The α-ketoglutarate dehydrogenase complex in cancer metabolic plasticity
© The Author(s). 2017
Received: 21 December 2016
Accepted: 18 January 2017
Published: 2 February 2017
Deregulated metabolism is a well-established hallmark of cancer. At the hub of various metabolic pathways deeply integrated within mitochondrial functions, the α-ketoglutarate dehydrogenase complex represents a major modulator of electron transport chain activity and tricarboxylic acid cycle (TCA) flux, and is a pivotal enzyme in the metabolic reprogramming following a cancer cell’s change in bioenergetic requirements. By contributing to the control of α-ketoglutarate levels, dynamics, and oxidation state, the α-ketoglutarate dehydrogenase is also essential in modulating the epigenetic landscape of cancer cells. In this review, we will discuss the manifold roles that this TCA enzyme and its substrate play in cancer.
Keywordsα-Ketoglutarate dehydrogenase complex α-Ketoglutarate Mitochondrial function Metabolic stresses Cancer plasticity Cell signaling Oncometabolite Epigenetics
Cancer cells must acquire several biological properties in order to survive, proliferate, and disseminate. These functional features, or “hallmarks of cancer”, comprise sustaining proliferative signaling, evading growth suppressors, escaping cell death, and activating invasion/metastasis, all of which conspire to lead to pathologically high levels of cell survival and growth, and ultimately tumorigenesis . In the last 10 years, an increasing number of studies suggests that cancer cells reprogram their metabolism in order to most effectively support growth and proliferation. Thus, metabolic rewiring has become an additional hallmark of cancer . Increased aerobic glycolysis, as initially described by Otto Warburg , is observed in the majority of neoplasms in vivo, where it is believed to confer advantages to cancer cells for the production of energy, biomass, and reducing equivalents . Although Warburg hypothesized that such a biochemical phenotype arises from the accumulation of mitochondrial defects, it is now known that, upon nutrient deprivation, oxidative metabolism can be promptly re-established, and a significant level of OXPHOS is maintained both in vitro and in vivo [4–9]. A common feature of solid tumors is that cells rapidly accumulate in bulks, with limited blood supply, and will hence cope with fluctuations in oxygen and nutrients, which will inevitably force them to modulate mitochondrial function consequently. Interestingly, it has been shown that neither hypoxia nor OXPHOS defects imply a complete shutoff of mitochondrial metabolism, and in either case the tricarboxylic acid (TCA) cycle may adjust metabolic fluxes to promote a glutamine-dependent biosynthetic pathway that sustains tumor progression . Hence, the TCA cycle represents a metabolic hub that drives substrate utilization upon changes in resources availability. With respect to this, the discovery of mutations in genes encoding key enzymes of the TCA cycle has brought into light the importance of intracellular TCA cycle metabolite levels in modifying both the metabolic and the epigenetic landscape of cancer cells. Modification of TCA metabolic fluxes and metabolites levels in response to environmental pressures might therefore account for tumor adaptation and plasticity in the changing environment. In this frame, the α-ketoglutarate dehydrogenase complex (α-KGDC) stands out as being deeply interconnected with the respiratory chain, tightly regulated upon tumor microenvironmental changes, a modulator of the level of the signaling metabolite α-ketoglutarate (α-KG), a regulator of cellular redox state, and at the crossroads of numerous metabolic routes. In this review, we will discuss the manifold roles this enzymatic complex and its substrate α-KG play in cancer.
The α-KGDC in cell metabolism
The TCA cycle is fueled by substrates entering at different gateways to convey the carbon source for both energy production and biosynthesis. In the canonical view, acetyl CoA is provided by the oxidation of carbohydrates, mostly glucose and fatty acids, and is then condensed with oxaloacetate to form citrate. The subsequent series of oxidative reactions leads to the production of the reducing equivalents NADH and FADH2 that feed respiratory complex I (CI) and respiratory complex II (CII), respectively, to generate the mitochondrial membrane potential (Δψm) required for ATP production. Glutamine, the most abundant amino acid in the plasma, has been widely described as an additional key source of both carbon and nitrogen, especially for fast proliferating cells . Glutaminolysis results in the production of α-KG, either following dehydrogenation of glutamate or through a transamination reaction. In turn, α-KG can fuel both energetic and anabolic pathways: it may be oxidized by the α-KGDC inside the mitochondria or it may be reduced, thereby pushing the TCA cycle towards citrate [10, 12–14]. The latter may be extruded to the cytosol, where it may be converted back into acetyl CoA, and thereby used for lipid biosynthesis.
How the α-KGDC contributes to adapt mitochondrial metabolism to bioenergetic requirements
Structure and energetic regulation of the α-KGDC
In the TCA cycle, the α-KGDC catalyzes the reaction between α-KG and CoA, using thiamine pyrophosphate (TPP) as a cofactor and reducing the pyridine nucleotide NAD+ to NADH, finally generating succ-CoA and CO2. The α-KGDC is a multienzyme complex composed of three subunits (Fig. 1). The E1 subunit, encoded by the human OGDH gene, is a dehydrogenase that catalyzes the decarboxylation of α-KG, the first step required to produce succ-CoA. The second step is the reductive succinylation of the dihydrolipoyl groups, a reaction carried out by the E2 subunit, i.e., the dihydrolipoamide succinyltransferase, encoded by the human DLST gene. The E3 subunit, encoded by the human DLD gene, is the dihydrolipoamide dehydrogenase, which catalyzes the reoxidation of the E2 dihydrolipoyl groups, eventually reducing the final acceptor NAD+ to NADH . The regulation of the α-KGDC highlights a dynamic interplay between the enzyme and the OXPHOS to adjust mitochondrial metabolism through cell energy status sensing. Both the E1 and the E3 subunits are inhibited by NADH , which accumulates following a decrease of CI function . Indeed, the latter complex is the first and the largest of the respiratory chain and catalyzes NADH oxidation to transfer electrons to flavin mononucleotide, which are used to reduce coenzyme Q to ubiquinol (QH2). The latter is subsequently used by complex III to reduce cytochrome c in the mitochondrial intermembrane space (IMS), and complex IV uses cytochrome c to reduce molecular oxygen, which is the final electron acceptor . Hence, CI actively participates to the generation of the electrochemical gradient by feeding the ETC to generate ATP, which makes NADH an essential substrate for oxidative metabolism. Interestingly, evidence is given for the existence of a direct interaction between CI and α-KGDC, which not only would provide an effective NADH oxidation mechanism via substrate channeling compared to free diffusion [19–21] but also implicates a higher sensitivity of α-KGDC to NADH levels, placing the enzyme on the front line to adapt to variations in ETC efficiency. In addition, a high ADP/ATP ratio and a high concentration of Pi independently enhance the activity of the α-KGDC, with a low ADP/ATP ratio having opposite effects [22, 23]. The levels of Pi and ADP are indicators of a low energetic condition, and both molecules act as positive effectors by increasing the affinity of the enzyme for its substrate. Conversely, higher ATP levels increase the amount of substrate necessary to reach the half-maximum rate of the enzyme, therefore reducing its activity [22, 24]. The regulation of α-KGDC by both the adenine nucleotide phosphorylation state and the NADH/NAD+ ratio is tightly dependent on the Δψm: on the one side, ATP extrusion from the mitochondria to the cytosol is controlled by the ADP/ATP carrier that is regulated by high Δψm and exchanges ATP with ADP in a 1:1 ratio . On the other side, in cases when the ETC is damaged, the production of mitochondrial NADH, driven by cytosolic reductive power, is decreased . This implies that the energetic control on the α-KGDC might be exclusively mitochondrial, and that a feedback loop relying on both substrate and energy availability is triggered between the OXPHOS and the enzyme, thereby ensuring an optimal cooperation. In this light, it may be envisioned that a decrease in mitochondrial respiration, or a significant ATP accumulation, may be associated with a decrease in α-KGDC activity. Changes in the enzyme function would in turn balance mitochondrial NADH levels, thus modulating CI activity and thereby ATP production. However, it has been observed in human neuroblastoma cells that decreasing α-KGDC activity up to half its maximum decreases neither Δψm nor mitochondrial ATP levels . In line with this, the existence of a threshold for the α-KGDC capacity has been demonstrated, which can be greatly inhibited before affecting the maximal mitochondrial oxygen consumption rate . NADH levels can therefore vary broadly before becoming a limiting factor for cellular respiration, suggesting that any reduction of α-KGDC activity might represent a first attempt to adapt metabolism by modulating TCA flux, before impinging on ETC function.
