Association of glyceraldehyde-3-phosphate dehydrogenase with mono- and polyribosomes of rabbit reticulocytes

The mutual interaction of glycolytic enzymes and RNA in post-transcriptional regulation

About three decades ago, researchers suggested that metabolic enzymes participate in cellular processes that are unrelated to their catalytic activity, and the term "moonlighting functions" was proposed. Recently developed advanced technologies in the field of RNA interactome capture now unveil the unexpected RNA binding activity of many metabolic enzymes, as exemplified here for the enzymes of glycolysis. Although for most of these proteins a precise binding mechanism, binding conditions, and physiological relevance of the binding events still await in-depth clarification, several well explored examples demonstrate that metabolic enzymes hold crucial functions in post-transcriptional regulation of protein synthesis. This widely conserved RNA-binding function of glycolytic enzymes plays major roles in controlling cell activities. The best explored examples are glyceraldehyde 3-phosphate dehydrogenase, enolase, phosphoglycerate kinase, and pyruvate kinase. This review summarizes current knowledge about the RNA-binding activity of the ten core enzymes of glycolysis in plant, yeast, and animal cells, its regulation and physiological relevance. Apparently, a tight bidirectional regulation connects core metabolism and RNA biology, forcing us to rethink long established functional singularities.

Glycation of glyceraldehyde-3-phosphate dehydrogenase inhibits the binding with α-synuclein and RNA

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) shows great diversity of functions, interaction partners and post-translational modifications. GAPDH undergoes glycation of positively charged residues in diabetic patient's tissues and therefore may change interaction with partners. The influence of GAPDH glycation on interaction with two important partners, α-synuclein and RNA, has been investigated in silico using molecular dynamics simulations and in vitro using surface plasmon resonance measurements. Since positively charged groove including substrate- and NAD⁺-binding sites is proposed as potential binding site for α-synuclein and RNA, GAPDH was glycated on residues in grooves and randomly distributed over the whole surface. Lysine residues were replaced with negatively charged carboxymethyl lysine as a widespread advanced glycation end product. As results, GAPDH glycation suppressed the interaction with α-synuclein and RNA. Although the modified GAPDH residues participated in binding with α-synuclein, no stable binding site with both glycated forms was observed. Glycation along the whole GAPDH surface completely suppressed interaction with RNA, whereas the alternative possible RNA binding site was identified in case of groove glycation. The findings were supported by direct measurement of the binding affinity. The obtained results clarify effect of glycation on GAPDH interaction with α-synuclein and RNA and elucidate a possible mechanism of interplay between glycation occurred in diabetes and neurodegenerative diseases, which GAPDH and α-synuclein are involved in.

Influence of Oxidative Stress on Catalytic and Non-glycolytic Functions of Glyceraldehyde-3-phosphate Dehydrogenase

BACKGROUND

Glyceraldehyde-3-phosphate Dehydrogenase (GAPDH) is a unique enzyme that, besides its main function in glycolysis (catalysis of glyceraldehyde-3-phosphate oxidation), possesses a number of non-glycolytic activities. The present review summarizes information on the role of oxidative stress in the regulation of the enzymatic activity as well as non-glycolytic functions of GAPDH.

METHODS

Based on the analysis of literature data and the results obtained in our research group, mechanisms of the regulation of GAPDH functions through the oxidation of the sulfhydryl groups in the active site of the enzyme have been suggested.

RESULTS

Mechanism of GAPDH oxidation includes consecutive oxidation of the catalytic Cysteine (Cys150) into sulfenic, sulfinic, and sulfonic acid derivatives, resulting in the complete inactivation of the enzyme. The cysteine sulfenic acid reacts with reduced glutathione (GSH) to form a mixed disulfide (S-glutathionylated GAPDH) that further reacts with Cys154 yielding the disulfide bond in the active site of the enzyme. In contrast to the sulfinic and sulfonic acids, the mixed disulfide and the intramolecular disulfide bond are reversible oxidation products that can be reduced in the presence of GSH or thioredoxin.

CONCLUSION

Oxidation of sulfhydryl groups in the active site of GAPDH is unavoidable due to the enhanced reactivity of Cys150. The irreversible oxidation of Cys150 is prevented by Sglutathionylation and disulfide bonding with Cys154. The oxidation/reduction of the sulfhydryl groups in the active site of GAPDH can be used for regulation of glycolysis and numerous side activities of this enzyme including the induction of apoptosis.

