Wnt/beta-catenin and retinoic acid receptor signaling pathways interact to regulate chondrocyte function and matrix turnover.
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.
Department of Orthopaedic Surgery, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA.
Rika
R
Yasuhara
Takahito
T
Yuasa
Julie A
JA
Williams
Stephen W
SW
Byers
Salim
S
Shah
Maurizio
M
Pacifici
Masahiro
M
Iwamoto
Motomi
M
Enomoto-Iwamoto
D000818:Animals; D019902:Chondrocytes / Q000187:drug effects / Q000378:metabolism*; D005109:Extracellular Matrix / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D036341:Intercellular Signaling Peptides and Proteins / Q000378:metabolism; D051821:Lymphoid Enhancer-Binding Factor 1 / Q000378:metabolism; D051379:Mice; D008954:Models, Biological; D011485:Protein Binding / Q000187:drug effects; D011509:Proteoglycans / Q000235:genetics / Q000378:metabolism; D018168:Receptors, Retinoic Acid / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D014212:Tretinoin / Q000819:agonists / Q000037:antagonists & inhibitors / Q000494:pharmacology; D015854:Up-Regulation / Q000187:drug effects / Q000235:genetics; D051153:Wnt Proteins / Q000378:metabolism*; D051176:beta Catenin / Q000378:metabolism*; D000097768:Retinoic Acid Receptor gamma
D036341:Intercellular Signaling Peptides and Proteins; D051821:Lymphoid Enhancer-Binding Factor 1; D011509:Proteoglycans; D018168:Receptors, Retinoic Acid; D014212:Tretinoin; D051153:Wnt Proteins; D051176:beta Catenin; D000097768:Retinoic Acid Receptor gamma; C501127:Dkk1 protein, mouse