O-GlcNAcylation disrupts glyceraldehyde-3-phosphate dehydrogenase homo-tetramer formation and mediates its nuclear translocation

O-GlcNAcylation mediates Wnt-stimulated bone formation by rewiring aerobic glycolysis

Wnt signaling is an important target for anabolic therapies in osteoporosis. A sclerostin-neutralizing antibody (Scl-Ab), that blocks the Wnt signaling inhibitor (sclerostin), has been shown to promote bone mass in animal models and clinical studies. However, the cellular mechanisms by which Wnt signaling promotes osteogenesis remain to be further investigated. O-GlcNAcylation, a dynamic post-translational modification of proteins, controls multiple critical biological processes including transcription, translation, and cell fate determination. Here, we report that Wnt3a either induces O-GlcNAcylation rapidly via the Ca2+-PKA-Gfat1 axis, or increases it in a Wnt-β-catenin-dependent manner following prolonged stimulation. Importantly, we find O-GlcNAcylation indispensable for osteoblastogenesis both in vivo and in vitro. Genetic ablation of O-GlcNAcylation in the osteoblast-lineage diminishes bone formation and delays bone fracture healing in response to Wnt stimulation in vivo. Mechanistically, Wnt3a induces O-GlcNAcylation at Serine 174 of PDK1 to stabilize the protein, resulting in increased glycolysis and osteogenesis. These findings highlight O-GlcNAcylation as an important mechanism regulating Wnt-induced glucose metabolism and bone anabolism.

Glycosyltransferase Slr1064 regulates carbon metabolism by modulating the levels of UDP-GlcNAc in Synechocystis sp. PCC 6803

Glycosyltransferases (GTs) are enzymes that transfer sugars to various targets. They play important roles in diverse biological processes, including photosynthesis, cell motility, exopolysaccharide biosynthesis, and lipid metabolism; however, their involvement in regulating carbon metabolism in Synechocystis sp. PCC 6803 has not been reported. We identified a novel GT protein, Slr1064, involved in carbon metabolism. The effect of slr1064 deletion on the growth of Synechocystis cells and functional mechanisms of Slr1064 on carbon metabolism were thoroughly investigated through physiological, biochemistry, proteomic, and metabolic analyses. We found that this GT, which is mainly distributed in the membrane compartment, is essential for the growth of Synechocystis under heterotrophic and mixotrophic conditions, but not under autotrophic conditions. The deletion of slr1064 hampers the turnover rate of Gap2 under mixotrophic conditions and disrupts the assembly of the PRK/GAPDH/CP12 complex under dark culture conditions. Additionally, UDP-GlcNAc, the pivotal metabolite responsible for the O-GlcNAc modification of GAPDH, is downregulated in the Δslr1064. Our work provides new insights into the role of GTs in carbon metabolism in Synechocystis and elucidate the mechanism by which carbon metabolism is regulated in this important model organism.

O-GlcNAcylation: A Crucial Regulator in Cancer-Associated Biological Events

O-GlcNAcylation, a recently discovered post-translational modification of proteins, plays a crucial role in regulating protein structure and function, and is closely associated with multiple diseases. Research has shown that O-GlcNAcylation is abnormally upregulated in most cancers, promoting disease progression. To elucidate the roles of O-GlcNAcylation in cancer, this review summarizes various cancer-associated biological events regulated by O-GlcNAcylation and the corresponding signaling pathways. This work may provide insights for future studies on the function or underlying mechanisms of O-GlcNAcylation in cancer.

The uncommon function and mechanism of the common enzyme glyceraldehyde-3-phosphate dehydrogenase in the metamorphosis of Helicoverpa armigera

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH), a key enzyme in glycolysis, is commonly used as an internal reference gene in humans, mice, and insects. However, the function of GAPDH in insect development, especially in metamorphosis, has not been reported. In the present study, Helicoverpa armigera and Spodoptera frugiperda ovarian cell lines (Sf9 cells) were used as materials to study the function and molecular mechanism of GAPDH in larval metamorphosis. The results showed that HaGAPDH was more closely related to GAPDH of S. frugiperda and Spodoptera litura. The transcript peaks of HaGAPDH in sixth instar larvae were 6L-3 (epidermal and midgut) and 6L-1 (fat body) days, and 20E and methoprene significantly upregulated the transcripts of HaGAPDH of larvae in qRT-PCR. HaGAPDH–GFP–His was specifically localized in mitochondria in Sf9 cells. Knockdown of HaGAPDH by RNA interference (RNAi) in sixth instar larvae resulted in weight loss, increased mortality, and decreases in the pupation rate and emergence rates. HaGAPDH is directly bound to soluble trehalase (HaTreh1) physically and under 20E treatment in yeast two-hybrid, coimmunoprecipitation, and colocalization experiments. In addition, knockdown of HaGAPDH increased the Treh1 activity, which in turn decreased the trehalose content but increased the glucose content in larvae. Therefore, these data demonstrated that GAPDH controlled the glucose content within the normal range to ensure glucose metabolism and metamorphosis by directly binding with HaTreh1.

