gms | German Medical Science

Objective: Cystine-glutamate exchange transporter xc- is important for glutamate (Glu) release and cysteine uptake in glioma cells and essential for excitotoxic glutamate release and synthesis of glutathione (GSH). Recent data demonstrated that strong expression of the light-chain subunit SLC7A11 of xc- correlates with short progression free survival and short overall survival in patients with glioblastoma. In order to understand the mechanism responsible we analyzed Glu release, GSH concentration, expression of SLC7A11, resistance against reactive oxygen species (ROS) and the inhibition of xc- in glioblastoma cell lines.

Method: Cells from the lines U87, LN405, T98G and 1321N1 were incubated in the absence and presence of the xc- inhibitor sulfasalazine (SAS) and the pro-oxidant tert-butylhydroperoxide (tBHP). After treatment, cell viability, intracellular GSH and release of Glu were determined. In addition, mRNA expression of SLC7A11 was quantified and compared to expression in glioblastoma tissue.

Results: We observed that release of Glu correlated qualitatively with intracellular GSH concentration. Surprisingly, cells from the line T98G with the highest concentration of GSH (58.1 nmol/mg protein) exhibited a very rapid and similar loss of viability in the presence of tBHP as cells from the line 1321N1 (13.8 nmol/mg protein). Cells from the line LN405 (19.3 nmol/mg protein) were more resistant towards tBHP than cells from the line U87 (25.6 nmol/mg protein) and both more resistant than the two other lines. SAS inhibition of system xc- revealed no additional response in 1321N1, a moderate and similar response in T98G and LN405 and a strong response in U87 cells. qRT-PCR revealed a more than ten times higher expression of SLC7A11 in T98G compared to LN405 and 1321N1 and very low expression in U87 cells. Expression of SLC7A11 in glioblastoma tissue was comparable to expression in LN405 and 1321N1.

Conclusions: Our results revealed a qualitative correlation between the release of glutamate and the concentration of GSH. Since there was no significant correlation between GSH, and the response towards ROS the presence of additional ROS defense systems in the cells has to be assumed. All cells responded with a higher vulnerability towards ROS in the presence of the xc- inhibitor SAS but the size of the response did not correlate with the expression of mRNA encoding SLC7A11. We conclude that pure survival of patients with high expression of SLC7A11 may be independent from enhanced resistance towards ROS.