Germline and somatic mutations in the Apc (Adenomatous polyposis coli ) gene are thought to be one of the seminal genetic events in the etiology of human and murine colorectal cancer. ApcMin mice carry a germline mutation in the Apc gene and experience reduced lifespan due to adenocarcinoma burden. Wild type, but not truncated, APC binds to and regulates beta-catenin, the mammalian homolog of armadillo required for cadherin-mediated cell adhesion. Apc heterozygosity caused by the Min mutation may contribute to the deregulation of beta-catenin protein levels and result in overexpression of an inducible, proinflammatory enzyme cyclooxygenase-2 (COX-2). Evidence for the regulation of COX-2 expression by APC and possible interaction between NO and COX-2 prompted us to examine the expression of inducible nitric oxide synthase (NOSII) and COX-2 in cells with ApcMin mutation. Using two conditionally immortal murine intestinal epithelial cell lines contrasting in Apc genotype (?Immortomouse?/Min Colonic Epithelia, Apc +/-; Young Adult Mouse Colon epithelia, Apc +/+), we have demonstrated that IMCE cells had significantly higher expression of both NOSII and COX-2 in response to lipopolysaccharide (LPS) and interferon-gamma (IFN-g) as compared to YAMC cells. Levels of the metabolic products of these two enzymes, NO and PGE2, respectively, were also elevated markedly. Since NO may play a role in regulating cellular metabolism, we investigated its role in the regulation of PGE2. Interestingly, the induction of COX-2 by inflammatory stimuli is blunted by inhibitors of NOS II. Additionally, COX-2 can be induced by NO-releasing compounds, such as SNAP and NOR-1. These drugs increased PGE2 generation in IMCE and YAMC cells as well. IMCE cells, however, consistently expressed higher COX-2 mRNA and protein and produced more PGE2 in comparison to YAMC cells in response to the same treatment. The differential response in the two cells differing in Apc genotype suggested that beta-catenin may be involved in the response. Electrophoretic mobility shift assays showed that the beta-catenin/LEF-1 transcriptional factor was activated by NO treatment and that IMCE cells had a higher response. Preliminary data indicates that NO may increase the nuclear translocation of beta- catenin, possibly by modulating its phosphorylation and processing by other interacting proteins. We conclude that overproduction of NO, observed in IMCE cells in our study, may further potentiate COX-2 overexpression and PGE2 generation modulated by the Apc genotype. - beta-catenin, adherens junction, Apc, Cancer genetics, colorectal cancer, phospholipase,
