Potential role of nuclear translocation of glyceraldehyde-3-phosphate dehydrogenase in apoptosis and oxidative stress

Calicum microdomains form within neutrophils at the neutrophil-tumor cell synapse: role in antibody-dependent target cell apoptosis

Ca(2+) messages are broadly important in cellular signal transduction. In immune cells, Ca(2+) signaling is an essential step in many forms of activation. Neutrophil-mediated antibody-dependent cell-mediated cytotoxicity (ADCC) is one form of leukocyte activation that plays an important role in tumor cell killing in vitro and in patient care. Using fluorescence methodologies, we found that neutrophils exhibit Ca(2+) signals during ADCC directed against breast fibrosarcoma cells. Importantly, these signals were localized to Ca(2+) microdomains at the neutrophil-to-tumor cell interface where they display dynamic features such as movement, fusion, and fission. These signals were blocked by the intracellular Ca(2+) buffer BAPTA. At the neutrophil-tumor cell synapse, the neutrophil's cytoplasm was enriched in STIM1, a crucial mediator of Ca(2+) signaling, whereas the Ca(2+)-binding proteins calbindin and parvalbumin were not affected. Our findings suggest that Ca(2+) microdomains are due to an active signaling process. As Ca(2+) signals within neutrophils were necessary for specific tumor cell apoptosis, a central role of microdomains in leukocyte-mediated tumor cell destruction is indicated.

CGP 3466B has no effect on disease course of (G93A) mSOD1 transgenic mice

BACKGROUND

There is an accumulating body of evidence that apoptosis is involved in the motor neuron death that occurs in ALS, and in the (G93A) mSOD1 transgenic mouse model (mSOD1 mice). CGP 3466B, a tricyclic propargylamine structurally related to (-)-deprenyl, was found to inhibit apoptosis in a wide variety of in vitro and in vivo models. We therefore studied the effect of CGP 3466B in mSOD1 mice.

METHODS

As the effect of CGP 3466B was previously reported to have a bell-shaped curve, we performed a dose-ranging study. High-copy G93A mSOD1 mice were treated subcutaneously from the age of 50 days until death with four concentrations of CGP 3466B (0.39 microg kg(-1), 3.9 microg kg(-1), 39 microg kg(-1), and 390 microg kg(-1)). Behavioural tests were performed daily to determine disease onset, disease progression and survival. At the age of 110 days, two mice per group were sacrificed for histopathological analysis of the lumbar ventral horn and for semiquantitative analysis of motor neuron number.

RESULTS

We observed no effect on disease onset, disease progression, or survival of the mice. We also did not observe a significant effect on the number of motor neurons due to CGP 3466B.

CONCLUSIONS

We conclude that in high-copy G93A mSOD1 mice, chronic subcutaneous treatment with CGP 3466B offers no clinical benefit.

A proteomic approach links decreased pyruvate kinase M2 expression to oxaliplatin resistance in patients with colorectal cancer and in human cell lines

We aimed to gain further understanding of the molecular mechanisms involved in oxaliplatin resistance in colorectal cancer by using a proteomic approach. A 5-fold oxaliplatin-resistant cell line, HTOXAR3, was compared with its parental cell line, HT29, using two-dimensional PAGE. Mass spectrometry, Western blot, and real-time quantitative PCR confirmed the down-regulation of pyruvate kinase M2 (PK-M2) in HTOXAR3 cells. In a panel of eight colorectal cancer cell lines, we found a negative correlation between oxaliplatin resistance and PK-M2 mRNA levels (Spearman r=-0.846, P=0.008). Oxaliplatin exposure in both HT29 and HTOXAR3 led to PK-M2 mRNA up-regulation. PK-M2 mRNA levels were measured by real-time quantitative PCR in 41 tumors treated with oxaliplatin/5-fluorouracil. Tumors with the lowest PK-M2 levels attained the lowest response rates (20% versus 64.5%, P=0.026). High PK-M2 levels were associated with high p53 levels (P=0.032). In conclusion, the data provided clearly link PK-M2 expression and oxaliplatin resistance mechanisms and further implicate PK-M2 as a predictive marker of response in patients with oxaliplatin-treated colorectal cancer.

Interfering with glycolysis causes Sir2-dependent hyper-recombination of Saccharomyces cerevisiae plasmids

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a key metabolic regulator implicated in a variety of cellular processes. It functions as a glycolytic enzyme, a protein kinase, and a metabolic switch under oxidative stress. Its enzymatic inactivation causes a major shift in the primary carbohydrate flux. Furthermore, the protein is implicated in regulating transcription, ER-to-Golgi transport, and apoptosis. We found that Saccharomyces cerevisiae cells null for all GAPDH paralogues (Tdh1, Tdh2, and Tdh3) survived the counter-selection of a GAPDH-encoding plasmid when the NAD(+) metabolizing deacetylase Sir2 was overexpressed. This phenotype required a fully functional copy of SIR2 and resulted from hyper-recombination between S. cerevisiae plasmids. In the wild-type background, GAPDH overexpression increased the plasmid recombination rate in a growth-condition dependent manner. We conclude that GAPDH influences yeast episome stability via Sir2 and propose a model for the interplay of Sir2, GAPDH, and the glycolytic flux.

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) interaction with 3' ends of Japanese encephalitis virus RNA and colocalization with the viral NS5 protein

Replication of the Japanese encephalitis virus (JEV) genome depends on host factors for successfully completing their life cycles; to do this, host factors have been recruited and/or relocated to the site of viral replication. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH), a cellular metabolic protein, was found to colocalize with viral RNA-dependent RNA polymerase (NS5) in JEV-infected cells. Subcellular fractionation further indicated that GAPDH remained relatively constant in the cytosol, while increasing at 12 to 24 hours postinfection (hpi) and decreasing at 36 hpi in the nuclear fraction of infected cells. In contrast, the redistribution patterns of GAPDH were not observed in the uninfected cells. Co-immunoprecipitation of GAPDH and JEV NS5 protein revealed no direct protein-protein interaction; instead, GAPDH binds to the 3' termini of plus- and minus-strand RNAs of JEV by electrophoretic mobility shift assays. Accordingly, GAPDH binds to the minus strand more efficiently than to the plus strand of JEV RNAs. This study highlights the findings that infection of JEV changes subcellular localization of GAPDH suggesting that this metabolic enzyme may play a role in JEV replication.

