Monocarboxylate Transporter Isoform Research Articles

Polymorphisms in MCT1, CD147, PDK4, and DMRT3 genes in Arabian and Quarter Horses

Monocarboxylate transporter isoform 1 (MCT1) and its ancillary protein, CD147 function to transport H+ and lactate ions, retarding systemic acidosis and fatigue. The PDK4 gene is involved in the adenosine triphosphate production, and the DMRT3 gene is involved in the locomotor system. This study investigated polymorphisms of MCT1, CD147, PDK4, and DMRT3 in Arabian and Quarter Horses to associate polymorphisms with performance. Arabian Horses were divided into high performance and untrained horses groups based on success in endurance competition, whereas Quarter Horses were separated by a speed index. Polymorphisms were analyzed by sequencing (MCT1 and CD147), ARMS-PCR (PDK4), and PCR-RFLP (DMRT3). To compare the frequencies of SNPs, the Fisher's exact test was performed in the software R at 5% of significance. The A alleles from the polymorphisms Lys457Gln:1573A>C of MCT1 and Ile51Val:168A>G of CD147 were essentially fixed in both breeds. Only two Arabian from the high performance and one from the untrained horses group appeared AC in MCT1. For the DMRT3 polymorphism (g.22999655C>A:ECA23), all the animals were CC, except one Arabian in the high and two Quarter Horses in the low performance group that were AC. For the PDK4 polymorphism (g.38973231A>G:ECA4), Arabian showed a significantly greater frequency of the G allele than Quarter Horses (P < .01). Considering the kind of exercise practiced by each breed, it is likely that the PDK4 polymorphism influences the pathway to energy production.

Both monensin and plant extract alter ruminal fermentation in sheep but only monensin affects the expression of genes involved in acid-base transport of the ruminal epithelium

The effects of a plant extract (broadleaf plantain, peppermint) or monensin on dry matter intake (DMI), growth performance, ruminal fermentation products, as well as morphology and the expression of genes involved in acid-base regulation of the ruminal epithelium were determined. Thirty two male Afshari finishing lambs on a high-concentrate diet were subjected to four consecutive 14-d periods on one of four treatments with supplementation of (1) no additive (control, CON), (2) 2g blend of plant extract/(d×lamb) (PE), or (3) 30mg monensin/(d×lamb) (MON) over all four treatment periods. The fourth group received periodical inclusion of 30mg monensin/(d×lamb) in periods 1 and 3 with no additive in periods 2 and 4 (MON-p). Despite no significant overall effects on DMI, ruminal pH, average daily gain (ADG), ADG:DMI ratio and plasma albumin, the interactions of treatment×period were significant for these measures (P<0.01). Compared with CON, periods with decreased DMI occurred selectively in groups MON (period 1 and 2) and MON-p (period 2 and 3), a period with decreased ruminal pH occurred in PE (period 1), and periods with decreased plasma albumin occurred in groups MON (period 1) and MON-p (period 2) (all P<0.05 or lower). In period 2, MON sheep had higher ADG than PE and MON-p (P<0.05) and a higher ADG:DMI ratio than all other groups (P<0.05). While total concentrations of ruminal short chain fatty acids were unchanged, increased propionate proportions and decreased acetate proportions were observed in PE (P<0.05) and, as a trend, in MON, resulting in decreased acetate:propionate ratios in PE and MON compared to CON (P<0.05). The proportion of butyrate was decreased by MON only (P<0.05). Compared with CON, the relative mRNA abundance of Na+/H+ exchanger isoforms NHE1 and NHE3 were lower and that of monocarboxylate transporter isoform MCT1 was greater for MON (P<0.05). In MON-p animals, the mRNA abundance of NHE1 was lower and that of MCT4 was greater compared to CON (P<0.05). Morphometry results did not differ between treatments. It is concluded that monensin and the used plant extract were equally effective to increase ruminal propionate fermentation. Moreover, the study elucidated for the first time that the ruminal epithelium itself is affected by the ionophore properties of monensin and needs to adapt epithelial acid-base transporter expression.

MCT4 as a potential therapeutic target for metastatic gastric cancer with peritoneal carcinomatosis.

