Expression and regulation of gamma-glutamyl transpeptidase-related enzyme in tracheal cells

Glutathione plays an essential role in protecting the pulmonary system from toxic insults. gamma-Glutamyl transpeptidase-related enzyme (GGT-rel) is a novel protein capable of cleaving the gamma-glutamyl peptide bond of glutathione and of converting leukotriene C4 to leukotriene D4. A rat homologue of GGT-rel was identified and was found to be highly expressed in cultures of differentiating rat tracheal epithelial (RTE) cells. The 2.6-kb cDNA predicts a 572-amino acid protein with 79% identity to human GGT-rel. GGT-rel was weakly expressed in normal trachea but was strongly induced by epidermal growth factor in cultures of RTE cells. GGT-rel was also highly expressed in lung tumors induced by inhalation of isobutyl nitrite. These results demonstrate that GGT-rel 1) is expressed in normal tracheal cells, 2) can be induced by epidermal growth factor, and 3) is elevated after chemical exposure. The induction of high levels of GGT-rel may play an important role in protecting the lung from oxidative stress or other toxic insults.