Zhen X, Bonjour J P, Caverzasio J
Department of Medicine, University of Geneva, Switzerland.
J Bone Miner Res. 1997 Jan;12(1):36-44. doi: 10.1359/jbmr.1997.12.1.36.
Inorganic phosphate (Pi) is a major regulator of cell metabolism. The Pi transport activity in the plasma membrane is a main determinant of the intracellular level of this ion. In bone-forming cells, Pi transport is important for the calcification of the bone matrix. In this study, the effect of platelet-derived growth factor (PDGF) on Pi transport activity and the signaling mechanism involved in this cellular response were analyzed. The results indicate that PDGF is a potent and selective stimulator of sodium-dependent Pi transport in the mouse calvaria-derived MC3T3-E1 osteoblast-like cells. The change in Pi transport induced by PDGF-BB was dependent on translational processes and affected the Vmax of the Pi transport system. These observations suggested that enhanced Pi transport activity in response to PDGF resulted from insertion of newly synthesized Pi transporters in the plasma membrane. The role of activation of mitogen activated protein (MAP) kinase, phospholipase C (PLC)gamma or phosphatidylinositol 3-kinase (PI-3-kinase), in mediating this effect of PDGF, was investigated. A selective inhibitor of the PDGF receptor tyrosine kinase activity (CGP 53716) completely blocked PDGF-induced protein tyrosine phosphorylation of several proteins including the PDGF receptor, PLCgamma, MAP kinase, and association of the p85 subunit of PI-3'-kinase. Associated with this effect, the increase in Pi transport induced by PDGF was completely blunted by 5 microM CGP 53716. Inhibition of MAP kinase activity by cAMP agonists did not influence Pi transport stimulation induced by PDGF. However, inhibitors of protein kinase C completely blocked this response. A selective inhibitor of PI-3-kinase, LY294002, also significantly reduced this effect of PDGF. In summary, these results indicate that PDGF is a potent and selective stimulator of Pi transport in osteoblastic cells. The mechanism responsible for this effect is not mediated by MAP kinase but involves tyrosine phosphorylation-dependent activation of PLCgamma and PI-3-kinase.
无机磷酸盐（Pi）是细胞代谢的主要调节因子。质膜中的Pi转运活性是该离子细胞内水平的主要决定因素。在成骨细胞中，Pi转运对骨基质的钙化很重要。在本研究中，分析了血小板衍生生长因子（PDGF）对Pi转运活性的影响以及参与这种细胞反应的信号传导机制。结果表明，PDGF是小鼠颅骨来源的MC3T3-E1成骨样细胞中钠依赖性Pi转运的有效且选择性刺激剂。PDGF-BB诱导的Pi转运变化依赖于翻译过程，并影响Pi转运系统的Vmax。这些观察结果表明，对PDGF的反应中Pi转运活性增强是由于新合成的Pi转运体插入质膜所致。研究了丝裂原活化蛋白（MAP）激酶、磷脂酶C（PLC）γ或磷脂酰肌醇3激酶（PI-3激酶）的激活在介导PDGF这种作用中的作用。PDGF受体酪氨酸激酶活性的选择性抑制剂（CGP 53716）完全阻断了PDGF诱导的几种蛋白质的蛋白质酪氨酸磷酸化，包括PDGF受体、PLCγ、MAP激酶以及PI-3'激酶p85亚基的缔合。与此效应相关，5 microM CGP 53716完全抑制了PDGF诱导的Pi转运增加。cAMP激动剂对MAP激酶活性的抑制不影响PDGF诱导的Pi转运刺激。然而，蛋白激酶C抑制剂完全阻断了这种反应。PI-3激酶的选择性抑制剂LY294002也显著降低了PDGF的这种作用。总之，这些结果表明，PDGF是成骨细胞中Pi转运的有效且选择性刺激剂。这种作用的机制不是由MAP激酶介导的，而是涉及PLCγ和PI-3激酶的酪氨酸磷酸化依赖性激活。
