Glyceraldehyde-3-phosphate dehydrogenase associates with actin filaments in serum deprived NIH 3T3 cells only

Local glycolysis fuels actomyosin contraction during axonal retraction

In response to repulsive cues, axonal growth cones can quickly retract. This requires the prompt activity of contractile actomyosin, which is formed by the non-muscle myosin II (NMII) bound to actin filaments. NMII is a molecular motor that provides the necessary mechanical force at the expense of ATP. Here, we report that this process is energetically coupled to glycolysis and is independent of cellular ATP levels. Induction of axonal retraction requires simultaneous generation of ATP by glycolysis, as shown by chemical inhibition and genetic knock-down of GAPDH. Co-immunoprecipitation and proximal-ligation assay showed that actomyosin associates with ATP-generating glycolytic enzymes and that this association is strongly enhanced during retraction. Using microfluidics, we confirmed that the energetic coupling between glycolysis and actomyosin necessary for axonal retraction is localized to the growth cone and near axonal shaft. These results indicate a tight coupling between on-demand energy production by glycolysis and energy consumption by actomyosin contraction suggesting a function of glycolysis in axonal guidance.

The Role of Hypoxia in Improving the Therapeutic Potential of Mesenchymal Stromal Cells. A Comparative Study From Healthy Lung and Congenital Pulmonary Airway Malformations in Infants

Mesenchymal stromal cells (MSCs) play an important role in the field of regenerative medicine thanks to their immunomodulatory properties and their ability to secrete paracrine factors. The use of MSCs has also been tested in children with congenital lung diseases inducing fibrosis and a decrease in lung function. Congenital malformations of the pulmonary airways (CPAM) are the most frequently encountered lung lesion that results from defects in early development of airways. Despite the beneficial properties of MSCs, interventions aimed at improving the outcome of cell therapy are needed. Hypoxia may be an approach aimed to ameliorate the therapeutic potential of MSCs. In this regard, we evaluated the transcriptomic profile of MSCs collected from pediatric patients with CPAM, analyzing similarities and differences between healthy tissue (MSCs-lung) and cystic tissue (MSCs-CPAM) both in normoxia and in cells preconditioned with hypoxia (0.2%) for 24 h. Study results showed that hypoxia induces cell cycle activation, increasing in such a way the cell proliferation ability, and enhancing cell anaerobic metabolism in both MSCs-lung and MSCs-CPAM-lung. Additionally, hypoxia downregulated several pro-apoptotic genes preserving MSCs from apoptosis and, at the same time, improving their viability in both comparisons. Finally, data obtained indicates that hypoxia leads to a greater expression of genes involved in the regulation of the cytoskeleton in MSCs-lung than MSCs-CPAM.

Effect of protein oxidation in meat and exudates on the water holding capacity in bighead carp (Hypophthalmichthys nobilis) subjected to frozen storage

This study aimed to investigate the effect of myofiber changes and protein oxidation on water holding capacity (WHC) of bighead carp fillets stored at -20 °C. WHC, microstructure, protein oxidation parameters, and specific modifications of oxidized amino acids were analyzed during 9 months of frozen storage. Results indicated that WHC decreased accompanied by myofibers' structural changes (including the formation of cavities among myofibers, breakage of myofibrils and myofibers, and shortening of sarcomeres) and protein oxidation. SDS-PAGE and carbonyl and sulfhydryl content determination of myofibrillar proteins and exudates gave a detailed description of the protein oxidation. LC-MS/MS analysis demonstrated that oxidation, di-oxidation, and 4-hydroxy-2-nonenal (HNE) and malondialdehyde (MDA) adduction were the top four oxidative modifications of proteins. Oxidative modifications impaired configuration and polarity of proteins, which may further affect WHC. This study provides plausible explanations to support the role of protein oxidation in the decrease of WHC in frozen fillets.

Oxidized GAPDH transfers S-glutathionylation to a nuclear protein Sirtuin-1 leading to apoptosis

AIMS

S-glutathionylation is a reversible oxidative modification of protein cysteines that plays a critical role in redox signaling. Glutaredoxin-1 (Glrx), a glutathione-specific thioltransferase, removes protein S-glutathionylation. Glrx, though a cytosolic protein, can activate a nuclear protein Sirtuin-1 (SirT1) by removing its S-glutathionylation. Glrx ablation causes metabolic abnormalities and promotes controlled cell death and fibrosis in mice. Glyceraldehyde 3-phosphate dehydrogenase (GAPDH), a key enzyme of glycolysis, is sensitive to oxidative modifications and involved in apoptotic signaling via the SirT1/p53 pathway in the nucleus. We aimed to elucidate the extent to which S-glutathionylation of GAPDH and glutaredoxin-1 contribute to GAPDH/SirT1/p53 apoptosis pathway.

RESULTS

Exposure of HEK 293T cells to hydrogen peroxide (H₂O₂) caused rapid S-glutathionylation and nuclear translocation of GAPDH. Nuclear GAPDH peaked 10-15 min after the addition of H₂O₂. Overexpression of Glrx or redox dead mutant GAPDH inhibited S-glutathionylation and nuclear translocation. Nuclear GAPDH formed a protein complex with SirT1 and exchanged S-glutathionylation to SirT1 and inhibited its deacetylase activity. Inactivated SirT1 remained stably bound to acetylated-p53 and initiated apoptotic signaling resulting in cleavage of caspase-3. We observed similar effects in human primary aortic endothelial cells suggesting the GAPDH/SirT1/p53 pathway as a common apoptotic mechanism.

