A second form (beta isoform) of nucleoside diphosphate kinase from rat. Isolation and characterization of complementary and genomic DNA and expression

Involvement of nucleotide diphosphate kinase 2 in the reopening of the sensitive period of filial imprinting of domestic chicks (Gallus gallus domesticus)

Filial imprinting is a behavior characterized by the sensitive or critical period restricted to the first few days after hatching. Once the sensitive period is closed, it is widely believed that chicks can never be imprinted under natural conditions. Previously, we showed that the exogenous injection of T3 reopened the sensitive period which was already closed. That study suggested that T3 functioned by way of a rapid non-genomic action; however, the molecular mechanism of how T3 reopens the sensitive period remains unknown. Here, we show that the phosphorylation level of nucleotide diphosphate kinase 2 (NDPK2) was upregulated following T3 injection. Pharmacological deprivation of the kinase activity of NDPK hampered the molecular process prerequisite for the reopening of the sensitive period of filial imprinting. Moreover, it is shown that the kinase activity of NDPK2 participates in the priming process by T3 signaling which endows the potential for learning. Our data indicate that NDPK2 plays a crucial role downstream of T3 action and that its phosphorylation is involved in the non-genomic signaling during imprinting.

Characterization of a novel nm23 gene and its potential roles in gametogenesis in the prawn Macrobrachium rosenbergii (de Man, 1879) (Crustacea: Decapoda)

Nm23 is a family of genes encoding the nucleoside diphosphate (NDP) kinase, which functions in a wide variety of biological processes, including growth, development, differentiation and tumor metastasis. In this study, a novel nm23 gene, designated as Mrnm23, was identified from the freshwater giant prawn Macrobrachium rosenbergii. The full-length cDNA was 776bp in length, encoding for a protein of 176 amino acids with one typical NDP kinase domain that harbored all the crucial residues for nucleotide binding and enzymatic activity. Like human novel nm23-H1B, the putative protein contained a unique 21-amino-acid NH2-terminal extension as compared to human nm23 (nm23-H1) homologs. Further, 3 extra amino acid residues prolonged the COOH-terminus. The Mrnm23 was ubiquitously expressed in all tissues examined, including androgenic gland, gill, heart, liver, muscle, ovary, and testis. In situ hybridization to gonad sections indicated that the Mrnm23 mRNA was localized in the cytoplasm of cup-base of differentiating spermatids, in the spike of the umbrella-shaped spermatozoa and in the cytoplasm of the early previtellogenic oocytes, suggesting that the Mrnm23 has potential roles in spermiogenesis and early differentiation of oocyte.

Activity of nucleoside diphosphate kinase α (NDPK α) capable of binding to outer mitochondrial membrane accounts for less than 10% of total NDPK activity present in cytoplasm of liver cells

During incubation of a constant volume of rat liver cytosol with an increasing quantity of mitochondrial protein in the presence of 3.3 mM MgCl(2), the binding of nucleoside diphosphate kinase (NDPK) from the cytosol to mitochondrial membranes is described by a saturation curve. The highest bound NDPK activity accounts for less than 9% of the added activity. Analysis of the results suggests that only one NDPK isozyme is bound to the membranes. Western blotting showed it to be NDPK α, a homolog of human NDPK-B. Substrates of NDPK, hexokinase, and glycerol kinase, as well as N,N'-dicyclohexylcarbodiimide and palmitate, did not influence the association of NDPK with mitochondrial membranes. We conclude that the sites of NDPK binding to the outer mitochondrial membrane are not identical to those of hexokinase and glycerol kinase.

