Overexpression of gamma-glutamylcysteine synthetase suppresses tumor necrosis factor-induced apoptosis and activation of nuclear transcription factor-kappa B and activator protein-1

Tumor necrosis factor (TNF) is a highly pleiotropic cytokine whose activity is at least partially regulated by the redox status of the cell. The cellu lar redox status is controlled primarily by glutathione, a major cellular a ntioxidant, whose synthesis is regulated by the rate-limiting enzyme gamma- glutamylcysteine synthetase (gamma-GCS). In the present report we investiga ted the effect of gamma-GCS overexpression on the TNF-induced activation of nuclear transcription factors NF-kappa B and AP-I, stress-activated protei n kinase/c-Jun amino-terminal kinase (JNK) and apoptosis, Transfection of c ells with gamma-GCS cDNA blocked TNF-induced NF-kappa B activation, cytopla smic I kappa-B alpha degradation, nuclear translocation of p65, and NF-kapp a B-dependent gene transcription. gamma-GCS overexpression also completely suppressed NF-kappa B activation induced by phorbol ester and okadaic acid, whereas that induced by H2O2, ceramide, and lipopolysaccharide was minimal ly affected. gamma-GCS also abolished the activation of AP-1 induced by TNF and inhibited TNF-induced activation of JNK and mitogen-activated protein kinase kinase. TNF-mediated cytotoxicity and activation of caspase-3 were b oth abrogated in gamma-GCS-overexpressing cells. Overall, our results indic ate that most of the pleiotropic actions of TNF are regulated by glutathion e-controlled redox status of the cell.