Role of Glyceraldehyde-3-Phosphate Dehydrogenase (GAPDH) in DNA Repair

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is widely known as a glycolytic enzyme. Nevertheless, various functions of GAPDH have been found that are unrelated to glycolysis. Some of these functions presume interaction of GAPDH with DNA, but the mechanism of its translocation to the nucleus is not fully understood. When in the nucleus, GAPDH participates in the initiation of apoptosis and transcription of genes involved in antiapoptotic pathways and cell proliferation and plays a role in the regulation of telomere length. Several authors have shown that GAPDH displays the uracil-DNA glycosylase activity and interacts with some types of DNA damages, such as apurinic/apyrimidinic sites, nucleotide analogs, and covalent DNA adducts with alkylating agents. Moreover, GAPDH can interact with proteins participating in DNA repair, such as APE1, PARP1, HMGB1, and HMGB2. In this review, the functions of GAPDH associated with DNA repair are discussed in detail.

Sperm-Specific Glyceraldehyde-3-Phosphate Dehydrogenase - An Evolutionary Acquisition of Mammals

This review is focused on the mammalian sperm-specific glyceraldehyde-3-phosphate dehydrogenase (GAPDS). GAPDS plays the major role in the production of energy required for sperm cell movement and does not perform non-glycolytic functions that are characteristic of the somatic isoenzyme of glyceraldehyde-3-phosphate dehydrogenase. The GAPDS sequence is composed of 408 amino acid residues and includes an additional N-terminal region of 72 a.a. that binds the protein to the sperm tail cytoskeleton. GAPDS is present only in the sperm cells of mammals and lizards, possibly providing them with certain evolutionary advantages in reproduction. In this review, studies concerning the problems of GAPDS isolation, its catalytic properties, and its structural features are described in detail. GAPDS is much more stable compared to the somatic isoenzyme, perhaps due to the necessity of maintaining the enzyme function in the absence of protein expression. The site-directed mutagenesis approach revealed the two GAPDS-specific proline residues, as well as three salt bridges, which seem to be the basis of the increased stability of this protein. As distinct from the somatic isoenzyme, GAPDS exhibits positive cooperativity in binding of the coenzyme NAD+. The key role in transduction of structural changes induced by NAD+ is played by the salt bridge D311-H124. Disruption of this salt bridge cancels GAPDS cooperativity and twofold increases its enzymatic activity instead. The expression of GAPDS was detected in some melanoma cells as well. Its role in the development of certain pathologies, such as cancer and neurodegenerative diseases, is discussed.

Metabolic Enzymes Enjoying New Partnerships as RNA-Binding Proteins

In the past century, few areas of biology advanced as much as our understanding of the pathways of intermediary metabolism. Initially considered unimportant in terms of gene regulation, crucial cellular fate changes, cell differentiation, or malignant transformation are now known to involve 'metabolic remodeling' with profound changes in the expression of many metabolic enzyme genes. This review focuses on the recent identification of RNA-binding activity of numerous metabolic enzymes. We discuss possible roles of this unexpected second activity in feedback gene regulation ('moonlighting') and/or in the control of enzymatic function. We also consider how metabolism-driven post-translational modifications could regulate enzyme-RNA interactions. Thus, RNA emerges as a new partner of metabolic enzymes with far-reaching possible consequences to be unraveled in the future.

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) interacts with apurinic/apyrimidinic sites in DNA

