New insights into an old protein: the functional diversity of mammalian glyceraldehyde-3-phosphate dehydrogenase

Subcellular alteration of glyceraldehyde-3-phosphate dehydrogenase in Alzheimer's disease fibroblasts

The regulation of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) has been implicated both in age-related neurodegenerative disease and in apoptosis. Previous in vitro studies suggest an interaction between GAPDH and the beta-amyloid precursor protein (beta-APP), a protein directly involved in Alzheimer's disease (AD). New studies indicate that GAPDH is a multidimensional protein with diverse membrane, cytoplasmic, and nuclear functions; each is distinct from its role in glycolysis. The nuclear functions of GAPDH include a role in apoptosis that requires its translocation to the nucleus. Accordingly, beta-APP-GAPDH interactions, altering GAPDH structure in vivo, may affect energy generation, inducing hypometabolism, a characteristic AD phenotype. Because GAPDH is a multifunctional protein, pleiotropic effects may also occur in a variety of fundamental cellular pathways in AD cells. This may include unique GAPDH-RNA interactions. We report here the identification of a high-molecular-weight (HMW) GAPDH species present exclusively in the postnuclear fraction of AD cells. The latter is characterized by reduced GAPDH activity. The HMW GAPDH species was not detected in postnuclear age-matched control (AMC) fractions nor in AD whole-cell preparations. Each is characterized by normal GAPDH activity. By definition, the preparation of whole-cell extracts entails the destruction of subcellular structure. The latter findings indicate that the dissociation of the GAPDH protein from the HMW species restores its enzymatic activity. Thus, these results reveal a new, unique intracellular phenotype in AD cells. The functional consequences of subcellular alteration in GAPDH structure in AD cells are considered.

Structure and dynamics of thioguanine-modified duplex DNA

Mercaptopurine and thioguanine, two of the most widely used antileukemic agents, exert their cytotoxic, therapeutic effects by being incorporated into DNA as deoxy-6-thioguanosine. However, the molecular mechanism(s) by which incorporation of these thiopurines into DNA translates into cytotoxicity is unknown. The solution structure of thioguanine-modified duplex DNA presented here shows that the effects of the modification on DNA structure were subtle and localized to the modified base pair. Specifically, thioguanine existed in the keto form, formed weakened Watson-Crick hydrogen bonds with cytosine and caused a modest approximately 10 degrees opening of the modified base pair toward the major groove. In contrast, thioguanine significantly altered base pair dynamics, causing an approximately 80-fold decrease in the base pair lifetime with cytosine compared with normal guanine. This perturbation was consistent with the approximately 6 degrees C decrease in DNA melting temperature of the modified oligonucleotide, the 1.13 ppm upfield shift of the thioguanine imino proton resonance, and the large increase in the exchange rate of the thioguanine imino proton with water. Our studies provide new mechanistic insight into the effects of thioguanine incorporation into DNA at the level of DNA structure and dynamics, provide explanations for the effects of thioguanine incorporation on the activity of DNA-processing enzymes, and provide a molecular basis for the specific recognition of thioguanine-substituted sites by proteins. These combined effects likely cooperate to produce the cellular responses that underlie the therapeutic effects of thiopurines.

Structural characterization of transglutaminase-catalyzed cross-linking between glyceraldehyde 3-phosphate dehydrogenase and polyglutamine repeats

The accumulation of abnormal polyglutamine-containing protein aggregates within the cytosol and nuclei of affected neurons is a hallmark of the progressive neurodegenerative disorders caused by an elongated (CAG)(n) repeat in the genome. The polyglutamine domains are excellent substrates for the enzyme transglutaminase type 2 (tissue), resulting in the formation of cross-links with polypeptides containing lysyl groups. Enzymatic activity toward the Q(n) domains increases greatly upon lengthening of such Q(n) stretches (n > 40). Among the possible amine donors, the glycolytic enzyme glyceraldehyde-3-phosphate-dehydrogenase was shown to tightly bind several proteins involved in polyglutamine expansion diseases. Recently, the authors have shown that K191, K268, and K331, out of the 26 lysines present in glyceraldehyde-3-phosphate-dehydrogenase, are the reactive amine-donor sites forming cross-links with substance P, which bears the simplest Q(n) domain (n = 2). The present study reports that synthetic peptides of both pathological and nonpathological length (n = 43 and 17, respectively) form cross-links with the same K residues located in the C-terminal region of glyceraldehyde-3-phosphate-dehydrogenase. In addition, it is shown that extra K residues present in the C termini of glyceraldehyde-3-phosphate-dehydrogenase are susceptible to cross-linking in the presence of transglutaminase. The present results indicate a possible modulating effect of Q(n) stretches on tissue transglutaminase substrate specificity and mechanism of recognition.

Housekeeping enzymes as virulence factors for pathogens

Housekeeping enzymes are ubiquitously present in almost all living beings to perform essential metabolic functions for the purpose of survival. These enzymes have been characterized in detail for many years. In recent years, there has been a number of reports indicating that some of these enzymes perform a variety of other functions. In case of many pathogens, certain enzymes play a role to enhance virulence. To perform such a function, enzymes must be located on the surface of pathogens. Although they do not have the typical signal sequence or membrane anchoring mechanisms, they do get secreted and are displayed on the surface, probably by their reassociation. Once on the surface, these enzymes interact with host components, such as fibronectin and plasminogen, or interact directly with the host cells, to trigger signal transduction and thereby enable the pathogens to colonize, persist and invade the host tissue. Therefore, certain housekeeping enzymes may act as putative virulence factors and targets for the development of new strategies to control the infection by using agents that can block their secretion and/or reassociation.

Conformational Change of Glyceraldehyde-3-phosphate Dehydrogenase Induced by Acetylleucine Chloromethyl Ketone is Followed by Unique Enzymatic Degradation

We have previously reported that acetylleucine chloromethyl ketone (ALCK), an inhibitor of acylpeptidehydrolase, induces the inhibition and degradation of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) in the U937 cell extract. In the present study, the process of ALCK-induced GAPDH degradation was investigated. A kinetic study revealed that GAPDH was irreversibly inhibited by ALCK. ALCK treatment induced a change in the signal intensity of GAPDH in the near-UV region of the circular dichroism (CD) spectrum, and the fluorescence intensity of GAPDH at 330 nm increased to about 10% when excited at 280 nm, suggesting that a significant conformational change of GAPDH was induced by ALCK. When the U937 cell extract was incubated with ALCK and the products were separated by SDS-polyacrylamide gel electrophoresis (PAGE), a 23-kDa fragment from GAPDH was detected by Western blotting using anti-GAPDH serum. When ALCK-treated GAPDH was incubated with protease fractions from the U937 cell extract, a 17-kDa fragment was also detected. Sequence analysis showed that the N-terminal amino acid sequence of the 23-kDa fragment was GKVKVG and that of 17-kDa fragment was RDGRGAL. Therefore, ALCK-modified GAPDH is deduced to be digested at the peptide bond Trp(195)-Arg(196). The protease activity liberating a 23-kDa fragment from ALCK-treated GAPDH was effective under the basic condition. Results suggested that ALCK binds to GAPDH to modulate the conformation of enzyme, which is susceptible to chymotrypsin-like protease activity.

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.

