Hif-1α Knockdown Reduces Glycolytic Metabolism and Induces Cell Death of Human Synovial Fibroblasts Under Normoxic Conditions.

Increased glycolysis and HIF-1α activity are characteristics of cells under hypoxic or inflammatory conditions. Besides, in normal O2 environments, elevated rates of glycolysis support critical cellular mechanisms such as cell survival. The purpose of this study was to analyze the contribution of HIF-1α to the energy metabolism and survival of human synovial fibroblasts (SF) under normoxic conditions. HIF-1α was silenced using lentiviral vectors or small-interfering RNA (siRNA) duplexes. Expression analysis by qRT-PCR and western blot of known HIF-1α target genes in hypoxia demonstrated the presence of functional HIF-1α in normoxic SF and confirmed the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) as a HIF-1α target even in normoxia. HIF-1α silencing induced apoptotic cell death in cultured SF and, similarly, treatment with glycolytic, but not with OXPHOS inhibitors, induced SF death. Finally, in vivo HIF-1α targeting by siRNA showed a significant reduction in the viability of human SF engrafted into a murine air pouch. Our results demonstrate that SF are highly dependent on glycolytic metabolism and that HIF-1α plays a regulatory role in glycolysis even under aerobic conditions. Local targeting of HIF-1α provides a feasible strategy to reduce SF hyperplasia in chronic arthritic diseases.

Plasma metabolome and skin proteins in Charcot-Marie-Tooth 1A patients.

OBJECTIVE: Charcot-Marie-Tooth 1A (CMT1A) disease is the most common inherited neuropathy that lacks of therapy and of molecular markers to assess disease severity. Herein, we have pursued the identification of potential biomarkers in plasma samples and skin biopsies that could define the phenotype of CMT1A patients at mild (Mi), moderate (Mo) and severe (Se) stages of disease as assessed by the CMT neuropathy score to contribute to the understanding of CMT pathophysiology and eventually inform of the severity of the disease. METHODS: We have used: (i) a high-throughput untargeted metabolomic approach of plasma samples in a cohort of 42 CMT1A patients and 15 healthy controls (CRL) using ultrahigh liquid chromatography coupled to mass spectrometry and (ii) reverse phase protein microarrays to quantitate the expression of some proteins of energy metabolism and of the antioxidant response in skin biopsies of a cohort of 70 CMT1A patients and 13 healthy controls. RESULTS: The metabolomic approach identified 194 metabolites with significant differences among the four groups (Mi, Mo, Se, CRL) of samples. A multivariate Linear Discriminant Analysis model using 12 metabolites afforded the correct classification of the samples. These metabolites indicate an increase in protein catabolism and the mobilization of membrane lipids involved in signaling inflammation with severity of CMT1A. A concurrent depletion of leucine, which is required for the biogenesis of the muscle, is also observed in the patients. Protein expression in skin biopsies indicates early loss of mitochondrial and antioxidant proteins in patients' biopsies. CONCLUSION: The findings indicate that CMT1A disease is associated with a metabolic state resembling inflammation and sarcopenia suggesting that it might represent a potential target to prevent the nerve and muscle wasting phenotype in these patients. The observed changes in metabolites could be useful as potential biomarkers of CMT1A disease after appropriate validation in future longitudinal studies.

Pyruvate kinase M2 and the mitochondrial ATPase Inhibitory Factor 1 provide novel biomarkers of dermatomyositis: a metabolic link to oncogenesis.

