PARATHYROID-HORMONE INDUCES C-FOS PROMOTER ACTIVITY IN OSTEOBLASTIC CELLS THROUGH PHOSPHORYLATED CAMP RESPONSE ELEMENT (CRE)-BINDING PROTEIN-BINDING TO THE MAJOR CRE

Many parathyroid hormone (PTH)-mediated events in osteoblasts are thou ght to require immediate early gene expression, PTH induces the immedi ate early gene, c-fos, in this cell type through a cAMP-dependent path way, The present work investigated the nuclear mechanisms involved in PTH regulation of c-fos in the osteoblastic cell line, UMR 106-01. By transiently transfecting c-fos promoter 5' deletion constructs into UM R cells, we demonstrated that PTH induction of the c-fos promoter requ ires the major cAMP response element (CRE). Point mutations created in the major CRE within the largest construct inhibited both PTH-stimula ted and basal expression, This element, therefore, performs concerted basal and PTH-responsive cis-acting functions, Gel retardation and Wes tern blotting techniques revealed that CRE-binding protein (CREB) cons titutively binds the major CRE but becomes phosphorylated at its cAMP- dependent protein kinase consensus recognition site following PTH trea tment, CREB was functionally implicated in c-fos regulation by coexpre ssing a dominant CREB repressor, KCREB (killer CREB), with the c-fos p romoter constructs. KCREB suppressed both basal and PTH-mediated c-fos induction. We conclude that PTH activates c-fos in osteoblasts throug h cAMP-dependent protein kinase-phosphorylated CREB interaction with t he major CRE in the promoter region of the c-fos gene.