Thapa Narendra, Kang Kae-Bok, Kim In-San
Institute of Cell and Matrix Biology Research, Department of Biochemistry, School of Medicine, Kyungpook National University, Daegu 700-422, South Korea.
Bone. 2005 Feb;36(2):232-42. doi: 10.1016/j.bone.2004.08.007.
betaig-h3 is an extracellular matrix (ECM) protein induced by TGF-beta, and it has motifs interacting with the alpha3beta1, alphavbeta5, and alphavbeta3 integrins. Our previous study shows the role of betaig-h3 in osteoblast differentiation and its involvement in melorheostosis, a rare bone disease. Here we demonstrate that betaig-h3 expression is down-regulated during the early stage of differentiation of the murine preosteoblastic cell line, KS483. The recombinant betaig-h3 and its FAS1 domain significantly inhibited in vitro osteoblast differentiation as evaluated by matrix mineralization/bone nodule formation. Furthermore, inhibition of expression of osteoblast differentiation marker genes [such as type I collagen, alkaline phosphatase, and osteocalcin (OC)] was accompanied by suppression of osteoblast-specific transcription factors, Cbfa1/Runx2 and osterix. Flow cytometric analyses, cell adhesion, and inhibition assays disclosed alphavbeta3 and alphavbeta5 as the principal integrins mediating the adhesion of osteoblastic cells to betaig-h3. The disruption of interactions between betaig-h3 and osteoblasts by a function-blocking antibody specific for alphavbeta3 but not for alphavbeta5 abolished the inhibitory effect of betaig-h3 on osteoblast differentiation. We suggest that these interacting integrins may play an important role in betaig-h3-mediated inhibition of osteoblast differentiation.
βig-h3是一种由转化生长因子-β（TGF-β）诱导产生的细胞外基质（ECM）蛋白，它具有与α3β1、αvβ5和αvβ3整合素相互作用的基序。我们之前的研究表明βig-h3在成骨细胞分化中的作用及其与一种罕见的骨病——进行性骨化性纤维发育不良的关系。在此我们证明，在小鼠前成骨细胞系KS483分化的早期阶段，βig-h3的表达下调。通过基质矿化/骨结节形成评估，重组βig-h3及其FAS1结构域显著抑制体外成骨细胞分化。此外，成骨细胞分化标志物基因[如I型胶原、碱性磷酸酶和骨钙素（OC）]表达的抑制伴随着成骨细胞特异性转录因子Cbfa1/Runx2和osterix的抑制。流式细胞术分析、细胞黏附及抑制试验表明，αvβ3和αvβ5是介导成骨细胞与βig-h3黏附的主要整合素。一种针对αvβ3而非αvβ5的功能阻断抗体破坏了βig-h3与成骨细胞之间的相互作用，消除了βig-h3对成骨细胞分化的抑制作用。我们认为，这些相互作用的整合素可能在βig-h3介导的成骨细胞分化抑制中发挥重要作用。
