Yamaguchi T, Chattopadhyay N, Kifor O, Brown E M
Department of Medicine, Brigham and Women's Hospital, and Harvard Medical School, Boston, Massachusetts 02115, USA.
Endocrinology. 1998 Aug;139(8):3561-8. doi: 10.1210/endo.139.8.6163.
The calcium-sensing receptor (CaR) is a G protein-coupled receptor that plays key roles in extracellular calcium ion (Ca2+(o)) homeostasis by mediating the actions of Ca2+(o) on parathyroid gland and kidney. Bone marrow stromal cells support the formation of osteoclasts from their progenitors as well as the growth of hematopoietic stem cells by secreting humoral factors and through cell to cell contact. Stromal cells also have the capacity to differentiate into bone-forming osteoblasts. Bone resorption by osteoclasts probably produces substantial local increases in Ca2+(o) that could provide a signal for stromal cells in the immediate vicinity, leading us to determine whether such stromal cells express the CaR. In this study, we used the murine bone marrow-derived, stromal cell line, ST2. Both immunocytochemistry and Western blot analysis, using an antiserum specific for the CaR, detected CaR protein in ST2 cells. We also identified CaR transcripts in ST2 cells by Northern analysis using a CaR-specific probe and by RT-PCR with CaR-specific primers, followed by nucleotide sequencing of the amplified products. Exposure of ST2 cells to high Ca2+(o) (4.8 mM) or to the polycationic CaR agonists, neomycin (300 microM) or gadolinium (100 microM), stimulated both chemotaxis and DNA synthesis in ST2 cells. Therefore, taken together, our data strongly suggest that the bone marrow-derived stromal cell line, ST2, possesses both CaR protein and messenger RNA that are very similar if not identical to those in parathyroid and kidney. Furthermore, as ST2 cells have the potential to differentiate into osteoblasts, the CaR in stromal cells could participate in bone turnover by stimulating the proliferation and migration of such cells to sites of bone resorption as a result of local, osteoclast-mediated release of Ca2+(o) and, thereafter, initiating bone formation after their differentiation into osteoblasts.
钙敏感受体（CaR）是一种G蛋白偶联受体，通过介导细胞外钙离子（Ca2+(o)）对甲状旁腺和肾脏的作用，在细胞外钙离子稳态中发挥关键作用。骨髓基质细胞通过分泌体液因子以及细胞间接触，支持破骨细胞从其祖细胞形成以及造血干细胞的生长。基质细胞也有分化为成骨的成骨细胞的能力。破骨细胞引起的骨吸收可能会使局部Ca2+(o)大量增加，这可能为紧邻的基质细胞提供信号，促使我们去确定此类基质细胞是否表达CaR。在本研究中，我们使用了源自小鼠骨髓的基质细胞系ST2。使用针对CaR的抗血清进行免疫细胞化学和蛋白质印迹分析，均在ST2细胞中检测到了CaR蛋白。我们还通过使用CaR特异性探针的Northern分析以及使用CaR特异性引物的RT-PCR，随后对扩增产物进行核苷酸测序，在ST2细胞中鉴定出了CaR转录本。将ST2细胞暴露于高Ca2+(o)（4.8 mM）或多阳离子CaR激动剂新霉素（300 microM）或钆（100 microM），可刺激ST2细胞的趋化性和DNA合成。因此，综合来看，我们的数据强烈表明，源自骨髓的基质细胞系ST2拥有CaR蛋白和信使RNA，它们与甲状旁腺和肾脏中的CaR蛋白和信使RNA即便不完全相同也极为相似。此外，由于ST2细胞有分化为成骨细胞的潜力，基质细胞中的CaR可能通过刺激此类细胞的增殖和迁移至骨吸收部位而参与骨转换，这是局部破骨细胞介导的Ca2+(o)释放的结果，此后，它们分化为成骨细胞后启动骨形成。