Monocarboxylate transporters (MCTs) play a major role in up-regulation of glycolysis and adaptation to acidosis. However, the role of MCTs in gastric cancer (GC) is not fully understood. We investigated the potential utilization of a new cancer therapy for GC. We characterized the expression patterns of the MCT isoforms 1, 2, and 4 and investigated the role of MCT in GC through in vitro and in vivo tests using siRNA targeting MCTs. In GC cell lines, MCT1, 2, and 4 were up-regulated with different expression levels; MCT1 and MCT4 were more widely expressed in GC cell lines compared with MCT2. Inhibition of MCTs by siRNA or AR-C155858 reduced cell viability and lactate uptake in GC cell lines. The effect of inhibition of MCTs on tumor growth was also confirmed in xenograft models. Furthermore, MCT inhibition in GC cells increased the sensitivity of cells to radiotherapy or chemotherapy. Compared with normal gastric tissue, no significant alterations of expression levels in tumors were identified for MCT1 and MCT2, whereas a significant increase in MCT4 expression was observed. Most importantly, MCT4 was highly overexpressed in malignant cells of acsites and its silencing resulted in reduced tumor cell proliferation and lactate uptake in malignant ascites. Our study suggests that MCT4 is a clinically relevant target in GC with peritoneal carcinomatosis.

Quantification of MCT1 and CD147 in Red Blood Cells of Arabian and Quarter Horses

During anaerobic glycolysis for energy production, lactate and H+ ions accumulate in muscle fibers and pass into the blood stream. The monocarboxylate transporter isoform 1 (MCT1) and its ancillary protein cluster of differentiation 147 (CD147) transport H+ and lactate ions from the plasma into red blood cells (RBCs), thereby maintaining acid/base homeostasis and retarding systemic acidosis and fatigue. The aim of this study was to compare the levels of MCT1 and CD147 protein in the RBC membranes of Arabian and Quarter Horses with different levels of athletic ability. Blood samples were collected from 40 Arabian and 40 Quarter Horses, both males and females, ranging from 3 to 16 years and 2 to 23 years, respectively. The horses were divided into two groups: 20 animals of low performance and 20 animals of high performance for each breed. The amount of MCT1 and CD147 in the plasma membranes of their RBCs was determined by Western blotting analysis with arbitrary optical density (OD) units, using a human-specific anti-MCT1 and anti-CD147 antibodies that were previously validated for horses. The means ± standard errors were analyzed by repeated measures analysis of variance using the PROC MIXED procedure of SAS software. The effect of age was included as covariate and sex as a class effect in the model. The correlations were analyzed by Pearson correlation test at P < .05. Monocarboxylate transporter isoform 1 with a molecular mass of approximately 52 and 49 kDa was found in the RBC membranes of all the Arabian and Quarter Horses, respectively. Cluster of differentiation 147 also was observed in all Arabian and Quarter Horses at approximately 52 and 48 kDa, respectively. A positive correlation was observed between the total amount of MCT1 and CD147 (r = 0.932, P < .001) in the RBC. The amount of MCT1 was significantly (P < .0001) higher in Quarter Horses (3.03 ± 0.37 OD) than in Arabians (1.02 ± 0.07 OD). Quarter Horses (3.23 ± 0.39 OD) also showed increased contents of CD147 than Arabians (0.89 ± 0.06 OD). However, there was no statistical difference in the amount of the protein between the low- and high-performance groups in either breed. Results indicate that the levels of MCT1 and CD147 are different between Arabian and Quarter Horses and the most probable explanation is that different pathways are used for the production of energy for each breed.

The altered glucose metabolism in tumor and a tumor acidic microenvironment associated with extracellular matrix metalloproteinase inducer and monocarboxylate transporters.

Extracellular matrix metalloproteinase inducer, also knowns as cluster of differentiation 147 (CD147) or basigin, is a widely distributed cell surface glycoprotein that is involved in numerous physiological and pathological functions, especially in tumor invasion and metastasis. Monocarboxylate transporters (MCTs) catalyze the proton-linked transport of monocarboxylates such as L-lactate across the plasma membrane to preserve the intracellular pH and maintain cell homeostasis. As a chaperone to some MCT isoforms, CD147 overexpression significantly contributes to the metabolic transformation of tumor. This overexpression is characterized by accelerated aerobic glycolysis and lactate efflux, and it eventually provides the tumor cells with a metabolic advantage and an invasive phenotype in the acidic tumor microenvironment. This review highlights the roles of CD147 and MCTs in tumor cell metabolism and the associated molecular mechanisms. The regulation of CD147 and MCTs may prove to be with a therapeutic potential for tumors through the metabolic modification of the tumor microenvironment.

