Kaufmann K, Thiel G
Department of Medical Biochemistry and Molecular Biology, University of Saarland Medical Center, D-66421 Homburg, Germany.
J Neurol Sci. 2001 Aug 15;189(1-2):83-91. doi: 10.1016/s0022-510x(01)00562-7.
Amplification and/or mutations of the epidermal growth factor (EGF) receptor have been frequently reported in human malignant gliomas, the most common primary tumor of the adult central nervous system. We have analyzed a panel of established human glioma cell lines for EGF receptor expression. The EGF receptor was expressed in all of the glioma cell lines tested, with highest levels found in the cell line U343MG-a. In addition, various amounts of a truncated form of the EGF receptor were detected. The platelet-derived growth factor (PDGF) alpha receptor, analyzed for comparison, was expressed at low levels in human glioma cells, with the exception of U-118MG and U-373MG cells. The truncated form of the EGF receptor has been discussed as a constitutively active variant of the receptor. Using antibodies directed against the active form of the EGF receptor, we show here that the truncated variant of the EGF receptor in U343MG-a cells is not in the active conformation. However, the full-length EGF receptor, highly expressed in U343MG-a cells, was very rapidly activated following EGF treatment. In line with this, phosphorylation and activation of the mitogen-activated protein kinase/extracellular signal-regulated protein kinase (ERK) in U343MG-a cells required administration of EGF. Moreover, using highly specific riboprobes we observed that EGF signaling increased the Egr-1 mRNA concentration in human glioma cells within 30 min. The increase in the Egr-1 mRNA concentration was followed by a transient synthesis of the Egr-1 protein. Likewise, Egr-1 mRNA and protein concentrations were increased in U-118MG and U-373MG cells treated with PDGF. The synthesis of Egr-1 in human glioma cells as a result of EGF or PDGF stimulation indicates that Egr-1 may be an important "late" part of the EGF and PDGF-initiated signaling cascades suggesting that Egr-1 functions as a "third messenger" in glioma cells connecting growth factor stimulation with changes in gene transcription.
表皮生长因子（EGF）受体的扩增和/或突变在人类恶性胶质瘤中经常被报道，恶性胶质瘤是成人中枢神经系统最常见的原发性肿瘤。我们分析了一组已建立的人类胶质瘤细胞系的EGF受体表达情况。在所测试的所有胶质瘤细胞系中均表达EGF受体，其中在U343MG-a细胞系中表达水平最高。此外，还检测到了各种数量的EGF受体截短形式。作为对照分析的血小板衍生生长因子（PDGF）α受体，在人类胶质瘤细胞中低水平表达，U-118MG和U-373MG细胞除外。EGF受体的截短形式已被认为是该受体的一种组成型活性变体。使用针对EGF受体活性形式的抗体，我们在此表明U343MG-a细胞中EGF受体的截短变体不处于活性构象。然而，在U343MG-a细胞中高表达的全长EGF受体在EGF处理后很快被激活。与此一致的是，U343MG-a细胞中丝裂原活化蛋白激酶/细胞外信号调节蛋白激酶（ERK）的磷酸化和激活需要给予EGF。此外，使用高度特异性的核糖探针，我们观察到EGF信号在30分钟内增加了人类胶质瘤细胞中Egr-1 mRNA的浓度。Egr-1 mRNA浓度增加后紧接着是Egr-1蛋白的短暂合成。同样，在用PDGF处理的U-118MG和U-373MG细胞中，Egr-1 mRNA和蛋白浓度也增加。由于EGF或PDGF刺激导致人类胶质瘤细胞中Egr-1的合成表明，Egr-1可能是EGF和PDGF启动的信号级联反应中重要的“晚期”部分，这表明Egr-1在胶质瘤细胞中作为“第三信使”，将生长因子刺激与基因转录变化联系起来。
