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Inducible nitric oxide synthase up-regulates Notch-1 in mouse cholangiocytes: implications for carcinogenesis.

BACKGROUND & AIMS
Inflammatory mediators and cell fate genes, such as the Notch gene family, both have been implicated in cancer biology. Because cholangiocarcinomas arise in a background of inflammation and express the inflammatory mediator inducible nitric oxide synthase (iNOS), we aimed to determine whether iNOS expression alters Notch expression and signaling.


METHODS
Notch receptor and ligand expression in human liver was evaluated by immunohistochemistry. The effect of iNOS and NO on Notch-1 expression was examined in cell lines.


RESULTS
Notch-1, but not other Notch receptors, were up-regulated by cholangiocytes in primary sclerosing cholangitis and cholangiocarcinoma. The colocalization of Notch-1 and iNOS also was observed in large bile ducts from the hilar region of primary sclerosing cholangitis patients. Notch-1 expression in murine cholangiocytes was iNOS dependent. iNOS expression also facilitated Notch signaling by inducing the nuclear translocation of its intracellular domain and the expression of a transcriptional target, hairy and enhancer of split (Hes)-1. The gamma-secretase inhibitor N-[N-(3,5-Difluorophenacetyl-L-alanyl)-S-phenylglycine]-t-butyl ester, which blocks Notch signaling, enhanced tumor necrosis factor-related apoptosis-inducing ligand-induced apoptosis in cholangiocarcinoma cells.


CONCLUSIONS
These data implicate a direct link between the inflammatory mediator iNOS and Notch signaling, and have implications for the development and progression of cholangiocarcinoma.