The glucocorticoid properties of the synthetic steroid pregna-1,4-diene-11 β-ol-3,20-dione (ΔHOP) are not entirely correlated with the steroid binding to the glucocorticoid receptor

Abstract

The natural steroid 11 β-hydroxyprogesterone is not only a modulator of 11 β-hydroxy-steroid dehydrogenase activity, but also an efficient inducer of tyrosine aminotransferase activity in hepatocytes. In contrast with the low affinity for the mineralocorticoid receptor, 11 β-hydroxyprogesterone binds well to both the glucocorticoid receptor and the carrier protein transcortin. It is accepted that the introduction of a 1:ene double bond into 3-keto 4:ene steroids increases the glucocorticoid potency, so that 3-keto-1,4:diene steroids show improved chemical stability and are more potent glucocorticoids than their respective 4:ene analogs. The steroid pregna-1,4-diene-11 β-ol-3,20-dione (ΔHOP) had previously been described as an anti-inflamatory compound and an inhibitor of macromolecular biosynthesis in thymocytes and lymphocytes. In such studies, ΔHOP also exhibited some particular glucocorticoid properties which made it attractive as a tool for the study of the mechanism of action of glucocorticoids. In the present paper we show that ΔHOP possesses some classical biological actions of glucocorticoids such as deposition of glycogen in rat liver, induction of TAT activity in hepatocytes, and inhibition of the uptake of leucine and thymidine by thymocytes. It also exhibits minimal sodium-retaining properties. Consistent with these biological effects, ΔHOP shows a 70 times lower relative binding affinity for the mineralocortioid receptor than aldosterone, but a reasonable affinity for the glucocorticoid receptor, and is as efficient as dexamethasone in dissociating the 90 kDa heat shock protein from the glucocorticoid receptor heterocomplex. However, the inhibition of the uptake of amino acids and nucleotides observed in the presence of ΔHOP is not efficiently blocked when thymocytes are coincubated in the presence of steroids with known antiglucocorticoid activity. ΔHOP is similarly inefficient in inducing chloramphenicol–acetyl transferase activity in cells transfected with a plasmid that possesses two canonical glucocorticoid-responsive elements. Unlike most glucocorticoids, ΔHOP does not induce the fragmentation of DNA in a regular pattern characteristic of apoptosis and it does not reduce thymus weight. This unusual dissociation of glucocorticoid parameters makes ΔHOP a useful tool to discriminate between mechanisms of action by which steroids can exert their biological effects.