Retinoic acid stimulates chondrocyte differentiation and enhances bone morphogenetic protein effects through induction of Smad1 and Smad5.
Whereas bone morphogenetic protein (BMP)-signaling events induce maturational characteristics in vitro, recent evidence suggests that the effects of other regulators might be mediated through BMP-signaling events. The present study examines the mechanism through which retinoic acid (RA) stimulates differentiation in chicken embryonic caudal sternal chondrocyte cultures. Both RA and BMP-2 induced expression of the chondrocyte maturational marker, colX, in chondrocyte cultures by 8 d. Though the RA effect was small, it synergistically enhanced the effect of BMP-2 on colX and phosphatase activity. Inhibition of either RA or BMP signaling, with selective inhibitors, interfered with the inductive effects of these agents but also inhibited the complementary pathway, demonstrating a codependence of RA and BMP signaling during chondrocyte maturation. BMP-2 did not enhance the effects of RA on an RA-responsive reporter construct, but RA enhanced basal activity and synergistically enhanced BMP-2 stimulation of the BMP-responsive chicken type X collagen reporter. A similar synergistic interaction between RA and BMP-2 was observed on colX expression. RA did not increase the expression of the type IA BMP receptor but did markedly up-regulate the expression of Smad1 and Smad5 proteins, important participants in the BMP pathway. Inhibition of RA signaling, with the selective inhibitor AGN 193109, blocked RA-mediated induction of the Smad proteins and chondrocyte differentiation. These findings demonstrate that RA induces the expression of BMP-signaling molecules and enhances BMP effects in chondrocytes.
Li
Xuefeng
X
Center for Musculoskeletal Research, University of Rochester School of Medicine and Dentistry, Rochester, New York 14642, USA.
Schwarz
Edward M
EM
Zuscik
Michael J
MJ
Rosier
Randy N
RN
Ionescu
Andreia M
AM
Puzas
J Edward
JE
Drissi
Hicham
H
Sheu
Tzong-Jen
TJ
O'Keefe
Regis J
RJ
D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins / Q000494:pharmacology*; D002454:Cell Differentiation / Q000187:drug effects; D002642:Chick Embryo; D002645:Chickens; D019902:Chondrocytes / Q000166:cytology* / Q000502:physiology; D024121:Collagen Type X / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics*; D004357:Drug Synergism; D010750:Phosphoproteins / Q000235:genetics; D015398:Signal Transduction / Q000187:drug effects; D051785:Smad Proteins; D051902:Smad5 Protein; D013249:Sternum / Q000166:cytology; D015534:Trans-Activators / Q000235:genetics*; D016212:Transforming Growth Factor beta; D014212:Tretinoin / Q000494:pharmacology*
D000970:Antineoplastic Agents; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins; D024121:Collagen Type X; D004268:DNA-Binding Proteins; D010750:Phosphoproteins; D051785:Smad Proteins; D051902:Smad5 Protein; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D014212:Tretinoin; D000469:Alkaline Phosphatase