Synthetic polymeric substrates as potent pro-oxidant versus anti-oxidant regulators of cytoskeletal remodeling and cell apoptosis

The role of reactive oxygen species (ROS)-mediated cell signal transduction pathways emanating from engineered cell substrates remains unclear. To elucidate the role, polymers derived from the amino acid L-tyrosine were used as synthetic matrix substrates. Variations in their chemical properties were created by co-polymerizing hydrophobic L-tyrosine derivatives with uncharged hydrophilic poly(ethylene glycol) (PEG, Mw = 1,000 Da), and negatively charged desaminotyrosyl-tyrosine (DT). These substrates were characterized for their intrinsic ability to generate ROS, as well as their ability to elicit Saos-2 cell responses in terms of intracellular ROS production, actin remodeling, and apoptosis. PEG-containing substrates induced both exogenous and intracellular ROS production, whereas the charged substrates reduced production of both types, indicating a coupling of exogenous ROS generation and intracellular ROS production. Furthermore, PEG-mediated ROS induction caused nuclear translocation of glyceraldehyde-3-phosphate dehydrogenase and an increase in caspase-3 activity, confirming a link with apoptosis. PEG-rich pro-oxidant substrates caused cytoskeletal actin remodeling through beta-actin cleavage by caspase-3 into fractins. The fractins co-localized to the mitochondria and reduced the mitochondrial membrane potential. The remnant cytosolic beta-actin was polymerized and condensed, events consistent with apoptotic cell shrinkage. The cytoskeletal remodeling was integral to the further augmentation of intracellular ROS production. Conversely, the anti-oxidant DT-containing charged substrates suppressed the entire cascade of apoptotic progression. We demonstrate that ROS activity serves an important role in "outside-in" signaling for cells grown on substrates: the ROS activity couples exogenous stress, driven by substrate composition, to changes in intracellular signaling. This signaling causes cell apoptosis, which is mediated by actin remodeling.

The biochemistry, metabolism and inherited defects of the pentose phosphate pathway: a review

The recent discovery of two defects (ribose-5-phosphate isomerase deficiency and transaldolase deficiency) in the reversible part of the pentose phosphate pathway (PPP) has stimulated interest in this pathway. In this review we describe the functions of the PPP, its relation to other pathways of carbohydrate metabolism and an overview of the metabolic defects in the reversible part of the PPP.

Discovery, identification, and characterization of candidate pharmacodynamic markers of methionine aminopeptidase-2 inhibition

The catalytic activity of methionine aminopeptidase-2 (MetAP2) has been pharmacologically linked to cell growth, angiogenesis, and tumor progression, making this an attractive target for cancer therapy. An assay for monitoring specific protein changes in response to MetAP2 inhibition, allowing pharmacokinetic (PK)/pharmacodynamic (PD) models to be established, could dramatically improve clinical decision-making. Candidate MetAP2-specific protein substrates were discovered from undigested cell culture-derived proteomes by MALDI-/SELDI-MS profiling and a biochemical method using (35)S-Met labeled protein lysates. Substrates were identified either as intact proteins by FT-ICR-MS or applying in-gel protease digestions followed by LC-MS/MS. The combination of these approaches led to the discovery of novel MetAP2-specific substrates including thioredoxin-1 (Trx-1), SH3 binding glutamic acid rich-like protein (SH3BGRL), and eukaryotic elongation factor-2 (eEF2). These studies also confirmed glyceraldehye 3-phosphate dehydrogenase (GAPDH) and cyclophillin A (CypA) as MetAP2 substrates. Additional data in support of these proteins as MetAP2-specific substrates were provided by in vitro MetAP1/MetAP2 enzyme assays with the corresponding N-terminal derived peptides and 1D/2D Western analyses of cellular and tissue lysates. FT-ICR-MS characterization of all intact species of the 18 kDa substrate, CypA, enabled a SELDI-MS cell-based assay to be developed for correlating N-terminal processing and inhibition of proliferation. The MetAP2-specific protein substrates discovered in this study have diverse properties that should facilitate the development of reagents for testing in preclinical and clinical environments.

Human glyceraldehyde-3-phosphate dehydrogenase plays a direct role in reactivating oxidized forms of the DNA repair enzyme APE1

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) has diverse biological functions including its nuclear translocation in response to oxidative stress. We show that GAPDH physically associates with APE1, an essential enzyme involved in the repair of abasic sites in damaged DNA, as well as in the redox regulation of several transcription factors. This interaction allows GAPDH to convert the oxidized species of APE1 to the reduced form, thereby reactivating its endonuclease activity to cleave abasic sites. The GAPDH variants C152G and C156G retain the ability to interact with but are unable to reactivate APE1, implicating these cysteines in catalyzing the reduction of APE1. Interestingly, GAPDH-small interfering RNA knockdown sensitized the cells to methyl methane sulfonate and bleomycin, which generate lesions that are repaired by APE1, but showed normal sensitivity to 254-nm UV. Moreover, the GAPDH knockdown cells exhibited an increased level of spontaneous abasic sites in the genomic DNA as a result of diminished APE1 endonuclease activity. Thus, the nuclear translocation of GAPDH during oxidative stress constitutes a protective mechanism to safeguard the genome by preventing structural inactivation of APE1.

Environmental proteomics and metallomics

Monitoring environmental pollution using biomarkers requires detailed knowledge about the markers, and many only allow a partial assessment of pollution. New proteomic methods (environmental proteomics) can identify proteins that, after validation, might be useful as alternative biomarkers, although this approach also has its limitations, derived mainly from their application to non-model organisms. Initial studies using environmental proteomics were carried out in animals exposed to model pollutants, and led to the concept of protein expression signatures. Experiments have been carried out in model organisms (yeast, Arabidopsis, rat cells, or mice) exposed to model contaminants. Over the last few years, proteomics has been applied to organisms from ecosystems with different pollution levels, forming the basis of an environmental branch in proteomics. Another focus is connected with the presence of metals bound to biomolecules, which adds an additional dimension to metal-biomolecule and metalloprotein characterization - the field of metallomics. The metallomic approach considers the metallome: a whole individual metal or metalloid species within a cell or tissue. A metallomic analytical approach (MAA) is proposed as a new tool to study and identify metalloproteins.

HIF-1-regulated glucose metabolism in the control of apoptosis signaling

Resistance of human cancers to current treatment approaches remains a major concern in oncology. Therefore, much effort has been focused on identifying molecular pathways that are responsible for primary or acquired resistance of cancers in order to overcome resistance. Hypoxia is one of the hallmarks of solid tumors and usually correlates with poor prognosis. Under hypoxic conditions, cancer cells undergo a variety of adoptive changes, including the activation of signaling pathways, which promote cancer cell survival and block cell death. Hypoxia inducible factor (HIF)-1 is the key transcription factor that mediates adaptation of cancer cells to the hypoxic environment. There is increasing evidence that HIF-1 promotes tumor growth, at least in part, by upregulating genes that are involved in cellular energy metabolism. Thus, HIF-1 and hypoxia-inducible genes represent attractive targets for the design of molecular targeted therapies, which may offer new therapeutic options for a wide range of malignancies.

Suppression of reactive oxygen species by glyceraldehyde-3-phosphate dehydrogenase

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH), a classical glycolytic enzyme, is involved in cellular energy production and has important housekeeping functions. In this report, we show that a GAPDH from Arabidopsis, GAPDHa, has a novel function involved in H(2)O(2)-mediated cell death in yeast and Arabidopsis protoplasts. GAPDHa was cloned along with other plant genes that suppress Bax-induced cell death in yeast. Flow cytometry analyses with dihydrorhodamine 123 indicated that H(2)O(2) production mediated by Bax expression in yeast cells was greatly reduced when Bax was coexpressed with GAPDHa. In plants, GAPDHa transcript levels were greatly increased by H(2)O(2) treatment. Furthermore, transformation of GAPDHa into Arabidopsis protoplasts strongly suppressed heat shock-induced H(2)O(2) production and cell death. Together, our results indicate that GAPDH controls generation of H(2)O(2) by Bax and heat shock, which in turn suppresses cell death in yeast and plant cells.

