The authors state that they have no conflicts of interest.
Enhanced Expression of the Inorganic Phosphate Transporter Pit-1 Is Involved in BMP-2–Induced Matrix Mineralization in Osteoblast-Like Cells†
Article first published online: 20 FEB 2006
Copyright © 2006 ASBMR
Journal of Bone and Mineral Research
Volume 21, Issue 5, pages 674–683, May 2006
How to Cite
Suzuki, A., Ghayor, C., Guicheux, J., Magne, D., Quillard, S., Kakita, A., Ono, Y., Miura, Y., Oiso, Y., Itoh, M. and Caverzasio, J. (2006), Enhanced Expression of the Inorganic Phosphate Transporter Pit-1 Is Involved in BMP-2–Induced Matrix Mineralization in Osteoblast-Like Cells. J Bone Miner Res, 21: 674–683. doi: 10.1359/jbmr.020603
- Issue published online: 4 DEC 2009
- Article first published online: 20 FEB 2006
- Manuscript Accepted: 13 FEB 2006
- Manuscript Revised: 30 JAN 2006
- Manuscript Received: 6 DEC 2005
- Pit-1 transporter;
- c-Jun-N-terminal kinase;
Pi handling by osteogenic cells is important for bone mineralization. The role of Pi transport in BMP-2–induced matrix calcification was studied. BMP-2 enhances Pit-1 Pi transporters in osteogenic cells. Experimental analysis suggest that this response is required for bone matrix calcification.
Introduction: Bone morphogenetic proteins (BMPs) are produced by osteogenic cells and play an important role in bone formation. Inorganic phosphate (Pi) is a fundamental constituent of hydroxyapatite, and its transport by osteogenic cells is an important function for primary calcification of the bone matrix. In this study, we investigated the role of Pi transport in BMP-2–induced matrix mineralization.
Materials and Methods: Confluent MC3T3-E1 osteoblast-like cells were exposed to BMP-2 for various time periods. Pi and alanine transport was determined using radiolabeled substrate, Pit-1 and Pit-2 expression by Northern blot analysis, cell differentiation by alkaline phosphatase activity, matrix mineralization by alizarin red staining, and the characteristics of mineral deposited in the matrix by transmission electron microscopy, electron diffraction analysis, and Fourier transformed infrared resolution (FTIR).
Results: BMP-2 time- and dose-dependently stimulated Na-dependent Pi transport in MC3T3-E1 cells by increasing the Vmax of the transport system. This effect was preceded by an increase in mRNA encoding Pit-1 but not Pit-2. BMP-2 also dose-dependently enhanced extracellular matrix mineralization, an effect blunted by either phosphonoformic acid or expression of antisense Pit-1. Enhanced Pi transport and matrix mineralization induced by BMP-2 were blunted by a specific inhibitor of the c-Jun-N-terminal kinase (JNK) pathway.
Conclusions: Results presented in this study indicate that, in addition to its well-known effect on several markers of the differentiation of osteoblastic cells, BMP-2 also stimulates Pi transport activity through a selective increase in expression of type III Pi transporters Pit-1. In MC3T3-E1 cells, this effect is mediated by the JNK pathway and plays an essential role in bone matrix calcification induced by BMP-2.