gamma-Glutamyl transpeptidase is increased by oxidative stress in rat alveolar L2 epithelial cells.

Abstract

The tripeptide glutathione (GSH) is used by cells to detoxify hydroperoxides, produced during oxidative stress, and is consumed in the process. Previous studies have indicated that cells can be protected against oxidative stress by extracellular GSH through its degradation catalyzed by the exoenzyme gamma-glutamyl transpeptidase (gamma GT) and its de novo synthesis within the cytosol. We hypothesized that gamma GT would be increased as part of the adaptation of cells to oxidative stress. We examined whether oxidative stress could increase gamma GT activity, protein, and mRNA in a lung epithelial cell line (L2). Cultures were subjected to H2O2-mediated toxicity by 15 min of exposure to the redox cycling quinone, menadione. Menadione (50 microM) caused an initial decrease (27 +/- 9% of baseline after 15 min) in intracellular GSH, followed by resynthesis to levels significantly higher than baseline (335 +/- 40% after 24 h, P < 0.001). This elevation was prevented by acivicin, a gamma GT inhibitor. Menadione also caused a dose-dependent increase in gamma GT enzymatic activity (715 +/- 125% of control at 24 h after 15 min of exposure to 100 microM menadione, P < 0.001) that was prevented by actinomycin D. Western blot analysis indicated increased levels of gamma GT protein with increasing menadione. A concentration-dependent increase in gamma GT-mRNA was also observed. Previous investigation has demonstrated that an increase in gamma GT activity enhances the capacity of cells to utilize extracellular GSH. The findings presented here are consistent with a role for gamma GT in cellular adaptation to oxidative stress.

γ-Glutamyl transpeptidase is induced by 4-hydroxynonenal via EpRE/Nrf2 signaling in rat epithelial type II cells

“…The data also suggest that HNE could induce GGT mRNA V expression via this EpRE. Based on the evidence that GGT mRNA V-2 is abundant in the lung and that the induction of mRNA V-2 is through EpRE, it can be inferred that EpRE/Nrf2 signaling is at least partially involved in GGT induction by other oxidative stress generators, including the redox-cycling quinones [11][12][13][14], NO 2 [10], and hyperoxia [15]. Because every investigated type of oxidative stress results in increased HNE production [41,88], the underlying mechanism of GGT induction by these agents likely involves the production of the common inducer HNE.…”

“…These substances include aflatoxin B1 [9], NO 2 [10], redox cycling quinones [11][12][13][14], and hyperoxia [15]. Induction of GGT by oxidative stress facilitates GSH turnover, de novo GSH synthesis, and the metabolism and detoxification of GSH conjugates and therefore is an important adaptive response that protects cells from oxidative and xenobiotic injury.…”

Oxidative stress and regulation of glutathione in lung inflammation

“…c-GT expression is increased in rat lung epithelial cells by oxidants such as menadione and tbutyl hydroquinone [118], suggesting that c-GT might play a role in protection against oxidative stress. However, cigarette smoke condensate and oxidative stress had no effect on c-GT activity in a human type II alveolar epithelial cell lines (A549 cells) [71].…”

Antioxidants in cystic fibrosis☆Conclusions from the CF Antioxidant Workshop, Bethesda, Maryland, November 11-12, 2003

“…GGT activity is typically increased by oxidative stress [64]: very young children with CF but without inflammation can have normal GSH levels, perhaps due to alternative, developmentally regulated mechanisms for GSH transport that are lost with age [58].…”