Control of glycolytic enzymes through binding to cell structures and by glucose-1,6-bisphosphate under different conditions. The role of Ca2+ and calmodulin

The miRNA expression profile directly reflects the energy metabolic differences between slow and fast muscle with nutritional regulation of the Chinese perch (Siniperca chuatsi)

Fish skeletal muscles are composed of two distinct types, slow and fast muscles, and they play important roles in maintaining the body's movement and energy metabolism. The two types of muscle are easy to separate, so they are often used as the model system for studies on their physiological and functional characteristics. In this study, we revealed that the carbohydrate and lipid metabolic KEGG pathways are different between slow and fast muscles of Chinese perch with transcriptome analysis. In fast muscle, glucose metabolism was catabolic with higher glycolysis capacity, while in slow muscle, glucose metabolism was anabolic with more glycogen synthesis. In addition, oxidative metabolism in slow muscle was stronger than that in fast muscle. By analyzing the expression levels of 40 miRNAs involved in metabolism in the muscles of Chinese perch, 18 miRNAs were significantly upregulated and 7 were significantly downregulated in slow muscle compared with fast muscle. Based on functional enrichment analysis of their target genes, the differential expression levels of 17 miRNAs in slow and fast muscles were reflected in their carbohydrate and lipid metabolism. Among these, 15 miRNAs were associated with carbohydrate metabolism, and 6 miRNAs were associated with lipid metabolism. After 3 days of starvation, the expression levels of 15 miRNAs involved in glucose metabolism in fast and slow muscles increased. However, after 7 days of starvation, the mRNA levels of miR-22a, miR-23a, miR-133a-3p, miR-139, miR-143, miR-144, miR-181a and miR-206 decreased to basal levels. Our data suggest that the possible reason for the difference in glucose and lipid metabolism is that more miRNAs inhibit the expression of target genes in slow muscle.

Contribution of Early-Postmortem Proteome and Metabolome to Ultimate pH and Pork Quality

This study's objectives were to identify how subtle differences in ultimate pH relate to differences in pork quality and to understand how early-postmortem glycolysis contributes to variation in ultimate pH. The hypothesis was that elements in early-postmortem longissimus thoracis et lumborum proteome and metabolome could be used to predict quality defects associated with pH decline. Temperature and pH of the longissimus thoracis et lumborum were measured at 45 min, 24 h, and 14 d postmortem. Quality measurements were made after 14 d of aging. Groups were classified as normal pH (NpH; x̄ = 5 . 59 [5.53–5.67]; NpH, n = 10) and low pH (LpH; x̄ = 5 . 42 [5.38–5.45]; LpH, n = 10) at 14 d postmortem. Metabolites from 45 min postmortem were identified using GC-MS. Relative differences between proteins were quantified with two-dimensional difference in gel electrophoreses, and spots were identified with MALDI-MS. Western blot analyses were used to measure phosphofructokinase, peroxiredoxin-2, and reduced and non-reduced adenosine monophosphate deaminase-2 at 45 min and 14 d postmortem. Ultimate pH classification did not affect 45-min-postmortem pH (P = 0.64); 14-d pH was different between groups (P < 0.01). NpH had less purge loss (P < 0.01), was darker (P < 0.01), had lower star probe (P < 0.01), and had less intact day-7 desmin (P = 0.02). More pyruvate (P = 0.01) and less lactate (P = 0.09) was observed in NpH, along with more soluble lactate dehydrogenase (P = 0.03) and pyruvate kinase (P < 0.10). These observations indicate that differences in enzyme abundance or solubility may produce more pyruvate and less lactate. Fructose 6-phosphate was more abundant (P = 0.08) in the LpH group, indicating that phosphofructokinase may be involved in glycolytic differences. Furthermore, greater abundance of heat shock proteins, peroxiredoxin-2 (P = 0.02), and malate (P = 0.01) early postmortem all suggest differences in mitochondrial function and oxidative stability that contribute to quality differences. These results show that even subtle changes in ultimate pH can influence pork quality. The proteome and metabolome at 45 min postmortem are associated with variation in the extent of pH decline.

Phosphoglycerate kinase: structural aspects and functions, with special emphasis on the enzyme from Kinetoplastea

Phosphoglycerate kinase (PGK) is a glycolytic enzyme that is well conserved among the three domains of life. PGK is usually a monomeric enzyme of about 45 kDa that catalyses one of the two ATP-producing reactions in the glycolytic pathway, through the conversion of 1,3-bisphosphoglycerate (1,3BPGA) to 3-phosphoglycerate (3PGA). It also participates in gluconeogenesis, catalysing the opposite reaction to produce 1,3BPGA and ADP. Like most other glycolytic enzymes, PGK has also been catalogued as a moonlighting protein, due to its involvement in different functions not associated with energy metabolism, which include pathogenesis, interaction with nucleic acids, tumorigenesis progression, cell death and viral replication. In this review, we have highlighted the overall aspects of this enzyme, such as its structure, reaction kinetics, activity regulation and possible moonlighting functions in different protistan organisms, especially both free-living and parasitic Kinetoplastea. Our analysis of the genomes of different kinetoplastids revealed the presence of open-reading frames (ORFs) for multiple PGK isoforms in several species. Some of these ORFs code for unusually large PGKs. The products appear to contain additional structural domains fused to the PGK domain. A striking aspect is that some of these PGK isoforms are predicted to be catalytically inactive enzymes or ‘dead’ enzymes. The roles of PGKs in kinetoplastid parasites are analysed, and the apparent significance of the PGK gene duplication that gave rise to the different isoforms and their expression in Trypanosoma cruzi is discussed.

Expression and immunological characteristics of the surface-localized pyruvate kinase in Mycoplasma gallisepticum

The widespread avian pathogen Mycoplasma gallisepticum is a causative agent of respiratory disease. The wall-less prokaryotes lack some tricarboxylic acid cycle enzymes, therefore, the glycolysis metabolic pathway is of great importance to these organisms. Pyruvate kinase (PK) is one of the key enzymes of the glycolytic pathway, and its immunological characteristics in Mycoplasma are not well known. In this study, the M. gallisepticum pyruvate kinase fusion protein (PykF) was expressed in a pET system. The full-length of the gene was subcloned into the expression vector pET28a(+) to construct the pET28a-rMGPykF plasmid, which was then transformed into Escherichia coli strain BL21 (DE3) cells. The expression of the 62 kDa recombinant protein of rMGPykF in E. coli strain BL21 (DE3) was confirmed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis with Coomassie blue staining. Purified rMGPykF exhibited PK catalytic activity, which could reflect the conversion of NADH to NAD(+). Mouse anti-PykF antibodies were generated by immunization of mice with rMGPykF. Immunoblot and immunoelectron microscopy assays identified PykF as an immunogenic protein expressed on the surface of M. gallisepticum cells. Bactericidal assay showed that anti-rMGPykF antiserum killed 70.55% of M. gallisepticum cells, suggesting the protective potential of PykF. Adherence inhibition assay on immortalized chicken fibroblasts (DF-1) cells revealed more than 39.31% inhibition of adhesion in the presence of anti-rMGPykF antiserum, suggesting that PykF of M. gallisepticum participates in bacterial adhesion to DF-1 cells.

