Enhanced resistance of HeLa cells to cisplatin by overexpression of gamma-glutamyltransferase.
Gamma-glutamyltransferase (GGT), which is a key enzyme for the cellular glutathione (GSH) homeostasis, was shown to be overexpressed in human tumor cells selected for resistance to cisplatin and to influence the resistance of experimental tumors in vivo. We first established that cisplatin treatment of HeLa cells was accompanied by an early 3-fold induction of GGT synthesis, enhancing the possibility that this enzyme plays an important role in the cell defenses against this anticancer drug. This role was then studied using a GGT-transfected HeLa cell line (HeLa-GGT) exhibiting 10 times the activity of the parental HeLa cells (120-150 and 10-14 mU/mg protein, respectively). Both cell lines showed comparable intracellular GSH levels and cisplatin resistance when cultured in high (250 microM) or low (50 microM) cysteine-containing medium. When 50 microM of GSH were included in the low-cysteine culture medium only HeLa-GGT cells partially recovered their intracellular GSH and exhibited an increased resistance to cisplatin. Cisplatin treatment also inhibited GGT-dependent production of reactive oxygen species, a process depending on the availability of cysteinylglycine produced during GSH catabolism. Furthermore, we showed that cisplatin forms adducts with cysteinylglycine 10 times more rapidly than with GSH, and that these adducts were formed only in the extracellular medium of HeLa GGT cells. This extracellular mechanism could at least partially account for the increased resistance of GGT-rich cells to cisplatin.
Thiols et Fonctions Cellulaires, Faculté de Pharmacie, Université Henri Poincaré-Nancy 1, 30 rue Lionnois, 54000 Nancy, France.
Sandrine
S
Daubeuf
Pierre
P
Leroy
Aldo
A
Paolicchi
Alfonso
A
Pompella
Maria
M
Wellman
Marie Madeleine
MM
Galteau
Athanase
A
Visvikis
D000970:Antineoplastic Agents / Q000494:pharmacology*; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D002945:Cisplatin / Q000494:pharmacology*; D019008:Drug Resistance, Neoplasm / Q000502:physiology*; D005978:Glutathione / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D017382:Reactive Oxygen Species / Q000378:metabolism; D005723:gamma-Glutamyltransferase / Q000378:metabolism*
D000970:Antineoplastic Agents; D017382:Reactive Oxygen Species; D005723:gamma-Glutamyltransferase; D005978:Glutathione; D002945:Cisplatin