Multiple functions of Nm23-H1 are regulated by oxido-reduction system

PRUNE1 and NME/NDPK family proteins influence energy metabolism and signaling in cancer metastases

We describe here the molecular basis of the complex formation of PRUNE1 with the tumor metastasis suppressors NME1 and NME2, two isoforms appertaining to the nucleoside diphosphate kinase (NDPK) enzyme family, and how this complex regulates signaling the immune system and energy metabolism, thereby shaping the tumor microenvironment (TME). Disrupting the interaction between NME1/2 and PRUNE1, as suggested, holds the potential to be an excellent therapeutic target for the treatment of cancer and the inhibition of metastasis dissemination. Furthermore, we postulate an interaction and regulation of the other Class I NME proteins, NME3 and NME4 proteins, with PRUNE1 and discuss potential functions. Class I NME1-4 proteins are NTP/NDP transphosphorylases required for balancing the intracellular pools of nucleotide diphosphates and triphosphates. They regulate different cellular functions by interacting with a large variety of other proteins, and in cancer and metastasis processes, they can exert pro- and anti-oncogenic properties depending on the cellular context. In this review, we therefore additionally discuss general aspects of class1 NME and PRUNE1 molecular structures as well as their posttranslational modifications and subcellular localization. The current knowledge on the contributions of PRUNE1 as well as NME proteins to signaling cascades is summarized with a special regard to cancer and metastasis.

A Unique Mode of Coenzyme A Binding to the Nucleotide Binding Pocket of Human Metastasis Suppressor NME1

Coenzyme A (CoA) is a key cellular metabolite which participates in diverse metabolic pathways, regulation of gene expression and the antioxidant defense mechanism. Human NME1 (hNME1), which is a moonlighting protein, was identified as a major CoA-binding protein. Biochemical studies showed that hNME1 is regulated by CoA through both covalent and non-covalent binding, which leads to a decrease in the hNME1 nucleoside diphosphate kinase (NDPK) activity. In this study, we expanded the knowledge on previous findings by focusing on the non-covalent mode of CoA binding to the hNME1. With X-ray crystallography, we solved the CoA bound structure of hNME1 (hNME1-CoA) and determined the stabilization interactions CoA forms within the nucleotide-binding site of hNME1. A hydrophobic patch stabilizing the CoA adenine ring, while salt bridges and hydrogen bonds stabilizing the phosphate groups of CoA were observed. With molecular dynamics studies, we extended our structural analysis by characterizing the hNME1-CoA structure and elucidating possible orientations of the pantetheine tail, which is absent in the X-ray structure due to its flexibility. Crystallographic studies suggested the involvement of arginine 58 and threonine 94 in mediating specific interactions with CoA. Site-directed mutagenesis and CoA-based affinity purifications showed that arginine 58 mutation to glutamate (R58E) and threonine 94 mutation to aspartate (T94D) prevent hNME1 from binding to CoA. Overall, our results reveal a unique mode by which hNME1 binds CoA, which differs significantly from that of ADP binding: the α- and β-phosphates of CoA are oriented away from the nucleotide-binding site, while 3'-phosphate faces catalytic histidine 118 (H118). The interactions formed by the CoA adenine ring and phosphate groups contribute to the specific mode of CoA binding to hNME1.

Regulation of metastasis suppressor NME1 by a key metabolic cofactor coenzyme A

The metastasis suppressor protein NME1 is an evolutionarily conserved and multifunctional enzyme that plays an important role in suppressing the invasion and metastasis of tumour cells. The nucleoside diphosphate kinase (NDPK) activity of NME1 is well recognized in balancing the intracellular pools of nucleotide diphosphates and triphosphates to regulate cytoskeletal rearrangement and cell motility, endocytosis, intracellular trafficking, and metastasis. In addition, NME1 was found to function as a protein-histidine kinase, 3′-5′ exonuclease and geranyl/farnesyl pyrophosphate kinase. These diverse cellular functions are regulated at the level of expression, post-translational modifications, and regulatory interactions. The NDPK activity of NME1 has been shown to be inhibited in vitro and in vivo under oxidative stress, and the inhibitory effect mediated via redox-sensitive cysteine residues. In this study, affinity purification followed by mass spectrometric analysis revealed NME1 to be a major coenzyme A (CoA) binding protein in cultured cells and rat tissues. NME1 is also found covalently modified by CoA (CoAlation) at Cys109 in the CoAlome analysis of HEK293/Pank1β cells treated with the disulfide-stress inducer, diamide. Further analysis showed that recombinant NME1 is efficiently CoAlated in vitro and in cellular response to oxidising agents and metabolic stress. In vitro CoAlation of recombinant wild type NME1, but not the C109A mutant, results in the inhibition of its NDPK activity. Moreover, CoA also functions as a competitive inhibitor of the NME1 NDPK activity by binding non-covalently to the nucleotide binding site. Taken together, our data reveal metastasis suppressor protein NME1 as a novel binding partner of the key metabolic regulator CoA, which inhibits its nucleoside diphosphate kinase activity via non-covalent and covalent interactions.

•

NME1 is a major CoA-binding protein.

•

CoA can bind NME1 through covalent and non-covalent interactions.

•

NME1 CoAlation is induced by oxidative and metabolic stress in mammalian cells.

•

CoA inhibits the NDPK activity of NME1 in vitro.

Activation of Nm23-H1 to suppress breast cancer metastasis via redox regulation

Non-metastatic protein 23 H1 (Nm23-H1), a housekeeping enzyme, is a nucleoside diphosphate kinase-A (NDPK-A). It was the first identified metastasis suppressor protein. Nm23-H1 prolongs disease-free survival and is associated with a good prognosis in breast cancer patients. However, the molecular mechanisms underlying the role of Nm23-H1 in biological processes are still not well understood. This is a review of recent studies focusing on controlling NDPK activity based on the redox regulation of Nm23-H1, structural, and functional changes associated with the oxidation of cysteine residues, and the relationship between NDPK activity and cancer metastasis. Further understanding of the redox regulation of the NDPK function will likely provide a new perspective for developing new strategies for the activation of NDPK-A in suppressing cancer metastasis.