Absolute quantitative profiling of the key metabolic pathways in slow and fast skeletal muscle

Slow and fast skeletal muscles are composed of, respectively, mainly oxidative and glycolytic muscle fibers, which are the basic cellular motor units of the motility apparatus. They largely differ in excitability, contraction mechanism, and metabolism. Because of their pivotal role in body motion and homeostasis, the skeletal muscles have been extensively studied using biochemical and molecular biology approaches. Here we describe a simple analytical and computational approach to estimate titers of enzymes of basic metabolic pathways and proteins of the contractile machinery in the skeletal muscles. Proteomic analysis of mouse slow and fast muscles allowed estimation of the titers of enzymes involved in the carbohydrate, lipid, and energy metabolism. Notably, we observed that differences observed between the two muscle types occur simultaneously for all proteins involved in a specific process such as glycolysis, free fatty acid catabolism, Krebs cycle, or oxidative phosphorylation. These differences are in a good agreement with the well-established biochemical picture of the muscle types. We show a correlation between maximal activity and the enzyme titer, suggesting that change in enzyme concentration is a good proxy for its catalytic potential in vivo. As a consequence, proteomic profiling of enzyme titers can be used to monitor metabolic changes in cells. Additionally, quantitative data of structural proteins allowed studying muscle type specific cell architecture and its remodeling. The presented proteomic approach can be applied to study metabolism in any other tissue or cell line.

Calcium in red blood cells-a perilous balance

Ca2+ is a universal signalling molecule involved in regulating cell cycle and fate, metabolism and structural integrity, motility and volume. Like other cells, red blood cells (RBCs) rely on Ca2+ dependent signalling during differentiation from precursor cells. Intracellular Ca2+ levels in the circulating human RBCs take part not only in controlling biophysical properties such as membrane composition, volume and rheological properties, but also physiological parameters such as metabolic activity, redox state and cell clearance. Extremely low basal permeability of the human RBC membrane to Ca2+ and a powerful Ca2+ pump maintains intracellular free Ca2+ levels between 30 and 60 nM, whereas blood plasma Ca2+ is approximately 1.8 mM. Thus, activation of Ca2+ uptake has an impressive impact on multiple processes in the cells rendering Ca2+ a master regulator in RBCs. Malfunction of Ca2+ transporters in human RBCs leads to excessive accumulation of Ca2+ within the cells. This is associated with a number of pathological states including sickle cell disease, thalassemia, phosphofructokinase deficiency and other forms of hereditary anaemia. Continuous progress in unravelling the molecular nature of Ca2+ transport pathways allows harnessing Ca2+ uptake, avoiding premature RBC clearance and thrombotic complications. This review summarizes our current knowledge of Ca2+ signalling in RBCs emphasizing the importance of this inorganic cation in RBC function and survival.

Protein fishing using magnetic nanobeads containing calmodulin site-specifically immobilized via an azido group

We developed a novel method for capturing proteins that interact with a target protein. This method utilizes a protein containing a site-specifically incorporated 3-azidotyrosine (N3-Y) and FG beads for immobilization of the protein via an azido group. Using calmodulin (CaM) as the target protein, we introduced N3-Y at position 72 and conjugated it to FG beads by copper-free click chemistry. From the Ca(2+)/CaM-binding proteins captured from mouse brain cell lysate and analysis by mass spectrometry, we identified six proteins: alpha-enolase (ENOA), glucose-6-phosphate isomerase (GPI), annexin A5 (ANXA5), malate dehydrogenase 1 (MDH1), glyceraldehyde-3-phosphate dehydrogenase and the well-known CaM-binding protein phosphoglycerate kinase 1 (PGK1). The presence of photo-crosslinking products via N3-Y for all the captured proteins except GPI indicated that they bound directly to CaM. In this study, ENOA, ANXA5 and MDH1 were identified as novel CaM-binding proteins, and PGK1 was bound to Ca(2+)/CaM and also Ca(2+)-free CaM. This method should prove useful for capturing novel interacting proteins and serve as a useful tool for proteomic analyses.

Combined in vivo and in silico investigations of activation of glycolysis in contracting skeletal muscle

The hypothesis was tested that the variation of in vivo glycolytic flux with contraction frequency in skeletal muscle can be qualitatively and quantitatively explained by calcium-calmodulin activation of phosphofructokinase (PFK-1). Ischemic rat tibialis anterior muscle was electrically stimulated at frequencies between 0 and 80 Hz to covary the ATP turnover rate and calcium concentration in the tissue. Estimates of in vivo glycolytic rates and cellular free energetic states were derived from dynamic changes in intramuscular pH and phosphocreatine content, respectively, determined by phosphorus magnetic resonance spectroscopy ((31)P-MRS). Computational modeling was applied to relate these empirical observations to understanding of the biochemistry of muscle glycolysis. Hereto, the kinetic model of PFK activity in a previously reported mathematical model of the glycolytic pathway (Vinnakota KC, Rusk J, Palmer L, Shankland E, Kushmerick MJ. J Physiol 588: 1961-1983, 2010) was adapted to contain a calcium-calmodulin binding sensitivity. The two main results were introduction of regulation of PFK-1 activity by binding of a calcium-calmodulin complex in combination with activation by increased concentrations of AMP and ADP was essential to qualitatively and quantitatively explain the experimental observations. Secondly, the model predicted that shutdown of glycolytic ATP production flux in muscle postexercise may lag behind deactivation of PFK-1 (timescales: 5-10 s vs. 100-200 ms, respectively) as a result of accumulation of glycolytic intermediates downstream of PFK during contractions.

Regulation of mammalian muscle type 6-phosphofructo-1-kinase and its implication for the control of the metabolism

Phosphofructokinase (PFK) is a major regulatory glycolytic enzyme and is considered to be the pacemaker of glycolysis. This enzyme presents a puzzling regulatory mechanism that is modulated by a large variety of metabolites, drugs, and intracellular proteins. To date, the mammalian enzyme structure has not yet been resolved. However, it is known that PFK undergoes an intricate oligomerization process, shifting among monomers, dimers, tetramers, and more complex oligomeric structures. The equilibrium between PFK dimers and tetramers is directly correlated with the enzyme regulation, because the dimer exhibits very low catalytic activity, whereas the tetramer is fully active. Several PFK ligands modulate the enzyme, favoring the formation of its dimers or tetramers. The present review integrates recent findings regarding the regulatory aspects of muscle type PFK and discusses their relation to the control of metabolism.

Role of NADH/NAD+ transport activity and glycogen store on skeletal muscle energy metabolism during exercise: in silico studies

Skeletal muscle can maintain ATP concentration constant during the transition from rest to exercise, whereas metabolic reaction rates may increase substantially. Among the key regulatory factors of skeletal muscle energy metabolism during exercise, the dynamics of cytosolic and mitochondrial NADH and NAD+ have not been characterized. To quantify these regulatory factors, we have developed a physiologically based computational model of skeletal muscle energy metabolism. This model integrates transport and reaction fluxes in distinct capillary, cytosolic, and mitochondrial domains and investigates the roles of mitochondrial NADH/NAD+ transport (shuttling) activity and muscle glycogen concentration (stores) during moderate intensity exercise (60% maximal O2 consumption). The underlying hypothesis is that the cytosolic redox state (NADH/NAD+) is much more sensitive to a metabolic disturbance in contracting skeletal muscle than the mitochondrial redox state. This hypothesis was tested by simulating the dynamic metabolic responses of skeletal muscle to exercise while altering the transport rate of reducing equivalents (NADH and NAD+) between cytosol and mitochondria and muscle glycogen stores. Simulations with optimal parameter estimates showed good agreement with the available experimental data from muscle biopsies in human subjects. Compared with these simulations, a 20% increase (or approximately 20% decrease) in mitochondrial NADH/NAD+ shuttling activity led to an approximately 70% decrease (or approximately 3-fold increase) in cytosolic redox state and an approximately 35% decrease (or approximately 25% increase) in muscle lactate level. Doubling (or halving) muscle glycogen concentration resulted in an approximately 50% increase (or approximately 35% decrease) in cytosolic redox state and an approximately 30% increase (or approximately 25% decrease) in muscle lactate concentration. In both cases, changes in mitochondrial redox state were minimal. In conclusion, the model simulations of exercise response are consistent with the hypothesis that mitochondrial NADH/NAD+ shuttling activity and muscle glycogen stores affect primarily the cytosolic redox state. Furthermore, muscle lactate production is regulated primarily by the cytosolic redox state.

