Targeting YAP Activity and Glutamine Metabolism Cooperatively Suppresses Tumor Progression by Preventing Extracellular Matrix Accumulation.

Cancer cells use multiple mechanisms to evade the effects of glutamine metabolism inhibitors. The pathways that govern responses to alterations in glutamine availability within the tumor may represent therapeutic targets for combinatorial strategies with these inhibitors. Here, we showed that targeting glutamine utilization stimulated Yes-associated protein (YAP) signaling in cancer cells by reducing cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA)-dependent phosphorylation of large tumor suppressor (LATS). Elevated YAP activation induced extracellular matrix (ECM) deposition by increasing secretion of connective tissue growth factor (CTGF) that promoted production of fibronectin and collagen by surrounding fibroblasts. Consequently, inhibiting YAP synergized with inhibition of glutamine utilization to effectively suppress tumor growth in vivo, along with a concurrent decrease in ECM deposition. Blocking ECM remodeling also augmented the tumor suppressive effects of the glutamine utilization inhibitor. Collectively, these data reveal mechanisms by which targeting glutamine utilization increases ECM accumulation and identify potential strategies to reduce ECM levels and increase the efficacy of glutamine metabolism inhibitors.

Glutamine-derived aspartate is required for eIF5A hypusination-mediated translation of HIF-1α to induce the polarization of tumor-associated macrophages.

Tumor-associated macrophages (TAMs) are vital contributors to the growth, metastasis, and therapeutic resistance of various cancers, including hepatocellular carcinoma (HCC). However, the exact phenotype of TAMs and the mechanisms underlying their modulation for therapeutic purposes have not been determined. Here, we present compelling evidence that glutamine-derived aspartate in TAMs stimulates spermidine production through the polyamine synthesis pathway, thereby increasing the translation efficiency of HIF-1α via eIF5A hypusination. Consequently, augmented translation of HIF-1α drives TAMs to undergo an increase glycolysis and acquire a metabolic phenotype distinct from that of M2 macrophages. Finally, eIF5A levels in tumor stromal lesions were greater than those in nontumor stromal lesions. Additionally, a higher degree of tumor stromal eIF5A hypusination was significantly associated with a more advanced tumor stage. Taken together, these data highlight the potential of inhibiting hypusinated eIF5A by targeting glutamine metabolism in TAMs, thereby opening a promising avenue for the development of novel therapeutic approaches for HCC.

Inhibition of Glutamine Utilization Synergizes with Immune Checkpoint Inhibitor to Promote Antitumor Immunity.

Despite its outstanding clinical success, immune checkpoint blockade remains ineffective in many patients. Accordingly, combination therapy capable of achieving greater antitumor immunity is urgently required. Here, we report that limiting glutamine metabolism in cancer cells bolsters the effectiveness of anti-programmed death ligand-1 (PD-L1) antibody. Inhibition of glutamine utilization increased PD-L1 levels in cancer cells, thereby inactivating co-cultured T cells. Under glutamine-limited conditions, reduced cellular GSH levels caused an upregulation of PD-L1 expression by impairing SERCA activity, which activates the calcium/NF-κB signaling cascade. Consequently, in tumors grown in immunocompetent mice, inhibition of glutamine metabolism decreased the antitumor activity of T cells. In combination with anti-PD-L1, however, glutamine depletion strongly promoted the antitumor efficacy of T cells in vitro and in vivo due to simultaneous increases in Fas/CD95 levels. Our results demonstrate the relevance of cancer glutamine metabolism to antitumor immunity and suggest that co-targeting of glutamine metabolism and PD-L1 represents a promising therapeutic approach.

Oncogenic KRAS signaling activates mTORC1 through COUP-TFII-mediated lactate production.

Oncogenic signals contribute to enhanced glycolysis and mTORC1 activity, leading to rapid cell proliferation in cancer. Regulation of glycolysis and mTORC1 by PI3K/Akt signaling is well established, but how KRAS-induced MEK signaling regulates these pathways remains poorly understood. Here, we report a role for MEK-driven lactate production in mTORC1 activation in KRAS-activated cells. KRAS/MEK-induced upregulation of the chicken ovalbumin upstream promoter transcriptional factor II (COUP-TFII) increases the expression of lactate dehydrogenase A (LDHA), resulting in lactate production and mTORC1 activation. Further, lactate inhibits the interaction of TSC2 and Rheb, leading to the cellular activation of mTORC1 irrespective of growth factor stimulation. These findings suggest that COUP-TFII is a novel oncogenic mediator, connecting KRAS signaling and glycolysis, and leading to mTORC1 activation and cellular growth.