Wnt/beta-catenin and retinoic acid receptor signaling pathways interact to regulate chondrocyte function and matrix turnover

J Biol Chem. 2010 Jan 1;285(1):317-27. doi: 10.1074/jbc.M109.053926. Epub 2009 Oct 26.

Abstract

Activation of the Wnt/beta-catenin and retinoid signaling pathways is known to tilt cartilage matrix homeostasis toward catabolism. Here, we investigated possible interactions between these pathways. We found that all-trans-retinoic acid (RA) treatment of mouse epiphyseal chondrocytes in culture did increase Wnt/beta-catenin signaling in the absence or presence of exogenous Wnt3a, as revealed by lymphoid enhancer factor/T-cell factor/beta-catenin reporter activity and beta-catenin nuclear accumulation. This stimulation was accompanied by increased gene expression of Wnt proteins and receptors and was inhibited by co-treatment with Dickkopf-related protein-1, an extracellular inhibitor of Wnt/beta-catenin signaling, suggesting that RA modulates Wnt signaling at Wnt cell surface receptor level. RA also enhanced matrix loss triggered by Wnt/beta-catenin signaling, whereas treatment with a retinoid antagonist reduced it. Interestingly, overexpression of retinoic acid receptor gamma (RARgamma) strongly inhibited Wnt/beta-catenin signaling in retinoid-free cultures, whereas small interfering RNA-mediated silencing of endogenous RARgamma expression strongly increased it. Small interfering RNA-mediated silencing of RARalpha or RARbeta had minimal effects. Co-immunoprecipitation and two-hybrid assays indicated that RARgamma interacts with beta-catenin and induces dissociation of beta-catenin from lymphoid enhancer factor in retinoid-free cultures. The N-terminal domain (AF-1) of RARgamma but not the C-terminal domain (AF-2) was required for association with beta-catenin, whereas both AF-1 and AF-2 were necessary for inhibition of beta-catenin transcriptional activity. Taken together, our data indicate that the Wnt and retinoid signaling pathways do interact in chondrocytes, and their cross-talks and cross-regulation play important roles in the regulation of cartilage matrix homeostasis.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Chondrocytes / drug effects
  • Chondrocytes / metabolism*
  • Extracellular Matrix / drug effects
  • Extracellular Matrix / genetics
  • Extracellular Matrix / metabolism*
  • Intercellular Signaling Peptides and Proteins / metabolism
  • Lymphoid Enhancer-Binding Factor 1 / metabolism
  • Mice
  • Models, Biological
  • Protein Binding / drug effects
  • Proteoglycans / genetics
  • Proteoglycans / metabolism
  • Receptors, Retinoic Acid / metabolism*
  • Retinoic Acid Receptor gamma
  • Signal Transduction* / drug effects
  • Tretinoin / agonists
  • Tretinoin / antagonists & inhibitors
  • Tretinoin / pharmacology
  • Up-Regulation / drug effects
  • Up-Regulation / genetics
  • Wnt Proteins / metabolism*
  • beta Catenin / metabolism*

Substances

  • Dkk1 protein, mouse
  • Intercellular Signaling Peptides and Proteins
  • Lymphoid Enhancer-Binding Factor 1
  • Proteoglycans
  • Receptors, Retinoic Acid
  • Wnt Proteins
  • beta Catenin
  • Tretinoin