Membrane subproteomic analysis of Mycobacterium bovis bacillus Calmette-Guérin

Mycobacterium bovis bacillus Calmette-Guérin (BCG) vaccine has been known for a long time to prevent tuberculosis (TB) worldwide since 1921. Nonetheless, we know little about BCG membrane proteome. In the present study, we utilized alkaline incubation and Triton X-114-based methods to enrich BCG membrane proteins and subsequently digested them using proteolytic enzyme. The recovered peptides were further separated by 2-D LC and identified by ESI-MS/MS. As a result, total 474 proteins were identified, including 78 integral membrane proteins (IMPs). Notably, 18 BCG IMPs were described for the first time in mycobacterium. Further analysis of the 78 IMPs indicated that the theoretical molecular mass distribution of them ranged from 8.06 to 167.86 kDa and pI scores ranged from 4.40 to 11.60. Functional classification revealed that a large proportion of the identified IMPs (67.9%, 53 out of 78) were involved in cell wall and cell processes functional group. In conclusion, here we reported a comprehensive profile of the BCG membrane subproteome. The present investigation may allow the identification of some valuable vaccine and drug target candidates and thus provide basement for future designing of preventive, diagnostic, and therapeutic strategies against TB.

Transcriptional analysis of insecticide resistance in Anopheles stephensi using cross-species microarray hybridization

A large scale microarray (20k MMC1) from the African malaria vector Anopheles gambiae was used to monitor gene expression in insecticide resistant and susceptible strains of the Asian mosquito Anopheles stephensi. Heterologous hybridization at slightly reduced stringency yielded approximately 7000 significant signals. Thirty-six putative genes were differentially transcribed between the pyrethroid-resistant (DUB-R) and the susceptible (BEECH) strains. The expression profiles of selected transcripts were verified by real-time PCR. A gene putatively involved in the thickening of the adult cuticle showed the most striking up-regulation in DUB-R. A more specialized microarray containing 231 An. gambiae genes putatively involved in insecticide detoxification was used to further analyse classical insecticide resistance genes. Three glutathione S-transferase (GST) transcripts, one esterase and a cytochrome P450 were up-regulated in the resistant strain, while two peroxidases were down-regulated.

A comparative analysis of metabolism and viability in porcine oocytes during in vitro maturation

The importance of oocyte quality cannot be overstated, because it impacts all subsequent events during development of the embryo, the fetus and even the resulting offspring. Oocyte metabolism plays a critical role in supporting developmental competence via multiple mechanisms. It is beginning to be understood that metabolic pathways not only affect cytoplasmic maturation but may control nuclear maturation as well. A complete understanding of the precise roles that metabolism plays in determining oocyte quality is crucial for developing efficient in vitro maturation systems to support acquisition of oocyte competence. To date, this pursuit has not been entirely successful. Work in our laboratory on porcine oocyte metabolism has elucidated some of the intricate control mechanisms at work within the oocyte, not only for energy production, but also encompassing progression of nuclear maturation, mitochondrial activity and distribution, and oxidative and ionic stresses. We hypothesize that by utilizing oocyte metabolic data, we can develop more appropriate in vitro maturation systems that result in increased oocyte and embryo developmental competence.

Escherichia coli AspP activity is enhanced by macromolecular crowding and by both glucose-1,6-bisphosphate and nucleotide-sugars

Escherichia coli ADP-sugar pyrophosphatase (AspP) is a "Nudix" hydrolase that catalyzes the hydrolytic breakdown of ADP-glucose linked to glycogen biosynthesis. Moderate increases of AspP activity in the cell are accompanied by significant reductions of the glycogen content. In vitro analyses showed that AspP activity is strongly enhanced by macromolecular crowding and by both glucose-1,6-bisphosphate and nucleotide-sugars, providing a first set of indicative evidences that AspP is a highly regulated enzyme. To our knowledge, AspP is the sole bacterial enzyme described to date which is activated by both G1,6P(2) and nucleotide-sugars.

Modulation of 6-phosphofructo-1-kinase oligomeric equilibrium by calmodulin: formation of active dimers

Muscle 6-phospho-1-kinase (PFK) is the key regulatory enzyme of the glycolytic pathway and is a calmodulin-binding protein binding two calmodulin molecules per PFK protomer. This enzyme is characterized by a complex regulation that involves its allosteric behavior modulated by several ligands, which modulate the equilibrium between the active tetramers and the inactive dimers of the enzyme. Calmodulin is described to induce the dimerization of PFK, so inhibiting its catalytic activity. Here, we show that binding of calmodulin specifically to its higher-affinity site of PFK induce its dimerization without compromising enzyme catalytic activity forming a hitherto not described active dimmer of PFK. It is also shown that the dimerization is a Ca2+ -dependent event that responds to physiological intracellular Ca2+ concentrations and decrease the interaction of the enzyme to membrane site, which stimulate its catalytic activity. We propose that the effects of calmodulin on PFK reported here are of great physiological significance due to the response to physiological concentrations of Ca2+ and due to be in accordance to the known effects of calmodulin on cell ATP production. We also propose that calmodulin might affect the interaction of PFK to other cellular components as the cytoskeleton.

Overexpression of caveolin-1 results in increased plasma membrane targeting of glycolytic enzymes: The structural basis for a membrane associated metabolic compartment

Although membrane-associated glycolysis has been observed in a variety of cell types, the mechanism of localization of glycolytic enzymes to the plasma membrane is not known. We hypothesized that caveolin-1 (CAV-1) serves as a scaffolding protein for glycolytic enzymes and may play a role in the organization of cell metabolism. To test this hypothesis, we over-expressed CAV-1 in cultured A7r5 (rat aorta vascular smooth muscle; VSM) cells. Confocal immunofluorescence microscopy was used to study the distribution of phosphofructokinase (PFK) and CAV-1 in the transfected cells. Areas of interest (AOI) were analyzed in a central Z-plane across the cell transversing the perinuclear region. To quantify any shift in PFK localization resulting from CAV-1 over-expression, we calculated a periphery to center (PC) index by taking the average of the two outer AOIs from each membrane region and dividing by the central one or two AOIs. We found the PC index to be 1.92 +/- 0.57 (mean +/- SEM, N = 8) for transfected cells and 0.59 +/- 0.05 (mean +/- SEM, N = 11) for control cells. Colocalization analysis demonstrated that the percentage of PFK associated with CAV-1 increased in transfected cells compared to control cells. The localization of aldolase (ALD) was also shifted towards the plasma membrane (and colocalized with PFK) in CAV-1 over-expressing cells. These results demonstrate that CAV-1 creates binding sites for PFK and ALD that may be of higher affinity than those binding sites localized in the cytoplasm. We conclude that CAV-1 functions as a scaffolding protein for PFK, ALD and perhaps other glycolytic enzymes, either through direct interaction or accessory proteins, thus contributing to compartmented metabolism in vascular smooth muscle.

