Oxidant stress induces gamma‐glutamylcysteine synthetase and glutathione synthesis in human bronchial epithelial NCI‐H292 cells

BACKGROUND: The bronchial epithelium is exposed to reactive oxygen species (ROS) derived from cigarette smoke, air pollutants and activated leucocytes. Glutathione (GSH) prevents ROS-mediated loss of cell function, tissue injury and inflammation, and its synthesis is regulated by gamma-glutamylcysteine synthetase (gamma-GCS). However, the capacity of bronchial epithelial cells to adapt to oxidative stress and the mechanisms involved are not known. OBJECTIVE: To investigate the effects of oxidative stress on the regulation of GSH synthesis in human bronchial epithelial (NCI-H292) cells. METHODS: NCI-H292 cells were exposed to menadione and intracellular GSH concentrations were measured by spectrophotometry. gamma-GCS activity was measured by HPLC assay and changes in gamma-GCS mRNA by Northern blotting. RESULTS: Exposure to menadione (MQ, 10-200 microm, 30-120 min) decreased total cellular GSH content, measured immediately after exposure to MQ. However, GSH content measured 6-12 h after withdrawal of the oxidant stress (MQ, 50 microm, 30 min), increased c. two fold over baseline levels (P < 0.001). gamma-GCS activity measured 6 h (21.7 +/- 3.4 nmol/min/mg, SD, n = 5, P < 0.01) or 12 h (23.2 +/- 4.6, P < 0.001) after MQ treatment was also significantly increased compared with untreated cells (12.8 +/- 1.0). Similarly, gamma-GCS mRNA expression increased 1.3-1.6-fold relative to GAPDH mRNA, 3-6 h after MQ treatment. The MQ-induced increase in gamma-GCS mRNA expression was completely inhibited by actinomycin D. CONCLUSIONS: Bronchial epithelial (NCI-H292) cells respond rapidly and sensitively to oxidant stress, and this adaptive response is mediated by increased gamma-GCS mRNA transcription and enzyme activity.