DisABLing Kidney Cancers Caused by Fumarate Hydratase Mutations

Reprogramming of cellular metabolism by oncogenic mutations probably creates specific vulnerabilities that could be exploited therapeutically. In this issue of Cancer Cell, Sourbier and colleagues show that kidney cancers lacking fumarate hydratase display increased sensitivity to agents that interfere with their ability to cope with reactive oxygen species

Influence of Metabolism on Epigenetics and Disease

Chemical modifications of histones and DNA, such as histone methylation, histone acetylation, and DNA methylation, play critical roles in epigenetic gene regulation. Many of the enzymes that add or remove such chemical modifications are known, or might be suspected, to be sensitive to changes in intracellular metabolism. This knowledge provides a conceptual foundation for understanding how mutations in the metabolic enzymes SDH, FH, and IDH can result in cancer and, more broadly, for how alterations in metabolism and nutrition might contribute to disease. Here, we review literature pertinent to hypothetical connections between metabolic and epigenetic states in eukaryotic cells

Inhibition of vascular endothelial growth factor with a sequence-specific hypoxia response element antagonist

Vascular endothelial growth factor (VEGF) and its receptors have been implicated as key factors in tumor angiogenesis that are up-regulated by hypoxia. We evaluated the effects of DNA-binding small molecules on hypoxia-inducible transcription of VEGF. A synthetic pyrrole-imidazole polyamide designed to bind the hypoxia response element (HRE) was found to disrupt hypoxia-inducible factor (HIF) binding to HIRE. In cultured HeLa cells, this resulted in a reduction of VEGF mRNA and secreted protein levels. The observed effects were polyamide-specific and dose-dependent. Analysis of genome-wide effects of the HIRE-specific polyamide revealed that a number of hypoxia-inducible genes were down-regulated. Pathway-based regulation of hypoxia-inducible gene expression with DNA-binding small molecules may represent a new approach for targeting angiogenesis

Control of Cyclin D1 and Breast Tumorigenesis by the EglN2 Prolyl Hydroxylase

Summary2-Oxoglutarate-dependent dioxygenases, including the EglN prolyl hydroxylases that regulate HIF, can be inhibited with drug-like molecules. EglN2 is estrogen inducible in breast carcinoma cells and the lone Drosophila EglN interacts genetically with Cyclin D1. Although EglN2 is a nonessential gene, we found that EglN2 inactivation decreases Cyclin D1 levels and suppresses mammary gland proliferation in vivo. Regulation of Cyclin D1 is a specific attribute of EglN2 among the EglN proteins and is HIF independent. Loss of EglN2 catalytic activity inhibits estrogen-dependent breast cancer tumorigenesis and can be rescued by exogenous Cyclin D1. EglN2 depletion also impairs the fitness of lung, brain, and hematopoietic cancer lines. These findings support the exploration of EglN2 inhibitors as therapeutics for estrogen-dependent breast cancer and other malignancies

EGLN1 Inhibition and Rerouting of α-Ketoglutarate Suffice for Remote Ischemic Protection

Ischemic preconditioning is the phenomenon whereby brief periods of sublethal ischemia protect against a subsequent, more prolonged, ischemic insult. In remote ischemic preconditioning (RIPC), ischemia to one organ protects others organs at a distance. We created mouse models to ask if inhibition of the alpha-ketoglutarate (αKG)-dependent dioxygenase Egln1, which senses oxygen and regulates the hypoxia-inducible factor (HIF) transcription factor, could suffice to mediate local and remote ischemic preconditioning. Using somatic gene deletion and a pharmacological inhibitor, we found that inhibiting Egln1 systemically or in skeletal muscles protects mice against myocardial ischemia-reperfusion (I/R) injury. Parabiosis experiments confirmed that RIPC in this latter model was mediated by a secreted factor. Egln1 loss causes accumulation of circulating αKG, which drives hepatic production and secretion of kynurenic acid (KYNA) that is necessary and sufficient to mediate cardiac ischemic protection in this setting.Broad Institute of MIT and Harvard. SPARC ProgramBurroughs Wellcome Fun

pVHL Acts as an Adaptor to Promote the Inhibitory Phosphorylation of the NF-κB Agonist Card9 by CK2

The VHL tumor suppressor protein (pVHL) is part of an E3 ubiquitin ligase that targets HIF for destruction. pVHL-defective renal carcinoma cells exhibit increased NF-κB activity but the mechanism is unclear. NF-κB affects tumorigenesis and therapeutic resistance in some settings. We found that pVHL associates with the NF-κB agonist Card9 but does not target Card9 for destruction. Instead, pVHL serves as an adaptor that promotes the phosphorylation of the Card9 C-terminus by CK2. Elimination of these sites markedly enhanced Card9's ability to activate NF-κB in VHL+/+ cells and Card9 siRNA normalized NF-κB activity in VHL−/− cells and restored their sensitivity to cytokine-induced apoptosis. Furthermore, downregulation of Card9 in VHL−/− cancer cells reduced their tumorigenic potential. Therefore pVHL can serve as an adaptor for both an ubiquitin conjugating enzyme and for a kinase. The latter activity, which promotes Card9 phosphorylation, links pVHL to control of NF-κB activity and tumorigenesis

Paracrine Induction of HIF by Glutamate in Breast Cancer: EglN1 Senses Cysteine

The HIF transcription factor promotes adaptation to hypoxia and stimulates the growth of certain cancers, including triple-negative breast cancer (TNBC). The HIFα subunit is usually prolyl-hydroxylated by EglN family members under normoxic conditions, causing its rapid degradation. We confirmed that TNBC cells secrete glutamate, which we found is both necessary and sufficient for the paracrine induction of HIF1α in such cells under normoxic conditions. Glutamate inhibits the xCT glutamate-cystine antiporter, leading to intracellular cysteine depletion. EglN1, the main HIFα prolyl-hydroxylase, undergoes oxidative self-inactivation in the absence of cysteine both in biochemical assays and in cells, resulting in HIF1α accumulation. Therefore, EglN1 senses both oxygen and cysteine

Transformation by the R Enantiomer of 2-Hydroxyglutarate Linked to EglN Activation

The identification of succinate dehydrogenase (SDH), fumarate hydratase (FH), and isocitrate dehydrogenase (IDH) mutations in human cancers has rekindled the idea that altered cellular metabolism can transform cells. Inactivating SDH and FH mutations cause the accumulation of succinate and fumarate, respectively, which can inhibit 2-oxoglutarate (2-OG)-dependent enzymes, including the EglN prolyl 4-hydroxylases that mark the HIF transcription factor for polyubiquitylation and proteasomal degradation 1. Inappropriate HIF activation is suspected of contributing to the pathogenesis of SDH-defective and FH-defective tumors but can suppress tumor growth in some other contexts. IDH1 and IDH2, which catalyze the interconversion of isocitrate and 2-OG, are frequently mutated in human brain tumors and leukemias. The resulting mutants display the neomorphic ability to convert 2-OG to the R-enantiomer of 2-hydroxyglutarate (R-2HG) 2, 3. Here we show that R-2HG, but not S-2HG, stimulates EglN activity leading to diminished HIF levels, which enhances the proliferation and soft agar growth of human astrocytes