Cyclooxygenase-2 alters transforming growth factor-β1 response during intestinal tumorigenesis

Background: Recent investigation suggests that cyclooxygenase-2 plays an important role in colorectal carcinogenesis. Transforming growth factor- betal (TGF-β1) is one of the most potent stimulators of cyclooxygenase-2 expression. A key step in intestinal tumorigenesis involves alteration of the normal cellular response to TGF-β1. We have hypothesized that overexpression of cyclooxygenase-2 alters intestinal epithelial response to TGF-β1. Methods: RIE-1 cells were stably transfected with rat cyclooxygenase-2 complementary DNA in either the sense (RIE-S) or antisense (RIE-AS) orientation. Tumor cell invasion was assessed with a modified Boyden collagen type I invasion assay in the presence of TGF-β1, antibody to urokinase plasminogen activator (uPA), or the selective cyclooxygenase-2 inhibitor SC- 58125. Expression of uPA, uPA receptor, and plasminogen activator inhibitor- 1 were determined by Western blot and enzyme-linked immunosorbent assay. Results: RIE-1 and RIE-AS did not invade although RIE-S cells were minimally invasive at baseline. TGF-β1 had no effect on RIE-1 or RIE-AS invasion; however, TGF-β1 significantly upregulated RIE-S cell invasion. All 3 RIE cell lines produce minimal uPA under basal conditions. TGF-β1 upregulated uPA production only in the RIE-S cells. Both antibody to uPA and SC-58125 reversed TGF-β-mediated RIE-S cell invasion. SC-58125 inhibited TGF-β- mediated RIE-S uPA production. Conclusions: These results demonstrate that overexpression of cyclooxygenase-2 alters intestinal epithelial response to TGF-β1, which may be a mechanism by which cyclooxygenase-2 promotes colon carcinogenesis.