Activator-Mediated Pyruvate Kinase M2 Activation Contributes to Endotoxin Tolerance by Promoting Mitochondrial Biogenesis

Pyruvate kinase M2 (PKM2) is a key glycolysis enzyme, and its effect on macrophages has not been entirely elucidated. Here, we identified that the PKM2 small-molecule agonist TEPP-46 mediated PKM2 activation by inducing the formation of PKM2 tetramer and promoted macrophage endotoxin tolerance. Lipopolysaccharide (LPS)-tolerant mice had higher expression of the PKM2 tetramer, which was associated with a reduced in vivo immune response to LPS. Pretreatment of macrophages with TEPP-46 resulted in tolerance to LPS stimulation, as demonstrated by a significant reduction in the production of TNF-α and IL-6. We found that TEPP-46 induced mitochondrial biogenesis in macrophages. Inhibition of mitochondrial biogenesis by mtTFA knockdown effectively inhibited TEPP-46-mediated macrophage tolerance to endotoxins. We discovered that TEPP-46 promoted the expression of PGC-1α and that PGC-1α was the key regulator of mitochondrial biogenesis in macrophages induced by TEPP-46. PGC-1α was negatively regulated by the PI3K/Akt signaling pathway. Knockdown of PKM2 or PGC-1α uniformly inhibited TEPP-46-mediated endotoxin tolerance by inhibiting mitochondrial biogenesis. In addition, TEPP-46 protected mice from lethal endotoxemia and sepsis. Collectively, these findings reveal novel mechanisms for the metabolic control of inflammation and for the induction of endotoxin tolerance by promoting mitochondrial biogenesis. Targeting PKM2 appears to be a new therapeutic option for the treatment of sepsis and other inflammatory diseases.

Estrogen activates pyruvate kinase M2 and increases the growth of TSC2-deficient cells

Lymphangioleiomyomatosis (LAM) is a devastating lung disease caused by inactivating gene mutations in either TSC1 or TSC2 that result in hyperactivation of the mechanistic target of rapamycin complex 1 (mTORC1). As LAM occurs predominantly in women during their reproductive age and is exacerbated by pregnancy, the female hormonal environment, and in particular estrogen, is implicated in LAM pathogenesis and progression. However, detailed underlying molecular mechanisms are not well understood. In this study, utilizing human pulmonary LAM specimens and cell culture models of TSC2-deficient LAM patient-derived and rat uterine leiomyoma-derived cells, we tested the hypothesis that estrogen promotes the growth of mTORC1-hyperactive cells through pyruvate kinase M2 (PKM2). Estrogen increased the phosphorylation of PKM2 at Ser37 and induced the nuclear translocation of phospho-PKM2. The estrogen receptor antagonist Faslodex reversed these effects. Restoration of TSC2 inhibited the phosphorylation of PKM2 in an mTORC1 inhibitor-insensitive manner. Finally, accumulation of phosphorylated PKM2 was evident in pulmonary nodule from LAM patients. Together, our data suggest that female predominance of LAM might be at least in part attributed to estrogen stimulation of PKM2-mediated cellular metabolic alterations. Targeting metabolic regulators of PKM2 might have therapeutic benefits for women with LAM and other female-specific neoplasms.

Pyruvate Kinase M2 serves as blockade for nucleosome repositioning and abrogates Chd7 remodeling activity

Pyruvate Kinase M2 (PKM2) mediates metabolic reshuffling and is ubiquitously upregulated in several cancer types. The non-metabolic function of PKM2 as key nuclear kinase and modulator of gene expression is instrumental in cancer progression and tumorigenesis. Here, we attempt to discern the non-canonical function of PKM2 as an epigenetic modulator and the underlying implication of this activity. Using 5'-FAM labelled reconstituted mononucleosome we have shown that PKM2 interacts with the complex through Histone H3 and possibly obstruct the access to DNA binding factors. Subsequently, the interaction negatively impacts the ATP dependent remodeling activity of Chromodomain Helicase DNA binding protein-7 (Chd7). Chd7 remodeling activity is required to ameliorate DNA damage and is crucial to genome stability. Our study shows that PKM2 blocks the Chd7 mediated sliding of nucleosome. It can be conjectured that stalling Chd7 may lead to impaired DNA damage and increased genomic instability. We propose a mechanism in which PKM2 negatively regulate nucleosome repositioning in chromatin and may exacerbate cancer by altering the nucleosome architecture. This research is imperative to our understanding of how altered cancer metabolism can potentially modulate the gene expression and sustain incessant proliferation by tweaking the chromatin topography.

OsPK2 encodes a plastidic pyruvate kinase involved in rice endosperm starch synthesis, compound granule formation and grain filling

Starch is the main form of energy storage in higher plants. Although several enzymes and regulators of starch biosynthesis have been defined, the complete molecular machinery remains largely unknown. Screening for irregularities in endosperm formation in rice represents valuable prospect for studying starch synthesis pathway. Here, we identified a novel rice white-core endosperm and defective grain filling mutant, ospk2, which displays significantly lower grain weight, decreased starch content and alteration of starch physicochemical properties when compared to wild-type grains. The normal starch compound granules were drastically reduced and more single granules filled the endosperm cells of ospk2. Meanwhile, the germination rate of ospk2 seeds after 1-year storage was observably reduced compared with wild-type. Map-based cloning of OsPK2 indicated that it encodes a pyruvate kinase (PK, ATP: pyruvate 2-O-phosphotransferase, EC 2.7.1.40), which catalyses an irreversible step of glycolysis. OsPK2 has a constitutive expression in rice and its protein localizes in chloroplasts. Enzyme assay showed that the protein product from expressed OsPK2 and the crude protein extracted from tissues of wild-type exhibits strong PK activity; however, the mutant presented reduced protein activity. OsPK2 (PKpα1) and three other putative rice plastidic isozymes, PKpα2, PKpβ1 and PKpβ2, can interact to form heteromer. Moreover, the mutation leads to multiple metabolic disorders. Altogether, these results denote new insights into the role of OsPK2 in plant seed development, especially in starch synthesis, compound granules formation and grain filling, which would be useful for genetic improvement of high yield and rice grain quality.

