Next we sought to address the expression of p-DNA-PKcs in glioma cell lines. Data in Figure 2A revealed that, in contrast to normal human astrocyte (NHA) which possessed an undetectable level of activated DNA-PKcs, p-DNA-PKcs were expressed in a panel of glioma cells. We also examined the γH2AX level in these cells. However, none of them demonstrated an obvious band of γH2AX (Supplementary Figure S3). Notably, cell lines with high levels of p-DNA-PKcs (U87 and M059K) demonstrated higher IC50 values of TMZ compared with A172 and H4. We then determined whether DNA-PKcs contributed to glioma cell growth and TMZ sensitivity. Strikingly, DNA-PKcs siRNA transfection effectively suppressed the proliferation of U87 and M059K cells and enhanced the cytotoxic effect of TMZ using MTS assays (Figure 2B and Supplementary Figure S4).