Sequence conserved for subcellular localization

The more proteins diverged in sequence, the more difficult it becomes for bioinformatics to infer similarities of protein function and structure from sequence. The precise thresholds used in automated genome annotations depend on the particular aspect of protein function transferred by homology. Here, we presented the first large-scale analysis of the relation between sequence similarity and identity in subcellular localization. Three results stood out: (1) The subcellular compartment is generally more conserved than what might have been expected given that short sequence motifs like nuclear localization signals can alter the native compartment; (2) the sequence conservation of localization is similar between different compartments; and (3) it is similar to the conservation of structure and enzymatic activity. In particular, we found the transition between the regions of conserved and nonconserved localization to be very sharp, although the thresholds for conservation were less well defined than for structure and enzymatic activity. We found that a simple measure for sequence similarity accounting for pairwise sequence identity and alignment length, the HSSP distance, distinguished accurately between protein pairs of identical and different localizations. In fact, BLAST expectation values outperformed the HSSP distance only for alignments in the subtwilight zone. We succeeded in slightly improving the accuracy of inferring localization through homology by fine tuning the thresholds. Finally, we applied our results to the entire SWISS-PROT database and five entirely sequenced eukaryotes.

Dehydrogenases from all three domains of life cleave RNA

Specific interactions of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) with RNA have been reported both in vitro and in vivo. We show that eukaryotic and bacterial GAPDH and two proteins from the hyperthermophilic archaeon Sulfolobus solfataricus, which are annotated as dehydrogenases, cleave RNA producing similar degradation patterns. RNA cleavage is most efficient at 60 degrees C, at MgCl(2) concentrations up to 5 mm, and takes place between pyrimidine and adenosine. The RNase active center of the putative aspartate semialdehyde dehydrogenase from S. solfataricus is located within the N-terminal 73 amino acids, which comprise the first mononucleotide-binding site of the predicted Rossmann fold. Thus, RNA cleavage has to be taken into account in the ongoing discussion of the possible biological function of RNA binding by dehydrogenases.

Tubulin is the endogenous inhibitor of the glyceraldehyde 3-phosphate dehydrogenase isoform that catalyzes membrane fusion: Implications for the coordinated regulation of glycolysis and membrane fusion

Previously we demonstrated that specific chromatographically resolvable isoforms of rabbit brain GAPDH catalyze either glycolytic flux or membrane fusion activity (but not both). Moreover, GAPDH membrane fusion activity was latent until it was separated from an endogenous cytosolic inhibitor by anion-exchange chromatography. Herein we demonstrate that the cytosolic inhibitor is nondialyzable, heat-labile, and trypsin-sensitive, thereby identifying it as a cytosolic protein constituent. Chromatographic purification of the rabbit-brain cytosolic protein inhibitor of GAPDH isoform-catalyzed membrane fusion identified a predominant 55-kDa doublet that contained an internal 15-aa peptide identical to a sequence present in alpha-tubulin (residues 65-79). The identity of the 55-kDa doublet as tubulin was substantiated through Western blot analysis and inhibition of GAPDH-catalyzed membrane fusion by authentic tubulin. Stopped-flow kinetic analysis demonstrated the high-affinity, rapid, and direct modulation of GAPDH-catalyzed fusion activity by tubulin. Because GTP-activated Rab 2 recruits GAPDH to membranes about to undergo fusion [Tisdale, E. J. (2001) J. Biol. Chem. 276, 2480-2486] and protein kinase Ciota/lambda phosphorylates GAPDH modulating its interactions with tubulin [Tisdale, E. J. (2001) J. Biol. Chem. 277, 3334-3341], the present study suggests a coordinated mechanism through which membrane trafficking and cellular signaling can be integrated with glycolytic flux.

Alteration of intracellular structure and function of glyceraldehyde-3-phosphate dehydrogenase: a common phenotype of neurodegenerative disorders?

Recent evidence reveals that glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is not simply a classical glycolytic protein of little interest. Instead, it is a multifunctional protein with diverse cytoplasmic, membrane and nuclear activities. Significantly, each activity is separate and distinctfrom its role in energy production. Its nuclear activities include its emerging role in apoptosis especially in neuronal cells. GAPDH translocates into the nucleus during programmed cell death. Introduction of antisense GAPDH sequences reduces apoptosis and prevents its nuclear translocation. Independent analyses demonstrate that GAPDH may be involved in the cellular phenotype of age-related neurodegenerative disorders. GAPDH binds uniquely in vitro to the beta-amyloid precursor protein (betaAPP), to huntingtin as well as to other triplet repeat neuronal disorder proteins. In Parkinson's disease (PD) cells, immunofluorescent data suggests the co-l localization of GAPDH and alpha-synuclein in Lewy bodies. Drugs used to treat PD bind specifically to GAPDH. Our recent findings (Mazzola and Sirover, 2001) demonstrate a subcellular reduction in GAPDH glycolytic activity in Alzheimer's disease (AD) and in Huntington's disease (HD) cells. The latter may be due to intracellular alteration of GAPDH structure (Mazzola and Sirover 2002). We discuss the hypothesis that the intracellularformation of GAPDH: neuronal protein complexes may represent an emerging cellular phenotype of neurodegenerative disorders. The cytoplasmic binding of neuronal proteins to GAPDH could affect energy production. Nuclear interactions could affect its apoptotic activity. Other functions of this multidimensional protein may also be inhibited. Experimental paradigms to test this hypothesis are considered.

Transcriptome analysis of monocytic leukemia cell differentiation

The human leukemia cell line U937 is a well-established model for studying monocytic cell differentiation. We used a modified protocol (SADE) of serial analysis of gene expression (SAGE) and developed a SADE linker-anchored PCR assay to investigate the pattern of expression of known genes and to identify new transcripts in proliferating cells and during cell growth arrest and differentiation. We implemented new informatic tools to compare expression profiles before and after exposure of cells to differentiation inducers. From the analysis of 47,388 tags, we identified 13,806 distinct transcripts, 265 of which showed significant variations (P<0.01). Among 1219 well-identified genes, major changes concerned transcription and translation components, cytoskeleton, and macrophage-specific genes. Nearly half of the tags, some of them expressed at high levels, matched partially characterized genes or ESTs, or revealed yet-unknown transcripts, providing a wealth of new candidate genes that may reveal novel aspects of terminal monocytic differentiation.

beta-Actin and GAPDH housekeeping gene expression in asthmatic airways is variable and not suitable for normalising mRNA levels

BACKGROUND

The use of reverse transcription-polymerase chain reaction (RT-PCR) to measure mRNA levels has led to the common use of beta-actin and GAPDH housekeeping genes as denominators for comparison of samples. Expression of these genes is assumed to remain constant, so normalising for variations in processing and signal quantitation. However, it is well documented that beta-actin and GAPDH expression is upregulated with proliferation, activation, and differentiation. We hypothesised that airway samples which differ in their cellular profiles and activation status have different levels of expression of GAPDH and beta-actin.

METHODS

The mRNA for beta-actin, GAPDH, and interleukin (IL)-2 was measured in bronchoalveolar lavage (BAL) fluid cells and endobronchial biopsy tissue by competitive RT-PCR in a cross sectional study of 26 normal controls and 92 asthmatic subjects.

RESULTS

For both BAL fluid cells and biopsy tissue, asthmatics overall had reduced expression of GAPDH and beta-actin mRNA. In asthmatic subjects not using inhaled corticosteroids (ICS), GAPDH mRNA levels in both BAL fluid and biopsy tissue, and beta-actin mRNA in BAL fluid cells were 10 times lower than samples from both normal controls and from asthmatic subjects using ICS. beta-Actin mRNA in biopsy specimens showed the same pattern of expression, but asthmatic subjects not using ICS were not significantly different from those receiving ICS treatment. IL-2 mRNA levels did not differ between the subject or treatment groups but, when expressed as a ratio with beta-actin, significant differences were seen.

CONCLUSIONS

beta-Actin and GAPDH used as denominators of gene expression quantitation in asthma research can cause confounding. Housekeeping genes need careful validation before their use in such quantitative mRNA assays.