CONCLUSIONS

Abundant GAPDH with its highly reactive-cysteine thiolate may function as a cytoplasmic rheostat to sense oxidative stress. S-glutathionylation of GAPDH may relay the signal to the nucleus where GAPDH trans-glutathionylates nuclear proteins such as SirT1 to initiate apoptosis. Glrx reverses GAPDH S-glutathionylation and prevents its nuclear translocation and cytoplasmic-nuclear redox signaling leading to apoptosis. Our data suggest that trans-glutathionylation is a critical step in apoptotic signaling and a potential mechanism that cytosolic Glrx controls nuclear transcription factors.

Fueling the cytoskeleton - links between cell metabolism and actin remodeling

Attention has long focused on the actin cytoskeleton as a unit capable of organizing into ensembles that control cell shape, polarity, migration and the establishment of intercellular contacts that support tissue architecture. However, these investigations do not consider observations made over 40 years ago that the actin cytoskeleton directly binds metabolic enzymes, or emerging evidence suggesting that the rearrangement and assembly of the actin cytoskeleton is a major energetic drain. This Review examines recent studies probing how cells adjust their metabolism to provide the energy necessary for cytoskeletal remodeling that occurs during cell migration, epithelial to mesenchymal transitions, and the cellular response to external forces. These studies have revealed that mechanotransduction, cell migration, and epithelial to mesenchymal transitions are accompanied by alterations in glycolysis and oxidative phosphorylation. These metabolic changes provide energy to support the actin cytoskeletal rearrangements necessary to allow cells to assemble the branched actin networks required for cell movement and epithelial to mesenchymal transitions and the large actin bundles necessary for cells to withstand forces. In this Review, we discuss the emerging evidence suggesting that the regulation of these events is highly complex with metabolism affecting the actin cytoskeleton and vice versa.

Metabolic regulation of T lymphocyte motility and migration

In order to fulfill their effector and patrolling functions, lymphocytes traffic through the body and need to adapt to different tissue microenvironments. First, mature lymphocytes egress the bone marrow and the thymus into the vascular system. Circulating lymphocytes can exit the vasculature and penetrate into the tissues, either for patrolling in search for pathogens or to eliminate infection and activate the adaptive immune response. The cytoskeletal reorganization necessary to sustain migration require high levels of energy thus presenting a substantial bioenergetic challenge to migrating cells. The metabolic regulation of lymphocyte motility and trafficking has only recently begun to be investigated. In this review we will summarize current knowledge of the crosstalk between cell metabolism and the cytoskeleton in T lymphocytes, and discuss the concept that lymphocyte metabolism may reprogram in response to migratory stimuli and adapt to the different environmental cues received during recirculation in tissues.

Regulation of Autophagy by Nuclear GAPDH and Its Aggregates in Cancer and Neurodegenerative Disorders

Several studies indicate that the cytosolic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) has pleiotropic functions independent of its canonical role in glycolysis. The GAPDH functional diversity is mainly due to post-translational modifications in different amino acid residues or due to protein–protein interactions altering its localization from cytosol to nucleus, mitochondria or extracellular microenvironment. Non-glycolytic functions of GAPDH include the regulation of cell death, autophagy, DNA repair and RNA export, and they are observed in physiological and pathological conditions as cancer and neurodegenerative disorders. In disease, the knowledge of the mechanisms regarding GAPDH-mediated cell death is becoming fundamental for the identification of novel therapies. Here, we elucidate the correlation between autophagy and GAPDH in cancer, describing the molecular mechanisms involved and its impact in cancer development. Since autophagy is a degradative pathway associated with the regulation of cell death, we discuss recent evidence supporting GAPDH as a therapeutic target for autophagy regulation in cancer therapy. Furthermore, we summarize the molecular mechanisms and the cellular effects of GAPDH aggregates, which are correlated with mitochondrial malfunctions and can be considered a potential therapeutic target for various diseases, including cancer and neurodegenerative disorders.

Metabolic regulation of leukocyte motility and migration

Dynamic reorganization of the cytoskeleton is essential for numerous cellular processes including leukocyte migration. This process presents a substantial bioenergetic challenge to migrating cells as actin polymerization is dependent on ATP hydrolysis. Hence, migrating cells must increase ATP production to meet the increased metabolic demands of cytoskeletal reorganization. Despite this long-standing evidence, the metabolic regulation of leukocyte motility and trafficking has only recently begun to be investigated. In this review, we will summarize current knowledge of the crosstalk between cell metabolism and the cytoskeleton in leukocytes, and discuss the concept that leukocyte metabolism may reprogram in response to migratory stimuli and the different environmental cues received during recirculation ultimately regulating leukocyte motility and migration.

Identification of reference genes for qPCR analysis during hASC long culture maintenance

Up to now quantitative PCR based assay is the most common method for characterizing or confirming gene expression patterns and comparing mRNA levels in different sample populations. Since this technique is relative easy and low cost compared to other methods of characterization, e.g. flow cytometry, we used it to typify human adipose-derived stem cells (hASCs). hASCs possess several characteristics that make them attractive for scientific research and clinical applications. Accurate normalization of gene expression relies on good selection of reference genes and the best way to choose them appropriately is to follow the common rule of the “Best 3”, at least three reference genes, three different validation software and three sample replicates. Analysis was performed on hASCs cultivated until the eleventh cell confluence using twelve candidate reference genes, initially selected from literature, whose stability was evaluated by the algorithms NormFinder, BestKeeper, RefFinder and IdealRef, a home-made version of GeNorm. The best gene panel (RPL13A, RPS18, GAPDH, B2M, PPIA and ACTB), determined in one patient by IdealRef calculation, was then investigated in other four donors. Although patients demonstrated a certain gene expression variability, we can assert that ACTB is the most unreliable gene whereas ribosomal proteins (RPL13A and RPS18) show minor inconstancy in their mRNA expression. This work underlines the importance of validating reference genes before conducting each experiment and proposes a free software as alternative to those existing.

