Co-stimulation of the Bone-related Runx2 P1 Promoter in Mesenchymal Cells by SP1 and ETS Transcription Factors at Polymorphic Purine-rich DNA Sequences (Y-repeats)

Abstract

Transcriptional control of Runx2 gene expression through two alternative promoters (P1 and P2) is critical for the execution of its function as an osteogenic cell fate determining factor. In all vertebrates examined to date, the bone related P1 promoter contains a purine-rich region (؊303 to ؊128 bp in the rat) that separates two regulatory domains. The length of this region differs dramatically between species even within the same order. Using deletion analysis, we show that part of this purine-rich region (؊200 to ؊128) containing a duplicated element (Y-repeat) positively regulates Runx2 P1 transcription. Electrophoretic mobility assays and chromatin immunoprecipitations reveal that Y-repeat binds at least two different classes of transcription factors related to GC box binding proteins (e.g. SP1 and SP7/Osterix) and ETS-like factors (e.g. ETS1 and ELK1). Forced expression of SP1 increases Runx2 P1 promoter activity through the Y-repeats, and small interfering RNA depletion of SP1 decreases Runx2 expression. Similarly, exogenous expression of wild type ELK1, but not a defective mutant that cannot be phosphorylated, enhances Runx2 gene expression. SP1 is most abundant in proliferating cells, and ELK1 is most abundant in postconfluent cells; during MC3T3-E1 osteoblast differentiation, both proteins are transiently co-expressed when Runx2 expression is enhanced. Taken together, our data suggest that basal Runx2 gene transcription is regulated by dynamic interactions between SP1 and ETS-like factors during progression of osteogenesis.

Conserved regulatory motifs in osteogenic gene promoters integrate cooperative effects of canonical Wnt and BMP pathways

“…A similar purine-rich linker sequence has been identified in the Runx2 P1 promoter and shown to be activated by ETS and Sp1-like factors. (34) Our studies indicate that Smad 1 and Smad 4 are equally efficient in recruitment of b-catenin in vivo. Mapping of the interaction domains indicates that Smads and TCF4 bind to different regions of b-catenin: TCF4 binds to the central armadillo repeats, whereas Smads bind to the amino-and/or carboxl-terminal extensions.…”

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).…”

A program of microRNAs controls osteogenic lineage progression by targeting transcription factor Runx2

“…Runx2 is a critical regulator of the osteogenic lineage, and its epigenetic functions modulate expression of bone-related genes (9,10). Bone-specific transcription of Runx2 (5,11) is autoregulated (12) and controlled by networks of homeodomain proteins (13,14), helix-loop-helix factors (15,16), and Ets factors and Zn finger proteins (17,18) during osteoblastogenesis. Runx2 is also physiologically regulated by several cell-signaling pathways, including vitamin D3 (19), TGFβ/BMP2 (20,21), and Wnt (22).…”