Pyruvate Kinase M2 Modulates the Glycolysis of Chondrocyte and Extracellular Matrix in Osteoarthritis

Pyruvate kinase M2 (PKM2) has been wildly verified to modulate glycolysis in tumor cells. However, the role of PKM2 on the glycolysis of osteoarthritis (OA) chondrocytes is still unclear. In present study, we investigate the function of PKM2 on OA chondrocyte glycolysis and the collagen matrix generation in vitro. Results showed that PKM2 was upregulated in OA chondrocytes compared with healthy control chondrocytes. In OA chondrocytes, ATP expression was lower compared with healthy control chondrocytes. Loss-of-function experiment showed that PKM2 knockdown mediated by lentivirus transfection could significantly suppress the glucose consumption and lactate secretion levels and decrease glucose transporter-1 (Glut-1), lactate dehydrogenase A (LDHA), and hypoxia inducible factor 1-alpha (HIF-1α), indicating the inhibition of PKM2 knockdown on glycolysis. Moreover, Cell Counting Kit-8 (CCK-8), flow cytometry, and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay showed that PKM2 knockdown inhibited OA chondrocyte proliferation and promoted the apoptosis. Western blot and immunocytochemical staining showed that PKM2 knockdown downregulated the expression levels of COL2A1 and SOX-9. In summary, our results conclude that PKM2 modulates the glycolysis and extracellular matrix generation, providing the vital role of PKM2 on OA pathogenesis and a novel therapeutic target for OA.

Prognostic significance of metabolic enzyme pyruvate kinase M2 in breast cancer: A meta-analysis

BACKGROUNDS

Numerous studies have reported that aberrant pyruvate kinase M2 isoform (PKM2) expressed in cancer, indicating that PKM2 plays a critical role in tumor initiation and progression. Nevertheless, its prognostic value in breast cancer tumor is yet contentious. Therefore, we performed this meta-analysis to evaluate the prognostic significance of PKM2 in breast cancer.

METHODS

Eligible relevant literatures were retrieved by searching PubMed, the Cochrane Library, Embase through December 2016. Articles that comparing different PKM2 expression levels in human breast cancer tissues and prognostic significance were included. Software RevMan 5.3 and STATA (Review Manager (RevMan): [Computer program]. Version 5.3. Copenhagen: The Nordic Cochrane Centre, The Cochrane Collaboration, 2014.

STATA

StataCorp. 2011. Stata Statistical Software: Release 12. College Station, TX: StataCorp LP) were applied to analyze the outcomes. Pooled results were presented in hazardous ratios (HRs) of 5-year overall survival (OS), progression-free survival (PFS), and odds ratios (ORs) of clinicopathological features with 95% confidence intervals.

RESULTS

Data from 6 involved studies with 895 patients were summarized. Breast cancer patients with high PKM2 had a worse OS (pooled HR = 1.65, 95% CI = 1.31-2.08, P < .001) and PFS (pooled HR = 2.49, 95% CI = 1.84-3.36, P < .00001). High PKM2 expression is related to lymph node metastasis (N1+N2+N3 vs N0, OR = 1.97, 95%CI = 1.39-2.80, P = .0001). The outcome stability was verified via sensitivity analysis. But elevated PKM2 expression was not correlated to tumor stage (T2+T3 vs T1, pooled OR = 0.80, 95% CI = 0.36-1.77, P = .58) and differential grade (G2+G3 vs G1, OR = 2.74, 95%CI = 0.76-9.84, P = .12). No publication bias was found in the included studies for OS (Begg test, P = .260; Egger test, P = .747).

CONCLUSIONS

High PKM2 expression denotes worse OS and PFS in breast cancer patients, and correlate with the lymph node metastasis. However, there is no evidence for the impact of PKM2 expression on T stage and tumor differentiation.

Niche-specific regulation of central metabolic pathways in a fungal pathogen

To establish an infection, the pathogen Candida albicans must assimilate carbon and grow in its mammalian host. This fungus assimilates six-carbon compounds via the glycolytic pathway, and two-carbon compounds via the glyoxylate cycle and gluconeogenesis. We address a paradox regarding the roles of these central metabolic pathways in C. albicans pathogenesis: the glyoxylate cycle is apparently required for virulence although glyoxylate cycle genes are repressed by glucose at concentrations present in the bloodstream. Using GFP fusions, we confirm that glyoxylate cycle and gluconeogenic genes in C. albicans are repressed by physiologically relevant concentrations of glucose, and show that these genes are inactive in the majority of fungal cells infecting the mouse kidney. However, these pathways are induced following phagocytosis by macrophages or neutrophils. In contrast, glycolytic genes are not induced following phagocytosis and are expressed in infected kidney. Mutations in all three pathways attenuate the virulence of this fungus, highlighting the importance of central carbon metabolism for the establishment of C. albicans infections. We conclude that C. albicans displays a metabolic program whereby the glyoxylate cycle and gluconeogenesis are activated early, when the pathogen is phagocytosed by host cells, while the subsequent progression of systemic disease is dependent upon glycolysis.

Pyruvate kinase type M2 and its role in tumor growth and spreading

Proliferating cells and tumor cells in particular express the pyruvate kinase isoenzyme type M2 (M2-PK). Within the tumor metabolome M2-PK regulates the proportions of glucose carbons that are channelled to synthetic processes (inactive dimeric form) or used for glycolytic energy production (highly active tetrameric form, a component of the glycolytic enzyme complex). In tumor cells, the dimeric form of M2-PK (Tumor M2-PK) is always predominant. The dimerization is caused by direct interaction of M2-PK with certain oncoproteins. The switch between the tetrameric and dimeric form of M2-PK allows tumor cells to survive in environments with varying oxygen und nutrient supply.

