Tandem repeat of C/EBP binding sites mediates PPARγ2 gene transcription in glucocorticoid-induced adipocyte differentiation
✍ Scribed by Xing Ming Shi; Harry C. Blair; Xiangli Yang; Jay M. McDonald; Xu Cao
- Publisher
- John Wiley and Sons
- Year
- 2000
- Tongue
- English
- Weight
- 374 KB
- Volume
- 76
- Category
- Article
- ISSN
- 0730-2312
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✦ Synopsis
Bone marrow stromal stem cells differentiate into many different types of cells including osteoblasts and adipocytes. Long-term glucocorticoid treatment decreases osteoblastic activity but increases adipocytes. We investigated the mechanism of glucocorticoid-induced PPAR␥2 transcription. Treatment of human bone marrow stromal cells with dexamethasone induced the differentiation of these cells into adipocytes as measured by oil-red O staining, and Northern blot analysis showed that dexamethasone strongly induced PPAR␥2 mRNA expression in cells cultured in adipocyte induction medium. Moreover, the mRNA of C/EBP␦, an adipocyte-promoting transcription factor, was also induced by dexamethasone in the presence of induction medium. Gel mobility shift assays using purified GST-C/EBP␦ fusion protein showed that C/EBP␦ specifically binds to a 40-base pair DNA element from PPAR␥2 promoter, which was found to contain a tandem repeat of C/EBP binding sites. Transfection studies in mouse mesenchymal C3H10T1/2 cells showed that it is the tandem repeat of the C/EBP binding site in PPAR␥2 promoter region that regulates dexamethasonemediated PPAR␥2 gene activation. We conclude that glucocorticoid-induced adipogenesis from bone marrow stromal cells is mediated through a reaction cascade in which dexamethasone transcriptionally activates C/EBP␦; C/EBP␦ then binds to PPAR␥2 promoter and transactivates PPAR␥2 gene expression. This activated master regulator, in turn, initiates the adipocyte differentiation.