two types of SR asthma is that the GR defect in Type I, but not Type II, SR asthma is reversible in culture and is sustained by incubation with combination IL-2 and IL-4. The treatment of these patients requires a systematic approach to rule out confounding factors, including triggers of immune activation, optimizing steroid therapy, and use of alternative strategies to inhibit airway inflammation.

Anti-inflammatory drugs in the treatment of allergic disease

The treatment of asthma is undergoing significant change with an emphasis on anti-inflammatory therapy. While glucocorticoids are the most potent anti-inflammatory agent, certain patients fail to respond. These patients may be candidates for alternative anti-inflammatory therapy, such as troleandomycin, methotrexate, gold, hydroxychloroquine, or dapsone. In addition, the application of immunomodulator therapy, such as intravenous gamma globulin or cyclosporine, may be useful.

Regulation of glucocorticoid receptor expression in cultured fibroblasts from a patient with familial glucocorticoid resistance

The thermolabile glucocorticoid receptor (GR) in fibroblasts from a patient with familial glucocorticoid resistance (FGR) was characterized by solution hybridization, Northern blot analysis and Western immunoblotting using an hGR and cRNA probe and a GR specific monoclonal antibody. Specific DNA binding was measured by binding of cytosolic GR to mouse mammary tumour virus (MMTV) DNA. Northern blot analysis of total cellular RNA isolated from the fibroblasts showed hybridization of the hGR probe to 7.0 and 6.1 kb RNA species. Basal expression of hGR mRNA was 1.8 times higher in fibroblasts derived from the patient compared to control fibroblasts as assayed by solution hybridization. Even though nonsignificant, dexamethasone treatment maximally caused at 60% down-regulation of GR mRNA in normal fibroblasts after 12 h but only a 40% down-regulation in fibroblasts from the patient. In both cases, the initial mRNA values were restored after 72 h. No difference in GR mRNA stability was observed between fibroblasts from the patient and from controls. The induction of the glucocorticoid-regulated gene metallothionein IIA (MTIIA) by dexamethasone and cadmium sulphate was studied at different temperatures using a cRNA probe for human MTIIA. At elevated temperatures, cadmium sulphate but not dexamethasone increased MTIIA mRNA levels approximately three-fold in fibroblasts from the patient, whereas in normal fibroblasts regardless of temperature both cadmium sulphate and dexamethasone increased MTIIA mRNA levels approximately three- and two-fold, respectively. Cytosolic GR from FGR-fibroblasts showed an increased specific binding to MMTV DNA at 4 degrees C. These data support our previous findings of a thermolabile GR, probably due to a defect intrinsic to the GR protein, in this patient with primary cortisol resistance and indicate a compensatory mechanism at the transcriptional level of GR expression. The data also indicate a receptor defect affecting specific DNA binding in vitro.

Steroids and depression

Patients with endogenous depression (major affective disorder) frequently have high cortisol levels, but the diurnal rhythm is usually maintained and they do not develop the physical signs of Cushing's syndrome. On the other hand, depression is a frequent feature of Cushing's syndrome regardless of etiology, and it is often relieved when the cortisol levels are reduced, by whatever means. The mechanisms of the hypercortisolemia and resistance to dexamethasone suppression commonly found in endogenous depression are poorly understood; contrary to expectations, ACTH levels are not clearly elevated. There is a striking difference in the psychiatric features seen in endogenous hypercorticism compared to those seen after exogenous administration of glucocorticoids or ACTH. This suggests that either there are other stimulating or modifying factors besides ACTH or that the steroids stimulated by ACTH or other peptides differ from those in control subjects, i.e. there may be an alteration in the metabolism of steroids in depression. Little is known about the metabolic changes or the many steroids besides glucocorticoids produced by the hyperactive steroid-producing tissue. Preliminary studies suggest that major depression may be improved by steroid suppression. It is hypothesized that steroids themselves may be important in causing and perpetuating depression.

Point mutation causing a single amino acid substitution in the hormone binding domain of the glucocorticoid receptor in familial glucocorticoid resistance

Familial glucocorticoid resistance is a hypertensive, hyperandrogenic disorder characterized by increased serum cortisol concentrations in the absence of stigmata of Cushing's syndrome. Our previous studies of the first reported kindred showed a two- to threefold reduction in glucocorticoid receptor-ligand binding affinity in the propositus, and a lesser reduction in affinity in his mildly affected son and nephew. Glucocorticoid receptor cDNA from these three patients was amplified by polymerase chain reaction and sequenced. The cDNA nucleotide sequence was normal, except for nucleotide 2054, which substituted valine for aspartic acid at amino acid residue 641. The propositus was homozygous while the other relatives were heterozygous for the mutation. COS-7 monkey kidney cells were cotransfected with expression vectors for either wild type or Val 641-mutant receptors, together with the reporter plasmid pMMTV-CAT. Dexamethasone increased chloramphenicol acetyltransferase activity in cells expressing wild type receptor, but had no effect in cells expressing Val 641-mutant receptors, despite similar receptor concentrations, as indicated by Western blotting. The binding affinity for dexamethasone of the Val 641-mutant receptor was threefold lower than that of the wild type receptor. These results suggest that glucocorticoid resistance in this family is due to a point mutation in the steroid-binding domain of the glucocorticoid receptor.