|
KMID : 1007020030010010040
|
|
Korean Soceity of Osteroporosis
2003 Volume.1 No. 1 p.40 ~ p.54
|
|
|
Activation of Peroxisome Proliferator-Activated Receptor-[gamma]Inhibits the Runx2-Mediated Transcriptonof Osteocalcin in Osteoblasts
|
|
Jeon Min-Jae
Kwon Sung-Hee
Kim Jeong-Ah
Kim Sang-Wan
Park Kyong-Soo
Park Sung-Woo
Kim Seong-Yeon
Shin Chan-Soo
|
|
|
Abstract
|
|
|
Objectives: Mesenchymal cells are able to differentiate into several distinct cell types, including osteoblasts and adipocytes. The commitment to a particular lineage may be regulated by specific transcription factors. Peroxisome proliferator activated receptor γ(PPARγ) acting in conjunction with C/EBPα has been suggested as a key regulator of adipogenic differentiation. Previous studies have shown that the activation of PPARγ in osteoblasts suppresses osteoblast differentiation and the expression of osteocalcin, one of the osteoblast-specific proteins. However, the mechanism of this inhibition remains unclear. We investigated the effect of PPARγ activation on the expression of osteocalcin and analyzed the underlying molecular mechanism.
Methods: Mouse osteoblastic MC3T3-E1 cells, rat osteosarcoma cell line ROS 17/2.8 cells and mouse mesenchymal C3H10T1/2 cells were used. Expression of PPARγ was assessed using Western blot and RT-PCR analysis. To activate PPARγ-mediated transcription, cells were treated with PPARγ ligand, 15-deoxy-Δ12,14 prostaglandin J2. Transcriptional activity of reporter vectors were analyzed by luciferase assay. Interaction of transcription factors and cis-acting element was investigated using gel shift assay and in vivo protein interactions were assessed by immunoprecipitation.
Results: Mouse osteoblastic cell line MC3T3-E1 cells express PPARγ, which is transcriptionally active, whereas rat osteosarcoma cell line, ROS 17/2.8 does not. Treatment of MC3T3-E1 osteoblasts and ROS 17/2.8 cells stably transfected with PPARγ2 with the PPARγ activator, 15-deoxy-Δ12,14 prostaglandin J2 (15d-PGJ2), inhibited the mRNA expression of osteocalcin and Runx2, the latter of which is a key transcription factor in the osteoblastic differentiation. These decreased expressions of osteocalcin and Runx2 were partly explained by the decreased abundance of Runx2 resulting from the suppressed transcription from Runx2 promoter. However, in addition to this indirect effect, the activation of PPARγ by 15d-PGJ2 directly suppressed the Runx2-mediated induction of osteocalcin promoter activity and of the activity of the artificial promoter p6OSE2, which contained six tandem copies of the OSE2 element, the Runx2-binding promoter sequence. This inhibition was found to be mediated by a physical interaction between PPARγ and Runx2 and the subsequent repression of the transcriptional activity of the OSE2 sequence.
Conclusion: This study demonstrates that the activation of PPARγ inhibits osteocalcin expression both by suppressing the expression of Runx2 and by interfering with the transactivation ability of Runx2.
|
|
|
KEYWORD
|
|
|
PPAR (peroxisome proliferator-activated receptor)gamma, Osteocalcin, Promoter
|
|
|
FullTexts / Linksout information
|
|
|
|
|
|
Listed journal information
|
|
|
|