Mutations at the dimer interface and surface residues of Nm23-H1 metastasis suppressor affect its expression and function

The Nm23 metastasis suppressor family is involved in a variety of physiological and pathological processes including cell proliferation, differentiation, tumorigenesis, and metastasis. Given that Nm23 proteins may function as hexamers composed of different members of the family, especially Nm23-H1 and H2 isoforms, it is pertinent to assess the importance of interface and surface residues in defining the functional characteristics of Nm23 proteins. Using molecular modeling to identify clusters of residues that may affect dimer formation and isoform specificity, mutants of Nm23-H1 were constructed and assayed for their ability to modulate cell migration. Mutations of dimer interface residues Gly²² and Lys³⁹ affected the expression level of Nm23-H1, without altering the transcript level. The reduced protein expression was not due to increased protein degradation or altered subcellular distribution. Substitution of the surface residues of Nm23-H1 with Nm23-H2-specific Ser¹³¹ and/or Lys^124/135 affected the electrophoretic mobility of the protein. Moreover, in cell migration assays, several mutants with altered surface residues exhibited impaired ability to suppress the mobility of MDA-MB-231 cells. Collectively, the study suggests that disrupting the dimer interface may affect the expression of Nm23-H1, while the residues at α-helix and β-sheet on the surface of Nm23-H1 may contribute to its metastasis suppressive function.

deMix: Decoding Deuterated Distributions from Heterogeneous Protein States via HDX-MS

Characterization of protein structural changes in response to protein modifications, ligand or chemical binding, or protein-protein interactions is essential for understanding protein function and its regulation. Amide hydrogen/deuterium exchange (HDX) coupled with mass spectrometry (MS) is one of the most favorable tools for characterizing the protein dynamics and changes of protein conformation. However, currently the analysis of HDX-MS data is not up to its full power as it still requires manual validation by mass spectrometry experts. Especially, with the advent of high throughput technologies, the data size grows everyday and an automated tool is essential for the analysis. Here, we introduce a fully automated software, referred to as ‘deMix’, for the HDX-MS data analysis. deMix deals directly with the deuterated isotopic distributions, but not considering their centroid masses and is designed to be robust over random noises. In addition, unlike the existing approaches that can only determine a single state from an isotopic distribution, deMix can also detect a bimodal deuterated distribution, arising from EX1 behavior or heterogeneous peptides in conformational isomer proteins. Furthermore, deMix comes with visualization software to facilitate validation and representation of the analysis results.

Small molecule activator of Nm23/NDPK as an inhibitor of metastasis

Nm23-H1/NDPK-A is a tumor metastasis suppressor having NDP kinase (NDPK) activity. Nm23-H1 is positively associated with prolonged disease-free survival and good prognosis of cancer patients. Approaches to increasing the cellular levels of Nm23-H1 therefore have significance in the therapy of metastatic cancers. We found a small molecule, (±)-trans-3-(3,4-dimethoxyphenyl)-4-[(E)-3,4-dimethoxystyryl]cyclohex-1-ene, that activates Nm23, hereafter called NMac1. NMac1 directly binds to Nm23-H1 and increases its NDPK activity. Employing various NMac1 derivatives and hydrogen/deuterium mass spectrometry (HDX-MS), we identified the pharmacophore and mode of action of NMac1. We found that NMac1 binds to the C-terminal of Nm23-H1 and induces the NDPK activation through its allosteric conformational changes. NMac1-treated MDA-MB-231 breast cancer cells showed dramatic changes in morphology and actin-cytoskeletal organization following inhibition of Rac1 activation. NMac1 also suppressed invasion and migration in vitro, and metastasis in vivo, in a breast cancer mouse model. NMac1 as an activator of NDPK has potential as an anti-metastatic agent.

Stress-Induced Protein S-Glutathionylation and S-Trypanothionylation in African Trypanosomes-A Quantitative Redox Proteome and Thiol Analysis

AIMS

Trypanosomatids have a unique trypanothione-based thiol redox metabolism. The parasite-specific dithiol is synthesized from glutathione and spermidine, with glutathionylspermidine as intermediate catalyzed by trypanothione synthetase. In this study, we address the oxidative stress response of African trypanosomes with special focus on putative protein S-thiolation.

RESULTS

Challenging bloodstream Trypanosoma brucei with diamide, H₂O₂ or hypochlorite results in distinct levels of reversible overall protein S-thiolation. Quantitative proteome analyses reveal 84 proteins oxidized in diamide-stressed parasites. Fourteen of them, including several essential thiol redox proteins and chaperones, are also enriched when glutathione/glutaredoxin serves as a reducing system indicating S-thiolation. In parasites exposed to H₂O₂, other sets of proteins are modified. Only three proteins are S-thiolated under all stress conditions studied in accordance with a highly specific response. H₂O₂ causes primarily the formation of free disulfides. In contrast, in diamide-treated cells, glutathione, glutathionylspermidine, and trypanothione are almost completely protein bound. Remarkably, the total level of trypanothione is decreased, whereas those of glutathione and glutathionylspermidine are increased, indicating partial hydrolysis of protein-bound trypanothione. Depletion of trypanothione synthetase exclusively induces protein S-glutathionylation. Total mass analyses of a recombinant peroxidase treated with T(SH)₂ and either diamide or hydrogen peroxide verify protein S-trypanothionylation as stable modification.

INNOVATION

Our data reveal for the first time that trypanosomes employ protein S-thiolation when exposed to exogenous and endogenous oxidative stresses and trypanothione, despite its dithiol character, forms protein-mixed disulfides.

CONCLUSION

The stress-specific responses shown here emphasize protein S-trypanothionylation and S-glutathionylation as reversible protection mechanism in these parasites. Antioxid. Redox Signal. 27, 517-533.

Affinity purification with metabolomic and proteomic analysis unravels diverse roles of nucleoside diphosphate kinases

Interactions between metabolites and proteins play an integral role in all cellular functions. Here we describe an affinity purification (AP) approach in combination with LC/MS-based metabolomics and proteomics that allows, to our knowledge for the first time, analysis of protein-metabolite and protein-protein interactions simultaneously in plant systems. More specifically, we examined protein and small-molecule partners of the three (of five) nucleoside diphosphate kinases present in the Arabidopsis genome (NDPK1-NDPK3). The bona fide role of NDPKs is the exchange of terminal phosphate groups between nucleoside diphosphates (NDPs) and triphosphates (NTPs). However, other functions have been reported, which probably depend on both the proteins and small molecules specifically interacting with the NDPK. Using our approach we identified 23, 17, and 8 novel protein partners of NDPK1, NDPK2, and NDPK3, respectively, with nucleotide-dependent proteins such as actin and adenosine kinase 2 being enriched. Particularly interesting, however, was the co-elution of glutathione S-transferases (GSTs) and reduced glutathione (GSH) with the affinity-purified NDPK1 complexes. Following up on this finding, we could demonstrate that NDPK1 undergoes glutathionylation, opening a new paradigm of NDPK regulation in plants. The described results extend our knowledge of NDPKs, the key enzymes regulating NDP/NTP homeostasis.

