Induction and activity of nitric oxide synthase in cultured human intestinal epithelial monolayers

We have examined the induction and activity of inducible nitric oxide (NO) synthase (iNOS) in monolayers of DLD-1 cells, an epithelial cell line derived from a human intestinal adenocarcinoma. Induction of iNOS transcription?by a combination of the cytokines interferon-gamma and IL-1 beta was inhibited by genistein, pyrrolidine dithiocarbamate, or dexamethasone and unaffected by pretreatment with ethylene glycol-bis(beta-aminoethyl ether)-N, N,N',N'-tetraacetic acid, basic fibroblast growth factor (bFGF), epidermal growth factor (EGF), or the isoflavone daidzein. iNOS activity and NO synthesis were inhibited by nitro-L-arginine methyl ester, NG-monomethyl-L-arginine, S-methyl-isothiourea sulfate, or aminoethyl-isothiourea, but not by dexamethasone. NO synthesis was potently inhibited by N-alpha-p-tosyl-lysine chloromethyl ketone and hypoxia. In the absence of cytokines no iNOS induction was observed with oxidant stress (H2O2), growth factors (bFGF, EGF), hypoxia or hypoxia reoxygenation. We conclude that in this model of the human intestinal epithelium 1) cytokine-mediated induction of iNOS is Ca2+ independent, weakly steroid sensitive, and may involve the activation of nuclear factor-kappa B and a tyrosine kinase, and 2) iNOS activity is Ca2+ -independent and inhibited by hypoxia, NG-substituted L-arginine analogues, and isothioureas.