BACKGROUND: Metabolic alterations play a role in the development of inflammatory myopathies (IMs). Herein, we have investigated through a multiplex assay whether proteins of energy metabolism could provide biomarkers of IMs. METHODS: A cohort of thirty-two muscle biopsies and forty plasma samples comprising polymyositis (PM), dermatomyositis (DM) and sporadic inclusion body myositis (sIBM) and control donors was interrogated with monoclonal antibodies against proteins of energy metabolism using reverse phase protein microarrays (RPPA). RESULTS: When compared to controls the expression of the proteins is not significantly affected in the muscle of PM patients. However, the expression of ß-actin is significantly increased in DM and sIBM in consistence with muscle and fiber regeneration. Concurrently, the expression of some proteins involved in glucose metabolism displayed a significant reduction in muscle of sIBM suggesting a repression of glycolytic metabolism in these patients. In contrasts to these findings, the expression of the glycolytic pyruvate kinase isoform M2 (PKM2) and of the mitochondrial ATPase Inhibitor Factor 1 (IF1) and Hsp60 were significantly augmented in DM when compared to other IMs in accordance with a metabolic shift prone to cancer development. PKM2 alone or in combination with other biomarkers allowed the discrimination of control and IMs with very high (>95%) sensitivity and specificity. Unfortunately, plasma levels of PKM2 were not significantly altered in DM patients to recommend its use as a non-invasive biomarker of the disease. CONCLUSIONS: Expression of proteins of energy metabolism in muscle enabled discrimination of patients with IMs. RPPA identified the glycolysis promoting PKM2 and IF1 proteins as specific biomarkers of dermatomyositis, providing a biochemical link of this IM with oncogenesis.

Down-regulation of oxidative phosphorylation in the liver by expression of the ATPase inhibitory factor 1 induces a tumor-promoter metabolic state.

The ATPase Inhibitory Factor 1 (IF1) is an inhibitor of the mitochondrial H+-ATP synthase that regulates the activity of both oxidative phosphorylation (OXPHOS) and cell death. Here, we have developed transgenic Tet-On and Tet-Off mice that express a mutant active form of hIF1 in the hepatocytes to restrain OXPHOS in the liver to investigate the relevance of mitochondrial activity in hepatocarcinogenesis. The expression of hIF1 promotes the inhibition of OXPHOS in both Tet-On and Tet-Off mouse models and induces a state of metabolic preconditioning guided by the activation of the stress kinases AMPK and p38 MAPK. Expression of the transgene significantly augmented proliferation and apoptotic resistance of carcinoma cells, which contributed to an enhanced diethylnitrosamine-induced liver carcinogenesis. Moreover, the expression of hIF1 also diminished acetaminophen-induced apoptosis, which is unrelated to differences in permeability transition pore opening. Mechanistically, cell survival in hIF1-preconditioned hepatocytes results from a nuclear factor-erythroid 2-related factor (Nrf2)-guided antioxidant response. The results emphasize in vivo that a metabolic phenotype with a restrained OXPHOS in the liver is prone to the development of cancer.

PKA Phosphorylates the ATPase Inhibitory Factor 1 and Inactivates Its Capacity to Bind and Inhibit the Mitochondrial H(+)-ATP Synthase.

The mitochondrial H(+)-ATP synthase synthesizes most of cellular ATP requirements by oxidative phosphorylation (OXPHOS). The ATPase Inhibitory Factor 1 (IF1) is known to inhibit the hydrolase activity of the H(+)-ATP synthase in situations that compromise OXPHOS. Herein, we demonstrate that phosphorylation of S39 in IF1 by mitochondrial protein kinase A abolishes its capacity to bind the H(+)-ATP synthase. Only dephosphorylated IF1 binds and inhibits both the hydrolase and synthase activities of the enzyme. The phosphorylation status of IF1 regulates the flux of aerobic glycolysis and ATP production through OXPHOS in hypoxia and during the cell cycle. Dephosphorylated IF1 is present in human carcinomas. Remarkably, mouse heart contains a large fraction of dephosphorylated IF1 that becomes phosphorylated and inactivated upon in vivo ß-adrenergic stimulation. Overall, we demonstrate the essential function of the phosphorylation of IF1 in regulating energy metabolism and speculate that dephosho-IF1 might play a role in signaling mitohormesis.

Adalimumab Reduces Photoreceptor Cell Death in A Mouse Model of Retinal Degeneration.