Molecular adaptability of nucleoside diphosphate kinase b from trypanosomatid parasites: stability, oligomerization and structural determinants of nucleotide binding

Nucleoside diphosphate kinases play a crucial role in the purine-salvage pathway of trypanosomatid protozoa and have been found in the secretome of Leishmania sp., suggesting a function related to host-cell integrity for the benefit of the parasite. Due to their importance for housekeeping functions in the parasite and by prolonging the life of host cells in infection, they become an attractive target for drug discovery and design. In this work, we describe the first structural characterization of nucleoside diphosphate kinases b from trypanosomatid parasites (tNDKbs) providing insights into their oligomerization, stability and structural determinants for nucleotide binding. Crystallographic studies of LmNDKb when complexed with phosphate, AMP and ADP showed that the crucial hydrogen-bonding residues involved in the nucleotide interaction are fully conserved in tNDKbs. Depending on the nature of the ligand, the nucleotide-binding pocket undergoes conformational changes, which leads to different cavity volumes. SAXS experiments showed that tNDKbs, like other eukaryotic NDKs, form a hexamer in solution and their oligomeric state does not rely on the presence of nucleotides or mimetics. Fluorescence-based thermal-shift assays demonstrated slightly higher stability of tNDKbs compared to human NDKb (HsNDKb), which is in agreement with the fact that tNDKbs are secreted and subjected to variations of temperature in the host cells during infection and disease development. Moreover, tNDKbs were stabilized upon nucleotide binding, whereas HsNDKb was not influenced. Contrasts on the surface electrostatic potential around the nucleotide-binding pocket might be a determinant for nucleotide affinity and protein stability differentiation. All these together demonstrated the molecular adaptation of parasite NDKbs in order to exert their biological functions intra-parasite and when secreted by regulating ATP levels of host cells.

Nme protein family evolutionary history, a vertebrate perspective

BACKGROUND

The Nme family, previously known as Nm23 or NDPK, is involved in various molecular processes including tumor metastasis and some members of the family, but not all, exhibit a Nucleoside Diphosphate Kinase (NDPK) activity. Ten genes are known in humans, in which some members have been extensively studied. In non-mammalian species, the Nme protein family has received, in contrast, far less attention. The picture of the vertebrate Nme family remains thus incomplete and orthology relationships with mammalian counterparts were only partially characterized. The present study therefore aimed at characterizing the Nme gene repertoire in vertebrates with special interest for teleosts, and providing a comprehensive overview of the Nme gene family evolutionary history in vertebrates.

RESULTS

In the present study, we present the evolutionary history of the Nme family in vertebrates and characterize the gene family repertoire for the first time in several non-mammalian species. Our observations show that vertebrate Nme genes can be separated in two evolutionary distinct groups. Nme1, Nme2, Nme3, and Nme4 belong to Group I while vertebrate Nme5, Nme6, Nme7, Nme8, and Nme9 belong to Group II. The position of Nme10 is in contrast more debatable due to its very specific evolutionary history. The present study clearly indicates that Nme5, Nme6, Nme7, and Nme8 originate from duplication events that occurred before the chordate radiation. In contrast, Nme genes of the Group I have a very different evolutionary history as our results suggest that they all arise from a common gene present in the chordate ancestor. In addition, expression patterns of all zebrafish nme transcripts were studied in a broad range of tissues by quantitative PCR and discussed in the light of the function of their mammalian counterparts.

CONCLUSION

This work offers an evolutionary framework that will pave the way for future studies on vertebrate Nme proteins and provides a unified vertebrate Nme nomenclature that is consistent with the nomenclature in use in mammals. Based on protein structure and expression data, we also provide new insight into molecular functions of Nme proteins among vertebrates and raise intriguing questions on the roles of Nme proteins in gonads.