Calcium-mediated regulation of the α-KGDC
The relationship between α-KGDC and Ca2+ further emphasizes the pivotal role of the enzyme in regulating cell metabolism. The mitochondria have long been thought to be a Ca2+ sink, with the main scope of regulating this cation homeostasis in cells. Cytosolic Ca2+ has been shown to foster NADH oxidation by the glycerol dehydrogenase to ultimately produce and import FADH2 within the mitochondria as a substrate for CII . Furthermore, Ca2+ stimulates NADH production through the reactions of the TCA enzymes pyruvate dehydrogenase (PDH), isocitrate dehydrogenase (IDH) and α-KGDC [16, 30]. Among these three enzymes, α-KGDC has been shown to be the most responsive to Ca2+, as the cation lowers the enzyme K M for α-KG [22, 25, 29, 31]. Interestingly, the sensibility of α-KGDC to Ca2+ depends on the concentration of NADH, and on the ATP/ADP ratio, again highlighting a regulatory role of the ETC on the enzyme activity. Indeed, an increase in both cofactors lowers α-KGDC stimulation by Ca2+ . Also, calcium enters the mitochondria through a uniporter, a process driven by the negative potential across the IMM . With respect to this, cancer cells have been shown to be particularly sensitive to an arrest of mitochondrial metabolism through the inhibition of Ca2+ transfer into the mitochondria. Indeed, while normal cells slow down proliferation when Ca2+ import is inhibited, cancer cells proceed through mitosis and end up necrotic, a route that may be rescued through dimethyl-α-KG supplementation . This finding indicates that cancer cells ought to rely on a functional TCA cycle to sustain successful proliferation, and that α-KG may help overcome calcium shortage and sustain a minimal OXPHOS activity, or may drive adaptive responses to oxidative metabolism impairment.
pH-mediated regulation of the α-KGDC
A tight link between α-KGDC and OXPHOS is further exemplified when considering the role of pH in α-KGDC regulation. It has been widely shown that cytosolic Ca2+ elevation leads to rapid mitochondrial acidification, boosting oxidative metabolism. A range of pH between 6.6 and 7.4 has been demonstrated to increase α-KGDC activity . Nonetheless, cytosolic pH is ~7.6 whereas in the mitochondrial matrix it ranges between 7.5 and 8.2 [34, 35]. The α-KGDC activity would thus be promoted upon environment acidification. In agreement with this, α-KG concentration in acidotic rat kidneys significantly decreases due to an increase of α-KGDC activity , which raises the question of whether changes in pH affect mitochondrial function in cancers, since they mostly rely on aerobic glycolysis and undergo a prominent acidosis . However, cancer cells secrete lactate/H+ to maintain intracellular pH at physiological values, leading to the acidification of the extracellular microenvironment . Noticeably, pH in the mitochondria is inherently related to the activity of the ETC that is driven by the proton motive force and Δψm . Thus, the pH of the mitochondrial matrix would rather reflect the equilibrium between proton extrusion and entry into the matrix, mainly driven by OXPHOS activity . It may be easily argued that a low OXPHOS activity is associated with a decrease of pH in the mitochondrial matrix due to proton accumulation, at least around the inner membrane. In this respect, the subsequent induction of α-KGDC activity and of the subsequent NADH generation might help maintaining a proper chemical gradient by fostering CI proton pumping in the IMS. Hence, beside the adenine nucleotide phosphorylation state, the NADH/NAD+ ratio and calcium levels, the OXPHOS might exert an additional control on the α-KGDC through the modulation of pH in the matrix of mitochondria.
ROS and α-KGDC activity
ROS are by-products of mitochondrial oxidative metabolism and their levels are a reliable indicator of ETC damage . Noteworthy, α-KGDC can both sense and generate ROS (Fig. 1). An increase in ROS levels may decrease or completely inhibit α-KGDC function via two different mechanisms involving the modification of LA. While a post-translational modification may lead to the partial and reversible inhibition of the enzyme, the generation of a thiyl radical on the cofactor precedes its complete inactivation [40–42]. On the other hand, in response to NADH accumulation, stimulated by increased α-KG levels, the E3 subunit may generate H2O2 [43, 44] (Fig. 1) at much higher levels than CI . Although physiological amounts of ROS are essential for cell survival, their excess fosters cancer initiation and progression through the induction of genomic instability, gene expression modifications, and the activation of signaling pathways [46, 47]. The aconitase is the most ROS-sensitive TCA cycle enzyme , and its inhibition in cells may therefore limit NADH production by interrupting the cycle from pyruvate to α-KG, and thus electron flux through the respiratory chain, ultimately reducing ROS in a negative loop. Conversely, cancer cells’ high reliance on glutamine metabolism may allow the α-KGDC to fully sustain NADH-linked respiration , even upon a great reduction of aconitase activity. However, unlike the latter, high ROS levels are required to inhibit the α-KGDC . In this light, the elevated threshold might play a prominent role in the progression of tumors with ETC defects. Similarly, prolonged metabolic perturbations such as NADH and α-KG accumulation may lead to α-KGDC-dependent oxidative stress, which in turn may profoundly affect cancer cell redox state and metabolism through a ROS-mediated self-inactivation of the enzyme . Based on these characteristics, with the aim of proposing potential anti-cancer treatment, Stuart and co-workers described a member of anti-cancer lipoate derivatives, CPI-613, which induces an E3-mediated burst of ROS leading to E2 inactivation in cancer cells . Although CPI-613 is known to be implicated in cell death, whether this is due to α-KGDC inhibition, ROS overproduction, or to the reduction of the activity of other lipoate-dependent mitochondrial metabolic enzymes remains unclear [51, 52].
The α-KGDC in cancer metabolic reprogramming
Silencing OGDH in cancer cells with mitochondrial defects has been shown to prevent the production of sufficient levels of NADH, ultimately increasing the NADP+/NADPH ratio and preventing the NADPH-dependent IDHs to reduce α-KG . This observation demonstrates that a minimal activity of α-KGDC is essential for the occurrence of reductive carboxylation and that this enzyme may operate even in the presence of respiration defects. Accordingly, HIF1 does not mediate a complete inhibition of α-KGDC activity, but only up to approximately 60% . Moreover, accumulation of α-KG represses HIF1α stabilization and its downstream pathway by fostering the activity of the metabolic sensor prolyl hydroxylases (PHDs). This may represent a feedback control to keep the enzyme under the stringent regulation required for metabolic adaptation to hypoxia. To the same extent, the NADH and ROS-mediated regulation of α-KGDC activity represents additional feedback mechanisms that prevent complete enzyme inactivation. Since the forward and reverse modes of the TCA cycle are not exclusive, a fine-tuning of α-KGDC activity is required to balance α-KG fate in both energetic and anabolic pathways, according to oxygen levels and to ETC status.
In great contrast with impaired respiration, conditions of nutrient deprivation lead to OXPHOS enhancement and increase the NAD+/NADH ratio in the matrix, hence promoting mitochondrial biogenesis, fatty acids oxidation, and preventing oxidative stress [65, 66]. Surprisingly, a decrease in α-KGDC activity and thereby of mitochondrial ATP synthesis, due to the accumulation of α-KG and subsequent inhibition of the ATP synthase, has been shown to mimic calorie restriction in Caenorhabditis elegans . This mechanism is proposed to ensure energetic efficiency in response to nutrient deprivation  and suggests that decreasing α-KGDC activity is not in contradiction with optimal cellular respiration. However, the accumulation of α-KG in starved animals appears to come from an increase in glutamine metabolism to sustain anaplerotic gluconeogenesis from amino acids catabolism and not from a decrease in α-KGDC activity . Thus, the relevance of this mechanism has yet to be proven in cancer cells, where nutrient requirements and metabolic networks are known to be drastically different from non-malignant cells. In cancer cells, glutaminolysis exceeds the cellular requirement for glutamine in the production of amino acids, nucleotides, and energy . Duràn and co-workers have shown that α-KG levels are a crucial sign of amino acids availability status. In this scenario, high cytosolic levels of α-KG may promote mammalian target of rapamycin 1 (mTORC1) signaling, which in turn blocks autophagy, the housekeeping mechanism to survive nutrient deprivation stress, and increases anabolism in neoplastic cells. On the other hand, low levels of α-KG have opposite effects and correlate with reduced mitochondrial respiration and ATP levels [70, 71]. In this light, it might be hypothesized that the high α-KG production due to enhanced glutamine metabolism might be beneficial for cancer cells by promoting proliferation while inhibiting autophagy . However, the complex interplay between glutamine metabolism and the regulation of mTOR and autophagic processes in cancer cells makes an uncertainty whether α-KG plays a pivotal role in this respect . In addition, upon glucose deprivation, treatment with α-KG derivatives and its reduced form 2-hydroxyglutarate (2-HG) has revealed the ability to inhibit the ATP synthase, resulting in mTOR signaling reduction and autophagy blockage in cancer cells . Overall, these findings suggest that α-KG levels variation may differently affect autophagy regulation according to nutrient availability and compartmentalization of the metabolite (i.e., cytosolic versus mitochondrial), whose regulation still warrants investigation.
