Bone morphogenetic protein-2 (BMP-2) signaling to the Col2alpha1 gene in chondroblasts requires the homeobox gene Dlx-2.
To understand the role of Dlx genes in the process of chondrogenesis, we studied the expression of Dlx-2 and Dlx-5 mRNAs in a mouse clonal chondroblast cell line, TMC23. We also examined the involvement of Dlx2 in the bone morphogenetic protein-2 (BMP-2) signaling to the type II collagen gene, Col2alpha1, in this cell line. In this report, we show that the TMC23 cells express Dlx-2 and Dlx-5 mRNAs, and the levels can be upregulated by recombinant BMP-2 at an early stage of chondroblast differentiation. Addition of rBMP-2 dramatically increased type II collagen expression at both the mRNA and the protein level. Also, rBMP-2 increased transcription of Col2alpha1, as shown by stimulation of a chondrocyte-specific Col2alpha1 enhancer. The mechanism involves Dlx-2, as the stimulatory effect of rBMP-2 on the Col2alpha enhancer was blocked by an antisense oligonucleotide against Dlx-2 mRNA. The rBMP-2 signaling to the Col2alpha1 enhancer was also blocked by a dominant-negative Smad1 expression vector. These data demonstrate that Dlx-2 is a downstream target of the BMP-2 signaling pathway in chondroblasts. Therefore, we propose a model in which rBMP-2 stimulates Dlx-2 expression, which then serves as a necessary transcription factor for Col2alpha1 gene expression through a chondrocyte-specific enhancer fragment.
Xu
S C
SC
Procter & Gamble Pharmaceuticals, Mason, Ohio 45040, USA. xu.sc@pg.com
Harris
M A
MA
Rubenstein
J L
JL
Mundy
G R
GR
Harris
S E
SE
D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins / Q000378:metabolism*; D002454:Cell Differentiation; D002460:Cell Line; D019902:Chondrocytes / Q000378:metabolism*; D003094:Collagen / Q000235:genetics*; D003598:Cytoskeletal Proteins; D004268:DNA-Binding Proteins / Q000235:genetics*; D004742:Enhancer Elements, Genetic; D005786:Gene Expression Regulation / Q000187:drug effects; D005801:Genes, Homeobox; D018398:Homeodomain Proteins / Q000235:genetics; D016372:RNA, Antisense / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D016601:RNA-Binding Proteins; D015398:Signal Transduction; D014157:Transcription Factors; D016212:Transforming Growth Factor beta
C525719:Bmp2 protein, mouse; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins; D003598:Cytoskeletal Proteins; D004268:DNA-Binding Proteins; C088334:Distal-less homeobox proteins; C501120:Dlx5 protein, mouse; D018398:Homeodomain Proteins; D016372:RNA, Antisense; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; C093661:Tes protein, mouse; D014157:Transcription Factors; D016212:Transforming Growth Factor beta; D003094:Collagen