Figure 6. ATF4 modulates the amino acids secretion of glioma cells.

(A) Extracellular glutamate and cystine levels were evaluated by automized amino acid s analyzer. **P < 0.01, ***P < 0.001, Student's t-test; n = 3 per group. (B) ATF4 modulated U87 cells were treated with 100 μM TMZ for 3 days. Band densities of xCT immunoblots were normalized to the corresponding GAPDH density. (C) The ATF4^OE overexpression cells were transfected with xCT shRNA, and ATF4^KD knockdown cells were transfected with xCT cDNA. Cells in 96-well plates were treated with the indicated concentration of TMZ for 3 days and survival measured by MTT assay. Statistical analysis was performed by one-way ANOVA followed by LSD test where appropriate with n ≥ 8 per group, *P < 0.05, **P < 0.01, ***P < 0.001, compared with ctrl (peGFP-N1) or ctrl shRNA. ^#P < 0.05, ^##P < 0.01, ^###P < 0.001 compared with cells transfected with ATF4^OE or ATF4^KD, ΔP < 0.05, ΔΔP < 0.01, ^ΔΔΔP < 0.001 compared with cells transfected with ATF4^OE + xCT^KD or ATF4^KD + xCT^OE.