Apurinic/apyrimidinic (AP) sites are some of the most frequent DNA damages and the key intermediates of base excision repair. Certain proteins can interact with the deoxyribose of the AP site to form a Schiff base, which can be stabilized by NaBH4 treatment. Several types of DNA containing the AP site were used to trap proteins in human cell extracts by this method. In the case of single-stranded AP DNA and AP DNA duplex with both 5' and 3' dangling ends, the major crosslinking product had an apparent molecular mass of 45 kDa. Using peptide mass mapping based on mass spectrometry data, we identified the protein forming this adduct as an isoform of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) called "uracil-DNA glycosylase". GAPDH is a glycolytic enzyme with many additional putative functions, which include interaction with nucleic acids, different DNA damages and DNA repair enzymes. We investigated interaction of GAPDH purified from HeLa cells and rabbit muscles with different AP DNAs. In spite of the ability to form a Schiff-base intermediate with the deoxyribose of the AP site, GAPDH does not display the AP lyase activity. In addition, along with the borohydride-dependent adducts with AP DNAs containing single-stranded regions, GAPDH was also shown to form the stable borohydride-independent crosslinks with these AP DNAs. GAPDH was proven to crosslink preferentially to AP DNAs cleaved via the β-elimination mechanism (spontaneously or by AP lyases) as compared to DNAs containing the intact AP site. The level of GAPDH-AP DNA adduct formation depends on oxidation of the protein SH-groups; disulfide bond reduction in GAPDH leads to the loss of its ability to form the adducts with AP DNA. A possible role of formation of the stable adducts with AP sites by GAPDH is discussed.

Functional diversity

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

Lysozyme stimulates immunoglobulin production by human-human hybridoma and human peripheral blood lymphocytes

Lysozyme [EC 3.2.1.17] derived from hen egg white stimulated immunoglobulin production by human-human hybridoma, HB4C5 cells producing human lung cancer specific monoclonal IgM. IgM production by HB4C5 cells was enhanced more than 13-fold by the addition of lysozyme at 380 μg/ml in a serum-free medium. The immunoglobulin production stimulating effect of lysozyme was observed immediately after inoculation and maintained for 5 days. Lysozyme enhanced immunoglobulin production by the hybridoma line without growth promotion. This enzyme also accelerated IgM and IgG production of human peripheral blood lymphocytes 5.3-fold and 2.3-fold, respectively. These results suggest that lysozyme stimulates immunoglobuling production of not only specific hybridoma line, but also non-specific immunoglobulin producers. However, although the enzymatic activity of lysozyme was almost lost by heat-treatment at 100 °C for 30 min, the IPSF activity was retained. This fact suggests that IPSF activity of lysozyme does not come from its enzymatic activity or reaction products. All these findings clearly indicate that lysozyme has a novel function as an immunoglobulin production stimulating factor. GAPDH - glyceraldehyde-3-phosphate dehydrogenase; Ig - immunoglobulin; IPSF - immunoglobulin production stimulating factor; PBL - peripheral blood lymphocytes; HPLC - high-performance liquid chromatography.

Effects of DNA on immunoglobulin production stimulating activity of alcohol dehydrogenase

Alcohol dehydrogenase-I (ADH-I) derived from horse liver stimulated IgM production by human-human hybridoma, HB4C5 cells and lymphocytes. The IPSF activity of ADH-I was suppressed by coexistence of short DNA whose chain length is less than 200 base pairs (bp) and fibrous DNA in a dose-dependent manner. These DNA preparations completely inhibited the IPSF activity at the concentration of 250 mug/ml and 1.0 mg/ml, respectively. DNA sample termed long DNA whose average chain length is 400-7000 bp slightly stimulated IPSF activity at 0.06 mug/ml. However, long DNA suppressed IPSF activity by half at 1.0 mg/ml. The laser confocal microscopic analysis had revealed that ADH-I was incorporated by HB4C5 cells. The uptake of ADH-I was strongly inhibited by short DNA and fibrous DNA. However, long DNA did not suppress the internalization of ADH-I into HB4C5 cells. These findings indicate that short DNA and fibrous DNA depress IPSF activity of ADH-I by inhibiting the internalization of this enzyme. According to the gel-filtration analysis using HPLC, ADH-I did not directly interact with short DNA. It is expected from these findings that short DNA influences HB4C5 cells to suppress the internalization of ADH-I. Moreover, these facts also strongly suggest that ADH-I acts as IPSF after internalization into the cell.