The pyruvate kinase of Stigmatella aurantiaca is an indole binding protein and essential for development

Myxospore formation of the myxobacterium Stigmatella aurantiaca can be uncoupled from the cooperative development i.e. fruiting body formation, by low concentrations of indole. Two putative indole receptor proteins were isolated by their capacity to bind indole and identified as pyruvate kinase (PK) and aldehyde dehydrogenase. The PK activity of Stigmatella crude extracts was stimulated by indole. Cloning of the PK gene (pykA) and the construction of a pykA disruption mutant strikingly revealed that PK is essential for multicellular development: Fruiting body formation was abolished in the mutant strain and indole-induced spore formation was delayed. The developmental defects could be complemented by insertion of the pykA gene at the mtaB locus of the Stigmatella genome excluding any polar effects of the pykA disruption.

The malic enzyme is required for optimal photoautotrophic growth of Synechocystis sp. strain PCC 6803 under continuous light but not under a diurnal light regimen

A mutation was recovered in the slr0721 gene, which encodes the decarboxylating NADP(+)-dependent malic enzyme in the cyanobacterium Synechocystis sp. strain PCC 6803, yielding the mutant 3WEZ. Under continuous light, 3WEZ exhibits poor photoautotrophic growth while growing photoheterotrophically on glucose at rates nearly indistinguishable from wild-type rates. Interestingly, under diurnal light conditions (12 h of light and 12 h of dark), normal photoautotrophic growth of the mutant is completely restored.

Possible involvement of pyruvate kinase in acquisition of tolerance to hypoxic stress in glial cells

Neurons are highly vulnerable to ischemic/hypoxic stress, while glial cells show tolerance to such stress. However, the mechanisms for tolerance acquisition in glial cells have yet to be established. We attempted to isolate and identify a stress protein that is upregulated in response to hypoxia in human astrocytoma CCF-STTG1 cells. In particular, pyruvate kinase (PK) was upregulated by hypoxia in CCF-STTG1 cells. Hypoxia-inducible factor 1 (HIF-1), the primary transcription factor that is responsible for multiple gene activation under hypoxia, plays a critical role in PK expression during hypoxic challenge. To determine whether newly synthesized PK is involved in tolerance to hypoxic stress, we established the PK-overexpressing neuronal cells. Overexpression of the wild-type, but not the kinase-negative mutant, resulted in attenuation of the loss of cell viability and the typical apoptotic features by hypoxia or oxidative stress in SK-N-MC cells. These findings suggest that upregulation of PK may result in acquisition of tolerance against hypoxic stress, and that the antioxidant effect may be involved in the protective effect of PK.

Possible Structure and Function of the Extra C-Terminal Sequence of Pyruvate Kinase from Bacillus stearothermophilus

The pyruvate kinases from Genus Bacillus and a few other bacteria have an extra C-terminal sequence with a phosphoenolpyruvate binding motif composed of about 110 amino acids. To elucidate the possible structure and function of this sequence, the enzyme lacking the sequence was prepared and characterized. The N-terminal sequences of the peptides, which were found only in the lysylendopeptidase digest of the wild enzyme and not in that of the truncated enzyme, were determined. All the determined sequences were found in the extra C-terminal sequence deduced from the DNA sequence. The truncated enzyme showed decreased affinity for phosphoenolpyruvate and the allosteric effector ribose 5-phosphate, and had a reduced thermostability. Other properties, such as tetrameric structure, specific activity, and allosteric characteristics were unchanged. A comparison of the CD spectra of the truncated enzyme and the recombinant enzyme indicated that the structure of the C-terminal sequence should be rich in beta-sheet. These findings suggest that the sequence actually exists and that it may form a steady domain interacting with the A-domain and C-domain, which are the catalytic domain and allosteric effector binding domain, respectively.

Comparative analysis of pyruvate kinases from the hyperthermophilic archaea Archaeoglobus fulgidus, Aeropyrum pernix, and Pyrobaculum aerophilum and the hyperthermophilic bacterium Thermotoga maritima: unusual regulatory properties in hyperthermophilic archaea

Pyruvate kinases (PK, EC 2.7.1.40) from three hyperthermophilic archaea (Archaeoglobus fulgidus strain 7324, Aeropyrum pernix, and Pyrobaculum aerophilum) and from the hyperthermophilic bacterium Thermotoga maritima were compared with respect to their thermophilic, kinetic, and regulatory properties. PKs from the archaea are 200-kDa homotetramers composed of 50-kDa subunits. The enzymes required divalent cations, Mg2+ and Mn2+ being most effective, but were independent of K+. Temperature optima for activity were 85 degrees C (A. fulgidus) and above 98 degrees C (A. pernix and P. aerophilum). The PKs were highly thermostable up to 110 degrees C (A. pernix) and showed melting temperatures for thermal unfolding at 93 degrees C (A. fulgidus) or above 98 degrees C (A. pernix and P. aerophilum). All archaeal PKs exhibited sigmoidal saturation kinetics with phosphoenolpyruvate (PEP) and ADP indicating positive homotropic cooperative response with both substrates. Classic heterotropic allosteric regulators of PKs from eukarya and bacteria, e.g. fructose 1,6-bisphosphate or AMP, did not affect PK activity of hyperthermophilic archaea, suggesting the absence of heterotropic allosteric regulation. PK from the bacterium T. maritima is also a homotetramer of 50-kDa subunits. The enzyme was independent of K+ ions, had a temperature optimum of 80 degrees C, was highly thermostable up to 90 degrees C, and had a melting temperature above 98 degrees C. The enzyme showed cooperative response to PEP and ADP. In contrast to its archaeal counterparts, the T. maritima enzyme exhibited the classic allosteric response to the activator AMP and to the inhibitor ATP. Sequences of hyperthermophilic PKs showed significant similarity to characterized PKs from bacteria and eukarya. Phylogenetic analysis of PK sequences of all three domains indicates a distinct archaeal cluster that includes the PK from the hyperthermophilic bacterium T. maritima.

