Fig. 4.

GCN2 is required for the survival of activated T cells during amino acid starvation, but not the control of proliferation. CD4⁺ T cells from C57BL/6 or C57BL/6.GCN2^−/− mice, either naïve (A) or previously activated by plate bound anti-CD3 plus soluble CD28 for 48 h (B), were stimulated by anti-CD3+CD28 beads at 37 °C in the absence of individual EAAs. Cell samples were taken daily and analyzed by flow cytometry for the uptake or 7AAD and the fluorescent caspase product of FITC-VAD-FMK to indicate the proportion of dead (necrotic and apoptotic) cells. Plots show the geometric mean percentage of surviving cells (7AAD⁻Caspase⁻) for C57BL/6 wild type (square) compared with C57BL/6.GCN2^−/− (triangles) T cells under conditions lacking individual branched-chain (P < 0.05; 2-way ANOVA), compared with nonbranched chain EAAs (P < 0.0001), respectively.