Oxidative modifications of glyceraldehyde-3-phosphate dehydrogenase play a key role in its multiple cellular functions

Knowledge of the cellular targets of ROS (reactive oxygen species) and their regulation is an essential prerequisite for understanding ROS-mediated signalling. GAPDH (glyceraldehyde-3-phosphate dehydrogenase) is known as a major target protein in oxidative stresses and becomes thiolated in its active site. However, the molecular and functional changes of oxidized GAPDH, the inactive form, have not yet been characterized. To examine the modifications of GAPDH under oxidative stress, we separated the oxidation products by two-dimensional gel electrophoresis and identified them using nanoLC-ESI-q-TOF MS/MS (nano column liquid chromatography coupled to electrospray ionization quadrupole time-of-flight tandem MS). Intracellular GAPDH subjected to oxidative stress separated into multiple acidic spots on two-dimensional gel electrophoresis and were identified as cysteine disulfide and cysteic acids on Cys152 in the active site. We identified the interacting proteins of oxidized inactive GAPDH as p54nrb (54 kDa nuclear RNA-binding protein) and PSF (polypyrimidine tract-binding protein-associated splicing factor), both of which are known to exist as heterodimers and bind to RNA and DNA. Interaction between oxidized GAPDH and p54nrb was abolished upon expression of the GAPDH active site mutant C152S. The C-terminal of p54nrb binds to GAPDH in the cytosol in a manner dependent on the dose of hydrogen peroxide. The GAPDH–p54nrb complex enhances the intrinsic topoisomerase I activation by p54nrb–PSF binding. These results suggest that GAPDH exerts other functions beyond glycolysis, and that oxidatively modified GAPDH regulates its cellular functions by changing its interacting proteins, i.e. the RNA splicing by interacting with the p54nrb–PSF complex.

On the origin of life in the zinc world: 1. Photosynthesizing, porous edifices built of hydrothermally precipitated zinc sulfide as cradles of life on Earth

BACKGROUND

The complexity of the problem of the origin of life has spawned a large number of possible evolutionary scenarios. Their number, however, can be dramatically reduced by the simultaneous consideration of various bioenergetic, physical, and geological constraints.

RESULTS

This work puts forward an evolutionary scenario that satisfies the known constraints by proposing that life on Earth emerged, powered by UV-rich solar radiation, at photosynthetically active porous edifices made of precipitated zinc sulfide (ZnS) similar to those found around modern deep-sea hydrothermal vents. Under the high pressure of the primeval, carbon dioxide-dominated atmosphere ZnS could precipitate at the surface of the first continents, within reach of solar light. It is suggested that the ZnS surfaces (1) used the solar radiation to drive carbon dioxide reduction, yielding the building blocks for the first biopolymers, (2) served as templates for the synthesis of longer biopolymers from simpler building blocks, and (3) prevented the first biopolymers from photo-dissociation, by absorbing from them the excess radiation. In addition, the UV light may have favoured the selective enrichment of photostable, RNA-like polymers. Falsification tests of this hypothesis are described in the accompanying article (A.Y. Mulkidjanian, M.Y. Galperin, Biology Direct 2009, 4:27).

CONCLUSION

The suggested "Zn world" scenario identifies the geological conditions under which photosynthesizing ZnS edifices of hydrothermal origin could emerge and persist on primordial Earth, includes a mechanism of the transient storage and utilization of solar light for the production of diverse organic compounds, and identifies the driving forces and selective factors that could have promoted the transition from the first simple, photostable polymers to more complex living organisms.

Monocyte differentiation up-regulates the expression of the lysosomal sialidase, Neu1, and triggers its targeting to the plasma membrane via major histocompatibility complex class II-positive compartments

Human sialidase (neuraminidase) Neu1 catalyzes lysosomal catabolism of sialylated glycoconjugates. Here we show that during the differentiation of monocytes and the monocytic cell line, THP-1, into macrophages, the majority of Neu1 relocalizes from the lysosomes to the cell surface. In contrast to other cellular sialidases Neu2, Neu3, and Neu4, whose expression either remains unchanged or is down-regulated, Neu1 mRNA, protein and activity are specifically increased during the phorbol 12-myristate 13-acetate-induced differentiation, consistent with a significant induction of the transcriptional activity of the Neu1 gene promoter. The lysosomal carboxypeptidase, cathepsin A, which forms a complex with and activates Neu1 in the lysosome, is sorted to the plasma membrane of the differentiating cells similarly to Neu1. Both proteins are first targeted to the lysosome and then are sorted to the LAMP-2-negative, major histo-compatibility complex II-positive vesicles, which later merge with the plasma membrane. Similar trafficking was observed for the internalized fluorescent dextran or horseradish peroxidase initially stored in the lysosomal/endosomal compartment. The suppression of Neu1 expression in the THP-1-derived macrophages by small interfering RNA or with anti-Neu1 antibodies significantly reduced the ability of the cells to engulf bacteria or to produce cytokines. Altogether our data suggest that the upregulation of the Neu1 expression is important for the primary function of macrophages and establish the link between Neu1 and the cellular immune response.

