Beck George R, Knecht Nicole
National Cancer Institute-Frederick, Center for Cancer Research, Basic Research Laboratory, Bldg. 576 Rm. 110, Frederick, MD 21702, USA.
J Biol Chem. 2003 Oct 24;278(43):41921-9. doi: 10.1074/jbc.M304470200. Epub 2003 Aug 13.
The generation of inorganic phosphate by alkaline phosphatase during osteoblast differentiation represents an important signaling event, although the molecular and cellular consequences are currently undefined. We have previously described osteopontin as a gene regulated by an increase in inorganic phosphate not only in osteoblasts but also in other cell types. We describe here the identification of specific signaling pathways required for the stimulation of osteopontin expression by inorganic phosphate. We have determined that phosphate selectively activates the extracellular signal-regulated kinase (ERK1/2) signaling pathway but does not activate the other mitogen-activated protein kinase signaling proteins, p38, or the c-Jun N-terminal kinase. In addition, our results suggest that cellular exposure to 10 mm inorganic phosphate causes a biphasic ERK1/2 activation. The second ERK1/2 activation is required for osteopontin regulation, whereas the first is not sufficient. Analysis of common protein kinase families has revealed that phosphate-induced osteopontin expression specifically uses a protein kinase C-dependent signaling pathway. In addition, our results suggest that protein kinase C and ERK1/2 are not part of the same pathway but constitute two distinct pathways. Finally, we have determined that the proteasomal activity is required not only for phosphate-induced expression of osteopontin but also for the induction of osteopontin in response to 12-O-tetradecanoylphorbol 13-acetate and okadaic acid. The data presented here define for the first time the ability of increased inorganic phosphate to stimulate specific signaling pathways resulting in functionally significant changes in gene expression and identify three important signaling pathways in the regulation of osteopontin.
在成骨细胞分化过程中，碱性磷酸酶产生无机磷酸盐代表了一个重要的信号事件，尽管目前其分子和细胞层面的后果尚不清楚。我们之前曾描述骨桥蛋白是一个不仅在成骨细胞中，而且在其他细胞类型中都受无机磷酸盐增加调控的基因。我们在此描述了鉴定无机磷酸盐刺激骨桥蛋白表达所需的特定信号通路。我们已经确定磷酸盐选择性激活细胞外信号调节激酶（ERK1/2）信号通路，但不激活其他丝裂原活化蛋白激酶信号蛋白、p38或c-Jun氨基末端激酶。此外，我们的结果表明细胞暴露于10 mM无机磷酸盐会导致ERK1/2的双相激活。第二次ERK1/2激活是骨桥蛋白调节所必需的，而第一次则不充分。对常见蛋白激酶家族的分析表明，磷酸盐诱导的骨桥蛋白表达特异性地使用了一条依赖蛋白激酶C的信号通路。此外，我们的结果表明蛋白激酶C和ERK1/2不是同一通路的一部分，而是构成两条不同的通路。最后，我们已经确定蛋白酶体活性不仅是磷酸盐诱导骨桥蛋白表达所必需的，也是对12-O-十四烷酰佛波醇-13-乙酸酯和冈田酸响应诱导骨桥蛋白所必需的。此处呈现的数据首次定义了无机磷酸盐增加刺激特定信号通路从而导致基因表达发生功能上显著变化的能力，并确定了骨桥蛋白调节中的三条重要信号通路。