Calcium influx: a possible role for insulin modulation of intracellular distribution and activity of 6-phosphofructo-1-kinase in human erythrocytes

Human erythrocyte cells contain specific, active insulin receptor. However, the physiological relevance of this receptor is unclear. Here we show that Ca2+ influx is 4-fold higher in erythrocytes upon insulin stimulation. These effects are dose-dependent and are diminished by insulin concentrations of 150 nM and higher. The insulin-stimulated Ca2+ influx depends on a tyrosine-kinase activity and involves the verapamil-dependent Ca2+ channels. Elevated intracellular Ca2+, in association with the Ca2+-binding protein, calmodulin, stimulates erythrocytes 6-phosphofructo-1-kinase activity. This activation involves the detachment of the enzyme from erythrocyte membranes, which has been described as an important mechanism of glycolysis regulation on these cells. Altogether, these results support evidence that insulin may increases glucose consumption in human erythrocytes, through a mechanism involving Ca2+ influx, calmodulin and the detachment of 6-phosphofructo-1-kinase from the erythrocyte membrane.

Clotrimazole decreases human breast cancer cells viability through alterations in cytoskeleton-associated glycolytic enzymes

Cancer cells are characterized by a high rate of glycolysis, which is their primary energy source. Glycolysis is known to be controlled by allosteric regulators, as well as by reversible binding of glycolytic enzymes to cytoskeleton. Clotrimazole is an anti-fungal azole derivative recently recognized as a calmodulin antagonist with promising anti-cancer effect. Here, we show that clotrimazole induced morphological and functional alterations on human breast cancer derived cell line, MCF-7. The drug decreased cell viability in a dose- and time-dependent manner, exhibiting an IC50 of 88.6+/-5.3 microM and a t0.5 of 89.7+/-7.2 min, with 50 microM clotrimazole. Morphological changes were evident as observed by scanning electron microscopy, which revealed the completely loss of protrusion responsible for cell adhesion after a 180 min of treatment with 50 microM clotrimazole. Giemsa stained cells observed by optical microscopy show morphological alterations and a marked nuclear condensation. These changes occurred in parallel to the detachment of the glycolytic enzymes, 6-phosphofructo-1-kinase and aldolase, from cytoskeleton. After a 45 min treatment with 50 microM clotrimazole, the remaining activities in a cytoskeleton enriched fraction was 16.4+/-3.6% and 41.0+/-15.6% of control for 6-phosphofructo-1-kinase and aldolase, respectively. Immunocytochemistry experiments revealed a decrease in the co-localization of 6-phosphofructo-1-kinase and F-actin after clotrimazole treatment, suggesting the site of detachment of the enzymes. Altogether, our results support evidence for apoptotic events that might be started by clotrimazole involving inhibition of glycolytic flux in MCF-7 cells and makes this drug a promising agent in the fight against human breast cancer.

Calmodulin binds to and inhibits the activity of phosphoglycerate kinase

Phosphoglycerate kinase (PGK) functions as a cytoplasmic ATP-generating glycolytic enzyme, a nuclear mediator in DNA replication and repair, a stimulator of Sendai virus transcription and an extracellular disulfide reductase in angiogenesis. Probing of a developmental expression library from Dictyostelium discoideum with radiolabelled calmodulin led to the isolation of a cDNA encoding a putative calmodulin-binding protein (DdPGK) with 68% sequence similarity to human PGK. Dictyostelium, rabbit and yeast PGKs bound to calmodulin-agarose in a calcium-dependent manner while DdPGK constructs lacking the calmodulin-binding domain (209KPFLAILGGAKVSDKIKLIE228) failed to bind. The calmodulin-binding domain shows 80% identity between diverse organisms and is situated beside the hinge and within the ATP binding domain adjacent to nine mutations associated with PGK deficiency. Calmodulin addition inhibits yeast PGK activity in vitro while the calmodulin antagonist W-7 abrogates this inhibition. Together, these data suggest that PGK activity may be negatively regulated by calcium and calmodulin signalling in eukaryotic cells.

Tissue-specific differences in 2-fluoro-2-deoxyglucose metabolism beyond FDG-6-P: a 19F NMR spectroscopy study in the rat

2-Fluoro-[(18)F]-2-deoxy-glucose (FDG) is a positron-emitting analogue of glucose used clinically in positron emission tomography (PET) to assess glucose utilization in diseased and healthy tissue. Originally developed to measure local cerebral glucose utilization rates, it has now found applications in tumour diagnosis and in the study of myocardial glucose uptake. Once taken up into the cell, FDG is phosphorylated to FDG-6-phosphate (FDG-6-P) by hexokinase and was originally believed to be trapped as a terminal metabolite. This 'metabolic trapping' of FDG-6-P forms the basis of the analysis of PET data. In this study, we have used (19)F NMR spectroscopy to investigate FDG metabolism following the injection of a bolus of the glucose tracer into the rat (n=6). Ninety minutes after the (19)FDG injection, the brain, heart, liver and kidneys were removed and the (19)FDG metabolites in each were extracted and quantified. We report that significant metabolism of FDG occurs beyond FDG-6-P in all organs examined and that the extent of this metabolism varies from tissue to tissue (degree of metabolism beyond FDG-6-P, expressed as percentage of total organ FDG content, was brain 45 +/- 3%; heart 29 +/- 2%; liver 22+/-3% and kidney 17 +/- 3%, mean +/- SEM n=6). Furthermore, we demonstrate that the relative accumulation of each metabolite was tissue-dependent and reflected the metabolic and regulatory characteristics of each organ. Such inter-tissue differences may have implications for the mathematical modelling of glucose uptake and phosphorylation using FDG as a glucose tracer.

Pyruvate kinase: current status of regulatory and functional properties

Pyruvate kinase (PK) is a key enzyme for the glycolytic pathway and carbon metabolism in general. On the basis of the relevance and enormous diverse properties of this enzyme, this paper describes the results of a current and extensive review that determines the sites of conservation and/or difference in PK sequences, and the differences in the functional and regulatory properties of the enzymes. An alignment and analysis of 50 PK sequences from different sources and a phylogenetic tree are presented. This analysis was performed with reference to crystallographically characterized PK principally from E. coli, cat and rabbit muscle. A number of attributes of the enzyme that make it of particular interest in biomedicine and industry are also discussed.

Clotrimazole decreases glycolysis and the viability of lung carcinoma and colon adenocarcinoma cells

Glycolysis is known to be the primary energy source in most cancer cells. We investigated here the effect of clotrimazole (1-(alpha-2-chlorotrityl)imidazole), the antifungal azole derivative, which was recently recognized as calmodulin antagonist, on the levels of glucose 1,6-bisphosphate and fructose 1,6-bisphosphate, the two stimulatory signal molecules of glycolysis, and on ATP content and cell viability in LL/2 Lewis lung carcinoma cells and CT-26 colon adenocarcinoma cells. We found that clotrimazole induced a significant, dose- and time-dependent reduction in the levels of glucose 1,6-bisphosphate, fructose 1,6-bisphosphate, ATP, and cell viability. These findings suggest that clotrimazole causes a reduction in glycolysis and ATP levels, which eventually leads to cell destruction after 3 h of treatment. Since cell proliferation was also reported to be inhibited by calmodulin antagonists, this substance is most promising agent in treatment of cancer by inhibiting both cell proliferation and the glycolytic supply of ATP required for cancer cell growth.

