Dexamethasone 21-mesylate: an affinity label of glucocorticoid receptors from rat hepatoma tissue culture cells.

Abstract

The biological properties of an .alpha.-keto mesylate derivative of cortisol, cortisol-Mes were recently described. Cortisol-Mes exhibited long-term antiglucocorticoid activity, but there was no firm evidence that this activity was irreversible or receptor-mediated. Dexamethasone mesylate (Dex-Mes), which is the .alpha.-keto mesylate derivative of the more active glucocorticoid dexamethasone, is a candidate for a steroid-specific affinity label of glucocorticoid receptors. Dex-Mes is relatively stable, like cortisol-Mes, but possesses greater whole-cell antiglucocorticoid activity. Dex-Mes also possesses partial agonist activity, which is expressed at somewhat high concentrations of Dex-Mes than the antagonist activity. Dex-Mes is more efficient than cortisol-Mes in competing for dexamethasone binding to glucocorticoid receptors. Dex-Mes is effective at lower concentrations than cortisol-Mes in causing long-term apparently irreversible antiglucocorticoid effects in whole and broken cells. The cell-free effect of Dex-Mes is specifically prevented by coincubation with an excess of cortisol. The apparently irreversible effects of Dex-Mes evidently are steroid mediated. [3H]Dex-Mes has been used to identify a glucocorticoid-specific, covalently labeled fraction on sodium dodecyl sulfate/polyacrylamide gels with a MW of = 85,000. Thus Dex-Mes appears to have been established as an affinity label for glucocorticoid receptors.