GSBS Student Publications

Title

Bone-specific transcription factor Runx2 interacts with the 1alpha,25-dihydroxyvitamin D3 receptor to up-regulate rat osteocalcin gene expression in osteoblastic cells

UMMS Affiliation

Graduate School of Biomedical Sciences; Department of Cell Biology

Date

10-1-2004

Document Type

Article

Medical Subject Headings

Animals; Binding Sites; Cell Line; Core Binding Factor Alpha 1 Subunit; DNA-Binding Proteins; *Gene Expression Regulation; Genes, Reporter; Macromolecular Substances; Osteoblasts; Osteocalcin; Promoter Regions (Genetics); Protein Structure, Tertiary; Rats; Receptors, Calcitriol; Recombinant Fusion Proteins; Transcription Factor AP-2; Transcription Factors; Transcription, Genetic; Up-Regulation; *Vitamin D Response Element

Disciplines

Life Sciences | Medicine and Health Sciences

Abstract

Bone-specific transcription of the osteocalcin (OC) gene is regulated principally by the Runx2 transcription factor and is further stimulated in response to 1alpha,25-dihydroxyvitamin D3 via its specific receptor (VDR). The rat OC gene promoter contains three recognition sites for Runx2 (sites A, B, and C). Mutation of sites A and B, which flank the 1alpha,25-dihydroxyvitamin D3-responsive element (VDRE), abolishes 1alpha,25-dihydroxyvitamin D3-dependent enhancement of OC transcription, indicating a tight functional relationship between the VDR and Runx2 factors. In contrast to most of the members of the nuclear receptor family, VDR possesses a very short N-terminal A/B domain, which has led to the suggestion that its N-terminal region does not contribute to transcriptional enhancement. Here, we have combined transient-overexpression, coimmunoprecipitation, in situ colocalization, chromatin immunoprecipitation, and glutathione S-transferase pull-down analyses to demonstrate that in osteoblastic cells expressing OC, VDR interacts directly with Runx2 bound to site B, which is located immediately adjacent to the VDRE. This interaction contributes significantly to 1alpha,25-dihydroxyvitamin D3-dependent enhancement of the OC promoter and requires a region located C terminal to the runt homology DNA binding domain of Runx2 and the N-terminal region of VDR. Together, our results indicate that Runx2 plays a key role in the 1alpha,25-dihydroxyvitamin D3-dependent stimulation of the OC promoter in osteoblastic cells by further stabilizing the interaction of the VDR with the VDRE. These studies demonstrate a novel mechanism for combinatorial control of bone tissue-specific gene expression. This mechanism involves the intersection of two major pathways: Runx2, a "master" transcriptional regulator of osteoblast differentiation, and 1alpha,25-dihydroxyvitamin D3, a hormone that promotes expression of genes associated with these terminally differentiated bone cells.

Rights and Permissions

Citation: Mol Cell Biol. 2004 Oct;24(20):8847-61. Link to article on publisher's site

Related Resources

Link to article in PubMed

Journal Title

Molecular and cellular biology

PubMed ID

15456860