Affinity purification with metabolomic and proteomic analysis unravels diverse roles of nucleoside diphosphate kinases

Interactions between metabolites and proteins play an integral role in all cellular functions. Here we describe an affinity purification (AP) approach in combination with LC/MS-based metabolomics and proteomics that allows, to our knowledge for the first time, analysis of protein-metabolite and protein-protein interactions simultaneously in plant systems. More specifically, we examined protein and small-molecule partners of the three (of five) nucleoside diphosphate kinases present in the Arabidopsis genome (NDPK1-NDPK3). The bona fide role of NDPKs is the exchange of terminal phosphate groups between nucleoside diphosphates (NDPs) and triphosphates (NTPs). However, other functions have been reported, which probably depend on both the proteins and small molecules specifically interacting with the NDPK. Using our approach we identified 23, 17, and 8 novel protein partners of NDPK1, NDPK2, and NDPK3, respectively, with nucleotide-dependent proteins such as actin and adenosine kinase 2 being enriched. Particularly interesting, however, was the co-elution of glutathione S-transferases (GSTs) and reduced glutathione (GSH) with the affinity-purified NDPK1 complexes. Following up on this finding, we could demonstrate that NDPK1 undergoes glutathionylation, opening a new paradigm of NDPK regulation in plants. The described results extend our knowledge of NDPKs, the key enzymes regulating NDP/NTP homeostasis.

Minocycline restores cognitive-relative altered proteins in young bile duct-ligated rat prefrontal cortex

AIMS

Bile duct ligation (BDL) model is used to study hepatic encephalopathy accompanied by cognitive impairment. We employed the proteomic analysis approach to evaluate cognition-related proteins in the prefrontal cortex of young BDL rats and analyzed the effect of minocycline on these proteins and spatial memory.

MAIN METHODS

BDL was induced in young rats at postnatal day 17. Minocycline as a slow-release pellet was implanted into the peritoneum. Morris water maze test and two-dimensional liquid chromatography-tandem mass spectrometry were used to evaluate spatial memory and prefrontal cortex protein expression, respectively. We used 2D/LC-MS/MS to analyze for affected proteins in the prefrontal cortex of young BDL rats. Results were verified with Western blotting, immunohistochemistry, and quantitative real-time PCR. The effect of minocycline in BDL rats was assessed.

KEY FINDINGS

BDL induced spatial deficits, while minocycline rescued it. Collapsin response mediator protein 2 (CRMP2) and manganese-dependent superoxide dismutase (MnSOD) were upregulated and nucleoside diphosphate kinase B (NME2) was downregulated in young BDL rats. BDL rats exhibited decreased levels of brain-derived neurotrophic factor (BDNF) mRNA as compared with those by the control. However, minocycline treatment restored CRMP2 and NME2 protein expression, BDNF mRNA level, and MnSOD activity to control levels.

SIGNIFICANCE

We demonstrated that BDL altered the expression of CRMP2, NME2, MnSOD, and BDNF in the prefrontal cortex of young BDL rats. However, minocycline treatment restored the expression of the affected mediators that are implicated in cognition.

Degradation of Redox-Sensitive Proteins including Peroxiredoxins and DJ-1 is Promoted by Oxidation-induced Conformational Changes and Ubiquitination

Reactive oxygen species (ROS) are key molecules regulating various cellular processes. However, what the cellular targets of ROS are and how their functions are regulated is unclear. This study explored the cellular proteomic changes in response to oxidative stress using H₂O₂ in dose- and recovery time-dependent ways. We found discernible changes in 76 proteins appearing as 103 spots on 2D-PAGE. Of these, Prxs, DJ-1, UCH-L3 and Rla0 are readily oxidized in response to mild H₂O₂ stress, and then degraded and active proteins are newly synthesized during recovery. In studies designed to understand the degradation process, multiple cellular modifications of redox-sensitive proteins were identified by peptide sequencing with nanoUPLC-ESI-q-TOF tandem mass spectrometry and the oxidative structural changes of Prx2 explored employing hydrogen/deuterium exchange-mass spectrometry (HDX-MS). We found that hydrogen/deuterium exchange rate increased in C-terminal region of oxidized Prx2, suggesting the exposure of this region to solvent under oxidation. We also found that Lys191 residue in this exposed C-terminal region of oxidized Prx2 is polyubiquitinated and the ubiquitinated Prx2 is readily degraded in proteasome and autophagy. These findings suggest that oxidation-induced ubiquitination and degradation can be a quality control mechanism of oxidized redox-sensitive proteins including Prxs and DJ-1.

Characterization of Functional Domains in NME1L Regulation of NF-κB Signaling

NME1 is a well-known metastasis suppressor which has been reported to be downregulated in some highly aggressive cancer cells. Although most studies have focused on NME1, the NME1 gene also encodes the protein (NME1L) containing N-terminal 25 extra amino acids by alternative splicing. According to previous studies, NME1L has potent anti-metastatic activity, in comparison with NME1, by interacting with IKKβ and regulating its activity. In the present study, we tried to define the role of the N-terminal 25 amino acids of NME1L in NF-κB activation signaling. Unfortunately, the sequence itself did not interact with IKKβ, suggesting that it may be not enough to constitute the functional structure. Further construction of NME1L fragments and biochemical analysis revealed that N-terminal 84 residues constitute minimal structure for homodimerization, IKKβ interaction and regulation of NF-κB signaling. The inhibitory effect of the fragment on cancer cell migration and NF-κB-stimulated gene expression was equivalent to that of whole NME1L. The data suggest that the N-terminal 84 residues may be a core region for the anti-metastatic activity of NME1L. Based on this result, further structural analysis of the binding between NME1L and IKKβ may help in understanding the anti-metastatic activity of NME1L and provide direction to NME1L and IKKβ-related anti-cancer drug design.

