Species specificity of the cytokine function of phosphoglucose isomerase

Digging deeper through glucose metabolism and its regulators in cancer and metastasis

Glucose metabolism enzymes and transporters play major role in cancer development and metastasis. In this study, we discuss glucose metabolism, transporters, receptors, hormones, oncogenes and tumor suppressors which interact with glucose metabolism and we try to discuss their major role in cancer development and cancer metabolism. We try to highlight the. Metabolic changes in cancer and metastasis upregulation of glycolysis is observed in many primary and metastatic cancers and aerobic glycolysis is the most favorable mechanism for glucose metabolism in cancer cells, and it is a kind of evolutionary change. The question that is posed at this juncture is: Can we use aerobic glycolysis phenotype and enzymes beyond this mechanism in estimating cancer prognosis and metastasis? Lactate is a metabolite of glucose metabolism and it is a key player in cancer and metastasis in both normoxic and hypoxic condition so lactate dehydrogenase can be a good prognostic biomarker. Furthermore, monocarboxylic transporter which is the main lactate transporter can be good target in therapeutic studies. Glycolysis enzymes are valuable enzymes in cancer and metastasis diagnosis and can be used as therapeutic targets in cancer treatment. Designing a diagnostic and prognostic profile for cancer metastasis seems to be possible base on glycolysis enzymes and glucose transporters. Also, glucose metabolism enzymes and agents can give us a clear vision in estimating cancer metastasis. We can promote a panel of genes that detect genetic changes in glucose metabolism agents to diagnose cancer metastasis.

AMF/PGI-mediated tumorigenesis through MAPK-ERK signaling in endometrial carcinoma

Autocrine motility factor (AMF), which is also known as phosphoglucose isomerase (PGI), enhances tumor cell growth and motility. In this study, we found that AMF and its receptor were both highly expressed in Endometrial Carcinoma (EC) tissues compared to normal tissues. Levels of AMF were increased in serum of endometrial cancer patients. Downregulation of AMF by shRNA inhibited invasion, migration and proliferation as well as growth in a three-dimensional culture. AMF cytokine function, but not enzymatic activity of PGI, regulated tumorigenic activities of AMF. The MAPK-ERK1/2 pathway contributed to AMF-induced effects in EC cells. In agreement, Mek inhibitor decreased AMF-induced invasion, migration and proliferation of EC cells. In addition, in two mouse tumor metastasis models (EC cells delivered through left ventricle or intraperitoneally) AMF-silenced EC cells showed decreased tumor proliferative and metastatic capacities. We suggest that AMF/PGI is a potential therapeutic target in endometrial carcinoma.

Bacterial virulence in the moonlight: multitasking bacterial moonlighting proteins are virulence determinants in infectious disease

Men may not be able to multitask, but it is emerging that proteins can. This capacity of proteins to exhibit more than one function is termed protein moonlighting, and, surprisingly, many highly conserved proteins involved in metabolic regulation or the cell stress response have a range of additional biological actions which are involved in bacterial virulence. This review highlights the multiple roles exhibited by a range of bacterial proteins, such as glycolytic and other metabolic enzymes and molecular chaperones, and the role that such moonlighting activity plays in the virulence characteristics of a number of important human pathogens, including Staphylococcus aureus, Streptococcus pyogenes, Streptococcus pneumoniae, Helicobacter pylori, and Mycobacterium tuberculosis.

Crystallization and preliminary X-ray crystallographic study of phosphoglucose isomerase from Plasmodium falciparum

Phosphoglucose isomerase (PGI) is a key enzyme in glycolysis and glycogenesis that catalyses the interconversion of glucose 6-phosphate (G6P) and fructose 6-phosphate (F6P). For crystallographic studies, PGI from the human malaria parasite Plasmodium falciparum (PfPGI) was overproduced in Escherichia coli, purified and crystallized using the hanging-drop vapour-diffusion method. X-ray diffraction data to 1.5 A resolution were collected from an orthorhombic crystal form belonging to space group P2(1)2(1)2(1) with unit-cell parameters a = 103.3, b = 104.1, c = 114.6 A. Structural analysis by molecular replacement is in progress.