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

AIMS

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

RESULTS

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

CONCLUSIONS

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

Prolyl oligopeptidase participates in the cytosine arabinoside-induced nuclear translocation of glyceraldehyde 3-phosphate dehydrogenase in a human neuroblastoma cell line

Previously, we reported that glyceraldehyde 3-phosphate dehydrogenase (GAPDH) is a binding partner of prolyl oligopeptidase (POP) in neuroblastoma NB-1 cells and that the POP inhibitor, SUAM-14746, inhibits cytosine arabinoside (Ara-C)-induced nuclear translocation of GAPDH and protects against Ara-C cytotoxicity. To carry out a more in-depth analysis of the interaction between POP and GAPDH, we generated POP-KO NB-1 cells and compared the nuclear translocation of GAPDH after Ara-C with or without SUAM-14746 treatment to wild-type NB-1 cells by western blotting and fluorescence immunostaining. Ara-C did not induce the nuclear translocation of GAPDH and SUAM-14746 did not protect against Ara-C cytotoxicity in POP-KO cells. These results indicate that the anticancer effects of Ara-C not only include the commonly known antimetabolic effects, but also the induction of cell death by nuclear transfer of GAPDH through interaction with POP.

The role of posttranslational modification in moonlighting glyceraldehyde-3-phosphate dehydrogenase structure and function

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a moonlighting protein exhibiting distinct activities apart from its classical role in glycolysis. Regulation of its moonlighting functions and its subcellular localization may be dependent on its posttranslational modification (PTM). The latter include its phosphorylation, which is required for its role in intermembrane trafficking, synaptic transmission and cancer survival; nitrosylation, which is required for its function in apoptosis, heme metabolism and the immune response; acetylation which is necessary for its modulation of apoptotic gene regulation; and N-acetylglucosamine modification which may induce changes in GAPDH oligomeric structure. These findings suggest a structure function relationship between GAPDH posttranslational modification and its diverse moonlighting activities.

Mind the GAP: Purification and characterization of urea resistant GAPDH during extreme dehydration

The African clawed frog (Xenopus laevis) withstands prolonged periods of extreme whole-body dehydration that lead to impaired blood flow, global hypoxia, and ischemic stress. During dehydration, these frogs shift from oxidative metabolism to a reliance on anaerobic glycolysis. In this study, we purified the central glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) to electrophoretic homogeneity and investigated structural, kinetic, subcellular localization, and post-translational modification properties between control and 30% dehydrated X. laevis liver. GAPDH from dehydrated liver displayed a 25.4% reduction in maximal velocity and a 55.7% increase in its affinity for GAP, as compared to enzyme from hydrated frogs. Under dehydration mimicking conditions (150 mM urea and 1% PEG), GAP affinity was reduced with a K_m value 53.8% higher than controls. Frog dehydration also induced a significant increase in serine phosphorylation, methylation, acetylation, beta-N-acetylglucosamination, and cysteine nitrosylation, post-translational modifications (PTMs). These modifications were bioinformatically predicted and experimentally validated to govern protein stability, enzymatic activity, and nuclear translocation, which increased during dehydration. These dehydration-responsive protein modifications, however, did not appear to affect enzymatic thermostability as GAPDH melting temperatures remained unchanged when tested with differential scanning fluorimetry. PTMs could promote extreme urea resistance in dehydrated GAPDH since the enzyme from dehydrated animals had a urea I₅₀ of 7.3 M, while the I₅₀ from the hydrated enzyme was 5.3 M. The physiological consequences of these dehydration-induced molecular modifications of GAPDH likely suppress GADPH glycolytic functions during the reduced circulation and global hypoxia experienced in dehydrated X. laevis.

The Writers, Readers, and Erasers in Redox Regulation of GAPDH

Glyceraldehyde 3–phosphate dehydrogenase (GAPDH) is a key glycolytic enzyme, which is crucial for the breakdown of glucose to provide cellular energy. Over the past decade, GAPDH has been reported to be one of the most prominent cellular targets of post-translational modifications (PTMs), which divert GAPDH toward different non-glycolytic functions. Hence, it is termed a moonlighting protein. During metabolic and oxidative stress, GAPDH is a target of different oxidative PTMs (oxPTM), e.g., sulfenylation, S-thiolation, nitrosylation, and sulfhydration. These modifications alter the enzyme’s conformation, subcellular localization, and regulatory interactions with downstream partners, which impact its glycolytic and non-glycolytic functions. In this review, we discuss the redox regulation of GAPDH by different redox writers, which introduce the oxPTM code on GAPDH to instruct a redox response; the GAPDH readers, which decipher the oxPTM code through regulatory interactions and coordinate cellular response via the formation of multi-enzyme signaling complexes; and the redox erasers, which are the reducing systems that regenerate the GAPDH catalytic activity. Human pathologies associated with the oxidation-induced dysregulation of GAPDH are also discussed, featuring the importance of the redox regulation of GAPDH in neurodegeneration and metabolic disorders.