Is α-KG an oncometabolite?
Mutations in fumarate hydratase (FH), succinate dehydrogenase (SDH), and IDH1 and IDH2 are associated to specific human neoplasms that hence accumulate succinate, fumarate, and (R)-2-HG, respectively, all conveying broad oncogenic signals . Mutations in FH and SDH follow the classic Knudson “two-hit” model, with somatic loss of gene function leading to the accumulation of their substrates. In a non-canonic fashion, a single allele mutation in IDH1/2 creates a neomorphic enzyme with increased affinity for α-KG, from which an excess of the (R)-2-HG metabolite is produced [75, 76]. The prime mechanism of action of these so-called “oncometabolites” lies within the fact that they are structurally and metabolically similar to α-KG and retain the capacity to regulate a family of more than 60 enzymes involved in fatty acid metabolism, collagen biosynthesis, nutrient sensing, oxygen sensing, and epigenome editing [77, 78]. These enzymes are the Fe(II)/α-KG-dependent dioxygenases, and they include the PHDs introduced earlier. They are ubiquitously expressed and catalyze hydroxylation reactions on several targets. Moreover, they all use α-KG and O2 as co-substrates and require Fe(II) as a cofactor to produce succinate and CO2 . Additionally, ascorbate is required to induce the reduction of Fe(III) to Fe(II), thus restoring enzyme activity [80, 81]. Noticeably, even in the absence of O2, α-KG alone is sufficient to promote the activity of a subset of Fe(II)/α-KG-dependent dioxygenases, , which are instead inhibited by succinate and fumarate . (R)-2-HG occupies the same binding site of α-KG and thereby acts as a competitive inhibitor . Since the KM of dioxygenases for α-KG is close to the metabolite physiological concentration, any condition causing even a modest variation in the cytosolic levels of α-KG may profoundly modify dioxygenases-mediated signals.
Understanding α-KG dynamics and their effect on its downstream targets
Besides mTOR, autophagy is also modulated by HIF1 , making PHDs and thereby α-KG levels pivotal in organelles catabolism. Accumulation of α-KG may also promote mTOR function via ATP synthase inhibition in the mitochondrion, without involving PHDs  (Fig. 3). Hence, while cytosolic accumulation of α-KG might prevent autophagy by activating PHDs, the elevation of its levels in the mitochondria would instead promote it, via ATP synthase inhibition. Nonetheless, cytosolic Fe(II)/α-KG-dependent dioxygenases respond to the ratio between α-KG and its various competitors, whereas α-KG mediates the inhibition of ATP synthase in a non-competitive manner . Consequently, the former mechanism is sensitive to high cytosolic α-KG/2-HG ratio, generated by an increase in amino acids metabolism or a decrease in OXPHOS. The latter may instead be triggered by both α-KG and its reduced forms in the mitochondrial matrix with respect to ATP synthase abundance, and would serve to optimize cell respiration according to substrate availability, thereby contributing to caloric restriction adaptation.
In conclusion, the response to fluctuations of α-KG levels in cells is multifactorial and remains an open area of research. The α-KG signaling is likely to be defined by the metabolite abundance, its oxidation state, and dynamics, which are determined by ETC status and oxygen levels, perhaps among other yet unknown mechanisms. Based on these considerations, it is plausible to argue that fluctuations of α-KG levels may be an intrinsic characteristic of tumor progression, useful to trigger the bioenergetic changes in response to selective pressures. In this light, the role of α-KG remains dual as it may promote both oncogenic and tumor suppressive functions, paralleling the oncojanus function of mitochondrial genes, as we have previously proposed .
Impact of α-ketoglutarate on cancer cell epigenetics
Epigenetics alterations at both DNA and histone levels are increasingly being recognized as modifiers of tumorigenesis . CpG islands are widely hypermethylated in many cancer types compared to the corresponding normal tissue, while the rest of the genome is rather subject to demethylation. The hypermethylation of CpG islands has been utilized as a criterion to distinguish different tumor types from non-malignant tissue , and tumors characterized by high levels of DNA methylation have been classified as having a CpG island methylator phenotype and are predominantly associated with worse prognosis, potentially due to a silencing of tumor suppressor genes. In many cases, this phenotype originates in early phases of tumorigenesis of many tumor types such as glioblastomas, acute myeloid leukemias, gastric cancer, and ependymomas [106–111], where drugs targeting the DNA methylation machinery are a promising strategy.
The large family of α-KG-dependent dioxygenases includes two classes of enzymes involved in demethylation and hydroxylation reactions of DNA and histones. The ten-eleven translocation hydroxylases (TET 1 to 3) catalyze DNA demethylation, whereas the Jumonji C domain containing lysine demethylases (KDM 2 to 7) is the largest family of histone demethylases [112–114]. Both (L)-2-HG and (R)-2-HG are competitive inhibitors of TETs and KDMs, and are thus important modifiers of the epigenetic landscape of cancer cells [84, 94, 115, 116]. Accordingly, accumulation of (L)-2-HG and (R)-2-HG has been associated to several types of cancers [96, 117–119]. Similarly, recent studies have revealed that together with 2HGs, succinate and fumarate can also induce alterations in DNA and histones methylation, thus enhancing cancer formation [84, 120–125]. These findings suggest that different cytosolic concentrations of α-KG affect the methylation status of both histones and DNA and thereby trigger epigenetic changes. Accordingly, Thompson’s group has demonstrated how maintenance of a proper α-KG to succinate ratio is fundamental to determine the identity and the fate of embryonic stem cells (ESC) . In particular, a high α-KG/succinate ratio promotes the activity of DNA and histone demethylases, and modifying this ratio is sufficient to regulate multiple chromatin modifications. Indeed, treatment with α-KG supports ESC self-renewal, which is known to display an unusual “open” chromatin structure, associated to hypertranscription . In this light, high cytosolic levels of α-KG would promote high energy-consuming processes, a hypothesis that is supported by the existence of the PHD-driven mTOR activation mediated by α-KG, which fosters anabolic processes. Conversely, in cancer cells facing hypoxia, it is plausible that α-KG conversion into (L)-2-HG most likely helps in reducing the energetic demand while promoting HIF1α stabilization for hypoxic adaptation. Consistent with this, hypoxia induces a global increase in trimethylation of histone H3 at lysine 9 (H3K9me3) marks, known to repress gene expression, through the accumulation of (L)-2-HG that inhibits the activity of the demethylase KDM4C . Furthermore, oxygen shortage has recently been shown to directly cause DNA hypermethylation by reducing TET activity in cancer cells, predominantly at the level of gene promoters . Notwithstanding this, both TETs and KDMs may stimulate the transcription of specific HIF1-targeted genes, while being themselves transcriptional targets of HIF1 [125, 128–133], a mechanism that most likely compensates for their lower enzymatic activity. Hence, while oncometabolites and low oxygen availability can promote a closed chromatin state and a drop in global gene expression through α-KG-dependent dioxygenases activity, it is plausible that retaining a minimal activity of these enzymes would induce a specific genetic response in cells by restraining transcription machinery to HIF1-targeted genes.
Similarly, given the role of α-KG as an indicator of amino acids availability, it is plausible to speculate the occurrence of an epigenetic remodeling upon glutamine deprivation, which may be faced by solid cancers. Accordingly, a recent study has demonstrated that glutamine deficiency is associated to low α-KG levels, which may in turn determine the inhibition of KDMs in the core regions of the tumor. In this context, the increase in histone methylation induces cancer cells dedifferentiation and may cause therapy resistance .
