TRANSCRIPTIONAL ACTIVATION OF THE MACROPHAGE MIGRATION-INHIBITORY FACTOR GENE BY THE CORTICOTROPIN-RELEASING FACTOR IS MEDIATED BY THE CYCLIC ADENOSINE-3',5'-MONOPHOSPHATE RESPONSIVE ELEMENT-BINDING PROTEIN CREB IN PITUITARY-CELLS

Macrophage migration-inhibitory factor (MIF) has recently been identif ied as a pituitary hormone that functions as a counterregulatory modul ator of glucocorticoid action within the immune system. In the anterio r pituitary gland, MIF is expressed in TSH-and ACTH-producing cells, a nd its secretion is induced by CRF. To investigate MIF function and re gulation within pituitary cells, we initiated the characterization of the MIF 5'-regulatory region of the gene. The -1033 to +63 bp of the m urine MIF promoter was cloned 5' to a luciferase reporter gene and tra nsiently transfected into freshly isolated rat anterior pituitary cell s. This construct drove high basal transcriptional activity that was f urther enhanced after stimulation with CRF or with an activator of ade nylate cyclase. These transcriptional effects were associated with a c oncomitant rise in ACTH secretion in the transfected cells and by an i ncrease in MIF gene expression as assessed by Northern blot analysis. A CAMP-responsive element (CRE) was identified within the MIF promoter region which, once mutated, abolished the CAMP responsiveness of the gene. Using this newly identified CRE, DNA-binding activity was detect ed by gel retardation assay in nuclear extracts prepared from isolated anterior pituitary cells and AtT-20 corticotrope tumor cells. Supersh ift experiments using antibodies against the CRE-binding protein CREB, together with competition assays and the use of recombinant CREB, all owed the detection of CREB-binding activity with the identified MIF CR E. These data demonstrate that CREB is the mediator of the CRF-induced MIF gene transcription in pituitary cells through an identified CRE i n the proximal region of the MIF promoter.