Lithium detaches hexokinase from mitochondria and inhibits proliferation of B16 melanoma cells

Glycolysis is known to be the primary energy source in cancer cells. Hexokinase (ATP: D-hexose 6-phosphotransferase, EC 2.7.1.1), the only glycolytic enzyme which binds to mitochondria, is exceptionally high in cancer cells, and believed to play a key role in regulating cell energy metabolism and cancer cell growth rate. We show here that lithium induces a detachment of hexokinase from mitochondria of B16 melanoma cells. This effect eventually leads to inhibition of cell proliferation. These results reveal a novel, additional, mechanism of action of lithium and suggest that lithium may be promising drug in treatment of melanoma.

Detachment of glycolytic enzymes from cytoskeleton of Lewis lung carcinoma and colon adenocarcinoma cells induced by clotrimazole and its correlation to cell viability and morphology

Cancer cells are characterized by a high rate of glycolysis, which is their primary energy source. Glycolysis is known to be controlled by allosteric regulators, as well as by reversible binding of glycolytic enzymes to cytoskeleton. We report here that clotrimazole (l-(alpha-2-chlorotrityl)imidazole), the antifungal azole derivative, which was recently recognized as calmodulin antagonist, induced a dose-dependent detachment of the glycolytic enzymes, phosphofructokinase (ATP: D-fructose-6-phosphate 1-phosphotransferase, EC 2.7.1.11) and aldolase (D-fructose-l,6-bisphosphate D-glyceraldehyde-3-phosphate-lyase, EC 4.1.2.13), from cytoskeleton of LL/2 Lewis lung carcinoma cells and CT-26 colon adenocarcinoma cells. The detachment of glycolytic enzymes from cytoskeleton would reduce the provision of local ATP, in the vicinity of the cytoskeleton membrane, and would also affect cytoskeleton structure and cell shape. We show here that clotrimazole decreased the viability of LL/2 Lewis lung carcinoma cells and CT-26 colon adenocarcinoma cells. After 3h of incubation with clotrimazole, complete cell destruction was detected. Ultrastructural cell damage was manifested by disintegration of the outer membrane by scanning electron microscopy (SEM). The detachment of glycolytic enzymes from cytoskeleton, induced by clotrimazole, preceded the decrease in cell viability, which indicates that this is an early effect and not a result of cell death. Since the cytoskeleton is being recognized as an important modulator of cell function, proliferation, differentiation, and neoplasia, detachment of the glycolytic enzymes from cytoskeleton induced by clotrimazole, as well as its reported inhibitory action on cell proliferation, makes this drug the most promising agent in the treatment of cancer.

Control of glycolysis in contracting skeletal muscle. II. Turning it off

Glycolytic flux in muscle declines rapidly after exercise stops, indicating that muscle activation is a key controller of glycolysis. The mechanism underlying this control could be 1) a Ca(2+)-mediated modulation of glycogenolysis, which supplies substrate (hexose phosphates, HP) to the glycolytic pathway, or 2) a direct effect on glycolytic enzymes. To distinguish between these possibilities, HP levels were raised by voluntary 1-Hz exercise, and glycolytic flux was measured after the exercise ceased. Glycolytic H(+) and ATP production were quantified from changes in muscle pH, phosphocreatine concentration, and P(i) concentration as measured by 31P magnetic resonance spectroscopy. Substrate (HP) and metabolite (P(i), ADP, and AMP) levels remained high when exercise stopped because of the occlusion of blood flow with a pressure cuff. Glycolytic flux declined to basal levels within approximately 20 s of the end of exercise despite elevated levels of HP and metabolites. Therefore, this flux does not subside because of insufficient HP substrate; rather, glycolysis is controlled independently of glycogenolytic HP production. We conclude that the inactivation of glycolysis after exercise reflects the cessation of contractile activity and is mediated within the glycolytic pathway rather than via the control of glycogen breakdown.

Aldolase-localization in cultured cells: Cell-type and substrate-specific regulation of cytoskeletal associations

The role of aldolase as a true F- and G-actin binding protein, including modulating actin polymerization, initiating bundling, and giving rise to supramolecular structures that emanate from actin fibrils, has been established using indirect immunofluorescence, permeabilization of XTH-2 cells and keratocytes, and microinjection of fluorescence-labeled aldolase. In addition, binding to intermediate filaments, vimentin, and cytokeratins has been demonstrated. In permeabilized cells in the presence of fructose-1,6-bisphosphate (20–2000 µM) aldolase shifts from association with actin fibres to intermediate filaments. Plenty of free binding sites on microtubules have been revealed by addition of fluorochromed aldolase derived from rabbit skeletal muscle. However, endogenous aldolase was never found associated with microtubules. Differences in actin polymerization in the presence of aldolase as revealed by pyrene-labeled actin fluorimetry and viscosimetry were explained by electron microscopy showing the formation of rod-like structures (10 nm wide, 20–60 nm in length) by association of aldolase with G-actin, which prevents further polymerization. Upon the addition of fructose-1,6-bisphosphate, G-actin–aldolase mixture polymerizes to a higher viscosity and forms stiffer filaments than pure actin of the same concentration.Key words: aldolase, cytoskeleton, electron microscopy, viscosimetry.

N-terminal truncation affects the kinetics and structure of fructose-6-phosphate 2-kinase/fructose-2,6-bisphosphatase from Arabidopsis thaliana

The enzyme fructose-6-phosphate 2-kinase (F6P,2K; 6-phosphofructo-2-kinase)/fructose-2,6-bisphosphatase (F26BPase) catalyses the formation and degradation of the regulatory metabolite fructose 2,6-bisphosphate. A cDNA encoding the bifunctional plant enzyme isolated from Arabidopsis thaliana (AtF2KP) was expressed in yeast, and the substrate affinities and allosteric properties of the affinity-purified enzyme were characterized. In addition to the known regulators 3-phosphoglycerate, dihydroxyacetone phosphate, fructose 6-phosphate and P(i), several metabolites were identified as important new effectors. PP(i), phosphoenolpyruvate and 2-phosphoglycerate strongly inhibited F6P,2K activity, whereas fructose 1,6-bisphosphate and 6-phosphogluconate inhibited F26BPase activity. Furthermore, pyruvate was an activator of F6P,2K and an inhibitor of F26BPase. Both kinase and phosphatase activities were rapidly inactivated by mild heat treatment (42 degrees C, 10 min), but the presence of phosphate protected both enzyme activities from inactivation. In addition to the catalytic regions, the Arabidopsis enzyme comprises a 345-amino-acid N-terminus of unknown function. The role of this region was examined by the expression of a series of N-terminally truncated enzymes. The full-length and truncated enzymes were analysed by gel-filtration chromatography. The full-length enzyme was eluted as a homotetramer, whereas the truncated enzymes were eluted as monomers. Deletion of the N-terminus decreased the kinase/phosphatase activity ratio by 4-fold, and decreased the affinity for the substrate fructose 6-phosphate. The data show that the N-terminus is important both for subunit assembly and for defining the kinetic properties of the enzyme.