Growing evidence suggests that inflammation is involved in the progression of retinitis pigmentosa (RP) both in patients and in animal models. The aim of this study was to investigate the effect of Adalimumab, a monoclonal anti-TNFα antibody, on retinal degeneration in a murine model of human autosomal recessive RP, the rd10 mice at postnatal day (P) 18. In our housing conditions, rd10 retinas were seriously damaged at P18. Adalimumab reduced photoreceptor cell death, as determined by scoring the number of TUNEL-positive cells. In addition, nuclear poly (ADP) ribose (PAR) content, an indirect measure of PAR polymerase (PARP) activity, was also reduced after treatment. The blockade of TNFα ameliorated reactive gliosis, as visualized by decreased GFAP and IBA1 immunolabelling (Müller cell and microglial markers, respectively) and decreased up-regulation of TNFα gene expression. Adalimumab also improved antioxidant response by restoring total antioxidant capacity and superoxide dismutase activity. Finally, we observed that Adalimumab normalized energetic and metabolic pattern in rd10 mouse retinas. Our study suggests that the TNFα blockade could be a successful therapeutic approach to increase photoreceptor survival during the progression of RP. Further studies are needed to characterize its effect along the progression of the disease.

Quantitative analysis of proteins of metabolism by reverse phase protein microarrays identifies potential biomarkers of rare neuromuscular diseases.

BACKGROUND: Muscle diseases have been associated with changes in the expression of proteins involved in energy metabolism. To this aim we have developed a number of monoclonal antibodies against proteins of energy metabolism. METHODS: Herein, we have used Reverse Phase Protein Microarrays (RPMA), a high throughput technique, to investigate quantitative changes in protein expression with the aim of identifying potential biomarkers in rare neuromuscular diseases. A cohort of 73 muscle biopsies that included samples from patients diagnosed of Duchenne (DMD), Becker (BMD), symptomatic forms of DMD and BMD in female carriers (Xp21 Carriers), Limb Girdle Muscular Dystrophy Type 2C (LGMD2C), neuronal ceroid lipofuscinosis (NCL), glycogenosis type V (Mc Ardle disease), isolated mitochondrial complex I deficiency, intensive care unit myopathy and control donors were investigated. The nineteen proteins of energy metabolism studied included members of the mitochondrial oxidation of pyruvate, the tricarboxylic acid cycle, ß-oxidation of fatty acids, electron transport and oxidative phosphorylation, glycogen metabolism, glycolysis and oxidative stress using highly specific antibodies. RESULTS: The results indicate that the phenotype of energy metabolism offers potential biomarkers that could be implemented to refine the understanding of the biological principles of rare diseases and, eventually, the management of these patients. CONCLUSIONS: We suggest that some biomarkers of energy metabolism could be translated into the clinics to contribute to the improvement of the clinical handling of patients affected by rare diseases.

Lack of GDAP1 induces neuronal calcium and mitochondrial defects in a knockout mouse model of charcot-marie-tooth neuropathy.

Mutations in GDAP1, which encodes protein located in the mitochondrial outer membrane, cause axonal recessive (AR-CMT2), axonal dominant (CMT2K) and demyelinating recessive (CMT4A) forms of Charcot-Marie-Tooth (CMT) neuropathy. Loss of function recessive mutations in GDAP1 are associated with decreased mitochondrial fission activity, while dominant mutations result in impairment of mitochondrial fusion with increased production of reactive oxygen species and susceptibility to apoptotic stimuli. GDAP1 silencing in vitro reduces Ca2+ inflow through store-operated Ca2+ entry (SOCE) upon mobilization of endoplasmic reticulum (ER) Ca2+, likely in association with an abnormal distribution of the mitochondrial network. To investigate the functional consequences of lack of GDAP1 in vivo, we generated a Gdap1 knockout mouse. The affected animals presented abnormal motor behavior starting at the age of 3 months. Electrophysiological and biochemical studies confirmed the axonal nature of the neuropathy whereas histopathological studies over time showed progressive loss of motor neurons (MNs) in the anterior horn of the spinal cord and defects in neuromuscular junctions. Analyses of cultured embryonic MNs and adult dorsal root ganglia neurons from affected animals demonstrated large and defective mitochondria, changes in the ER cisternae, reduced acetylation of cytoskeletal α-tubulin and increased autophagy vesicles. Importantly, MNs showed reduced cytosolic calcium and SOCE response. The development and characterization of the GDAP1 neuropathy mice model thus revealed that some of the pathophysiological changes present in axonal recessive form of the GDAP1-related CMT might be the consequence of changes in the mitochondrial network biology and mitochondria-endoplasmic reticulum interaction leading to abnormalities in calcium homeostasis.