D-Glyceraldehyde-3-Phosphate Dehydrogenase Structure and Function

Aside from its well-established role in glycolysis, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) has been shown to possess many key functions in cells. These functions are regulated by protein oligomerization , biomolecular interactions, post-translational modifications , and variations in subcellular localization . Several GAPDH functions and regulatory mechanisms overlap with one another and converge around its role in intermediary metabolism. Several structural determinants of the protein dictate its function and regulation. GAPDH is ubiquitously expressed and is found in all domains of life. GAPDH has been implicated in many diseases, including those of pathogenic, cardiovascular, degenerative, diabetic, and tumorigenic origins. Understanding the mechanisms by which GAPDH can switch between its functions and how these functions are regulated can provide insights into ways the protein can be modulated for therapeutic outcomes.

The sweet side of RNA regulation: glyceraldehyde-3-phosphate dehydrogenase as a noncanonical RNA-binding protein

The glycolytic protein, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), has a vast array of extraglycolytic cellular functions, including interactions with nucleic acids. GAPDH has been implicated in the translocation of transfer RNA (tRNA), the regulation of cellular messenger RNA (mRNA) stability and translation, as well as the regulation of replication and gene expression of many single-stranded RNA viruses. A growing body of evidence supports GAPDH-RNA interactions serving as part of a larger coordination between intermediary metabolism and RNA biogenesis. Despite the established role of GAPDH in nucleic acid regulation, it is still unclear how and where GAPDH binds to its RNA targets, highlighted by the absence of any conserved RNA-binding sequences. This review will summarize our current understanding of GAPDH-mediated regulation of RNA function. WIREs RNA 2016, 7:53-70. doi: 10.1002/wrna.1315 For further resources related to this article, please visit the WIREs website.

Protein Recognition in Drug-Induced DNA Alkylation: When the Moonlight Protein GAPDH Meets S23906-1/DNA Minor Groove Adducts

DNA alkylating drugs have been used in clinics for more than seventy years. The diversity of their mechanism of action (major/minor groove; mono-/bis-alkylation; intra-/inter-strand crosslinks; DNA stabilization/destabilization, etc.) has undoubtedly major consequences on the cellular response to treatment. The aim of this review is to highlight the variety of established protein recognition of DNA adducts to then particularly focus on glyceraldehyde-3-phosphate dehydrogenase (GAPDH) function in DNA adduct interaction with illustration using original experiments performed with S23906-1/DNA adduct. The introduction of this review is a state of the art of protein/DNA adducts recognition, depending on the major or minor groove orientation of the DNA bonding as well as on the molecular consequences in terms of double-stranded DNA maintenance. It reviews the implication of proteins from both DNA repair, transcription, replication and chromatin maintenance in selective DNA adduct recognition. The main section of the manuscript is focusing on the implication of the moonlighting protein GAPDH in DNA adduct recognition with the model of the peculiar DNA minor groove alkylating and destabilizing drug S23906-1. The mechanism of action of S23906-1 alkylating drug and the large variety of GAPDH cellular functions are presented prior to focus on GAPDH direct binding to S23906-1 adducts.

The effects of endogenous non-peptide molecule isatin and hydrogen peroxide on proteomic profiling of rat brain amyloid-β binding proteins: relevance to Alzheimer's disease?

The amyloid-β peptide is considered as a key player in the development and progression of Alzheimer’s disease (AD). Although good evidence exists that amyloid-β accumulates inside cells, intracellular brain amyloid-binding proteins remain poorly characterized. Proteomic profiling of rat brain homogenates, performed in this study, resulted in identification of 89 individual intracellular amyloid-binding proteins, and approximately 25% of them were proteins that we had previously identified as specifically binding to isatin, an endogenous neuroprotector molecule. A significant proportion of the amyloid-binding proteins (more than 30%) are differentially expressed or altered/oxidatively modified in AD patients. Incubation of brain homogenates with 70 µM hydrogen peroxide significantly influenced the profile of amyloid-β binding proteins and 0.1 mM isatin decreased the number of identified amyloid-β binding proteins both in control and hydrogen peroxide treated brain homogenates. The effects of hydrogen peroxide and isatin have been confirmed in optical biosensor experiments with purified glyceraldehyde-3-phosphate dehydrogenase, one of the known crucial amyloid-β binding proteins (also identified in this study). Data obtained suggest that isatin protects crucial intracellular protein targets against amyloid binding, and possibly favors intracellular degradation of this protein via preventing formation of amyloid-β oligomers described in the literature for some isatin derivatives.

The structural and functional coordination of glycolytic enzymes in muscle: evidence of a metabolon?

Metabolism sustains life through enzyme-catalyzed chemical reactions within the cells of all organisms. The coupling of catalytic function to the structural organization of enzymes contributes to the kinetic optimization important to tissue-specific and whole-body function. This coupling is of paramount importance in the role that muscle plays in the success of Animalia. The structure and function of glycolytic enzyme complexes in anaerobic metabolism have long been regarded as a major regulatory element necessary for muscle activity and whole-body homeostasis. While the details of this complex remain to be elucidated through in vivo studies, this review will touch on recent studies that suggest the existence of such a complex and its structure. A potential model for glycolytic complexes and related subcomplexes is introduced.