Hydrogen-deuterium exchange mass spectrometry for determining protein structural changes in drug discovery

Protein structures are dynamically changed in response to post-translational modifications, ligand or chemical binding, or protein-protein interactions. Understanding the structural changes that occur in proteins in response to potential candidate drugs is important for predicting the modes of action of drugs and their functions and regulations. Recent advances in hydrogen/deuterium exchange mass spectrometry (HDX-MS) have the potential to offer a tool for obtaining such understanding similarly to other biophysical techniques, such as X-ray crystallography and high resolution NMR. We present here, a review of basic concept and methodology of HDX-MS, how it is being applied for identifying the sites and structural changes in proteins following their interactions with other proteins and small molecules, and the potential of this tool to help in drug discovery.

ROSics: chemistry and proteomics of cysteine modifications in redox biology

Post-translational modifications (PTMs) occurring in proteins determine their functions and regulations. Proteomic tools are available to identify PTMs and have proved invaluable to expanding the inventory of these tools of nature that hold the keys to biological processes. Cysteine (Cys), the least abundant (1-2%) of amino acid residues, are unique in that they play key roles in maintaining stability of protein structure, participating in active sites of enzymes, regulating protein function and binding to metals, among others. Cys residues are major targets of reactive oxygen species (ROS), which are important mediators and modulators of various biological processes. It is therefore necessary to identify the Cys-containing ROS target proteins, as well as the sites and species of their PTMs. Cutting edge proteomic tools which have helped identify the PTMs at reactive Cys residues, have also revealed that Cys residues are modified in numerous ways. These modifications include formation of disulfide, thiosulfinate and thiosulfonate, oxidation to sulfenic, sulfinic, sulfonic acids and thiosulfonic acid, transformation to dehydroalanine (DHA) and serine, palmitoylation and farnesylation, formation of chemical adducts with glutathione, 4-hydroxynonenal and 15-deoxy PGJ2, and various other chemicals. We present here, a review of relevant ROS biology, possible chemical reactions of Cys residues and details of the proteomic strategies employed for rapid, efficient and sensitive identification of diverse and novel PTMs involving reactive Cys residues of redox-sensitive proteins. We propose a new name, "ROSics," for the science which describes the principles of mode of action of ROS at molecular levels.

Sulfhydryl-specific probe for monitoring protein redox sensitivity

Reactive oxygen species (ROS) regulate various biological processes by modifying reactive cysteine residues in the proteins participating in the relevant signaling pathways. Identification of ROS target proteins requires specific reagents that identify ROS-sensitive cysteine sulfhydryls that differ from the known alkylating agents, iodoacetamide and N-ethylmaleimide, which react nonspecifically with oxidized cysteines including sulfenic and sulfinic acid. We designed and synthesized a novel reagent, methyl-3-nitro-4-(piperidin-1-ylsulfonyl)benzoate (NPSB-1), that selectively and specifically reacts with the sulfhydryl of cysteines in model compounds. We validated the specificity of this reagent by allowing it to react with recombinant proteins followed by peptide sequencing with nanoUPLC-ESI-q-TOF tandem mass spectrometry (MS/MS), and mutant studies employed it to identify cellular proteins containing redox-sensitive cysteine residues. We also obtained proteins from cells treated with various concentrations of hydrogen peroxide, labeled them with biotinylated NPSB-1 (NPSB-B), pulled them down with streptavidin beads, and identified them with MS/MS. We grouped these proteins into four families: (1) those having reactive cysteine residues easily oxidized by hydrogen peroxide, (2) those with cysteines reactive only under mild oxidative stress, (3) those with cysteines reactive only after exposure to oxidative stress, and (4) those with cysteines that are reactive regardless of oxidative stress. These results confirm that NPSBs can serve as novel chemical probes for specifically capturing reactive cysteine residues and as powerful tools for measuring their oxidative sensitivity and can help to understand the function of cysteine modifications in ROS-mediated signaling pathways.

Redox regulation of cytoskeletal dynamics during differentiation and de-differentiation

BACKGROUND

The cytoskeleton, unlike the bony vertebrate skeleton or the exoskeleton of invertebrates, is a highly dynamic meshwork of protein filaments that spans through the cytosol of eukaryotic cells. Especially actin filaments and microtubuli do not only provide structure and points of attachments, but they also shape cells, they are the basis for intracellular transport and distribution, all types of cell movement, and--through specific junctions and points of adhesion--join cells together to form tissues, organs, and organisms.

SCOPE OF REVIEW

The fine tuned regulation of cytoskeletal dynamics is thus indispensible for cell differentiation and all developmental processes. Here, we discussed redox signalling mechanisms that control this dynamic remodeling. Foremost, we emphasised recent discoveries that demonstrated reversible thiol and methionyl switches in the regulation of actin dynamics.

MAJOR CONCLUSIONS

Thiol and methionyl switches play an essential role in the regulation of cytoskeletal dynamics.

GENERAL SIGNIFICANCE

The dynamic remodeling of the cytoskeleton is controlled by various redox switches. These mechanisms are indispensible during development and organogenesis and might contribute to numerous pathological conditions. This article is part of a Special Issue entitled Redox regulation of differentiation and de-differentiation.

Purification, characterization and structure of nucleoside diphosphate kinase from Drosophila melanogaster

Nucleoside diphosphate kinase (NDPK) is a ubiquitous enzyme found in all organisms and cell types, which catalyzes the transfer of the phosphoryl group from a nucleoside triphosphate to a nucleoside diphosphate. The gene encoding for NDPK from Drosophila melanogaster was amplified from the genomic DNA. The recombinant NDPK (rNDPK) was overexpressed in Escherichia coli and purified to homogeneity by Ni-NTA agarose affinity chromatography, HiTrap SP HP cation exchange chromatography and HiLoad 16/60 Superdex 200 gel filtration chromatography. The gel filtration chromatography and analytical ultracentrifugation showed that rNDPK was a trimer in solution. The binding affinity of NDPs with rNDPK, measured by isothermal titration calorimetry, indicated that the purines nucleotides show higher binding affinity compared with pyrimidines. The rNDPK had a definite nuclease activity in vitro, which could cleave supercoiled plasmid DNA, but had no effect on dsDNA and ssDNA. Furthermore, the structure for NDPK was determined by using the sitting drop vapor diffusion method. In the final model, the asymmetric unit is made of three molecules, each of which consists of a four-stranded anti-parallel β-sheets and seven α-helices. Sequence alignment and structure comparison illustrated that the simulated nucleotide-binding active site are conserved.

