CYTOKINE INDUCTION OF NO SYNTHASE-II IN HUMAN DLD-1 CELLS - ROLES OF THE JAK-STAT, AP-1 AND NF-KAPPA-B-SIGNALING PATHWAYS

1 In human epithelial-like DLD-1 cells, nitric oxide synthase (NOS) II expression was induced by interferon-gamma (100 u ml(-1)) alone and, to a larger extent, by a cytokine mixture (CM) consisting of interfero n-gamma, interleukin-1 beta (50 u ml(-1)) and tumor necrosis factor-al pha (10 ng ml(-1)). 2 CM-induced NOS II expression was inhibited by ty rphostin B42 (mRNA down to 1%; nitrite production down to 0.5% at 300 mu M) and tyrphostin A25 (mRNA down to 24%, nitrite production down to 1% at 200 mu M), suggesting the involvement of janus kinase 2 (JAK-2) . Tyrphostin B42 also blocked the CM-induced JAK-2 phosphorylation (ki nase assay) and reduced the CM-stimulated STAT1 alpha binding activity (gel shift analysis). 3 CM reduced the nuclear binding activity of tr anscription factor AP-1. A heterogenous group of compounds, that stimu lated the expression of c-fos/c-jun, enhanced the nuclear binding acti vity of AP-l. This group includes the protein phosphatase inhibitors c alyculin A, okadaic acid, and phenylarsine oxide, as well as the inhib itor of translation anisomycin. All of these compounds reduced CM-indu ced NOS II mRNA expression (to 9% at 50 nM calyculin A; to 28% at 500 nM okadaic acid; to 18% at 10 mu M phenylarsine oxide; and to 19% at 1 00 ng ml(-1) anisomycin) without changing NOS II mRNA stability. In co transfection experiments, overexpression of c-Jun and c-Fos reduced pr omoter activity of a 7 kb DNA fragment of the 5'-flanking sequence of the human NOS II gene to 63%. 4 Nuclear extracts from resting DLD-1 ce lls showed significant binding activity for transcription factor NF-ka ppa B, which was only slightly enhanced by CM. The NF-kappa B inhibito rs dexamethasone (1 mu M), 3,4-dichloroisocoumarin (50 mu M), panepoxy done (5 mu g ml(-1)) and pyrrolidine dithiocarbamate (100 mu M) produc ed no inhibition of CM-induced NOS II induction. 5 We conclude that in human DLD-1 cells, the interferon-gamma-JAK-2-STAT1 alpha pathway is important for NOS II induction. AP-1 (that is downregulated by CM) see ms to be a negative regulator of NOS II expression. NF-kappa B, which is probably important for basal activity of the human NOS II promoter, is unlikely to function as a major effector of CM in DLD-1 cells.