4-Hydroxy-2-nonenal-modified glyceraldehyde-3-phosphate dehydrogenase is degraded by cathepsin G

Degradation of oxidized or oxidatively modified proteins is an essential part of the antioxidant defenses of cells. 4-Hydroxy-2-nonenal (HNE), a major reactive aldehyde formed by lipid peroxidation, causes many types of cellular damage. It has been reported that HNE-modified proteins are degraded by the ubiquitin-proteasome pathway or, in some cases, by the lysosomal pathway. However, our previous studies using U937 cells showed that HNE-modified glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is degraded by an enzyme that is sensitive to a serine protease inhibitor, diisopropyl fluorophosphate (DFP), but not a proteasome inhibitor, MG-132, and that its degradation is not catalyzed in the acidic pH range where lysosomal enzymes are active. In the present study, we purified an HNE-modified GAPDH-degrading enzyme from a U937 cell extract to a final active fraction containing two proteins of 28 kDa (P28) and 27 kDa (P27) that became labeled with [(3)H]DFP. Using peptide mass fingerprinting and a specific antibody, P28 and P27 were both identified as cathepsin G. The degradation activity was inhibited by cathepsin G inhibitors. Furthermore, a cell extract from U937 cells transfected with a cathepsin G-specific siRNA hardly degraded HNE-modified GAPDH. These results suggest that cathepsin G plays a role in the degradation of HNE-modified GAPDH.

Interaction of glyceraldehyde-3-phosphate dehydrogenase in the light-induced rod alpha-transducin translocation

The light-dependent subcellular translocation of rod alpha-transducin (GNAT-1, or rod Talpha) has been well documented. In dark-adapted animals, rod Talpha (rTalpha) is predominantly located in the rod outer segment (ROS) and translocates into the rod inner segment (RIS) upon exposure to the light. Neither the molecular participants nor the mechanism(s) involved in this protein trafficking are known. We hypothesized that other proteins must interact with rTalpha to affect the translocations. Using the MBP-rTalpha fusion pulldown assay, the yeast two-hybrid assay and the co-immunoprecipitation assay, we identified glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and rTalpha as interacting proteins. Immunoprecipitation also showed beta-actin associates with rTalpha in the dark but not in the light. To further investigate the involvement of GAPDH in light-induced rod Talpha translocation, GAPDH mRNA was knocked down in vivo by transient expression of siRNAs in rat photoreceptor cells. Under completely dark- and light-adapted conditions, the translocation of rTalpha was not significantly different within the 'GAPDH knock-down photoreceptor cells' compared to the non-transfected control cells. However, under partial dark-adaptation, rTalpha translocated more slowly in the 'GAPDH knock-down cells' supporting the conclusion that GAPDH is involved in rTalpha translocation from the RIS to the ROS during dark adaptation.

Profiling cell-biomaterial interactions via cell-based fluororeporter imaging

Cell-based, high-throughput screening has revolutionized the development of small-molecule pharmaceuticals. A similar paradigm for the accelerated development of biomaterials for cell and tissue engineering involves the iterative use of combinatorial biomaterial synthesis, rapid cellular response screens, and computational modeling methods. However assays to probe cell responses to biomaterials are frequently subjective, lack dynamic responsiveness, and are limited to low-throughput experimentation. In this report, we highlight the use of high-resolution imaging of cell-based fluororeporters to establish and correlate quantifiable metrics of cell functional endpoints (e.g., cell growth, cell adhesion, cell attachment strength), as well as of intracellular cytoskeletalfeatures (e.g., descriptors of actin organization) on a set of model biomaterial substrates synthesized by combinatorial variations. Selected mammalian cell lines were genetically engineered with a series of green fluorescent protein (GFP)fusion genes to allow for live cell imaging on biomaterials. We demonstrate that high-content imaging yields a large number of quantifiable morphometric descriptors of ultrastructural cell features (e.g., cell cytoskeleton) in conjunction with densitometric descriptors of cell behaviors (e.g., cell apoptosis). We illustrate how such descriptors can be used to discern combinatorial variations in substrate composition, and how living GFP reporters are uniquely suited to generate such descriptors unlike fixed tissue preparations. This quantitative approach of live fluororeporter cell imaging could be valuable for metrology of cell-material interactions.

Sequestration of glyceraldehyde-3-phosphate dehydrogenase to aggregates formed by mutant huntingtin

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) has been reported to interact with proteins containing the polyglutamine (polyQ) domain. The present study was undertaken to evaluate the potential contributions of the polyQ and polyproline (polyP) domains to the co-localization of mutant huntingtin (htt) and GAPDH. Overexpression of N-terminal htt (1-969 amino acids) with 100Q and 46Q (htt1-969-100Q and httl-969-46Q, mutant htt) in human mammary gland carcinoma MCF-7 cells formed more htt aggregates than that of htt1-969-18Q (wild-type htt). The co-localization of GAPDH with htt aggregates was found in the cells expressing mutant but not wild-type htt. Deletion of the polyP region in the N-terminal htt had no effect on the co-localization of GAPDH and mutant htt aggregates. These results suggest that the polyQ domain, but not the polyP domain, plays a role in the sequestration of GAPDH to aggregates by mutant htt. This effect might contribute to the dysfunction of neurons caused by mutant htt in Huntington's disease.

Diagnostic utility of serum or cerebrospinal fluid levels of toxic advanced glycation end-products (TAGE) in early detection of Alzheimer's disease

Alzheimer's disease (AD) is the most common cause of dementia in developed countries. AD is characterized pathologically by the presence of senile plaques and neurofibrillary tangles (NFTs), the major constituents of which are amyloid beta protein (A beta) and tau protein, respectively. Based on the disease pathology, numerous blood and cerebrospinal fluid (CSF) tests have been proposed for early detection of AD. However, there is no definite clinical method to determine in which patients with mild cognitive impairment will progress to AD with dementia. Therefore, to develop a novel promising biomarker for early diagnosis of AD is urgently needed. Several epidemiological studies have reported moderately increased risks for AD in diabetic patients compared with general population. In diabetes mellitus, the formation and accumulation of advanced glycation end-products (AGEs), senescent macroprotein derivatives, progress more rapidly. In addition, recent understanding of this process has confirmed that AGEs-their receptor (RAGE) interactions may play a role in the pathogenesis of neurodegenerative disorders including AD. In human AD brains, AGEs are distributed in the cytosol of neurons in the hippocampus and para-hippocampal gyrus. In this paper, we discuss the pathophysiological role for toxic AGEs (TAGE) in AD. We further review here the possibility that serum or cerebrospinal fluid levels of TAGE could become a promising biomarker for early detection of AD.

