Interleukin-6 is overexpressed and augments invasiveness of human glioma stem cells in vitro.

In the present study, we carried out a series of assays to investigate the expression of interleukin-6 in glioma stem cells and its role in glioma stem cells invasion. Glioma stem cells from eight surgical glioma specimens were cultured and identified. Real-time reverse transcription polymerase chain reaction and immunoassay were used to measure and compare the expression levels of interleukin-6 in glioma stem cells and matched primary glioma cells. Subsequently, neutralizing antibody against interleukin-6 or exogenous interleukin-6 was used in a Matrigel-invasion assay and effects of interleukin-6 on glioma stem cells invasiveness was then determined. The results revealed that interleukin-6 mRNA and protein expression levels were significantly higher in glioma stem cells than in primary glioma cells from the same tumor. However, its expression levels were not apparently higher in glioma stem cells from grade IV gliomas than from grade III gliomas. In Matrigel-invasion assay, glioma stem cells invasiveness markedly decreased after interleukin-6 was blocked with neutralizing antibody, but significantly increased when exogenous interleukin-6 was added. Additionally, the similar effects of interleukin-6 were also found on primary glioma cells invasiveness. Our results suggest that glioma stem cells are likely to be the major tumor source of immunosuppressive cytokines interleukin-6 and thereby play a crucial role in determining glioma malignancy, immunosuppression and immune evasion. Furthermore, interleukin-6 can significantly augment glioma stem cells invasiveness in vitro, suggesting a potential target in future therapy for glioma stem cells rather than for their derivatives.