Redox proteomics as biomarker for assessing the biological effects of contaminants in crayfish from Doñana National Park

Despite its environmental relevance and sensitivity, Doñana National Park (DNP) is under high ecological pressure. In crayfish (Procambarus clarkii), the utility of redox proteomics as a novel biomarker was evaluated in the aquatic ecosystems of DNP and its surroundings, where agricultural activity is a serious concern. After fluorescence labeling of reversibly oxidized Cys and 2-DE separation, the total density of proteins with reversibly oxidized thiols was found to be much higher in animals from the Matochal (MAT) and Rocina (ROC) streams, while no difference was found in crayfish from Partido (PAR) stream compared to those from the DNP core at Lucio del Palacio (the negative control). The 2-DE analysis revealed 35 spots with significant differences in thiol oxidation, among which 19 proteins were identified via MALDI-TOF/TOF. While 3 spots, identified as ferritin, showed higher oxidation levels in ROC, other identified proteins were more intense at MAT than at ROC (superoxide dismutase, protein disulfide isomerase and actin) or were overoxidized only in MAT (nucleoside diphosphate kinase, fructose-biphosphate aldolase, fatty acid-binding protein, phosphopyruvate hydratase). For most of the identified proteins, spots corresponding to different Cys oxidized forms were detected, and the native forms, without oxidized thiol groups were also found in some of them. Evidence of reversible oxidation was found for specific Cys residues, including Cys13 in ferritin as well as Cys76 and Cys108 in nucleoside diphosphate kinase. The identified thiol-oxidized proteins provide information about the metabolic pathways and/or physiological processes affected by pollutant-elicited oxidative stress.

N-terminal truncated UCH-L1 prevents Parkinson's disease associated damage

Ubiquitin C-terminal hydrolase-L1 (UCH-L1) has been proposed as one of the Parkinson's disease (PD) related genes, but the possible molecular connection between UCH-L1 and PD is not well understood. In this study, we discovered an N-terminal 11 amino acid truncated variant UCH-L1 that we called NT-UCH-L1, in mouse brain tissue as well as in NCI-H157 lung cancer and SH-SY5Y neuroblastoma cell lines. In vivo experiments and hydrogen-deuterium exchange (HDX) with tandem mass spectrometry (MS) studies showed that NT-UCH-L1 is readily aggregated and degraded, and has more flexible structure than UCH-L1. Post-translational modifications including monoubiquitination and disulfide crosslinking regulate the stability and cellular localization of NT-UCH-L1, as confirmed by mutational and proteomic studies. Stable expression of NT-UCH-L1 decreases cellular ROS levels and protects cells from H₂O₂, rotenone and CCCP-induced cell death. NT-UCH-L1-expressing transgenic mice are less susceptible to degeneration of nigrostriatal dopaminergic neurons seen in the MPTP mouse model of PD, in comparison to control animals. These results suggest that NT-UCH-L1 may have the potential to prevent neural damage in diseases like PD.

Proteome-wide detection and quantitative analysis of irreversible cysteine oxidation using long column UPLC-pSRM

Reactive oxygen species (ROS) play an important role in normal biological functions and pathological processes. ROS is one of the driving forces for oxidizing proteins, especially on cysteine thiols. The labile, transient, and dynamic nature of oxidative modifications poses enormous technical challenges for both accurate modification site determination and quantitation of cysteine thiols. The present study describes a mass spectrometry-based approach that allows effective discovery and quantification of irreversible cysteine modifications. The utilization of a long reverse phase column provides high-resolution chromatography to separate different forms of modified cysteine thiols from protein complexes or cell lysates. This Fourier transform mass spectrometry (FT-MS) approach enabled detection and quantitation of ataxia telangiectasia mutated (ATM) complex cysteine sulfoxidation states using Skyline MS1 filtering. When we applied the long column ultra high pressure liquid chromatography (UPLC)-MS/MS analysis, 61 and 44 peptides from cell lysates and cells were identified with cysteine modifications in response to in vitro and in vivo H2O2 oxidation, respectively. Long column ultra high pressure liquid chromatography pseudo selected reaction monitoring (UPLC-pSRM) was then developed to monitor the oxidative level of cysteine thiols in cell lysate under varying concentrations of H2O2 treatment. From UPLC-pSRM analysis, the dynamic conversion of sulfinic (S-O2H) and sulfonic acid (S-O3H) was observed within nucleoside diphosphate kinase (Nm23-H1) and heat shock 70 kDa protein 8 (Hsc70). These methods are suitable for proteome-wide studies, providing a highly sensitive, straightforward approach to identify proteins containing redox-sensitive cysteine thiols in biological systems.

Structure of Nm23-H1 under oxidative conditions

Nm23-H1/NDPK-A, a tumour metastasis suppressor, is a multifunctional housekeeping enzyme with nucleoside diphosphate kinase activity. Hexameric Nm23-H1 is required for suppression of tumour metastasis and it is dissociated into dimers under oxidative conditions. Here, the crystal structure of oxidized Nm23-H1 is presented. It reveals the formation of an intramolecular disulfide bond between Cys4 and Cys145 that triggers a large conformational change that destabilizes the hexameric state. The dependence of the dissociation dynamics on the H2O2 concentration was determined using hydrogen/deuterium-exchange experiments. The quaternary conformational change provides a suitable environment for the oxidation of Cys109 to sulfonic acid, as demonstrated by peptide sequencing using nanoUPLC-ESI-q-TOF tandem MS. From these and other data, it is proposed that the molecular and cellular functions of Nm23-H1 are regulated by a series of oxidative modifications coupled to its oligomeric states and that the modified cysteines are resolvable by NADPH-dependent reduction systems. These findings broaden the understanding of the complicated enzyme-regulatory mechanisms that operate under oxidative conditions.