Sensitivity to anti-Fas is independent of increased cathepsin D activity and adrenodoxin reductase expression occurring in NOS-3 overexpressing HepG2 cells.

Stable overexpression of endothelial nitric oxide synthase (NOS-3) in HepG2 cells (4TO-NOS) leads to increased nitro-oxidative stress and upregulation of the cell death mediators p53 and Fas. Thus, NOS-3 overexpression has been suggested as a useful antiproliferative mechanism in hepatocarcinoma cells. We aimed to identify the underlying mechanism of cell death induced by NOS-3 overexpression at basal conditions and with anti-Fas treatment. The intracellular localization of NOS-3, the nitro-oxidative stress and the mitochondrial activity were analysed. In addition, the protein expression profile in 4TO-NOS was screened for differentially expressed proteins potentially involved in the induction of apoptosis. NOS-3 localization in the mitochondrial outer membrane was not associated with changes in the respiratory cellular capacity, but was related to the mitochondrial biogenesis increase and with a higher protein expression of mitochondrial complex IV. Nitro-oxidative stress and cell death in NOS-3 overexpressing cells occurred with the expression increase of pro-apoptotic genes and a higher expression/activity of the enzymes adrenodoxin reductase mitochondrial (AR) and cathepsin D (CatD). CatD overexpression in 4TO-NOS was related to the apoptosis induction independently of its catalytic activity. In addition, CatD activity inhibition by pepstatin A was not effective in blocking apoptosis induced by anti-Fas. In summary, NOS-3 overexpression resulted in an increased sensitivity to anti-Fas induced cell death, independently of AR expression and CatD activity.

Short-term exposure of nontumorigenic human bronchial epithelial cells to carcinogenic chromium(VI) compromises their respiratory capacity and alters their bioenergetic signature.

Previous studies on the impact of hexavalent chromium [Cr(VI)] on mammalian cell energetics revealed alterations suggestive of a shift to a more fermentative metabolism. Aiming at a more defined understanding of the metabolic effects of Cr(VI) and of their molecular basis, we assessed the impact of a mild Cr(VI) exposure on critical bioenergetic parameters (lactate production, oxygen consumption and intracellular ATP levels). Cells derived from normal human bronchial epithelium (BEAS-2B cell line), the main in vivo target of Cr(VI) carcinogenicity, were subjected for 48 h to 1 µM Cr(VI). We could confirm a shift to a more fermentative metabolism, resulting from the simultaneous inhibition of respiration and stimulation of glycolysis. This shift was accompanied by a decrease in the protein levels of the catalytic subunit (subunit ß) of the mitochondrial H(+)-ATP synthase (ß-F1-ATPase) and a concomitant marked increase in those of glyceraldehyde-3-phosphate dehydrogenase (GAPDH). The corresponding alteration in the ß-F1-ATPase/GAPDH protein ratio (viewed as a bioenergetic signature) upon Cr(VI) exposure was in agreement with the observed attenuation of cellular respiration and enhancement of glycolytic flux. Altogether, these results constitute a novel finding in terms of the molecular mechanisms of Cr(VI) effects.

Degradation of IF1 controls energy metabolism during osteogenic differentiation of stem cells.

Differentiation of human mesenchymal stem cells (hMSCs) requires the rewiring of energy metabolism. Herein, we demonstrate that the ATPase inhibitory factor 1 (IF1) is expressed in hMSCs and in prostate and colon stem cells but is not expressed in the differentiated cells. IF1 inhibits oxidative phosphorylation and regulates the activity of aerobic glycolysis in hMSCs. Silencing of IF1 in hMSCs mimics the metabolic changes observed in osteocytes and accelerates cellular differentiation. Activation of IF1 degradation acts as the switch that regulates energy metabolism during differentiation. We conclude that IF1 is a stemness marker important for maintaining the quiescence state.

