Abstract 3808: Bidirectional glutamine transport prevents mitochondrial stress in B-cell transformation

Comparing cell surface proteome changes during B-cell transformation, we found strong induction of SLC7A5, which simultaneously mediates leucine uptake and glutamine export. However, the significance of glutamine export is unknown.Slc7a5 deletion in transformed B cells (BCR-ABL1), but not primary resting B-cells, resulted in accumulated intracellular glutamine, reduced cell proliferation and viability, and prolonged survival of transplant recipients. Interestingly, glutamine deprivation, and pharmacological glutamine sequestration, partially rescued cell fitness, suggesting abnormal accumulation of glutamine impedes malignant transformation.Mechanistically, Slc7a5 deletion and glutamine accumulation resulted in integrated mitochondrial stress response, which signals through mTORC1 to activate ATF4 expression. Treatment with rapamycin significantly rescued growth disadvantage of Slc7a5-deficient cells, whereas treatment with p70 S6K1 inhibitor (PF-470671) had no rescue effect. These results suggested that activated mTORC1 in Slc7a5-deficient cells induced ATF4-mediated stress response rather than global protein synthesis. Chemogenomic screen with a selective SLC7A5 inhibitor in human B-cell leukemia revealed that deletion of genes involved in integrated stress response, including ATF4, led to synthetic lethality. By contrast, deletion of genes involved in mitochondrial tRNA aminoacylation and protein translation had rescue effects. Consistently, alleviation of mitochondrial stress by inhibiting protein synthesis with CHX completely rescued cell defects. In addition, metabolomic analysis and isotope tracing of (15N)2-glutamine revealed that Slc7a5-deficient cells directed glutamine metabolism towards purine synthesis, at the expense of glutathione and NAD+ synthesis. This is consistent with previous findings that mTORC1-ATF4 axis directly induced purine synthesis. Despite the critical role of glutaminolysis in cancer metabolism, our study show that SLC7A5-mediated glutamine export is critical in preventing mitochondrial stress and that abnormal accumulation of glutamine could be detrimental. Citation Format: Ruifeng Sun, Gauri Deb, Kohei Kume, Yanzhi Feng, Johanna Scott, Thomas Graeber, Markus Müschen. Bidirectional glutamine transport prevents mitochondrial stress in B-cell transformation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 3808.