The consequence of epigenetics modifications is the transduction of external stimuli into a transcriptional response, thus adjusting cells phenotype without affecting their genotype . It is most likely that cell bioenergetic changes driven by external and internal selective pressures promote an intricate epigenetic remodeling through α-KG signaling.
A revisited role of mitochondria highlights that they are not mere bystanders during carcinogenesis. The ever-changing tumor microenvironment may force cells to rely on fluctuating levels of oxygen, as well as varying availability and types of nutrients, whereby optimization of substrates utilization and a continuous restructuring of both metabolic and genetic signatures becomes mandatory for survival. In this review, we have highlighted a hub role for the TCA cycle enzyme α-KGDC as a front-line player in the adaptation of cancer cells to a demanding environment in vivo. This enzyme may be considered a gatekeeper of the OXPHOS system and one of the major regulators of mitochondrial metabolism. Indeed, α-KGDC responds to OXPHOS activity fluctuations, controls the mitochondrial redox status through NADH and ROS levels balance, and directs the TCA metabolite fluxes towards energetic, anabolic, and signaling pathways. Changes in α-KGDC activity, and consequently in overall mitochondrial bioenergetics, may impact not only on TCA cycle fluxes but may become amplified and eventually drive an intricate metabolic and epigenetic remodeling. Overall, NADH/NAD+ and AMP/ATP ratio, oxidative stress, membrane potential, and oxygen levels are pivotal players in the translation of the α-KG signal. In turn, α-KG and its reduced forms may influence the activity of dioxygenases to shape cells metabolic and epigenetic landscape according to oxygen and nutrient availability and ETC efficiency. In this light, the α-KGDC and its substrate appear to be inescapable actors in cancer cells plasticity. It is remarkable that genetic and metabolic modifications within a tumor mass are likely to differ from cell to cell thereby contributing to a phenotypic heterogeneity, thus accounting for therapy resistance and disease progression [134, 136]. Several studies have considered the anti-tumorigenic properties of α-KG but its mechanisms of action are still not fully understood. The anti-tumorigenic effect observed upon in vivo treatment with derivatives of α-KG has been shown not only to depend on impaired HIF1 signaling pathway but also to a much greater extent on multiple unknown side effects of α-KG on tumor growth . In this frame, it has been reported that α-KG antagonizes the effect of other oncometabolites, and might therefore be considered a tumor suppressor metabolite. Nevertheless, α-KG supplementation leads to the risk of feeding oncogenic pathways not only due to its conversion into (L)-2-HG in respiratory deficient cells but also into succinate and fumarate, on a long-term treatment . On the other hand, several human Fe(II)/α-KG-dependent dioxygenases have been investigated as possible therapeutic targets and might represent an interesting alternative strategy to render tumors more sensitive to radiotherapy and chemotherapy . A complete understanding of the α-KG-mediated interplay between metabolic and genetic reprogramming will help us to disclose a new therapeutic window in which cancer progression can be restrained. While cancer is defined as a genetic disease, there is nowadays a growing and legitimate interest in its metabolic dimension. In particular, these two aspects are increasingly recognized as being so interconnected that they are likely to represent the two edges of the same sword.
- Ca2+ :
Electron transport chain
Trimethylation of histone H3 at lysine 9
Hypoxia inducible factor 1
Inner mitochondrial membrane
Mitochondrial intermembrane space
- KM :
Mammalian target of rapamycin 1
Oxygen-dependent degradation domain
Von Hippel Lindau protein
Reactive oxygen species
Succinyl coenzyme A
Ten-eleven translocation hydroxylases
Target of rapamycin
α-Ketoglutarate dehydrogenase complex
- Δψm :
We would like to thank Dr. Rosanna Clima from the University of Bari (Italy) for her bioinformatics support.
This paper was supported by the European Commission FP7 Marie Curie ITN-317433 MEET and the Italian Ministry of Health project GR-2013-02356666 DISCO TRIP to G.Gasparre. It was also supported by the Italian Association for Cancer Research (AIRC) grants IG14242 JANEUTICS to G.Gasparre and IG17387 TOUCHME to A.M.Porcelli. G.Girolimetti is supported by a triennial AIRC fellowship “Livia Perotti”.
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RV wrote the manuscript and prepared the figures. GL, MDL, GGirolimetti, and MV have all supported this work by carrying out the literature search and summarizing the key information. GGasparre and AM Porcelli supervised the design of the review and wrote the manuscript. All authors read and approved the final manuscript.
The authors declare that they have no competing interests.
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- Hanahan D, Weinberg RA. Hallmarks of cancer: the next generation. Cell. 2011;144:646–74.PubMedView ArticleGoogle Scholar
- Warburg O, Wind F, Negelein E. The metabolism of tumors in the body. J Gen Physiol. 1927;8:519–30.PubMedPubMed CentralView ArticleGoogle Scholar
- Chen X, Qian Y, Wu S. The Warburg effect: evolving interpretations of an established concept. Free Radic Biol Med. 2015;79:253–63.PubMedView ArticleGoogle Scholar
- Marin-Valencia I, Yang C, Mashimo T, Cho S, Baek H, Yang X-L, et al. Analysis of tumor metabolism reveals mitochondrial glucose oxidation in genetically diverse human glioblastomas in the mouse brain in vivo. Cell Metab. 2012;15:827–37.PubMedPubMed CentralView ArticleGoogle Scholar
- Smolková K, Plecitá-Hlavatá L, Bellance N, Benard G, Rossignol R, Ježek P. Waves of gene regulation suppress and then restore oxidative phosphorylation in cancer cells. Int J Biochem Cell Biol. 2011;43:950–68.PubMedView ArticleGoogle Scholar
- Jose C, Bellance N, Rossignol R. Choosing between glycolysis and oxidative phosphorylation: a tumor’s dilemma? Biochim Biophys Acta. 2011;1807:552–61.PubMedView ArticleGoogle Scholar
- Tan AS, Baty JW, Berridge MV. The role of mitochondrial electron transport in tumorigenesis and metastasis. Biochim Biophys Acta. 2014;1840:1454–63.PubMedView ArticleGoogle Scholar
- Birsoy K, Possemato R, Lorbeer FK, Bayraktar EC, Thiru P, Yucel B, et al. Metabolic determinants of cancer cell sensitivity to glucose limitation and biguanides. Nature. 2014;508:108–12.PubMedPubMed CentralView ArticleGoogle Scholar
- Wolf DA. Is reliance on mitochondrial respiration a “chink in the armor” of therapy-resistant cancer? Cancer Cell. 2014;26:788–95.PubMedPubMed CentralView ArticleGoogle Scholar
- DeBerardinis RJ, Mancuso A, Daikhin E, Nissim I, Yudkoff M, Wehrli S, et al. Beyond aerobic glycolysis: transformed cells can engage in glutamine metabolism that exceeds the requirement for protein and nucleotide synthesis. Proc Natl Acad Sci U S A. 2007;104:19345–50.PubMedPubMed CentralView ArticleGoogle Scholar
- Hosios AM, Hecht VC, Danai LV, Johnson MO, Rathmell JC, Steinhauser ML, et al. Amino acids rather than glucose account for the majority of cell mass in proliferating mammalian cells. Dev Cell. 2016;36:540–9.PubMedView ArticleGoogle Scholar
- Wise DR, Ward PS, Shay JES, Cross JR, Gruber JJ, Sachdeva UM, et al. Hypoxia promotes isocitrate dehydrogenase-dependent carboxylation of α-ketoglutarate to citrate to support cell growth and viability. Proc Natl Acad Sci U S A. 2011;108:19611–6.PubMedPubMed CentralView ArticleGoogle Scholar
- Mullen AR, Wheaton WW, Jin ES, Chen P-H, Sullivan LB, Cheng T, et al. Reductive carboxylation supports growth in tumour cells with defective mitochondria. Nature. 2011;481:385–8.PubMedPubMed CentralGoogle Scholar
- Fendt S-M, Bell EL, Keibler MA, Olenchock BA, Mayers JR, Wasylenko TM, et al. Reductive glutamine metabolism is a function of the α-ketoglutarate to citrate ratio in cells. Nat Commun. 2013;4:2236.PubMedPubMed CentralView ArticleGoogle Scholar
- Reed LJ, Hackert ML. Structure-function relationships in dihydrolipoamide acyltransferases. J Biol Chem. 1990;265:8971–4.PubMedGoogle Scholar
- Strumilo S. Short-term regulation of the alpha-ketoglutarate dehydrogenase complex by energy-linked and some other effectors. Biochem Biokhimiia. 2005;70:726–9.View ArticleGoogle Scholar
- Robinson BH. Use of fibroblast and lymphoblast cultures for detection of respiratory chain defects. Methods Enzymol. 1996;264:454–64.PubMedView ArticleGoogle Scholar
- Nelson UDL, Cox UMM. Lehninger Principles of Biochemistry. New York: 7th edition. W. H. Freeman; 2017.
