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

Faiza Afzal, Jitesh Pratap, Kosei Ito, Yoshiaki Ito, Janet L. Stein, Andre J. Van Wijnen, Gary S. Stein, Jane B. Lian, Amjad Javed

Research output: Contribution to journalArticle

110 Scopus citations

Abstract

The coordinated activity of Runx2 and BMP/TGFβ-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 TGFβ 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 MARK 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 TGFβ/BMP2 signaling, MAPK dependent phosphorylation, and Runx2 subnuclear targeting converge to induce the osteogenic phenotype.

Original languageEnglish (US)
Pages (from-to)63-72
Number of pages10
JournalJournal of Cellular Physiology
Volume204
Issue number1
DOIs
StatePublished - Jul 2005

ASJC Scopus subject areas

  • Physiology
  • Clinical Biochemistry
  • Cell Biology

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    Afzal, F., Pratap, J., Ito, K., Ito, Y., Stein, J. L., Van Wijnen, A. J., Stein, G. S., Lian, J. B., & Javed, A. (2005). Smad function and intranuclear targeting share a Runx2 motif required for osteogenic lineage induction and BMP2 responsive transcription. Journal of Cellular Physiology, 204(1), 63-72. https://doi.org/10.1002/jcp.20258