Free-radical polymer science structural cancer model: a review

Polymer free-radical lipid alkene chain-growth biological models particularly for hypoxic cellular mitochondrial metabolic waste can be used to better understand abnormal cancer cell morphology and invasive metastasis. Without oxygen as the final electron acceptor for mitochondrial energy synthesis, protons cannot combine to form water and instead mitochondria produce free radicals and acid during hypoxia. Nonuniform bond-length shrinkage of membranes related to erratic free-radical covalent crosslinking can explain cancer-cell pleomorphism with epithelial-mesenchymal transition for irregular membrane borders that "ruffle" and warp over stiff underlying actin fibers. Further, mitochondrial hypoxic conditions produce acid that can cause molecular degradation. Subsequent low pH-activated enzymes then provide paths for invasive cell movement through tissue and eventually blood-born metastasis. Although free-radical crosslinking creates irregularly shaped membranes with structural actin-polymerized fiber extensions as filopodia and lamellipodia, due to rapid cell division the overall cell modulus (approximately stiffness) is lower than normal cells. When combined with low pH-activated enzymes and lower modulus cells, smaller cancer stem cells subsequently have a large advantage to follow molecular destructive pathways and leave the central tumor. In addition, forward structural spike-like lamellipodia protrusions can leverage to force lower-modulus cancer cells through narrow openings. By squeezing and deforming even smaller to allow for easier movement through difficult passageways, cancer cells can travel into adjacent tissues or possibly metastasize through the blood to new tissue.

Comprehensive identification of novel post-translational modifications in cellular peroxiredoxin 6

Peroxiredoxin 6 (PRDX6), a 1-Cys peroxiredoxin, is a bifunctional enzyme acting both as a glutathione peroxidase and a phospholipase A2. However, the underlying mechanisms and their regulation mechanisms are not well understood. Because post-translational modifications (PTMs) have been shown to play important roles in the function of many proteins, we undertook, in this study, to identify the PTMs in PRDX6 utilizing proteomic tools including nanoUPLC-ESI-q-TOF MS/MS employing selectively excluded mass screening analysis (SEMSA) in conjunction with MOD(i) and MODmap algorithm. We chose PRDX6 obtained from liver tissues from two inbred mouse strains, C57BL/6J and C3H/HeJ, which vary in their susceptibility to high-fat diet-induced obesity and atherosclerosis, and a B16F10 melanoma cell line for this study. When PRDX6 protein samples were separated on 2D-PAGE based on pI, several PRDX6 spots appeared. They were purified and the low abundant PTMs in each PRDX6 spot were analyzed. Unexpected mass shifts (Δm = -34, +25, +64, +87, +103, +134, +150, +284 Da) observed at active site cysteine residue (Cys47) were quantified using precursor ion intensities. Mass differences of -34, +25, and +64 Da are presumed to reflect the conversion of cysteine to dehydroalanine, cyano, and Cys-SO(2) -SH, respectively. We also detected acrylamide adducts of sulfenic and sulfinic acids (+87 and +103 Da) as well as unknown modifications (+134, +150, +284 Da). Comprehensive analysis of these PTMs revealed that the PRDX6 exists as a heterogeneous mixture of molecules containing a multitude of PTMs. Several of these modifications occur at cysteine residue in the enzyme active site. Other modifications observed, in PRDX6 from mouse liver tissues included, among others, mono- and dioxidation at Trp and Met, acetylation at Lys, and deamidation at Asn and Gln. Comprehensive identification of the diverse PTMs occurring in this bifunctional PRDX6 enzyme should help understand how PRDX6 plays key roles in oxidative stresses.

SET protein accumulates in HNSCC and contributes to cell survival: antioxidant defense, Akt phosphorylation and AVOs acidification

OBJECTIVES

Determination of the SET protein levels in head and neck squamous cell carcinoma (HNSCC) tissue samples and the SET role in cell survival and response to oxidative stress in HNSCC cell lineages.

MATERIALS AND METHODS

SET protein was analyzed in 372 HNSCC tissue samples by immunohistochemistry using tissue microarray and HNSCC cell lineages. Oxidative stress was induced with the pro-oxidant tert-butylhydroperoxide (50 and 250μM) in the HNSCC HN13 cell lineage either with (siSET) or without (siNC) SET knockdown. Cell viability was evaluated by trypan blue exclusion and annexin V/propidium iodide assays. It was assessed caspase-3 and -9, PARP-1, DNA fragmentation, NM23-H1, SET, Akt and phosphorylated Akt (p-Akt) status. Acidic vesicular organelles (AVOs) were assessed by the acridine orange assay. Glutathione levels and transcripts of antioxidant genes were assayed by fluorometry and real time PCR, respectively.

RESULTS

SET levels were up-regulated in 97% tumor tissue samples and in HNSCC cell lineages. SiSET in HN13 cells (i) promoted cell death but did not induced caspases, PARP-1 cleavage or DNA fragmentation, and (ii) decreased resistance to death induced by oxidative stress, indicating SET involvement through caspase-independent mechanism. The red fluorescence induced by siSET in HN13 cells in the acridine orange assay suggests SET-dependent prevention of AVOs acidification. NM23-H1 protein was restricted to the cytoplasm of siSET/siNC HN13 cells under oxidative stress, in association with decrease of cleaved SET levels. In the presence of oxidative stress, siNC HN13 cells showed lower GSH antioxidant defense (GSH/GSSG ratio) but higher expression of the antioxidant genes PRDX6, SOD2 and TXN compared to siSET HN13 cells. Still under oxidative stress, p-Akt levels were increased in siNC HN13 cells but not in siSET HN13, indicating its involvement in HN13 cell survival. Similar results for the main SET effects were observed in HN12 and CAL 27 cell lineages, except that HN13 cells were more resistant to death.

CONCLUSION

SET is potential (i) marker for HNSCC associated with cancer cell resistance and (ii) new target in cancer therapy.

Energy determinants GAPDH and NDPK act as genetic modifiers for hepatocyte inclusion formation

Differential expression and activity of the cellular energy regulators GAPDH and NDPK underlie reactive oxygen species–induced damage in the mouse liver and may contribute to human liver disease progression.

Genetic factors impact liver injury susceptibility and disease progression. Prominent histological features of some chronic human liver diseases are hepatocyte ballooning and Mallory-Denk bodies. In mice, these features are induced by 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) in a strain-dependent manner, with the C57BL and C3H strains showing high and low susceptibility, respectively. To identify modifiers of DDC-induced liver injury, we compared C57BL and C3H mice using proteomic, biochemical, and cell biological tools. DDC elevated reactive oxygen species (ROS) and oxidative stress enzymes preferentially in C57BL livers and isolated hepatocytes. C57BL livers and hepatocytes also manifested significant down-regulation, aggregation, and nuclear translocation of glyceraldehyde 3-phosphate dehydrogenase (GAPDH). GAPDH knockdown depleted bioenergetic and antioxidant enzymes and elevated hepatocyte ROS, whereas GAPDH overexpression decreased hepatocyte ROS. On the other hand, C3H livers had higher expression and activity of the energy-generating nucleoside-diphosphate kinase (NDPK), and knockdown of hepatocyte NDPK augmented DDC-induced ROS formation. Consistent with these findings, cirrhotic, but not normal, human livers contained GAPDH aggregates and NDPK complexes. We propose that GAPDH and NDPK are genetic modifiers of murine DDC-induced liver injury and potentially human liver disease.