Cross-species analysis of the glycolytic pathway by comparison of molecular interaction fields

The electrostatic potential of an enzyme is a key determinant of its substrate interactions and catalytic turnover. Here we invoke comparative analysis of protein electrostatic potentials, along with sequence and structural analysis, to classify and characterize all the enzymes in an entire pathway across a set of different organisms. The electrostatic potentials of the enzymes from the glycolytic pathway of 11 eukaryotes were analyzed by qPIPSA (quantitative protein interaction property similarity analysis). The comparison allows the functional assignment of neuron-specific isoforms of triosephosphate isomerase from zebrafish, the identification of unusual protein surface interaction properties of the mosquito glucose-6-phosphate isomerase and the functional annotation of ATP-dependent phosphofructokinases and cofactor-dependent phosphoglycerate mutases from plants. We here show that plants possess two parallel pathways to convert glucose. One is similar to glycolysis in humans, the other is specialized to let plants adapt to their environmental conditions. We use differences in electrostatic potentials to estimate kinetic parameters for the triosephosphate isomerases from nine species for which published parameters are not available. Along the core glycolytic pathway, phosphoglycerate mutase displays the most conserved electrostatic potential. The largest cross-species variations are found for glucose-6-phosphate isomerase, enolase and fructose-1,6-bisphosphate aldolase. The extent of conservation of electrostatic potentials along the pathway is consistent with the absence of a single rate-limiting step in glycolysis.

AMF/G6PI induces differentiation of leukemic cells via an unknown receptor that differs from gp78

Autocrine Motility Factor (AMF)/maturation factor (MF)/neuroleukin (NLK) is a multifunctional protein, which acts as a glucose 6-phosphate isomerase (G6PI) intracellularly. Exto-G6PI stimulates invasion and metastasis of tumor cells, neurotropic growth and differentiation of leukemic cells. The cell motility and proliferation receptor is known to be gp78 (78 kilo-Dalton glycoprotein), which has seven transmembrane domains in its N-terminal region, but the maturation factor receptor remains unclear. The human acute monocytic leukemia line does not express gp78 and its motile activity is not enhanced by AMF though it is well differentiated by AMF exposure. The forced expression of gp78 in leukemic cells recovered acceptable motile stimulation, concomitant with reduced differentiation ability. Two unknown proteins were detected by crosslinking between AMF and leukemic cells. The results of this report suggest that the receptor molecule for AMF/NLK/MF in leukemic differentiation is not gp78.

The complex biology of autocrine motility factor/phosphoglucose isomerase (AMF/PGI) and its receptor, the gp78/AMFR E3 ubiquitin ligase

Phosphoglucose isomerase (PGI) is a glycolytic enzyme that exhibits a dual function as an extracellular cytokine, under the name autocrine motility factor (AMF). Its cell surface receptor, gp78/AMFR, is also localized to the endoplasmic reticulum where it functions as an E3 ubiquitin ligase. Expression of both AMF/PGI and gp78/AMFR is associated with cancer and, in this review, we will discuss various aspects of the biology of this ligand-receptor complex and its role in tumor progression.

The Autocrine Motility Factor (AMF) and AMF-receptor Combination Needs Sugar Chain Recognition Ability and Interaction Using the C-terminal Region of AMF