Mitochondria-mediated energy adaption in cancer: the H(+)-ATP synthase-geared switch of metabolism in human tumors.

SIGNIFICANCE: Since the signing of the National Cancer Act in 1971, cancer still remains a major cause of death despite significant progresses made in understanding the biology and treatment of the disease. After many years of ostracism, the peculiar energy metabolism of tumors has been recognized as an additional phenotypic trait of the cancer cell. RECENT ADVANCES: While the enhanced aerobic glycolysis of carcinomas has already been translated to bedside for precise tumor imaging and staging of cancer patients, accepting that an impaired bioenergetic function of mitochondria is pivotal to understand energy metabolism of tumors and in its progression is debated. However, mitochondrial bioenergetics and cell death are tightly connected. CRITICAL ISSUES: Recent clinical findings indicate that H(+)-ATP synthase, a core component of mitochondrial oxidative phosphorylation, is repressed at both the protein and activity levels in human carcinomas. This review summarizes the relevance that mitochondrial function has to understand energy metabolism of tumors and explores the connection between the bioenergetic function of the organelle and the activity of mitochondria as tumor suppressors. FUTURE DIRECTIONS: The reversible nature of energy metabolism in tumors highlights the relevance that the microenvironment has for tumor progression. Moreover, the stimulation of mitochondrial activity or the inhibition of glycolysis suppresses tumor growth. Future research should elucidate the mechanisms promoting the silencing of oxidative phosphorylation in carcinomas. The aim is the development of new therapeutic strategies tackling energy metabolism to eradicate tumors or at least, to maintain tumor dormancy and transform cancer into a chronic disease.

AMPK and GCN2-ATF4 signal the repression of mitochondria in colon cancer cells.

Reprogramming of energetic metabolism is a phenotypic trait of cancer in which mitochondrial dysfunction represents a key event in tumour progression. In the present study, we show that the acquisition of the tumour-promoting phenotype in colon cancer HCT116 cells treated with oligomycin to inhibit ATP synthase is exerted by repression of the synthesis of nuclear-encoded mitochondrial proteins in a process that is regulated at the level of translation. Remarkably, the synthesis of glycolytic proteins is not affected in this situation. Changes in translational control of mitochondrial proteins are signalled by the activation of AMPK (AMP-activated protein kinase) and the GCN2 (general control non-derepressible 2) kinase, leading also to the activation of autophagy. Changes in the bioenergetic function of mitochondria are mimicked by the activation of AMPK and the silencing of ATF4 (activating transcription factor 4). These findings emphasize the relevance of translational control for normal mitochondrial function and for the progression of cancer. Moreover, they demonstrate that glycolysis and oxidative phosphorylation are controlled at different levels of gene expression, offering the cell a mechanistic safeguard strategy for metabolic adaptation under stressful conditions.

The mitochondrial ATPase inhibitory factor 1 triggers a ROS-mediated retrograde prosurvival and proliferative response.

Recent findings indicate that prevalent human carcinomas overexpress the mitochondrial ATPase Inhibitory Factor 1 (IF1). Overexpression of IF1 inhibits the synthase activity of the mitochondrial H(+)-ATP synthase and plays a crucial role in metabolic adaptation of cancer cells to enhanced aerobic glycolysis. Herein, we demonstrate that IF1 overexpression in colon cancer cells triggers mitochondrial hyperpolarization and the subsequent production of superoxide radical, a reactive oxygen species (ROS). ROS are required to promote the transcriptional activation of the NFκB pathway via phosphorylation-dependent IκBα degradation. Activation of NFκB results in a cellular adaptive response that includes proliferation and Bcl-xL mediated resistance to drug-induced cell death. Quenching the mitochondrial production of ROS prevents the activation of NFκB and abolishes the IF1-mediated cellular adaptive response. Overall, our findings provide evidence linking the activity of a mitochondrial protein with retrograde signaling to the nucleus to promote cellular proliferation and survival.