Aliphatic propargylamines as symptomatic and neuroprotective treatments for neurodegenerative diseases

Over the past several years, we have developed a number of novel aliphatic propargylamine-related compounds. These can be divided into 14 main chemical families. These families have been shown to possess members that selectively and stereochemically (i.e. R-enantiomer) rescue neurons from p53-dependent apoptosis in vitro. In contrast, no rescue has been observed by the enantiomers of the opposite configuration or in p53-independent apoptosis. In vivo, several compounds have been shown to possess neural rescue properties in models of unilateral hypoxia/ischaemia, focal ischaemia, facial nerve axotomy, pmn mice, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse and MPTP non-human primate. Our prototype compound, R-2HMP, has been shown to be metabolised in a manner analogous to that of R-deprenyl but devoid of amphetaminergic metabolites. These compounds have been shown to be active through an interaction with the same binding site as R-deprenyl and CGP 3466. This site is suggested to be the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH).

Direct detection of potential selenium delivery proteins by using an Escherichia coli strain unable to incorporate selenium from selenite into proteins

Selenium can be metabolized for protein synthesis by two major pathways in vivo. In a specific pathway it can be inserted into polypeptide chains as the amino acid selenocysteine, as directed by the UGA codon. Alternatively, selenium can be substituted for sulfur to generate the free amino acids selenocysteine and selenomethionine, and these are incorporated nonspecifically into proteins in place of cysteine and methionine, respectively. A mutant strain of Escherichia coli was constructed that is deficient in utilization of inorganic selenium for both specific and nonspecific pathways of selenoprotein synthesis. Disruption of the cysK gene prevented synthesis of free cysteine and selenocysteine from inorganic S and Se precursors. Inactivation of the selD gene prevented synthesis of selenophosphate, the reactive selenium donor, required for the specific incorporation pathway. As expected, the double mutant strain, RL165 Delta selD, when grown anaerobically in LB + glucose medium containing (75)SeO(3)(2-), failed to synthesize selenium-dependent formate dehydrogenase H and seleno-tRNAs. However, it incorporated 24% as much selenium as the wild-type strain. Selenium in the deficient strain was bound to five different proteins. A 39-kDa species was identified as glyceraldehyde-3-phosphate dehydrogenase. It is possible that selenium was bound as a perselenide derivative to the reactive cysteine residue of this enzyme. A 28-kDa protein identified as deoxyribose phosphate aldolase also contained bound selenium. These (75)Se-labeled proteins may have alternate roles as selenium delivery proteins.

Interaction of the GTS1 gene product with glyceraldehyde- 3-phosphate dehydrogenase 1 required for the maintenance of the metabolic oscillations of the yeast Saccharomyces cerevisiae

We previously reported that GTS1 is involved in regulating ultradian oscillations of the glycolytic pathway induced by cyanide in cell suspensions as well as oscillations of energy metabolism in aerobic continuous cultures. Here, we screened a yeast cDNA library for proteins that bind to Gts1p using the yeast two-hybrid system and cloned multiple TDH cDNAs encoding the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH). We found that the zinc-finger and dimerization sites of Gts1p were required for full ability to bind GAPDH, and Gts1ps mutated at these sites lost the ability to regulate both aerobic and unaerobic ultradian oscillations of energy metabolism. Of the three TDH genes, only TDH1 fluctuated at the mRNA level in continuous culture and its deletion resulted in the disappearance of the oscillation without any affect on growth rate. This loss of biological rhythms in the TDH1-deleted mutant was rescued by the expression of TDH1 but not of TDH2 or TDH3 under the control of the TDH1 promoter. Thus, we hypothesized that Gts1p plays a role in the regulation of metabolic oscillation by interacting with the TDH1 product, GAPDH1, in yeast.

Immunisation of dairy cattle with recombinant Streptococcus uberis GapC or a chimeric CAMP antigen confers protection against heterologous bacterial challenge

The gapC genes, encoding the cell surface-associated GapC proteins of S. uberis and S. agalactiae, have been cloned and sequenced. To identify potential vaccine candidates against S. uberis-induced bovine mastitis, lactating dairy cows were vaccinated with either (6 x His)GapC of S. uberis or S. dysgalactiae, or with a chimeric CAMP-factor antigen, CAMP-3. For 7 days following heterologous challenge with S. uberis, milk somatic cell counts were determined to assess differences in the severity of mastitis between vaccinates and an unvaccinated control group. Vaccination with S. uberis (6 x His)GapC or CAMP-3 resulted in a significant reduction in inflammation on several days post-challenge, most significantly for the former antigen. Inflammation was not reduced in S. dysgalactiae (6 x His)GapC vaccinates, suggesting that it does not confer cross-species protection.

Degradation of glyceraldehyde-3-phosphate dehydrogenase induced by acetylleucine chloromethyl ketone in U937 cells

We examined whether any changes were induced in cellular proteins by an inhibitor of acylpeptide hydrolase (ACPH) (EC 3.4.19.1), acetylleucine chloromethyl ketone (ALCK), which was shown in our previous report to induce apoptosis of human U937 cells. Extract prepared from U937 cells in 0.05% Triton X-100-PBS was incubated with ALCK at 37 degrees, and then analyzed using SDS-PAGE. A 36kDa protein in the cell extract was decreased markedly during the incubation period. This protein was purified and identified as glyceraldehyde-3-phosphate dehydrogenase (GAPDH, EC 1.2.1.12) by its specific enzyme activity, N-terminal amino acid sequence, and Western blotting. Incubation of purified GAPDH with ALCK resulted in a decrease of GAPDH activity, but not in a decrease in the amount of GAPDH. The ALCK-induced GAPDH decrease in the cell extract was abrogated by co-incubation with a serine protease inhibitor, diisopropyl fluorophosphate, suggesting that GAPDH was first inactivated by ALCK, and subsequently degraded by a serine protease(s). GAPDH degradation was also observed in U937 cell cultures in the presence of ALCK. The significance of GAPDH inhibition in the apoptotic process is discussed.

Alteration of nuclear glyceraldehyde-3-phosphate dehydrogenase structure in Huntington's disease fibroblasts

The expression of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) may be involved in neuronal disease and in programmed cell death. Recent investigations indicate an in vitro physical association between GAPDH and huntingtin, the mutated protein in Huntington's disease (HD). Previous studies reveal the functional diversity of GAPDH as a membrane, cytoplasmic and nuclear protein. These activities are independent of its classical glycolytic function. Thus, huntingtin-GAPDH interactions could affect not only energy production but also result in pleiotropic effects involving various biochemical pathways in HD cells. We now report the identification of a nuclear high molecular weight (HMW) GAPDH species in Huntington's disease cells. In contrast, nuclei from age-matched control normal human cells did not contain the HMW GAPDH species. Further, this GAPDH structure was not observed in HD whole cell sonicates which are characterized by normal GAPDH activity. The disruption of intracellular structure is implicit in the preparation of whole cell sonicates. Therefore, these results suggest that the dissociation of the GAPDH protein from its high molecular weight structure results in the recovery of its function. These findings reveal a singular, new subcellular phenotype in HD cells. As such, they indicate an interrelationship between nuclear GAPDH function and huntingtin localization in this CAG expansion neuronal disease.

Differential alteration of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) mRNA in the central nervous system of hens treated with diisopropylphosphorofluoridate (DFP)

A single dose (1.7 mg/kg, s.c.) of diisopropylphosphorofluoridate (DFP) causes organophosphorus ester-induced delayed neurotoxicity (OPIDN) in susceptible species. We studied the effects of DFP administration on the mRNA expression of glyceraldehyde-3-phosphate dehydrogenase (GAPDH), an important glycolytic protein at different time points (1, 2, 5, 10 and 20 days) post-treatment. Total RNA was extracted from cerebrum, cerebellum, brainstem, midbrain, and spinal cord of the control and DFP-treated hens, and northern blots were prepared using standard protocols and hybridized with GAPDH, as well as beta-actin and 28S RNA cDNA (control) probes. There was a distinct spatial/temporal mRNA expression pattern for the different tissues studied. Non-susceptible tissue, cerebrum showed a dramatic increase in GAPDH mRNA at day 1, post-treatment and levels remained high at all time points, suggestive of protective mechanisms from the beginning. In contrast, highly susceptible tissues like brainstem, spinal cord and midbrain showed either no elevation or slight down-regulation at day 1, suggesting trauma and cell injury/cell death. Overall, there was moderate level of induction during the subsequent time points in these tissues, indicative of pathways of either recovery or degeneration. Cerebellum being the less susceptible tissue showed moderate increase initially, followed by higher induction, suggestive of rapid recovery. Our current data on GAPDH provides an important link in this complex network of molecular changes involving pathways identified by our group and others, such as nitric oxide (NO), CaM kinase-II (CaMK-II), protein kinase-A (PKA), c-fos, and phosphorylated-CREB (p-CREB) in DFP-induced OPIDN.