The autocrine motility factor (AMF) promotes cellular locomotion or invasion, and regulates tumor angiogenesis or ascites accumulation. These signals are triggered by binding between AMF and its receptor (AMFR), a glycoprotein on the cell surface. AMF has been identified as phosphohexose isomerase (PHI). Previous reports have suggested that the substrate-recognition of exo-PHI is significant for receptor binding. Crystallographic studies have shown that AMF consists of three domains, and that the substrate or inhibitor of PHI is stored between the large and small domains, corresponding to approximately residues 117-288. Here, site-directed mutagenesis was used to investigate 18 recombinant human AMF point mutants involving critical amino acid residues for substrate or enzyme inhibitor recognition or binding. Mutation of residues that interact with the phosphate group of the PHI substrate significantly reduced the cell motility-stimulating activity. Their binding capacities for AMFR were also lower than wild-type human AMF. Mutants that retained the enzymic activity showed the motility-stimulating effect and receptor binding and had sensitivity to a PHI inhibitor. Mutant AMFR lacking the N-sugar chain was expressed on the cell membrane but did not respond to AMF-stimulation, and N-glycosidase-treated AMFR did not compete with receptor binding of AMF. Furthermore, the AMF domains that contain the substrate storage domain and C-terminal region stimulate cell locomotion. These results suggest that the N-glyco side-chain of AMFR is a trigger and that interaction between the 117-C-terminal part of AMF and the extracellular core protein of AMFR is needed during AMF-AMFR interactions.

pH-specific sequestration of phosphoglucose isomerase/autocrine motility factor by fibronectin and heparan sulphate

Phosphoglucose isomerase (PGI) is a glycolytic enzyme that moonlights as a cytokine under the aliases autocrine motility factor (AMF), neuroleukin and maturation factor. The cytokine function of PGI/AMF targets multiple cell types however mechanisms that regulate and sequester this ubiquitous, circulating cytokine remain largely unidentified. PGI/AMF is shown here to exhibit fibronectin (FN)-dependent cell surface association at both neutral and acid pH. Direct PGI/AMF binding to FN and fluorescence resonance energy transfer (FRET) between PGI/AMF and FN were detected only at pH 5. At neutral pH, the interaction of PGI/AMF with FN is receptor-mediated requiring prior clathrin-dependent endocytosis. PGI/AMF and FN do not co-internalize and PGI/AMF undergoes a second round of endocytosis upon recycling to the plasma membrane indicating that recycling PGI/AMF receptor complexes associate with FN fibrils. Heparan sulphate does not affect cell association of PGI/AMF at neutral pH but enhances the FN-independent cell surface association of PGI/AMF at acid pH identifying two distinct mechanisms for PGI/AMF sequestration under acidic conditions. However, only PGI/AMF sequestration by FN at acid pH was able to stimulate cell motility upon pH neutralization identifying FN as a pH-dependent cytokine trap for PGI/AMF. The multiple ways of cellular association of PGI/AMF may represent acquired mechanisms to regulate and harness the cytokine function of PGI/AMF.

Single-gene disorders: what role could moonlighting enzymes play?

Single-gene disorders with "simple" Mendelian inheritance do not always imply that there will be an easy prediction of the phenotype from the genotype, which has been shown for a number of metabolic disorders. We propose that moonlighting enzymes (i.e., metabolic enzymes with additional functional activities) could contribute to the complexity of such disorders. The lack of knowledge about the additional functional activities of proteins could result in a lack of correlation between genotype and phenotype. In this review, we highlight some notable and recent examples of moonlighting enzymes and their possible contributions to human disease. Because knowledge and cataloging of the moonlighting activities of proteins are essential for the study of cellular function and human physiology, we also review recently reported and recommended methods for the discovery of moonlighting activities.

A Possibility that AMF will Serve as a Target Molecule for the Diagnosis and Treatment in a Metastatic Neoplasm

The Autocrine Motility Factor (AMF) identified as a tumor cell motile stimulation factor is a key molecule of invasion and metastasis. The AMF is also identified as neuroleukin (NLK) and maturation factor (MF) which are secreted phosphohexose isomerase (PHI, PGI) from anaplastic cells. Tumor AMF promotes cellular locomotion or invasion, and regulates tumor MMPs secretion or apoptotic resistance. The AMF was thought to be an autocrine factor as the name shows it, and it is peculiar to malignant cells. However we found paracrine effect of AMF against tumor surrounding host tissues. Especially, endothelial cells which are essential parts of tumor induced angiogenesis or ascites accumulation express the AMF-receptor and they responded to AMF stimulation. Metastasis is a most complicated biological phenomenon that a large number of molecules or factors induced by tumor and host are related, thus AMF is also unusual molecule reacting between tumor and host tissues, and therefore AMF should be a target of treatment or diagnosis of cancer.