The bioenergetic signature of isogenic colon cancer cells predicts the cell death response to treatment with 3-bromopyruvate, iodoacetate or 5-fluorouracil.

BACKGROUND: Metabolic reprogramming resulting in enhanced glycolysis is a phenotypic trait of cancer cells, which is imposed by the tumor microenvironment and is linked to the down-regulation of the catalytic subunit of the mitochondrial H+-ATPase (ß-F1-ATPase). The bioenergetic signature is a protein ratio (ß-F1-ATPase/GAPDH), which provides an estimate of glucose metabolism in tumors and serves as a prognostic indicator for cancer patients. Targeting energetic metabolism could be a viable alternative to conventional anticancer chemotherapies. Herein, we document that the bioenergetic signature of isogenic colon cancer cells provides a gauge to predict the cell-death response to the metabolic inhibitors, 3-bromopyruvate (3BrP) and iodoacetate (IA), and the anti-metabolite, 5-fluorouracil (5-FU). METHODS: The bioenergetic signature of the cells was determined by western blotting. Aerobic glycolysis was determined from lactate production rates. The cell death was analyzed by fluorescence microscopy and flow cytometry. Cellular ATP concentrations were determined using bioluminiscence. Pearson's correlation coefficient was applied to assess the relationship between the bioenergetic signature and the cell death response. In vivo tumor regression activities of the compounds were assessed using a xenograft mouse model injected with the highly glycolytic HCT116 colocarcinoma cells. RESULTS: We demonstrate that the bioenergetic signature of isogenic HCT116 cancer cells inversely correlates with the potential to execute necrosis in response to 3BrP or IA treatment. Conversely, the bioenergetic signature directly correlates with the potential to execute apoptosis in response to 5-FU treatment in the same cells. However, despite the large differences observed in the in vitro cell-death responses associated with 3BrP, IA and 5-FU, the in vivo tumor regression activities of these agents were comparable. CONCLUSIONS: Overall, we suggest that the determination of the bioenergetic signature of colon carcinomas could provide a tool for predicting the therapeutic response to various chemotherapeutic strategies aimed at combating tumor progression.

Up-regulation of the ATPase inhibitory factor 1 (IF1) of the mitochondrial H+-ATP synthase in human tumors mediates the metabolic shift of cancer cells to a Warburg phenotype.

The H(+)-ATP synthase is a reversible engine of mitochondria that synthesizes or hydrolyzes ATP upon changes in cell physiology. ATP synthase dysfunction is involved in the onset and progression of diverse human pathologies. During ischemia, the ATP hydrolytic activity of the enzyme is inhibited by the ATPase inhibitory factor 1 (IF1). The expression of IF1 in human tissues and its participation in the development of human pathology are unknown. Here, we have developed monoclonal antibodies against human IF1 and determined its expression in paired normal and tumor biopsies of human carcinomas. We show that the relative mitochondrial content of IF1 increases significantly in carcinomas, suggesting the participation of IF1 in oncogenesis. The expression of IF1 varies significantly in cancer cell lines. To investigate the functional activity of IF1 in cancer, we have manipulated its cellular content. Overexpression of IF1 or of its pH-insensitive H49K mutant in cells that express low levels of IF1 triggers the up-regulation of aerobic glycolysis and the inhibition of oxidative phosphorylation with concurrent mitochondrial hyperpolarization. Treatment of the cells with the H(+)-ATP synthase inhibitor oligomycin mimicked the effects of IF1 overexpression. Conversely, small interfering RNA-mediated silencing of IF1 in cells that express high levels of IF1 promotes the down-regulation of aerobic glycolysis and the increase in oxidative phosphorylation. Overall, these findings support that the mitochondrial content of IF1 controls the activity of oxidative phosphorylation mediating the shift of cancer cells to an enhanced aerobic glycolysis, thus supporting an oncogenic role for the de-regulated expression of IF1 in cancer.

Selection of cancer cells with repressed mitochondria triggers colon cancer progression.