Reversibility of nucleoside diphosphate kinase solubilization from the surface of the outer mitochondrial membrane

It was found that in medium with low ionic strength nucleoside diphosphate kinase (NDPK) solubilization from the outer membrane of liver mitochondria could be partially reversed by the addition of 3.3 mM MgCl2. Complete rebinding of the enzyme after the addition of MgCl2 was observed when the mitochondrial washing and storage medium contained leupeptin, an inhibitor of cathepsins. It was demonstrated that leupeptin and another inhibitor of cysteine proteinases, E-64, do not influence the rate of NDPK solubilization as well as its solubilized and membrane-associated activity. We conclude that NDPK becomes sensitive to proteolysis only after its solubilization; proteolysis does not affect the part of the enzyme molecule that is responsible for catalysis. After solubilization of NDPK in the absence of leupeptin, cathepsins damage sites of its binding on the membranes. The rate of the enzyme solubilization is dependent on the pH of the storage medium (pH 6.0-8.0); it decreases with increase in pH. It was shown that in the medium with high ionic strength, MgCl2 does not reverse pH-dependent NDPK solubilization, but solubilization could be reversed by increase in medium pH in the presence of E-64 and BSA. The physiological importance of these results is discussed.

Functional coupling between nucleoside diphosphate kinase of the outer mitochondrial compartment and oxidative phosphorylation

In rat liver mitochondria all nucleoside diphosphate kinase of the outer compartment is associated with the outer surface of the outer membrane (Lipskaya, T. Yu., and Plakida, K. N. (2003) Biochemistry (Moscow), 68, 1136-1144). In the present study, three systems operating as ADP donors for oxidative phosphorylation have been investigated. The outer membrane bound nucleoside diphosphate kinase was the first system tested. Two others employed yeast hexokinase and yeast nucleoside diphosphate kinase. The two enzymes exhibited the same activity but could not bind to mitochondrial membranes. In all three systems, muscle creatine phosphokinase was the external agent competing with the oxidative phosphorylation system for ADP. Determination of mitochondrial respiration rate in the presence of increasing quantities of creatine phosphokinase revealed that at large excess of creatine phosphokinase activity over other kinase activities (of the three systems tested) and oxidative phosphorylation the creatine phosphokinase reaction reached a quasi-equilibrium state. Under these conditions equilibrium concentrations of all creatine phosphokinase substrates were determined and K(eq)app of this reaction was calculated for the system with yeast hexokinase. In samples containing active mitochondrial nucleoside diphosphate kinase the concentrations of ATP, creatine, and phosphocreatine were determined and the quasi-equilibrium concentration of ADP was calculated using the K(eq)app value. At balance of quasi-equilibrium concentrations of ADP and ATP/ADP ratio the mitochondrial respiration rate in the system containing nucleoside diphosphate kinase was 21% of the respiration rate assayed in the absence of creatine phosphokinase; in the system containing yeast hexokinase this parameter was only 7% of the respiration rate assayed in the absence of creatine phosphokinase. Substitution of mitochondrial nucleoside diphosphate kinase with yeast nucleoside diphosphate kinase abolished this difference. It is concluded that oxidative phosphorylation is accompanied by appearance of functional coupling between mitochondrial nucleoside diphosphate kinase and the oxidative phosphorylation system. Possible mechanisms of this coupling are discussed.

Expression patterns of nm23 genes during mouse organogenesis

Nucleoside di-phosphate kinase enzyme (NDPK) isoforms, encoded by the nm23 family of genes, may be involved in various cellular differentiation and proliferation processes. We have therefore analyzed the expression of nm23-M1, -M2, -M3, and -M4 during embryonic mouse development. In situ hybridization data has revealed the differential expression of nm23 mRNA during organogenesis. Whereas nm23-M1 and -M3 are preferentially expressed in the nervous and sensory systems, nm23-M2 mRNA is found ubiquitously. Irrespective of the developmental state studied, nm23-M4 mRNA is only expressed at low levels in a few embryonic organs. In the cerebellum and cerebral cortex, nm23-M1, -M2, and -M3 are present in the neuronal differentiation layer, whereas nm23-M4 mRNA is distributed in the proliferating layer. Thus, nm23 mRNA is differentially expressed, and the diverse NDPK isoforms are sequentially involved in various developmental processes.