Lactate dehydrogenase is an AU-rich element-binding protein that directly interacts with AUF1

Post-transcriptional pathways provide a major means of regulating eukaryotic gene expression. Reiterations of the AU-rich element (ARE) within the 3'-untranslated region of many cytokine and proto-oncogene mRNAs serve as signals for rapid degradation and translational repression. The identification of this cis-acting stability determinant has fueled the search for ARE-binding proteins (AUBP) that function as trans-acting factors that transduce this function. Previous work identified heterogeneous nuclear ribonucleoprotein (hnRNP) A1 as a major AUBP capable of binding the ARE of granulocyte-macrophage colony stimulating factor (GM-CSF) RNA in the context of a full-length mRNA. We report here that functional studies failed to indicate a role for hnRNP A1 in ARE-dependent mRNA turnover. In an effort to identify other functionally relevant AUBP, the major GM-CSF ARE-specific binding protein in cells lacking hnRNP A1 was purified from CB3 mouse erythroleukemia cells. Microsequencing identified this protein as the glycolytic enzyme lactate dehydrogenase (LDH) M. RNA binding by LDH was shown to occur in the NAD(+)-binding region (Rossmann fold). Polysome gradient analysis demonstrates that LDH is found in the translationally active fraction. Polysomal localization of LDH was dependent on RNA binding. Moreover, polysomal LDH exists in a complex with AUF1 and hsp-70, which has been implicated previously in the regulation of mRNA turnover. The interaction between LDH and AUF1 is direct as it can be demonstrated in vitro with purified proteins. Collectively these data implicate a role for LDH in the post-transcriptional regulation of gene expression.

The mode of actions of lysozyme as an immunoglobulin production stimulating factor

As we demonstrated before, hen egg white lysozyme stimulates immunoglobulin production by a human-human hybridoma line, HB4C5 cells and human peripheral blood lymphocytes. Then, the mode of actions of lysozyme as an immunoglobulin production stimulating factor was investigated. The immunoglobulin production stimulating activity of lysozyme was inactivated by trypsin digestion, even though the enzymatic activity was completely preserved. This fact suggests that the immunoglobulin production stimulating effect of lysozyme is irrelevant to its enzymatic function. Furthermore, this means that the effect is a novel function of this enzyme. Lysozyme enhanced IgM production by transcription-suppressed HB4C5 cells treated with actinomycin D. However, the enzyme was ineffective to accelerate IgM production by translation-suppressed HB4C5 cells treated with cycloheximide or sodium fluoride. In addition, the intracellular IgM content of HB4C5 cells treated with monensin for suppression of the post-transcription activity was obviously increased by lysozyme, although the secretion of IgM was inhibited. These findings suggest that lysozyme accelerates the translation process to enhance immunoglobulin productivity.

Specific phosphorylated forms of glyceraldehyde 3-phosphate dehydrogenase associate with human parainfluenza virus type 3 and inhibit viral transcription in vitro

We previously reported specific interaction of cellular glyceraldehyde 3-phosphate dehydrogenase (GAPDH), the key glycolytic enzyme, and La protein, the RNA polymerase III transcription factor, with the cis-acting RNAs of human parainfluenza virus type 3 (HPIV3) and packaging of these proteins within purified virions (B. P. De, S. Gupta, H. Zhao, J. Z. Drazba, and A. K. Banerjee, J. Biol. Chem. 271:24728-24735, 1996). To gain further insight into these molecular interactions, we analyzed the virion-associated GAPDH and La protein using two-dimensional gel electrophoresis and immunoblotting. The GAPDH was resolved into two major and one minor molecular species migrating in the pI range of 7.6 to 8.3, while the La protein was resolved into five molecular species in the pI range of 6.8 to 7.5. The GAPDH isoforms present in the virions were also detected in the cytoplasmic fraction of CV-1 cell extract, albeit as minor species. On the other hand, the multiple molecular forms of La protein as seen within the virions were readily detected in the total CV-1 cell extract. Further analysis of virion-associated GAPDH by in vivo labeling with [(32)P]orthophosphate revealed the presence of multiple phosphorylated species. The phosphorylated species were able to bind specifically to the viral cis-acting 3' genome sense RNA but failed to bind to the leader sense RNA, as determined by gel mobility shift assay. In contrast, the La protein isoforms present within the virions were not phosphorylated and bound to the viral cis-acting RNAs in a phosphorylation-independent manner. The GAPDH isoforms purified from the CV-1 cell cytoplasmic fraction inhibited viral transcription in vitro. Consistent with this, flag-tagged recombinant GAPDH synthesized by using the vaccinia virus expression system also inhibited viral transcription. Together, these data indicate that specific phosphorylated forms of GAPDH associate with HPIV3 and are involved in the regulation of virus gene expression.

