NEGATIVE TRANSCRIPTIONAL REGULATION OF THE INTERFERON-GAMMA PROMOTER BY GLUCOCORTICOIDS AND DOMINANT-NEGATIVE MUTANTS OF C-JUN

Interferon-gamma (IFN-gamma) is an immunoregulatory cytokine expressed in large granular lymphocytes and T cells. However, the molecular mec hanisms underlying IFN-gamma gene transcription have not been fully de fined. Here, we analyze the mechanisms responsible for the inhibition of IFN-gamma promoter activity by the glucocorticoid hormone dexametha sone. Cotransfection assays performed in Jurkat T cells demonstrated t hat the activity of the initial 108 base pairs of the IFN-gamma promot er was down-regulated in the presence of dexamethasone. Furthermore, u tilizing electrophoretic mobility shift analysis, we identified activa tor protein 1 AP-1-cAMP response element binding protein-activating tr anscription factor (CREB-ATF) binding elements situated in positions o f the IFN-gamma promoter previously identified as essential for promot er activity. Moreover, dominant negative mutants of the c-Jun proto-on cogene were able to mimic the same down-regulatory effect exerted by d examethasone, and mutations that abolished the binding of the AP-1 . C REB-ATF factors were able to block the glucocorticoid effect. These re sults suggest a model involving the inhibition of IFN-gamma AP-1 CREB- ATF DNA binding complexes as one of the mechanisms involved in the neg ative regulatory action of glucocorticoids on IFN-gamma gene expressio n and support the relevance of AP-1 . CREB-ATF binding factors during the transcriptional activation of the IFN-gamma promoter in T cells.