Amino acid deprivation is a strategy that
malignancies utilize to blunt anti-
tumor T-cell immune responses. It has been proposed that
amino acid insufficiency in T-cells is detected by GCN2
kinase, which through phosphorylation of EIF2α, shuts down global
protein synthesis leading to T-cell arrest. The role of this
amino acid stress sensor in the context of malignant
brain tumors has not yet been studied, and may elucidate important insights into the mechanisms of T-cell survival in this harsh environment. Using animal models of
glioblastoma and animals with deficiency in GCN2, we explored the importance of this pathway in T-cell function within
brain tumors. Our results show that GCN2 deficiency limited CD8+ T-cell activation and expression of cytotoxic markers in two separate murine models of
glioblastoma in vivo. Importantly, adoptive transfer of
antigen-specific T-cells from GCN2 KO mice did not control
tumor burden as well as wild-type CD8+ T-cells. Our in vitro and in vivo data demonstrated that reduction in
amino acid availability caused GCN2 deficient CD8+ T-cells to become rapidly necrotic. Mechanistically, reduced CD8+ T-cell activation and
necrosis was due to a disruption in TCR signaling, as we observed reductions in PKCθ and phoshpo-PKCθ on CD8+ T-cells from GCN2 KO mice in the absence of
tryptophan. Validating these observations, treatment of wild-type CD8+ T-cells with a downstream inhibitor of GCN2 activation also triggered
necrosis of CD8+ T-cells in the absence of
tryptophan. In conclusion, our data demonstrate the vital importance of intact GCN2 signaling on CD8+ T-cell function and survival in
glioblastoma.