The need for metabolic mapping in living cells and tissues

The ultimate activity of an enzyme depends on many regulatory steps from transcription of the gene up to complex formation of the enzyme. Therefore, gene expression (mRNA levels) or protein expression (protein levels) are not reliable parameters to predict the functional activity of an enzyme. Activity measurements in cell homogenates or in frozen or fixed (and thus dead) cell preparations are not appropriate either because post-translational regulation mechanisms that exist in living cells may be lost by homogenization or freezing or chemical fixation of cells. Therefore, metabolic mapping in living cells or, in other words, visualization and quantification using microscopy and image analysis of enzyme reactions in living cells is the approach of choice to understand the functional role of enzymes in vivo as is demonstrated here with a number of examples in recent literature.

Glucose-6-phosphate isomerase variants play a key role in the generation of anti-GPI antibodies: possible mechanism of autoantibody production

Glucose-6-phosphate isomerase (GPI), recognized as an autoantigen in the K/BxN arthritis model, is a ubiquitous cytoplasmic enzyme. Anti-GPI antibodies (Abs) are also detected in the serum of patients with arthritic diseases including rheumatoid arthritis (RA). So far, 24 GPI variants have been reported and most of these variants relate to non-spherocytic hemolytic disease. To understand the mechanisms of anti-GPI Ab production, cDNAs from peripheral blood mononuclear cells of subjects with or without anti-GPI Abs were cloned and sequenced. We identified 39 new GPI variants (57-1596 bp). The frequency of GPI variants in healthy control subjects (HS) with anti-GPI Abs (27/73, 31.5%) was significantly higher than that in anti-GPI Ab-negative HS (5/78, 6.4%, p < 0.001). The frequency of GPI variants in anti-GPI Ab-positive RA patients (22/77, 28.6%) was more significantly higher than in anti-GPI Ab-negative patients (1/63, 1.6%, p < 0.0001). Our results suggest that GPI variants may play a crucial role in the production of autoantibodies against ubiquitous GPI autoantigens.

Characterization of a lysyl aminopeptidase activity associated with phosphoglucose isomerase of Vibrio vulnificus

Phosphoglucose isomerase (PGI) is a multifunctional enzyme involved in glycolysis and gluconeogenesis and, in mammalian cells, functions as neuroleukin, autocrine motility factor (AMF), and differentiation and maturation factor (MF). We isolated and characterized PGI with a novel lysyl aminopeptidase (LysAP) activity (PGI-LysAP) from Vibrio vulnificus. Mass spectrometry revealed that PGI-LysAP is a heterodimer consisting of 23.4- and 60.8-kDa subunits. Only the heterodimer displayed LysAP activity. PGI-LysAP has a pI around 6.0 and high specificity toward the synthetic, fluorogenic substrate l-lysyl-7-amino-4-methylcoumarin. LysAP activity is optimal at pH 8.0, is 64% higher at 37 degrees C than at 21 degrees C, does not directly correlate with virulence, and is strongly inhibited by serine protease and metalloprotease inhibitors. PGI-LysAP was also identified in Vibrio parahaemolyticus and V. cholerae, but was absent from non-Vibrio human pathogens. Sequencing of the pgi gene revealed 1653 bp coding for a 550-amino-acid protein. Cloned and expressed PGI formed a homodimer with isomerase activity, but not LysAP activity. The finding of LysAP activity associated with heterodimeric PGI should foster a broad search for putative substrates in an effort to elucidate the role of PGI-LysAP in bacteria and its roles in the pathophysiology of diseases.