Identification of an additional hypoxia responsive element in the glyceraldehyde-3-phosphate dehydrogenase gene promoter

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a multifunctional enzyme overexpressed in many tumors and induced by hypoxia in normal and malignant cells. The degree to which hypoxia transcriptionally activates GAPDH is cell type specific. The GAPDH promoter region contains a hypoxia responsive element (HRE) consisting of a hypoxia inducible factor-1 (HIF-1) consensus binding site plus adjacent sequence [Graven et al. (1999) Biochim. Biophys. Acta 1447, 208-218]. Using transient transfection experiments with the GAPDH promoter region linked to a luciferase reporter gene, we found that GAPDH was transcriptionally activated by hypoxia in each of three human prostate cancer cell lines tested, with the greatest level of induction in the most differentiated cell line. Using sequence analysis of the GAPDH promoter region, we identified a novel HRE distinct from the previously characterized one that consists of two consensus HIF-1 sites arranged as inverted repeats separated by 5 bp. Hypoxia transcriptionally activated a promoter construct in which the previously characterized HRE was mutated and the novel HRE remained intact. Heterologous promoter constructs containing only one or two copies of the novel HRE plus a minimal promoter consisting of a TATA box drove hypoxia inducible expression of the luciferase reporter gene in transient transfection assays. Mutation of HIF-1 sites within the novel HRE resulted in complete loss of function.

Glyceraldehyde-3-phospate dehydrogenase is translocated into nuclei through Golgi apparatus during apoptosis induced by 6-hydroxydopamine in human dopaminergic SH-SY5Y cells

6-Hydroxydopamine is a neurotoxin specific to dopamine neurons, and this neurotoxin at 20 muM was confirmed to induce mainly apoptosis in human dopaminergic neuroblastoma SH-SY5Y cells. During the apoptotic process, translocation of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) into nuclei was observed, which is now proposed as an apoptogenic signal in various types of apoptosis. However, it remains to be clarified, how GAPDH is translocated into nuclei. In this paper, GAPDH translocation was followed by fluoro- and electron-microscopic observation using antibody against GAPDH. Before the nuclear translocation, a condensed mass of GAPDH protein was detected in the Golgi apparatus, which was identified by 6-([N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]hexanoyl)-sphingosine, a selective marker of Golgi apparatus. These results suggest that the Golgi apparatus may be involved in the compartmentalization of GAPDH from cytosol to nuclei.

Interactions of the neurotoxin 6-hydroxydopamine with glyceraldehyde-3-phosphate dehydrogenase

The neurotoxin 6-hydroxydopamine (6-OHDA) oxidised sulphydryl groups in glyceraldenyde-3-phosphate dehydrogenase (GAPDH) with loss of the dehydrogenase activity of the enzyme. 5-Hydroxydopamine behaved similarly at higher concentrations. This oxidation was accompanied by a transient rise in the acyl phosphatase (non-phosphorylating) activity of GAPDH. Treatment with arsenite resulted in loss of the acyl phosphatase activity and restoration of the dehydrogenase activity, consistent with the process involving sulphydryl-group oxidation to the corresponding sulphenate. Prolonged incubation with 6-OHDA resulted in a loss of both enzyme activities. Arsenite was unable to reverse this inhibition, indicating further oxidation, perhaps to sulphinate and sulphonate, to have occurred. RNA, but not DNA, was a partial inhibitor of both the dehydrogenase and acyl phosphatase activities of GAPDH, whereas DNA (both single- and double-stranded) was ineffective. Both single-stranded DNA and RNA inhibited the esterase activity of GAPDH, an activity that requires the absence of NAD+, in a process that was relieved at higher polynucleotide concentrations. Except at very high concentrations (1 mM), treatment of GAPDH 6-OHDA was ineffective at abolishing its to single-stranded DNA. Since GAPDH is an essential enzyme in glycolysis and also plays a role in apoptotic cell death, these results suggest that the effects on this enzyme may contribute to the neurotoxicity of 6-OHDA.

Glyceraldehyde-3-phosphate dehydrogenase from the newt Pleurodeles waltl. Protein purification and characterization of a GapC gene

The NAD(+)-dependent cytosolic glyceraldehyde-3-phosphate dehydrogenase (GAPDH, EC 1.2.1.12) has been purified to homogeneity from skeletal muscle of the newt Pleurodeles waltl (Amphibia, Urodela). The purification procedure including ammonium sulfate fractionation followed by Blue Sepharose CL-6B chromatography resulted in a 24-fold increase in specific activity and a final yield of approximately 46%. The native protein exhibited an apparent molecular weight of approximately 146 kDa with absolute specificity for NAD(+). Only one GAPDH isoform (pI 7.57) was obtained by chromatofocusing. The enzyme is an homotetrameric protein composed of identical subunits with an apparent molecular weight of approximately 37 kDa. Monospecific polyclonal antibodies raised in rabbits against the purified newt GAPDH immunostained a single 37-kDa GAPDH band in extracts from different tissues blotted onto nitrocellulose. A 510-bp cDNA fragment that corresponds to an internal region of a GapC gene was obtained by RT-PCR amplification using degenerate primers. The deduced amino acid sequence has been used to establish the phylogenetic relationships of the Pleurodeles enzyme--the first GAPDH from an amphibian of the Caudata group studied so far--with other GAPDHs of major vertebrate phyla.

Induction of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) expression in rat brain after focal ischemia/reperfusion

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH), a glycolytic enzyme, has been recently identified to be involved in the initiation of neuronal apoptosis. To investigate the serial changes and cellular localization of GAPDH expression, and its role in ischemia/reperfusion-induced neuronal apoptosis, the authors analyzed immunohistochemically brain areas of rats subjected to middle cerebral artery occlusion (MCAO) and reperfusion. Nuclear overexpression of GAPDH was noted in the ischemic core area after 2 hours of MCAO without reperfusion. During the subsequent reperfusion, nuclear accumulation of GAPDH in this area decreased in a time-dependent manner. However, cytoplasmic and nuclear GAPDH immunoreactivity was detected in neurons of the penumbra area of the parietal cortex, in rats subjected to 2-hour MCAO followed by 3-hour reperfusion. The increase of nuclear GAPDH immunoreactivity was persistently noted up to 48 hours of reperfusion, whereas cytoplasmic immunoreactivity correlated inversely with the duration of reperfusion. Moreover, double staining revealed colocalization of nuclear GAPDH and TUNEL in the penumbra area. The authors' study demonstrated that overexpression of GAPDH and nuclear translocation occurred in both the ischemic core and penumbra area soon after focal ischemia. These processes could be viewed as an early marker of ischemia/reperfusion-induced apoptotic neuronal death. The results suggest that GAPDH may play a critical role in the progression and spread of ischemic neuronal damage.