Protein interactomics based on direct molecular fishing on paramagnetic particles: practical realization and further SPR validation

There is increasing evidence that proteins function in the cell as integrated stable or temporally formed protein complexes, interactomes. Previously, using model systems we demonstrated applicability of direct molecular fishing on paramagnetic particles for protein interactomics (Ershov et al. Proteomics, 2012, 12, 3295). In the present study, we have used a combination of affinity-based molecular fishing and subsequent MS for investigation of human liver proteins involved in interactions with immobilized microsomal cytochrome b5 (CYB5A), and also transthyretin and BSA as alternative affinity ligands (baits). The LC-MS/MS identification of prey proteins fished on these baits revealed three sets of proteins: 98, 120, and 220, respectively. Comparison analysis of these sets revealed only three proteins common for all the baits. In the case of paired analysis, the number of common proteins varied from 2 to 9. The binding capacity of some identified proteins has been validated by a SPR-based biosensor. All the investigated proteins effectively interacted with the immobilized CYB5A (Kd values ranged from 0.07 to 1.1 μM). Results of this study suggest that direct molecular fishing is applicable for analysis of protein-protein interactions (PPI) under normal and pathological conditions, in which altered PPIs are especially important.

Moonlighting microtubule-associated proteins: regulatory functions by day and pathological functions at night

The sensing, integrating, and coordinating features of the eukaryotic cells are achieved by the complex ultrastructural arrays and multifarious functions of the cytoskeletal network. Cytoskeleton comprises fibrous protein networks of microtubules, actin, and intermediate filaments. These filamentous polymer structures are highly dynamic and undergo constant and rapid reorganization during cellular processes. The microtubular system plays a crucial role in the brain, as it is involved in an enormous number of cellular events including cell differentiation and pathological inclusion formation. These multifarious functions of microtubules can be achieved by their decoration with proteins/enzymes that exert specific effects on the dynamics and organization of the cytoskeleton and mediate distinct functions due to their moonlighting features. This mini-review focuses on two aspects of the microtubule cytoskeleton. On the one hand, we describe the heteroassociation of tubulin/microtubules with metabolic enzymes, which in addition to their catalytic activities stabilize microtubule structures via their cross-linking functions. On the other hand, we focus on the recently identified moonlighting tubulin polymerization promoting protein, TPPP/p25. TPPP/p25 is a microtubule-associated protein and it displays distinct physiological or pathological (aberrant) functions; thus it is a prototype of Neomorphic Moonlighting Proteins. The expression of TPPP/p25 is finely controlled in the human brain; this protein is indispensable for the development of projections of oligodendrocytes that are responsible for the ensheathment of axons. The nonphysiological, higher or lower TPPP/p25 level leads to distinct CNS diseases. Mechanisms contributing to the control of microtubule stability and dynamics by metabolic enzymes and TPPP/p25 will be discussed.

Sensor potency of the moonlighting enzyme-decorated cytoskeleton: the cytoskeleton as a metabolic sensor

Background

There is extensive evidence for the interaction of metabolic enzymes with the eukaryotic cytoskeleton. The significance of these interactions is far from clear.

Presentation of the hypothesis

In the cytoskeletal integrative sensor hypothesis presented here, the cytoskeleton senses and integrates the general metabolic activity of the cell. This activity depends on the binding to the cytoskeleton of enzymes and, depending on the nature of the enzyme, this binding may occur if the enzyme is either active or inactive but not both. This enzyme-binding is further proposed to stabilize microtubules and microfilaments and to alter rates of GTP and ATP hydrolysis and their levels.

Testing the hypothesis

Evidence consistent with the cytoskeletal integrative sensor hypothesis is presented in the case of glycolysis. Several testable predictions are made. There should be a relationship between post-translational modifications of tubulin and of actin and their interaction with metabolic enzymes. Different conditions of cytoskeletal dynamics and enzyme-cytoskeleton binding should reveal significant differences in local and perhaps global levels and ratios of ATP and GTP. The different functions of moonlighting enzymes should depend on cytoskeletal binding.

Implications of the hypothesis

The physical and chemical effects arising from metabolic sensing by the cytoskeleton would have major consequences on cell shape, dynamics and cell cycle progression. The hypothesis provides a framework that helps the significance of the enzyme-decorated cytoskeleton be determined.

Functional diversity

There is increasing evidence to support a gene economy model that is fully based on the principles of evolution in which a limited number of proteins does not necessarily reflect a finite number of biochemical processes. The concept of 'gene sharing' proposes that a single protein can have alternate functions that are typically attributed to other proteins. GAPDH appears to play this role quite well in that it exhibits more than one function. GAPDH represents the prototype for this new paradigm of protein multi-functionality. The chapter discusses the diverse functions of GAPDH among three broad categories: cell structure, gene expression and signal transduction. Protein function is curiously re-specified given the cell's unique needs. GAPDH provides the cell with the means of linking metabolic activity to various cellular processes. While interpretations may often lead to GAPDH's role in meeting focal energy demands, this chapter discusses several other very distinct GAPDH functions (i.e. membrane fusogenic properties) that are quite different from its ability to catalyze oxidative phosphorylation of the triose, glyceraldehyde 3-phosphate. It is suggested that a single protein participates in multiple processes in the structural organization of the cell, controls the transmission of genetic information (i.e. GAPDH's involvement may not be finite) and mediates intracellular signaling.

