Gastroenterology

Gastroenterology

Volume 128, Issue 5, May 2005, Pages 1354-1368
Gastroenterology

Basic-liver, pancreas, and biliary tract
Inducible Nitric Oxide Synthase Up-Regulates Notch-1 in Mouse Cholangiocytes: Implications for Carcinogenesis

https://doi.org/10.1053/j.gastro.2005.01.055Get rights and content

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 γ-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.

Section snippets

Human Liver Tissue

This minimal-risk study was approved by the institutional review board. Archival liver specimens were obtained from patients who had undergone liver transplantation for PSC (N = 16) and surgical resection for cholangiocarcinoma (CCA) (N = 12). Normal liver specimens were obtained from 15 liver biopsy samples of 7 living and 8 deceased liver transplant donors. Patients with other potential causes for their liver disease were excluded from the study by examination of the medical record and

Notch-1 Protein Expression Is Enhanced in PSC and CCA

We assessed the expression of Notch-1 protein by immunohistochemistry in PSC, CCA, and normal human liver. In either normal or diseased liver tissue, Notch-1 immunoreactivity was localized exclusively to cholangiocytes and never was observed in hepatocytes (Figure 1A). In normal liver specimens, moderate- to high-level expression (defined as a score of 2 on a scale of 0–2) was observed only in 27% (4 of 15) of the normal liver specimens. In contrast, Notch-1 expression was observed in the

Discussion

The principal findings of this study relate to the cellular mechanisms by which iNOS alters cell-fate decisions, promoting malignant transformation in biliary epithelia. The observations show the following: (1) Notch-1, but not other Notch receptors, were up-regulated by cholangiocytes in PSC, a preneoplastic biliary tract disease, and this expression pattern was retained by human cholangiocarcinoma; (2) Notch-1 and iNOS also were colocalized in large bile duct obtained from the hilar region of

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