- Porpaczy Z, Sumegi B, Alkonyi I. Interaction between NAD-dependent isocitrate dehydrogenase, alpha-ketoglutarate dehydrogenase complex, and NADH: ubiquinone oxidoreductase. J Biol Chem. 1987;262:9509–14.PubMedGoogle Scholar
- Fukushima T, Decker RV, Anderson WM, Spivey HO. Substrate channeling of NADH and binding of dehydrogenases to complex I. J Biol Chem. 1989;264:16483–8.PubMedGoogle Scholar
- Maas E, Bisswanger H. Localization of the alpha-oxoacid dehydrogenase multienzyme complexes within the mitochondrion. FEBS Lett. 1990;277:189–90.PubMedView ArticleGoogle Scholar
- McCormack JG, Denton RM. The effects of calcium ions and adenine nucleotides on the activity of pig heart 2-oxoglutarate dehydrogenase complex. Biochem J. 1979;180:533–44.PubMedPubMed CentralView ArticleGoogle Scholar
- Lawlis VB, Roche TE. Inhibition of bovine kidney alpha-ketoglutarate dehydrogenase complex by reduced nicotinamide adenine dinucleotide in the presence or absence of calcium ion and effect of adenosine 5’-diphosphate on reduced nicotinamide adenine dinucleotide inhibition. Biochemistry (Mosc). 1981;20:2519–24.View ArticleGoogle Scholar
- Armstrong CT, Anderson JLR, Denton RM. Studies on the regulation of the human E1 subunit of the 2-oxoglutarate dehydrogenase complex, including the identification of a novel calcium-binding site. Biochem J. 2014;459:369–81.PubMedView ArticleGoogle Scholar
- Klingenberg M. The ADP, and ATP transport in mitochondria and its carrier. Biochim Biophys Acta. 2008;1778:1978–2021.PubMedView ArticleGoogle Scholar
- Birsoy K, Wang T, Chen WW, Freinkman E, Abu-Remaileh M, Sabatini DM. An essential role of the mitochondrial electron transport chain in cell proliferation is to enable aspartate synthesis. Cell. 2015;162:540–51.PubMedPubMed CentralView ArticleGoogle Scholar
- Banerjee K, Munshi S, Xu H, Frank DE, Chen H-L, Chu CT, et al. Mild mitochondrial metabolic deficits by α-ketoglutarate dehydrogenase inhibition cause prominent changes in intracellular autophagic signaling: potential role in the pathobiology of Alzheimer’s disease. Neurochem Int. 2016;96:32–45.PubMedView ArticleGoogle Scholar
- Kumar MJ, Nicholls DG, Andersen JK. Oxidative alpha-ketoglutarate dehydrogenase inhibition via subtle elevations in monoamine oxidase B levels results in loss of spare respiratory capacity: implications for Parkinson’s disease. J Biol Chem. 2003;278:46432–9.PubMedView ArticleGoogle Scholar
- Denton RM. Regulation of mitochondrial dehydrogenases by calcium ions. Biochim Biophys Acta. 2009;1787:1309–16.PubMedView ArticleGoogle Scholar
- Tarasov AI, Griffiths EJ, Rutter GA. Regulation of ATP production by mitochondrial Ca(2+). Cell Calcium. 2012;52:28–35.PubMedPubMed CentralView ArticleGoogle Scholar
- McCormack JG, Halestrap AP, Denton RM. Role of calcium ions in regulation of mammalian intramitochondrial metabolism. Physiol Rev. 1990;70:391–425.PubMedGoogle Scholar
- Santo-Domingo J, Demaurex N. Calcium uptake mechanisms of mitochondria. Biochim Biophys Acta. 2010;1797:907–12.PubMedView ArticleGoogle Scholar
- Cárdenas C, Müller M, McNeal A, Lovy A, Jaňa F, Bustos G, et al. Selective vulnerability of cancer cells by inhibition of Ca(2+) transfer from endoplasmic reticulum to mitochondria. Cell Rep. 2016;15:219–20.PubMedView ArticleGoogle Scholar
- Rottenberg H, Lee CP. Energy dependent hydrogen ion accumulation in submitochondrial particles. Biochemistry (Mosc). 1975;14:2675–80.View ArticleGoogle Scholar
- Porcelli AM, Ghelli A, Zanna C, Pinton P, Rizzuto R, Rugolo M. pH difference across the outer mitochondrial membrane measured with a green fluorescent protein mutant. Biochem Biophys Res Commun. 2005;326:799–804.PubMedView ArticleGoogle Scholar
- Lowry M, Ross BD. Activation of oxoglutarate dehydrogenase in the kidney in response to acute acidosis. Biochem J. 1980;190:771–80.PubMedPubMed CentralView ArticleGoogle Scholar
- Damaghi M, Wojtkowiak JW, Gillies RJ. pH sensing and regulation in cancer. Front Physiol. 2013;4:370.PubMedPubMed CentralView ArticleGoogle Scholar
- Santo-Domingo J, Demaurex N. Perspectives on: SGP symposium on mitochondrial physiology and medicine: the renaissance of mitochondrial pH. J Gen Physiol. 2012;139:415–23.PubMedPubMed CentralView ArticleGoogle Scholar
- Murphy MP. How mitochondria produce reactive oxygen species. Biochem J. 2009;417:1–13.PubMedView ArticleGoogle Scholar
- Nulton-Persson AC, Starke DW, Mieyal JJ, Szweda LI. Reversible inactivation of alpha-ketoglutarate dehydrogenase in response to alterations in the mitochondrial glutathione status. Biochemistry (Mosc). 2003;42:4235–42.View ArticleGoogle Scholar
- Applegate MAB, Humphries KM, Szweda LI. Reversible inhibition of alpha-ketoglutarate dehydrogenase by hydrogen peroxide: glutathionylation and protection of lipoic acid. Biochemistry (Mosc). 2008;47:473–8.View ArticleGoogle Scholar
- McLain AL, Szweda PA, Szweda LI. α-Ketoglutarate dehydrogenase: a mitochondrial redox sensor. Free Radic Res. 2011;45:29–36.PubMedView ArticleGoogle Scholar
- Starkov AA, Fiskum G, Chinopoulos C, Lorenzo BJ, Browne SE, Patel MS, et al. Mitochondrial alpha-ketoglutarate dehydrogenase complex generates reactive oxygen species. J Neurosci Off J Soc Neurosci. 2004;24:7779–88.View ArticleGoogle Scholar
- Tretter L, Adam-Vizi V. Generation of reactive oxygen species in the reaction catalyzed by alpha-ketoglutarate dehydrogenase. J Neurosci Off J Soc Neurosci. 2004;24:7771–8.View ArticleGoogle Scholar
- Quinlan CL, Goncalves RLS, Hey-Mogensen M, Yadava N, Bunik VI, Brand MD. The 2-oxoacid dehydrogenase complexes in mitochondria can produce superoxide/hydrogen peroxide at much higher rates than complex I. J Biol Chem. 2014;289:8312–25.PubMedPubMed CentralView ArticleGoogle Scholar
- Szatrowski TP, Nathan CF. Production of large amounts of hydrogen peroxide by human tumor cells. Cancer Res. 1991;51:794–8.PubMedGoogle Scholar
- Ray PD, Huang B-W, Tsuji Y. Reactive oxygen species (ROS) homeostasis and redox regulation in cellular signaling. Cell Signal. 2012;24:981–90.PubMedPubMed CentralView ArticleGoogle Scholar