Subcellular proteome analysis of camptothecin analogue NSC606985-treated acute myeloid leukemic cells

We reported previously that NSC606985, a camptothecin analogue, induces apoptosis of acute myeloid leukemia (AML) cells through proteolytic activation of protein kinase Cdelta. Here, we analyzed protein expression profiles of fractionated nuclei, mitochondria, raw endoplasmic reticula, and cytosols of NSC606985-induced apoptotic AML cell line NB4 cells by two-dimensional electrophoresis combined with MALDI-TOF/TOF tandem mass spectrometry. In total, 90 unique deregulated proteins, including 16 compartment-compartment translocated ones, were identified. They contributed to multiple functional activities such as DNA damage repairing, chromosome assembly, mRNA processing, biosynthesis, modification, and degradation of proteins. More interestingly, several increased oxidative stress-related proteins mainly presented in mitochondria, while upregulated glycolysis proteins mainly occurred in the nuclei. With their functional analyses, the possible roles of these deregulated proteins in NSC606985-induced apoptosis were discussed. Collectively, these discoveries would shed new insights for systematically understanding the mechanisms of the camptothecin-induced apoptosis.

Involvement of glyceraldehyde-3-phosphate dehydrogenase in tumor necrosis factor-related apoptosis-inducing ligand-mediated death of thyroid cancer cells

TNF-related apoptosis-inducing ligand (TRAIL) is cytotoxic to most thyroid cancer cell lines, including those originating from anaplastic carcinomas, implying TRAIL as a promising therapeutic agent against thyroid cancers. However, signal transduction in TRAIL-mediated apoptosis is not clearly understood. In addition to its well-known glycolytic functions, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a multifunctional protein, including its surprising role as a mediator for cell death. In this study we explored the involvement of GAPDH in TRAIL-mediated thyroid cancer cell death. In follicular undifferentiated thyroid cells, S-nitrosylation and nuclear translocation of GAPDH appear to mediate TRAIL-induced cell death at least partially, as evidenced by pretreatment with N-nitro-L-arginine methyl ester, a competitive nitric oxide synthase inhibitor that partially but significantly attenuated TRAIL-induced apoptosis through the reduction of S-nitrosylation and nuclear translocation of GAPDH. In addition, GAPDH small interfering RNA partially prevented the apoptotic effect of TRAIL, although TRAIL-induced nitric oxide synthase stimulation and production of nitric oxide were not attenuated. Furthermore, nuclear localization of GAPDH was observed in another thyroid cancer cell line, KTC2, which is also sensitive to TRAIL, but not in those TRAIL insensitive cell lines: ARO, KTC1, and KTC3. These data indicate that nitric oxide-mediated S-nitrosylation of GAPDH and subsequent nuclear translocation of GAPDH might function as a mediator of TRAIL-induced cell death in thyroid cancer cells.

GAPDH and autophagy preserve survival after apoptotic cytochrome c release in the absence of caspase activation

In cells undergoing apoptosis, mitochondrial outer-membrane permeabilization (MOMP) is followed by caspase activation promoted by released cytochrome c. Although caspases mediate the apoptotic phenotype, caspase inhibition is generally not sufficient for survival following MOMP; instead cells undergo a "caspase-independent cell death" (CICD). Thus, MOMP may represent a point of commitment to cell death. Here, we identify glyceraldehyde-3-phosphate dehydrogenase (GAPDH) as a critical regulator of CICD. GAPDH-expressing cells preserved their clonogenic potential following MOMP, provided that caspase activation was blocked. GAPDH-mediated protection of cells from CICD involved an elevation in glycolysis and a nuclear function that correlated with and was replaced by an increase in Atg12 expression. Consistent with this, protection from CICD reflected an increase in and a dependence upon autophagy, associated with a transient decrease in mitochondrial mass. Therefore, GAPDH mediates an elevation in glycolysis and enhanced autophagy that cooperate to protect cells from CICD.

Glyceraldehyde-3-phosphate dehydrogenase exerts different biologic activities in apoptotic and proliferating hepatocytes according to its subcellular localization

Recent evidences indicate new roles for the glycolytic protein glyceraldehyde-3-phosphate dehydrogenase (GAPDH) in essential mammalian cell processes, such as apoptosis and proliferation. To clarify the involvement of this protein in growth and programmed cell death in the liver, cell models of hepatocytes in culture were used to study GAPDH expression, localization and enzymatic activity in hepatocyte proliferation and apoptosis. GAPDH expression in cell compartments was studied by Western blot. Nuclear expression of GAPDH increased in apoptosis, and cytoplasmic expression was elevated in apoptosis and proliferation. Subcellular localization was determined by GAPDH immunostaining and confocal microscopic analysis. Quiescent and proliferating hepatocytes showed cytoplasmic GAPDH, while apoptotic cells showed cytoplasmic but also some nuclear staining. The glycolytic activity of GAPDH was studied in nuclear and cytoplasmic cell compartments. GAPDH enzymatic activity increased in the nucleus of apoptotic cells and in cytoplasms of apoptotic and proliferating hepatocytes. Our observations indicate that during hepatocyte apoptosis GAPDH translocates to the nucleus, maintaining in part its dehydrogenase activity, and suggest that this translocation may play a role in programmed hepatocyte death. GAPDH over-expression and the increased enzymatic activity in proliferating cells, with preservation of its cytoplasmic localization, would occur in response to the elevated energy requirements of dividing hepatocytes. In conclusion, GAPDH plays different roles or biological activities in proliferating and apoptotic hepatocytes, according to its subcellular localization.

Degradation of the encephalomyocarditis virus and hepatitis A virus 3C proteases by the ubiquitin/26S proteasome system in vivo

We have isolated stably transfected mouse embryonic fibroblast cell lines that inducibly express either the mature encephalomyocarditis virus (EMCV) or hepatitis A virus (HAV) 3C protease and have used these cells to demonstrate that both proteins are subject to degradation in vivo by the ubiquitin/26S proteasome system. The detection of 3C protease expression in these cells requires inducing conditions and the presence of one of several proteasome inhibitors. Both 3C proteases are incorporated into conjugates with ubiquitin in vivo. HAV 3C protease expression has deleterious effects on cell viability, as determined by observation and counting of cells cultured in the absence or presence of inducing conditions. The EMCV 3C protease was found to be preferentially localized to the nucleus of induced cells, while the HAV 3C protease remains in the cytoplasm. The absence of polyubiquitinated EMCV 3C protease conjugates in nuclear fraction preparations suggests that localization to the nucleus can protect this protein from ubiquitination.

Nuclear translocation of the tumor marker pyruvate kinase M2 induces programmed cell death

Cancer cells often fail to respond to stimuli that normally activate their intrinsic apoptotic machinery. Moreover, they are able to adapt to hypoxia by changing their glycolytic rate. Pyruvate kinase (PK) is a rate-limiting enzyme in glycolysis that is converted to a less active dimer form of PKM2 isoenzyme during oncogenesis. Here, we show that both somatostatin and the structural analogue TT-232 interact with the PKM subtype. We further show that the PKM2 is translocated to the nucleus in response to TT-232 and different apoptotic agents. Nuclear translocation of PKM2 is sufficient to induce cell death that is caspase independent, isoform specific, and independent of its enzymatic activity. These results show that the tumor marker PKM2 plays a general role in caspase-independent cell death of tumor cells and thereby defines this glycolytic enzyme as a novel target for cancer therapy development.

