Cherukuri Durga Prasad, Chen Xiao B O, Goulet Anne-Christine, Young Robert N, Han Yongxin, Heimark Ronald L, Regan John W, Meuillet Emmanuelle, Nelson Mark A
Department of Pathology, Arizona Cancer Center, University of Arizona, 1501N Campbell Avenue # 550, Tucson, AZ 85724, USA.
Exp Cell Res. 2007 Aug 15;313(14):2969-79. doi: 10.1016/j.yexcr.2007.06.004. Epub 2007 Jun 22.
Accumulating evidence indicates that elevated levels of prostaglandin E(2) (PGE(2)) can increase intestinal epithelial cell proliferation, and thus play a role in colorectal tumorigenesis. PGE(2) exerts its effects through four G-protein-coupled PGE receptor (EP) subtypes, named the EP1, EP2, EP3, and EP4. Increased phosphorylation of extracellular regulated kinases (ERK1/2) is required for PGE(2) to stimulate cell proliferation of human colon cancer cells. However, the EP receptor(s) that are involved in this process remain unknown. We provide evidence that L-161,982, a selective EP4 receptor antagonist, completely blocks PGE(2)-induced ERK phosphorylation and cell proliferation of HCA-7 cells. In order to identify downstream target genes of ERK1/2 signaling, we found that PGE(2) induces expression of early growth response gene-1 (EGR-1) downstream of ERK1/2 and regulates its expression at the level of transcription. PGE(2) treatment induces phosphorylation of cyclic AMP response element binding protein (CREB) at Ser133 residue and CRE-mediated luciferase activity in HCA-7 cells. Studies with dominant-negative CREB mutant (ACREB) provide clear evidence for the involvement of CREB in PGE(2) driven egr-1 transcription in HCA-7 cells. In conclusion, this study reveals that egr-1 is a target gene of PGE(2) in HCA-7 cells and is regulated via the newly identified EP4/ERK/CREB pathway. Finally our results support the notion that antagonizing EP4 receptors may provide a novel therapeutic approach to the treatment of colon cancer.
越来越多的证据表明，前列腺素E2（PGE2）水平升高可增加肠道上皮细胞增殖，从而在结直肠癌发生中发挥作用。PGE2通过四种G蛋白偶联的PGE受体（EP）亚型发挥作用，分别命名为EP1、EP2、EP3和EP4。PGE2刺激人结肠癌细胞增殖需要细胞外调节激酶（ERK1/2）的磷酸化增加。然而，参与这一过程的EP受体仍不清楚。我们提供的证据表明，选择性EP4受体拮抗剂L-161,982可完全阻断PGE2诱导的HCA-7细胞ERK磷酸化和细胞增殖。为了确定ERK1/2信号的下游靶基因，我们发现PGE2在ERK1/2下游诱导早期生长反应基因-1（EGR-1）的表达，并在转录水平调节其表达。PGE2处理可诱导HCA-7细胞中cAMP反应元件结合蛋白（CREB）在Ser133残基处的磷酸化以及CRE介导的荧光素酶活性。对显性负性CREB突变体（ACREB）的研究为CREB参与HCA-7细胞中PGE2驱动的egr-1转录提供了明确证据。总之，本研究揭示了egr-1是HCA-7细胞中PGE2的靶基因，并通过新发现的EP4/ERK/CREB途径进行调节。最后，我们的结果支持这样一种观点，即拮抗EP4受体可能为结肠癌治疗提供一种新的治疗方法。
