Cyclooxygenase-2 expression and prostanoid biogenesis reflect clinical phenotype in human colorectal fibroblast strains

Abstract

Up-regulated cyclooxygenase (COX)-2 expression and prostaglandin E2 (PGE2)synthesis contribute causally to the early stages of colorectal neoplasia and carcinogenesis, yet COX-2 expression is barely detectable in normal and premalignant colorectal epithelium. Rather, COX-2 expression in nonmalignant colonic tissue is probably confined to subepithelial cells, such as fibroblasts. We established a panel of 33 primary subepithelial fibroblast strains from human colonoscopic biopsies of normal colon (group I), normal segments of colons that harbored synchronous advanced neoplasms in remote segments (group II), advanced neoplasms (group III), and segments of active ulcerative colitis (group IV). In group I strains, mean basal and peak PGE2 levels after 24 h of interleukin (IL)-1beta stimulation were 5.4 +/- 1.1 and 32.8 +/- 4.9 ng/mg protein, respectively. Mean IL-1beta-stimulated peak levels in groups II, III, and IV strains were, respectively, 6-, 9-, and 7-fold greater than that in group I (P < 0.001 for each comparison), and inductions of COX-2 mRNA and protein were consistent with these findings. IL-1beta-mediated stimulation of PGE2 was fully blocked in the presence of a nonselective COX inhibitor (indomethacin) or a selective COX-2 inhibitor (NS-398). IL-1beta treatment elicited from group I (normal) and group III (cancer-associated) fibroblasts, respectively, approximately 2- and 3-fold inductions of COX-2 transcriptional activity and approximately 1.4- and 1.7-fold inductions of COX-2 promoter activity. This modestly greater COX-2 transcription rate could not alone account for the dramatically higher levels of COX-2 mRNA and protein and PGE2 in cancer-associated compared with normal fibroblasts. However, incubation of fibroblasts with PGE2 after IL-1beta stimulation prolonged COX-2 mRNA half-life from approximately 1 to 9 h. Our results strengthen the evidence that fibroblasts and other mesenchymal cells are the source of COX-2 expression in normal and premalignant colorectal tissue. Group II fibroblasts from normal segments of colons that harbored synchronous remote advanced neoplasms behaved like group III fibroblasts from advanced neoplasms and not group I fibroblasts from normal colons. We hypothesize that the effects of modestly greater COX-2 transcription in groups II-IV fibroblasts yield corresponding modest increases in PGE2 synthesis whose effects are progressively amplified through robust stabilization of COX-2 mRNA.