title: Ras-mediated intestinal epithelial cell transformation requires cyclooxygenase-2-induced prostaglandin E2 signaling.
abstract: 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.
authors.affiliation: Department of Pharmacology and Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.
authors.forename: Gretchen A
authors.initials: GA
authors.lastname: Repasky
authors.forename: Yixing
authors.initials: Y
authors.lastname: Zhou
authors.forename: Staeci
authors.initials: S
authors.lastname: Morita
authors.forename: Channing J
authors.initials: CJ
authors.lastname: Der
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002460:Cell Line; D051546:Cyclooxygenase 2 / Q000378:metabolism*; D015232:Dinoprostone / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism; D066246:ErbB Receptors / Q000378:metabolism; D007413:Intestinal Mucosa / Q000378:metabolism; D007422:Intestines / Q000166:cytology*; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D020930:MAP Kinase Kinase Kinases / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism; D051381:Rats; D015398:Signal Transduction; D014170:Transformation, Genetic; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism; D018631:ras Proteins / Q000378:metabolism*
chemical_list: D051546:Cyclooxygenase 2; C489691:Ptgs2 protein, rat; D019869:Phosphatidylinositol 3-Kinases; C512478:EGFR protein, human; D066246:ErbB Receptors; D019908:Proto-Oncogene Proteins c-raf; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D020930:MAP Kinase Kinase Kinases; D018631:ras Proteins; D015232:Dinoprostone