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 -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 -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. Interestingly, the expression of COX-2 can be also 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 consistently expressed higher COX-2 mRNA and protein and produced more PGE2 in comparison to YAMC cells in response to the same treatment. Preliminary data indicates that NO may induce COX-2 expression and PGE2 generation by increasing the nuclear translocation of the transcription factor -catenin, possibly through affecting the degradation of -catenin by APC protein. Therefore, over- production of NO, observed in IMCE cells in our study, may further potentiate COX-2 overexpression and PGE2 generation affected by Apc genotype.