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.

[From gene to disease; hereditary non-spherocytic hemolytic anemia caused by pyruvate kinase deficiency]

Pyruvate kinase (PK) deficiency is a common cause of hereditary non-spherocytic haemolytic anaemia. It is an autosomal recessive disorder caused by mutations in the gene coding for erythrocyte and liver-type pyruvate kinase (PKLR). So far, more than 130 mutations in this gene have been identified. Clinical symptoms, usually restricted to homozygous and compound-heterozygous individuals, are variable, ranging from neonatal jaundice requiring erythrocyte transfusions to a fully compensated haemolytic anaemia. The exact mechanism of erythrocyte destruction is unknown, however adenosine-triphosphate depletion and an increase in 2,3-disphosphoglycerate are thought to be important. The diagnosis of pyruvate kinase deficiency depends upon the demonstration of low PK enzyme activity. Due to the pitfalls in determining true PK activity, DNA testing is a valuable tool in the diagnosis of pyruvate kinase deficiency. By centralizing the molecular diagnostics of pyruvate kinase deficiency in Utrecht, more care can be provided for the diagnosis, treatment and support of patients.

Structure and function of human erythrocyte pyruvate kinase. Molecular basis of nonspherocytic hemolytic anemia

Deficiency of human erythrocyte isozyme (RPK) is, together with glucose-6-phosphate dehydrogenase deficiency, the most common cause of the nonspherocytic hemolytic anemia. To provide a molecular framework to the disease, we have solved the 2.7 A resolution crystal structure of human RPK in complex with fructose 1,6-bisphosphate, the allosteric activator, and phosphoglycolate, a substrate analogue, and we have functionally and structurally characterized eight mutants (G332S, G364D, T384M, D390N, R479H, R486W, R504L, and R532W) found in RPK-deficient patients. The mutations target distinct regions of RPK structure, including domain interfaces and catalytic and allosteric sites. The mutations affect to a different extent thermostability, catalytic efficiency, and regulatory properties. These studies are the first to correlate the clinical symptoms with the molecular properties of the mutant enzymes. Mutations greatly impairing thermostability and/or activity are associated with severe anemia. Some mutant proteins exhibit moderate changes in the kinetic parameters, which are sufficient to cause mild to severe anemia, underlining the crucial role of RPK for erythrocyte metabolism. Prediction of the effects of mutations is difficult because there is no relation between the nature and location of the replaced amino acid and the type of molecular perturbation. Characterization of mutant proteins may serve as a valuable tool to assist with diagnosis and genetic counseling.

Pyruvate kinase type M2: a crossroad in the tumor metabolome

Cell proliferation is a process that consumes large amounts of energy. A reduction in the nutrient supply can lead to cell death by ATP depletion, if cell proliferation is not limited. A key sensor for this regulation is the glycolytic enzyme pyruvate kinase, which determines whether glucose carbons are channelled to synthetic processes or used for glycolytic energy production. In unicellular organisms pyruvate kinase is regulated by ATP, ADP and AMP, by ribose 5-P, the precursor of the nucleic acid synthesis, and by the glycolytic intermediate fructose 1,6-P2 (FBP), thereby adapting cell proliferation to nutrient supply. The mammalian pyruvate kinase isoenzyme type M2 (M2-PK) displays the same kinetic properties as the pyruvate kinase enzyme from unicellular organisms. The mammalian M2-PK isoenzyme can switch between a less active dimeric form and a highly active tetrameric form which regulates the channeling of glucose carbons either to synthetic processes (dimeric form) or to glycolytic energy production (tetrameric form). Tumor cells are usually characterized by a high amount of the dimeric form leading to a strong accumulation of all glycolytic phosphometabolites above pyruvate kinase. The tetramer-dimer ratio is regulated by ATP, FBP and serine and by direct interactions with different oncoproteins (pp60v-src, HPV-16 E7). In solid tumors with sufficient oxygen supply pyruvate is supplied by glutaminolysis. Pyruvate produced in glycolysis and glutaminolysis is used for the synthesis of lactate, glutamate and fatty acids thereby releasing the hydrogen produced in the glycolytic glyceraldehyde 3-phosphate dehydrogenase reaction.

Dendritic cells presenting pyruvate kinase M1/M2 isozyme peptide can induce experimental allergic myositis in BALB/c mice

Polymyositis (PM) is an inflammatory muscle disease caused by autoimmune dysfunction, considered to be caused by cytotoxic CD8 T cells. To date, no autoantigens have been identified. We attempted to induce an experimental allergic myositis (EAM) in BALB/c mice by inoculating syngeneic dendritic cells (DC) presenting peptides that are expected to match the binding anchor motif of H-2K(d) (BALB/c). We selected peptides that are highly expressed in skeletal muscle. Only when we inoculated syngeneic bone marrow-derived DC presenting pyruvate kinase M1/M2 peptide 464-472 in BALB/c mice, 41.7% of the mice (EAM) developed pathological changes in skeletal muscle compatible to human PM. Under other conditions (when we inoculated DC presenting no synthetic peptides into BALB/c or C57BL/6 mice and DC presenting pyruvate kinase M1/M2 peptide into C57BL/6 mice), there were no necrotizing and inflammatory lesions. Induction of EAM in the same manner as above also induced CTL activity against P815 cells with the same peptide and syngeneic differentiated cultured myotubes without peptides by the chromium release assay. Consistent with the similarity of the binding anchor motif of H-2K(d) (BALB/c) and HLA A*2402, we conclude that pyruvate kinase M1/M2 peptide is a candidate autoantigen not only in BALB/c-EAM but also in human-PM with the HLA A*2402 allele.