Altered levels of growth-related and novel gene transcripts in reproductive and other tissues of female mice overexpressing spermidine/spermine N1-acetyltransferase (SSAT)

Overexpression of SSAT (polyamine catabolic enzyme) in female mice results in impaired ovarian folliculogenesis and uterine hypoplasia. To identify the molecular basis for this, the gene expression profiles in uterus and ovary and for comparison, liver and kidney, from non-transgenic (NT) and SSAT transgenic (ST) mice were compared. The mRNA abundance for lipoprotein lipase and glyceraldehyde-3-phosphate dehydrogenase was elevated in all four ST (>NT) tissues. The translation initiation factor-3 subunit 5 mRNA, and transcripts related to endogenous murine leukemia provirus (MLV-related) and murine retrovirus-related sequences (MuRRS) were decreased in ST tissues. A novel calmodulin-related mRNA was strongly induced in ST liver and kidney. SSAT overexpression was associated with increased levels of IGF-binding protein-2 (IGFBP-2) in the uterus and ovary, and a reduction in IGFBP-3 mRNA levels in the uterus. Exogenous spermidine and spermine elevated endogenous IGFBP-2 and SSAT mRNA abundance, whereas, putrescine stimulated IGFBP-2 mRNA abundance and transfected IGFBP-2 gene promoter activity in human (Hec-1-A) uterine cells. Sp1 and BTEB1 mRNAs that encode transcription factors for the IGFBP-2 gene also were induced in some ST tissues. The data suggest that SSAT and polyamines are important for the control of molecular pathways underlying reproductive tract tissue growth, phenotype, and function.

Identification of a rice RNA- and microtubule-binding protein as the multifunctional protein, a peroxisomal enzyme involved in the beta -oxidation of fatty acids

The control of subcellular mRNA localization and translation is often mediated by protein factors that are directly or indirectly associated with the cytoskeleton. We report the identification and characterization of a rice seed protein that possesses both RNA and microtubule binding activities. In vitro UV cross-linking assays indicated that this protein binds to all mRNA sequences tested, although there was evidence for preferential binding to RNAs that contained A-C nucleotide sequence motifs. The protein was purified to homogeneity using a two-step procedure, and amino acid sequencing identified it as the multifunctional protein (MFP), a peroxisomal enzyme known to possess a number of activities involved in the beta-oxidation of fatty acids. The recombinant version of this rice MFP binds to RNA in UV cross-linking and gel mobility shift experiments, co-sediments specifically with microtubules, and possesses at least two enzymatic activities involved in peroxisomal fatty acid beta-oxidation. Taken together these data suggest that MFP has an important role in mRNA physiology in the cytoplasm, perhaps in regulating the localization or translation of mRNAs through an interaction with microtubules, in addition to its peroxisomal function.

HSP90, HSP70, and GAPDH directly interact with the cytoplasmic domain of macrophage scavenger receptors

The macrophage scavenger receptor (MSR) is a trimeric membrane protein which binds to modified low-density lipoprotein (LDL) and has been indicated in the development of atherosclerosis. It has recently been demonstrated that the N-terminal cytoplasmic domain of MSR has an important role in the efficient internalization and cell-surface expression of the receptor. This study shows that the N-terminal cytoplasmic domain in bovine was constructed using a peptide architecture technique in which the peptide chain was bundled at their C-terminus to yield a trimeric form and that this did not form an ordered structure. Furthermore, the binding proteins to the cytoplasmic domain of MSR were determined for the first time using a peptide affinity column. Sequence analyses of the specific binding proteins in bovine revealed that heat shock protein 90 (HSP90), heat shock protein 70 (HSP70), leucine aminopeptidase (LAP), adenocylhomocysteinase, and glyceraldehyde 3-phosphate dehydrogenase (GAPDH) were included. GST-pull-down assay and immunoprecipitation analyses on HSP90, HSP70, and GAPDH showed that all these proteins could bind to the cytoplasmic domain of MSR in vitro and in vivo. These proteins interact with the cytoplasmic domain directly and may have an effect on the functions of MSR such as internalization, cell-surface expression, and signal transduction.

Identification of tissue transglutaminase-reactive lysine residues in glyceraldehyde-3-phosphate dehydrogenase

Polyglutamine domains are excellent substrates for tissue transglutaminase resulting in the formation of cross-links with polypeptides containing lysyl residues. This finding suggests that tissue transglutaminase may play a role in the pathology of neurodegenerative diseases associated with polyglutamine expansion. The glycolytic enzyme GAPDH previously was shown to tightly bind several proteins involved in such diseases. The present study confirms that GAPDH is an in vitro lysyl donor substrate of tissue transglutaminase. A dansylated glutamine-containing peptide was used as probe for labeling the amino-donor sites. SDS gel electrophoresis of a time-course reaction mixture revealed the presence of both fluorescent GAPDH monomers and high molecular weight polymers. Western blot analysis performed using antitransglutaminase antibodies reveals that tissue transglutaminase takes part in the formation of heteropolymers. The reactive amino-donor sites were identified using mass spectrometry. Here, we report that of the 26 lysines present in GAPDH, K191, K268, and K331 were the only amino-donor residues modified by tissue transglutaminase.

Oxygen-dependent regulation of in vivo replication of simian virus 40 DNA is modulated by glucose

Simian virus 40 (SV40)-infected CV1 cells exposed to hypoxia show an inhibition of viral replication. Reoxygenation after several hours of hypoxia results in new initiations followed by a nearly synchronous round of SV40 replication. In this communication, we examined the effect of glucose on inhibition of viral DNA replication under hypoxia. We found that glucose stimulated SV40 DNA replication under hypoxia in two different ways. First, the rate of DNA synthesis, i.e. the fork propagation rate, increased. This effect seemed to be mediated by inhibition of mitochondrial respiration by glucose (Crabtree effect). Inhibition of mitochondrial respiration probably resulted in a higher intracellular oxygen concentration and an activation of oxygen-dependent ribonucleotide reductase, which provides the precursors for DNA synthesis. This glucose effect was consequently strongly dependent on the strength of hypoxia and the extent of intracellular respiration; hypoxic gassing with 10 ppm instead of 200-400 ppm O(2) or treatment of hypoxic cells with a mitochondrial uncoupler (carbonyl cyanide m-chlorophenylhydrazone) reduced the glucose effect on replication, whereas antimycin A, an inhibitor of respiration, increased it. The second effect of glucose concerned initiation, i.e. stimulation of unwinding of the viral origin. This effect was not influenced by the strength of hypoxia or the extent of cellular respiration and seemed, therefore, not to be mediated through a Crabtree effect. No evidence for a direct correlation between the cellular ATP concentration and the extent of SV40 replication under hypoxia was found. The effect of glucose on replication under hypoxia was not restricted to SV40-infected CV1 cells but was also detectable in HeLa cells. This suggests it to be a mechanism of more general validity.

GAPDH gene diversity in spirochetes: a paradigm for genetic promiscuity

In this study we have determined gap sequences from nine different spirochetes. Phylogenetic analyses of these sequences in the context of all other available eubacterial and a selection of eukaryotic Gap sequences demonstrated that the eubacterial glyceraldehyde-3-phosphate dehydrogenase (GAPDH) gene diversity encompasses at least five highly distinct gene families. Within these gene families, spirochetes show an extreme degree of sequence divergence that is probably the result of several lateral gene transfer events between spirochetes and other eubacterial phyla, and early gene duplications in the eubacterial ancestor. A Gap1 sequence from the syphilis spirochete Treponema pallidum has recently been shown to be closely related to GapC sequences from Euglenozoa. Here we demonstrate that several other spirochetal species are part of this cluster, supporting the conclusion that an interkingdom gene transfer from spirochetes to Euglenozoa must have occurred. Furthermore, we provide evidence that the GAPDH genes present in the protists Parabasalia may also be of spirochetal descent.