Detachment of the glycolytic enzymes, phosphofructokinase and aldolase, from cytoskeleton of melanoma cells, induced by local anesthetics

Cancer cells are characterized by a high rate of glycolysis, which is their primary energy source. An important mechanism that controls glycolysis is the reversible binding of glycolytic enzymes to cytoskeleton. We report here that the local anesthetics, lidocaine and bupivacaine, induced a dose-dependent detachment of the glycolytic enzymes, phosphofructokinase (EC 2.7.1.11) and aldolase (EC 4.1.2.13), from cytoskeleton of B16 melanoma cells. The detachment of glycolytic enzymes from cytoskeleton would reduce the provision of local ATP, in the vicinity of cytoskeleton-membrane and would also affect cytoskeleton structure. We show here that the local anesthetics decreased the viability of melanoma cells. The detachment of the glycolytic enzymes from cytoskeleton, induced by the drugs, preceded melanoma cell death, which indicates that this is an early effect and not a result of cell death. Bupivacaine was more potent than lidocaine both on the glycolytic enzymes and on cell viability. The present results suggest that local anesthetics, and especially bupivacaine, are promising drugs for the treatment of melanoma.

Local anesthetics induce a decrease in the levels of glucose 1, 6-bisphosphate, fructose 1,6-bisphosphate, and ATP, and in the viability of melanoma cells

Glycolysis is known to be the primary energy source in cancer cells. We investigated here the effect of local anesthetics, lidocaine and bupivacaine, on the levels of glucose 1,6-bisphosphate and fructose 1,6-bisphosphate, the two stimulatory signal molecules of glycolysis, and on ATP levels and cell viability in B16 melanoma cells. We found that both drugs induced a significant, dose-dependent reduction in the levels of glucose 1,6-bisphosphate, fructose 1, 6-bisphosphate, ATP, and cell viability. Bupivacaine was more potent than lidocaine. The decrease in glucose 1,6-bisphosphate and fructose 1,6-bisphosphate, induced by the local anesthetics, preceded the reduction in the viability of melanoma cells, indicating that these are early changes and not a result of cell death. Cell viability was reduced in a close correlation with the fall in ATP. These findings suggest that the fall in the levels of the two signal allosteric regulators of glycolysis, induced by the local anesthetics, is one of the mechanisms that causes a reduction in glycolysis and ATP levels, which eventually leads to melanoma cell death. These experiments suggest that local anesthetics, and especially bupivacaine, are most promising agents in the treatment of melanoma.

Ca2+-induced changes in energy metabolism and viability of melanoma cells

Cancer cells are characterized by a high rate of glycolysis, which is their primary energy source. We show here that a rise in intracellular-free calcium ion (Ca2+), induced by Ca2+-ionophore A23187, exerted a deleterious effect on glycolysis and viability of B16 melanoma cells. Ca2+-ionophore caused a dose-dependent detachment of phosphofructokinase (EC 2.7.1.11), one of the key enzymes of glycolysis, from cytoskeleton. It also induced a decrease in the levels of glucose 1,6-bisphosphate and fructose 1,6-bisphosphate, the two stimulatory signal molecules of glycolysis. All these changes occurred at lower concentrations of the drug than those required to induce a reduction in viability of melanoma cells. We also found that low concentrations of Ca2+-ionophore induced an increase in adenosine 5'-triphosphate (ATP), which most probably resulted from the increase in mitochondrial-bound hexokinase, which reflects a defence mechanism. This mechanism can no longer operate at high concentrations of the Ca2+-ionophore, which causes a decrease in mitochondrial and cytosolic hexokinase, leading to a drastic fall in ATP and melanoma cell death. The present results suggest that drugs which are capable of inducing accumulation of intracellular-free Ca2+ in melanoma cells would cause a reduction in energy-producing systems, leading to melanoma cell death.

Effects of Ca(2+)-ionophore A23187 and calmodulin antagonists on regulatory mechanisms of glycolysis and cell viability of NIH-3T3 fibroblasts

We studied here, in NIH-3T3 fibroblasts, the effect of the Ca(2+)-ionophore A23187 (which is known to increase intracellular-free Ca(2+)) on the control of glycolysis and cell viability and the action of calmodulin antagonists. Time-response studies with Ca(2+)-ionophore A23187 have revealed dual effects on the distribution of phosphofructokinase (PFK) (EC 2.7.1.11), the rate-limiting enzyme of glycolysis, between the cytoskeletal and cytosolic (soluble) fractions of the cell. A short incubation (maximal effect after 7 min) caused an increase in cytoskeleton-bound PFK with a corresponding decrease in soluble activity. This leads to an enhancement of cytoskeletal glycolysis. A longer incubation with Ca(2+)-ionophore caused a reduction in both cytoskeletal and cytosolic PFK and cell death. Both the "physiological" and "pathological" phases of the Ca(2+)-induced changes in the distribution of PFK were prevented by treatment with three structurally different calmodulin antagonists, thioridazine, an antipsychotic phenothiazine, clotrimazole, from the group of antifungal azole derivatives that were recently recognized as calmodulin antagonists, and CGS 9343B, a more selective inhibitor of calmodulin activity. The longer incubation with Ca(2+)-ionophore also induced a decrease in the levels of glucose 1,6-bisphosphate and fructose 1,6-bisphosphate, the two allosteric stimulatory signal molecules of glycolysis. All these pathological changes preceded the reduction in cell viability, and a strong correlation was found between the fall in ATP and cell death. All three calmodulin antagonists prevented the pathological reduction in the levels of the allosteric effectors, ATP and cell viability. These experiments may throw light on the mechanisms underlying the therapeutic action of calmodulin antagonists that we previously found in treatment of the proliferating melanoma cells, on the one hand, and skin injuries, on the other hand.

Taxol (paclitaxel) induces a detachment of phosphofructokinase from cytoskeleton of melanoma cells and decreases the levels of glucose 1,6-bisphosphate, fructose 1,6-bisphosphate and ATP

Glucose utilization through glycolysis, which is the primary energy source in cancer cells, is known to be controlled by allosteric regulators, as well as by reversible binding of glycolytic enzymes to cytoskeleton. Here we report of a novel mechanism of action of taxol (paclitaxel; Baccatin III N-benzyl-beta-phenylisoserine ester), the anti-microtubule agent with remarkable anticancer activity. We show that taxol affects both levels of regulation of glycolysis in melanoma cells; it decreases the levels of glucose 1,6-bisphosphate and fructose 1,6-bisphosphate, the two allosteric stimulatory signal molecules of glycolysis, and also causes a detachment of phosphofructokinase (ATP: D-fructose-6-phosphate 1-phosphotransferase, EC 2.7.1.11), the rate-limiting enzyme of glycolysis, from the cytoskeleton of B16 melanoma cells. These effects of taxol were dose-dependent, and preceded the decrease in ATP levels and cell viability. Thus, taxol not only inhibits the essential dynamic processes of microtubule network, but also reduces glycolysis, through the novel mechanisms described here.

