SWI/SNF-independent nuclease hypersensitivity and an increased level of histone acetylation at the P1 promoter accompany active transcription of the bone master gene Runx2.
The Runx2 transcription factor is essential for skeletal development as it regulates expression of several key bone-related genes. Multiple lines of evidence indicate that expression of the Runx2/p57 isoform in osteoblasts is controlled by the distal P1 promoter. Alterations of chromatin structure are often associated with transcription and can be mediated by members of the SWI/SNF family of chromatin remodeling complexes, or by transcriptional coactivators that possess enzymatic activities that covalently modify structural components of the chromatin. Here, we report that a specific chromatin remodeling process at the proximal region (residues -400 to 35) of the Runx2 gene P1 promoter accompanies transcriptional activity in osteoblasts. This altered chromatin organization is reflected by the presence of two DNase I hypersensitive sites that span key regulatory elements for Runx2/p57 transcription. Chromatin remodeling and transcription of the Runx2 gene are associated with elevated levels of histone acetylation at the P1 promoter region and binding of active RNA polymerase II and are independent of the activity of the SWI/SNF chromatin remodeling complex. Changes in chromatin organization at the P1 promoter are stimulated during differentiation of C2C12 mesenchymal cells to the osteoblastic lineage by treatment with BMP2. Together, our results support a model in which changes in chromatin organization occur at very early stages of mesenchymal differentiation to facilitate subsequent expression of the Runx2/p57 isoform in osteoblastic cells.
Cruzat
Fernando
F
Departamento de Bioquimica y Biologia Molecular, Facultad de Ciencias Biologicas, Universidad de Concepcion, Concepcion, Chile.
Henriquez
Berta
B
Villagra
Alejandro
A
Hepp
Matias
M
Lian
Jane B
JB
van Wijnen
Andre J
AJ
Stein
Janet L
JL
Imbalzano
Anthony N
AN
Stein
Gary S
GS
Montecino
Martin
M
D000107:Acetylation; D000818:Animals; D055396:Bone Morphogenetic Protein 2 / Q000235:genetics / Q000378:metabolism; D002454:Cell Differentiation / Q000502:physiology; D002460:Cell Line; D042002:Chromatin Assembly and Disassembly; D002868:Chromosomal Proteins, Non-Histone / Q000235:genetics / Q000378:metabolism*; D050659:Core Binding Factor Alpha 1 Subunit / Q000235:genetics / Q000378:metabolism*; D003851:Deoxyribonucleases / Q000378:metabolism*; D005786:Gene Expression Regulation; D006657:Histones / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D010006:Osteoblasts / Q000166:cytology / Q000502:physiology; D011401:Promoter Regions, Genetic; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic
D055396:Bone Morphogenetic Protein 2; D002868:Chromosomal Proteins, Non-Histone; D050659:Core Binding Factor Alpha 1 Subunit; D006657:Histones; D020033:Protein Isoforms; C445179:SWI-SNF-B chromatin-remodeling complex; D014157:Transcription Factors; D003851:Deoxyribonucleases