The Candida albicans cell wall-associated glyceraldehyde-3-phosphate dehydrogenase activity increases in response to starvation and temperature upshift

We have determined the effect of environmental factors (mild thermal upshift and starvation) on the Candida albicans cell wall-associated glyceraldehyde-3-phosphate dehydrogenase (cwGAPDH) activity. Temperature upshift (from 28 to 37 degrees C) and/ or starvation (at 28 or 37 degrees C in water) of exponentially growing yeast cells caused an increase in cwGAPDH activity (3 to 5-, and 7 to 8-fold, respectively). This increase in activity did not correlate with an increase in the amount of cwGAPDH protein present, as determined by flow cytometry, immunoelectron microscopy and Western-blotting. These results indicate that thermal upshift and starvation cause an activation of the cwGAPDH in C. albicans cells.

Characterizations of highly expressed genes of four fast-growing bacteria

Predicted highly expressed (PHX) genes are characterized for the completely sequenced genomes of the four fast-growing bacteria Escherichia coli, Haemophilus influenzae, Vibrio cholerae, and Bacillus subtilis. Our approach to ascertaining gene expression levels relates to codon usage differences among certain gene classes: the collection of all genes (average gene), the ensemble of ribosomal protein genes, major translation/transcription processing factors, and genes for polypeptides of chaperone/degradation complexes. A gene is predicted highly expressed (PHX) if its codon frequencies are close to those of the ribosomal proteins, major translation/transcription processing factor, and chaperone/degradation standards but strongly deviant from the average gene codon frequencies. PHX genes identified by their codon usage frequencies among prokaryotic genomes commonly include those for ribosomal proteins, major transcription/translation processing factors (several occurring in multiple copies), and major chaperone/degradation proteins. Also PHX genes generally include those encoding enzymes of essential energy metabolism pathways of glycolysis, pyruvate oxidation, and respiration (aerobic and anaerobic), genes of fatty acid biosynthesis, and the principal genes of amino acid and nucleotide biosyntheses. Gene classes generally not PHX include most repair protein genes, virtually all vitamin biosynthesis genes, genes of two-component sensor systems, most regulatory genes, and most genes expressed in stationary phase or during starvation. Members of the set of PHX aminoacyl-tRNA synthetase genes contrast sharply between genomes. There are also subtle differences among the PHX energy metabolism genes between E. coli and B. subtilis, particularly with respect to genes of the tricarboxylic acid cycle. The good agreement of PHX genes of E. coli and B. subtilis with high protein abundances, as assessed by two-dimensional gel determination, is verified. Relationships of PHX genes with stoichiometry, multifunctionality, and operon structures are also examined. The spatial distribution of PHX genes within each genome reveals clusters and significantly long regions without PHX genes.

Damage to nuclear DNA in Lewy body disease

To assess the significance of damaged nuclear DNA in autopsy brain tissue in Lewy body disease (LBD), we examined the patterns of expression of two DNA repair enzymes (PARP and DNA-PKCS), TUNEL and caspase-3 activation, in sections of midbrain and frontal cortex from nine patients with LBD who had not received L-DOPA, and from five neurologically normal controls. In LBD but not controls, many neurons and glia in the midbrain had translocated DNA-PKCS and PARP from the cytoplasm into the nucleus, particularly in the substantia nigra. LBD midbrains contained sparse TUNEL-positive neurons. Caspase-3 activity was largely restricted to microglia but was detected in an occasional nigral neuron. Nuclear DNA damage occurs in vivo in LBD but only rarely indicates neuronal apoptosis.

GAPDH knockdown rescues mesencephalic dopaminergic neurons from MPP+ -induced apoptosis

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH; EC 1.2.1.12) has a number of diverse functions apart from glycolytic function. We explored the possible involvement of GAPDH in 1-methyl-4-phenylpyridinium (MPP+)-induced death of mesencephalic dopaminergic neurons (MDNs) in culture. MPP+ (10 and 20 microM, 24 h) exposure selectively decreased the survival of tyrosine hydroxylase positive (TH+) MDNs, which manifested apoptotic features including shrinkage of the cell body, chromatin condensation and nuclear fragmentation. Two types of GAPDH antisense oligonucleotides almost completely rescued MDNs from MPP+ toxicity. GAPDH was strongly expressed in apoptotic TH+ neurons, and MPP+ exposure significantly increased the percentage of TH+ neurons in which GAPDH is over-expressed. Confocal microscopic analysis demonstrated the nuclear accumulation of GAPDH in neurons undergoing MPP+-induced apoptosis. These results suggest that MPP+ causes apoptosis of MDNs, concomitant with the over-expression and nuclear accumulation of GAPDH.

Reversible nuclear translocation of glyceraldehyde-3-phosphate dehydrogenase upon serum depletion

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH; E.C. 1.2.1.12) functions as a glycolytic enzyme within the cytoplasm, but beside its metabolic function it is involved in early steps of apoptosis, which trigger the translocation of GAPDH into the nucleus. As apoptosis can be induced by serum withdrawal, which otherwise causes cell cycle arrest, the linkage between serum deprivation, cell cycle and nuclear transport of GAPDH has been investigated. The intracellular distribution of GAPDH was monitored by confocal laser scanning microscopy of either immuno-stained NIH 3T3 fibroblasts or of cells overexpressing GFP-tagged GAPDH. Serum withdrawal led to an accumulation of GAPDH in the nucleus. In contrast to investigations published so far, this nuclear translocation was a reversible process: cytoplasmic location of endogenous GAPDH or of GFP-GAPDH could be recovered upon serum addition to arrested cells and was not inhibited by cycloheximide treatment. In addition, the nuclear import upon serum depletion had no influence neither on the catalytic activity nor on the expression level of GAPDH. The nuclear export of GFP-GAPDH in serum-deprived cells could be stimulated by serum or directly by the growth factors EGF or PDGE The transport process is not regulated via an initiation of cell cycle arrest, as olomoucine, which causes G1-arrest neither stimulated nuclear accumulation nor prevented nuclear export after serum addition to serum-depleted cultures. Moreover, SV40-transformed 3T3 cells transported GAPDH into the nucleus upon serum deprivation, though the expression of the viral large T-antigen enabled growth factor-independent cell proliferation in this cell line. The recruitment of GAPDH to the cytoplasm upon serum stimulation of arrested cells was not impaired by the inhibition of the MAPK signalling pathway with PD 098059. However, further analysis of the growth factor signalling pathway with specific inhibitors revealed that nuclear export was prevented by LY 294002, an inhibitor of the PI-3 kinase. PI3K links the growth factor signalling pathway with cell death via the repression of an apoptotic inducer. Thus, the nuclear accumulation of GAPDH upon growth factor depletion is a reversible process not related directly to cell cycle and likely triggered by survival signals.

Complexities in the neurotoxic actions of 6-hydroxydopamine in relation to the cytoprotective properties of taurine

The neurotoxin 6-hydroxydopamine was shown to cause an imbalance between the direct and indirect pathways of the striato-nigral system as evidenced by a decreased release of gamma-aminobutyric acid and taurine in the substantia nigra but not in the globus pallidus following neostriatal stimulation with kainate (100 microM). The neurotoxicity of 6-hydroxydopamine is generally believed to result from reactive-oxygen radical formation, although it is also known to inhibit mitochondrial NADH dehydrogenase. The release of Fe(II) from the unactivated form [3Fe(III)-4S] of cytoplasmic aconitase (EC(50) < 8 microM) was shown to be followed by the slower oxidation of thiol groups in the protein. Complete loss of -SH groups, and enzyme activity, was seen after incubation of glyceraldenyde-3-phosphate dehydrogenase with 200 microM 6-hydroxydopamine for 75 min at 37 degrees C (IC(50) = 70.8 +/- 0.3 microM). Thus the cellular effects of 6-hydroxydopamine are complex, involving impairment of mitochondrial function, iron- release, sulphydryl-group oxidation, and enzyme inhibition in addition to direct generation of reactive oxygen radicals. Taurine, which is known to be neuroprotective in some other systems, only affords protection against some of these effects, thereby explaining its reported ineffectiveness against 6-hydroxydopamine toxicity.