Localisation of Lactate Transporters in Rat and Rabbit Placentae.

The distribution of monocarboxylate transporter (MCT) isoforms 1 and 4, which mediate the plasmalemmal transport of l-lactic and pyruvic acids, has been identified in the placentae of rats and rabbits at different ages of gestation. Groups of three pregnant Sprague-Dawley rats and New Zealand White rabbits were sacrificed on gestation days (GD) 11, 14, 18, or 20 and on GD 13, 18, or 28, respectively. Placentae were removed and processed for immunohistochemical detection of MCT1 and MCT4. In the rat, staining for MCT1 was associated with lakes and blood vessels containing enucleated red blood cells (maternal vessels) while staining for MCT4 was associated with vessels containing nucleated red blood cells (embryofoetal vessels). In the rabbit, staining for MCT1 was associated with blood vessels containing nucleated red blood cells while staining for MCT4 was associated with vessels containing enucleated red blood cells. Strength of staining for MCT1 decreased during gestation in both species, but that for MCT4 was stronger than that for MCT1 and was consistent between gestation days. The results imply an opposite polarity of MCT1 and MCT4 across the trophoblast between rat and rabbit.

Expression of Monocarboxylate Transporter Isoforms in Rat Skeletal Muscle Under Hypoxic Preconditioning and Endurance Training

Previously, we have reported the regulation of monocarboxylate transporters (MCT)1 and MCT4 by physiological stimuli such as hypoxia and exercise. In the present study, we have evaluated the effect of hypoxic preconditioning and training on expression of different MCT isoforms in muscles. We found the increased mRNA expression of MCT1, MCT11, and MCT12 after hypoxic preconditioning with cobalt chloride and training. However, the expression of other MCT isoforms increased marginally or even reduced after hypoxic preconditioning. Only the protein expression of MCT1 increased after hypoxia preconditioning. MCT2 protein expression increased after training only and MCT4 protein expression decreased both in preconditioning and hypoxic training. Furthermore, we found decreased plasma lactate level during hypoxia preconditioning (0.74-fold), exercise (0.78-fold), and hypoxia preconditioning along with exercise (0.67-fold), which indicates increased lactate uptake by skeletal muscle. The protein-protein interactions with hypoxia inducible factor-1 and MCT isoforms were also evaluated, but no interaction was found. In conclusion, we say that almost all MCTs are expressed in red gastrocnemius muscle at the mRNA level and their expression is regulated differently under hypoxia preconditioning and exercise condition.

Inhibition of monocarboxylate transporter by N-cyanosulphonamide S0859

The synthetic compound N-cyanosulphonamide S0859 has been described as a selective inhibitor of sodium-bicarbonate cotransporters (NBC, SLC4) in mammalian heart (Ch'en et al., 2008). First, for comparison, the electrogenic human NBCe1 (SLC4A4) was heterologously expressed in Xenopus laevis oocytes, where its transport activity was inhibited by S0859 with an IC50 of 9µM. The activity of monocarboxylate transporter (MCT) isoforms 1, 2, and 4 (SLC16A1, SLC16A7, SLC16A3), which transport lactate, pyruvate and ketone bodies, were also heterologously expressed in Xenopus oocytes, and their transport activity was similarly and reversibly inhibited by S0859 with an IC50 of 4–10µM. Partial inhibition of lactate transport by S0859 (50µM) was also obtained in cultured astrocytes of mice. Thus, S0859 appears to be an inhibitor of anion transport with a broader spectrum than previously thought, and may also interfere with cellular metabolite uptake/release.