Red cell pyruvate kinase deficiency: from genetics to clinical manifestations

Pyruvate kinase deficiency is the most frequent enzyme abnormality of the Embden-Meyerhof pathway causing hereditary non-spherocytic haemolytic anaemia. The degree of haemolysis varies widely, ranging from very mild or fully compensated forms, to life-threatening neonatal anaemia and jaundice necessitating exchange transfusions. Splenectomy should be reserved for young patients who require regular blood transfusions. The gene encoding for pyruvate kinase (PK-LR) has been localized to the long arm of chromosome I; the cDNA of R-type is 2060 bp long and codes for 574 amino acids. More than 130 different mutations, mostly missense, have so far been described in association with PK deficiency, 1529A and 1456T being considered to be the most common mutations in Caucasians. Analysis of the three-dimensional structure of the enzyme may help in predicting the severity of the molecular defect. Further data on clinical features of homozygous patients are needed, at least for some mutations, to allow a more precise genotype/phenotype correlation.

Leishmania pyruvate kinase: the crystal structure reveals the structural basis of its unique regulatory properties

Glycolysis occupies a central role in cellular metabolism, and is of particular importance for the catabolic production of ATP in protozoan parasites such as Leishmania and Trypanosoma. In these organisms pyruvate kinase plays a key regulatory role, and is unique in responding to fructose 2,6-bisphosphate as allosteric activator. The determination of the crystal structure of the first eukaryotic pyruvate kinase in the T-state (the inactive or 'tense' conformation of allosteric enzymes) is described. A comparison of the effector sites of the Leishmania and yeast enzymes reveals the structural basis for the different effector specificity. Two loops, comprising residues 443-453 and 480-489, adopt very different conformations in the two enzymes, and Lys-453 and His-480 that are a feature of trypanosomatid enzymes provide probable ligands for the 2-phospho group of the effector molecule. These and other differences offer an opportunity for the design of drugs that would exploit regulatory differences between parasite and host.

Transgenic inhibitors identify two roles for protein kinase A in Drosophila development

We have initiated an analysis of protein kinase A (PKA) in Drosophila using transgenic techniques to modulate PKA activity in specific tissues during development. We have constructed GAL4/UAS-regulated transgenes in active and mutant forms that encode PKAc, the catalytic subunit of PKA, and PKI(1-31), a competitive inhibitor of PKAc. We present evidence that the wild-type transgenes are active and summarize the phenotypes produced by a number of GAL4 enhancer-detector strains. We compare the effects of transgenes encoding PKI(1-31) with those encoding PKAr*, a mutant regulatory subunit that constitutively inhibits PKAc because of its inability to bind cyclic AMP. Both inhibitors block larval growth, but only PKAr* alters pattern formation by activating the Hedgehog signaling pathway. Therefore, transgenic PKI(1-31) should provide a tool to investigate the role of PKAc in larval growth regulation without concomitant changes in pattern formation. The different effects of PKI(1-31) and PKAr* suggest two distinct roles, cytoplasmic and nuclear, for PKAc in Hedgehog signal transduction. Alternatively, PKAr* may target proteins other than PKAc, suggesting a role for free PKAr in signal transduction, a role inhibited by PKAc in reversal of the classical relationship of these subunits.

Regulatory properties and active site groups of cytosolic mung bean pyruvate kinase

Properties of mung bean pyruvate kinase were studied and the active site groups were derived. Metabolites like AMP, glucose, glucose-6-phosphate, fructose-6-phosphate, fructose-1, 6-bisphosphate, 3-phospho-glycerate, isocitrate, malate and alpha-ketoglutarate had practically no effect on pyruvate kinase activity. Alanine, serine, glutamine, methionine and GMP had a weak activating effect on the enzyme. Some metabolites such as ATP, GTP, and UMP were found to be weakly inhibitory. Moderate to strong inhibition was observed with citrate, succinate, glutamate and oxalate. Inhibition brought about by ATP and citrate when present together showed synergistic effect. Inhibition by citrate was non-competitive with respect to both PEP and ADP suggesting the presence of a regulatory site. Mung bean pyruvate kinase showed half optimal activity at pH 6.6 and 8.9 at saturating concentrations of PEP, ADP and Mg2+. Small concentrations of the SH specific reagents, namely iodoacetamide (0.1 and 0.2 mM), N-ethylmaleimide(0.05-0.1 mM) and p-chloromercuribenzoate (0.1 mM) inactivated the enzyme; single exponential loss of activity was observed in each case. Photooxidation of the enzyme in the presence of methylene blue (100 and 200 micrograms/ml) and rose bengal (5 and 10 micrograms/ml) also led to a single exponential activity decay. When the enzyme was treated with diethyl pyrocarbonate (DEP), a time dependent exponential decay in its activity was observed with a parallel increase in absorbance at 240 nm. PEP protected the enzyme against inactivation by DEP. Reagents specific for tyrosine (iodine and tetranitromethane) and tryptophan residues (N-bromosuccinimide) residues had no effect. These observations confirm that SH and imidazole groups are vital for the activity of the enzyme.

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.

