Faccio R, Grano M, Colucci S, Zallone A Z, Quaranta V, Pelletier A J
Institute of Human Anatomy, University of Bari, Italy.
Biochem Biophys Res Commun. 1998 Aug 19;249(2):522-5. doi: 10.1006/bbrc.1998.9180.
Integrins mediate cell adhesion and can induce different cellular responses, including changes in intracellular pH, changes and oscillation in intracellular free calcium, and protein phosphorylation on tyrosine. During bone resorption, the integrin alphav beta3 regulates adhesion of osteoclasts to bone extracellular matrix proteins, such us osteopontin (Opn). Adhesion via alphav beta3 is followed by osteoclast polarization onto the bone surface and by the onset of bone resorption. To characterize these events at the molecular level, we investigated the state of activation of alphav beta3 on the human osteoclast-like cell line GCT23 using the monoclonal antibody AP5 which binds to and can induce, under low calcium conditions, activated alphav beta3. By flow cytometry, approximately 50% of alphav beta3 on the surface of the osteoclast-like cell line GCT23 was reactive with AP5 and was therefore in the activated state. Incubation with AP5 in the presence of low calcium concentrations increased activated alphav beta3 to 90-100%. Activation of alphav beta3 increased the efficiency of GCT23 adhesion to Opn by 2-fold. Furthermore, haptotactic migration on Opn was also enhanced about 40% compared to control. We propose that changes in the activation state of alphav beta3 may be a regulation point for osteoclasts during bone resorption.
整合素介导细胞黏附，并可诱导不同的细胞反应，包括细胞内pH值变化、细胞内游离钙的变化和振荡，以及酪氨酸蛋白磷酸化。在骨吸收过程中，整合素αvβ3调节破骨细胞与骨细胞外基质蛋白（如骨桥蛋白（Opn））的黏附。通过αvβ3黏附后，破骨细胞在骨表面极化并开始骨吸收。为了在分子水平上表征这些事件，我们使用单克隆抗体AP5研究了人破骨细胞样细胞系GCT23上αvβ3的激活状态，该抗体在低钙条件下可结合并诱导激活的αvβ3。通过流式细胞术，破骨细胞样细胞系GCT23表面约50%的αvβ3与AP5反应，因此处于激活状态。在低钙浓度下与AP5孵育可使激活的αvβ3增加到90-100%。αvβ3的激活使GCT23与Opn的黏附效率提高了2倍。此外，与对照相比，在Opn上的趋触性迁移也增强了约40%。我们认为，αvβ3激活状态的变化可能是骨吸收过程中破骨细胞的一个调节点。
