Transforming growth factor-beta 1 responsiveness of the rat osteocalcin gene is mediated by an activator protein-1 binding site
Biochemistry & Molecular Pharmacology
Graduate School of Biomedical Sciences; Department of Cell Biology
Life Sciences | Medicine and Health Sciences
Osteocalcin (OC), a bone specific protein expressed during differentiation and mineralization of the bone extracellular matrix, is down-regulated upon treatment with transforming growth factor (TGF)-beta 1. To address the potential role of OC gene expression in relation to TGF-beta 1 regulation of bone formation and resorption, we examined the transcriptional activity of the rat OC promoter after TGF-beta 1 treatment. 5' deletion analysis of rat OC promoter-chloramphenicol acetyltransferase constructs demonstrated that TGF-beta 1 treatment repressed chloramphenicol acetyltransferase activity by 2.4-fold in transient transfections of ROS 17/2.8 cells. A 29-bp region between -162 and -134 identified as the TGF-beta 1 response domain, conferred TGF-beta 1 responsiveness to the -108 to +24 rat OC basal promoter in an orientation dependent manner. Mutation of an activator protein-1/cAMP-response element-like motif (- 146 to -139) abolished TGF-beta 1 responsiveness of the construct. In vitro gel-mobility shift and competition assays using wild-type and mutated oligonucleotides and antibodies indicate that Fra-2, a Fos related transcription factor, binds to this motif. We show that Fra-2 is an activator of the OC promoter, and TGF-beta 1 inhibits this activation. Our results demonstrate that Fra-2 is hyperphosphorylated upon TGF-beta 1 treatment of ROS 17/2.8 cells. Additionally, treatment of cells with a staurosporine protein kinase C inhibitor abrogates TGF-beta 1 mediated down-regulation of the OC promoter activity. Together, these results demonstrate that TGF-beta 1 responsiveness of the rat osteocalcin gene in ROS 17/2.8 cells is mediated through an activator protein-1 like cis-acting element that interacts with Fra-2. Furthermore, our results are consistent with a critical role for TGF-beta 1 induced phosphorylation of Fra-2 in the repression of OC gene transcription.
DOI of Published Version
Endocrinology. 1996 May;137(5):1991-2000.
Banerjee C, Stein JL, Van Wijnen AJ, Frenkel B, Lian JB, Stein GS. (1996). Transforming growth factor-beta 1 responsiveness of the rat osteocalcin gene is mediated by an activator protein-1 binding site. GSBS Student Publications. https://doi.org/10.1210/en.137.5.1991. Retrieved from https://escholarship.umassmed.edu/gsbs_sp/75