Regulatory role of phosphatidylinositol 3-kinase on TNF-α-induced cyclooxygenase 2 expression in colonic epithelial cells.

Weaver, Sean A. and Russo, Maria Pia and Wright, Karen L. and Kolios, George and Jobin, Christian and Robertson, Duncan A. F. and Ward, Stephen G. (2001) Regulatory role of phosphatidylinositol 3-kinase on TNF-α-induced cyclooxygenase 2 expression in colonic epithelial cells. Gastroenterology, 120 (5). pp. 1117-1127. ISSN 0016-5085

Abstract

Background & Aims: Cyclooxygenase (COX)-2 is up-regulated in most colonic cancers and in inflammatory bowel disease in which tumor necrosis factor (TNF)-α is believed to play a central role. There has been recent speculation on the activation of phosphatidylinositol 3-kinase (PI 3-kinase) by TNF-α and its role in the regulation of genes controlled by NF-κB. We investigated the regulatory role of PI 3-kinase on COX-2 expression in colonic epithelial cells. Methods: In HT-29 and Caco-2 colonic epithelial cells, COX-2 expression was induced by either TNF-α or interleukin (IL)-1α as observed by Northern and Western analyses. COX-2 activity was assessed by measuring prostaglandin E2 (PGE2) production by enzyme-linked immunosorbent assay. NF-κB binding activity was assessed by electrophoretic mobility shift assay. PI 3-kinase activity was measured by quantifying the accumulation of PI 3-kinase-dependent D-3 lipid products by high-performance liquid chromatography. Results: The PI 3-kinase inhibitor wortmannin up-regulated induced COX-2 expression in a concentration-dependent manner in both HT-29 and Caco-2 cells. An alternative PI 3-kinase inhibitor, LY294002, caused upregulation of induced COX-2 messenger RNA (mRNA) in HT-29 cells at concentrations of ≤1 μmol/L. IL-4 and IL-13, which are known to activate PI 3-kinase, downregulated HT-29 COX-2 mRNA, protein, and PGE2 production. NF-κB binding activity was unaltered by PI 3-kinase inhibition in HT-29 cells, in which TNF-α was shown to activate PI 3-kinase directly. Conclusions: COX-2 is negatively regulated by PI 3-kinase; we propose that the inhibitory effect of IL-4 and IL-43 is mediated via a PI 3-kinase-dependent pathway. This mechanism does not appear to involve NF-κB because PI 3-kinase inhibition did not alter NF-κB binding activity. TNF-α can activate PI 3-kinase directly in addition to inducing COX-2. Abbreviations: COX, cyclooxygenase; ELISA, enzyme-linked immunosorbent assay; HPLC, high-performance liquid chromatography; IBD, inflammatory bowel disease; IL, interleukin; iNOS, inducible nitric oxide synthase; NF-κB, nuclear factor-κB; NSAID, nonsteroidal anti-inflammatory drug; PGE2, prostaglandin E2; PGJ2, 15-deoxy δ12,14 prostaglandin J2; PI 3-kinase, phosphatidylinositol 3-kinase; PΚB, protein kinase B; Ptdlns, phosphatidylinositol; MAP, kinase mitogen-activated protein kinase; SDS-PAGE, sodium dodecyl sulfatepolyacrylamide gel electrophoresis; Th2, helper 2; TNF, tumor necrosis factor.