Calcineurin homologous protein: a multifunctional Ca2+-binding protein family

The calcineurin homologous protein (CHP) belongs to an evolutionarily conserved Ca(2+)-binding protein subfamily. The CHP subfamily is composed of CHP1, CHP2, and CHP3, which in vertebrates share significant homology at the protein level with each other and between other Ca(2+)-binding proteins. The CHP structure consists of two globular domains containing from one to four EF-hand structural motifs (calcium-binding regions composed of two helixes, E and F, joined by a loop), the myristoylation, and nuclear export signals. These structural features are essential for the function of the three members of the CHP subfamily. Indeed, CHP1-CHP3 have multiple and diverse essential functions, ranging from the regulation of the plasma membrane Na(+)/H(+) exchanger protein function, to carrier vesicle trafficking and gene transcription. The diverse functions attributed to the CHP subfamily rendered an understanding of its action highly complex and often controversial. This review provides a comprehensive and organized examination of the properties and physiological roles of the CHP subfamily with a view to revealing a link between CHP diverse functions.

Transfer of a Redox-Signal through the Cytosol by Redox-Dependent Microcompartmentation of Glycolytic Enzymes at Mitochondria and Actin Cytoskeleton

The cytosolic glyceraldehyde-3-phosphate dehydrogenase (GAPDH, EC 1.2.1.12, GapC) plays an important role in glycolysis by providing the cell with ATP and NADH. Interestingly, despite its glycolytic function in the cytosol, GAPDH was reported to possess additional non-glycolytic activities, correlating with its nuclear, or cytoskeletal localization in animal cells. In transiently transformed mesophyll protoplasts from Arabidopsis thaliana colocalization and interaction of the glycolytic enzymes with the mitochondria and with the actin cytoskeleton was visualized by confocal laser scanning microscopy (cLSM) using fluorescent protein fusions and by bimolecular fluorescence complementation, respectively. Yeast two-hybrid screens, dot-blot overlay assays, and co-sedimentation assays were used to identify potential protein-protein interactions between two cytosolic GAPDH isoforms (GapC1, At3g04120; GapC2, At1g13440) from A. thaliana with the neighboring glycolytic enzyme, fructose 1,6-bisphosphate aldolase (FBA6, At2g36460), the mitochondrial porin (VDAC3; At5g15090), and actin in vitro. From these experiments, a mitochondrial association is suggested for both glycolytic enzymes, GAPDH and aldolase, which appear to bind to the outer mitochondrial membrane, in a redox-dependent manner. In addition, both glycolytic enzymes were found to bind to F-actin in co-sedimentation assays, and lead to bundling of purified rabbit actin, as visualized by cLSM. Actin-binding and bundling occurred reversibly under oxidizing conditions. We speculate that such dynamic formation of microcompartments is part of a redox-dependent retrograde signal transduction network for adaptation upon oxidative stress.

Osmoprotective proteome adjustments in mouse kidney papilla

The papilla of the mammalian kidney must tolerate greatly varying degrees of hyperosmotic stress during urine concentration and depending on whole organism hydration state. To identify proteome adaptations supporting cell function and survival in such a harsh environment we compared the proteome of a) the hyperosmotic renal papilla with that of adjacent iso-osmotic cortex tissue and b) the renal papilla of diuretic versus that of anti-diuretic mice. Though functionally distinct the papilla is in close physical proximity to the renal cortex, an iso-osmotic region. Proteomic differences between the papilla and cortex of C57BL6 mice were identified using two-dimensional gel electrophoresis and MALDI-TOF/TOF mass spectrometry. We found 37 different proteins characteristic of the cortex and 16 proteins over-represented in the papilla. Regional specificity was confirmed by Western blot and further substantiated by immunohistochemistry for selected proteins. Proteins that are characteristic of the renal papilla include αB crystallin, Hsp beta-1, Hsp90, 14-3-3 protein, glutathione S-transferase, aldose reductase, actin and tropomyosin. Gene ontology analysis confirmed a significant increase in molecular functions associated with protein chaperoning and cell stabilization. Proteins over-represented in the cortex were largely related to routine metabolism. During antidiuresis 15 different proteins changed significantly while 18 different proteins changed significantly during diuresis relative to normally hydrated controls. Changes were confirmed by Western blot for selected proteins. Proteins that are significantly altered by diuretic state are associated with cell structure (actin, tubulin), signaling (Rho GDP dissociation inhibitor, abhydrolase domain-containing protein 14B), chaperone functioning (Hsp beta-1, αB crystallin, T complex protein-1) and anti-oxidant functions (α-enolase, GAPDH and LDH). Taken together our study reveals that specific proteins involved in protein folding, cytoskeletal stabilization, antioxidant responses, and stress signaling contribute greatly to the unique hyperosmotic stress resistant phenotype of the kidney papilla.