12-O-Tetradecanoylphorbol-13-acetate and UV Radiation-induced Nucleoside Diphosphate Protein Kinase B Mediates Neoplastic Transformation of Epidermal Cells

The molecular changes associated with early skin carcinogenesis are largely unknown. We have previously identified 11 genes whose expression was up- or down-regulated by 12-O-tetradecanoylphorbol-13-acetate (TPA) in mouse skin keratinocyte progenitor cells (Wei, S.-J., Trempus, C. S., Cannon, R. E., Bortner, C. D., and Tennant, R. W. (2003) J. Biol. Chem. 278, 1758-1768). Here, we show an induction of a nucleoside diphosphate protein kinase B (NDPK-B) gene in response to TPA or UV radiation (UVR). TPA or UVR significantly induced the expression of NDPK-B both in vivo hyperplastic mouse skin and in vitro mouse JB6 Cl 41-5a epidermal cells. Indeed, this gene was also up-regulated in TPA or UVR-mediated skin tumors including papillomas, spindle cell tumors, and squamous cell carcinomas, relative to adjacent normal skins. Functional studies by constitutive expression of nm23-M2/NDPK-B in TPA susceptible JB6 Cl 41-5a and TPA-resistant JB6 Cl 30-7b preneoplastic epidermal cell lines showed a remarkable gene dosage-dependent increase in foci-forming activity, as well as an enhancement in the efficiency of neoplastic transformation of these cells in soft agar but no effect on proliferation in monolayer cultures. Interestingly, stable transfection of the nm23-M2/NDPK-B del-RGD or G106A mutant gene in JB6 Cl 41-5a cells selectively abrogated NDPK-B-induced cellular transformation, implicating a possible Arg105-Gly106-Asp107 regulatory role in early skin carcinogenesis.

Molecular components of a cell death pathway activated by endoplasmic reticulum stress

Alterations in Ca2+ homeostasis and accumulation of misfolded proteins in the endoplasmic reticulum (ER) cause ER stress that ultimately leads to programmed cell death. Recent studies have shown that ER stress triggers programmed cell death via an alternative intrinsic pathway of apoptosis that, unlike the intrinsic pathway described previously, is independent of Apaf-1 and cytochrome c. In the present work, we have used a set of complementary approaches, including two-dimensional gel electrophoresis coupled with matrix-assisted laser desorption ionization-time-of-flight mass spectrometry and nano-liquid chromatography-electrospray ionization mass spectrometry with tandem mass spectrometry, RNA interference, co-immunoprecipitation, immunodepletion of candidate proteins, and reconstitution studies, to identify mediators of the ER stress-induced cell death pathway. Our data identify two molecules, valosin-containing protein and apoptosis-linked gene-2 (ALG-2), that appear to play a role in mediating ER stress-induced cell death.

New insights into the rat spermatogonial proteome: identification of 156 additional proteins

Despite the essential role played by spermatogonia in testicular function, little is known about these cells. To improve our understanding of their biology, our group recently identified a set of 53 spermatogonial proteins using two-dimensional (2-D) gel electrophoresis and mass spectrometry. To continue this work, we investigated a subset of the spermatogonial proteome using narrow range immobilized pH gradients to favor the detection of less abundant proteins. A 2-D reference map of spermatogonia in the pH range 4-9 was created, and protein entities fractionated in a pH 5-6 2-D gel were further processed for protein identification. A new set of 156 polypeptides was identified by peptide mass fingerprinting and tandem mass spectrometry. These polypeptides corresponded to 102 different proteins, which reflect the complexity of post-translational modifications. Seventy-nine of these proteins were identified for the first time in spermatogonia. All identified proteins were classified into functional groups. This work represents a first step toward the establishment of a systematic spermatogonia protein database.