“Panoptic Differential Training: Bio-Dynamics Approach for Sprint Time Trial Cycling Performance” – A Critical Perspective

Background: Intensity of the exercise mostly determines the dominant metabolic pathway for energy. In a sprint cycling 1km time trial, the dominant metabolic pathway must be ATP hydrolysis and glycolysis. Phosphocreatine (PCr) hydrolysis and Anaerobic Glycolysis lead to lactate and H+ accumulation in sarcolemmal cytosol, interfering the muscle contraction leading to fatigue and reduction of power output. To resist fatigue and to continue the high power output throughout the cycling sprint, the lactate flux is an essential phenomenon apart from the regeneration of the ATP. The appearance of H+ and lactate is simultaneous with high intensity exercise, hence the co transport of lactate-H+ is essential and the training should target both the systems to resist fatigue and sustain the cycling sprint power output at maximum throughout the time trial. Biodynamic Implications: Resting ATP and PCr stores of muscle seems less responsive to training and hence strengthening lactate transfer and oxidation appear better alternative along with more concentration on early oxidative phosphorylation. Monocarboxylate Transporter (MCT) isoforms like MCT1 and MCT4 expression should be increased to increase the lactate transport. Load of pH gradient along with lactate flux to be targeted during the training. MCTs also facilitate the H+ efflux and prevent the decrements in intracellular pH. Training Implications: High intensity training has significant influence on the status of both MCT1 and MCT4 ranging from 18% to 120%, though inter individual differences have been observed. Slow endurance training, like sub maximal sprint repetitions increases MCT1 and MCT4 expression leading to lactate uptake and oxidation. With the increase in sustaines sprints without much lactate accumulation during the initial seconds improves oxidative enzymal expression significantly. An acute high intensity sprint form of exercise could reduce the MCT1 expression considerably wherein high expression of H+ is seen in the myocyctes. . Recommendation: very high intensity sprint cycling in repetition need to be reduced to the minimum to avoid excess accumulation of H+. Instead differential training like repetitions of sub maximal runs with initial forty seconds of high intensity sprint cycling followed by sub maximal sprinting for

Tissue-specific expression of monocarboxylate transporters during fasting in mice.

Monocarboxylates such as pyruvate, lactate and ketone bodies are crucial for energy supply of all tissues, especially during energy restriction. The transport of monocarboxylates across the plasma membrane of cells is mediated by monocarboxylate transporters (MCTs). Out of 14 known mammalian MCTs, six isoforms have been functionally characterized to transport monocarboxylates and short chain fatty acids (MCT1-4), thyroid hormones (MCT8, -10) and aromatic amino acids (MCT10). Knowledge on the regulation of the different MCT isoforms is rare. In an attempt to get more insights in regulation of MCT expression upon energy deprivation, we carried out a comprehensive analysis of tissue specific expression of five MCT isoforms upon 48 h of fasting in mice. Due to the crucial role of peroxisome proliferator-activated receptor (PPAR)-α as a central regulator of energy metabolism and as known regulator of MCT1 expression, we included both wildtype (WT) and PPARα knockout (KO) mice in our study. Liver, kidney, heart, small intestine, hypothalamus, pituitary gland and thyroid gland of the mice were analyzed. Here we show that the expression of all examined MCT isoforms was markedly altered by fasting compared to feeding. Expression of MCT1, MCT2 and MCT10 was either increased or decreased by fasting dependent on the analyzed tissue. MCT4 and MCT8 were down-regulated by fasting in all examined tissues. However, PPARα appeared to have a minor impact on MCT isoform regulation. Due to the fundamental role of MCTs in transport of energy providing metabolites and hormones involved in the regulation of energy homeostasis, we assumed that the observed fasting-induced adaptations of MCT expression seem to ensure an adequate energy supply of tissues during the fasting state. Since, MCT isoforms 1–4 are also necessary for the cellular uptake of drugs, the fasting-induced modifications of MCT expression have to be considered in future clinical care algorithms.

The monocarboxylate transporters exist in the cattle endocrine pancreas.

Extensive studies are published concerning the distribution of monocarboxylate transporters (MCTs) in various animal issues including ruminants; nonetheless, nothing is known about their cellular expression and localization in the ruminant pancreas. The present study was carried out to examine the expression and cellular localization of all the fourteen MCT isoforms in cattle pancreas. RT-PCR verified the existence of mRNA transcripts for eight MCT isoforms, namely, MCT1, MCT2, MCT3, MCT4, MCT5, MCT8, MCT13, and MCT14 in cattle pancreas. Western blotting analysis confirmed the protein expression of these eight MCTs in the cattle pancreatic tissue. Immunohistochemical study, within the whole pancreas, was conducted to localize the eight MCTs identified, and the results showed strong positive immunoreactive staining for MCT1, MCT2, MCT4, MCT5, MCT13, and MCT14 on nearly all the islet cells of Langerhans, while we could not detect immunopositive signals in the acinar cells with any of MCTs antibodies used. This study, for the first time, showed the cellular localization and expression of MCT1-MCT5, MCT8, MCT13, and MCT14 within the ruminant pancreas. The distribution and expression pattern of MCT1, MCT2, MCT4, and CD147 in the cattle pancreas are different from that previously published on monogastric pancreas. Our study suggested that MCT1, MCT2, MCT4, MCT5, MCT13, and MCT14 may participate in the regulation of the pancreatic endocrine secretions in ruminants.