Functional modulation of the metastatic suppressor Nm23-H1 by oncogenic viruses

Evidence over the last two decades from a number of disciplines has solidified some fundamental concepts in metastasis, a major contributor to cancer associated deaths. However, significant advances have been made in controlling this critical cellular process by focusing on targeted therapy. A key set of factors associated with this invasive phenotype is the nm23 family of over twenty metastasis-associated genes. Among the eight known isoforms, Nm23-H1 is the most studied potential anti-metastatic factor associated with human cancers. Importantly, a growing body of work has clearly suggested a critical role for Nm23-H1 in limiting tumor cell motility and progression induced by several tumor viruses, including Epstein-Barr virus (EBV), Kaposi's sarcoma associated herpes virus (KSHV) and human papilloma virus (HPV). A more in depth understanding of the interactions between tumor viruses encoded antigens and Nm23-H1 will facilitate the elucidation of underlying mechanism(s) which contribute to virus-associated cancers. Here, we review recent studies to explore the molecular links between human oncogenic viruses and progression of metastasis, in particular the deregulation of Nm23-H1 mediated suppression.

Proteomic alterations in mouse kidney induced by andrographolide sodium bisulfite

AIM

To identify the key proteins involved in the nephrotoxicity induced by andrographolide sodium bisulfite (ASB).

METHODS

Male ICR mice were intravenously administrated with ASB (1000 or 150 mg·kg⁻¹·d⁻¹) for 7 d. The level of malondialdehyde (MDA) and the specific activity of superoxide dismutase (SOD) in kidneys were measured. The renal homogenates were separated by two-dimensional electrophoresis, and the differential protein spots were identified using a matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF)/TOF mass spectrometry.

RESULTS

The high dose (1000 mg/kg) of ASB significantly increased the MDA content, but decreased the SOD activity as compared to the control mice. The proteomic analysis revealed that 6 proteins were differentially expressed in the high-dose group. Two stress-responsive proteins, ie heat shock cognate 71 kDa protein (HSC70) and peroxiredoxin-6 (PRDX6), were regulated at the expression level. The remaining 4 proteins involving in cellular energy metabolism, including isoforms of methylmalonyl-coenzyme A mutase (MUT), nucleoside diphosphate-linked moiety X motif 19 (Nudix motif19), mitochondrial NADH dehydrogenase 1 alpha subcomplex subunit 10 (NDUFA10) and nucleoside diphosphate kinase B (NDK B), were modified at the post-translational levels.

CONCLUSION

Our findings suggest that the mitochondrion is the primary target of ASB and that ASB-induced nephrotoxicity results from oxidative stress mediated by superoxide produced by complex I.

S-glutathionylation: from molecular mechanisms to health outcomes

Redox homeostasis governs a number of critical cellular processes. In turn, imbalances in pathways that control oxidative and reductive conditions have been linked to a number of human disease pathologies, particularly those associated with aging. Reduced glutathione is the most prevalent biological thiol and plays a crucial role in maintaining a reduced intracellular environment. Exposure to reactive oxygen or nitrogen species is causatively linked to the disease pathologies associated with redox imbalance. In particular, reactive oxygen species can differentially oxidize certain cysteine residues in target proteins and the reversible process of S-glutathionylation may mitigate or mediate the damage. This post-translational modification adds a tripeptide and a net negative charge that can lead to distinct structural and functional changes in the target protein. Because it is reversible, S-glutathionylation has the potential to act as a biological switch and to be integral in a number of critical oxidative signaling events. The present review provides a comprehensive account of how the S-glutathionylation cycle influences protein structure/function and cellular regulatory events, and how these may impact on human diseases. By understanding the components of this cycle, there should be opportunities to intervene in stress- and aging-related pathologies, perhaps through prevention and diagnostic and therapeutic platforms.

Protein histidine [de]phosphorylation in insulin secretion: abnormalities in models of impaired insulin secretion

In the majority of cell types, including the islet β-cell, transduction of extracellular signals involves ligand binding to a receptor, often followed by the activation G proteins and their effector modules. The islet β-cell is unusual in that glucose lacks an extracellular receptor. Instead, events consequent to glucose metabolism promote insulin secretion via the generation of diffusible second messengers and mobilization of calcium. A selective increase in intracellular calcium has been shown to regulate the phosphorylation status key islet proteins thereby facilitating insulin secretion. In addition to classical protein kinases [e.g., protein kinases A and C], recent studies from our laboratory have focused on the expression and function of various forms of NDPK/nm23-like histidine kinases in clonal β-cells, normal rodent, and human islets. Further, we recently reported localization of a cytosolic protein histidine phosphatase [PHP] in INS 832/13 cells, normal rat islets, and human islets. siRNA-mediated knock down of nm23-H1 and PHP in insulin-secreting INS 832/13 cells significantly attenuated glucose-induced insulin secretion. We also observed significant alterations in the expression and function of nm23-H1/PHP in β-cells chronically exposed to elevated levels of glucose and saturated fatty acids, such as palmitate (i.e., glucolipotoxicity). Similar changes were also noted in islets from the Goto-Kakizaki and Zucker Diabetic Fatty rats, two known models for type 2 diabetes. It is concluded that protein histidine phosphorylation-dephosphorylation cycles play novel regulatory roles in G protein-mediated physiological insulin secretion and that abnormalities in this signaling axis lead to impaired insulin secretion in glucolipotoxicity and type 2 diabetes.