Simple method for isolation of glyceraldehyde 3-phosphate dehydrogenase and the improvement of myofibril gel properties

Porcine glycolytic enzyme, glyceraldehyde 3-phosphate dehydrogenase (G3PD) was prepared effectively by a combination of ethylene diamine tetra-acetate (EDTA) pretreatment and affinity purification. After salting out of porcine sarcoplasmic proteins (SP) with ammonium sulfate at 75% saturation, the obtained supernatant (SP-f3) was treated with EDTA, leaving G3PD in the supernatant (G3PD-E) and most other SPs in the precipitate. At that time, the separation of G3PD-E required more than 20 mmol/L EDTA. G3PD-E was then subjected to affinity purification by batchwise method using blue-sepharose CL-6B, and purified G3PD (G3PD-AP) was obtained using 2 mol/L potassium chloride (KCl) as an eluent. Texture analysis showed that the hardness, adhesiveness and gumminess of the myofibril gel at 0.2-mol/L NaCl increased with the addition of G3PD-AP. Scanning electron microscopy revealed that the G3PD-AP reinforced the gel network of the myofibril. However, scanning electron micrograph analysis showed that the network-structure of the gel by the addition of G3PD-AP developed in a different manner from that by adding 0.6 mol/L NaCl. These results showed that glycolytic enzyme, G3PD, contributes to the improvement of the rheological properties of meat products.

The diverse functions of GAPDH: views from different subcellular compartments

Multiple roles for glyceraldehyde-3-phosphate dehydrogenase (GAPDH) have been recently appreciated. In addition to the cytoplasm where the majority of GAPDH is located under the basal condition, GAPDH is also found in the particulate fractions, such as the nucleus, the mitochondria, and the small vesicular fractions. When cells are exposed to various stressors, dynamic subcellular re-distribution of GAPDH occurs. Here we review these multifunctional properties of GAPDH, especially linking them to its oligomerization, posttranslational modification, and subcellular localization. This includes mechanistic descriptions of how S-nitrosylation of GAPDH under oxidative stress may lead to cell death/dysfunction via nuclear translocation of GAPDH, which is counteracted by a cytosolic GOSPEL. GAPDH is also involved in various diseases, especially neurodegenerative disorders and cancers. Therapeutic strategies to these conditions based on molecular understanding of GAPDH are discussed.

Aromatic hydrocarbons upregulate glyceraldehyde-3-phosphate dehydrogenase and induce changes in actin cytoskeleton. Role of the aryl hydrocarbon receptor (AhR)

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a multifunctional enzyme involved in several cellular functions including glycolysis, membrane transport, microtubule assembly, DNA replication and repair, nuclear RNA export, apoptosis, and the detection of nitric oxide stress. Therefore, modifications in the regulatory ability and function of GAPDH may alter cellular homeostasis. We report here that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and beta-naphthoflavone, which are well-known ligands for the aryl hydrocarbon receptor (AhR), increase GAPDH mRNA levels in vivo and in vitro, respectively. These compounds fail to induce GAPDH transcription in an AhR-null mouse model, suggesting that the increase in GAPDH level is dependent upon AhR activation. To analyse the consequences of AhR ligands on GAPDH function, mice were treated with TCDD and the level of liver activity of GAPDH was determined. The results showed that TCDD treatment increased GAPDH activity. On the other hand, treatment of Hepa-1 cells with beta-naphthoflavone leads to an increase in microfilament density when compared to untreated cultures. Collectively, these results suggest that AhR ligands, such as polycyclic hydrocarbons, can modify GAPDH expression and, therefore, have the potential to alter the multiple functions of this enzyme.

Local ATP generation by brain-type creatine kinase (CK-B) facilitates cell motility

Background

Creatine Kinases (CK) catalyze the reversible transfer of high-energy phosphate groups between ATP and phosphocreatine, thereby playing a storage and distribution role in cellular energetics. Brain-type CK (CK-B) deficiency is coupled to loss of function in neural cell circuits, altered bone-remodeling by osteoclasts and complement-mediated phagocytotic activity of macrophages, processes sharing dependency on actomyosin dynamics.

Methodology/Principal Findings

Here, we provide evidence for direct coupling between CK-B and actomyosin activities in cortical microdomains of astrocytes and fibroblasts during spreading and migration. CK-B transiently accumulates in membrane ruffles and ablation of CK-B activity affects spreading and migration performance. Complementation experiments in CK-B-deficient fibroblasts, using new strategies to force protein relocalization from cytosol to cortical sites at membranes, confirmed the contribution of compartmentalized CK-B to cell morphogenetic dynamics.

Conclusion/Significance

Our results provide evidence that local cytoskeletal dynamics during cell motility is coupled to on-site availability of ATP generated by CK-B.

Mechanical loading by fluid shear is sufficient to alter the cytoskeletal composition of osteoblastic cells

Many structural modifications have been observed as a part of the cellular response to mechanical loading in a variety of cell types. Although changes in morphology and cytoskeletal rearrangement have been widely reported, few studies have investigated the change in cytoskeletal composition. Measuring how the amounts of specific structural proteins in the cytoskeleton change in response to mechanical loading will help to elucidate cellular mechanisms of functional adaptation to the applied forces. Therefore, the overall hypothesis of this study was that osteoblasts would respond to fluid shear stress by altering the amount of specific cross-linking proteins in the composition of the cytoskeleton. Mouse osteoblats cell line MC3T3-E1 and human fetal osteoblasts (hFOB) were exposed to 2 Pa of steady fluid shear for 2 h in a parallel plate flow chamber, and then the amount of actin, vimentin, α-actinin, filamin, and talin in the cytoskeleton was measured using Western blot analyses. After mechanical loading, there was no change in the amount of actin monomers in the cytoskeleton, but the cross-linking proteins α-actinin and filamin that cofractionated with the cytoskeleton increased by 29% ( P < 0.01) and 18% ( P < 0.02), respectively. Localization of the cross-linking proteins by fluorescent microscopy revealed that they were more widely distributed throughout the cell after exposure to fluid shear. The amount of vimentin in the cytoskeleton also increased by 15% ( P < 0.01). These results indicate that osteoblasts responded to mechanical loading by altering the cytoskeletal composition, which included an increase in specific proteins that would likely enhance the mechanical resistance of the cytoskeleton.

