Parathyroid Hormone Induces c-fos Promoter Activity in Osteoblastic Cells through Phosphorylated cAMP Response Element (CRE)-binding protein Binding to the Major CRE

Abstract

Many parathyroid hormone (PTH)-mediated events in osteoblasts are thought to require immediate early gene expression. PTH induces the immediate early gene, cfos, in this cell type through a cAMP-dependent pathway. 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 UMR cells, we demonstrated that PTH induction of the c-fos promoter requires the major cAMP response element (CRE). Point mutations created in the major CRE within the largest construct inhibited both PTH-stimulated and basal expression. This element, therefore, performs concerted basal and PTH-responsive cis-acting functions. Gel retardation and Western blotting techniques revealed that CRE-binding protein (CREB) constitutively binds the major CRE but becomes phosphorylated at its cAMP-dependent protein kinase consensus recognition site following PTH treatment. CREB was functionally implicated in c-fos regulation by coexpressing a dominant CREB repressor, KCREB (killer CREB), with the c-fos promoter constructs. KCREB suppressed both basal and PTH-mediated c-fos induction. We conclude that PTH activates c-fos in osteoblasts through cAMPdependent protein kinase-phosphorylated CREB interaction with the major CRE in the promoter region of the c-fos gene.We have shown previously that parathyroid hormone (PTH) 1 stimulates c-fos transcription in the osteoblastic UMR 106-01 cell line through a cAMP-mediated pathway (1). However, the events that follow cAMP induction are less clear. The present work was undertaken to describe the nuclear mechanisms involved in PTH-mediated c-fos induction in osteoblasts. Many PTH-responsive genes in osteoblasts are thought to be secondary responses due to their delayed nature and requirement for ongoing protein synthesis (2, 3). By definition, these genes require the expression of primary response genes, such as c-fos, for their induction.Several in vivo models have identified Fos as a player in bone biology. This factor was first linked to bone when it was discovered in a mouse osteosarcoma as the product of v-fos, the viral homolog of c-fos (4). Similarly, several groups have engineered mice that overexpress c-fos and display bone abnormalities including non-malignant bone neoplasms and collagenaseproducing bone tumors (5, 6). Conversely, Fos null mice exhibit osteopetrosis and disorganized bone growth (7). Transgenic mice, which express a fos-lacZ fusion gene, also identified bone as one of the major sites for c-fos expression (8). In agreement with the rodent models, evidence for Fos involvement in human bone disease has been provided by high c-fos expression in Pagetic bone (9) and human osteosarcomas (10).c-fos is regulated in a cell-specific manner through a variety of mechanisms. These signaling pathways most likely act through different combinations of highly conserved sites within the promoter region (11). The mechanism for c-fos induction in osteoblasts by the bone r...

Both AP-1 and Cbfa1-like factors are required for the induction of interstitial collagenase by parathyroid hormone

“…It is well accepted that in addition to DNA binding, post-translational modi®cations, particularly changes in the phosphorylation pattern, are required for Fos and Jun to act as transcriptional activators (Minden and Karin, 1997). PTH is a very potent inducer of cAMP-dependent PKA and induction of c-fos is mediated by this pathway involving phosphorylation of CREB which binds on a CRE responsive element in the c-fos promoter (Pearman et al, 1996). Although PTH has been found to activate PKC most e ects on gene regulation can be blocked by inhibitors of the PKA pathway (Evans et al, 1996;Yang and Gerstenfeld, 1996).…”

The Central Nervous System (CNS)-independent Anti-bone-resorptive Activity of Muscle Contraction and the Underlying Molecular and Cellular Signatures

“…4A). Expression of c-fos, a gene up-regulated by PTH in osteoblasts (32), was increased after SCI by ϳ15-fold with the level reduced, albeit not significantly, by ES (Fig. 4A).…”

Prostaglandin E2 Stimulates Bone Sialoprotein (BSP) Expression through cAMP and Fibroblast Growth Factor 2 Response Elements in the Proximal Promoter of the Rat BSP Gene

“…13). Although cAMP-dependent protein kinase signaling does not affect CREB binding to its cognate CRE element, it can direct phosphorylation of CREB, which is required for transcriptional activation (62,63). In comparison, the nuclear factor binding to the FRE element, which is regulated by tyrosine kinase, has yet to be characterized and is the focus of current studies because of its potential role in regulating basal and FGF2-induced transcription of BSP in osteoblasts (42), as well as mediating the PGE 2 effects.…”