Role of O-Linked N-Acetylglucosamine Protein Modification in Cellular (Patho)Physiology

In the mid-1980s, the identification of serine and threonine residues on nuclear and cytoplasmic proteins modified by a N-acetylglucosamine moiety (O-GlcNAc) via an O-linkage overturned the widely held assumption that glycosylation only occurred in the endoplasmic reticulum, Golgi apparatus, and secretory pathways. In contrast to traditional glycosylation, the O-GlcNAc modification does not lead to complex, branched glycan structures and is rapidly cycled on and off proteins by O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA), respectively. Since its discovery, O-GlcNAcylation has been shown to contribute to numerous cellular functions, including signaling, protein localization and stability, transcription, chromatin remodeling, mitochondrial function, and cell survival. Dysregulation in O-GlcNAc cycling has been implicated in the progression of a wide range of diseases, such as diabetes, diabetic complications, cancer, cardiovascular, and neurodegenerative diseases. This review will outline our current understanding of the processes involved in regulating O-GlcNAc turnover, the role of O-GlcNAcylation in regulating cellular physiology, and how dysregulation in O-GlcNAc cycling contributes to pathophysiological processes.

Moonlighting glyceraldehyde-3-phosphate dehydrogenase: posttranslational modification, protein and nucleic acid interactions in normal cells and in human pathology

Moonlighting glyceraldehyde-3-phosphate dehydrogenase (GAPDH) exhibits multiple functions separate and distinct from its historic role in energy production. Further, it exhibits dynamic changes in its subcellular localization which is an a priori requirement for its multiple activities. Separately, moonlighting GAPDH may function in the pathology of human disease, involved in tumorigenesis, diabetes, and age-related neurodegenerative disorders. It is suggested that moonlighting GAPDH function may be related to specific modifications of its protein structure as well as the formation of GAPDH protein: protein or GAPDH protein: nucleic acid complexes.

Glyceraldehyde-3-phosphate Dehydrogenase is a Multifaceted Therapeutic Target

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a glycolytic enzyme whose role in cell metabolism and homeostasis is well defined, while its function in pathologic processes needs further elucidation. Depending on the cell context, GAPDH may bind a number of physiologically important proteins, control their function and correspondingly affect the cell’s fate. These interprotein interactions and post-translational modifications of GAPDH mediate its cytotoxic or cytoprotective functions in the manner of a Janus-like molecule. In this review, we discuss the functional features of the enzyme in cellular physiology and its possible involvement in human pathologies. In the last part of the article, we describe drugs that can be employed to modulate this enzyme’s function in some pathologic states.

Clinicopathological and prognostic significance of nuclear UGDH localization in lung adenocarcinoma

This study aimed to clarify relationships among UDP-glucose-6 dehydrogenase (UGDH) expression, clinicopathological factors, and the prognosis of patients, and to determine the role of UGDH in lung adenocarcinoma (AC). Firstly, UGDH expression and localization in 126 lung AC tissues were immunohistochemically studied, and associations with clinicopathological parameters and patients' prognosis were evaluated. Secondly, serum UGDH levels were measured in 267 lung cancer patients and 100 healthy controls. Finally, the effects of UGDH knockdown by siRNA on migration and invasion abilities were analyzed. As a result, nuclear UGDH staining was significantly correlated with poorer differentiation, a larger tumor size, higher p-TNM stage, positive nodal metastasis, positive lymphatic invasion, and positive vascular invasion in lung AC patients. Nuclear UGDH-positive patients showed significantly poorer survival than nuclear UGDH-negative patients. Serum UGDH levels were especially higher in lung AC patients even in stage I than those in healthy controls. In lung AC cell lines, nuclear expression levels of UGDH were higher in LC-2/ad cells than in A549 cells. UGDH siRNA-treated LC-2/ad cells showed significantly decreased migration and invasion abilities, but no significant differences were observed in UGDH siRNA-treated A549 cells. These data indicate that UGDH expression and localization are an early sero-diagnostic marker in addition to a poor prognostic indicator in lung AC patients.

The Nutrient-Sensing Hexosamine Biosynthetic Pathway as the Hub of Cancer Metabolic Rewiring

Alterations in glucose and glutamine utilizing pathways and in fatty acid metabolism are currently considered the most significant and prevalent metabolic changes observed in almost all types of tumors. Glucose, glutamine and fatty acids are the substrates for the hexosamine biosynthetic pathway (HBP). This metabolic pathway generates the “sensing molecule” UDP-N-Acetylglucosamine (UDP-GlcNAc). UDP-GlcNAc is the substrate for the enzymes involved in protein N- and O-glycosylation, two important post-translational modifications (PTMs) identified in several proteins localized in the extracellular space, on the cell membrane and in the cytoplasm, nucleus and mitochondria. Since protein glycosylation controls several key aspects of cell physiology, aberrant protein glycosylation has been associated with different human diseases, including cancer. Here we review recent evidence indicating the tight association between the HBP flux and cell metabolism, with particular emphasis on the post-transcriptional and transcriptional mechanisms regulated by the HBP that may cause the metabolic rewiring observed in cancer. We describe the implications of both protein O- and N-glycosylation in cancer cell metabolism and bioenergetics; focusing our attention on the effect of these PTMs on nutrient transport and on the transcriptional regulation and function of cancer-specific metabolic pathways.

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.

