SWI/SNF chromatin remodeling complex is obligatory for BMP2-induced, Runx2-dependent skeletal gene expression that controls osteoblast differentiation.
Development of bone tissue requires maturation of osteoblasts from mesenchymal precursors. BMP2, a member of the TGFbeta superfamily, and the Runx2 (AML3/Cbfa1) transcription factor, a downstream BMP2 effector, are regulatory signals required for osteoblast differentiation. While Runx2 responsive osteogenic gene expression has been functionally linked to alterations in chromatin structure, the factors that govern this chromatin remodeling remain to be identified. Here, we address the role of the SWI/SNF chromatin remodeling enzymes in BMP2-induced, Runx2-dependent development of the osteoblast phenotype. For these studies, we have examined calvarial cells from wild-type (WT) mice and mice that are homozygous for the Runx2 null allele, as well as the C2C12 model of BMP2-induced osteogenesis. By the analysis of microarray data, we find that several components of the SWI/SNF complex are regulated during BMP2-mediated osteoblast differentiation. Brg1 is an essential DNA dependent ATPase subunit of the SWI/SNF complex. Thus, functional studies were carried out using a fibroblast cell line that conditionally expresses a mutant Brg1 protein, which exerts a dominant negative effect on SWI/SNF function. Our findings demonstrate that SWI/SNF is required for BMP2-induced expression of alkaline phosphatase (APase), an early marker reflecting Runx2 control of osteoblast differentiation. In addition, Brg1 is expressed in cells within the developing skeleton of the mouse embryo as well as in osteoblasts ex vivo. Taken together these results support the concept that BMP2-mediated osteogenesis requires Runx2, and demonstrates that initiation of BMP2-induced, Runx2-dependent skeletal gene expression requires SWI/SNF chromatin remodeling complexes.
Young
Daniel W
DW
Department of Cell Biology and Cancer Center, University of Massachusetts Medical School, Worcester, MA 01655-0105, USA.
Pratap
Jitesh
J
Javed
Amjad
A
Weiner
Brian
B
Ohkawa
Yasuyuki
Y
van Wijnen
Andre
A
Montecino
Martin
M
Stein
Gary S
GS
Stein
Janet L
JL
Imbalzano
Anthony N
AN
Lian
Jane B
JB
D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins / Q000494:pharmacology*; D002454:Cell Differentiation; D002460:Cell Line; D042002:Chromatin Assembly and Disassembly; D050659:Core Binding Factor Alpha 1 Subunit; D003598:Cytoskeletal Proteins / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D015870:Gene Expression; D006801:Humans; D051379:Mice; D020411:Oligonucleotide Array Sequence Analysis; D010006:Osteoblasts / Q000166:cytology* / Q000378:metabolism; D011485:Protein Binding; D021122:Protein Subunits / Q000378:metabolism; D051381:Rats; D050656:Transcription Factor AP-2; D014157:Transcription Factors / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000494:pharmacology*
C525718:BMP2 protein, human; C525719:Bmp2 protein, mouse; C525720:Bmp2 protein, rat; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins; D050659:Core Binding Factor Alpha 1 Subunit; D003598:Cytoskeletal Proteins; D004268:DNA-Binding Proteins; D021122:Protein Subunits; C493709:RUNX2 protein, human; C493716:Runx2 protein, mouse; C493717:Runx2 protein, rat; C499336:SMARCA1 protein, human; D050656:Transcription Factor AP-2; D014157:Transcription Factors; D016212:Transforming Growth Factor beta; D000469:Alkaline Phosphatase