Insulin resistance in obesity and its molecular control

The Wistar fatty rat is a model of obese non-insulin-dependent diabetes mellitus. Males, but not females, develop hyperglycemia, glucouria and polyuria within 8 weeks of age. The regulation of gene expression by insulin has been shown to be differentially impaired in the liver of the fatty rats. The genes resistant to insulin include glucokinase gene and phosphoenolpyruvate carboxykinase gene. In contrast, L-type pyruvate kinase gene responds to insulin normally, raising the possibility that the signaling pathway from the insulin receptor to the insulin-resistant genes, but not to the insulin-sensitive genes, is defective at a point beyond the receptor kinase in the fatty rats. On the other hand, female fatty rats develop hyperglycemia only when they are given sucrose for several weeks. This treatment causes a decrease in gucokinase while enzymes involved in gluconeogenesis are increased. Chronic feeding of sucrose also leads to hypertriglycemia and visceral fat accumulation, which is more frequently associated with abnormalities in glucose and lipid metabolisms. Fructose is believed to be the responsible component of sucrose for these effects. Hypertriglyceridemic effect of fructose is mainly due to an increase in hepatic production of VLDL. Most enzymes related to lipogenesis in the liver are induced by dietary fructose even in diabetes. L-type pyruvate kinase is one of such enzymes. Cis-acting element named PKL-III in the 5'-flanking region of this gene is shown to be responsive to dietary fructose as well as to dietary glucose. Thus, identification and characterization of a protein bound to this element could help in the further understanding of the molecular mechanism of the fructose actions.

Effects of estrogen on gluconeogenesis and related parameters in male rainbow trout

To investigate the effects of estrogen, the hormone responsible for vitellogenesis, on gluconeogenesis, male rainbow trout were implanted with 17 beta-estradiol or given a sham procedure. Plasma glucose concentration in estrogenized fish was 50% of the control fish (6.4 mM). Glucose synthesis from physiological concentrations of alanine was 0.08 mumol.g cells-1 x h-1 compared with 0.20 mumol.g cells-1 x h-1 in control fish; synthesis from physiological concentrations of lactate was reduced by over 50% (0.88 vs. 0.36 mumol.g cells-1 x h-1) in implanted fish. Gluconeogenesis from 5 mM lactate was also significantly depressed in implanted fish. Oxidation of alanine, serine, and lactate was not significantly affected by estrogen implantation. The maximum clearance velocity of a key enzyme negatively regulating gluconeogenesis, pyruvate kinase, was 3.03 mumol.g cells-1 x h-1 in estrogen (E2) implanted fish compared with 7.83 mumol.g cells-1 x h-1 in control fish. No significant differences in plasma insulin or glucagon were found in the two groups. We conclude that estrogen depresses gluconeogenesis and that this reduction contributes to the lower plasma glucose concentration seen in vitellogenic trout.

Molecular mechanism of induction of key enzymes related to lipogenesis

Key enzymes related to lipogenesis in the liver are induced by a high glucose diet or insulin and suppressed by starvation, diabetes, or glucagon. Most of these enzymes are also induced by dietary fructose, even in diabetic liver. This regulation occurs at the posttranscriptional level as well as at the transcriptional level. We studied extensively the molecular mechanism of induction of L-type pyruvate kinase (LPK). The transcription of the LPK gene in the liver was stimulated by insulin and inhibited by glucagon. This insulin action required ongoing protein synthesis and metabolism of glucose and was enhanced by glucocorticoid. On the other hand, the mechanism of induction of the LPK by dietary fructose depended on plasma insulin levels. Dietary fructose stimulated transcription of the LPK gene in normal rats, whereas it acted mainly at the posttranscriptional level in diabetic rats. These fructose effects were attributable to a common metabolite of fructose and glycerol. The induction of LPK mRNA by dietary glucose was impaired in the liver of Wistar fatty rats, a model of obese non-insulin-dependent diabetes mellitus, but fructose-induced accumulation of the mRNA was not. Studies on transgenic mice indicated that the 5'-flanking region up to -3 kb of the LPK gene contained all cis-acting elements necessary for tissue-specific expression of LPK and its stimulation by diets and insulin. Further analysis using a transient expression assay revealed the presence of three cis-acting elements necessary for expression of LPK in hepatocytes in the region up to -170 kb. However, these elements alone were not sufficient for dietary and hormonal regulation of this enzyme when analyzed in transgenic mice.

Characterization of pyruvate kinase of Trypanosoma brucei and its role in the regulation of carbohydrate metabolism

Pyruvate kinase from Trypanosoma brucei is a labile enzyme, losing its activity within several hours. In mixtures containing 50 mM triethanolamine buffer, pH 7.2, 25% glycerol and 0.5 mM inorganic phosphate the enzyme remained active and could be purified to homogeneity with a specific activity of 417 units mg-1 and a yield of 65%. The enzyme has an activation energy of 31.9 kJ mol-1. Magnesium and potassium ions are essential for activity. Cobalt or manganese ions replace Mg2+ but this leads to a decrease in maximal velocity. Potassium ions can be substituted by ammonium ions, while sodium ions behave as a competitive inhibitor with respect to both K+ and NH4+. All metal ions studied displayed sigmoidal kinetics. The enzyme is activated, with decreasing efficiency by fructose 2-phosphorothioate 6-phosphate, fructose 2,6-bisphosphate, fructose 1,6-bisphosphate and glucose 1,6-bisphosphate. They all display hyperbolic kinetics. Glycerate 2,3-bisphosphate, glyceraldehyde 3-phosphate, CoASAc, oxalate, AMP, ADP, and ATP inhibit the enzyme. At substrate saturation PK was activated by Pi up to a concentration of 0.8 mM. At higher Pi concentrations the enzyme is inhibited. The enzyme is unaffected by most amino acids, only phenylalanine stimulates and tyrosine inhibits.

Glycolysis preferentially inhibits ATP-sensitive K+ channels in isolated guinea pig cardiac myocytes

In heart, glycolysis may be a preferential source of adenosine triphosphate (ATP) for membrane functions. In this study the patch-clamp technique was used to study potassium channels sensitive to intracellular ATP levels in permeabilized ventricular myocytes. Activation of these K+ channels has been implicated in marked cellular K+ loss leading to electrophysiological abnormalities and arrhythmias during myocardial ischemia. The results showed that glycolysis was more effective than oxidative phosphorylation in preventing ATP-sensitive K+ channels from opening. Experiments in excised inside-out patches suggested that key glycolytic enzymes located in the membrane or adjacent cytoskeleton near the channels may account for their preference for glycolytic ATP.