The Retinal Pigment Epithelium Utilizes Fatty Acids for Ketogenesis: IMPLICATIONS FOR METABOLIC COUPLING WITH THE OUTER RETINA

Every day, shortly after light onset, photoreceptor cells shed approximately a tenth of their outer segment. The adjacent retinal pigment epithelial (RPE) cells phagocytize and digest shed photoreceptor outer segment, which provides a rich source of fatty acids that could be utilized as an energy substrate. From a microarray analysis, we found that RPE cells express particularly high levels of the mitochondrial HMG-CoA synthase 2 (Hmgcs2) compared with all other tissues (except the liver and colon), leading to the hypothesis that RPE cells, like hepatocytes, can produce β-hydroxybutyrate (β-HB) from fatty acids. Using primary human fetal RPE (hfRPE) cells cultured on Transwell filters with separate apical and basal chambers, we demonstrate that hfRPE cells can metabolize palmitate, a saturated fatty acid that constitutes .15% of all lipids in the photoreceptor outer segment, to produce β-HB. Importantly, we found that hfRPE cells preferentially release β-HB into the apical chamber and that this process is mediated primarily by monocarboxylate transporter isoform 1 (MCT1). Using a GC-MS analysis of (13)C-labeled metabolites, we showed that retinal cells can take up and metabolize (13)C-labeled β-HB into various TCA cycle intermediates and amino acids. Collectively, our data support a novel mechanism of RPE-retina metabolic coupling in which RPE cells metabolize fatty acids to produce β-HB, which is transported to the retina for use as a metabolic substrate.

Both butyrate incubation and hypoxia upregulate genes involved in the ruminal transport of SCFA and their metabolites.

Butyrate modulates the differentiation, proliferation and gene expression profiles of various cell types. Ruminal epithelium is exposed to a high intraluminal concentration and inflow of n-butyrate. We aimed to investigate the influence of n-butyrate on the mRNA expression of proteins involved in the transmembranal transfer of n-butyrate metabolites and short-chain fatty acids in ruminal epithelium. N-butyrate-induced changes were compared with the effects of hypoxia because metabolite accumulation after O2 depletion is at least partly comparable to the accumulation of metabolites after n-butyrate exposure. Furthermore, in various tissues, O2 depletion modulates the expression of transport proteins that are also involved in the extrusion of metabolites derived from n-butyrate breakdown in ruminal epithelium. Sheep ruminal epithelia mounted in Ussing chambers were exposed to 50 mM n-butyrate or incubated under hypoxic conditions for 6h. Electrophysiological measurements showed hypoxia-induced damage in the epithelia. The mRNA expression levels of monocarboxylate transporters (MCT) 1 and 4, anion exchanger (AE) 2, downregulated in adenoma (DRA), putative anion transporter (PAT) 1 and glucose transporter (GLUT) 1 were assessed by RT-qPCR. We also examined the mRNA expression of nuclear factor (NF) κB, cyclooxygenase (COX) 2, hypoxia-inducible factor (HIF) 1α and acyl-CoA oxidase (ACO) to elucidate the possible signalling pathways involved in the modulation of gene expression. The mRNA expression levels of MCT 1, MCT 4, GLUT 1, HIF 1α and COX 2 were upregulated after both n-butyrate exposure and hypoxia. ACO and PAT 1 were upregulated only after n-butyrate incubation. Upregulation of both MCT isoforms and NFκB after n-butyrate incubation could be detected on protein level as well. Our study suggests key roles for MCT 1 and 4 in the adaptation to an increased intracellular load of metabolites, whereas an involvement of PAT 1 in the transport of n-butyrate also seems possible.