O-GlcNAc cycling and the regulation of nucleocytoplasmic dynamics

The dynamic carbohydrate post-translational modification (PTM) O-linked β-N-acetyl glucosamine (O-GlcNAc) is found on thousands of proteins throughout the nucleus and cytoplasm, and rivals phosphorylation in terms of the number of substrates and pathways influenced. O-GlcNAc is highly conserved and essential in most organisms, with disruption of O-GlcNAc cycling linked to diseases ranging from cancer to neurodegeneration. Nuclear pore proteins were the first identified O-GlcNAc-modified substrates, generating intense and ongoing interest in understanding the role of O-GlcNAc cycling in nuclear pore complex structure and function. Recent advances in detecting and altering O-GlcNAcylation levels have provided insights into many mechanisms by which O-GlcNAcylation influences the nucleocytoplasmic localization and stability of protein targets. The emerging view is that the multifunctional enzymes of O-GlcNAc cycling are critical nutrient-sensing components of a complex network of signaling cascades involving multiple PTMs. Furthermore, O-GlcNAc plays a role in maintaining the structural integrity of the nuclear pore and regulating its function as the gatekeeper of nucleocytoplasmic trafficking.

D-Glyceraldehyde-3-Phosphate Dehydrogenase Structure and Function

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

Longevity and GAPDH Stability in Bivalves and Mammals: A Convenient Marker for Comparative Gerontology and Proteostasis

BACKGROUND

Comparative aging studies, particularly those that include species of exceptional resistance to aging processes, can potentially illuminate novel senescence-retarding mechanisms. In recent years, protein homeostasis (proteostasis) has been implicated in fundamental aging processes. Here we further evaluate the relationship between proteostasis and longevity in a selection of bivalve mollusks and mammals with maximum longevities ranging from 3 to 507 years.

METHODS & RESULTS

We experimentally examined proteostasis using glyceraldehyde-3-phosphate dehydrogenase (GAPDH) as a reporter, as it is ubiquitously expressed, highly conserved, and conveniently assayed. The ability to maintain this enzymatic function was tested with increasing concentrations of the chaotropic agent urea, revealing a robust relationship with longevity in bivalves and mice. While our shortest-lived mollusk and mouse lost all activity by 2.5 and 3.5 M urea respectively, the longest-lived mollusk species, Arctica islandica, still preserved 45% of its basal function even at 6 M urea. To confirm that GAPDH proteostasis has a broad association with longevity, we also investigated a selection of primate species ranging in maximum longevity from 22 to 122 years. They outperformed the mouse at all concentrations, but among the primates results were variable at low urea doses. Still, at 6 M urea baboon and human samples retained 10% of their activity while both mouse and marmoset samples had no activity.

MECHANISM OF EXCEPTIONAL STRESS RESISTANCE

To explore possible mechanisms of the exceptional stress resistance of A. islandica GAPDH we enzymatically removed post-translational glycosylation, but observed no decrease in stability. We also removed molecules smaller than 30 kDa, which includes most small heat shock proteins, but again did not compromise the exceptional stress resistance of Arctica GAPDH.

CONCLUSION

While the mechanism underlying A. islandica's exceptional stress resistance remains elusive, this research identifies an experimental system that may reveal hitherto unknown mechanisms of protein homeostasis.

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

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

Evidence for a Functional O-Linked N-Acetylglucosamine (O-GlcNAc) System in the Thermophilic Bacterium Thermobaculum terrenum

Post-translational modification of proteins is a ubiquitous mechanism of signal transduction in all kingdoms of life. One such modification is addition of O-linked N-acetylglucosamine to serine or threonine residues, known as O-GlcNAcylation. This unusual type of glycosylation is thought to be restricted to nucleocytoplasmic proteins of eukaryotes and is mediated by a pair of O-GlcNAc-transferase and O-GlcNAc hydrolase enzymes operating on a large number of substrate proteins. Protein O-GlcNAcylation is responsive to glucose and flux through the hexosamine biosynthetic pathway. Thus, a close relationship is thought to exist between the level of O-GlcNAc proteins within and the general metabolic state of the cell. Although isolated apparent orthologues of these enzymes are present in bacterial genomes, their biological functions remain largely unexplored. It is possible that understanding the function of these proteins will allow development of reductionist models to uncover the principles of O-GlcNAc signaling. Here, we identify orthologues of both O-GlcNAc cycling enzymes in the genome of the thermophilic eubacterium Thermobaculum terrenum. The O-GlcNAcase and O-GlcNAc-transferase are co-expressed and, like their mammalian orthologues, localize to the cytoplasm. The O-GlcNAcase orthologue possesses activity against O-GlcNAc proteins and model substrates. We describe crystal structures of both enzymes, including an O-GlcNAcase·peptide complex, showing conservation of active sites with the human orthologues. Although in vitro activity of the O-GlcNAc-transferase could not be detected, treatment of T. terrenum with an O-GlcNAc-transferase inhibitor led to inhibition of growth. T. terrenum may be the first example of a bacterium possessing a functional O-GlcNAc system.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: an update for 2009-2010

This review is the sixth update of the original article published in 1999 on the application of MALDI mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2010. General aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, arrays and fragmentation are covered in the first part of the review and applications to various structural typed constitutes the remainder. The main groups of compound that are discussed in this section are oligo and polysaccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals. Many of these applications are presented in tabular form. Also discussed are medical and industrial applications of the technique, studies of enzyme reactions and applications to chemical synthesis.

