Transcriptional regulation of bone sialoprotein gene expression by Osx.
Osteoporosis is the most common metabolic bone disease characterized by decreased bone mass, decreased bone strength, and increased risk of fracture. It is due to unbalance between bone formation and bone resorption. Bone formation is a complex process which involves the differentiation of mesenchymal stem cells to osteoblasts. Osteoblasts produce a characteristic extracellular collagenous matrix that subsequently becomes mineralized. Osterix (Osx) is an osteoblast-specific transcription factor required for osteoblast differentiation. Bone sialoprotein (Bsp) is a member of the SIBLING gene family. Expression of Bsp correlates with the differentiation of osteoblasts and the onset of mineralization. Our preliminary data showed that Bsp was abolished in Osx-null mice; however, the detailed mechanism of Osx regulation on Bsp is not fully understood. In this study, regulation of Bsp expression by Osx was further characterized. It was shown that overexpression of Osx led to Bsp upregulation. Inhibition of Osx by small interfering RNA resulted in Bsp downregulation in osteoblast. Transfection assay demonstrated that Osx was able to activate Bsp promoter reporter in a dose-dependent manner. To define minimal region of Bsp promoter activated by Osx, a series of deletion mutants of Bsp promoter were generated, and the minimal region was narrowed down to the proximal 100 bp. Point-mutagenesis studies showed that one GC-rich site was required for Bsp promoter activation by Osx. ChIP assays demonstrated that endogenous Osx associated with native Bsp promoter in primary osteoblasts. Our observations provide evidence that Osx targets Bsp expression directly.
Department of Endocrinology and Metabolism, The Second Affiliated Hospital of Nanchang University, Nanchang, Jiangxi 330006, China.
Ya
Y
Yang
Department of Research, Daobio, Inc., Dallas, TX 75093, USA.
Yehong
Y
Huang
Department of Research, Daobio, Inc., Dallas, TX 75093, USA.
Li
L
Zhang
Department of Research, Daobio, Inc., Dallas, TX 75093, USA; Bone Research Laboratory, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA. Electronic address: chi.zhang@case.edu.
Chi
C
Zhang
D000818:Animals; D001665:Binding Sites / Q000235:genetics; D002454:Cell Differentiation / Q000235:genetics; D002460:Cell Line; D020862:GC Rich Sequence; D005786:Gene Expression Regulation; D058574:Integrin-Binding Sialoprotein / Q000235:genetics*; D051379:Mice; D018345:Mice, Knockout; D016297:Mutagenesis, Site-Directed; D010006:Osteoblasts / Q000166:cytology / Q000378:metabolism*; D010012:Osteogenesis / Q000235:genetics; D011401:Promoter Regions, Genetic; D034741:RNA, Small Interfering / Q000235:genetics; D017384:Sequence Deletion; D000076182:Sp7 Transcription Factor; D014157:Transcription Factors / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*
C546872:Ibsp protein, mouse; D058574:Integrin-Binding Sialoprotein; D034741:RNA, Small Interfering; D000076182:Sp7 Transcription Factor; C479466:Sp7 protein, mouse; D014157:Transcription Factors
Bone sialoprotein; Bsp; Osteoblast; Osterix; Osx; Transcription