The present studies aimed to elucidate how the modulation of
gamma-glutamyl transpeptidase (gammaGT) activity in human
hepatoma (HepG2) cell line influences H(2)O(2) production,
caspase 3 activity,
protein S-thiolation by
glutathione (GSH),
cysteinyl-glycine (
Cys-Gly) and
cysteine (Cys), and the level of other redox forms of these
thiols. The experiments showed that 1-h stimulation of gammaGT elevated H(2)O(2) production, leading to prooxidant conditions. After 24-h stimulation, H(2)O(2) concentration was at the control level, while
Cys-Gly-, Cys- and GSH-dependent S-thiolation was markedly increased, which was accompanied by a drop in
caspase-3 activity. The inhibition of gammaGT activity by
acivicin led to H(2)O(2) decrease after 1-h incubation which still persisted after 24 h. The inhibition of gammaGT activity in HepG2 cells was also connected with the lowering of S-thiolation with Cys and
Cys-Gly and with increasing of
caspase-3 activity. The results of our studies indicate that the modulation of gammaGT activity can be used to change cellular redox status, and can affect Cys- and
Cys-Gly-dependent S-thiolation and
caspase-3 activity. We suggest that the role of high gammaGT activity in HepG2 cells can be connected with production of
reactive oxygen species and with S-thiolation with Cys and
Cys-Gly that can influence activity of
caspase 3.