4-hydroxy-2-nonenal increases gamma-glutamylcysteine synthetase gene expression in alveolar epithelial cells

Previous studies from this laboratory demonstrated that 4-hydroxy-2-nonenal (4HNE), a lipid peroxidation product, induces expression of gamma -glutamy lcysteine synthetase (CCS), the rate-limiting enzyme in de novo glutathione (GSH) synthesis, in rat alveolar epithelial L2 cells. The present study de monstrates that 4HNE also induces GCS in primary cultured alveolar epitheli al type II (AT2) cells. Enzyme activity, protein content, and messenger RNA levels of both the catalytic (CCS-HS) and regulatory (CCS-LS) subunits wer e significantly increased in AT2 cells treated with 5 or 10 muM 4HNE, the s ame concentrations that induced GCS expression in L2 cells. As in L2 cells, 4HNE induced a greater AT2-cell increase in CCS-LS than in GCS-HS, suggest ing that modulation of GCS-LS may play a dominant role in regulating GSH co ncentration in response to oxidative stress. Additional studies using mitog en-activated protein kinase pathway inhibitors showed that induction by 4HN E of GCS-HS, but not GCS-LS, was mediated through activation of the extrace llular regulated kinase pathway in L2 cells, The results demonstrate that L 2 cells maintain the same responsiveness to oxidant challenge as do primary cultured AT2 cells in terms of increasing GSH synthetic rapacity, and that different pathways are involved in the induction of two CCS subunits by 4H NE.