Glutamate-induced glioma cell proliferation is prevented by functional expression of the glutamate transporter GLT-1

Abstract 

A tetracycline-dependent inducible system was used to achieve controlled expression of the glutamate transporter 1 (GLT-1) in C6 glioma cells. Non-induced cells show modest glutamate uptake and, in the presence of l-cystine, these cells tend to release substantial amounts of glutamate. Overnight exposure to doxycycline increased d-[³H]-aspartate uptake, reaching similar capacity as observed in cultured astrocytes. Efficient clearance of exogenously applied glutamate was evidenced in these cells, even in the presence of l-cystine. The addition of glutamate (100μM) to the medium of non-induced cells significantly increased their proliferation rate, an effect that was blocked when the expression of GLT-1 was induced. This suggests that impaired glutamate uptake capacity in glioma cells indirectly contributes to their proliferation.

Abbreviations: C6-rtTA, transfected C6 cells expressing rtTA, C6-rtTA-GLT-1, transfected C6 cells with inducible expression of GLT-1, DHK, dihydrokainic acid, Dox, doxycycline, EAAC1, excitatory amino acid carrier 1, EAAT-2, excitatory amino acid transporter 2, GLAST, glutamate and aspartate transporter, GLT-1, glutamate transporter 1, l-SOS, l-serine-O-sulfate, LTHA, l-(−)-threo-3-hydroxyaspartic acid, MTT, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, rtTA, reverse Tet-responsive transcriptional activator, antiporter, glutamate/cystine exchanger

Keywords: Glutamate uptake, Astrocyte, Glial tumour, Excitotoxicity, Inducible expression