Characterization of the nm23-M2, nm23-M3 and nm23-M4 mouse genes: comparison with their human orthologs

The nm23 gene family is thought to be involved in physiopathological processes such as growth, differentiation and cancer promotion, progression or metastasis. We report here the mouse nm23-M3 and nm23-M4 complementary DNA sequences and the genomic cloning, characterization and tissue expression pattern of the nm23-M2, nm23-M3 and nm23-M4 genes, in comparison with their human and rat orthologs and with the human nm23-H1 and mouse nm23-M1 genes. The organization and structure of the members of this gene family are remarkably similar in human and rodents. Accordingly, the striking similarities between the human and mouse nm23 genes enable the use of mouse transgenic and knock-out models for studying the role of nucleoside diphosphate kinase isoforms in human physiopathology.

Interactions of phocein with nucleoside-diphosphate kinase, Eps15, and Dynamin I

Phocein, an intracellular protein interacting with striatin, bears a few homologies with the sigma-subunits of clathrin adaptor proteins (Baillat, G., Moqrich, A., Castets, F., Baude, A., Bailly, Y., Benmerah, A., and Monneron, A. (2001) Mol. Biol. Cell 12, 663-673). Using phocein as a bait in a yeast two-hybrid screen, we identified two novel interacting proteins, nucleoside-diphosphate kinase (NDPK) and Eps15. Immunoprecipitation and pull-down experiments involving native and/or recombinant phocein and, respectively, NDPK and Eps15, biochemically validated their interactions. NDPK and Eps15 were recently shown to be functional neighbors of dynamin. Dynamin I is shown here to directly interact with NDPK through its C-terminal proline-rich domain, whereas recombinant phocein associates with native dynamin I. Immunocytochemical studies of rat embryonic hippocampal neurons demonstrated partial co-localization of phocein and dynamin I. Phocein thus appears to be a component of the complexes involved in some steps of the vesicular traffic machinery.

Establishment of rat hepatocellular carcinoma cell lines with differing metastatic potential in nude mice

For better understanding of cancer metastasis, we have established an in vivo model for induction of highly metastatic hepatocellular carcinomas (HCC) in male F344 rats. From 1 tumor, 4 cell lines with differing metastatic potential (C1, C2, C6, C5F) were established by subcloning using the limited-dilution cloning technique. Two other lines, N1 and L2, arose from another primary HCC and a lung metastatic lesion, respectively. Although cell adhesion of each cell line in culture medium was different, tumors developing in the subcutis of nude mice after transplantation were all moderately differentiated HCC with a trabecular pattern. On subcutaneous injection into nude mice, all 6 cell lines proved to be tumorigenic in the injection site and C5F was highly metastatic to the lung. With injection into the tail vein, N1 and L2 formed frequent metastases in the lung as well as in lymph nodes. Using intraperitoneal injection, C1, C6, N1 and L2 showed marked disseminated growth in the abdominal cavity with bloody ascitis. Northern blot analysis revealed expression of known metastasis-related genes, KAI1 and heparanase, to be decreased in C5F, but no differences in expression of nm23-H1 were evident. A point mutation in the GSK-3beta phosphorylation site of the beta-catenin gene was found in L2. These transplantable HCC cell lines that have different metastatic ability should be useful for elucidation of mechanisms of metastasis.

Nucleoside diphosphate kinase beta (Nm23-R1/NDPKbeta) is associated with intermediate filaments and becomes upregulated upon cAMP-induced differentiation of rat C6 glioma

