title: SnoN suppresses maturation of chondrocytes by mediating signal cross-talk between transforming growth factor-β and bone morphogenetic protein pathways.
abstract: Hypertrophic maturation of chondrocytes is a crucial step in endochondral ossification, whereas abnormally accelerated differentiation of hypertrophic chondrocytes in articular cartilage is linked to pathogenesis of osteoarthritis. This cellular process is promoted or inhibited by bone morphogenetic protein (BMP) or transforming growth factor-β (TGF-β) signaling, respectively, suggesting that these signaling pathways cross-talk during chondrocyte maturation. Here, we demonstrated that expression of Tgfb1 was increased, followed by phosphorylation of Smad2, during BMP-2-induced hypertrophic maturation of ATDC5 chondrocytes. Application of a TGF-β type I receptor inhibitor compound, SB431542, increased the expression of Id1, without affecting the phosphorylation status of Smad1/5/8, indicating that the activated endogenous TGF-β pathway inhibited BMP signaling downstream of the Smad activation step. We searched for TGF-β-inducible effectors that are able to inhibit BMP signaling in ATDC5 cells and identified SnoN. Overexpression of SnoN suppressed the activity of a BMP-responsive luciferase reporter in COS-7 cells as well as expression of Id1 in ATDC5 cells and, subsequently, the expression of Col10a1, a hallmark of hypertrophic chondrocyte maturation. siRNA-mediated loss of SnoN showed opposite effects in BMP-treated ATDC5 cells. In adult mice, we found the highest level of SnoN expression in articular cartilage. Importantly, SnoN was expressed, in combination with phosphorylated Smad2/3, in prehypertrophic chondrocytes in the growth plate of mouse embryo bones and in chondrocytes around the ectopically existing hypertrophic chondrocytes of human osteoarthritis cartilage. Our results indicate that SnoN mediates a negative feedback mechanism evoked by TGF-β to inhibit BMP signaling and, subsequently, hypertrophic maturation of chondrocytes.
authors: Department of Medical Joint Materials, Graduate School of Medical and Dental Sciences, 8-35-1 Sakuragaoka, Kagoshima University, Kagoshima 890-8544, Japan.
authors: Ichiro
authors: I
authors: Kawamura
authors: Shingo
authors: S
authors: Maeda
authors: Katsuyuki
authors: K
authors: Imamura
authors: Takao
authors: T
authors: Setoguchi
authors: Masahiro
authors: M
authors: Yokouchi
authors: Yasuhiro
authors: Y
authors: Ishidou
authors: Setsuro
authors: S
authors: Komiya
mesh_terms: D000818:Animals; D001549:Benzamides / Q000494:pharmacology; D055396:Bone Morphogenetic Protein 2 / Q000235:genetics / Q000378:metabolism*; D019556:COS Cells; D002358:Cartilage, Articular / Q000378:metabolism / Q000473:pathology; D002522:Chlorocebus aethiops; D019902:Chondrocytes / Q000378:metabolism* / Q000473:pathology; D004149:Dioxoles / Q000494:pharmacology; D005786:Gene Expression Regulation; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D010003:Osteoarthritis / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D010766:Phosphorylation / Q000187:drug effects / Q000235:genetics; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D051899:Smad2 Protein / Q000235:genetics / Q000378:metabolism; D053773:Transforming Growth Factor beta1 / Q000037:antagonists & inhibitors / Q000096:biosynthesis* / Q000235:genetics
chemical_list: C459179:4-(5-benzo(1,3)dioxol-5-yl-4-pyridin-2-yl-1H-imidazol-2-yl)benzamide; C525718:BMP2 protein, human; D001549:Benzamides; C525719:Bmp2 protein, mouse; D055396:Bone Morphogenetic Protein 2; D004149:Dioxoles; D047908:Intracellular Signaling Peptides and Proteins; D011518:Proto-Oncogene Proteins; C060615:SKIL protein, human; C497782:SMAD2 protein, human; C486157:Skil protein, mouse; D051899:Smad2 Protein; C497783:Smad2 protein, mouse; C508960:TGFB1 protein, human; C508961:Tgfb1 protein, mouse; D053773:Transforming Growth Factor beta1