- Nulton-Persson AC, Szweda LI. Modulation of mitochondrial function by hydrogen peroxide. J Biol Chem. 2001;276:23357–61.PubMedView ArticleGoogle Scholar
- Coloff JL, Murphy JP, Braun CR, Harris IS, Shelton LM, Kami K, et al. Differential glutamate metabolism in proliferating and quiescent mammary epithelial cells. Cell Metab. 2016;23:867–80.PubMedView ArticleGoogle Scholar
- Bunik VI. 2-Oxo acid dehydrogenase complexes in redox regulation. Eur J Biochem. 2003;270:1036–42.PubMedView ArticleGoogle Scholar
- Stuart SD, Schauble A, Gupta S, Kennedy AD, Keppler BR, Bingham PM, et al. A strategically designed small molecule attacks alpha-ketoglutarate dehydrogenase in tumor cells through a redox process. Cancer Metab. 2014;2:4.PubMedPubMed CentralView ArticleGoogle Scholar
- Zachar Z, Marecek J, Maturo C, Gupta S, Stuart SD, Howell K, et al. Non-redox-active lipoate derivates disrupt cancer cell mitochondrial metabolism and are potent anticancer agents in vivo. J Mol Med Berl Ger. 2011;89:1137–48.View ArticleGoogle Scholar
- Hensley CT, Wasti AT, DeBerardinis RJ. Glutamine and cancer: cell biology, physiology, and clinical opportunities. J Clin Invest. 2013;123:3678–84.PubMedPubMed CentralView ArticleGoogle Scholar
- Kuhajda FP, Jenner K, Wood FD, Hennigar RA, Jacobs LB, Dick JD, et al. Fatty acid synthesis: a potential selective target for antineoplastic therapy. Proc Natl Acad Sci U S A. 1994;91:6379–83.PubMedPubMed CentralView ArticleGoogle Scholar
- Hatzivassiliou G, Zhao F, Bauer DE, Andreadis C, Shaw AN, Dhanak D, et al. ATP citrate lyase inhibition can suppress tumor cell growth. Cancer Cell. 2005;8:311–21.PubMedView ArticleGoogle Scholar
- Sun RC, Denko NC. Hypoxic regulation of glutamine metabolism through HIF1 and SIAH2 supports lipid synthesis that is necessary for tumor growth. Cell Metab. 2014;19:285–92.PubMedPubMed CentralView ArticleGoogle Scholar
- Metallo CM, Gameiro PA, Bell EL, Mattaini KR, Yang J, Hiller K, et al. Reductive glutamine metabolism by IDH1 mediates lipogenesis under hypoxia. Nature. 2011;481:380–4.PubMedPubMed CentralGoogle Scholar
- Semenza GL. Hypoxia-inducible factor 1 (HIF-1) pathway. Sci STKE Signal Transduct Knowl Environ. 2007;2007:cm8.Google Scholar
- Kim J, Tchernyshyov I, Semenza GL, Dang CV. HIF-1-mediated expression of pyruvate dehydrogenase kinase: a metabolic switch required for cellular adaptation to hypoxia. Cell Metab. 2006;3:177–85.PubMedView ArticleGoogle Scholar
- Gameiro PA, Yang J, Metelo AM, Pérez-Carro R, Baker R, Wang Z, et al. In vivo HIF-mediated reductive carboxylation is regulated by citrate levels and sensitizes VHL-deficient cells to glutamine deprivation. Cell Metab. 2013;17:372–85.PubMedPubMed CentralView ArticleGoogle Scholar
- Mullen AR, Hu Z, Shi X, Jiang L, Boroughs LK, Kovacs Z, et al. Oxidation of alpha-ketoglutarate is required for reductive carboxylation in cancer cells with mitochondrial defects. Cell Rep. 2014;7:1679–90.PubMedPubMed CentralView ArticleGoogle Scholar
- Calabrese C, Iommarini L, Kurelac I, Calvaruso MA, Capristo M, Lollini P-L, et al. Respiratory complex I is essential to induce a Warburg profile in mitochondria-defective tumor cells. Cancer Metab. 2013;1:11.PubMedPubMed CentralView ArticleGoogle Scholar
- Sullivan LB, Chandel NS. Mitochondrial reactive oxygen species and cancer. Cancer Metab. 2014;2:17. doi:10.1186/2049-3002-2-17.PubMedPubMed CentralView ArticleGoogle Scholar
- Armstrong JS, Whiteman M, Yang H, Jones DP. The redox regulation of intermediary metabolism by a superoxide-aconitase rheostat. BioEssays News Rev Mol Cell Dev Biol. 2004;26:894–900.View ArticleGoogle Scholar
- Smolková K, Bellance N, Scandurra F, Génot E, Gnaiger E, Plecitá-Hlavatá L, et al. Mitochondrial bioenergetic adaptations of breast cancer cells to aglycemia and hypoxia. J Bioenerg Biomembr. 2010;42:55–67.PubMedView ArticleGoogle Scholar
- Martin-Montalvo A, de Cabo R. Mitochondrial metabolic reprogramming induced by calorie restriction. Antioxid Redox Signal. 2013;19:310–20.PubMedPubMed CentralView ArticleGoogle Scholar
- Chin RM, Fu X, Pai MY, Vergnes L, Hwang H, Deng G, et al. The metabolite α-ketoglutarate extends lifespan by inhibiting ATP synthase and TOR. Nature. 2014;510:397–401.PubMedPubMed CentralGoogle Scholar
- Brugnara L, Vinaixa M, Murillo S, Samino S, Rodriguez MA, Beltran A, et al. Metabolomics approach for analyzing the effects of exercise in subjects with type 1 diabetes mellitus. PLoS One. 2012;7:e40600.PubMedPubMed CentralView ArticleGoogle Scholar
- Zu XL, Guppy M. Cancer metabolism: facts, fantasy, and fiction. Biochem Biophys Res Commun. 2004;313:459–65.PubMedView ArticleGoogle Scholar
- Durán RV, Oppliger W, Robitaille AM, Heiserich L, Skendaj R, Gottlieb E, et al. Glutaminolysis activates Rag-mTORC1 signaling. Mol Cell. 2012;47:349–58.PubMedView ArticleGoogle Scholar
- Durán RV, MacKenzie ED, Boulahbel H, Frezza C, Heiserich L, Tardito S, et al. HIF-independent role of prolyl hydroxylases in the cellular response to amino acids. Oncogene. 2013;32:4549–56.PubMedView ArticleGoogle Scholar
- Durán RV, Hall MN. Glutaminolysis feeds mTORC1. Cell Cycle (Georgetown, Texas). 2012;11:4107–8.View ArticleGoogle Scholar
- Altman BJ, Stine ZE, Dang CV. From Krebs to clinic: glutamine metabolism to cancer therapy. Nat Rev Cancer. 2016;16:619–34.PubMedView ArticleGoogle Scholar
- Fu X, Chin RM, Vergnes L, Hwang H, Deng G, Xing Y, et al. 2-Hydroxyglutarate inhibits ATP synthase and mTOR signaling. Cell Metab. 2015;22:508–15.PubMedPubMed CentralView ArticleGoogle Scholar
- Morin A, Letouzé E, Gimenez-Roqueplo A-P, Favier J. Oncometabolites-driven tumorigenesis: from genetics to targeted therapy. Int J Cancer. 2014;135:2237–48.PubMedView ArticleGoogle Scholar
- Dang L, White DW, Gross S, Bennett BD, Bittinger MA, Driggers EM, et al. Cancer-associated IDH1 mutations produce 2-hydroxyglutarate. Nature. 2009;462:739–44.PubMedPubMed CentralView ArticleGoogle Scholar
