Laboratory of Molecular Carcinogenesis, National Institute of Environmental Health Sciences, NIH, Research Triangle Park, NC 27709, USA.
Cancer Prev Res (Phila). 2009 Dec;2(12):1088-99. doi: 10.1158/1940-6207.CAPR-09-0140. Epub 2009 Nov 24.
EP4 expression in human glioblastoma cells correlates with growth on soft agar. The cyclooxygenase inhibitor sulindac sulfide first altered specificity protein-1 (Sp-1) and early growth response gene-1 expression, then increased the expression of nonsteroidal anti-inflammatory drug-activated gene 1 and activating transcription factor 3, and then decreased EP4 expression. EP4 suppression was dependent on blocking the Sp-1 binding sites in the human EP4 promoter. Mutation in the Sp-1 sites in EP4 altered the promoter activity and abolished sulindac sulfide effects. The inhibitory effect of sulindac sulfide on EP4 expression was reversed by PD98059, a mitogen-activated protein/extracellular signal-regulated kinase kinase-1/extracellular signal-regulated kinase inhibitor. Sp-1 phosphorylation was dependent on sulindac sulfide-induced Erk activation. Chromatin immunoprecipitation assay confirmed that Sp-1 phosphorylation decreases Sp-1 binding to DNA and leads to the suppression of EP4. Inhibition of cell growth on soft agar assay was found to be a highly complex process and seems to require not only the inhibition of cyclooxygenase activity but also increased expression of nonsteroidal anti-inflammatory drug-activated gene 1 and activating transcription factor 3 and suppression of EP4 expression. Our data suggest that the suppression of EP4 expression by sulindac sulfide represents a new mechanism for understanding the tumor suppressor activity.
EP4 在人类脑胶质瘤细胞中的表达与软琼脂上的生长相关。环氧化酶抑制剂舒林酸硫醚首先改变特异性蛋白-1（Sp-1）和早期生长反应基因-1 的表达，然后增加非甾体抗炎药激活基因 1 和激活转录因子 3 的表达，然后降低 EP4 的表达。EP4 的抑制依赖于阻断人 EP4 启动子中的 Sp-1 结合位点。EP4 中的 Sp-1 位点突变改变了启动子活性并消除了舒林酸硫醚的作用。MAPK/ERK 激酶-1/ERK 抑制剂 PD98059 逆转了舒林酸硫醚对 EP4 表达的抑制作用。Sp-1 磷酸化依赖于舒林酸硫醚诱导的 Erk 激活。染色质免疫沉淀分析证实，Sp-1 磷酸化降低了 Sp-1 与 DNA 的结合，导致 EP4 的抑制。我们发现，软琼脂细胞生长抑制试验是一个非常复杂的过程，似乎不仅需要抑制环氧化酶活性，还需要增加非甾体抗炎药激活基因 1 和激活转录因子 3 的表达，并抑制 EP4 的表达。我们的数据表明，舒林酸硫醚对 EP4 表达的抑制代表了理解肿瘤抑制活性的一种新机制。