Macromolecular compartmentation and channeling

One of the accepted characterizations of the living state is that it is complex to an extraordinary degree. Since our current understanding of the living condition is minimal and fragmentary, it is not surprising that our first descriptions are simplistic. However, in certain areas of metabolism, especially those that have been amenable to experimentation for the longest period of time, the simplistic explanations have been the most difficult to revise. For example, current texts of general biochemistry still view metabolism as occurring by a series of independent enzymes dispersed in a uniform aqueous environment. This notion has been shown to be deeply flawed by both experimental and theoretical considerations. Thus, there is ample evidence that, in many metabolic pathways, specific interactions between sequential enzymes occur as static and/or dynamic complexes. In addition, reversible interactions of enzymes with structural proteins and membranes is a common occurrence. The interactions of enzymes give rise to a higher level of complexity that must be accounted for when one wishes to understand the regulation of metabolism. One of the phenomena that occurs because of sequential enzyme interactions is the process of channeling. This article discusses enzyme interactions and channeling and summarizes experimental and theoretical results from a few well-studied examples.

Metabolic consequences of enzyme interactions

The fact that enzyme complexes, stable, quasi-stable, and dynamic, exist in cells can no longer be ignored. Experimental evidence done with a variety of techniques has demonstrated these interactions in vitro and in vivo. There is scarcely a single known metabolic pathway in which no interactions of any of its enzymes exist (see reference 27 for a list of these). Such interactions are not only ubiquitous throughout metabolism, but they exist in all cell types, procaryote and eucaryote. In many of these systems the advantages of and regulatory power of enzyme-enzyme or enzyme-structural protein interactions has been amply demonstrated. The more difficult task is to assess accurately quantitative aspects of a system that varies between the solid, gel, and aqueous state. It is clear that the metabolic paradigm of soluble randomly dispersed metabolic elements in cells must be replaced, and new theoretical and experimental approaches introduced into this vital area of biological research.

Specific interaction in vitro and in vivo of glyceraldehyde-3-phosphate dehydrogenase and LA protein with cis-acting RNAs of human parainfluenza virus type 3

Human parainfluenza virus type 3 (HPIV3) genome RNA is transcribed and replicated by the virus-encoded RNA-dependent RNA polymerase, and specific cellular proteins play a regulatory role in these processes. To search for cellular proteins potentially interacting with HPIV3 cis-acting regulatory RNAs, a gel mobility shift assay was used. Two cellular proteins specifically interacted with the viral cis-acting RNAs containing the genomic 3'-noncoding region and the plus-sense leader sequence region. Surprisingly, by biochemical and immunological analyses, one of the cellular proteins was identified as the key glycolytic enzyme, glyceraldehyde-3-phosphate dehydrogenase (GAPDH). The other protein was characterized as the autoantigen, LA protein. Both GAPDH and LA protein also interacted with the same cis-acting RNA sequences in vivo and were found to be associated with the HPIV3 ribonucleoprotein complex in the infected cells. By double immunofluorescent labeling, GAPDH was found to be co-localized with viral ribonucleoprotein in the perinuclear region. These observations strongly suggest that cellular GAPDH and LA Protein participate in the regulation of HPIV3 gene expression.

The mode of actions of glyceraldehyde-3-phosphate dehydrogenase identified as an immunoglobulin production stimulating factor

Immunoglobulin production stimulating factor-II alpha, which enhances immunoglobulin production of human and mouse hybridomas was purified from cell lysate of human Burkitt's lymphoma, Namalwa cells, and identified as glyceraldehyde-3-phosphate dehydrogenase. The enhancement of immunoglobulin production with this enzyme was not linked with its enzymatic activity. The enzyme enhanced immunoglobulin productivity of transcription-suppressed hybridomas, but did not enhance that of translation-suppressed hybridomas. From these results, it is suggested that this enzyme takes part in the post-translational control or the enhancement of translation activity to stimulate immunoglobulin production of hybridomas.