Abnormal cell calcium homeostasis in type 2 diabetes mellitus: a new look on old disease

Cumulative evidence reveals that diabetes is a condition in which cell Ca2+ homeostasis is impaired. Defects in cell Ca2+ regulation were found in erythrocytes, cardiac muscle, platelets, skeletal muscle, kidney, aorta, adipocytes, liver, osteoblasts, arteries, lens, peripheral nerves, brain synaptosomes, retinal tissue, and pancreatic beta cells, confirming that this defect in cell Ca2+ metabolism is a basic pathology associated with the diabetic state. Though different defects in a variety of functions that regulate cell Ca2+ homeostasis were described in diabetes, the most common finding is an increase in [Ca2+]i levels. However, it is not clear whether the defect in cell Ca2+ metabolism in diabetes precedes or succeeds the overt diabetic condition. It is also not clear which of the multiple functions involved in cell Ca2+ regulation has the primary defect. Defects in cell Ca2+ metabolism may be significant for the observed pathologies in insulin secretion and insulin action in diabetes. They may also play an important role in the vascular complications seen in this condition, such as hypertension, atherosclerosis, and microangiopathy. Therefore, better understanding of the impairment in cell Ca2+ metabolism in diabetes may markedly enhance our understanding of this condition.

Effects of Ca2+ on erythrocyte membrane skeleton-bound phosphofructokinase, ATP levels, and hemolysis

Erythrocyte Ca2+ overload is known to occur in several different disease states, and to affect the erythrocyte membrane deformability. We show here that an increase in intracellular Ca2+ concentration in erythrocytes, induced by ionomycin, caused a reduction in ATP levels. Concomitant to the fall in ATP, a marked activation of phosphofructokinase (PFK) (EC 2.7.1.11), the rate-limiting enzyme in glycolysis, in the membrane skeleton fraction occurred. The increase in the membrane skeleton-bound PFK activity was most probably mediated by Ca2+, as direct addition of Ca2+ to the membrane skeleton fraction from the erythrocyte induced an enhancement of the bound PFK activity. Time-response curves revealed that erythrocyte hemolysis did not occur during the first 30 min of incubation with ionomycin, when the membrane skeleton-bound PFK was activated. Longer incubation time resulted in solubilization of the membrane skeleton-bound PFK and a concomitant hemolysis of the erythrocytes. These results suggest that the Ca2+-induced activation of membrane skeleton-bound PFK, and thereby glycolysis, the sole source of energy in erythrocytes, may be a defense mechanism to surmount the damage induced by high Ca2+ levels.

Insulin stimulates binding of phosphofructokinase to cytoskeleton and increases glucose 1,6-bisphosphate levels in NIH-3T3 fibroblasts, which is prevented by calmodulin antagonists

We report here a novel mechanism of insulin action in cultures of NIH-3T3 fibroblasts. Our experiments revealed that in these cells, insulin induced a rapid and transient increase in cytoskeleton-bound phosphofructokinase (EC 2.7.1.11), the rate-limiting enzyme in glycolysis, with a corresponding decrease in soluble (cytosolic) activity. Insulin also induced a slower increase in the levels of glucose 1,6-bisphosphate, the potent activator of cytosolic glycolysis. Both the rapid and the slower stimulatory actions of insulin were prevented by treatment with structurally different calmodulin antagonists, which strongly suggest that calmodulin is involved in these effects of insulin. The present and our previous experiments in muscle suggest that rapid, Ca2+-calmodulin-mediated increase in the binding of glycolytic enzymes to cytoskeleton, as well as the slower increase in glucose 1,6-bisphosphate, may be a general mechanism, in different cells, in signal transduction of insulin.

Interaction of M1 and M2 isozymes pyruvate kinase from human tissues with phospholipids

The effect of pH and the presence of FBP on the interaction of skeletal muscle (PK-M1) and kidney or tumor meningioma (PK-M2) pyruvate kinase with the phospholipids liposomes were investigated by ultracentrifugation and steady-state kinetics and were compared with those results obtained using the bovine heart (PK-M1) isoenzyme which we previously studied. Pyruvate kinase specific activity increases upon the interaction with liposomes. The activation is specifically sensitive to presence of phosphatidylserine (PS) in liposomes. Liposomes made of phosphatidylcholine + phosphatidylserine mixture are good adsorptive systems for both human and bovine of M-type isozymes at low ionic strength. Interaction of PK-M1 with PS liposomes results in the change of Vmax and K(m) values for PEP without marked effect on Hill coefficients. Addition of PS liposomes to PK-M2 induces hyperbolic saturation curves for PEP.

Activation of membrane skeleton-bound phosphofructokinase in erythrocytes induced by serotonin

We show here that serotonin, both in vivo and in vitro, induced a marked activation of phosphofructokinase, the rate-limiting enzyme in glycolysis, in the membrane-skeleton fraction from erythrocytes. Concomitantly, the hormone induced a striking increase in lactate content, reflecting stimulation of glycolysis. The enzyme's activity in the cytosolic (soluble) fraction remained unchanged. These results suggest a defense mechanism in the erythrocytes against the damaging effects of serotonin, whose concentration in plasma increases in many diseases and is implicated as playing an important role in circulation disturbances.

Interaction of troponin-H and glutathione S-transferase-2 in the indirect flight muscles of Drosophila melanogaster

Drosophila indirect flight muscles (IFMs) contain a 35 kDa protein which cross-reacts with antibodies to the IFM specific protein troponin-H isoform 34 (TnH-34). Peptide fingerprinting and peptide sequencing showed that this 35 kDa protein is glutathione S-transferase-2 (GST-2). GST-2 is present in the asynchronous indirect flight muscles but not in the synchronous tergal depressor of the trochanter (jump muscle). Genetic dissection of the sarcomere showed that GST-2 is stably associated with the thin filaments but the presence of myosin is required to achieve the correct stoichiometry, suggesting that there is also an interaction with the thick filament. The two Drosophila TnHs (isoforms 33 and 34) are naturally occurring fusion proteins in which a proline-rich extension of approximately 250 amino acids replaces the 27 C-terminal residues of the muscle-specific tropomyosin II isoform. The proteolytic enzyme, Igase, cleaves the hydrophobic C-terminal sequence of TnH-34 at three sites and TnH-33 at one site. This results in the release of GST-2 from the myofibril. The amount of GST-2 stably bound to the myofibril is directly proportional to the total amount of undigested TnH. It is concluded that GST-2 in the thin filament is stabilized there by interaction with TnH. We speculate that the hydrophobic N-terminal region of GST-2 interacts with the hydrophobic C-terminal extension of TnH, and that both are close to a myosin cross-bridge.

Clotrimazole and bifonazole detach hexokinase from mitochondria of melanoma cells

Cancer cells are characterized by a high rate of glycolysis. Hexokinase (ATP: D-hexose 6-phosphotransferase, EC 2.7.1.1), the only glycolytic enzyme which binds to mitochondria, is exceptionally high in cancer cells, and believed to play a key role in regulating cell energy metabolism and cancer cell growth rate. We have previously found that clotrimazole (1-(alpha-2-chlorotrityl)imidazole) and bifonazole (1-(alpha-biphenyl-4-ylbenzyl)imidazole), the antifungal azole derivatives, which were recently recognized as calmodulin antagonists, are calmodulin antagonists which most effectively reduce glycolysis and ATP level in B16 melanoma cells. They act through allosteric regulation and detachment of glycolytic enzymes from cytoskeleton. Here we report of a novel, additional, mechanism of action of these drugs. We show that they induce a dose-dependent detachment of hexokinase from mitochondria of B16 melanoma cells. This effect preceded the decrease in cell viability. These results suggest that clotrimazole and bifonazole may be promising drugs in treatment of melanoma.