- Loenarz C, Schofield CJ. Expanding chemical biology of 2-oxoglutarate oxygenases. Nat Chem Biol. 2008;4:152–6.PubMedView ArticleGoogle Scholar
- Rose NR, McDonough MA, King ONF, Kawamura A, Schofield CJ. Inhibition of 2-oxoglutarate dependent oxygenases. Chem Soc Rev. 2011;40:4364–97.PubMedView ArticleGoogle Scholar
- McDonough MA, Loenarz C, Chowdhury R, Clifton IJ, Schofield CJ. Structural studies on human 2-oxoglutarate dependent oxygenases. Curr Opin Struct Biol. 2010;20:659–72.PubMedView ArticleGoogle Scholar
- Pan Y, Mansfield KD, Bertozzi CC, Rudenko V, Chan DA, Giaccia AJ, et al. Multiple factors affecting cellular redox status and energy metabolism modulate hypoxia-inducible factor prolyl hydroxylase activity in vivo and in vitro. Mol Cell Biol. 2007;27:912–25.PubMedView ArticleGoogle Scholar
- Flashman E, Hoffart LM, Hamed RB, Bollinger JM, Krebs C, Schofield CJ. Evidence for the slow reaction of hypoxia-inducible factor prolyl hydroxylase 2 with oxygen. FEBS J. 2010;277:4089–99.PubMedPubMed CentralView ArticleGoogle Scholar
- Tennant DA, Frezza C, MacKenzie ED, Nguyen QD, Zheng L, Selak MA, et al. Reactivating HIF prolyl hydroxylases under hypoxia results in metabolic catastrophe and cell death. Oncogene. 2009;28:4009–21.PubMedView ArticleGoogle Scholar
- Selak MA, Armour SM, MacKenzie ED, Boulahbel H, Watson DG, Mansfield KD, et al. Succinate links TCA cycle dysfunction to oncogenesis by inhibiting HIF-alpha prolyl hydroxylase. Cancer Cell. 2005;7:77–85.PubMedView ArticleGoogle Scholar
- Xu W, Yang H, Liu Y, Yang Y, Wang P, Kim S-H, et al. Oncometabolite 2-hydroxyglutarate is a competitive inhibitor of α-ketoglutarate-dependent dioxygenases. Cancer Cell. 2011;19:17–30.PubMedPubMed CentralView ArticleGoogle Scholar
- Dalgard CL, Lu H, Mohyeldin A, Verma A. Endogenous 2-oxoacids differentially regulate expression of oxygen sensors. Biochem J. 2004;380(Pt 2):419–24.PubMedPubMed CentralView ArticleGoogle Scholar
- Hewitson KS, Liénard BMR, McDonough MA, Clifton IJ, Butler D, Soares AS, et al. Structural and mechanistic studies on the inhibition of the hypoxia-inducible transcription factor hydroxylases by tricarboxylic acid cycle intermediates. J Biol Chem. 2007;282:3293–301.PubMedView ArticleGoogle Scholar
- Pollard PJ, Brière JJ, Alam NA, Barwell J, Barclay E, Wortham NC, et al. Accumulation of Krebs cycle intermediates and over-expression of HIF1alpha in tumours which result from germline FH and SDH mutations. Hum Mol Genet. 2005;14:2231–9.PubMedView ArticleGoogle Scholar
- Koivunen P, Hirsilä M, Remes AM, Hassinen IE, Kivirikko KI, Myllyharju J. Inhibition of hypoxia-inducible factor (HIF) hydroxylases by citric acid cycle intermediates: possible links between cell metabolism and stabilization of HIF. J Biol Chem. 2007;282:4524–32.PubMedView ArticleGoogle Scholar
- MacKenzie ED, Selak MA, Tennant DA, Payne LJ, Crosby S, Frederiksen CM, et al. Cell-permeating alpha-ketoglutarate derivatives alleviate pseudohypoxia in succinate dehydrogenase-deficient cells. Mol Cell Biol. 2007;27:3282–9.PubMedPubMed CentralView ArticleGoogle Scholar
- Porcelli AM, Ghelli A, Ceccarelli C, Lang M, Cenacchi G, Capristo M, et al. The genetic and metabolic signature of oncocytic transformation implicates HIF1alpha destabilization. Hum Mol Genet. 2010;19:1019–32.PubMedView ArticleGoogle Scholar
- Gasparre G, Kurelac I, Capristo M, Iommarini L, Ghelli A, Ceccarelli C, et al. A mutation threshold distinguishes the antitumorigenic effects of the mitochondrial gene MTND1, an oncojanus function. Cancer Res. 2011;71:6220–9.PubMedView ArticleGoogle Scholar
- Iommarini L, Kurelac I, Capristo M, Calvaruso MA, Giorgio V, Bergamini C, et al. Different mtDNA mutations modify tumor progression in dependence of the degree of respiratory complex I impairment. Hum Mol Genet. 2014;23:1453–66.PubMedView ArticleGoogle Scholar
- Oldham WM, Clish CB, Yang Y, Loscalzo J. Hypoxia-mediated increases in L-2-hydroxyglutarate coordinate the metabolic response to reductive stress. Cell Metab. 2015;22:291–303.PubMedPubMed CentralView ArticleGoogle Scholar
- Intlekofer AM, Dematteo RG, Venneti S, Finley LWS, Lu C, Judkins AR, et al. Hypoxia induces production of L-2-hydroxyglutarate. Cell Metab. 2015;22:304–11.PubMedPubMed CentralView ArticleGoogle Scholar
- Worth AJ, Gillespie KP, Mesaros C, Guo L, Basu SS, Snyder NW, et al. Rotenone stereospecifically increases (S)-2-hydroxyglutarate in SH-SY5Y neuronal cells. Chem Res Toxicol. 2015;28:948–54.PubMedPubMed CentralView ArticleGoogle Scholar
- Koivunen P, Lee S, Duncan CG, Lopez G, Lu G, Ramkissoon S, et al. Transformation by the (R)-enantiomer of 2-hydroxyglutarate linked to EGLN activation. Nature. 2012;483:484–8.PubMedPubMed CentralView ArticleGoogle Scholar
- Harris AL. A new hydroxy metabolite of 2-oxoglutarate regulates metabolism in hypoxia. Cell Metab. 2015;22:198–200.PubMedView ArticleGoogle Scholar
- Fan J, Teng X, Liu L, Mattaini KR, Looper RE, Vander Heiden MG, et al. Human phosphoglycerate dehydrogenase produces the oncometabolite D-2-hydroxyglutarate. ACS Chem Biol. 2015;10:510–6.PubMedView ArticleGoogle Scholar
- Sullivan LB, Gui DY, Hosios AM, Bush LN, Freinkman E, Vander Heiden MG. Supporting aspartate biosynthesis is an essential function of respiration in proliferating cells. Cell. 2015;162:552–63.PubMedPubMed CentralView ArticleGoogle Scholar
- Linster CL, Van Schaftingen E, Hanson AD. Metabolite damage and its repair or pre-emption. Nat Chem Biol. 2013;9:72–80.PubMedView ArticleGoogle Scholar
- Chandel NS, McClintock DS, Feliciano CE, Wood TM, Melendez JA, Rodriguez AM, et al. Reactive oxygen species generated at mitochondrial complex III stabilize hypoxia-inducible factor-1alpha during hypoxia: a mechanism of O2 sensing. J Biol Chem. 2000;275:25130–8.PubMedView ArticleGoogle Scholar
- Burr SP, Costa ASH, Grice GL, Timms RT, Lobb IT, Freisinger P, et al. Mitochondrial protein lipoylation and the 2-oxoglutarate dehydrogenase complex controls HIF1α stability in aerobic conditions. Cell Metab. 2016;24:740-52. doi:10.1016/j.cmet.2016.09.015.