Critical protein GAPDH and its regulatory mechanisms in cancer cells

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH), initially identified as a glycolytic enzyme and considered as a housekeeping gene, is widely used as an internal control in experiments on proteins, mRNA, and DNA. However, emerging evidence indicates that GAPDH is implicated in diverse functions independent of its role in energy metabolism; the expression status of GAPDH is also deregulated in various cancer cells. One of the most common effects of GAPDH is its inconsistent role in the determination of cancer cell fate. Furthermore, studies have described GAPDH as a regulator of cell death; other studies have suggested that GAPDH participates in tumor progression and serves as a new therapeutic target. However, related regulatory mechanisms of its numerous cellular functions and deregulated expression levels remain unclear. GAPDH is tightly regulated at transcriptional and posttranscriptional levels, which are involved in the regulation of diverse GAPDH functions. Several cancer-related factors, such as insulin, hypoxia inducible factor-1 (HIF-1), p53, nitric oxide (NO), and acetylated histone, not only modulate GAPDH gene expression but also affect protein functions via common pathways. Moreover, posttranslational modifications (PTMs) occurring in GAPDH in cancer cells result in new activities unrelated to the original glycolytic function of GAPDH. In this review, recent findings related to GAPDH transcriptional regulation and PTMs are summarized. Mechanisms and pathways involved in GAPDH regulation and its different roles in cancer cells are also described.

A dimer interface mutation in glyceraldehyde-3-phosphate dehydrogenase regulates its binding to AU-rich RNA

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is an enzyme best known for its role in glycolysis. However, extra-glycolytic functions of GAPDH have been described, including regulation of protein expression via RNA binding. GAPDH binds to numerous adenine-uridine rich elements (AREs) from various mRNA 3'-untranslated regions in vitro and in vivo despite its lack of a canonical RNA binding motif. How GAPDH binds to these AREs is still unknown. Here we discovered that GAPDH binds with high affinity to the core ARE from tumor necrosis factor-α mRNA via a two-step binding mechanism. We demonstrate that a mutation at the GAPDH dimer interface impairs formation of the second RNA-GAPDH complex and leads to changes in the RNA structure. We investigated the effect of this interfacial mutation on GAPDH oligomerization by crystallography, small-angle x-ray scattering, nano-electrospray ionization native mass spectrometry, and hydrogen-deuterium exchange mass spectrometry. We show that the mutation does not significantly affect GAPDH tetramerization as previously proposed. Instead, the mutation promotes short-range and long-range dynamic changes in regions located at the dimer and tetramer interface and in the NAD(+) binding site. These dynamic changes are localized along the P axis of the GAPDH tetramer, suggesting that this region is important for RNA binding. Based on our results, we propose a model for sequential GAPDH binding to RNA via residues located at the dimer and tetramer interfaces.

Chemical targeting of GAPDH moonlighting function in cancer cells reveals its role in tubulin regulation

Glycolytic enzymes are attractive anticancer targets. They also carry out numerous, nonglycolytic "moonlighting" functions in cells. In this study, we investigated the anticancer activity of the triazine small molecule, GAPDS, that targets the glycolytic enzyme glyceraldehyde 3-phosphate dehydrogenase (GAPDH). GAPDS showed greater toxicity against cancer cells compared to a known GAPDH enzyme inhibitor. GAPDS also selectively inhibited cell migration and invasion. Our analysis showed that GAPDS treatment reduced GAPDH levels in the cytoplasm, which would modulate the secondary, moonlighting functions of this enzyme. We then used GAPDS as a probe to demonstrate that a moonlighting function of GAPDH is tubulin regulation, which may explain its anti-invasive properties. We also observed that GAPDS has potent anticancer activity in vivo. Our study indicates that strategies to target the secondary functions of anticancer candidates may yield potent therapeutics and useful chemical probes.

Structural analysis of glyceraldehyde-3-phosphate dehydrogenase functional diversity

Multifunctional proteins provide a new mechanism to expand exponentially cell information and capability beyond that indicated by conventional gene analyses. As such, examination of their structure-function relationships provides a means to define the mechanisms through which cells accomplish critical yet disparate activities required for cell viability and survival. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) may be considered the quintessential multidimensional protein which exhibits a variety of functions unrelated to its classical role in energy production. This review discusses new insights into the structure-function mechanisms through which defined GAPDH amino acid domains are utilized for its diverse activities, the importance of its post-translational modification, and, intriguingly, the logic inherent in the presence or the absence of specific signaling domains.

Yeast Tdh3 (glyceraldehyde 3-phosphate dehydrogenase) is a Sir2-interacting factor that regulates transcriptional silencing and rDNA recombination

Sir2 is an NAD(+)-dependent histone deacetylase required to mediate transcriptional silencing and suppress rDNA recombination in budding yeast. We previously identified Tdh3, a glyceraldehyde 3-phosphate dehydrogenase (GAPDH), as a high expression suppressor of the lethality caused by Sir2 overexpression in yeast cells. Here we show that Tdh3 interacts with Sir2, localizes to silent chromatin in a Sir2-dependent manner, and promotes normal silencing at the telomere and rDNA. Characterization of specific TDH3 alleles suggests that Tdh3's influence on silencing requires nuclear localization but does not correlate with its catalytic activity. Interestingly, a genetic assay suggests that Tdh3, an NAD(+)-binding protein, influences nuclear NAD(+) levels; we speculate that Tdh3 links nuclear Sir2 with NAD(+) from the cytoplasm.

