Glutamine is thought to play an important role in cancer cells by being deaminated via glutaminolysis to α-ketoglutarate (aKG) to fuel the tricarboxylic acid (TCA) cycle. Supporting this notion, aKG supplementation can restore growth/survival of glutamine-deprived cells. However, pancreatic cancers are often poorly vascularized and limited in glutamine supply, in alignment with recent concerns on the significance of glutaminolysis in pancreatic cancer. Here, we show that aKG-mediated rescue of glutamine-deprived pancreatic ductal carcinoma (PDAC) cells requires glutamate ammonia ligase (GLUL), the enzyme responsible for de novo glutamine synthesis. GLUL-deficient PDAC cells are capable of the TCA cycle but defective in aKG-coupled glutamine biosynthesis and subsequent nitrogen anabolic processes. Importantly, GLUL expression is elevated in pancreatic cancer patient samples and in mouse PDAC models. GLUL ablation suppresses the development of KrasG12D-driven murine PDAC. Therefore, GLUL-mediated glutamine biosynthesis couples the TCA cycle with nitrogen anabolism and plays a critical role in PDAC.

Doxorubicin, an anthracycline chemotherapeutic agent, is widely used in the treatment of many cancers. However, doxorubicin posts a great risk of adverse cardiovascular events, which are thought to be caused by oxidative stress. We recently reported that the ubiquitin E3 ligase TRIM21 interacts and ubiquitylates p62 and negatively regulates the p62-Keap1-Nrf2 antioxidant pathway. Therefore, we sought to determine the role TRIM21 in cardiotoxicity induced by oxidative damage. Using TRIM21 knockout mice, we examined the effects of TRIM21 on cardiotoxicity induced by two oxidative damage models: the doxorubicin treatment model and the Left Anterior Descending (LAD) model. We also explored the underlying mechanism by RNA-sequencing of the heart tissues, and by treating the mouse embryonic fibroblasts (MEFs), immortalized rat cardiomyocyte line H9c2, and immortalized human cardiomyocyte line AC16 with doxorubicin. TRIM21 knockout mice are protected from heart failure and fatality in both the doxorubicin and LAD models. Hearts of doxorubicin-treated wild-type mice exhibit deformed mitochondria and elevated level of lipid peroxidation reminiscent of ferroptosis, which is alleviated in TRIM21 knockout hearts. Mechanistically, TRIM21-deficient heart tissues and cultured MEFs and H9c2 cells display enhanced p62 sequestration of Keap1 and are protected from doxorubicin-induced ferroptosis. Reconstitution of wild-type but not the E3 ligase-dead and the p62 binding-deficient TRIM21 mutants impedes the protection from doxorubicin-induced cell death. Our study demonstrates that TRIM21 ablation protects doxorubicin-induced cardiotoxicity and illustrates a new function of TRIM21 in ferroptosis, and suggests TRIM21 as a therapeutic target for reducing chemotherapy-related cardiotoxicity. NIH (CA129536; DK108989): data collection, analysis. Shanghai Pujiang Program (19PJ1401900): data collection. National Natural Science Foundation (31971161): data collection. Department of Veteran Affairs (BX004083): data collection. Tianjin Science and Technology Plan Project (17ZXMFSY00020): data collection.

Metabolic programs are known to be altered in cancers arising from various tissues. Malignant transformation can alter signaling pathways related to metabolism and increase the demand for both energy and biomass for the proliferating cancerous cells. This scenario is further complexed by the crosstalk between transformed cells and the microenvironment. One of the most common metabolic alterations, which occurs in many tissues and in the context of multiple oncogenic drivers, is the increased demand for the amino acid glutamine. Many studies have attributed this increased demand for glutamine to the carbon backbone and its role in the tricarboxylic acid (TCA) cycle anaplerosis. However, an increasing number of studies are now emphasizing the importance of glutamine functioning as a proteogenic building block, a nitrogen donor and carrier, an exchanger for import of other amino acids, and a signaling molecule. Herein, we highlight the recent literature on glutamine’s versatile role in cancer, with a focus on nitrogen metabolism, and therapeutic implications of glutamine metabolism in cancer.