- Mazure NM, Pouysségur J. Atypical BH3-domains of BNIP3 and BNIP3L lead to autophagy in hypoxia. Autophagy. 2009;5:868–9.PubMedView ArticleGoogle Scholar
- Feinberg AP, Koldobskiy MA, Göndör A. Epigenetic modulators, modifiers and mediators in cancer aetiology and progression. Nat Rev Genet. 2016;17:284–99.PubMedPubMed CentralView ArticleGoogle Scholar
- Christensen BC, Marsit CJ, Houseman EA, Godleski JJ, Longacker JL, Zheng S, et al. Differentiation of lung adenocarcinoma, pleural mesothelioma, and nonmalignant pulmonary tissues using DNA methylation profiles. Cancer Res. 2009;69:6315–21.PubMedPubMed CentralView ArticleGoogle Scholar
- Toyota M, Ahuja N, Ohe-Toyota M, Herman JG, Baylin SB, Issa JP. CpG island methylator phenotype in colorectal cancer. Proc Natl Acad Sci U S A. 1999;96:8681–6.PubMedPubMed CentralView ArticleGoogle Scholar
- Weisenberger DJ, Siegmund KD, Campan M, Young J, Long TI, Faasse MA, et al. CpG island methylator phenotype underlies sporadic microsatellite instability and is tightly associated with BRAF mutation in colorectal cancer. Nat Genet. 2006;38:787–93.PubMedView ArticleGoogle Scholar
- Figueroa ME, Abdel-Wahab O, Lu C, Ward PS, Patel J, Shih A, et al. Leukemic IDH1 and IDH2 mutations result in a hypermethylation phenotype, disrupt TET2 function, and impair hematopoietic differentiation. Cancer Cell. 2010;18:553–67.PubMedPubMed CentralView ArticleGoogle Scholar
- Noushmehr H, Weisenberger DJ, Diefes K, Phillips HS, Pujara K, Berman BP, et al. Identification of a CpG island methylator phenotype that defines a distinct subgroup of glioma. Cancer Cell. 2010;17:510–22.PubMedPubMed CentralView ArticleGoogle Scholar
- Zouridis H, Deng N, Ivanova T, Zhu Y, Wong B, Huang D, et al. Methylation subtypes and large-scale epigenetic alterations in gastric cancer. Sci Transl Med. 2012;4:156ra140.PubMedView ArticleGoogle Scholar
- Mack SC, Witt H, Piro RM, Gu L, Zuyderduyn S, Stütz AM, et al. Epigenomic alterations define lethal CIMP-positive ependymomas of infancy. Nature. 2014;506:445–50.PubMedPubMed CentralView ArticleGoogle Scholar
- Adam J, Yang M, Soga T, Pollard PJ. Rare insights into cancer biology. Oncogene. 2014;33:2547–56.PubMedView ArticleGoogle Scholar
- Loenarz C, Schofield CJ. Physiological and biochemical aspects of hydroxylations and demethylations catalyzed by human 2-oxoglutarate oxygenases. Trends Biochem Sci. 2011;36:7–18.PubMedView ArticleGoogle Scholar
- Kaelin WG, McKnight SL. Influence of metabolism on epigenetics and disease. Cell. 2013;153:56–69.PubMedPubMed CentralView ArticleGoogle Scholar
- Chowdhury R, Yeoh KK, Tian Y-M, Hillringhaus L, Bagg EA, Rose NR, et al. The oncometabolite 2-hydroxyglutarate inhibits histone lysine demethylases. EMBO Rep. 2011;12:463–9.PubMedPubMed CentralView ArticleGoogle Scholar
- Lu C, Ward PS, Kapoor GS, Rohle D, Turcan S, Abdel-Wahab O, et al. IDH mutation impairs histone demethylation and results in a block to cell differentiation. Nature. 2012;483:474–8.PubMedPubMed CentralView ArticleGoogle Scholar
- Losman J-A, Kaelin WG. What a difference a hydroxyl makes: mutant IDH, (R)-2-hydroxyglutarate, and cancer. Genes Dev. 2013;27:836–52.PubMedPubMed CentralView ArticleGoogle Scholar
- Moroni I, Bugiani M, D’Incerti L, Maccagnano C, Rimoldi M, Bissola L, et al. L-2-hydroxyglutaric aciduria and brain malignant tumors: a predisposing condition? Neurology. 2004;62:1882–4.PubMedView ArticleGoogle Scholar
- Shim E-H, Livi CB, Rakheja D, Tan J, Benson D, Parekh V, et al. L-2-Hydroxyglutarate: an epigenetic modifier and putative oncometabolite in renal cancer. Cancer Discov. 2014;4:1290–8.PubMedPubMed CentralView ArticleGoogle Scholar
- Cervera AM, Bayley J-P, Devilee P, McCreath KJ. Inhibition of succinate dehydrogenase dysregulates histone modification in mammalian cells. Mol Cancer. 2009;8:89.PubMedPubMed CentralView ArticleGoogle Scholar
- Xiao M, Yang H, Xu W, Ma S, Lin H, Zhu H, et al. Inhibition of α-KG-dependent histone and DNA demethylases by fumarate and succinate that are accumulated in mutations of FH and SDH tumor suppressors. Genes Dev. 2012;26:1326–38.PubMedPubMed CentralView ArticleGoogle Scholar
- Letouzé E, Martinelli C, Loriot C, Burnichon N, Abermil N, Ottolenghi C, et al. SDH mutations establish a hypermethylator phenotype in paraganglioma. Cancer Cell. 2013;23:739–52.PubMedView ArticleGoogle Scholar
- Mason EF, Hornick JL. Succinate dehydrogenase deficiency is associated with decreased 5-hydroxymethylcytosine production in gastrointestinal stromal tumors: implications for mechanisms of tumorigenesis. Mod Pathol Off J U S Can Acad Pathol Inc. 2013;26:1492–7.Google Scholar
- Sciacovelli M, Gonçalves E, Johnson TI, Zecchini VR, da Costa ASH, Gaude E, et al. Fumarate is an epigenetic modifier that elicits epithelial-to-mesenchymal transition. Nature. 2016;537:544–7.PubMedView ArticleGoogle Scholar
- Laukka T, Mariani CJ, Ihantola T, Cao JZ, Hokkanen J, Kaelin WG, et al. Fumarate and succinate regulate expression of hypoxia-inducible genes via TET enzymes. J Biol Chem. 2016;291:4256–65.PubMedView ArticleGoogle Scholar
- Carey BW, Finley LWS, Cross JR, Allis CD, Thompson CB. Intracellular α-ketoglutarate maintains the pluripotency of embryonic stem cells. Nature. 2015;518:413–6.PubMedView ArticleGoogle Scholar
- Turner BM. Open chromatin and hypertranscription in embryonic stem cells. Cell Stem Cell. 2008;2:408–10.PubMedView ArticleGoogle Scholar
- Thienpont B, Steinbacher J, Zhao H, D’Anna F, Kuchnio A, Ploumakis A, et al. Tumour hypoxia causes DNA hypermethylation by reducing TET activity. Nature. 2016;537:63–8.PubMedView ArticleGoogle Scholar
- Beyer S, Kristensen MM, Jensen KS, Johansen JV, Staller P. The histone demethylases JMJD1A and JMJD2B are transcriptional targets of hypoxia-inducible factor HIF. J Biol Chem. 2008;283:36542–52.PubMedPubMed CentralView ArticleGoogle Scholar
- Pollard PJ, Loenarz C, Mole DR, McDonough MA, Gleadle JM, Schofield CJ, et al. Regulation of Jumonji-domain-containing histone demethylases by hypoxia-inducible factor (HIF)-1alpha. Biochem J. 2008;416:387–94.PubMedView ArticleGoogle Scholar
- Luo W, Chang R, Zhong J, Pandey A, Semenza GL. Histone demethylase JMJD2C is a coactivator for hypoxia-inducible factor 1 that is required for breast cancer progression. Proc Natl Acad Sci U S A. 2012;109:E3367–76.PubMedPubMed CentralView ArticleGoogle Scholar
- Mimura I, Nangaku M, Kanki Y, Tsutsumi S, Inoue T, Kohro T, et al. Dynamic change of chromatin conformation in response to hypoxia enhances the expression of GLUT3 (SLC2A3) by cooperative interaction of hypoxia-inducible factor 1 and KDM3A. Mol Cell Biol. 2012;32:3018–32.PubMedPubMed CentralView ArticleGoogle Scholar
- Mariani CJ, Vasanthakumar A, Madzo J, Yesilkanal A, Bhagat T, Yu Y, et al. TET1-mediated hydroxymethylation facilitates hypoxic gene induction in neuroblastoma. Cell Rep. 2014;7:1343–52.PubMedPubMed CentralView ArticleGoogle Scholar
- Pan M, Reid MA, Lowman XH, Kulkarni RP, Tran TQ, Liu X, et al. Regional glutamine deficiency in tumours promotes dedifferentiation through inhibition of histone demethylation. Nat Cell Biol. 2016;18:1090–101.PubMedView ArticleGoogle Scholar
- Xu W, Wang F, Yu Z, Xin F. Epigenetics and cellular metabolism. Genet Epigenet. 2016;8:43–51.PubMedPubMed CentralGoogle Scholar
- Meacham CE, Morrison SJ. Tumour heterogeneity and cancer cell plasticity. Nature. 2013;501:328–37.PubMedPubMed CentralView ArticleGoogle Scholar
- Kuo C-Y, Cheng C-T, Hou P, Lin Y-P, Ma H, Chung Y, et al. HIF-1-alpha links mitochondrial perturbation to the dynamic acquisition of breast cancer tumorigenicity. Oncotarget. 2016;7:34052–69.PubMedPubMed CentralGoogle Scholar