Glutathione transferase omega 1-1 (GSTO1-1) plays an anti-apoptotic role in cell resistance to cisplatin toxicity

Abstract

Several lines of evidence correlate the overexpression of glutathione S-transferase omega 1-1 (GSTO1-1) with the onset of drug resistance of cancer cells; however, no direct evidence is yet available. In order to investigate the mechanisms involved, stable transfection with GSTO1-1 complementary DNA was performed in HeLa cells, which spontaneously express very low levels of GSTO1-1. When transfected cells were seeded at low density, a sharp increase in GSTO1-1 expression was observed as compared with controls, along with an increased resistance against cisplatin cytotoxicity. When seeded at increasing densities, control untransfected cells also presented with an increase in GSTO1-1 expression, again accompanied by cisplatin resistance; the latter was significantly reduced after transfection with GSTO1-1 small interfering RNA. Cisplatin resistance of transfected cells was not accounted for by changes in the intracellular drug concentration nor in the amount of DNA cross-links or content of glutathione. Rather, transfected cells presented with a marked decrease of apoptosis as compared with controls, suggesting that GSTO1-1 overexpression may prevent cisplatin toxicity by interfering with the apoptotic process. Cisplatin treatment was in fact followed at early times (1–2 h) by activation of both Akt kinase and extracellular signal-regulated kinase (ERK)-1/2 in the transfected cells but not in controls. Conversely, in transfected cells, the strong activation of Jun N-terminal kinase (JNK)-1 induced by cisplatin at later times (10–20 h) was completely prevented. In conclusion, GSTO1-1 overexpression appears to be associated with activation of survival pathways (Akt and ERK1/2) and inhibition of apoptotic pathways (JNK1), as well as protection against cisplatin-induced apoptosis.