Proteome map of Aspergillus nidulans during osmoadaptation

The model filamentous fungus Aspergillus nidulans, when grown in a moderate level of osmolyte (+0.6M KCl), was previously found to have a significantly reduced cell wall elasticity (Biotech Prog, 21:292, 2005). In this study, comparative proteomic analysis via two-dimensional gel electrophoresis (2de) and matrix-assisted laser desorption ionization/time-of-flight (MALDI-TOF) mass spectrometry was used to assess molecular level events associated with this phenomenon. Thirty of 90 differentially expressed proteins were identified. Sequence homology and conserved domains were used to assign probable function to twenty-one proteins currently annotated as "hypothetical." In osmoadapted cells, there was an increased expression of glyceraldehyde-3-phosphate dehydrogenase and aldehyde dehydrogenase, as well as a decreased expression of enolase, suggesting an increased glycerol biosynthesis and decreased use of the TCA cycle. There also was an increased expression of heat shock proteins and Shp1-like protein degradation protein, implicating increased protein turnover. Five novel osmoadaptation proteins of unknown functions were also identified.

A prolyl oligopeptidase inhibitor, Z-Pro-Prolinal, inhibits glyceraldehyde-3-phosphate dehydrogenase translocation and production of reactive oxygen species in CV1-P cells exposed to 6-hydroxydopamine

We studied the ability of prolyl oligopeptidase (POP) inhibitors, Z-Pro-Prolinal and JTP-4819, to prevent translocation of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and formation of reactive oxygen species (ROS), in 6-hydroxydopamine (6-OHDA) and cytosine arabinoside (Ara-C) treated monkey fibroblast (CV1-P) and human neuroblastoma (SH-SY5Y) cells. The cells were pretreated with POP inhibitors (30 min) before addition of toxicants. GAPDH was analyzed by Western hybridization, ROS by fluorescent 2'7'-dichlorodihydro-fluorescein diacetate, and viability by the MTT method. Both toxicants induced GAPDH translocation to the particulate fraction (mitochondria and nuclei). Z-Pro-Prolinal was able to inhibit the translocation in 6-OHDA-exposed CV1-P cells. In SH-SY5Y cells and in JTP-4819 pretreated cells, no prevention of translocation was seen. However, the intensity of GAPDH in cytosolic fraction increased. Both inhibitors blocked 6-OHDA-induced ROS-production to the control level in CV1-P but, not in SH-SY5Y cells, without affecting their viability. In conclusion, POP inhibitors are able to prevent certain cell stress related factors such as ROS production or GAPDH translocation.

Glycolysis inhibition for anticancer treatment

Most cancer cells exhibit increased glycolysis and use this metabolic pathway for generation of ATP as a main source of their energy supply. This phenomenon is known as the Warburg effect and is considered as one of the most fundamental metabolic alterations during malignant transformation. In recent years, there are significant progresses in our understanding of the underlying mechanisms and the potential therapeutic implications. Biochemical and molecular studies suggest several possible mechanisms by which this metabolic alteration may evolve during cancer development. These mechanisms include mitochondrial defects and malfunction, adaptation to hypoxic tumor microenvironment, oncogenic signaling, and abnormal expression of metabolic enzymes. Importantly, the increased dependence of cancer cells on glycolytic pathway for ATP generation provides a biochemical basis for the design of therapeutic strategies to preferentially kill cancer cells by pharmacological inhibition of glycolysis. Several small molecules have emerged that exhibit promising anticancer activity in vitro and in vivo, as single agent or in combination with other therapeutic modalities. The glycolytic inhibitors are particularly effective against cancer cells with mitochondrial defects or under hypoxic conditions, which are frequently associated with cellular resistance to conventional anticancer drugs and radiation therapy. Because increased aerobic glycolysis is commonly seen in a wide spectrum of human cancers and hypoxia is present in most tumor microenvironment, development of novel glycolytic inhibitors as a new class of anticancer agents is likely to have broad therapeutic applications.

Correlated resistance to glucose deprivation and cytotoxic agents in fibroblast cell lines from long-lived pituitary dwarf mice

Fibroblast cell lines derived from the skin of young adult mice of the long-lived Snell dwarf mutant mouse stock have been shown to be resistant to the cytotoxic effects of multiple agents, including hydrogen peroxide, cadmium, heat, ultraviolet light, and the carcinogen methyl methanesulfonate. Snell dwarf fibroblasts are here reported to differ from control cell lines in two other respects: they are relatively resistant to the metabolic inhibition induced by low glucose concentrations, and also resistant to the effects of the mitochondrial poison rotenone, a blocker of Complex I of the electron transport chain. Furthermore, analysis of cell lines derived from a group of genetically heterogeneous mice established that cell lines resistant to peroxide-induced cytotoxicity were also relatively resistant to death induced by paraquat, cadmium, and ultraviolet light. Resistance to the metabolic effects of low glucose medium was associated with resistance to peroxide and cadmium in cells from heterogeneous mice and Snell dwarf mice, though unexpectedly not associated with resistance to the lethal effects of paraquat or UV light. Further analysis of the basis for metabolic abnormalities in these cell lines may provide insights into the cause of stress resistance in dwarf-derived cultures and to the longevity and disease-resistance of these long-lived mutant mice.

Oxidative stress in glaucomatous neurodegeneration: mechanisms and consequences

Reactive oxygen species (ROS) are generated as by-products of cellular metabolism, primarily in the mitochondria. Although ROS are essential participants in cell signaling and regulation, when their cellular production overwhelms the intrinsic antioxidant capacity, damage to cellular macromolecules such as DNA, proteins, and lipids ensues. Such a state of "oxidative stress" is thought to contribute to the pathogenesis of a number of neurodegenerative diseases. Growing evidence supports the involvement of oxidative stress as a common component of glaucomatous neurodegeneration in different subcellular compartments of retinal ganglion cells (RGCs). Besides the evidence of direct cytotoxic consequences leading to RGC death, it also seems highly possible that ROS are involved in signaling RGC death by acting as a second messenger and/or modulating protein function by redox modifications of downstream effectors through enzymatic oxidation of specific amino acid residues. Different studies provide cumulating evidence, which supports the association of ROS with different aspects of the neurodegenerative process. Oxidative protein modifications during glaucomatous neurodegeneration increase neuronal susceptibility to damage and also lead to glial dysfunction. Oxidative stress-induced dysfunction of glial cells may contribute to spreading neuronal damage by secondary degeneration. Oxidative stress also promotes the accumulation of advanced glycation end products in glaucomatous tissues. In addition, oxidative stress takes part in the activation of immune response during glaucomatous neurodegeneration, as ROS stimulate the antigen presenting ability of glial cells and also function as co-stimulatory molecules during antigen presentation. By discussing current evidence, this review provides a broad perspective on cellular mechanisms and potential consequences of oxidative stress in glaucoma.

