GLUCOCORTICOIDS USE A POSITIVE LIVER ELEMENT TO REPRESS FIBRATE-INDUCED ADIPOSE TRANSCRIPTION OF THE PHOSPHOENOLPYRUVATE CARBOXYKINASE GENE

Glucocorticoids inhibit basal and hormone-induced phosphoenolpyruvate carboxykinase (PEPCK) gene transcription in adipocytes whereas beta-ad renergic agonists and fibrates are stimulatory. Here we show that dexa methasone inhibits the induction of PEPCK mRNA by isoprenaline or clof ibrate in 3T3-F442A adipocytes. RU 38486 antagonizes dexamethasone eff ect, suggesting the involvement of the glucocorticoid receptor. In H4I IE hepatoma cells, glucocorticoids enhance PEPCK gene transcription th rough a complex region which encompasses an element, AF1, with a direc t repeat 1-type sequence. Mutations in the AF1 sequence abolish bindin g of nuclear factors from liver and from 3T3-F442A adipocytes. We tran siently transfected 3T3-F442A cells with a wild type or an AF1-mutated PEPCK-CAT construct comprising -2100 to +69 base pairs of the promote r fused to the chloramphenicol acetyltransferase (CAT) gene. With both constructs, CAT activity is decreased by dexamethasone and is increas ed by isoprenaline or by clofibrate. However, dexamethasone is unable to inhibit clofibrate induction of CAT activity in cells transfected w ith the AF1-mutated construct whereas it prevents isoprenaline action on both constructs. Hence, although a single hormone can repress stimu lations originating from different intracellular routes, sites in the promoter which mediate inhibition of a specific stimulation are distin ct. (C) 1997 Elsevier Science Ireland Ltd.