High Nitric Oxide Production, secondary to inducible-Nitrix Oxide Synthase expression, is Essential for Regulation of the Tumor-Initiating Properties of Colon Cancer Stem Cells

Chronic inflammation is a leading cause of neoplastic transformation in many human cancers and especially incolon cancer (CC), in part due to tumour promotion by nitric oxide (NO) generated at inflammatory sites. It hasalso been suggested that high NO synthesis, secondary to inducible NO synthase (iNOS) expression, is a distinctivefeature of cancer stem cells (CSCs), a small subset of tumour cells with self-renewal capacity. In this study weexplored the contribution of NO to the development of colon CSC features and evaluated potential strategies totreat CC by modulating NO production. Our data show an integral role for endogenous NO and iNOS activityin the biology of colon CSCs. Indeed, colon CSCs with high endogenous NO production (NOhigh) displayed highertumourigenic abilities than NOlow fractions. The blockade of endogenous NO availability, using either a specific iNOSinhibitor or a genetic knock-down of iNOS, resulted in a significant reduction of colon CSC tumourigenic capacitiesin vitro and in vivo. Interestingly, analysis of genes altered by iNOS-directed shRNA showed that the knockdownof iNOS expression was associated with a significant down-regulation of signalling pathways involved in stemnessand tumour progression in colon CSCs. These findings confirm that endogenous NO plays an important role indefining the stemness properties of colon CSCs through cross-regulation of several cellular signalling pathways.This discovery could shed light on the mechanisms by which NO induces the growth and invasiveness of CC,providing new insights into the link between inflammation and colon tumourigenesis.Copyright © 2015 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.