Purification and characterization of immunoglobulin production stimulating factor-II? derived from Namalwa cells

Two immunoglobulin production stimulating factors (IPSF) have been found in human Burkitt's lymphoma Namalwa cells. One IPSF named IPSF-II alpha was purified and identified as glyceraldehyde-3-phosphate dehydrogenase as previously reported. We report here purification, identification and characterization of IPSF-II beta. IPSF-II beta was purified by the serial use of ammonium sulfate fractionation, hydrophobic interaction column chromatography, anion-exchange column chromatography and gel filtration. The IPSF-II beta was estimated as a 46 KD monomeric polypeptide by gel filtration and SDS-PAGE. Partial amino acid sequence of the 46 KD protein was analyzed for 26 amino acid residues. The sequence very closely coincided with enolase (EC 4.2.1.11) derived from various origins and, it was completely homologous with that of human enolase alpha-chain. Rabbit muscle enolase stimulated IgM production of hybridoma lines, and IPSF-II beta had the enzymic activity. These results suggested that IPSF-II beta was alpha-enolase or its isozyme. IPSF activities of IPSF-II beta was stable in alkaline conditions whereas the enzymic activity was rapidly lost in alkaline conditions. Though IPSF-II beta stimulated IgM production of both human-human and mouse-mouse hybridoma lines in serum-free condition, it partially suppressed IgE production of mouse-mouse hybridoma lines.

Glucose metabolism and the channeling of glycolytic intermediates in permeabilized L-929 cells

L-929 cells (mouse fibroblasts) permeabilized with dextran sulfate (DSP cells) carry out vigorous and linear rates of glycolysis when supplied with a suitable incubation medium. Glycolysis in DSP cells is pH dependent, being strongly inhibited at pH 6.5. Compared to their nonpermeabilized counterparts, DSP cells exhibit faster glycolytic rates, but tend to convert a smaller proportion of the glucose utilized to lactate. [14C]Glucose is converted to lactate by DSP cells without dilution from endogenous substrates. When exogenous 12C-labeled glycolytic intermediates (12C-I) are added to glycolyzing DSP cells the [14C]lactate produced from [14C]glucose is diluted to varying extents, depending on the intermediate. However, the extent of that dilution (reduced specific activity) is not that expected from the complete mixing of exogenous 12C-I with their corresponding 14C-labeled intermediates coming from [14C]-glucose. DSP cells also respire and convert glucose to CO2. The amount of 14CO2 produced from [14C]glucose is also reduced by addition of most 12C-I, an interesting exception being pyruvate, which had no measurable effect on 14CO2 production and caused only a modest stimulation of respiration in glycolyzing DSP cells. These results suggest that channeling, or some other form of coupling, takes place between the glycolytic production of pyruvate and its further oxidation. These observations confirm previously published data and add further support to the proposition that channeling of glycolytic intermediates occurs in DSP cells but is of the "leaky" type. Although abundant evidence in the literature indicates that various glycolytic enzymes associate with F-actin, as well as other elements of the cytomatrix, we observed no effect of cytochalasin D on lactate production even at very high concentrations of this compound. Our results are compared with those from other laboratories and discussed in the context of metabolic organization.

Evidence for intermediate channelling in the glycolytic pathway of permeabilized L-929 cells

L-929 cells permeabilized by dextran sulfate (DSP cells) carry out vigorous and linear rates of glycolysis when supplied with a suitable incubation medium. Unlabeled 3-phosphoglycerate (PGA) added to DSP cells reduces the specific activity of lactate coming from [14C]glucose but the extent of this reduction can not be accounted for on the basis of free diffusion of PGA coming from [14C]glucose. Studies on other glycolytic intermediates, although preliminary, yield similar results. PGA also inhibits the production of lactate from glucose; however, this effect, like that of the reduction of lactate specific activity, becomes apparent only at concentrations of PGA well in excess of those considered to be physiological. We conclude that channelling of PGA, and probably other intermediates, occurs but is of the "leaky" type.