Shankar G, Gadek T R, Burdick D J, Davison I, Mason W T, Horton M A
Imperial Cancer Research Fund, Department of Medicine, University College London Medical School, United Kingdom.
Exp Cell Res. 1995 Aug;219(2):364-71. doi: 10.1006/excr.1995.1240.
Extensive characterization of the vitronectin receptor (VNR), a member of the integrin group of cell adhesion molecules, which is abundantly expressed in osteoclasts, has revealed a role for this receptor in osteoclast adhesion as well as bone resorption. Earlier evidence from our laboratory suggests that VNR is also capable of transducing intracellular signals following receptor ligand interaction, although this function is poorly understood. Thus, addition of peptides containing the minimal tripeptide Arg-Gly-Asp (RGD) integrin recognition sequence elicits transient increases in intracellular free calcium ions, with maximal responses seen with a bone sialoprotein peptide, BSP-IIA. In the present study we have attempted to determine some of the structural requirements for calcium signaling in osteoclasts using derivatives of the peptide PRGDN/T sequence found in bone sialoprotein. While some peptides, such as the parent sequence PRGDN, can induce both signaling and retractile events, it was found that minor structural modifications yielded peptides such as PRADN which elicited a transient increase in intracellular free calcium ions without promoting a reduction in osteoclast spread area (retraction). Conversely, certain other modifications resulted in peptides, such as PrGDN and benzoyl-RGDN, which effect osteoclast retraction, while having minimal Ca2+ signaling capabilities. Osteoclast adhesion, and hence retraction, are known to be RGD-dependent and integrin-dependent events. However, intracellular Ca2+ signaling is RGD-independent and, based on lack of inhibition by an anti-beta 3 integrin antibody F11 and echistatin, very likely integrin-independent. These data suggest that signaling is not always via VNR and as yet unknown receptors on the osteoclast membrane play a role in osteoclast signaling and hence function.
骨桥蛋白受体（VNR）是整合素家族细胞黏附分子的一员，在破骨细胞中大量表达。对其进行的广泛表征揭示了该受体在破骨细胞黏附以及骨吸收中的作用。我们实验室早期的证据表明，VNR在受体配体相互作用后也能够转导细胞内信号，尽管对该功能的了解还很少。因此，添加含有最小三肽精氨酸 - 甘氨酸 - 天冬氨酸（RGD）整合素识别序列的肽会引起细胞内游离钙离子的短暂增加，骨唾液蛋白肽BSP-IIA能产生最大反应。在本研究中，我们试图使用在骨唾液蛋白中发现的肽PRGDN/T序列的衍生物来确定破骨细胞中钙信号传导的一些结构要求。虽然一些肽，如亲本序列PRGDN，既能诱导信号传导又能引起收缩事件，但发现微小的结构修饰产生了如PRADN这样的肽，它能引起细胞内游离钙离子的短暂增加，而不会促进破骨细胞铺展面积的减小（收缩）。相反，某些其他修饰产生了如PrGDN和苯甲酰 - RGDN这样的肽，它们会影响破骨细胞收缩，而钙信号传导能力最小。已知破骨细胞黏附以及因此的收缩是依赖RGD和整合素的事件。然而，细胞内钙信号传导不依赖RGD，并且基于抗β3整合素抗体F11和echistatin缺乏抑制作用，很可能也不依赖整合素。这些数据表明，信号传导并不总是通过VNR，破骨细胞膜上尚未知晓的受体在破骨细胞信号传导以及功能中发挥作用。