Discovery and confirmation of O-GlcNAcylated proteins in rat liver mitochondria by combination of mass spectrometry and immunological methods

O-linked β-N-acetylglucosamine (O-GlcNAc) is an important post-translational modification (PTM) consisting of a single N-acetylglucosamine moiety attached via an O-β-glycosidic linkage to serine and threonine residues. Glycosylation with O-GlcNAc occurs on myriad nuclear and cytosolic proteins from almost all functional classes. However, with respect to O-GlcNAcylated proteins special in mitochondria, little attention has been paid. In this study, we combined mass spectrometry and immunological methods to perform global exploration of O-GlcNAcylated proteins specific in mitochondria of rat liver. First, highly purified mitochondrial proteins were obviously shown to be O-GlcNAcylated by immunoblot profiling. Then, β-elimination followed by Michael Addition with Dithiothreitol (BEMAD) treatment and LC-MS/MS were performed to enrich and identify O-GlcNAcylated mitochondrial proteins, resulting in an unambiguous assignment of 14 O-GlcNAcylation sites, mapping to 11 O-GlcNAcylated proteins. Furthermore, the identified O-GlcNAcylated mitochondrial proteins were fully validated by both electron transfer dissociation tandem mass spectrometry (ETD/MS/MS) and western blot. Thus, for the first time, our study definitely not only identified but also validated that some mitochondrial proteins in rat liver are O-GlcNAcylated. Interestingly, all of these O-GlcNAcylated mitochondrial proteins are enzymes, the majority of which are involved in a wide variety of biological processes, such as urea cycle, tricarboxylic acid cycle and lipid metabolism, indicating a role for protein O-GlcNAcylation in mitochondrial function.

Glyceraldehyde-3-phosphate dehydrogenase: a promising target for molecular therapy in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most highly lethal malignancies ranking as the third leading-cause of cancer-related death worldwide. Although surgical resection and transplantation are effective curative therapies, very few patients qualify for such treatments due to the advanced stage of the disease at diagnosis. In this context, loco-regional therapies provide a viable therapeutic alternative with minimal systemic toxicity. However, as chemoresistance and tumor recurrence negatively impact the success of therapy resulting in poorer patient outcomes it is imperative to identify new molecular target(s) in cancer cells that could be effectively targeted by novel agents. Recent research has demonstrated that proliferation in HCC is associated with increased glucose metabolism. The glycolytic enzyme, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), a multifunctional protein primarily recognized for its role in glucose metabolism, has already been shown to affect the proliferative potential of cancer cells. In human HCC, the increased expression of GAPDH is invariably associated with enhanced glycolytic capacity facilitating tumor progression. Though it is not yet known whether GAPDH up-regulation contributes to tumorigenesis sensu stricto, emerging evidence points to the existence of a link between GAPDH up-regulation and the promotion of survival mechanisms in cancer cells as well as chemoresistance. The involvement of GAPDH in several hepatocarcinogenic mechanisms (e.g. viral hepatitis, metabolic alterations) and its sensitivity to a new class of prospective anticancer agents prompted us to review the current understanding of the therapeutic potential of targeting GAPDH in HCC.

Prolyl oligopeptidase is a glyceraldehyde-3-phosphate dehydrogenase-binding protein that regulates genotoxic stress-induced cell death

Prolyl oligopeptidase is a serine protease that cleaves peptides shorter 30-mer at carboxyl side of an internal proline. This enzyme has been proposed to be involved in the maturation and degradation of peptide hormones and neuropeptides. However, conclusive results have not yet been reported, and the primary physiological role remains to be elucidated. Here, we describe the identification of a novel protein that interacts with prolyl oligopeptidase in a human neuroblastoma cell line NB-1. Using an affinity column with immobilized recombinant human prolyl oligopeptidase as ligand, we identified glyceraldehyde-3-phosphate dehydrogenase as a novel prolyl oligopeptidase binding protein in NB-1 cell extracts. The interaction between prolyl oligopeptidase and glyceraldehyde-3-phosphate dehydrogenase was confirmed by immunoprecipitation both in vitro and in vivo. To study the functional relevance of prolyl oligopeptidase-glyceraldehyde-3-phosphate dehydrogenase interactions, we investigated whether this interaction was involved in cytosine arabinoside-induced glyceraldehyde-3-phosphate dehydrogenase nuclear translocation and cell death. Prolyl oligopeptidase inhibitor, SUAM-14746, and prolyl oligopeptidase knockdown successfully inhibited glyceraldehyde-3-phosphate dehydrogenase translocation and promoted the survival of cytosine arabinoside-treated NB-1 cells. We also found that the interactions between prolyl oligopeptidase and glyceraldehyde-3-phosphate dehydrogenase in the cytoplasm but not in nuclei of NB-1 cell treated with cytosine arabinoside using an in situ proximity ligation assay. These results indicate that the interaction between prolyl oligopeptidase and glyceraldehyde-3-phosphate dehydrogenase is required for cytosine arabinoside-induced glyceraldehyde-3-phosphate dehydrogenase nuclear translocation and cell death. Therefore, the results of the present study demonstrate a novel function for prolyl oligopeptidase in cell death.