Enzymology, structure, and dynamics of acetohydroxy acid isomeroreductase

Acetohydroxy acid isomeroreductase is a key enzyme involved in the biosynthetic pathway of the amino acids isoleucine, valine, and leucine. This enzyme is of great interest in agrochemical research because it is present only in plants and microorganisms, making it a potential target for specific herbicides and fungicides. Moreover, it catalyzes an unusual two-step reaction that is of great fundamental interest. With a view to characterizing both the mechanism of inhibition by potential herbicides and the complex reaction mechanism, various techniques of enzymology, molecular biology, mass spectrometry, X-ray crystallography, and theoretical simulation have been used. The results and conclusions of these studies are described briefly in this paper.

Glyceraldehyde-3-phosphate dehydrogenase in neurodegeneration and apoptosis signaling

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a well-studied glycolytic enzyme that plays a key role in energy metabolism. GAPDH catalyzes the conversion of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate in the glycolytic pathway. As part of the conversion, GAPDH converts NAD+ to the high-energy electron carrier NADH. GAPDH has been referred to as a "housekeeping" protein and based on the view that GAPDH gene expression remains constant under changing cellular conditions, the levels of GAPDH mRNA have frequently been used to normalize northern blots. In recent years, that view has changed since GAPDH is now known to contribute to a number of diverse cellular functions unrelated to glycolysis. Normative functions of GAPDH now include nuclear RNA export, DNA replication, DNA repair, exocytotic membrane fusion, cytoskeletal organization and phosphotransferase activity. Pathologically, GAPDH has been implicated in apoptosis, neurodegenerative disease, prostate cancer and viral pathogenesis (see Sirover (1999) for a recent review of GAPDH functions). Most recently, it has been shown that GAPDH is a target for deprenyl related compounds (Carlile et al., 2000; Kragten et al., 1998) and may contribute to the neuroprotection offered by those compounds.

Glyceraldehyde-3-phosphate dehydrogenase is responsible for intranuclear localization of some oligonucleotides

Nuclear accumulation of ODNs has been associated with their binding to a series of nuclear proteins. These interactions could be responsible for the sequence-independent effects of ODNs as well as for their sequence-specific interactions and their intracellular distribution. Investigation of interaction of ODNs with these proteins may shed light on the mechanisms of cellular uptake and nuclear accumulation of oligonucleotides.

Nitric-oxide-induced inhibition of glyceraldehyde-3-phosphate dehydrogenase may mediate reduced endothelial cell monolayer integrity in an in vitro model blood-brain barrier

The process of nitric-oxide (NO)-induced cellular toxicity may involve energy deprivation since the radical is reported to prevent both mitochondrial oxidative phosphorylation and glycolysis. In order to determine whether these processes are important in NO-induced blood-brain barrier (BBB) dysfunction, we used a cell culture model of the BBB and compared the effects of gaseous NO, potassium cyanide (KCN, a mitochondrial respiratory chain inhibitor) and iodoacetate [IA, an inhibitor of the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH)] on endothelial cell ATP content, GAPDH activity and barrier integrity. NO lead to a rapid breakdown in model barrier integrity and resulted in a reduction in endothelial cell ATP content and GAPDH activity. KCN had no effect on endothelial cell ATP content or barrier integrity, while IA, at a concentration that completely blocked endothelial cell GAPDH activity, resulted in a rapid decline in ATP content but did not lead to a decline in barrier integrity until at least 2 h of exposure. These results indicate that inhibition of endothelial cell GAPDH activity rather than mitochondrial respiration causes an energy deficiency and delayed barrier dysfunction. However, the rapid detrimental effects of gaseous NO on barrier integrity cannot be fully explained by endothelial cell energy depletion and may be related to the actions of the free radical and its products on cellular lipids.

A novel alcohol oxidase/RNA-binding protein with affinity for mycovirus double-stranded RNA from the filamentous fungus Helminthosporium (Cochliobolus) victoriae: molecular and functional characterization

We have cloned and sequenced a novel alcohol oxidase (Hv-p68) from the filamentous fungus Helminthosporium (Cochliobolus) victoriae that copurifies with mycoviral double-stranded RNAs. Sequence analysis revealed that Hv-p68 belongs to the large family of FAD-dependent glucose methanol choline oxidoreductases and that it shares significant sequence identity (>67%) with the alcohol oxidases of the methylotrophic yeasts. Unlike the intronless alcohol oxidases from methylotrophic yeasts, a genomic fragment of the Hv-p68 gene was found to contain four introns. Hv-p68, purified from fungal extracts, showed only limited methanol oxidizing activity, and its expression was not induced in cultures supplemented with methanol as the sole carbon source. Northern hybridization analysis indicated that overexpression of Hv-p68 is associated with virus infection, because significantly higher Hv-p68 mRNA levels (10- to 20-fold) were detected in virus-infected isolates compared with virus-free ones. We confirmed by Northwestern blot analysis that Hv-p68 exhibits RNA binding activity and demonstrated that the RNA-binding domain is localized within the N-terminal region that contains a typical ADP-binding beta-alpha-beta fold motif. The Hv-p68 gene, or closely similar genes, was present in all species of the genus Cochliobolus but absent in the filamentous fungus, Penicillium chrysogenum, as well as in two nonmethylotrophic yeasts examined. This study represents the first reported case that a member of the FAD-dependent glucose methanol choline oxidoreductase family, Hv-p68, may function as an RNA-binding protein.

The glyceraldehyde-3-phosphate dehydrogenase polypeptides encoded by the Saccharomyces cerevisiae TDH1, TDH2 and TDH3 genes are also cell wall proteins

The authors show that the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) of Saccharomyces cerevisiae, previously thought to be restricted to the cell interior, is also present in the cell wall. GAPDH activity, proportional to cell number and time of incubation, was detected in intact wild-type yeast cells. Intact cells of yeast strains containing insertion mutations in each of the three structural TDH genes (tdh1, tdh2 and tdh3) and double mutants (tdh1 tdh2 and tdh1 tdh3) also displayed a cell-wall-associated GAPDH activity, in the range of parental wild-type cells, although with significant differences among strains. A cell wall location of GAPDH was further confirmed in wild-type and tdh mutants by indirect immunofluorescence and flow cytometry analysis with a polyclonal antibody against S. cerevisiae GAPDH. By immunoelectron microscopy, the GAPDH protein was detected at the outer surface of the cell wall of wild-type cells, as well as in the cytoplasm. Western immunoblot analysis of cell wall extracts and cytosol showed that Tdh2 and Tdh3 polypeptides are present in the cell wall, as well as in the cytosol, of exponentially growing cells. Tdh1 is only detected in stationary-phase cells, again in both cytosol and cell wall extracts. The results incorporate the GAPDH of S. cerevisiae, encoded by TDH1-3, into the newly emerging family of multifunctional cell-wall-associated GAPDHs which retain their catalytic activity.