Variations in platelet protein associated with arterial thrombosis

INTRODUCTION

Hyperactivity of platelets has been associated with thrombotic episodes by molecular mechanisms not yet elucidated. The present work aimed at identifying whether the platelet protein content from patients who had suffered an arterial thrombosis episode differed from that of platelets obtained from normal healthy donors.

METHODS

Differential platelet protein profiles were determined by 2-dimensional (2-D) gel electrophoresis and Western blot analysis of total platelet lysates. Identification of differentially expressed proteins was carried out by mass spectrometry (MALDI-TOF).

RESULTS

We found a decreased platelet content of three protein spots in patients of arterial thrombosis: integrin linked kinase (ILK), fructose bisphosphate aldolase (aldolase) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) whereas the content of four other protein spots was increased: actin binding protein, coronine like (p57), non-muscle myosin heavy chain (NMMHC-A), pyruvate kinase M2 isoenzyme (PK) and phosphoglycerate kinase (PGK). The variations in ILK, GAPDH and PK were validated by Western blot analysis. The proteins showing a decreased platelet content in arterial thrombosis patients are associated with the cytoskeletal insoluble fraction and the detected increase in some proteins seems to be due to the generation of peptides caused by a limited proteolysis. Differences in the protein profiles of circulating platelets from arterial thrombosis were maintained months after the acute thrombotic event and disappear in the long term.

CONCLUSIONS

The observed variations in some platelet proteins suggest the existence of a perturbation in the cytoskeletal organization and increased proteolysis, both indicative of a platelet pro-active state, persistent after the thrombotic event.

Microtubule-associated protein 1B binds glyceraldehyde-3-phosphate dehydrogenase

Microtubule-associated protein 1B, MAP1B, is a major cytoskeletal protein during brain development and one of the largest brain MAPs associated with microtubules and microfilaments. Here, we identified several proteins that bind to MAP1B via immunoprecipitation with a MAP1B-specific antibody, by one and two-dimensional gel electrophoresis and subsequent mass spectrometry identification of precipitated proteins. In addition to tubulin and actin, a variety of proteins were identified. Among these proteins were glyceraldehyde-3-phosphate dehydrogenase (GAPDH), heat shock protein 8, dihydropyrimidinase related proteins 2 and 3, protein-L-isoaspartate O-methyltransferase, beta-spectrin, and clathrin protein MKIAA0034, linking either directly or indirectly to MAP1B. In particular, GAPDH, a key glycolytic enzyme, was bound in large quantity to the heavy chain of MAP1B in adult brain tissue. In vitro binding studies confirmed a direct binding of GAPDH to MAP1B. In PC12 cells, GAPDH was found in cytoplasm and nuclei and partially co-localized with MAP1B. It disappeared from the cytoplasm under oxidative stress or after a disruption of cytoskeletal elements after colcemid or cytochalasin exposure. GAPDH may be essential in the local energy provision of cytoskeletal structures and MAP1B may help to keep this key enzyme close to the cytoskeleton.

The recombinant beta subunit of C-phycocyanin inhibits cell proliferation and induces apoptosis

C-Phycocyanin (C-PC) from blue-green algae has been reported to have various pharmacological characteristics, including anti-inflammatory and anti-tumor activities. In this study, we expressed the beta-subunit of C-PC (ref to as C-PC/beta) in Escherichia coli. We found that the recombinant C-PC/beta has anti-cancer properties. Under the treatment of 5 microM of the recombinant C-PC/beta, four different cancer cell lines accrued high proliferation inhibition and apoptotic induction. Substantially, a lower response occurred in non-cancer cells. We investigated the mechanism by which C-PC/beta inhibits cancer cell proliferation and induces apoptosis. We found that the C-PC/beta interacts with membrane-associated beta-tubulin and glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Under the treatment of the C-PC/beta, depolymerization of microtubules and actin-filaments were observed. The cells underwent apoptosis with an increase in caspase-3, and caspase-8 activities. The cell cycle was arrested at the G0/G1 phase under the treatment of C-PC/beta. In addition, the nuclear level of GAPDH decreased significantly. Decrease in the nuclear level of GAPDH prevents the cell cycle from entering into the S phase. Inhibition of cancer cell proliferation and induction of apoptosis may potentate the C-PC/beta as a promising cancer prevention or therapy agent.

Interactions among p22, glyceraldehyde-3-phosphate dehydrogenase and microtubules

Previously, we have shown that p22, an EF-hand Ca2+-binding protein, interacts indirectly with microtubules in an N-myristoylation-dependent and Ca2+-independent manner. In the present study, we report that N-myristoylated p22 interacts with several microtubule-associated proteins within the 30-100 kDa range using overlay blots of microtubule pellets containing cytosolic proteins. One of those p22-binding partners, a 35-40 kDa microtubule-binding protein, has been identified by MS as GAPDH (glyceraldehyde-3-phosphate dehydrogenase). Several lines of evidence suggest a functional relationship between GAPDH and p22. First, endogenous p22 interacts with GAPDH by immunoprecipitation. Secondly, p22 and GAPDH align along microtubule tracks in analogous punctate structures in BHK cells. Thirdly, GAPDH facilitates the p22-dependent interactions between microtubules and microsomal membranes, by increasing the ability of p22 to bind microtubules but not membranes. We have also shown a direct interaction between N-myristoylated p22 and GAPDH in vitro with a K(D) of approximately 0.5 microM. The removal of either the N-myristoyl group or the last six C-terminal amino acids abolishes the binding of p22 to GAPDH and reduces the ability of p22 to associate with microtubules. In summary, we report that GAPDH is involved in the ability of p22 to facilitate microtubule-membrane interactions by affecting the p22-microtubule, but not the p22-membrane, association.