NleB, a bacterial effector with glycosyltransferase activity, targets GAPDH function to inhibit NF-κB activation

Modulation of NF-κB-dependent responses is critical to the success of attaching/effacing (A/E) human pathogenic E. coli (EPEC and EHEC) and the natural mouse pathogen Citrobacter rodentium. NleB, a highly conserved type III secretion system effector of A/E pathogens, suppresses NF-κB activation, but the underlying mechanisms are unknown. We identified the mammalian glycolysis enzyme glyceraldehyde 3-phosphate dehydrogenase (GAPDH) as an NleB-interacting protein. Further, we discovered that GAPDH interacts with the TNF receptor-associated factor 2 (TRAF2), a protein required for TNF-α-mediated NF-κB activation, and regulates TRAF2 polyubiquitination. During infection, NleB functions as a translocated N-acetyl-D-glucosamine (O-GlcNAc) transferase that modifies GAPDH. NleB-mediated GAPDH O-GlcNAcylation disrupts the TRAF2-GAPDH interaction to suppress TRAF2 polyubiquitination and NF-κB activation. Eliminating NleB O-GlcNAcylation activity attenuates C. rodentium colonization of mice. These data identify GAPDH as a TRAF2 signaling cofactor and reveal a virulence strategy employed by A/E pathogens to inhibit NF-κB-dependent host innate immune responses.

Subcellular dynamics of multifunctional protein regulation: mechanisms of GAPDH intracellular translocation

Multidimensional proteins such as glyceraldehyde-3-phosphate dehydrogenase (GAPDH) exhibit distinct activities unrelated to their originally identified functions. Apart from glycolysis, GAPDH participates in iron metabolism, membrane trafficking, histone biosynthesis, the maintenance of DNA integrity and receptor mediated cell signaling. Further, multifunctional proteins exhibit distinct changes in their subcellular localization reflecting their new activities. As such, GAPDH is not only a cytosolic protein but is localized in the membrane, the nucleus, polysomes, the ER and the Golgi. In addition, although the initial subcellular localizations of multifunctional proteins may be of significance, dynamic changes in intracellular distribution may occur as a consequence of those new activities. As such, regulatory mechanisms may exist through which cells control multifunctional protein expression as a function of their subcellular localization. The temporal sequence through which subcellular translocation and the acquisition of new GAPDH functions is considered as well as post-translational modification as a basis for its intracellular transport.

Mechanistic insights into the regulation of metabolic enzymes by acetylation

The activity of metabolic enzymes is controlled by three principle levels: the amount of enzyme, the catalytic activity, and the accessibility of substrates. Reversible lysine acetylation is emerging as a major regulatory mechanism in metabolism that is involved in all three levels of controlling metabolic enzymes and is altered frequently in human diseases. Acetylation rivals other common posttranslational modifications in cell regulation not only in the number of substrates it modifies, but also the variety of regulatory mechanisms it facilitates.

Evaluation of different methods of protein extraction and identification of differentially expressed proteins upon ethylene-induced early-ripening in banana peels

BACKGROUND

Banana peels (Musa spp.) are a good example of a plant tissue where protein extraction is challenging due to the abundance of interfering metabolites. Sample preparation is a critical step in proteomic research and is critical for good results.

RESULTS

We sought to evaluate three methods of protein extraction: trichloroacetic acid (TCA)-acetone precipitation, phenol extraction, and TCA precipitation. We found that a modified phenol extraction protocol was the most optimal method. SDS-PAGE and two-dimensional gel electrophoresis (2-DE) demonstrated good protein separation and distinct spots of high quality protein. Approximately 300 and 550 protein spots were detected on 2-DE gels at pH values of 3-10 and 4-7, respectively. Several spots were excised from the 2-DE gels and identified by mass spectrometry.

CONCLUSIONS

The protein spots identified were found to be involved in glycolysis, the tricarboxylic acid cycle, and the biosynthesis of ethylene. Several of the identified proteins may play important roles in banana ripening.

A proteomic view at T cell costimulation

The "two-signal paradigm" in T cell activation predicts that the cooperation of "signal 1," provided by the T cell receptor (TCR) through engagement of major histocompatility complex (MHC)-presented peptide, with "signal 2″ provided by costimulatory molecules, the prototype of which is CD28, is required to induce T cell effector functions. While the individual signalling pathways are well understood, little is known about global changes in the proteome pattern during TCR/CD28-mediated activation. Therefore, comparative 2-DE-based proteome analyses of CD3(+) CD69(-) resting T cells versus cells incubated with (i) the agonistic anti-CD3 antibody OKT3 mimicking signal 1 in absence or presence of IL-2 and/or with (ii) the agonistic antibody 15E8 triggering CD28-mediated signaling were performed. Differentially regulated spots were defined leading to the identification of proteins involved in the regulation of the metabolism, shaping and maintenance of the cytoskeleton and signal transduction. Representative members of the differentially expressed protein families, such as calmodulin (CALM), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), L-lactate dehydrogenase (LDH), Rho GDP-dissociation inhibitor 2 (GDIR2), and platelet basic protein (CXCL7), were independently verified by flow cytometry. Data provide a detailed map of individual protein alterations at the global proteome level in response to TCR/CD28-mediated T cell activation.

Nuclear transport: a switch for the oxidative stress-signaling circuit?