Localization and role of pyruvate kinase isoenzymes in the regulation of carbohydrate metabolism and pyruvate recycling in rat kidney cortex

This work was performed to gain more information on the role of pyruvate kinase isoenzymes in the regulation of renal carbohydrate metabolism. Immunohistochemically, pyruvate kinase type L is shown to be localized in the proximal tubule of the nephron and pyruvate kinase type M2 in the distal tubule and the collecting duct. a tight relationship between gluconeogenesis and pyruvate recycling was found. The rate of gluconeogenesis (8 mumol/g wet wt. per 30 min) was of the same order of magnitude as the rate of pyruvate recycling (10.92 mumol/g wet wt. per 30 min). Stimulation of gluconeogenesis from 20 mM lactate in kidney cortex slices of 24-h-starved rats by dibutyryl-cAMP, alanine and parathyroid hormone was connected with a decrease in pyruvate recycling; inhibition of gluconeogenesis due to a lack of Ca2+ in the incubation medium was linked with an increase in pyruvate recycling. The degradation of [6-14C]glucose to lactate, pyruvate, ketone bodies and CO2 and of [2-14C]lactate was unaffected by dibutyryl-cAMP, alanine, epinephrine, vasopressin or the omission of Ca2+ from the incubation medium. 1 mM dibutyryl-cAMP or 5 mM alanine did not alter the activities of oxaloacetate decarboxylase, 'malic' enzyme and malate dehydrogenase from rat kidney cortex. Since aerobic glycolysis in the distal tubules and the collecting ducts is not influenced by hormones, dibutyryl-cAMP and Ca2+, pyruvate kinase type M2 residing in this tissue is unlikely to be a control point of glycolysis. Since this tissue degrades only one-seventh of the glucose formed via gluconeogenesis, it does not contribute significantly to pyruvate recycling. Therefore, the decrease of pyruvate recycling in the presence of dibutyryl-cAMP and alanine in rat kidney cortex slices, leading to increased renal gluconeogenesis, has to be ascribed to the regulation of pyruvate kinase type L.

Sequences complementary to the brain-specific "identifier" sequences exist in L-type pyruvate kinase mRNA (a liver-specific messenger) and in transcripts especially abundant in muscle

A sequence complementary to the brain-specific identifier sequence has been found in the 3' untranslated extension of the heavy 3.2-kilobase (kb) long liver L-type pyruvate kinase mRNA while it is absent in the other two 2- and 2.2-kb long pyruvate kinase mRNA species. A 53-base fragment corresponding to this identifier sequence was subcloned in both orientations in the single-stranded bacteriophage M13, both strands being used as probes to detect homologous sequence in different tissues. Both strands are transcribed in various tissues and are detected in heterogeneous high molecular weight RNA species which are especially abundant in the adult muscle. In addition, the probe identical to the identifier sequence recognized a discrete 0.6-kb RNA species in the muscle and the probe complementary to the identifier-sequence recognized the expected two small brain-specific identifier BC-1 and BC-2 RNAs described by Sutcliffe et al. (Sutcliffe, J. G., Milner, R. J., Bloom, F. E., and Lerner, R. A. (1982) Proc. Natl. Acad. Sci. U. S. A. 79, 4942-4946; Sutcliffe, J. G., Milner, R. J., Gottesfeld, J. M., and Lerner, R. A. (1984) Nature 308, 237-241; Milner, R. J., Bloom, F. E., Lai, C., Lerner, R. A., and Sutcliffe, J. G. (1984) Proc. Natl. Acad. Sci. U. S. A. 81, 713-717; Sutcliffe, J. G., Milner, R. J., Gottesfeld, J. M., and Reynolds, W. (1984) Science 225, 1308-1314).

Evolution of the functional properties of pyruvate kinase isozymes: pyruvate kinase L from Rana pipiens

The regulatory properties of type L pyruvate kinase from Rana pipiens are intermediate between those of the mammalian K and L isozymes. As with mammalian type L, the levels of the frog isozyme are affected by the animal's nutritional state. The mammalian and amphibian isozymes show similar sensitivities to fructose 1,6-bisphosphate activation and amino acid inhibition. By contrast, the frog L isozyme shares several properties of the K class: i.e. irreversible inactivation by oxidized glutathione and lack of response to a cyclic AMP stimulated phosphorylation. Furthermore, as for some mammalian K isozymes, frog type L shows a high PEP affinity and a low cooperativity of PEP binding. Insofar as the properties of this present day enzyme reflect those of its counterpart in the amphibian ancestor of higher vertebrates, our results suggest that at its first expression, the type L resembled the type K. Many important regulatory properties of the L isozyme, especially the sensitivity to phosphorylation, were acquired more recently perhaps in association with an increased importance of constant blood glucose.

