Nitrogen Dioxide Exposure Activates γ-Glutamyl Transferase Gene Expression in Rat Lung

Abstract

Exposure to nitrogen dioxide (NO2) has been shown to activate glutathione metabolism in lung and lung lavage. Since GGT is a key enzyme in glutathione metabolism and we have previously characterized GGT expression in distal lung epithelium and in lung surfactant, we examined the NO2exposed lung for induction of γ-glutamyl transferase (GGT) mRNA, protein, and enzyme activity. We found that the GGT gene product is induced in lung by NO2. The GGT mRNA level in lung increases 2-fold within 6 hr and 3-fold after 24 hr of exposure to this oxidant gas, and this 3-fold elevation persists even after 14 days of exposure. The pattern of GGT mRNA expression switches from the single GGT mRNA III transcript in the normal lung to the dual expression of GGT mRNA I and mRNA III. Enzyme activity in whole lung increases 1.6- to 2.5-fold while extracellular surfactant-associated GGT activity accumulates 5.5-fold and GGT protein accumulates in lung surfactant. Induction of GGT mRNA and protein is evident in cells of the bronchioles byin situhybridization and immunolocalization, respectively. In contrast, alveolar type 2 cells lack anin situhybridization signal and exhibit a reduction in the intensity of immunostaining with prolonged exposure. Our studies show that NO2induces GGT mRNA expression, including GGT mRNA1, in lung and GGT protein and enzyme activity in lung and lung lavage in response to the oxidative stress of NO2inhalation.