Rack-1, GAPDH3, and actin: proteins of Myzus persicae potentially involved in the transcytosis of beet western yellows virus particles in the aphid

Beet western yellows virus (BWYV) is a Polerovirus that relies on the aphid Myzus persicae for its transmission, in a persistent-circulative mode. To be transmitted, the virus must cross the midgut and the accessory salivary glands (ASG) epithelial barriers in a transcytosis mechanism where vector receptors interact with virions. In this paper, we report in vitro interaction experiments between BWYV and aphid components. Using the M. persicae clone from Colmar, we showed that a set of aphid polypeptides, separated by SDS-PAGE or 2D electrophoresis (2DE), can bind in vitro to purified wild type or mutant particles. Using subcellular fractionation, we showed that the 65-kDa polypeptide identified as symbionin is a soluble protein whereas the other polypeptides seem to be associated more or less strongly to the membrane. We hypothesize that three polypeptides, identified by mass spectrometry as Rack-1, GAPDH3, and actin, may be involved in the epithelial transcytosis of virus particles in the aphid vector.

A novel CRM1-mediated nuclear export signal governs nuclear accumulation of glyceraldehyde-3-phosphate dehydrogenase following genotoxic stress

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a multifunctional protein with glycolytic and non-glycolytic functions, including pro-apoptotic activity. GAPDH accumulates in the nucleus after cells are treated with genotoxic drugs, and it is present in a protein complex that binds DNA modified by thioguanine incorporation. We identified a novel CRM1-dependent nuclear export signal (NES) comprising 13 amino acids (KKVVKQASEGPLK) in the C-terminal domain of GAPDH, truncation or mutation of which abrogated CRM1 binding and caused nuclear accumulation of GAPDH. Alanine scanning of the sequence encompassing the putative NES demonstrated at least two regions important for nuclear export. Site mutagenesis of Lys259 did not affect oligomerization but impaired nuclear efflux of GAPDH, indicating that this amino acid residue is essential for proper functioning of this NES. This novel NES does not contain multiple leucine residues unlike other CRM1-interacting NES, is conserved in GAPDH from multiple species, and has sequence similarities to the export signal found in feline immunodeficiency virus Rev protein. Similar sequences (KKVV*7-13PLK) were found in two other human proteins, U5 small nuclear ribonucleoprotein, and transcription factor BT3.

Subcellular localization of human glyceraldehyde-3-phosphate dehydrogenase is independent of its glycolytic function

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) was considered a classical glycolytic protein involved exclusively in cytosolic energy production. However, recent evidence suggests that it is a multifunctional protein displaying diverse activities distinct from its conventional metabolic role. These new roles for GAPDH may be dependent on its subcellular localization, oligomeric state or on the proliferative state of the cell. GAPDH is encoded by a single gene without alternate splicing. The regulatory mechanisms are unknown through which an individual GAPDH molecule fulfills its non-glycolytic functions or is targeted to a specific intracellular localization. Accordingly, as a first step to elucidate these subcellular regulatory mechanisms, we examined the interrelationship between the intracellular expression of the GAPDH protein and its glycolytic function in normal human fetal and senior cells. GAPDH localization was determined by immunoblot analysis. Enzyme activity was quantitated by in vitro biochemical assay. We now report that the subcellular expression of GAPDH was independent of its classical glycolytic function. In particular, in both fetal and senior cells, considerable GADPH protein was present in intracellular domains characterized by significantly reduced catalysis. Gradient analysis indicated that this lower activity was not due to the dissociation of tetrameric GAPDH. These results suggest that human cells contain significant intracellular levels of enzymatically inactive GAPDH which is age-independent. The possibility is considered that the functional diversity of GAPDH may be mediated either by posttranslational alteration or by subcellular protein:protein and/or protein:nucleic acid interactions.

Exportin 1-independent nuclear export of GAPDH

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a key enzyme of the glycolytic pathway. Recent studies have demonstrated an additional role in apoptosis: GAPDH is targeted to the nucleus during apoptotic signalling. This nuclear transport has also been observed in serum-depleted cells, but it is reversible in fibroblasts, in contrast to apoptotic-induced transport (Eur J Cell Biol 80 (2001) 419). Here, we analyse the serum depletion-induced transport processes of GAPDH in NIH 3T3 cells. Prolonged serum depletion did not cause cell death, nuclear fragmentation (hoechst staining) or a significant increase in DNA strand-breaks (comet assay). Using cells expressing green fluorescent protein (GFP)-tagged GAPDH allowed us to monitor its intracellular localisation by confocal laser scanning microscopy (CLSM). Treatment of cells with the exportin1 inhibitor leptomycin B (LMB) did not influence cytoplasmic localisation of GFP-GAPDH, indicating that nuclear targeting of GAPDH is not constitutive and may be altered via a serum-dependent regulatory export process. Suprisingly, the export of nuclear GFP-GAPDH after re-addition of serum to starved cells was not prevented by LMB. Thus, nuclear export of GAPDH upon serum depletion is not mediated by exportin1.