Runx2- and histone deacetylase 3-mediated repression is relieved in differentiating human osteoblast cells to allow high bone sialoprotein expression.
Bone sialoprotein (BSP) is a bone matrix glycoprotein whose expression coincides with terminal osteoblastic differentiation and the onset of mineralization. In this study we show that BSP expression is considerably increased in confluent Saos-2 human osteosarcoma cells and in differentiating normal human osteoblasts, concomitantly with the decrease of Runx2, a key transcription factor controlling bone formation. Therefore, we investigated the role of Runx2 in the regulation of BSP expression in Saos-2 cells. Using a mobility shift assay, we demonstrated that Runx2 binds to the BSP promoter only in preconfluent cells. Histone deacetylase 3 (HDAC3) has been recently shown to act as a Runx2 co-repressor. Chromatin immunoprecipitation assays demonstrated that both Runx2 and HDAC3 are detectable at the BSP promoter in preconfluent Saos-2 cells but not when they are confluent and overexpress BSP. Consistently, nuclear Runx2 protein level is down-regulated, whereas Saos-2 cells became increasingly confluent. Finally, the suppression of HDAC3, Runx2, or both by RNA interference induced the expression of BSP at both mRNA and protein levels in Saos-2 cells. Our data demonstrate that Runx2 and HDAC3 repress BSP gene expression and that this repression is suspended upon osteoblastic cell differentiation. Both the nuclear disappearance of Runx2 and the non-recruitment of HDAC3 represent new means to relieve Runx2-mediated suppression of BSP expression, thus allowing the acquisition of a fully differentiated and mineralization-competent phenotype by osteoblast cells.
Lamour
Virginie
V
Metastasis Research Laboratory, Center of Experimental Cancer Research and Bone and Cartilage Metabolism Research Unit, University of Liège, 4000 Liège, Belgium.
Detry
Cédric
C
Sanchez
Christelle
C
Henrotin
Yves
Y
Castronovo
Vincent
V
Bellahcène
Akeila
A
D002113:Calcification, Physiologic / Q000502:physiology; D002454:Cell Differentiation / Q000502:physiology*; D045744:Cell Line, Tumor; D050659:Core Binding Factor Alpha 1 Subunit / Q000235:genetics / Q000378:metabolism*; D015536:Down-Regulation / Q000502:physiology; D006655:Histone Deacetylases / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D058574:Integrin-Binding Sialoprotein; D010006:Osteoblasts / Q000166:cytology / Q000378:metabolism*; D010012:Osteogenesis / Q000502:physiology*; D011401:Promoter Regions, Genetic / Q000502:physiology; D034622:RNA Interference; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D012795:Sialoglycoproteins / Q000096:biosynthesis*; D000099186:Histone Deacetylase 3
D050659:Core Binding Factor Alpha 1 Subunit; D006655:Histone Deacetylases; D058574:Integrin-Binding Sialoprotein; D012097:Repressor Proteins; D012795:Sialoglycoproteins; D000099186:Histone Deacetylase 3; C546871:IBSP protein, human; C493709:RUNX2 protein, human