Extracellular glutathione peroxidase induction in asthmatic lungs: evidence for redox regulation of expression in human airway epithelial cells.

A critical first-line antioxidant defense on the airway epithelial surface against reactive oxygen and nitrogen species (ROS and RNS) is extracellular glutathione peroxidase (eGPx). Little is known about the regulation of eGPx or its role in ROS-mediated lung diseases such as asthma. Here we show that eGPx is increased in the asthmatic airway in comparison to healthy controls. Higher levels of eGPx mRNA in asthmatic airway epithelium verified bronchial epithelial cells as the source for the increased eGPx. The eGPx mRNA in bronchial epithelial cells in vitro increased eightfold after exposure to ROS and glutathione, an essential cofactor for eGPx activity. Alterations in intracellular and extracellular oxidized and reduced glutathione were temporally associated with eGPx induction, further supporting redox mechanisms in gene expression. Overexpression of superoxide dismutase, but not catalase, inhibited induction and identified superoxide as a key intermediary. The eGPx mRNA half-life was not affected by ROS, suggesting a transcriptional mechanism for eGPx regulation. Fusion genes of deletion fragments of the eGPx gene 5' flanking region driving a reporter gene conclusively identified the ROS-responsive region, which contained the consensus DNA binding site for the redox-regulated transcription factor, activator protein 1.