A novel protein complex distinct from mismatch repair binds thioguanylated DNA

To elucidate molecular mechanism(s) of cellular response to mercaptopurine, a widely used antileukemic agent, we assessed mercaptopurine (MP) sensitivity in mismatch repair (MMR) proficient and MMR deficient human acute lymphoblastic leukemia (ALL) cells. Sensitivity to thiopurine cytotoxicity was not dependent on MMR (i.e., MutSalpha) competence among six cell lines tested. Using electrophoretic mobility shift assay analysis, we found that the incubation of nuclear extracts from ALL cells with synthetic 34-mer DNA duplexes containing deoxythioguanosine (G(S)) within either G(S).T or G(S).C pairs, resulted in formation of a DNA-protein complex distinct from the DNA-MutSalpha complex and unaffected by ATP. Isolation and sequence analysis of proteins involved in this DNA-protein complex identified glyceraldehyde 3-phosphate dehydrogenase (GAPDH) as a component. Western blot analysis of nuclear extracts from a panel of human lymphoblastic leukemia cell lines revealed markedly different basal levels of GAPDH in nuclei, which was significantly related to thiopurine sensitivity (p = 0.001). Confocal analysis revealed markedly different intracellular distribution of GAPDH between nucleus and cytosol in six human ALL cell lines. Redistribution of GAPDH from cytosol to nucleus was evident after MP treatment. These findings indicate that a new DNA-protein complex containing GAPDH and distinct from known MMR protein-DNA complexes binds directly to thioguanylated DNA, suggesting that this may act as a sensor of structural alterations in DNA and serve as an interface between these DNA modifications and apoptosis.

Glyceraldehyde-3-phosphate dehydrogenase is required for vesicular transport in the early secretory pathway

Protein transport in the early secretory pathway requires Rab2 GTPase. This protein promotes the recruitment of soluble components that participate in protein sorting and recycling from pre-Golgi intermediates (vesicular tubular clusters (VTCs)). We previously reported that a constitutively activated form of Rab2 (Q65L) as well as Rab2 wild type promoted vesicle formation from VTCs. These vesicles contained Rab2, beta-COP, p53/gp58, and protein kinase Ciota/lambda but lacked anterograde-directed cargo. To identify other candidate Rab2 effectors, the polypeptide composition of the vesicles was further analyzed. We found that vesicles released in response to Rab2 also contained the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH). To study the relationship of this enzyme to Rab2 function, we performed a quantitative binding assay to measure recruitment of GAPDH to membrane when incubated with Rab2. Rab2-treated microsomes showed a 5-10-fold increase in the level of membrane-associated GAPDH. We generated an affinity-purified anti-GAPDH polyclonal to study the biochemical role of GAPDH in the early secretory pathway. The antibody arrests transport of a reporter molecule in an assay that reconstitutes ER to Golgi traffic. Furthermore, the affinity-purified antibody blocked the ability of Rab2 to recruit GAPDH to membrane. However, the antibody did not interfere with Rab2 stimulated vesicle release. These data suggest that GAPDH is required for ER to Golgi transport. We propose that membranes incubated with anti-GAPDH and Rab2 form "dead end" vesicles that are unable to transport and fuse with the acceptor compartment.

The Rossmann fold of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a nuclear docking site for antisense oligonucleotides containing a TAAAT motif

The subcellular localisation of oligodeoxynucleotides (ODN) is a major limitation for their use against nuclear targets. In this study we demonstrate that an antisense ODN directed against cytosolic phospholipase A(2) (cPLA2) mRNA is efficiently taken up and accumulates in the nuclei of endothelial cells (HUVEC), human monocytes and HeLa cells. Gel shift experiments and incubation of cells with oligonucleotide derivatives show that the anti-cPLA2 oligo binds a 37 kDa protein in nuclear extracts. The TAAAT sequence was identified as the major binding motif for the nuclear protein in competition experiments with mutated ODNs. Modification of the AAA triplet resulted in an ODN which failed to localise in the nucleus. Moreover, inserting a TAAAT motif into an ODN localising in the cytosol did not modify its localisation. The 37 kDa protein was purified and identified after peptide sequencing as glyceraldehyde-3-phosphate dehydrogenase (GAPDH). It was shown by confocal microscopy that GAPDH co-localises with anti-cPLA2 ODN in the nucleus and commercial GAPDH effectively binds the oligo. Competition experiments with increasing concentration of NAD(+) co-factor indicate that the GAPDH Rossmann fold is a docking site for antisense oligonucleotides containing a TAAAT motif.

Reduction of glyceraldehyde-3-phosphate dehydrogenase activity in Alzheimer's disease and in Huntington's disease fibroblasts

New functions have been identified for glyceraldehyde-3-phosphate dehydrogenase (GAPDH) including its role in neurodegenerative disease and in apoptosis. GAPDH binds specifically to proteins implicated in the pathogenesis of a variety of neurodegenerative disorders including the beta-amyloid precursor protein and the huntingtin protein. However, the pathophysiological significance of such interactions is unknown. In accordance with published data, our initial results indicated there was no measurable difference in GAPDH glycolytic activity in crude whole-cell sonicates of Alzheimer's and Huntington's disease fibroblasts. However, subcellular-specific GAPDH-protein interactions resulting in diminution of GAPDH glycolytic activity may be disrupted or masked in whole-cell preparations. For that reason, we examined GAPDH glycolytic activity as well as GAPDH-protein distribution as a function of its subcellular localization in 12 separate cell strains. We now report evidence of an impairment of GAPDH glycolytic function in Alzheimer's and Huntington's disease subcellular fractions despite unchanged gene expression. In the postnuclear fraction, GAPDH was 27% less glycolytically active in Alzheimer's cells as compared with age-matched controls. In the nuclear fraction, deficits of 27% and 33% in GAPDH function were observed in Alzheimer's and Huntington's disease, respectively. This evidence supports a functional role for GAPDH in neurodegenerative diseases. The possibility is considered that GAPDH:neuronal protein interaction may affect its functional diversity including energy production and as well as its role in apoptosis.

pH-regulated secretion of a glyceraldehyde-3-phosphate dehydrogenase from Streptococcus gordonii FSS2: purification, characterization, and cloning of the gene encoding this enzyme

Streptococcus gordonii and other viridans streptococci (VS) are primary etiologic agents of infective endocarditis, despite being part of the normal oral microflora. Recently, a surface-bound glyceraldehyde-3-phosphate dehydrogenase (GAPDH) has been found on the cells of all tested streptococcal species, where it has been implicated as a virulence factor. In contrast, we observed that a soluble extracellular GAPDH was the major secreted protein from S. gordonii FSS2, an endocarditis strain. The biochemical properties and gene sequence of S. gordonii GAPDH are almost identical to those of other streptococcal GAPDHs. Growth at defined pHs showed that secretion of GAPDH is regulated by environmental pH. GAPDH was primarily surface-associated at growth pH 6.5 and shifted to > 90% secreted at growth pH 7.5. Others have identified S. gordonii promoters that are up-regulated by a pH shift similar to that experienced by organisms entering the blood stream (neutral) from the oral cavity (slightly acid). Analysis of our results suggests that secretion of GAPDH may be a similar adaptation by S. gordonii.

Involvement of T-complex protein-1delta in dopamine triggered apoptosis in chick embryo sympathetic neurons

The neurotransmitter dopamine (DA) is capable of inducing apoptosis in post-mitotic sympathetic neurons via its oxidative metabolites. The differential display method was applied to cultured sympathetic neurons in an effort to detect genes whose expression is transcriptionally regulated during the early stages of DA-triggered apoptosis. One of the up-regulated genes was identified as the chick homologue to T-complex polypeptide-1delta (TCP-1delta), a member of the molecular chaperone family of proteins. Each chaperone protein is a complex of seven to nine different subunits. A full-length clone of 1.9 kilobases was isolated containing an open reading frame of 536 amino acids with a predicted molecular weight of 57,736. Comparison with the mouse TCP-1delta revealed 78 and 91% homology on the DNA and protein levels, respectively. Northern blot analysis disclosed a steady and significant increase in mRNA levels of TCP-1delta after DA administration, reaching a peak between 4 and 9 h and declining thereafter. Induction of the TCP-1delta protein levels was also observed as a function of DA treatment. Overexpression of TCP-1delta in sympathetic neurons accelerated DA-induced apoptosis; inhibition of TCP-1delta expression in these neurons using antisense technology significantly reduced DA-induced neuronal death. These findings suggest a functional role for TCP-1delta as a positive mediator of DA-induced neuronal apoptosis.