Glucocorticoids use a positive liver element to repress fibrate-induced adipose transcription of the phosphoenolpyruvate carboxykinase gene

Abstract

Glucocorticoids inhibit basal and hormone-induced phosphoenolpyruvate carboxykinase (PEPCK) gene transcription in adipocytes whereas beta-adrenergic agonists and fibrates are stimulatory. Here we show that dexamethasone inhibits the induction of PEPCK mRNA by isoprenaline or clofibrate in 3T3-F442A adipocytes. RU 38486 antagonizes dexamethasone effect, suggesting the involvement of the glucocorticoid receptor. In H4IIE hepatoma cells, glucocorticoids enhance PEPCK gene transcription through a complex region which encompasses an element, AF1, with a direct repeat 1-type sequence. Mutations in the AF1 sequence abolish binding of nuclear factors from liver and from 3T3-F442A adipocytes. We transiently transfected 3T3-F442A cells with a wild type or an AF1-mutated PEPCK-CAT construct comprising -2100 to +69 base pairs of the promoter fused to the chloramphenicol acetyltransferase (CAT) gene. With both constructs, CAT activity is decreased by dexamethasone and is increased by isoprenaline or by clofibrate. However, dexamethasone is unable to inhibit clofibrate induction of CAT activity in cells transfected with the AF1-mutated construct whereas it prevents isoprenaline action on both constructs. Hence, although a single hormone can repress stimulations originating from different intracellular routes, sites in the promoter which mediate inhibition of a specific stimulation are distinct.