Effects of oxidative stress on behavior, physiology, and the redox thiol proteome of Caenorhabditis elegans

Accumulation of reactive oxygen species has been implicated in various diseases and aging. However, the precise physiological effects of accumulating oxidants are still largely undefined. Here, we applied a short-term peroxide stress treatment to young Caenorhabditis elegans and measured behavioral, physiological, and cellular consequences. We discovered that exposure to peroxide stress causes a number of immediate changes, including loss in mobility, decreased growth rate, and decreased cellular adenosine triphosphate levels. Many of these alterations, which are highly reminiscent of changes in aging animals, are reversible, suggesting the presence of effective antioxidant systems in young C. elegans. One of these antioxidant systems involves the highly abundant protein peroxiredoxin 2 (PRDX-2), whose gene deletion causes phenotypes symptomatic of chronic peroxide stress and shortens lifespan. Applying the quantitative redox proteomic technique OxICAT to oxidatively stressed wild-type and prdx-2 deletion worms, we identified oxidation-sensitive cysteines in 40 different proteins, including proteins involved in mobility and feeding (e.g., MYO-2 and LET-75), protein translation and homeostasis (e.g., elongation factor 1 [EFT-1] and heat shock protein 1), and adenosine triphosphate regeneration (e.g., nucleoside diphosphate kinase). The oxidative modification of some of these redox-sensitive cysteines may contribute to the physiological and behavioral changes observed in oxidatively stressed animals.

Novel oxidative modifications in redox-active cysteine residues

Redox-active cysteine, a highly reactive sulfhydryl, is one of the major targets of ROS. Formation of disulfide bonds and other oxidative derivatives of cysteine including sulfenic, sulfinic, and sulfonic acids, regulates the biological function of various proteins. We identified novel low-abundant cysteine modifications in cellular GAPDH purified on 2-dimensional gel electrophoresis (2D-PAGE) by employing selectively excluded mass screening analysis for nano ultraperformance liquid chromatography-electrospray-quadrupole-time of flight tandem mass spectrometry, in conjunction with MODi and MODmap algorithm. We observed unexpected mass shifts (Δm=-16, -34, +64, +87, and +103 Da) at redox-active cysteine residue in cellular GAPDH purified on 2D-PAGE, in oxidized NDP kinase A, peroxiredoxin 6, and in various mitochondrial proteins. Mass differences of -16, -34, and +64 Da are presumed to reflect the conversion of cysteine to serine, dehydroalanine (DHA), and Cys-SO2-SH respectively. To determine the plausible pathways to the formation of these products, we prepared model compounds and examined the hydrolysis and hydration of thiosulfonate (Cys-S-SO2-Cys) either to DHA (Δm=-34 Da) or serine along with Cys-SO2-SH (Δm=+64 Da). We also detected acrylamide adducts of sulfenic and sulfinic acids (+87 and +103 Da). These findings suggest that oxidations take place at redox-active cysteine residues in cellular proteins, with the formation of thiosulfonate, Cys-SO2-SH, and DHA, and conversion of cysteine to serine, in addition to sulfenic, sulfinic and sulfonic acids of reactive cysteine.

A preliminary X-ray study of human nucleoside diphosphate kinase A under oxidative conditions

Nucleoside diphosphate kinase (NDPK) catalyzes transfer of the γ-phosphoryl group from a nucleoside triphosphate (NTP) to a nucleoside diphosphate. The high-energy phosphate for this reaction is usually supplied by ATP. NDPK plays a primary role not only in maintaining cellular pools of all NTPs but also in the regulation of important cellular processes. NDPK-A (or Nm23-H1), one of eight human NDPKs, acts as a metastasis suppressor for some tumour types. A recent study showed that homohexameric human NDPK-A is regulated in response to oxidative stress. The activity of NDPK-A is reduced, with a concomitant increase in the population of dimeric NDPK-A, under oxidative conditions. In this study, human NDPK-A has been crystallized under oxidative conditions and X-ray data have been collected to 2.80 Å resolution using synchrotron radiation. The crystal belonged to the primitive cubic space group P2(1)3, with unit-cell parameters a = b = c = 106.8 Å. There is one NDPK-A dimer in the asymmetric unit. The preliminary electron-density map shows a large conformational change of the C-terminal domain of NDPK-A induced by a novel disulfide bond that is formed under oxidative conditions.

Substrate specificity and nucleotides binding properties of NM23H2/nucleoside diphosphate kinase homolog from Plasmodium falciparum

Nucleoside diphosphate kinases (NDKs) play a key role in maintaining the intracellular energy resources as well as the balance of nucleotide pools. Recently, attention has been directed to NDKs owing to its role in activating various chemotherapeutic agents. The binding affinity of different nucleotides with P. falciparum NDK was varied according to the following order ADP ~ GDP > dGDP > dADP > dTDP > CDP > dCDP > UDP. The binding of purines nucleotides was stronger than pyrimidines. Furthermore, PfNDK showed more preferences to ribonucleotides over deoxyribonucleotides. Pyrimidines showed lower negative free energy compared with that of purines. The interaction of all nucleotides showed favorable enthalpic and entropic terms. However, the enthalpic terms were the main deriving forces for purine nucleotides, while the entropic contributions were the predominant forces for pyrimidines. Interestingly, TDP showed marked affinity and more favorable enthalpic and less entropic contributions. In conclusion, the size of nucleotide was the critical factor in PfNDK ligand affinity.

Nm23-H1 can induce cell cycle arrest and apoptosis in B cells

Nm23-H1 is a well-known tumor metastasis suppressor, which functions as a nucleoside-diphosphate kinase converting nucleoside diphosphates to nucleoside triphosphates with an expense of ATP. It regulates a variety of cellular activities, including proliferation, development, migration and differentiation known to be modulated by a series of complex signaling pathway. Few studies have addressed the mechanistic action of Nm23-H1 in the context of these cellular processes. To determine the downstream pathways modulated by Nm23-H1, we expressed Nm23-H1 in a Burkitt lymphoma derived B-cell line BJAB and performed pathway specific microarray analysis. The genes with significant changes in expression patterns were clustered in groups which are responsible for regulating cell cycle, p53 activities and apoptosis. We found a general reduction of cell cycle regulatory proteins including cyclins and cyclin dependent kinase inhibitors (anti proliferation), and upregulation of apoptotic genes which included caspase 3, 9 and Bcl-x. Nm23-H1 was also found to upregulate p53 and downregulate p21 expression. A number of these genes were validated by real time PCR and results from promoter assays indicated that Nm23-H1 expression downregulated cyclin D1 in a dose responsive manner. Further, we show that Nm23-H1 forms a complex with the cellular transcription factor AP1 to modulate cyclin D1 expression levels. BJAB cells expressing Nm23-H1 showed reduced proliferation rate and were susceptible to increased apoptosis which may in part be due to a direct interaction between Nm23-H1 and p53. These results suggest that Nm23-H1 may have a role in the regulation of cell cycle and apoptosis in human B-cells.