Acid-induced conformational changes in phosphoglucose isomerase result in its increased cell surface association and deposition on fibronectin fibrils

Phosphoglucose isomerase (PGI) is a glycolytic enzyme that exhibits extracellular cytokine activity as autocrine motility factor, neuroleukin, and maturation factor and that has been recently implicated as an autoantigen in rheumatoid arthritis. In contrast to its receptor-mediated endocytosis at neutral pH, addition of 25 microg/ml of either Alexa 568- or FITC-conjugated PGI to NIH-3T3 cells at progressively acid pH results in its quantitatively increased association with cell surface fibrillar structures that is particularly evident at pH 5. A similar pH-dependent cell surface association of PGI is observed for first passage human chondrocytes obtained from osteoarthritic joints. At acid pH, PGI colocalizes with fibronectin fibrils, and this association occurs directly upon addition of PGI to the cells. In contrast to the receptor-mediated endocytosis of PGI, fibril association of 25 microg/ml PGI at pH 5 is not competed with an excess (2 mg/ml) of unlabeled PGI. PGI binding at acid pH is therefore neither saturable nor mediated by its receptor. PGI is enzymatically active as a dimer and we show here by non-denaturing gel electrophoresis as well as by glutaraldehyde cross-linking that it exists at neutral pH in a tetrameric form. Increasingly acid pH results in the appearance of PGI monomers that correlates directly with its enhanced cell surface association. However, glutaraldehyde cross-linked PGI is endocytosed at neutral pH and still exhibits enhanced cell surface binding at pH 5. Circular dichroism analysis revealed pH-dependent changes in the near but not the far UV spectra indicating that the tertiary structure of the protein is specifically altered at pH 5. Conformational changes of PGI and exposure of the monomer-monomer interface under acidic conditions, such as those encountered in the synovial fluid of arthritic joints, could therefore result in its deposition on the surface of joints and the induction of an autoimmune response.

Intracellular renin and the nature of intracrine enzymes

Recently, the binding of renin and prorenin to cellular receptors with the subsequent generation of second messengers and the production of physiological effects has been demonstrated. In addition, the internalization of prorenin by target cells has been associated with increased cellular synthesis of angiotensin and cardiac pathology. Also, a renin transcript lacking the sequences encoding a secretory signal has been reported, and this transcript appears to produce a renin that acts in the cell that synthesized it. Some years ago, we coined the term intracrine for a peptide hormone or factor that acts in the intracellular space either after internalization or retention in its cell of synthesis. Thus defined, a wide variety of peptides display intracrine functionality, including hormones, growth factors, transcription factors, and enzymes. For example, considerable evidence indicates that angiotensin II is an intracrine. Also, general principles of intracrine functionality have been developed. Thus, recent evidence demonstrates that the prorenin/renin molecule is an intracrine enzyme. Here, the actions of intracrine enzymes (angiogenin, phosphoglucose isomerase, phospholipase A2, granzyme A and B, thioredoxin, platelet-derived endothelial growth factor, and serine protease inhibitors) are reviewed. The relation of prorenin/renin to other intracrine enzymes, and to intracrines in general, is discussed.

The enzymatic activity of phosphoglucose isomerase is not required for its cytokine function

PGI is a housekeeping gene encoding phosphoglucose isomerase (PGI) a glycolytic enzyme that also functions as a cytokine (autocrine motility factor (AMF)/neuroleukin/maturation factor) upon secretion from the cell and binding to its 78 kDa seven-transmembrane domain receptor (gp78/AMF-R). PGI contains a CXXC motif, characteristic of redox proteins and possibly evolutionarily related to the CC and CXC motif of the chemokine gene family. Using site-directed mutagenesis, single- and double-deletion (CXC, CC) mutants were created by deleting amino acids 331 and 332 of human PGI, respectively. The mutant proteins lost their enzymatic activity; however, neither of the deletions augmented the proteins' binding affinity to the receptor and all maintained cytokine function. The results demonstrate that the enzymatic activity of PGI is not essential for either receptor binding or cytokine function of human PGI.