Imbalances in the formation and clearance of reactive oxygen species (ROS) can lead to oxidative stress and subsequent changes that affect all aspects of physiology. To limit and repair the damage generated by ROS, cells have developed a multitude of responses. A hallmark of these responses is the activation of signaling pathways that modulate the function of downstream targets in different cellular locations. To this end, critical steps of the stress response that occur in the nucleus and cytoplasm have to be coordinated, which makes the proper communication between both compartments mandatory. Here, we discuss the interdependence of ROS-mediated signaling and the transport of macromolecules across the nuclear envelope. We highlight examples of oxidant-dependent nuclear trafficking and describe the impact of oxidative stress on the transport apparatus. Our paper concludes by proposing a cellular circuit of ROS-induced signaling, nuclear transport and repair.

Arginine 469 is a pivotal residue for the Hsc70-GlcNAc-binding property

The members of the 70kDa-heat shock proteins (HSP70) family play numerous fundamental functions in the cell such as promoting the assembly of multimeric complexes or helping the correct folding of nascent proteins to take place. In numerous previous studies we demonstrated that Hsp70 and its constitutive isoform Hsc70 are endowed of a GlcNAc-binding activity. The molecular modeling of the substrate binding domain of Hsc70 and in silico docking experiments using Ser/Thr-O-GlcNAc motifs allowed to define the potential carbohydrate-recognition region and to point out the crucial position of Arg469 as an amino-acid directly interacting with the sugar moiety. We cloned a flagged Hsc70 in a pCMV.SPORT6 vector and we showed that the mutation R469A decreased the GlcNAc-binding property of the chaperone of around 70%. This is the first work reporting the localization of the GlcNAc-binding domain of a member of the HSP70 family.

The diverse functions of GAPDH: views from different subcellular compartments

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

Nuclear translocation of glyceraldehyde-3-phosphate dehydrogenase is regulated by acetylation

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is considered a housekeeping glycolitic enzyme that recently has been implicated in cell signaling. Under apoptotic stresses, cells activate nitric oxide formation leading to S-nitrosylation of GAPDH that binds to Siah and translocates to the nucleus. The GAPDH-Siah interaction depends on the integrity of lysine 227 in human GAPDH, being the mutant K227A unable to associate with Siah. As lysine residues are susceptible to be modified by acetylation, we aimed to analyze whether acetylation could mediate transport of GAPDH from cytoplasm to the nucleus. We observed that the acetyltransferase P300/CBP-associated factor (PCAF) interacts with and acetylates GAPDH. We also found that over-expression of PCAF induces the nuclear translocation of GAPDH and that for this translocation its intact acetylase activity is needed. Finally, the knocking down of PCAF reduces nuclear translocation of GAPDH induced by apoptotic stimuli. By spot mapping analysis we first identified Lys 117 and 251 as the putative GAPDH residues that could be acetylated by PCAF. We further demonstrated that both Lys were necessary but not sufficient for nuclear translocation of GAPDH after apoptotic stimulation. Finally, we identified Lys 227 as a third GAPDH residue whose acetylation is needed for its transport from cytoplasm to the nucleus. Thus, results reported here indicate that nuclear translocation of GAPDH is mediated by acetylation of three specific Lys residues (117, 227 and 251 in human cells). Our results also revealed that PCAF participates in the GAPDH acetylation that leads to its translocation to the nucleus.

Novel roles for GAPDH in cell death and carcinogenesis

Growing evidence points to the fact that glucose metabolism has a central role in carcinogenesis. Among the enzymes controlling this energy production pathway, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is of particular interest. Initially identified as a glycolytic enzyme and considered as a housekeeping gene, this enzyme is actually tightly regulated and is involved in numerous cellular functions. Particularly intriguing are recent reports describing GAPDH as a regulator of cell death. However, its role in cell death is unclear; whereas some studies point toward a proapoptotic function, others describe a protective role and suggest its participation in tumor progression. In this study, we highlight recent findings and discuss potential mechanisms through which cells regulate GAPDH to fulfill its diverse functions to influence cell fate.

The hexosamine signaling pathway: O-GlcNAc cycling in feast or famine

The enzymes of O-GlcNAc cycling couple the nutrient-dependent synthesis of UDP-GlcNAc to O-GlcNAc modification of Ser/Thr residues of key nuclear and cytoplasmic targets. This series of reactions culminating in O-GlcNAcylation of targets has been termed the hexosamine signaling pathway (HSP). The evolutionarily ancient enzymes of O-GlcNAc cycling have co-evolved with other signaling effecter molecules; they are recruited to their targets by many of the same mechanisms used to organize canonic kinase-dependent signaling pathways. This co-recruitment of the enzymes of O-GlcNAc cycling drives a binary switch impacting pathways of anabolism and growth (nutrient uptake) and catabolic pathways (nutrient sparing and salvage). The hexosamine signaling pathway (HSP) has thus emerged as a versatile cellular regulator modulating numerous cellular signaling cascades influencing growth, metabolism, cellular stress, circadian rhythm, and host-pathogen interactions. In mammals, the nutrient-sensing HSP has been harnessed to regulate such cell-specific functions as neutrophil migration, and activation of B-cells and T-cells. This review summarizes the diverse approaches being used to examine O-GlcNAc cycling. It will emphasize the impact O-GlcNAcylation has upon signaling pathways that may be become deregulated in diseases of the immune system, diabetes mellitus, cancer, cardiovascular disease, and neurodegenerative diseases.