Repasky Gretchen A, Zhou Yixing, Morita Staeci, Der Channing J
Department of Pharmacology and Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.
Mol Carcinog. 2007 Dec;46(12):958-70. doi: 10.1002/mc.20333.
Ras-mediated transformation is associated with upregulation of cyclooxygenase-2 (COX-2), which in turn promotes prostaglandin E2 (PGE2) synthesis and secretion. Although recent studies have identified molecular mechanisms by which Ras mediates upregulation of COX-2, conflicting observations have been made. Furthermore, while COX-2 upregulation has been shown to be important for Ras transformation, the signaling pathways initiated by PGE2-stimulation of EP family of heterotrimeric G protein-coupled receptors (GPCR) and contribution of PGE2 signaling to Ras-mediated transformation are issues that remain unresolved. In this study, we first determined that Raf effector pathway activation of the extracellular-regulated kinase (ERK) mitogen-activated protein kinase (MAPK) cascade alone was sufficient and necessary for COX-2 and PGE2 upregulation. However, Raf-independent regulation of the c-jun N-terminal kinase (JNK) and p38 MAPK cascades is also involved in COX-2 and PGE2 upregulation, with the JNK and p38 pathways exhibiting opposing roles in COX-2 and PGE2 upregulation. Furthermore, in contrast to previous studies, we found that an epidermal growth factor (EGF) receptor autocrine growth mechanism, another Raf-independent signaling mechanism, was necessary for COX-2 and PGE2 upregulation. Second, we determined that inhibition of EP1/2 receptor function blocked growth transformation by Ras, demonstrating that PGE2 upregulation is a key transforming function of COX-2. Finally, we found that PGE2 stimulated the activation of Ras and ERK, but not Akt, and reduced matrix deprivation-induced apoptosis, in untransformed epithelial cells. In summary, our studies define additional, multiple signaling mechanisms that promote COX-2 and PGE2 expression and show that COX-2-stimulated PGE2-EP receptor signaling is required for growth and survival transformation by Ras.
Ras介导的细胞转化与环氧化酶-2（COX-2）的上调有关，而COX-2又反过来促进前列腺素E2（PGE2）的合成与分泌。尽管最近的研究已经确定了Ras介导COX-2上调的分子机制，但仍存在相互矛盾的观察结果。此外，虽然COX-2上调已被证明对Ras转化很重要，但由PGE2刺激异三聚体G蛋白偶联受体（GPCR）的EP家族引发的信号通路以及PGE2信号对Ras介导的转化的贡献仍是未解决的问题。在本研究中，我们首先确定，细胞外调节激酶（ERK）丝裂原活化蛋白激酶（MAPK）级联的Raf效应器途径激活单独对于COX-2和PGE2上调是充分且必要的。然而，c-jun氨基末端激酶（JNK）和p38 MAPK级联的Raf非依赖性调节也参与COX-2和PGE2上调，其中JNK和p38途径在COX-2和PGE2上调中表现出相反的作用。此外，与先前的研究相反，我们发现表皮生长因子（EGF）受体自分泌生长机制，另一种Raf非依赖性信号机制，对于COX-2和PGE2上调是必要的。其次，我们确定抑制EP1/2受体功能可阻断Ras介导的生长转化，表明PGE2上调是COX-2的关键转化功能。最后，我们发现PGE2刺激未转化的上皮细胞中Ras和ERK的激活，但不刺激Akt的激活，并减少基质剥夺诱导的细胞凋亡。总之，我们的研究定义了促进COX-2和PGE2表达的其他多种信号机制，并表明COX-2刺激的PGE2-EP受体信号是Ras介导的生长和存活转化所必需的。
