Shi X M, Blair H C, Yang X, McDonald J M, Cao X
Department of Pathology, University of Alabama at Birmingham, Birmingham, Alabama 35294, USA.
J Cell Biochem. 2000 Jan;76(3):518-27. doi: 10.1002/(sici)1097-4644(20000301)76:3<518::aid-jcb18>3.0.co;2-m.
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 PPARgamma2 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 PPARgamma2 mRNA expression in cells cultured in adipocyte induction medium. Moreover, the mRNA of C/EBPdelta, an adipocyte-promoting transcription factor, was also induced by dexamethasone in the presence of induction medium. Gel mobility shift assays using purified GST-C/EBPdelta fusion protein showed that C/EBPdelta specifically binds to a 40-base pair DNA element from PPARgamma2 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 PPARgamma2 promoter region that regulates dexamethasone-mediated PPARgamma2 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/EBPdelta; C/EBPdelta then binds to PPARgamma2 promoter and transactivates PPARgamma2 gene expression. This activated master regulator, in turn, initiates the adipocyte differentiation.
骨髓基质干细胞可分化为多种不同类型的细胞，包括成骨细胞和脂肪细胞。长期糖皮质激素治疗会降低成骨细胞活性，但会增加脂肪细胞。我们研究了糖皮质激素诱导PPARγ2转录的机制。用地塞米松处理人骨髓基质细胞，通过油红O染色测定，这些细胞分化为脂肪细胞，Northern印迹分析表明，地塞米松在脂肪细胞诱导培养基中培养的细胞中强烈诱导PPARγ2 mRNA表达。此外，在诱导培养基存在的情况下，地塞米松也诱导了促进脂肪细胞分化的转录因子C/EBPδ的mRNA表达。使用纯化的GST-C/EBPδ融合蛋白进行的凝胶迁移率变动分析表明，C/EBPδ特异性结合PPARγ2启动子的一个40碱基对的DNA元件，该元件被发现含有C/EBP结合位点的串联重复序列。在小鼠间充质C3H10T1/2细胞中的转染研究表明，正是PPARγ2启动子区域中C/EBP结合位点的串联重复序列调节了地塞米松介导的PPARγ2基因激活。我们得出结论，糖皮质激素诱导骨髓基质细胞向脂肪细胞分化是通过一个反应级联介导的，在地塞米松转录激活C/EBPδ；C/EBPδ然后结合到PPARγ2启动子并反式激活PPARγ2基因表达。这种激活的主调节因子进而启动脂肪细胞分化。
