EGFR is a member of the ErbB family of receptor tyrosine kinase inhibitor Bicalutamide kinases (77), which regulate proliferation (29, 64), survival (30, 45), and migration of epithelial cells (8, 48, 49, 75). EGFR is also a target of cross talk by other signaling cascades, such as G protein-coupled receptors (9) and receptors for bacterial LPS (36). Furthermore, signaling through TNF/TNFRs stimulates EGFR phosphorylation (33, 63), resulting in cellular proliferation (3), migration (72), and survival (76). TNF and EGF stimulate the expression of cyclooxygenase (COX)-2, the inducible PG synthase (12, 70). Through generation of PGs, COX-2 regulates diverse biological responses, including cell survival (28, 68, 71), proliferation (58), and migration (10), that promote homeostasis of the colon epithelial monolayer.

COX-2 is thought to be important in IBD, because COX-2 protein expression and PG levels are elevated in the GI tract of IBD patients (32, 59, 62). However, whether COX-2 is pathogenic or cytoprotective in IBD is unclear. Chronic elevation of COX-2 protein expression is a risk factor for colorectal adenocarcinomas (37), and chronic nonsteroidal anti-inflammatory drug use is associated with a decreased risk for the development of colorectal cancer (22, 23, 69). Detailed knowledge of COX-2 regulation by TNFRs and EGFR is critical to the development of therapeutic agents for the treatment of a number of GI diseases. These studies were designed to test the hypothesis that TNF-induced COX-2 expression in GI epithelial cells depends on EGFR transactivation and promotes cell survival.

We also tested which TNFR is required for induction of COX-2, since there are conflicting reports about the relative importance of TNFR1 and TNFR2 in this response (39, 50, 52). We report that COX-2 protects colon epithelial cells from TNF-induced cytotoxicity and that TNF-driven Entinostat COX-2 expression in colon and gastric epithelial cells is via a TNFR1-, EGFR-, Src-, and p38 MAPK-dependent mechanism. MATERIALS AND METHODS Cell lines. The conditionally immortalized young adult mouse colon (YAMC) cell line; TNFR1?/?, TNFR2?/?, and EGFR?/? mouse colon epithelial (MCE) cell lines; COX-1?/? and COX-2?/? MCE cell lines; and TNFR1?/?, TNFR2?/?, COX-1?/?, and COX-2?/? immortalized mouse stomach epithelial (ImSt) cells were isolated from wild-type (WT) or knockout mice crossed with the Immortomouse by Robert Whitehead at the Vanderbilt University Digestive Disease Research Center Novel Cell Line Development Core (74). The cell lines were maintained as previously reported (29). Most of the lines were derived on a C57BL/6 background, but in several cases the mice were of mixed (e.g., EGFR?/? from SV129/C57BL/6) or similar, but not identical (e.g., YAMC from C57BL/10), mice.