Expression of the Human Glucocorticoid Receptor α and β Isoforms in Human Respiratory Epithelial Cells and Their Regulation by Dexamethasone

Abstract

Two isoforms of the human glucocorticoid receptor (hGR) have been described, hGRalpha and hGRbeta. We analyzed the expression and regulation of both hGR isoforms in human respiratory epithelial cells (BEAS-2B, A549, and primary nasal epithelial cells). In BEAS-2B cells, the expression of hGRalpha messenger RNA (mRNA) was much higher than that of hGRbeta mRNA. Dexamethasone (DEX) (10(-6) M) downregulated hGRalpha mRNA at 6 and 24 h (55 +/- 8 and 58 +/- 5% of control, respectively; P < 0.01), whereas it decreased hGRbeta mRNA only at 6 h (55 +/- 7% of control; P < 0.01). Downregulation of hGRalpha and hGRbeta mRNAs occurred even in the presence of cycloheximide. Actinomycin-D studies revealed that DEX enhanced the stabilization of hGRalpha and hGRbeta messages. hGRalpha but not hGRbeta protein was detected in BEAS-2B, A549, and nasal epithelial cells. After 24 h of incubation, 10(-6) M DEX decreased the expression of hGRalpha protein in BEAS-2B, A549, and nasal epithelial cells (16 +/- 4, 14 +/- 4, and 28 +/- 7% of control, respectively; P < 0.01). These results suggest that in respiratory epithelial cells: (1) hGRalpha is much more expressed than hGRbeta at both the mRNA and protein levels; (2) hGRalpha is downregulated by corticosteroids both in cell lines (BEAS-2B, A549) and in nasal primary cells; and (3) transcriptional, post-transcriptional, and post-translational mechanisms appear to be involved in the regulation of hGR expression by corticosteroids.

Postnatal glucocorticoids induce α-ENaC formation and regulate glucocorticoid receptors in the preterm rabbit lung

“…To this end, we observed that in experiments carried out to 24 h, exposure of 29-day GA preterm rabbits to Dex after 12 h actually caused a decrease in basal lung GCR protein levels that was apparent up to 24 h. The data presented herein suggesting receptor downregulation by its cognate ligand in whole lung are in similar agreement with another published study that reported a downregulation of GCR protein levels by Dex in cultured human airway epithelial cells (40). Further analysis of our data demonstrates that postnatal treatment of 29-day GA preterm rabbits with Dex over a period of 16 h resulted in an elevation of lung GCR mRNA expression that was concurrent with the decline in protein levels, suggestive of a transcriptional mode of upregulating gene expression in response to the posttranslational mechanism of downregulating existing protein levels.…”

“…7A). Western blot analysis of the ␣-subunit of GCR detected, as previously reported, the 94-kDa protein in rabbit lung samples (8,40). GCR lung protein levels were evident in 23-and 27-day GA preterm rabbits and were elevated 1.8-fold (by densitometric analysis) from 27 to 29 days' GA (Fig.…”

“…*P Ͻ 0.05 was considered significantly different from saline-treated control fetuses at the same time point. intracellular GCR concentrations (40,42). Successful adaptation of the neonatal lung during the perinatal situation requires that there be a sufficient response of the immature lung in late gestation to elevated levels of circulating maternal GC, which in turn, acting via GCR, accelerate lung maturation in preparation for birth (22,29,48,49).…”

Smoking and Asthma

“…GR-␣ receptors are functional, whereas GR-␤ receptors are not; therefore, an increase in the number of GR-␤ receptors could lead to decreased binding and activity of glucocorticoids in vivo. 106,107 Altered corticosteroid cell-signaling systems may also play a role.…”

Nuclear bioavailability of the glucocorticoid receptor in a pediatric asthma cohort with variable corticosteroid responsiveness

“…TBP, TATA-binding protein. c d translation are linked, in a way that when translation is inhibited the mRNA is stabilized (17). GR-induced transcriptional responses are proportional to the number of receptor molecules present in the cell (18).…”