s-nitro-n-acetylpenicillamine and 10-10--dimethyl-9-9--biacridinium

Treatment of human hepatoma cells (HepG2) with NO-donors for 24 h inhibited hypoxia-induced erythropoietin (EPO) gene activation. NO was found to increase the production of reactive oxygen species (ROS), the putative signaling molecules between a cellular O2-sensor and hypoxia inducible factor 1 (HIF-1). HIF-1 is the prime regulator of O2-dependent genes such as EPO. NO-treatment for more than 20 h reduced HIF-1-driven reporter gene activity. In contrast, immediately after the addition of NO, ROS levels in HepG2 cells decreased below control values for as long as 4 h. Corresponding to these lowered ROS-levels, HIF-1 reporter gene activity and EPO gene expression transiently increased but were reduced when ROS levels rose thereafter. Our findings of a bimodal effect of NO on ROS production shed new light on the involvement of ROS in the mechanism of O2-sensing and may explain earlier conflicting data about the effect of NO on O2-dependent gene expression.

Topics: Acridines; Anaerobiosis; Carcinoma, Hepatocellular; DNA-Binding Proteins; Erythropoietin; Gene Expression Regulation, Neoplastic; Genes, Reporter; Humans; Hydrogen Peroxide; Hypoxia-Inducible Factor 1; Hypoxia-Inducible Factor 1, alpha Subunit; NADH, NADPH Oxidoreductases; NADPH Oxidases; Nitric Oxide; Nitric Oxide Donors; Nitrogen Oxides; Nuclear Proteins; Onium Compounds; Oxygen; Penicillamine; Reactive Oxygen Species; RNA, Messenger; Signal Transduction; Spermine; Transcription Factors; Transcriptional Activation; Transfection; Tumor Cells, Cultured