Nucleoside diphosphate kinases (Nm23/NDPK) are enzymes functional in cell proliferation, differentiation, development, tumor progression, and metastasis. Nevertheless, no consensus exists about the molecular mechanism by which Nm23/NDPK isoforms exert their role in these processes. We investigated the expression of the rat Nm23-R1/NDPKbeta and Nm23-R2/NDPKalpha isoforms, homologues of the human Nm23-H1/NDPK A and Nm23-H2/NDPK B proteins, respectively, upon cAMP-induced differentiation of rat C6 glioma cells and demonstrated a differential interaction with intermediate filaments. Semiquantitative RT-PCR, immunoblotting, and flow cytometry showed a constitutive expression of both Nm23 isoforms. After induction of differentiation in C6 cells with cAMP analogs or isoproterenol, a dose-dependent 2- and 2.5-fold upregulation of the Nm23-R1 mRNA and protein, respectively, was observed. In contrast, the expression of Nm23-R2 remained unchanged. Localization of both isoforms with confocal laser scanning microscopy demonstrated a punctate reticular staining pattern for both Nm23 isoforms in the cytosol and processes of the cells which was particularly intense in the perinuclear region. In addition, while Nm23-R2 was colocalized and coimmunoprecipitated with vimentin in nondifferentiated cells, both isoforms were associated with GFAP in differentiated cells. The significance of these findings in relation to a possible function of Nm23 isoforms in cell proliferation, differentiation, and tumor-associated mechanisms is discussed.

Mutational analysis of the NM23.H1 gene in human breast cancer

NM23.H1 is a protein connected with tumor progression. Loss of heterozygosity and reduced expression of the gene have been associated with poor prognosis and increased incidence of metastases in many epithelial tumors. The aim of this study was to detect the presence of NM23.H1 point mutations or small deletions in human breast carcinomas by using the single-strand-conformation polymorphism (SSCP) technique. Mutational analysis was performed on 76 breast tumors, 10 of which had allelic deletion of the gene. The NM23.H1 mRNA content also was evaluated in each sample. Only a C-to-A transversion leading to a stop codon was found in the 5' untranslated region of exon 1. A polymorphic SSCP pattern was identified in exon 1; direct sequencing showed a C-to-T transition 30 nucleotides upstream from the 5' splice site flanking exon 1. None of the tumors analyzed presented both alleles inactivated. Our results suggest that NM23.H1 is rarely inactivated by point mutations.

Organization and expression of mouse nm23-M1 gene. Comparison with nm23-M2 expression

Nm23 is a gene family encoding different isoforms of the nucleotide diphosphate kinase (NDPK), an enzyme involved in the synthesis of nucleoside triphosphates. In the present study, the organization and expression of the nm23-M1 gene encoding the mouse NDPKA isoform are described. This gene is about 10kb long and composed of five exons. The organization and the exon-intron boundaries are strictly conserved as compared to the human and rat related genes. The gene promoter region did not exhibit any consensus TATA box, SP1 binding element or Inr sequence. By contrast, TCF-1/LEF-1 binding elements and Pit-1 consensus sequence were present. Northern blotting and in situ hybridization methods were carried out in adult and 18.5 days post-coitum (dpc) mouse embryo, respectively. They showed tissue-specific expression of nm23-M1 transcripts, despite housekeeping gene promoter features. The strongest signals were detected in the nervous system, sensory organs and embryonic thymus. In contrast nm23-M2 mRNA was shown to be more widely expressed.The relationship between nm23-M1 gene tissue-specific expression and the putative binding element of the promoter region is discussed.

Cleavage of DNA by human NM23-H2/nucleoside diphosphate kinase involves formation of a covalent protein-DNA complex

The NM23 gene family in humans is implicated in differentiation and cancer, but the biochemical mechanisms are unknown. Most NM23 proteins have phosphotransferase (nucleoside diphosphate kinase) activity, and the second human isoform, NM23-H2, also binds to a nuclease-hypersensitive c-MYC promoter element through which it activates c-MYC transcription. It is shown here that this DNA binding can result in double-stranded breaks. The DNA breaks occur within repeated sequence elements in the linear nuclease-hypersensitive duplex and leave staggered ends with 5-nucleotide-long 3'-extensions. The enzyme also cleaves supercoiled plasmid DNA to yield nicked circular and unit length linear products. The cleavage reaction requires only NM23-H2, DNA, Mg(2+), and buffer, occurs in the absence of denaturing conditions, and can be reversed by EDTA. The cleaved DNA strands have free 3'-OH groups, and protein is attached to the 5'-phosphoryl ends. Transfer of (32)P radioactivity from DNA to NM23-H2 has been observed, and a covalent polypeptide-DNA complex has been isolated and identified by Western blotting as NM23-H2. Since covalent protein-DNA complexes are known to serve the role of breaking and rejoining DNA strands, the present findings suggest that NM23-H2 is involved in DNA structural transactions necessary for the activity of the c-MYC promoter.