Protein oxidation and cellular homeostasis: Emphasis on metabolism

Reactive oxygen species (ROS) are generated as the result of a number of physiological and pathological processes. Once formed ROS can promote multiple forms of oxidative damage, including protein oxidation, and thereby influence the function of a diverse array of cellular processes. This review summarizes the mechanisms by which ROS are generated in a variety of cell types, outlines the mechanisms which control the levels of ROS, and describes specific proteins which are common targets of ROS. Additionally, this review outlines cellular processes which can degrade or repair oxidized proteins, and ultimately describes the potential outcomes of protein oxidation on cellular homeostasis. In particular, this review focuses on the relationship between elevations in protein oxidation and multiple aspects of cellular metabolism. Together, this review describes a potential role for elevated levels of protein oxidation contributing to cellular dysfunction and oxidative stress via impacts on cellular metabolism.

Bacterial endotoxin lipopolysaccharide induces up-regulation of glyceraldehyde-3-phosphate dehydrogenase in rat liver and lungs

Bacterial endotoxin or lipopolysaccharide (LPS) can trigger inflammatory responses and cause damage in organs such as liver and lungs when it is introduced into mammals, but the exact molecular events that mediate these responses have remained obscure. In this study, by using 2D gel electrophoresis and cDNA microarray analysis, we found that both protein and mRNA levels of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) were significantly increased in rat liver and lungs after treatment with LPS. The results were further confirmed by Western blot and Northern blot. Given the known role of GAPDH in inducing apoptosis, our results suggest that LPS-induced GAPDH up-regulation may be an important mechanism responsible for the damage induced by Gram negative bacteria in mammalian tissue and GAPDH may be involved in the signaling pathway of LPS induced apoptosis. Our results also demonstrate that GAPDH is not a suitable internal control in gene expression studies, especially when bacterial infection is involved.

Toxic advanced glycation end products (TAGE) theory in Alzheimer's disease

Several epidemiological studies have reported moderately increased risks of Alzheimer's disease (AD) in diabetic patients compared with general population. In diabetes mellitus, the formation and accumulation of advanced glycation end products (AGEs) progress more rapidly. Recent understanding of this process has confirmed that interactions between AGEs and their receptor (RAGE) may play a role in the pathogenesis of diabetic complications and AD. The authors have recently found that glyceraldehyde-derived AGEs (AGE-2), which is predominantly the structure of toxic AGEs (TAGE), show significant toxicity on cortical neuronal cells and that the neurotoxic effect of diabetic serum is completely blocked by neutralizing antibody against the AGE-2 epitope. Moreover, in human AD brains, AGE-2 is distributed in the cytosol of neurons in the hippocampus and parahippocampal gyrus. These results suggest that TAGE is involved in the pathogenesis of AD as well as other age-related diseases. In this review, the authors discuss the molecular mechanisms of AD, especially focusing on TAGE-RAGE system.

Glyceraldehyde-3-phosphate dehydrogenase versus toluidine blue as a marker for infarct volume estimation following permanent middle cerebral artery occlusion in mice

Infarct size is a good predictor of the neurological outcome following stroke. Estimation of infarct size in the early phase following experimental stroke depends on the availability of reliable techniques that can distinguish ischemic from nonischemic tissue. The objective of this study was to provide a simple and robust method for reliable delineation of the ischemic infarct area in fresh frozen cryosections from mice subjected to focal cerebral ischemia. Mice were subjected to permanent middle cerebral artery (MCA) occlusion and euthanised after 30 min, 1, 2, 4, 6, 12 and 24 h. The size of the developing infarct was compared in parallel series of sections in situ hybridized for mRNA encoding the enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) or stained with toluidine blue (TB). The infarct was clearly delineated in GAPDH mRNA in situ hybridized sections as soon as 4 h after MCA occlusion. Infarct size was similar at 4 and 6 h in GAPDH mRNA in situ hybridized sections. Sections hybridized for GAPDH mRNA showed significantly larger infarcts than sections stained with TB after 6 h but not after 24 h of ischemia. Analysis of in situ hybridized sections revealed changes in neuronal GAPDH mRNA in areas prone to undergo degeneration 30 min to 1 h after MCA occlusion, thereby preceding visible pycnosis in TB-stained sections. The results showed that in situ hybridization for GAPDH mRNA was a reliable method and superior to TB staining for precise infarct delineation prior to 6 h of permanent MCA occlusion.

Utility of proteomics to assess pollutant response of clams from the Doñana bank of Guadalquivir Estuary (SW Spain)

The utility of proteomics to assess pollutant response of Scrobicularia plana clams from three sites of Guadalquivir Estuary at the southern end of the National Park of Doñana (SW Spain) has been studied. Protein expression profiles were analyzed by 2-DE in soluble fractions of S. plana gills. Nearly 2000 well-resolved spots were detected in silver-stained gels, with focused areas in the 4-6.5 pH range. Different protein expression signatures were found at each site, with the highest number of more intense spots in animals with the highest metal content. Nineteen more intense protein spots were analyzed out by nanospray-ion trap tandem mass spectrometry, de novo sequencing and a bioinformatics search for their possible identification. While sequence tags of 16 more intense protein spots were obtained, including several proteins induced by pollutant exposure of model organisms, only 2 proteins were unambiguously identified: hypoxanthine-guanine phosphoribosyltransferase (HPRT) and glyceraldehyde-3-phosphate dehydrogenase (G3PDH). Both enzymes were significantly higher in animals with the highest metal contents. Thus, we propose these two proteins, HPRT and G3PDH, as novel pollution biomarkers.

GAPDH as a sensor of NO stress

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a classic glycolytic enzyme, and accumulating evidence has suggested that GAPDH is a multi-functional protein. In particular, its role as a mediator for cell death has been highlighted. For the last decade, many groups reported that a pool of GAPDH translocates to the nucleus under a variety of stressors, most of which are associated with oxidative stress. At the molecular level, sequential steps lead to nuclear translocation of GAPDH during cell death as follows: first, a catalytic cysteine in GAPDH (C150 in rat GAPDH) is S-nitrosylated by nitric oxide (NO) that is generated from inducible nitric oxide synthase (iNOS) and/or neuronal NOS (nNOS); second, the modified GAPDH becomes capable of binding with Siah1, an E3 ubiquitin ligase, and stabilizes it; third, the GAPDH-Siah protein complex translocates to the nucleus, dependent on Siah1's nuclear localization signal, and degrades Siah1's substrates in the nucleus, which results in cytotoxicity. A recent report suggests that GAPDH may be genetically associated with late-onset of Alzheimer's disease. (-)-deprenyl, which has originally been used as a monoamine oxidase inhibitor for Parkinson's disease, binds to GAPDH and displays neuroprotective actions, but its molecular mechanism is still unclear. The NO/GAPDH/Siah1 death cascade will contribute to the molecular understanding of a role of GAPDH in neurodegenerative disorders and help to establish novel therapeutic strategies.

