Xu Kaiming, Shu Hui-Kuo G
Department of Radiation Oncology, Emory University, Atlanta, Georgia 30322, USA.
Cancer Res. 2007 Jul 1;67(13):6121-9. doi: 10.1158/0008-5472.CAN-07-0141.
Expression of cyclooxygenase-2 (COX-2) has been linked to many cancers and may contribute to malignant phenotypes, including enhanced proliferation, angiogenesis, and resistance to cytotoxic therapies. Malignant gliomas are highly aggressive brain tumors that display many of these characteristics. One prominent molecular abnormality discovered in these astrocytic brain tumors is alteration of epidermal growth factor (EGF) receptor (EGFR) through gene amplification and/or mutation resulting in excessive signaling from this receptor. We found that EGF-mediated stimulation of EGFR tyrosine kinase in human glioma cell lines induces expression of both COX-2 mRNA and protein. The p38 mitogen-activated protein kinase (p38-MAPK) pathway was a strong downstream factor in this activation with inhibition of this pathway leading to strong suppression of COX-2 induction. The p38-MAPK pathway can activate the Sp1/Sp3 transcription factors and this seems necessary for EGFR-dependent transactivation of the COX-2 promoter. Analysis of COX-2 promoter/luciferase constructs revealed that transcriptional activation of the COX-2 promoter by EGFR requires the Sp1 binding site located at -245/-240. Furthermore, Sp1/Sp3 binding to this site in the promoter is enhanced by EGFR activation both in vitro and in vivo. Enhanced DNA binding by Sp1/Sp3 requires p38-MAPK activity and correlates with increased phosphorylation of the Sp1 transcription factor. Thus, EGFR activation in malignant gliomas can transcriptionally activate COX-2 expression in a process that requires p38-MAPK and Sp1/Sp3. Finally, treatment of glioma cell lines with prostaglandin E2, the predominant product of COX-2 activity, results in increased vascular endothelial growth factor expression, thus potentially linking elevations in COX-2 expression with tumor angiogenesis in malignant gliomas.
环氧化酶-2（COX-2）的表达与多种癌症相关，并可能促成恶性表型，包括增殖增强、血管生成以及对细胞毒性疗法的抗性。恶性胶质瘤是极具侵袭性的脑肿瘤，表现出许多上述特征。在这些星形细胞脑肿瘤中发现的一个突出分子异常是表皮生长因子（EGF）受体（EGFR）通过基因扩增和/或突变发生改变，导致该受体过度信号传导。我们发现，EGF介导的对人胶质瘤细胞系中EGFR酪氨酸激酶的刺激可诱导COX-2 mRNA和蛋白的表达。p38丝裂原活化蛋白激酶（p38-MAPK）途径是这种激活过程中的一个重要下游因子，抑制该途径会导致COX-2诱导的强烈抑制。p38-MAPK途径可激活Sp1/Sp3转录因子，这似乎是EGFR依赖的COX-2启动子反式激活所必需的。对COX-2启动子/荧光素酶构建体的分析表明，EGFR对COX-2启动子的转录激活需要位于-245/-240的Sp1结合位点。此外，在体外和体内，EGFR激活均可增强Sp1/Sp3与启动子中该位点的结合。Sp1/Sp3增强的DNA结合需要p38-MAPK活性，并与Sp1转录因子磷酸化增加相关。因此，恶性胶质瘤中的EGFR激活可通过一个需要p38-MAPK和Sp1/Sp3的过程转录激活COX-2表达。最后，用COX-2活性的主要产物前列腺素E2处理胶质瘤细胞系会导致血管内皮生长因子表达增加，从而可能将COX-2表达的升高与恶性胶质瘤中的肿瘤血管生成联系起来。