Nm23-transfected MDA-MB-435 human breast carcinoma cells form tumors with altered phospholipid metabolism and pH: a 31P nuclear magnetic resonance study in vivo and in vitro

Nm23 genes are involved in the control of the metastatic potential of breast carcinoma cells. To understand the impact of nm23 genes on tumor physiology and metabolism, a 31P nuclear magnetic resonance (NMR) spectroscopic study was performed on tumors formed in the mammary fat pad of severe combined immunodeficiency mice by MDA-MB-435 human breast carcinoma cells transfected with cDNA encoding wild type nm23-H1 and nm23-H2 proteins. Tumors formed by MDA-MB-435 cells transfected with vector alone were used as controls. All transgene tumors exhibited significantly higher levels of phosphodiester (PDE) compounds relative to phosphomonoester (PME) compounds in vivo compared with control tumors. Similar differences in PDE and PME also were observed for spectra obtained from cells growing in culture. Intracellular pH was significantly lower and extracellular pH was significantly higher for transgene tumors compared with control tumors. Histologic analysis of lung sections confirmed reductions in incidence, number, and size of metastatic nodules for animals bearing transgene tumors. These results suggest that nm23 genes may affect suppression of metastasis through phospholipid-mediated signaling and cellular pH regulation.

Isolation of cDNA clones encoding two isoforms of nucleoside diphosphate kinase from bovine retina

The cDNA encoding bovine retinal isoforms of nucleoside diphosphate kinase (NDP-kinase, EC 2.7.4.6) has been cloned and sequenced. Based on the partial amino acid sequence of the enzyme determined after trypsin digestion of purified NDP-kinase, primers were synthesized and used to isolate two different cDNA clones encoding the full length of two NDP-kinase isoforms. The nucleotide sequences of these clones contained open reading frames encoding 152-residue polypeptides with calculated molecular masses of 17.262 and 17.299 kDa, similar to that determined for the subunits of purified enzyme (17.5 and 18.5 kDa). The deduced NDP-kinase sequences showed high similarity with the known NDP-kinase sequences from other sources.

Overexpression of nucleoside diphosphate kinases induces neurite outgrowth and their substitution to inactive forms leads to suppression of nerve growth factor- and dibutyryl cyclic AMP-induced effects in PC12D cells

Whether nucleoside diphosphate kinase (NDPK) is involved in neuronal differentiation was investigated with special reference to its enzyme activity. Neurite outgrowth of PC12D cells induced by nerve growth factor or a cyclic AMP analog was suppressed to some extent when inactive NDPKs (the active site histidine 118 was replaced with alanine), not active forms, were transiently overexpressed. This suppression was more definite in their stably expressed clones. NDPKbeta-transfected clones and, to a lesser extent, NDPKalpha-transfected clones, but not inactive NDPK-transfected clones, extended neurites without differentiation inducers. These results imply that NDPKs may play a role by exerting their enzyme activity during differentiation of PC12 cells.

Comparative study of recombinant rat nucleoside diphosphate kinases alpha and beta by intrinsic protein fluorescence

