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Cross-talk between 1,25-dihydroxyvitamin D3 and transforming growth factor-beta signaling requires binding of VDR and

N Subramaniam1, G M Leong, T A Cock

  • 1Bone and Mineral Research Program, The Garvan Institute of Medical Research, Sydney, New South Wales 2010, Australia. nsubramaniam@cmri.usyd.edu.au

The Journal of Biological Chemistry
|March 30, 2001
PubMed

Insights

Transforming growth factor-beta (TGF-beta) and vitamin D signaling pathways interact to regulate gene expression. This cross-talk requires both a vitamin D response element (VDRE) and a Smad binding element (SBE) near the target promoter for synergistic gene activation.

Area of Science:

  • Molecular Biology
  • Cell Signaling
  • Gene Regulation

Background:

  • 1,25-Dihydroxyvitamin D(3) (vitamin D) and transforming growth factor-beta (TGF-beta) are crucial regulators of cellular processes.
  • Smad proteins mediate TGF-beta signaling, while the vitamin D receptor (VDR) mediates vitamin D signaling.
  • Understanding the interplay between these pathways is vital for comprehending cellular regulation.

Purpose of the Study:

  • To elucidate the molecular mechanisms underlying the interaction between TGF-beta and vitamin D signaling pathways.
  • To investigate how these pathways regulate the human osteocalcin promoter.
  • To identify the specific DNA elements and protein interactions involved in this cross-talk.

Main Methods:

  • Transient transfection experiments to assess gene promoter activity.
  • Reporter gene assays utilizing heterologous promoters linked to specific DNA elements (VDRE, SBEs).
  • Gel shift assays to determine protein-DNA binding interactions (Smad3-Smad4 heterodimer).

Main Results:

  • Synergistic activation of the osteocalcin promoter by TGF-beta and vitamin D was observed.
  • This synergy required the presence of both VDRE and Smad binding elements (SBEs) in proximity.
  • Smad3-Smad4 heterodimers bind to specific SBEs (SBE1 and SBE3) on the osteocalcin promoter; deletion of proximal SBE1 abolished TGF-beta responsiveness and synergistic co-activation.

Conclusions:

  • The cross-talk between TGF-beta and vitamin D signaling pathways in regulating the osteocalcin promoter is dependent on the spatial arrangement of VDRE and SBEs.
  • Smad3 and VDR mediate this interaction, requiring both a VDRE and a proximal SBE for synergistic gene activation.
  • This finding provides critical insights into the molecular basis of gene regulation by interacting signaling pathways.

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