Detachment of glycolytic enzymes from cytoskeleton of melanoma cells induced by calmodulin antagonists

Glycolysis, which is the primary energy source in cancer cells, is known to be controlled by allosteric regulators, as well as by reversible binding of glycolytic enzymes to cytoskeleton. We have previously found that different calmodulin antagonists decrease the levels of allosteric activators of glycolysis, and reduce ATP content and cell viability in B16 melanoma cells. Here we report of a novel, additional, mechanism of action of calmodulin antagonists in melanoma cells. We show that these drugs cause a detachment of the glycolytic enzymes, phosphofructokinase (ATP: D-fructose-6-phosphate 1-phosphotransferase, EC 2.7.1.11) and aldolase (D-fructose-1,6-bisphosphate D-glyceraldehyde-3-phosphate-lyase, EC 4.1.2.13), from cytoskeleton of B16 melanoma cells. This effect was dose- and time-dependent, and preceded the decrease in cell viability. The detachment of glycolytic enzymes from cytoskeleton would reduce the provision of local ATP, in the vicinity of the cytoskeleton-membrane and would affect cytoskeleton structure. Since the cytoskeleton is being recognized as an important modulator of cell function, proliferation, differentiation and neoplasia, detachment of the glycolytic enzymes from cytoskeleton induced by calmodulin antagonists, as well as their reported inhibitory action on cell proliferation, make these drugs most promising agents in treatment of cancer.

Serotonin decreases cytoskeletal and cytosolic glycolytic enzymes and the levels of ATP and glucose 1,6-bisphosphate in skin, which is prevented by the calmodulin antagonists thioridazine and clotrimazole

Serotonin (5-hydroxytryptamine) is believed to play a pathogenic role in skin damage and various skin abnormalities; however, its mechanism of action remains unknown. We show here that intradermal injection of serotonin in rats induced a marked reduction in the activities of the glycolytic enzymes, phosphofructokinase (EC 2.7.1.11) and aldolase (EC 4.1.2.13), in both the cytoskeletal and cytosolic fractions from skin. Serotonin also decreased the levels of glucose 1,6-bisphosphate in skin, the powerful regulator of glucose metabolism. These serotonin-induced changes were accompanied by a marked decrease in ATP content in skin. All these pathological changes induced by serotonin were prevented by treatment with two structurally different calmodulin antagonists: thioridazine, an antipsychotic phenothiazine, or clotrimazole, from the group of the antifungal azole derivatives that were recently recognized as calmodulin antagonists. The present results suggest that calmodulin antagonists may be effective drugs in the treatment of skin damage under various pathological conditions and diseases in which serotonin levels are increased.

Ascorbate availability and neurodegeneration in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis is a fatal neurodegenerative disease in which upper and lower motoneurons progressively deteriorate and die. Neuronal damage is most evident in the lower central nervous system, and death generally occurs following central respiratory failure. Proposed and demonstrated mechanisms for amyotrophic lateral sclerosis are diverse, and include altered superoxide dismutase and neurofilament proteins, autoimmune attack, and hyperglutamatergic activity. However, they do not account for the late onset of the disease, its earlier onset in males, and the differential vulnerability of neurons located in the brainstem and spinal cord. It is proposed here that, within the context of a specific defect such as altered superoxide dismutase, age-dependent decline in ascorbate availability triggers the disease. A role for ascorbate, which is found in millimolar levels in neurons, is suggested by a number of consistencies: 1) superoxide radicals being a common substrate for superoxide dismutase and ascorbate; 2) a close association between central nervous system ascorbate levels and injury tolerance; 3) a steady decline in ascorbate plasma levels and cellular availability with age; 4) plasma ascorbate levels being lower in males; 5) an association of ascorbate release with motor activity in central nervous system regions, in vivo; 6) the coupling of brain-cell ascorbate release with glutamate uptake; 7) possible roles for ascorbate modulation of N-methyl-D-aspartate receptor activity; 9) the ability of ascorbate to prevent peroxynitrite anion formation; and 10) evidence supporting the scorbutic guinea pig as a model for amyotrophic lateral sclerosis. Emphasis is placed on the probable competition between superoxide dismutase and ascorbate within the context of a primary defect of metal-binding or metal access in high-concentration proteins such as superoxide dismutase and human heavy neurofilaments. Finally, distinct features of alpha-motoneuronal physiology suggest that cell physiological characteristics such as high metabolic activity and extensive calcium dynamics may render neurons differentially vulnerable in amyotrophic lateral sclerosis.

Glycolytic enzyme binding during entrance to daily torpor in deer mice (Peromyscus maniculatus)

Associations of glycolytic enzymes with the subcellular particulate fraction of skeletal muscle and heart were examined during entrance to daily torpor in deer mice (Peromyscus maniculatus). In skeletal muscle a significant decrease in enzyme binding occurred during torpor entrance for phosphofructokinase, glyceraldehyde-3-phosphate dehydrogenase, and pyruvate kinase, with an additional significant decrease for phosphofructokinase and pyruvate kinase during the deepest state of torpor. Reductions in enzyme binding during torpor entrance also occurred in heart; significant changes were observed in hexokinase, glyceraldehyde-3-phosphate dehydrogenase, and pyruvate kinase binding. Contrary to the finding of additional reductions in enzyme binding seen in skeletal muscle, significant increases in enzyme binding during the deepest torpor state were observed for hexokinase, phosphofructokinase, glyceraldehyde-3-phosphate dehydrogenase, pyruvate kinase, and lactate dehydrogenase in heart. These results suggest that a decrease in the binding of glycolytic enzymes to subcellular structures in skeletal muscle and heart may be at least partially responsible for initiating the reduction in metabolic rate during torpor entrance. This decreased binding may continue to mediate the metabolic reduction in skeletal muscle throughout torpor; heart, however, may require the use of different molecular mechanisms. The increased binding in heart during the deepest state of torpor may represent an anticipatory response in preparation for increased activity during arousal.

Calmodulin antagonists decrease glucose 1,6-bisphosphate, fructose 1,6-bisphosphate, ATP and viability of melanoma cells

Glycolysis is known to be the primary energy source in cancer cells. We investigated here the effect of four different calmodulin antagonists: thioridazine (10-[2-(1-methyl-2-piperidyl) ethyl]-2-methylthiophenothiazine), CGS 9343B (1,3-dihydro-1-[1-[(4-methyl-4H,6H-pyrrolo[1,2-a] [4,1]-benzoxazepin-4-yl)methyl]-4-piperidinyl]-2 H-benzimidazol-2-one (1:1) maleate), clotrimazole (1-(alpha-2-chlorotrityl)imidazole) and bifonazole (1-(alpha-biphenyl-4-ylbenzyl)imidazole), on the levels of glucose 1,6-bisphosphate and fructose 1,6-bisphosphate, the two stimulatory signal molecules of glycolysis, and on ATP content and cell viability in B16 melanoma cells. We found that all four substances significantly reduced the levels of glucose 1,6-bisphosphate, fructose 1,6-bisphosphate and ATP, in a dose- and time-dependent manner. Cell viability was reduced in a close correlation with the fall in ATP. The decrease in glucose 1,6-bisphosphate and fructose 1,6-bisphosphate did not result from the cytotoxic effects of the calmodulin antagonists, since their content was already reduced before any cytotoxic effect was observed. These findings suggest that the fall in the levels of the two signal molecules of glycolysis, induced by the calmodulin antagonists, causes a reduction in glycolysis and ATP levels, which eventually leads to cell death. Since cell proliferation was also reported to be inhibited by calmodulin antagonists, these substances are most promising agents in treatment of cancer by inhibiting both cell proliferation and the glycolytic supply of ATP required for cell growth.