The Warburg and Crabtree effects: On the origin of cancer cell energy metabolism and of yeast glucose repression

AbstractDuring the last decades a considerable amount of research has been focused on cancer. Recently, tumor cell metabolism has been considered as a possible target for cancer therapy. It is widely accepted that tumors display enhanced glycolytic activity and impaired oxidative phosphorylation (Warburg effect). Therefore, it seems reasonable that disruption of glycolysis might be a promising candidate for specific anti-cancer therapy. Nevertheless, the concept of aerobic glycolysis as the paradigm of tumor cell metabolism has been challenged, as some tumor cells exhibit high rates of oxidative phosphorylation. Mitochondrial physiology in cancer cells is linked to the Warburg effect. Besides, its central role in apoptosis makes this organelle a promising “dual hit target” to selectively eliminate tumor cells. From a metabolic point of view, the fermenting yeast Saccharomyces cerevisiae and tumor cells share several features. In this paper we will review these common metabolic properties as well as the possible origins of the Crabtree and Warburg effects. This article is part of a Special Issue entitled: Bioenergetics of Cancer

Stimulation of oxidative phosphorylation by electrophoretic K+ entry associated to electroneutral K+/H+ exchange in yeast mitochondria

AbstractThe effect of the addition of KCl, at constant osmolarity, was investigated on oxidative phosphorylation in isolated yeast mitochondria. KCl stimulated both respiration and ATP synthesis rates without changing the ATP/O ratio. KCl did not change the relationships between respiration rates and the protonmotive force. Since the K+/H+ exchange activity was active under these conditions, the stimulatory effect of respiration could be explained by the net proton entry caused by the electrophoretic K+ entry/electroneutral K+/H+ exchange cycle. On the other hand, K+ entry stimulated phosphate accumulation and transport under non-phosphorylating conditions and decreased the kinetic control by phosphate transport under phosphorylating conditions. Additionally, the stimulation of ATP synthesis strongly depended on the activity of phosphate transport. Taken together, these data showed that electrophoretic K+-entry and electroneutral K+/H+ exchange occurred in phosphorylating yeast mitochondria but did not promote any uncoupling between respiration and ATP synthesis

Etude des mécanismes de régulation de l'équipement enzymatique mitochondrial lors de la croissance de la levure S. cerevisiae (rôle des protéines kinases dépendantes de l'AMPc)

La voie AMPc contribue à l'ajustement des mitochondries à la demande énergétique lors de la croissance sur substrat non fermentescible. La sous-unité catalytique de la protéine kinase AMPc dépendante de la levure S. cerevisiae existe sous 3 isoformes codées par les gènes TPK. Nous avons montré que la protéine Tpk3p joue un rôle majeur dans la maintenance de l'équipement enzymatique mitochondrial lors de la croissance. Nous avons étudié les mécanismes moléculaires de cette signalisation et nous avons montré que l'absence de la protéine Tpk3p entraîne une augmentation de la production mitochondriale de ROS. Celle-ci semble affecter la biogenèse mitochondriale que nous avons estimé en mesurant l'activité des facteurs de transcription HAP2,3,4,5 impliqués dans la transcription de nombreux gènes mitochondriaux. Cette altération provoque une diminution de l'équipement enzymatique, réversible lors de l'ajout d'antioxydant. La diminution de l'activité du complexe HAP entraîne des modifications mitochondriales à l'origine d'une production de ROS encore plus importante. Afin de déterminer l'origine du processus d'ajustement des mitochondries à la demande énergétique, nous avons utilisé un autre modèle en incubant dans un milieu de "resting-cell" des levures prélevées lors d'une croissance. L'étude réalisée en absence de croissance suggère une modification de l'état stationnaire du fonctionnement des oxydations phosphorylantes sans une modification quantitative des mitochondries. A partir de ces données préliminaires nous pouvons émettre l'hypothèse que l'ajustement quantitatif des mitochondries lors de la croissance nécessite prolifération cellulaire.In yeast, cAMP pathway contributes to the mitochondrial adjustment to energy demand during growth on non-fermentable carbon source. cAMP-dependent protein kinase catalytic subunits are encoded by 3 different TPK genes. We showed that the Tpk3p plays a major role in the maintenance of optimal mitochondrial amount in response to energy demand. We investigated the molecular mechanisms and we have shown that lack of Tpk3p leads to an increase in mitochondrial ROS production. In order to demonstrate whether the decrease in amount of mitochondria was linked to a decrease in mitochondrial biogenesis, we assessed the activity of the Hap2/3/4/5p transcription factor which is known to be necessary for transcriptional activation of many mitochondrial genes. We show that ROS should be responsible for a decrease in Hap activity, which in turn leads to mitochondrial modifications. This generates a vicious circle which can be restored by using antioxidant, since modifications are responsible for more ROS production. cAMP pathway contributes to the adjustment of mitochondria to the energy demand by modulating the amount of mitochondria. In order to determine the origin of this adjustment we use another approach, we take cells in proliferation state and we arrest proliferation by transferring cells into a resting medium. Using various strains, our preliminary data show that regulation is identical regardless of the strain, involves a modification of the mitochondrial steady state respiration and there is no mitochondrial amount modification. We can hypothesis on these facts that mitochondrial amount adjustment during growth, needs cell proliferation in order to drops mitochondrial amount.BORDEAUX2-BU Santé (330632101) / SudocSudocFranceF

Mitochondria in obesity and type 2 diabetes: comprehensive review on Mitochondrial functioning and involvement in metabolic diseases: Preface

International audienceObesity and type 2 diabetes (T2DM) are metabolic disorders that have emerged as two of the most serious health issues in the world. Both are related to chronic inequality between food intake and energy expenditure, giving rise to energy imbalance over long-term periods of time. This imbalance has major consequences on the metabolic fluxes in the different tissues or organs and at the whole organism level. Within the cell, mitochondria are at the front line to initiate adaptation to these changes and, therefore, are the primary targets affected. Mitochondria are key organelles in which fuel substrates are oxidized to produce ATP from cascades of redox reactions. An important notion to understand the etiology of metabolic diseases, however, is that in all tissues and organs, energy and redox processes are closely interlinked within the mitochondria and govern major cell metabolic adaptations. This chapter is not a summary of the previous ones but has two objectives: to emphasize notions that, in the opinion of the three of us, appear to be most important, and to propose some directions for future research

Nitric oxide increases oxidative phosphorylation efficiency.

International audienceWe have studied the effect of nitric oxide (NO) and potassium cyanide (KCN) on oxidative phosphorylation efficiency. Concentrations of NO or KCN that decrease resting oxygen consumption by 10-20% increased oxidative phosphorylation efficiency in mitochondria oxidizing succinate or palmitoyl-L-carnitine, but not in mitochondria oxidizing malate plus glutamate. When compared to malate plus glutamate, succinate or palmitoyl-L-carnitine reduced the redox state of cytochrome oxidase. The relationship between membrane potential and oxygen consumption rates was measured at different degrees of ATP synthesis. The use of malate plus glutamate instead of succinate (that changes the H(+)/2e(-) stoichiometry of the respiratory chain) affected the relationship, whereas a change in membrane permeability did not affect it. NO or KCN also affected the relationship, suggesting that they change the H(+)/2e(-) stoichiometry of the respiratory chain. We propose that NO may be a natural short-term regulator of mitochondrial physiology that increases oxidative phosphorylation efficiency in a redox-sensitive manner by decreasing the slipping in the proton pumps