Dlx5 Specifically Regulates Runx2 Type II Expression by Binding to Homeodomain-response Elements in the Runx2 Distal Promoter

Abstract

Two major isoforms of theHere, Runx2-II expression was found to be specifically stimulated by BMP-2 treatment or by Dlx5 overexpression. In addition, BMP-2, Dlx5, and Runx2-II were found to be expressed in osteogenic fronts and parietal bones of the developing cranial vault and Runx2-I and Msx2 in the sutural mesenchyme. Furthermore, Runx2 P1 promoter activity was strongly stimulated by Dlx5 overexpression, whereas Runx2 P2 promoter activity was not. Runx2 P1 promoter deletion analysis indicated that the Dlx5-specific response is due to sequences between ؊756 and ؊342 bp of the P1 promoter, where three Dlx5-response elements are located. Dlx5 responsiveness to these elements was confirmed by gel mobility shift assay and site-directed mutagenesis. Moreover, Msx2 specifically suppressed the Runx2 P1 promoter, and the responsible region overlaps with that recognized by Dlx5. In summary, Dlx5 specifically transactivates the Runx2 P1 promoter, and its action on the P1 promoter is antagonized by Msx2.The Runt-related transcription factor Runx2 plays an essential role in osteoblast differentiation and bone mineralization (1, 2). Two major isoforms are expressed from the mouse Runx2 locus, and these isoforms are generated by different promoter usage. Runx2 type I (Runx2-I), 2 referred to as the Cbfa1/p56 isoform or PEBP2␣A, is a 513-amino acid protein that starts with the amino acid sequence MRIPV (3) and is derived from the proximal P2 promoter of the gene (4). More recently, upstream exons of the Runx2 gene that potentially encode the N termini of Runx2 isoforms expressed in osteoblasts have been identified (5, 6). These upstream exons contain a 5Ј-untranslated region and encode the N-terminal 19 amino acids of Runx2 type II (Runx2-II; also referred to as Cbfa1/p57 and OSF2), which starts with the sequence MASNSL (7). This isoform is expressed from the P1 or "bone-related" upstream promoter (8), and its expression is predominant in osteoblasts (9). The alternative promoter usage strongly implies that the expression pattern of each isoform differs temporally and/or spatially. Indeed, they exhibit distinct expression patterns during bone development (10, 11). Thus, it is natural to assume that these two promoters differently respond to different extracellular signals or their downstream transcription factors because these promoters have distinct transcription factor-binding sites.Runx2 plays a central role in the BMP-2-induced trans-differentiation of C2C12 cells at an early restriction point by diverting them from the myogenic pathway to the osteogenic pathway (12, 13). We found that the homeobox gene Dlx5 is an upstream target of BMP-2 signaling and that it plays a pivotal role in stimulating the downstream osteogenic master transcription factor Runx2. In turn, Runx2 acts simultaneously or sequentially to induce the expression of bone-specific genes that represent BMP-2-induced osteogenic trans-differentiation. In addition, it has also been suggested that Dlx5 is a critical target of the inhibitory action of transform...

Molecular Regulation of Matrix Extracellular Phosphoglycoprotein Expression by Bone Morphogenetic Protein-2

“…And it is well known that Mepe expression is specific in the bone (12,24). In addition, we have also reported that BMP-2 and its downstream transcription factors, Dlx5 and Runx2-II, are specifically expressed in mineralizing calvarial tissue, but not in sutural mesenchyme (16). Based on the common expression patterns of BMP-2 signaling molecules and Mepe, we can assume that BMP-2 signaling regulates Mepe expression in bone cells.…”

Epigenetic Control of the Bone-master Runx2 Gene during Osteoblast-lineage Commitment by the Histone Demethylase JARID1B/KDM5B

“…Similarly, hereditary mutations in the human Runx2 gene are linked to skeletal abnormalities as those found in cleidocranial dysplasia (6). Runx2 transcription in osteoblasts is controlled by regulatory elements distributed within the P1 promoter that are recognized by cognate transcription factors during osteogenesis (7)(8)(9)(10)(11)(12)(13)(14). Moreover, transcriptional activation of the Runx2 gene in osteoblasts involves a chromatin remodeling event within the proximal 500 bp of the P1 promoter region (15)(16)(17).…”

Polymethylmethacrylate particles impair osteoprogenitor viability and expression of osteogenic transcription factors Runx2, osterix, and Dlx5

“…11,12 Dlx5, a homeodomain transcription factor, is responsive to osteogenic signals from BMP-2 and mediates the expression of Runx2 and osterix. 13,[16][17][18][19] b-Catenin, when allowed to accumulate intracellularly in response to canonical Wnt signaling, combines with the transcriptional elements TCF and LEF and activates Runx2 expression. 11,24,25 PMMA particles could inhibit the expression of these transcription factors by disrupting upstream signaling pathways, receptor-matrix interactions, or cellular synthesis and transport mechanisms.…”

“…11 Osterix lies downstream of Runx2 and is required for the differentiation of pre-osteoblasts into mature osteoblasts. 11,12 Dlx5 is a homeobox domain transcription factor that also regulates osteogenesis [13][14][15] and is involved in the response of osteogenic cells to BMP-2. [16][17][18] Msx2, another homeodomain transcription factor, is a functional antagonist and repressor of Dlx5-induced osteogenesis.…”