Role of Monocarboxylate Transporters in Drug Delivery to the Brain

Monocarboxylate transporters (MCTs) are known to mediate the transport of short chain monocarboxylates such as lactate, pyruvate and butyrate. Currently, fourteen members of this transporter family have been identified by sequence homology, of which only the first four members (MCT1- MCT4) have been shown to mediate the proton-linked transport of monocarboxylates. Another transporter family involved in the transport of endogenous monocarboxylates is the sodium coupled MCTs (SMCTs). These act as a symporter and are dependent on a sodium gradient for their functional activity. MCT1 is the predominant transporter among the MCT isoforms and is present in almost all tissues including kidney, intestine, liver, heart, skeletal muscle and brain. The various isoforms differ in terms of their substrate specificity and tissue localization. Due to the expression of these transporters in the kidney, intestine, and brain, they may play an important role in influencing drug disposition. Apart from endogenous short chain monocarboxylates, they also mediate the transport of exogenous drugs such as salicylic acid, valproic acid, and simvastatin acid. The influence of MCTs on drug pharmacokinetics has been extensively studied for γ-hydroxybutyrate (GHB) including distribution of this drug of abuse into the brain and the results will be summarized in this review. The physiological role of these transporters in the brain and their specific cellular localization within the brain will also be discussed. This review will also focus on utilization of MCTs as potential targets for drug delivery into the brain including their role in the treatment of malignant brain tumors.

Acute exercise increases brain region-specific expression of MCT1, MCT2, MCT4, GLUT1, and COX IV proteins

The brain is capable of oxidizing lactate and ketone bodies through monocarboxylate transporters (MCTs). We examined the protein expression of MCT1, MCT2, MCT4, glucose transporter 1 (GLUT1), and cytochrome-c oxidase subunit IV (COX IV) in the rat brain within 24 h after a single exercise session. Brain samples were obtained from sedentary controls and treadmill-exercised rats (20 m/min, 8% grade). Acute exercise resulted in an increase in lactate in the cortex, hippocampus, and hypothalamus, but not the brainstem, and an increase in β-hydroxybutyrate in the cortex alone. After a 2-h exercise session MCT1 increased in the cortex and hippocampus 5 h postexercise, and the effect lasted in the cortex for 24 h postexercise. MCT2 increased in the cortex and hypothalamus 5-24 h postexercise, whereas MCT2 increased in the hippocampus immediately after exercise, and remained elevated for 10 h postexercise. Regional upregulation of MCT2 after exercise was associated with increases in brain-derived neurotrophic factor and tyrosine-related kinase B proteins, but not insulin-like growth factor 1. MCT4 increased 5-10 h postexercise only in the hypothalamus, and was associated with increased hypoxia-inducible factor-1α expression. However, none of the MCT isoforms in the brainstem was affected by exercise. Whereas GLUT 1 in the cortex increased only at 18 h postexercise, COX IV in the hippocampus increased 10 h after exercise and remained elevated for 24 h postexercise. These results suggest that acute prolonged exercise induces the brain region-specific upregulation of MCT1, MCT2, MCT4, GLUT1, and COX IV proteins.