Purification and properties of aerobic and anoxic forms of pyruvate kinase from red muscle tissue of the channelled whelk, Busycotypus canaliculatum

Aerobic and anoxic variants of radular retractor muscle pyruvate kinase (PK-aerobic and Pk-anoxic) from the gastropod mollusc, Busycotypus canaliculatum, were purified to homogeneity and respective specific activities of 368 and 186 mumol of product min-1 mg protein-1. Both PK variants were apparent homotetramers with native molecular masses of about 235 kDa, but differed in several other physical characteristics including pI (5.81 +/- 0.06 for PK-aerobic, 5.42 +/- 0.03 for PK-anoxic) and chromatographic behavior on several columns used during their respective purifications. The two enzymes differed greatly in several kinetic properties. Affinity for phosphoenolpyruvate was more than tenfold greater for PK-aerobic (K0.5 = 0.067 +/- 0.002 mM; h = 0.99 +/- 0.10), whereas the cooperative effect for phosphoenolpyruvate binding was greatly enhanced for PK-anoxic (K0.5 = 0.85 +/- 0.02 mM, h = 2.57 +/- 0.01). Although the affinities for the second substrate, ADP, were identical for both enzyme forms (apparent Km = 0.25 mM) pK-anoxic showed greater substrate inhibition by high concentrations of ADP. Likewise, affinities for K+ and Mg2+ were similar but PK-anoxic showed a greater degree of cooperativity with Mg2+ (h = 2.50 +/- 0.02) than did PK-aerobic (h = 1.70 +/- 0.06). Saturating concentrations of fructose 1,6-bisphosphate (50 microM) activated PK-anoxic resulting in an enzyme with properties similar to fructose-1,6-bisphosphate-activated PK-aerobic, with K0.5 values for phosphoenolpyruvate of about 0.04 mM and Hill coefficients of 1.1. PK-anoxic showed much stronger regulation by the allosteric inhibitors MgATP, phenylalanine, proline and alanine. Fructose 1,6-bisphosphate partially relieved the inhibitions by ADP, MgATP, alanine, proline and arginine phosphate of both enzyme forms. However, at 0.1 mM phosphoenolpyruvate PK-aerobic was much more sensitive to activation by fructose 1,6-bisphosphate, Ka values being 0.05 +/- 0.01 microM for PK-aerobic and 1.3 +/- 0.1 microM for PK-anoxic. In the presence of 1.0 mM alanine and 1.5 mM MgATP much higher concentrations of fructose 1,6-bisphosphate were required for activation of PK-anoxic (Ka = 5.2 +/- 0.4 microM) than for PK-aerobic (Ka = 0.02 +/- 0.01 microM). Variations in pH over the range likely occurring in vivo during anaerobiosis caused no significant additional kinetic differences between the two enzyme forms. The dissimilarity in kinetic properties of PK-aerobic and PK-anoxic indicate that red muscle PK activity is probably strongly depressed in vivo during anoxia stress.

Interrelationships and functions of the pyruvate kinase isozymes and their variant forms: a review

The relationships among and the properties of the pyruvate kinase isozymes are reviewed, emphasizing their potential role in carcinogenesis. Particular consideration is given to evaluation of the concept that the three major nonreadily interconvertible forms are the products of distinct genes, the relationship of these forms to additional separable forms of pyruvate kinase, the types and possible functions of interconvertible forms of the major isozymes, and mechanisms affecting the genetic expression of the isozymes. Emphasis is placed upon the apparent derepression of the fetal isozyme in hepatomas and the influence of neoplasms and their extracts on the expression of pyruvate kinase in the liver of host animals.

Energy metabolism of spermatozoa. V. The Embden-Myerhof pathway of glycolysis: activities of pathway enzymes in hypotonically treated rabbit epididymal spermatozoa

Seven enzymes of the Embden-Myerhof pathway of glycolysis were assayed in hypotonically treated epididymal sperm from mature rabbits. These were: fructose-biphosphate aldolase, triosephosphate isomerase, glyceraldehydephosphate dehydrogenase, 3-phosphoglyceromutase, enolase, pyruvate kinase, and lactate dehydrogenase. These enzymes were firmly enough bound to the cell structure to resist removal by washing after hypotonic treatment and had maximal activities comparable to, or greater than, the rate of mitochondrial pyruvate oxidation, so that rapid oxygen uptake was observed with intermediates of the glycolytic pathway. The activity of lactate dehydrogenase in a typical preparation of hypotonically treated cells was 5.3 mumoles/minute x 10(9) cells at 25 degrees C for pyruvate reduction in the hypotonically treated cells and 4.8 mumoles/minute x 10(9) cells in the thrice-washed hypotonically treated cells. The Km for pyruvate was 1.4 mM while that for lactate was 4.4 mM. By contrast, the maximal activity of pyruvate oxidation by mitochondria was 0.10 microgram atom of oxygen/minute x 10(9) cells, corresponding to 0.020 mumole of pyruvate/minute x 10(9) cells, and the Km for pyruvate was 5 microM. These enzyme parameters favor high lactate production from glucose in aerobic glycolysis.

Pyruvate kinase variants of the Alaskan king-crab. Evidence for a temperature-dependent interconversion between two forms having distinct and adaptive kinetic properties

1. Pyruvate kinase of Alaskan king-crab leg muscle exists in two kinetically distinct forms, each of which displays a different temperature-dependence in the K(m) for phosphoenolpyruvate. 2. A ;cold' variant of the enzyme has hyperbolic kinetics and exhibits a minimal K(m) for substrate at 5 degrees . At physiological concentrations of phosphoenolpyruvate the ;cold' enzyme is active only below 10 degrees . A ;warm' pyruvate kinase has a minimal K(m) for substrate at about 12 degrees . This enzyme displays sigmoidal kinetics and is likely to be inactive, at physiological substrate concentrations, at temperatures below 9 degrees . 3. The combined activities of these two pyruvate kinases yield highly temperature-independent rates of catalysis, at physiological substrate concentrations, over the range of habitat temperatures encountered by the organism, namely 4-12 degrees . 4. The two variants of pyruvate kinase do not appear to be isoenzymes in the conventional sense. Electrophoretic and electrofocus analyses revealed only single peaks of activity. 5. The results suggest that the ;warm' pyruvate kinase and the ;cold' pyruvate kinase are formed by a temperature-dependent interconversion of one protein species. This interconversion has major adaptive significance: as the temperature is lowered the ;warm' enzyme is converted into the ;cold' enzyme; the opposite situation obtains when the temperature is raised. Temperature changes thus mimic the effects noted for fructose 1,6-diphosphate on certain mammalian pyruvate kinases.