Induction of vascular endothelial growth factor by IGF-I in osteoblast-like cells is mediated by the PI3K signaling pathway through the hypoxia-inducible factor-2α
Induction of vascular endothelial growth factor by IGF-I in osteoblast-like cells is mediated by the PI3K signaling pathway through the hypoxia-inducible factor-2α
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DOI：
10.1210/en.143.2.420
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发表时间：
2002-02-01
期刊：
影响因子：
4.8
通讯作者：
Clemens, TL
中科院分区：
文献类型：
--
作者：
Akeno, N;Robins, J;Clemens, TL
众所周知，IGF-I 可刺激多种细胞类型中氧和营养敏感基因的表达。在这项研究中，我们研究了介导 IGF-I 诱导人成骨细胞样细胞中血管内皮生长因子 (VEGF) 表达的信号通路和转录机制。 IGF-I (50 ng/ml) 诱导成骨细胞中 VEGF mRNA 快速增加（3 倍），同时伴随着缺氧诱导因子 2α (HIF-2α) 蛋白水平的增加，但 HIF-2α mRNA 表达没有变化。这些效应是通过 HIF-2α 蛋白体降解的化学抑制来模拟的。与 HIF-2α（而非 HIF-1α）构建体共转染大大增强了近端 VEGF 启动子-荧光素酶构建体的转录激活。 IGF-I 强烈刺激 Akt 磷酸化，用 PI3K 抑制剂 LY294002 预处理细胞可消除这种磷酸化。用LY294002预处理细胞也大大减弱了IGF-I对HIF-2α的诱导，并减弱了IGF-I诱导的VEGF启动子活性。最后，强制表达组成型活性 PI3K 表达构建体诱导 VEGF 启动子达到与单独使用 IGF-I 观察到的水平相似的水平。这些数据表明，IGF-I 通过激活 PI3K 途径，通过激活 VEGF 和其他缺氧反应基因的转录控制机制，诱导成骨细胞中 VEGF 的表达。
IGF-I is known to stimulate the expression of oxygen- and nutrient-sensitive genes in several cell types. In this study we investigated the signaling pathways and transcriptional mechanisms that mediate IGF-I induction of vascular endothelial growth factor (VEGF) expression in human osteoblast-like cells. IGF-I (50 ng/ml) induced a rapid increase (3-fold) in VEGF mRNA in osteoblasts that was accompanied by an increase in the level of hypoxia-inducible factor-2alpha (HIF-2alpha) protein without changes in HIF-2alpha mRNA expression. These effects were mimicked by chemical inhibition of proteosomal degradation of HIF-2alpha. Transcriptional activation of a proximal VEGF promoter-luciferase construct was greatly enhanced by cotransfection with an HIF-2alpha, but not an HIF-1alpha, construct. IGF-I acutely stimulated Akt phosphorylation, which was abolished by pretreatment of cells with the PI3K inhibitor LY294002. Pretreatment of the cells with LY294002 also greatly attenuated IGF-I induction of HIF-2alpha and blunted IGF-I-induced VEGF promoter activity. Finally, forced expression of a constitutively active PI3K expression construct induced VEGF promoter to levels similar to those observed with IGF-I alone. These data indicate that IGF-I, by activation of the PI3K pathway, induces VEGF expression in osteoblasts through a transcriptional control mechanism common to those that activate VEGF and other hypoxia response genes.