Corticosteroid binder IB: A model of glucocorticoid receptor diversity

Differential up- and down-regulation of type I and type II receptors for adrenocorticosteroid hormones in mouse brain

Adult female mice were adrenalectomized and ovariectomized and the concentration of Type I and Type II receptors in whole brain, kidney, and liver cytosol determined at various time thereafter by incubation with [3H]aldosterone (+ RU 26988 to prevent binding to Type II receptors) or [3H]dexamethasone, respectively. Type I receptor binding in brain was found to undergo a dramatic biphasic up-regulation, with levels six times that of intact levels by 24 h post-surgery and a doubling again by 4-8 days post-surgery. By 16 days, however, Type I specific binding had returned to intact levels. Similar, but less dramatic fluctuations were seen in kidney and liver, whereas much smaller fluctuations were seen for Type II receptors in all three tissues. In a follow-up study with Scatchard analyses we observed a similar transient up- and down-regulation in maximal binding for Type I, and to a lesser extent Type II receptors in all three tissues. As expected, the apparent binding affinity for both receptors increased after surgical removal of competing endogenous steroids. Radioimmunoassays revealed that plasma concentrations of corticosterone were reduced to near undetectable levels by 24 h post-surgery. A direct comparison of male and female mice revealed no sex-related differences in Type I receptor binding capacity fluctuations in brain cytosol after adrenalectomy-gonadectomy. Lastly, treatment with exogenous aldosterone or corticosterone was found to prevent adrenalectomy-gonadectomy-induced up-regulation of Type I and, to a lesser extent, Type II receptors in brain. Somewhat surprisingly, the potency of these two adrenocorticosteroids appeared to be very similar for both receptor types.

Further chemical differentiation of type I and type II adrenocorticosteroid receptors in mouse brain cytosol: evidence for a new class of glucocorticoid receptors

There are at least two classes of intracellular receptors for adrenocorticosteroid hormones in brain. Type I receptors have a high affinity for the naturally occurring gluco- and mineralocorticoids, corticosterone (CORT) and aldosterone (ALDO), respectively, and a very low affinity for synthetic glucocorticoids such as dexamethasone (DEX). type II receptors have a high affinity for the synthetic glucocorticoids, a lower affinity for CORT and a very low affinity for ALDO. In recent studies with mouse brain cytosol we have found a number of other biochemical differences between these two receptor types. In the present study, brain cytosol from adrenalectomized mice was prepared in HEPES buffer and subjected to various potentially inactivating treatments prior to assessment of Type I and Type II receptor specific binding capacity by incubation for 24 h at 0 degrees C with [3H]ALDO +/- [1H]RU 26988 (to prevent or permit the cross-binding of [3H]ALDO to Type II receptors) or [3H]DEX +/- [1H]Prorenone (to prevent or permit the cross-binding of [3H]DEX to Type I receptors), respectively. These studies revealed that 10-20% of the high-affinity (Kd = 3 nM) [3H]DEX specific binding capacity remained even after extensive, high concentration and repeated pretreatments with dextran-coated charcoal (DDC. to remove endogenous sulfhydryl-reducing reagents and other biochemicals). These procedures had little effect on Type I receptors. Further analyses revealed that DCC-resistant [3H]DEX binders were not Type I receptors since they were not saturated by [1H]Prorenone. These binders were also not inactivated by aging steroid-free cytosol at 0 degree C or by treating it with buffers containing 0.3 M KCl. Since these

Glucocorticoid receptor IB: mediator of anti-inflammatory and teratogenic functions of both glucocorticoids and phenytoin

We studied the glucocorticoid receptor complexes of pulmonary and thymic cytosols of female A/J and CD-1 mice and of hepatoma G2 cells by two column-chromatographic systems, using both [3H]dexamethasone (DEX) and [3H]phenytoin (DPH) as ligands. Three DNA-cellulose adsorbable [3H]DEX-receptor complexes were separated in each system. Molecular sieving gave a 7-, a 5.4-, and a 3.5-nm complex (Stokes radii), and DEAE-Sephadex A-50 chromatography gave a complex eluting in the wash, one at 0.14 M KCl, and one at 0.20 M KCl by a KCl gradient. DPH blocked the binding of the 7- and 3.5-nm, wash, and 0.14 M KCl [3H]DEX complexes. Only two DNA-cellulose adsorbable [3H]DPH complexes, each blocked by DEX, were obtained in each system: a 7- and a 3.5-nm, a wash, and a 0.14 M KCl complex. Thus, there is a common receptor for both DPH and DEX. This receptor has two properties which distinguish it from the 5.4-nm DEX-specific receptor: (i) it binds with a variety of steroids other than glucocorticoids and DPH, and (ii) it rebinds new [3H]DEX or [3H]DPH after loss of ligand during chromatographic separation. These results indicate that DPH binds to receptor IB and not to receptor II of Litwack. [G. Litwack, 1976, in Glutathion: Metabolism and Function (Arias, I.M., and Jakoby, W.B., eds.), pp. 285-299, Raven Press, New York]. We have also found that hepatoma G2 cells have only receptor II. DPH affects neither the induction of tyrosine aminotransferase by DEX nor the basal level of this enzyme in these cells. Moreover, neither DEX nor DPH inhibits the release of [3H]arachidonic acid prelabeled in these cells, as they do in thymocytes which have the common receptor. Thus, it appears that glucocorticoid receptor IB binds DEX and DPH as glucocorticoid agonists mediating the anti-inflammatory and teratogenic action of these drugs, while receptor II apparently is responsible for the induction of tyrosine aminotransferase by DEX.