GSBS Student Publications

Title

Smad function and intranuclear targeting share a Runx2 motif required for osteogenic lineage induction and BMP2 responsive transcription

GSBS Program

Biochemistry & Molecular Pharmacology

UMMS Affiliation

Graduate School of Biomedical Sciences; Department of Cell Biology

Date

12-2-2004

Document Type

Article

Medical Subject Headings

Animals; Bone Morphogenetic Proteins; Cell Lineage; Cell Nucleus; Core Binding Factor Alpha 1 Subunit; DNA-Binding Proteins; Gene Deletion; Hela Cells; Humans; Kidney; Mice; Mutagenesis; Osteocytes; Phosphoproteins; Pluripotent Stem Cells; Point Mutation; Protein Structure, Tertiary; Signal Transduction; Smad5 Protein; Trans-Activators; Transcription Factor AP-2; Transcription Factors; Transcription, Genetic; Transforming Growth Factor beta

Disciplines

Life Sciences | Medicine and Health Sciences

Abstract

The coordinated activity of Runx2 and BMP/TGFbeta-activated Smads is critical for formation of the skeleton, but the precise structural basis for the Runx2/Smad interaction has not been resolved. By deletion mutagenesis, we have defined the Runx2 motif required for physical and functional interaction with either BMP or TGFbeta responsive Smads. Smad responsive transcriptional activity was retained upon deletion of the C-terminus to amino acid (aa) 432 but lost with deletion to aa 391. Thus the Smad interacting domain (SMID) of Runx2 (432-391) is embedded in the well-defined nuclear matrix targeting signal (NMTS) that mediates intranuclear trafficking. The SMID suffices as an interacting module when fused to the heterologous Gal-4 protein. Formation of the Runx2 and Smad complex is dependent on Runx2 phosphorylation through the MAPK signaling pathway, as determined by co-immunoprecipitation studies. We established that all SMID/NMTS deficient Runx2 mutants do not show in situ association with Smad in the nucleus nor do they support BMP2-mediated osteogenic induction of the mesenchymal C2C12 cell line. Thus, we provide direct evidence that the SMID/NMTS domain (391-432) of Runx2 is essential for BMP2-mediated osteoblast differentiation. Our findings suggest that TGFbeta/ BMP2 signaling, MAPK dependent phosphorylation, and Runx2 subnuclear targeting converge to induce the osteogenic phenotype.

Rights and Permissions

Citation: J Cell Physiol. 2005 Jul;204(1):63-72. Link to article on publisher's site

DOI of Published Version

10.1002/jcp.20258

Related Resources

Link to article in PubMed

Journal Title

Journal of cellular physiology

PubMed ID

15573378