SYNERGISTIC ACTIVATION OF NEUROTENSIN NEUROMEDIN-N GENE-EXPRESSION BYC-JUN AND GLUCOCORTICOIDS - NOVEL EFFECTS OF FOS FAMILY PROTEINS/

The cis-regulatory region of the neurotensin/neuromedin N (NT/N) gene integrates diverse environmental signals in the neuroendocrine PC12 ce ll line, resulting in remarkable synergistic regulation. An AP-1 site appears to play a pivotal role in cooperative NT/N gene activation, as mutations in this site decrease responses to all inducer combinations by at least an order of magnitude. Here we report that c-Jun acts syn ergistically with glucocorticoids to activate the NT/N promoter, and t hat Fos family proteins have novel regulatory effects on this interact ion. Cotransfection of individual pCMV-AP-1 expression plasmids reveal ed that c-jun most potently activates the NT/N promoter and that costi mulation with dexamethasone results in a further 6- to 12-fold increas e in expression. Unlike its general inhibitory effects on glucocortico id regulation in other systems, c-Fos potentiated activation by glucoc orticoids when coexpressed with c-Jun, and Fos B had a similar, but mo re limited, positive effect. In contrast, Fra-1 reversed the direction of glucocorticoid regulation, and Fra-2 abolished synergism. AP-1, cA MP response element, and glucocorticoid response element motifs are re quired for full cooperative activation by either c-Jun or c-Jun/c-Fos and glucocorticoids. These results indicate that NT/N promoter activat ion involves synergistic interactions between specific AP-1 complexes and ligand-activated glucocorticoid receptor, and similar mechanisms m ay regulate NT/N gene expression in central neurons.