Interaction of carbonic anhydrases with lactate-transporting MCTs

Event Abstract Back to Event Interaction of carbonic anhydrases with lactate-transporting MCTs Joachim W. Deitmer1*, Michael Klier1 and Holger M. Becker1 1 University of Kaisersautern, General Zoology, Germany Background and aim. Carbonic anhydrases (CAs) have not only been identified as ubiquitous enzymes catalyzing the fast reversible hydration of carbon dioxide to generate or consume protons and bicarbonate, but also as intra- and extracellular proteins, which facilitate transport function of acid/base transporting membrane proteins. Functional interactions between CAs and acid/base transporters, such as chloride/bicarbonate exchanger (AE), sodium-bicarbonate cotransporter (NBC) and sodium/hydrogen exchanger (NHE) have been reported, which appear to require both catalytic CA activity as well as direct binding of the enzyme to specific sites on the transporter. In contrast, functional interaction between different CA isoforms and lactate-proton-cotransporting monocarboxylate transporters (MCTs) has been found to be isoform-specific and independent of CA catalytic activity (1, 2). MCTs play a crucial role in the shuttling of lactate between glycolytic and oxidative cell types in different tissues like muscle and brain, and may also play a role in removing acid from cells. Methods. We have used Xenopus laevis oocytes as heterologous expression system to study MCTs and CA alone and when expressed together, and used H+-sensitive microelectrode and mass spectrometry to determine transporter and enzyme activity. Results. Our studies on the interaction between different CA isoforms, including CAIX, which is up-regulated in hypoxic/cancerous tissues, and MCT isoforms 1, 2, and 4 in Xenopus oocytes will be summarized and imbedded into a scheme which links H+ fluxes, CA and MCT expression with metabolic processes. In particular, CAs may act as H+-collecting antennae (3), which counteract the dissipation of the transmembrane H+ gradient driving the cotransport with lactate via MCTs. Conclusions. It is concluded that membrane transporters may directly interact with intracellular and extracellular carbonic anhydrases, leading to functional changes in transport activity, which may be relevant in particular in hypoxic cells and tissues. Acknowledgements Supported by grants from the Deutsche Forschungsgemeinschaft and the Landesschwerpunkt RIMP. References (1) Becker, H.M. and Deitmer, J.W. (2008) J. Biol. Chem. 283, 21655-67. (2) Klier, M. et al. (2011) J. Biol. Chem. 286, 27781-91. (3) Becker, H.M. et al. (2011) Proc Natl. Acad. Sci. U.S.A. 108, 3071-3076. Keywords: pH, Lactate, monocarboxylate transporter, CAIX, Xenopus oocyte Conference: 4th Annual Meeting of the International Society of Proton Dynamics in Cancer, Garching, Germany, 10 Oct - 12 Oct, 2013. Presentation Type: Abstract Topic: 3. pH, cell signalling and growth Citation: Deitmer JW, Klier M and Becker HM (2014). Interaction of carbonic anhydrases with lactate-transporting MCTs. Front. Pharmacol. Conference Abstract: 4th Annual Meeting of the International Society of Proton Dynamics in Cancer. doi: 10.3389/conf.fphar.2014.61.00017 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 17 Dec 2013; Published Online: 07 Feb 2014. * Correspondence: Prof. Joachim W Deitmer, University of Kaisersautern, General Zoology, Kaiserslautern, Rheinland-Pfalz, D-67663, Germany, deitmer@biologie.uni-kl.de Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Joachim W Deitmer Michael Klier Holger M Becker Google Joachim W Deitmer Michael Klier Holger M Becker Google Scholar Joachim W Deitmer Michael Klier Holger M Becker PubMed Joachim W Deitmer Michael Klier Holger M Becker Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Significance of monocarboxylate transporter (MCT) expression in human tumors

Event Abstract Back to Event Significance of monocarboxylate transporter (MCT) expression in human tumors Fatima Baltazar1* 1 University of Minho, Portugal Background and aim. One essential hallmark of tumour cells is the Warburg effect in which cells upregulate glycolysis, even in the presence of oxygen. The high rates of glycolysis lead to increased production of lactate, which must be transported out of the cells. Monocarboxylate transporters (MCTs) play a key role in the maintenance of glycolysis, by performing the plasma membrane efflux of lactate coupled with a proton, especially the isoforms 1 (MCT1) and 4 (MCT4). Results. Our group has been studying the expression of these MCT isoforms as well as their chaperone, CD147, known to be essential for MCT activity and plasma membrane expression, in several series of human cancers. We found upregulation of MCT1 and MCT4 in the plasma membrane of colorectal cancer, upregulation of MCT1, MCT4 and CD147 in cervical cancer, upregulation of MCT1 in breast cancer and upregulation of MCT1 and CD147 in glioblastomas, when compared to the corresponding non-neoplastic tissues. On the other hand, there was downregulation of MCT4 in gastric cancer and downregulation of MCT1 in prostate cancer. We also found important associations between MCT overexpression and the clinicopathological data of the cases, mostly with aggressiveness parameters. We have been also targeting lactate transport in in vitro and in vivo models. In gliomas, inhibition of lactate transport (with CHC or MCT1 downregulation) decreased glycolytic metabolism, migration, and invasion and induced cell death in U251 cells (more glycolytic) but only affected proliferation in SW1088 (more oxidative). The effectiveness of CHC in glioma cells appears to be dependent on MCT1/CD147 membrane expression. There was a synergistic effect when combining CHC with temozolomide treatment in U251 cells. In the CAM in vivo model, CHC decreased the size of tumors and the number of blood vessels formed. Conclusions / Discussion. Altogether, our results and the ones from other groups support lactate transporters as promising targets in cancer therapy. Acknowledgements FCT grant ref. PTDC/SAU-FCF/104347/2008, under the scope of “Programa Operacional Temático Factores de Competitividade” (COMPETE) of “Quadro Comunitário de Apoio III” and co-financed by Fundo Comunitário Europeu FEDER.

