Juan Liu

Tumor cells are known to undergo considerable metabolic reprogramming to meet their unique demands and drive tumor growth. At the same time, this reprogramming may come at a cost with resultant metabolic vulnerabilities. The small molecule l-2-hydroxyglutarate (l-2HG) is elevated in the most common histology of renal cancer. Similarly to other oncometabolites, l-2HG has the potential to profoundly impact gene expression. Here, we demonstrate that l-2HG remodels amino acid metabolism in renal cancer cells through combined effects on histone methylation and RNA N ⁶ -methyladenosine. The combined effects of l-2HG result in a metabolic liability that renders tumors cells reliant on exogenous serine to support proliferation, redox homeostasis, and tumor growth. In concert with these data, high–l-2HG kidney cancers demonstrate reduced expression of multiple serine biosynthetic enzymes. Collectively, our data indicate that high–l-2HG renal tumors could be specifically targeted by strategies that limit serine availability to tumors.

Mounting evidence points to alterations in mitochondrial metabolism in renal cell carcinoma (RCC). However, the mechanisms that regulate the TCA cycle in RCC remain uncharacterized. Here, we demonstrate that loss of TCA cycle enzyme expression is retained in RCC metastatic tissues. Moreover, proteomic analysis demonstrates that reduced TCA cycle enzyme expression is far more pronounced in RCC relative to other tumor types. Loss of TCA cycle enzyme expression is correlated with reduced expression of the transcription factor PGC-1 α , which is also lost in RCC tissues. PGC-1 α reexpression in RCC cells restores the expression of TCA cycle enzymes in vitro and in vivo and leads to enhanced glucose carbon incorporation into TCA cycle intermediates. Mechanistically, TGF- β signaling, in concert with histone deacetylase 7 (HDAC7), suppresses TCA cycle enzyme expression. Our studies show that pharmacologic inhibition of TGF- β restores the expression of TCA cycle enzymes and suppresses tumor growth in an orthotopic model of RCC. Taken together, this investigation reveals a potentially novel role for the TGF- β /HDAC7 axis in global suppression of TCA cycle enzymes in RCC and provides insight into the molecular basis of altered mitochondrial metabolism in this malignancy.

Summary: Oncogenic signaling pathways both directly and indirectly regulate anabolic metabolism, and this is required for tumor growth. Targeted therapies that inhibit oncogenic signaling have dramatic impacts on cellular metabolism. However, it is not known whether the acquisition of resistance to these therapies is associated with – or driven by – alterations in cellular metabolism. To address this, we used a conditional mouse model of Her2-driven breast cancer to study metabolic adaptations following Her2 inhibition, during residual disease, and after tumor recurrence. We found that Her2 downregulation caused widespread changes in cellular metabolism, culminating in oxidative stress. Tumor cells adapted to this metabolic stress by upregulation of the antioxidant transcription factor, NRF2. Constitutive NRF2 expression persisted during residual disease and tumor recurrence, and NRF2 was both sufficient to promote tumor recurrence, and necessary for recurrent tumor growth. These results are supported by clinical data showing that the NRF2 transcriptional program is activated in recurrent breast tumors, and that NRF2 is associated with poor prognosis in patients with breast cancer. Mechanistically, NRF2 signaling in recurrent tumors induced metabolic reprogramming to re-establish redox homeostasis and upregulate de novo nucleotide synthesis. Finally, this NRF2-driven metabolic state rendered recurrent tumor cells sensitive to glutaminase inhibition, suggesting that NRF2-high recurrent tumors can be therapeutically targeted. Together, these data provide evidence that NRF2-driven metabolic reprogramming is required for breast cancer recurrence following oncogene inhibition. Significance: Although tumor recurrence is the leading cause of mortality in breast cancer, the cellular properties that allow tumor cells to evade therapy and form recurrent tumors remain largely uncharacterized. Similarly, very little is known about how tumor metabolism changes following therapy, or whether alterations in cellular metabolism drive tumor recurrence. In this study, we identify the antioxidant transcription factor NRF2 as a critical positive regulator of breast cancer recurrence. We find that NRF2-dependent metabolic reprogramming is both sufficient and required to promote tumor recurrence. Additionally, we demonstrate that the NRF2-driven metabolic state renders recurrent tumors sensitive to glutaminase inhibitors, suggesting a novel therapeutic approach for the treatment of recurrent breast cancer.

Increasing NAD ⁺ levels by supplementing with the precursor nicotinamide mononucleotide (NMN) improves cardiac function in multiple mouse models of disease. While NMN influences several aspects of mitochondrial metabolism, the molecular mechanisms by which increased NAD ⁺ enhances cardiac function are poorly understood. A putative mechanism of NAD ⁺ therapeutic action exists via activation of the mitochondrial NAD ⁺ -dependent protein deacetylase sirtuin 3 (SIRT3). We assessed the therapeutic efficacy of NMN and the role of SIRT3 in the Friedreich’s ataxia cardiomyopathy mouse model (FXN-KO). At baseline, the FXN-KO heart has mitochondrial protein hyperacetylation, reduced Sirt3 mRNA expression, and evidence of increased NAD ⁺ salvage. Remarkably, NMN administered to FXN-KO mice restores cardiac function to near-normal levels. To determine whether SIRT3 is required for NMN therapeutic efficacy, we generated SIRT3-KO and SIRT3-KO/FXN-KO (double KO [dKO]) models. The improvement in cardiac function upon NMN treatment in the FXN-KO is lost in the dKO model, demonstrating that the effects of NMN are dependent upon cardiac SIRT3. Coupled with cardio-protection, SIRT3 mediates NMN-induced improvements in both cardiac and extracardiac metabolic function and energy metabolism. Taken together, these results serve as important preclinical data for NMN supplementation or SIRT3 activator therapy in Friedreich’s ataxia patients.