The contribution that mitochondrial bioenergetics could have in cancer development is debated. Here, we have generated HCT116-derived colocarcinoma cell lines expressing different levels of the beta catalytic subunit of the mitochondrial H+-adenosine triphosphate synthase to assess the contribution of mitochondrial bioenergetics in colon cancer progression. The generated cells exhibit large ultrastructural, transcriptomic, proteomic and functional differences in their mitochondria and in their in vivo tumor forming capacity. We show that the activity of oxidative phosphorylation defines the rate of glucose utilization by aerobic glycolysis. The aggressive cellular phenotype, which is highly glycolytic, is bound to the deregulated expression of genes involved in metabolic processes, the regulation of the cell cycle, apoptosis, angiogenesis and cell adhesion. Remarkably, the molecular and ultrastructural analysis of the tumors derived from the three HCT116 cell lines under study highlight that tumor promotion inevitably requires the selection of cancer cells with a repressed biogenesis and functional activity of mitochondria, i.e. the highly glycolytic phenotype is selected for tumor development. The tumor forming potential of the cells is a non-genetically acquired condition that provides the cancer cell with a cell-death resistant phenotype. An abrogated mitochondrial respiration contributes to a diminished potential for reactive oxygen species signaling in response to 5-fluorouracil treatment. Treatment of cancer cells with dichloroacetate partially restores the functional differentiation of mitochondria and promotes tumor regression, emphasizing the reversible nature of the metabolic trait of cancer.

The tumor suppressor function of mitochondria: translation into the clinics.

Recently, the inevitable metabolic reprogramming experienced by cancer cells as a result of the onset of cellular proliferation has been added to the list of hallmarks of the cancer cell phenotype. Proliferation is bound to the synchronous fluctuation of cycles of an increased glycolysis concurrent with a restrained oxidative phosphorylation. Mitochondria are key players in the metabolic cycling experienced during proliferation because of their essential roles in the transduction of biological energy and in defining the life-death fate of the cell. These two activities are molecularly and functionally integrated and are both targets of commonly altered cancer genes. Moreover, energetic metabolism of the cancer cell also affords a target to develop new therapies because the activity of mitochondria has an unquestionable tumor suppressor function. In this review, we summarize most of these findings paying special attention to the opportunity that translation of energetic metabolism into the clinics could afford for the management of cancer patients. More specifically, we emphasize the role that mitochondrial beta-F1-ATPase has as a marker for the prognosis of different cancer patients as well as in predicting the tumor response to therapy.

Glucose avidity of carcinomas.

The cancer cell phenotype has been summarized in six hallmarks [D. Hanahan, R.A. Weinberg, The hallmarks of cancer, Cell 100 (1) (2000) 57-70]. Following the conceptual trait established in that review towards the comprehension of cancer, herein we summarize the basis of an underlying principle that is fulfilled by cancer cells and tumors: its avidity for glucose. Our purpose is to push forward that the metabolic reprogramming that operates in the cancer cell represents a seventh hallmark of the phenotype that offers a vast array of possibilities for the future treatment of the disease. We summarize the metabolic pathways that extract matter and energy from glucose, paying special attention to the concerted regulation of these pathways by the ATP mass-action ratio. The molecular and functional evidences that support the high glucose uptake and the "abnormal" aerobic glycolysis of the carcinomas are detailed discussing also the role that some oncogenes and tumor suppressors have in these pathways. We overview past and present evidences that sustain that mitochondria of the cancer cell are impaired, supporting the original Warburg's formulation that ascribed the high glucose uptake of cancer cells to a defective mitochondria. A simple proteomic approach designed to assess the metabolic phenotype of cancer, i.e., its bioenergetic signature, molecularly and functionally supports Warburg's hypothesis. Furthermore, we discuss the clinical utility that the bioenergetic signature might provide. Glycolysis is presented as the "selfish" pathway used for cellular proliferation, providing both the metabolic precursors and the energy required for biosynthetic purposes, in the context of a plethora of substrates. The glucose avidity of carcinomas is thus presented as the result of both the installment of glycolysis for cellular proliferation and of the impairment of mitochondrial activity in the cancer cell. At the end, the repression of mitochondrial activity affords the cancer cell with a cell-death resistant phenotype making them prone to malignant growth.