Glucocorticoid receptor isoforms alpha and beta in in vitro cytokine-induced glucocorticoid insensitivity.

Abstract

We stimulated peripheral blood mononuclear cells from 14 healthy subjects, 14 patients with stable asthma, and 13 patients with unstable asthma with interleukin (IL)-2 and IL-4 to induce glucocorticoid insensitivity and we examined the relationship between insensitivity and the expression of glucocorticoid receptor (GR) isoforms. Results are expressed as IC(50) (nanomolar) values (means +/- SD) in proliferation assays and as 10(3) cDNA molecules per microgram of total RNA (means +/- SD) in real-time polymerase chain reaction analysis. Cells from patients with unstable asthma were less sensitive (316 +/- 7 nM) to dexamethasone antiproliferative effects than those from healthy control subjects (102 +/- 4 nM, p < 0.05) and patients with stable asthma (107 +/- 2 nM, p < 0.05). Coincubation with IL-2 and IL-4 repressed the inhibitory effect of dexamethasone on proliferation in all groups (unstable: 851 +/- 47 nM, p < 0.01; stable: 912 +/- 52 nM, p = 0.001; control subjects: 537 +/- 45 nM, p = 0.001). GR-alpha mRNA baseline expression was higher in patients with unstable asthma [(1.95 +/- 0.40) x 10(3) cDNA molecules/microg total RNA, p < 0.05] than in patients with stable asthma [(1.46 +/- 0.35) x 10(3) cDNA molecules/microg total RNA] and healthy subjects [(1.35 +/- 0.25) x 10(3) cDNA molecules/microg total RNA]. GR-beta mRNA was 600 times lower than GR-alpha in the three groups. Coincubation with IL-2 and IL-4 significantly increased GR-alpha mRNA expression in the three groups (p < 0.01), but caused no significant change in GR-beta mRNA. GR-alpha, but not GR-beta, protein was detected at baseline and after cytokine exposure. Our data do not support the hypothesis that increased GR-beta expression can contribute to cytokine-induced glucocorticoid insensitivity.