Nuclear translocation and overexpression of GAPDH by the hyper-pressure in retinal ganglion cell

To investigate the effect of hyper-pressure on retinal ganglion cells (RGC-5), RGC-5 cells were exposed to an ambient hydrostatic pressure of 100 mmHg. Upon treatment, the proliferation of RGC-5 cells was inhibited and neuronal apoptosis was detected by specific apoptosis marker TUNEL (terminal deoxynucleotidyl transferase dUTP nick-end labeling). To probe into the mechanism mediating the apoptosis of RGC-5 cells in 100 mmHg, protein profile alterations following hyper-pressure treatment were examined using two-dimensional gel electrophoresis (2-DE) followed by MALDI-TOF. Out of the 400 protein spots of RGC-5 cells detected on 2-DE gels, 37 differentially expressed protein spots were further identified using in gel tryptic digestion and mass spectrometry. Among these proteins, glyceraldehyde-3-phosphate-dehydrogenase (GAPDH) was significantly expressed 10 times more in 100 mmHg than in normal pressure. The accumulation of GAPDH in the nucleus and its translocation from the cytosol to the nucleus in 100 mmHg were observed using a microscope. These results suggest that the hyper-pressure-induced apoptosis in RGC-5 cells may be involved with not only the increase of GAPDH expression, but also the accumulation and the translocalization of GAPDH to the nucleus.

Nuclear localization of glyceraldehyde-3-phosphate dehydrogenase is not involved in the initiation of apoptosis induced by 1-Methyl-4-phenyl-pyridium iodide (MPP+)

Nuclear localization of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is implicated in the process of apoptosis. To study the function of GAPDH, we expressed GAPDH C-terminally fused with or without nuclear localization signal (NLS) in SH-SY5Y and NB41A3 cells using a retrovirus expression system. GAPDH carrying NLS (GAPDH-NLS) was expressed mainly in the nucleus. However, expression of GAPDH-NLS did not cause any difference in cell survival rate as compared to that of the vector alone or GAPDH without NLS. Treatment with 1-Methyl-4-phenyl-pyridium iodide (MPP+) caused no difference in the cell survival rate or in the pattern or extent of apoptosis among the three transductants. In the cells expressing GAPDH without NLS, MPP+ did not cause visible translocation of GAPDH into nucleus before the onset of apoptosis. Since GAPDH is known to comprise a CRM1-mediated nuclear export signal, we blocked the nuclear export of GAPDH by treatment with leptomycin B, an inhibitor of CRM1-mediated nuclear export. The treatment did not cause any difference in apoptosis among the three transductants. An additional treatment with MPP+ induced no apoptotic difference in these cells. Thus, we have concluded that a simple nuclear localization of GAPDH does not induce apoptosis, and that MPP+-induced apoptosis is not caused by nuclear translocation of GAPDH.

Depletion of reduced glutathione precedes inactivation of mitochondrial enzymes following limbic status epilepticus in the rat hippocampus

The time course and critical determinants of mitochondrial dysfunction and oxidative stress following limbic status epilepticus (SE) were investigated in hippocampal sub-regions of an electrical stimulation model in rats, at time points 4-44h after status. Mitochondrial and cytosolic enzyme activities were measured spectrophotometrically, and reduced glutathione (GSH) concentrations by HPLC, and compared to results from sham controls. The earliest change in any sub-region was a fall in GSH, appearing as early as 4h in CA3 (-13%, p<0.05), and persisting at all time points. This was followed by a transient fall in complex I activity (CA3, 16h, -13%, p<0.05), and later changes in aconitase (CA1,-18% and CA3, -22% at 44h, p<0.05). The activity of the cytosolic enzyme glyceraldehyde-3-phosphate-dehydrogenase was unaffected at all time points. It is known that GSH levels are dependent both on redox status, and on the availability of the precursor cysteine, in turn dependent on the cysteine/glutamate antiporter, for which extracellular glutamate concentrations are rate limiting. Both mechanisms are likely to contribute indirectly to GSH depletion following seizures. That a relative deficiency in GSH precedes later changes in the activities of complex I and aconitase in vulnerable hippocampal sub-regions, occurring within a clinically relevant therapeutic time window, suggests that strategies to boost GSH levels and/or otherwise reduce oxidative stress following seizures, deserve further study, both in terms of preventing the biochemical consequences of SE and the neuronal dysfunction and clinical consequences.

Proteomic Analysis of Cellular Response to Osmotic Stress in Thick Ascending Limb of Henle’s Loop (TALH) Cells

Epithelial cells of the thick ascending limb of Henle's loop (TALH cells) play a major role in the urinary concentrating mechanism. They are normally exposed to variable and often very high osmotic stress, which is particularly due to high sodium and chloride reabsorption and very low water permeability of the luminal membrane. It is already established that elevation of the activity of aldose reductase and hence an increase in intracellular sorbitol are indispensable for the osmotic adaptation and stability of the TALH cells. To identify new molecular factors potentially associated with the osmotic stress-resistant phenotype in kidney cells, TALH cells exhibiting low or high levels of resistance to osmotic stress were characterized using proteomic tools. Two-dimensional gel analysis showed a total number of 40 proteins that were differentially expressed in TALH cells under osmotic stress. Twenty-five proteins were overexpressed, whereas 15 proteins showed a down-regulation. Besides the sorbitol pathway enzyme aldose reductase, whose expression was 15 times increased, many other metabolic enzymes like glutathione S-transferase, malate dehydrogenase, lactate dehydrogenase, alpha enolase, glyceraldehyde-3-phosphate dehydrogenase, and triose-phosphate isomerase were up-regulated. Among the cytoskeleton proteins and cytoskeleton-associated proteins vimentin, cytokeratin, tropomyosin 4, and annexins I, II, and V were up-regulated, whereas tubulin and tropomyosins 1, 2, and 3 were down-regulated. The heat shock proteins alpha-crystallin chain B, HSP70, and HSP90 were found to be overexpressed. In contrast to the results in oxidative stress the endoplasmic reticulum stress proteins like glucose-regulated proteins (GRP78, GRP94, and GRP96), calreticulin, and protein-disulfide isomerase were down-regulated under hypertonic stress.

Amyloid‐β induces disulfide bonding and aggregation of GAPDH in Alzheimer's disease

GAPDH is a redox-sensitive glycolytic enzyme that also promotes apoptosis when translocated to the nucleus and associates with aggregate-prone proteins involved in neurodegenerative disorders. Recent evidence indicates that polymorphic variation within GAPDH genes is associated with an elevated risk of developing Alzheimer's disease (AD). We previously demonstrated that GAPDH readily undergoes disulfide bonding following oxidant exposure, although the consequence of disulfide bonding on GAPDH activity or function is unknown. Here we show that increased GAPDH disulfide bonding is observed in detergent-insoluble extracts from AD patient and transgenic AD mouse brain tissue compared with age-matched controls. Exposure of primary rat cortical neurons to the pro-oxidant amyloid beta peptide promotes nuclear accumulation of a disulfide-linked form of GAPDH, which becomes detergent-insoluble. Disulfide bonding leads to a reduction in GAPDH enzymatic activity and correlates with the appearance of punctate aggregate-like GAPDH staining within the cytoplasm of both oxidant-treated HT22 cells and amyloid beta-treated primary cortical neurons. Our findings suggest that disulfide bonding of GAPDH and subsequent protein aggregate formation may have relevance to the pathophysiology of AD.

