title: Sclerostin expression is induced by BMPs in human Saos-2 osteosarcoma cells but not via direct effects on the sclerostin gene promoter or ECR5 element.
abstract: Sclerostin is a secreted inhibitor of Wnt signaling and plays an essential role in the regulation of bone mass. The expression of sclerostin is largely restricted to osteocytes although its mode of transcriptional regulation is not well understood. We observed regulated expression of sclerostin mRNA and protein that was directly correlated with the mineralization response in cultured human Saos-2 osteosarcoma cells and rat primary calvarial cells. Sclerostin mRNA and protein levels were increased following treatment of cells with BMP2, BMP4 and BMP7. Analysis of deletion mutants from the -7.4 kb upstream region of the human sclerostin promoter did not reveal any specific regions that were responsive to BMPs, Wnt3a, PTH, TGFβ1 or Activin A in Saos-2 cells. The downstream ECR5 element did not show enhancer activity in Saos-2 cells and also was not affected when Saos-2 cells were treated with BMPs or PTH. Genome-wide microarray analysis of Saos-2 cells treated with BMP2 showed significant changes in expression of several transcription factors with putative consensus DNA binding sites in the region of the sclerostin promoter. However, whereas most factors tested showed either a range of inhibitory activity (DLX family, MSX2, HEY1, SMAD6/7) or lack of activity on the sclerostin promoter including SMAD9, only MEF2B showed a positive effect on both the promoter and ECR5 element. These results suggest that the dramatic induction of sclerostin gene expression by BMPs in Saos-2 cells occurs indirectly and is associated with late stage differentiation of osteoblasts and the mineralization process.
authors: Department of Metabolic Disorders, One Amgen Center Drive, Thousand Oaks, CA 91320, USA. lyu@amgen.com
authors: Longchuan
authors: L
authors: Yu
authors: Marissa
authors: M
authors: van der Valk
authors: Jin
authors: J
authors: Cao
authors: Chun-Ya E
authors: CY
authors: Han
authors: Todd
authors: T
authors: Juan
authors: Michael B
authors: MB
authors: Bass
authors: Chetan
authors: C
authors: Deshpande
authors: Michael A
authors: MA
authors: Damore
authors: Richard
authors: R
authors: Stanton
authors: Philip
authors: P
authors: Babij
mesh_terms: D028341:Activins / Q000494:pharmacology; D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D019485:Bone Morphogenetic Proteins / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology*; D002113:Calcification, Physiologic / Q000187:drug effects / Q000235:genetics; D045744:Cell Line, Tumor; D004742:Enhancer Elements, Genetic / Q000235:genetics*; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D005819:Genetic Markers / Q000235:genetics*; D006801:Humans; D010006:Osteoblasts / Q000187:drug effects / Q000378:metabolism; D010012:Osteogenesis / Q000187:drug effects / Q000235:genetics; D012516:Osteosarcoma / Q000235:genetics* / Q000473:pathology; D010281:Parathyroid Hormone / Q000494:pharmacology; D011401:Promoter Regions, Genetic / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D053773:Transforming Growth Factor beta1 / Q000494:pharmacology; D060509:Wnt3A Protein / Q000494:pharmacology
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D019485:Bone Morphogenetic Proteins; D005819:Genetic Markers; D010281:Parathyroid Hormone; D012333:RNA, Messenger; C422903:SOST protein, human; C486031:Sost protein, rat; D014157:Transcription Factors; D053773:Transforming Growth Factor beta1; D060509:Wnt3A Protein; C422405:activin A; D028341:Activins