Downregulation of MCT1 inhibits tumor growth, metastasis and enhances chemotherapeutic efficacy in osteosarcoma through regulation of the NF-κB pathway

Monocarboxylate transporter isoform 1 (MCT1) is an important member of the proton-linked MCT family and has been reported in an array of human cancer cell lines and primary human tumors. MCT1 expression is associated with developing a new therapeutic approach for cancer. In this study, we initially showed that MCT1 is expressed in a variety of human osteosarcoma cell lines. Moreover, we evaluated the therapeutic response of targeting MCT1 using shRNA or MCT1 inhibitor. Inhibiting MCT1 delayed tumor growth in vitro and in vivo, including in an orthotopic model of osteosarcoma. Targeting MCT1 greatly enhanced the sensitivity of human osteosarcoma cells to the chemotherapeutic drugs adriamycin (ADM). In addition, we observed that MCT1 knockdown significantly suppressed the metastatic activity of osteosarcoma, including wound healing, invasion and migration. Further mechanistic studies revealed that the antitumor effects of targeting MCT1 might be related to the NF-κB pathway. Immunochemistry assay showed that MCT1 was an independent positive prognostic marker in osteosarcoma patients. In conclusion, our data, for the first time, demonstrate that MCT1 inhibition has antitumor potential which is associated with the NF-κB pathway, and high MCT1 expression predicates poor overall survival in patients with osteosarcoma.

Spatial expression and functional flexibility of monocarboxylate transporter isoforms in the zebrafish brain

The present study provides in vivo evidence to prove the functional plasticity of monocarboxylate transporters (MCTs) in brains of vertebrates using zebrafish (Danio rerio) as a model. In the mammalian central nervous system (CNS), energy demands are largely met by oxidation of glucose. In recent studies, in addition to glucose, lactate is also considered an energy substrate for the CNS. Astrocytes were demonstrated to play an important role in transporting lactate as metabolic substrate from capillaries to neurons through monocarboxylate transporters (MCTs). The present study was to use zebrafish as an in vivo model to test the hypothesis of whether the various MCT homologs play differential roles in the development and functioning of the CNS. Using RT-PCR and double in situ hybridization coupling with immunocytochemical staining experiments, zebrafish MCTs1–4 were all found to be expressed in brains of embryos, and were further elucidated to be localized in both neurons and astrocytes. Loss-of-functions by morpholino knockdown further provided in vivo evidences to infer that zMCTs1, -2, and -4 may be involved in metabolite transport and functioning in the developing brain. Subsequent rescue experiments with capped mRNAs of specific isoforms further indicated that zMCT2 is an indispensable monocarboxylate-transporting route for CNS development and function in zebrafish. This information is essential for identifying proper candidates of MCT isoforms that are involved in the development and functioning of the CNS.

Spatial expression and functional flexibility of monocarboxylate transporter isoforms in the zebrafish brain

The present study provides in vivo evidence to prove the functional plasticity of monocarboxylate transporters (MCTs) in brains of vertebrates using zebrafish (Danio rerio) as a model. In the mammalian central nervous system (CNS), energy demands are largely met by oxidation of glucose. In recent studies, in addition to glucose, lactate is also considered an energy substrate for the CNS. Astrocytes were demonstrated to play an important role in transporting lactate as metabolic substrate from capillaries to neurons through monocarboxylate transporters (MCTs). The present study was to use zebrafish as an in vivo model to test the hypothesis of whether the various MCT homologues play differential roles in the development and functioning of the CNS. Using RT-PCR and double in situ hybridization coupling with immunocytochemical staining experiments, zebrafish MCTs1~4 were all found to be expressed in brains of embryos, and were further elucidated to be localized in both neurons and astrocytes. Loss-of-functions by morpholino knockdown further provided in vivo evidences to infer that zMCTs1, -2, and -4 may be involved in metabolite transport and functioning in the developing brain. Subsequent rescue experiments with capped mRNAs of specific isoforms further indicated that zMCT2 is an indispensable monocarboxylate-transporting route for CNS development and function in zebrafish. This information is essential for identifying proper candidates of MCT isoforms that are involved in the development and functioning of the CNS.