Proteomic identification of glyceraldehyde 3-phosphate dehydrogenase as an inhibitory target of hydrogen peroxide in Arabidopsis

Hydrogen peroxide (H2O2) is now recognised as a key signalling molecule in eukaryotes. In plants, H2O2 is involved in regulating stomatal closure, gravitropic responses, gene expression and programmed cell death. Although several kinases, such as oxidative signal-inducible 1 (OXI1) kinase and mitogen-activated protein kinases are known to be activated by exogenous H2O2, little is known about the proteins that directly react with H2O2. Here, we utilised a proteomic approach, using iodoacetamide-based fluorescence tagging of proteins in conjunction with mass spectrometric analysis, to identify several proteins that might be potential targets of H2O2 in the cytosolic fraction of Arabidopsis thaliana, the most prominent of which was cytosolic glyceraldehyde 3-phosphate dehydrogenase (cGAPDH; EC 1.2.1.12). cGAPDH from Arabidopsis is inactivated by H2O2 in vitro, and this inhibition is reversible by the subsequent addition of reductants such as reduced glutathione (GSH). It has been suggested recently that Arabidopsis GAPDH has roles outside of its catalysis as part of glycolysis, while in other systems this includes that of mediating reactive oxygen species (ROS) signalling. Here, we suggest that cGAPDH in Arabidopsis might also have such a role in mediating ROS signalling in plants.

S-nitrosylated GAPDH initiates apoptotic cell death by nuclear translocation following Siah1 binding

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) influences cytotoxicity, translocating to the nucleus during apoptosis. Here we report a signalling pathway in which nitric oxide (NO) generation that follows apoptotic stimulation elicits S-nitrosylation of GAPDH, which triggers binding to Siah1 (an E3 ubiquitin ligase), nuclear translocation and apoptosis. S-nitrosylation of GAPDH augments its binding to Siah1, whose nuclear localization signal mediates translocation of GAPDH. GAPDH stabilizes Siah1, facilitating its degradation of nuclear proteins. Activation of macrophages by endotoxin and of neurons by glutamate elicits GAPDH-Siah1 binding, nuclear translocation and apoptosis, which are prevented by NO deletion. The NO-S-nitrosylation-GAPDH-Siah1 cascade may represent an important molecular mechanism of cytotoxicity.

Glyceraldehyde-3-phosphate dehydrogenase, apoptosis, and neurodegenerative diseases

Increasing evidence supports the notion that glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a protein with multiple functions, including its surprising role in apoptosis. GAPDH is overexpressed and accumulates in the nucleus during apoptosis induced by a variety of insults in diverse cell types. Knockdown of GAPDH using an antisense strategy demonstrates its involvement in the apoptotic cascade in which GAPDH nuclear translocation appears essential. Knowledge concerning the mechanisms underlying GAPDH nuclear translocation and subsequent cell death is growing. Additional evidence suggests that GAPDH may be an intracellular sensor of oxidative stress during early apoptosis. Abnormal expression, nuclear accumulation, changes in physical properties, and loss of glycolytic activity of GAPDH have been found in cellular and transgenic models as well as postmortem tissues of several neurodegenerative diseases. The interaction of GAPDH with disease-related proteins as well as drugs used to treat these diseases suggests that it is a potential molecular target for drug development.

Multifaceted roles of glycolytic enzymes

Although glycolysis is a biochemical pathway that evolved under ancient anaerobic terrestrial conditions, recent studies have provided evidence that some glycolytic enzymes are more complicated, multifaceted proteins rather than simple components of the glycolytic pathway. These glycolytic enzymes have acquired additional non-glycolytic functions in transcriptional regulation [hexokinase (HK)-2, lactate dehydrogenase A, glyceraldehyde-3-phosphate dehydrogenase (GAPD) and enolase 1], stimulation of cell motility (glucose-6-phosphate isomerase) and the regulation of apoptosis (glucokinase, HK and GAPD). The existence of multifaceted roles of glycolytic proteins suggests that links between metabolic sensors and transcription are established directly through enzymes that participate in metabolism. These roles further underscore the need to consider the non-enzymatic functions of enzymes in proteomic studies of cells and tissues.

Monochloroacetic Acid Inhibits Liver Gluconeogenesis by Inactivating Glyceraldehyde-3-phosphate Dehydrogenase

We previously reported that a lethal dose of monochloroacetate (MCA) causes severe hypoglycemia and lactic acidosis. MCA has been thought to inhibit mitochondrial aconitase; however, the exact effect of MCA on hepatic glucose metabolism is not clear. In this study, we investigated the effects of MCA on liver gluconeogenesis using an isolated perfused rat liver system. Gluconeogenesis from 2.5 mM lactate was inhibited by 1 mM MCA and was completely abolished after 2 h of perfusion. Levels of citric acid cycle intermediates such as citrate, isocitrate, and 2-oxoglutarate (2-OG) were significantly reduced by MCA. The finding that the levels of citrate and 2-OG were similarly reduced (to 31 and 36% of control, respectively) indicates that aconitase was not inhibited by MCA. On the contrary, gluconeogenesis from glycerol, which can be converted to glucose without glyceraldehyde-3-phosphate dehydrogenase (GAPDH), was not inhibited by MCA. GAPDH was inactivated by MCA in vitro, but enolase, phosphoglycerate mutase, and phosphoglycerate kinase were not inactivated at the same or higher concentrations of MCA. Furthermore, GAPDH activity in the MCA-perfused liver decreased to 33-42% of control and that in the liver of rats exposed to MCA was reduced to 19% of control. We concluded that MCA inactivates GAPDH, and this is the cause of the inhibition of liver gluconeogenesis.

Proteome analysis of programmed cell death and defense signaling using the rice lesion mimic mutant cdr2

We have previously identified three lesion-mimic mutants, cell death and resistance (cdr), in rice. These mutants induce a series of defense responses, including expression of defense-related genes and high accumulation of phytoalexins, indicating that the cdr mutants are useful materials to study programmed cell death and defense signaling in rice. Here, we carried out a proteome analysis of the cdr2 mutant. Total proteins prepared from the wild type and the cdr2 mutant at three different stages of lesion formation were compared using two-dimensional electrophoresis. We found a total of 37 proteins that were differentially expressed between cdr2 and wild type. Among them, 28 spots were up-regulated and nine were down-regulated in the cdr2 mutant. All the protein spots were identified by mass spectrometric analysis. These differentially regulated proteins included defense-related proteins. In addition, 27 proteins were classified as metabolic enzymes, suggesting that the programmed cell death that occurs in the cdr2 mutant is associated with active metabolic changes. Our study shows that proteome analysis is a useful approach to study programmed cell death and defense signaling in plants.