Molecular mechanisms of dissociative glucocorticoid activity

Background Glucocorticoids mediate their effects on target cells via transa ctivation and transrepression of certain target genes. While conventional g lucocorticoids do not distinguish between transactivation and transrepressi on, new glucocoticoids should be able to dissociate these effects, thus low ering the potential of unwanted side-effects of glucocorticoids in clinical use. In this study, we developed a new experimental system to rest potenti ally selective glucocorticoids in normal lymphocytes. Materials and methods Following pretreatment with phytohaemagglutinin, norm al lymphocytes were transfected, using electroporation, with pGL3 luciferas e reporter vectors under the control: (1) of the human IL-2 promoter; and ( 2) of a glucocorticoid response element (GRE). Luciferase activity was meas ured in response to various steroid compounds, including the potentially di ssociative glucocorticoid medroxyprogesterone acetate (MPA). Results The IL-2 promoter was induced 267.2 +/- 27.5-fold (mean +/- SD) by phorbol ester and ionomycin. In these cells, hydrocortisone and dexamethaso ne caused a 22.9 +/- 3.6% and a 38.4 +/- 10% reduction in luciferase activi ty, respectively. Under GRE control, hydrocortisone stimulated luciferase a ctivity 6.4 +/- 0.50-fold and dexamethasone 8.2 +/- 0.4-fold. MPA-induced t ransrepression was 73.3 +/- 7.2% for the IL-2 promoter, and transactivation was 2.4 +/- 0.4-fold with the GRE-driven construct. The natural progestin progesterone did not have significant effects on either construct. Conclusions This is the first system that allows efficient analysis of gluc ocorticoid-dependent transactivation and transrepression in normal human ly mphocytes. Compared to conventional glucocorticoids, MPA can be reffered to as a dissociative glucocorticoid, its transrepression/transactivation rati o being 6.6 (transrepression 1.91/transactivation 0.29), with dexamethasone being the standard (transrepression 1/transactivation 1).We conclude chat MPA is a highly promising substance for the treatment of autoimmune/inflamm atory diseases.