Paradoxical effects of glucocorticoids on regulation of plasminogen activator activity : Mediation by glucocorticoid receptors

Abstract

Dexamethasone, a synthetic glucocorticoid, decreases the plasminogen activator (PA) activity of HTC rat hepatoma cells in tissue culture. Paradoxically, dexamethasone enhances the cyclic nucleotide stimulation of PA activity in these cells 2-4-fold. In this report, we investigated whether this paradoxical glucocorticoid effect is mediated by the same proximal events which mediate such direct regulatory actions of glucocorticoids as the induction of tyrosine aminotransferase activity. We compared the concentration-dependences for several classes of steroids, previously classified as full agonists, partial agonists, antagonists or inactive steroids with respect to induction of the transaminase, for both enhancement of cyclic nucleotide stimulation of PA activity and induction of tyrosine aminotransferase activity in parallel cultures. The full agonists dexamethasone and cortisol, the partial agonists deoxycorticosterone and 11[beta]-hydroxyprogesterone, the inactive steroid tetrahydrocortisol, and the antagonist 17[alpha]-methyltestosterone exhibited similar potencies with respect to both phenomena. Furthermore, when cells were incubated with both dexamethasone and 17[alpha]-methyltestosterone, the latter blocked enhancement by dexamethasone in a concentration-dependent fashion. We conclude that glucocorticoid enhancement of cyclic nucleotide stimulation of PA activity is mediated by the same glucocorticoid receptors which mediate direct regulatory effects.