Nucleoside diphosphate (NDP) kinases of mammals are hexamers of two sorts of randomly associated highly homologous subunits of 152 residues each and, therefore exist in cell as NDP kinase isoforms. The catalytic properties and three-dimensional structures of the isoforms are very similar. The physiological meaning of the existence of the isoforms in cells remained unclear, but studying recombinant rat NDP kinases alpha and beta, each containing only one sort of subunits, we discovered that, in contrast to the isoenzyme beta, NDP kinase alpha is able to interact with the complex between bleached rhodopsin and G-protein transducin in retinal rod membranes at lowered pH values (Orlov et al. FEBS Lett. 389, 186-190, 1996). In order to search for possible molecular basis of such differences between these isoenzymes, a detailed comparative study of their intrinsic fluorescence properties in a large range of solvent conditions was performed in this work. The isoenzymes alpha and beta both contain the same three tryptophan (Trp78, 133, Ind 149) and four tyrosine (Tyr 52, 67, 147, and 151) residues per subunit, but exhibit pronounced differences in their fluorescence properties (both in spectral positions and shape and quantum yield values) and behave differently under pH titration. Whereas NDP kinase alpha undergoes spectral changes in the pH range 5-7 with the mid-point at 6.2, no unequivocal indication of a structural change of NDP kinase beta under pH titration from 9 to 5 was obtained. Since the pH dependencies obtained for fluorescence of isoenzyme alpha resembles the dependence of its binding to the rhodopsin-transducin complex it was suggested that the differences between the NDP kinase isoenzymes alpha and beta in the pH-induced behavior, revealed by the fluorescence spectroscopy, and the differences in their ability to interact with rhodopsin-transducin complex may have the same physical nature, that would be a physico-chemical reason of possible functional dissimilarity of NDP kinase isoforms in cell. An additional analysis of three-dimensional structure of homologous NDP kinases revealed that the source of the differences in fluorescence properties and pH-titration behavior between the isoenzymes alpha and beta may be due to the difference in their global electrostatic charges, rather than to any structural differences between them at neutral pH. The unusually high positive electrostatic potential at he deeply buried active site Tyr52 makes possible that it exists in deprotonated tyrosinate form at neutral and moderately acidic solution. Such a possibility may account for rather unusual fluorescence properties of NDP kinase alpha: (i) rather long-wavelength emission of NDP kinase alpha at ca. 340 nm at pH ca. 8 at extremely low accessibility to external quenchers and, possibly, (ii) an unusually high quantum yield value (ca. 0.42).

Cytoskeletal association of the A and B nucleoside diphosphate kinases of interphasic but not mitotic human carcinoma cell lines: specific nuclear localization of the B subunit

The human A and B subunits of nucleoside diphosphate kinase (NDP kinase), encoded by the nm23-H1 and nm23-H2 genes, respectively, associate as homo- or heterohexamers to be catalytically active for the synthesis of nucleoside triphosphates. Despite 88% identity, they appear to possess specific functions. The nm23-H1 gene is implicated in tumor progression and metastasis, and the nm23-H2 gene product is a transcription factor for c-myc. To determine if these distinct functions reflect different subcellular localizations, the distribution of the A and B NDP kinases was analyzed by immunocytofluorescence microscopy in human breast cancer cell lines (MCF-7 and MDA-MB-231) using highly specific polyclonal and monoclonal antibodies. Interphasic cells exhibited a granular and filamentous cytoplasmic staining, particularly intense around nuclei, with both anti-NDP kinase A and B antibodies. The filamentous component observed with either anti-A or anti-B antibodies was altered in parallel to tubulin labeling with compounds interacting with microtubules, such as taxol and colchicine. Confirming published biochemical data, a partial colocalization with the vimentin network was observed in the MDA-231 cell line. A nuclear and nucleolar localization of NDP kinase B was shown by confocal microscopy which was not observed with the A enzyme. In dividing cells, NDP kinase labeling was punctiform and was not colocalized with the mitotic spindle. In conclusion, the A and B NDP kinases are similarly distributed in cytosol, associated partly to microtubules supporting a role in nucleotide channeling. Only the B enzyme is present in nuclei in accord with its role as a DNA binding protein. Their altered localization in dividing cells suggests colocalization with yet unidentified structures which are not intermediate filament aggregates.

Cloning of a second nm23-M1 cDNA: expression in the central nervous system of adult mouse and comparison with nm23-M2 mRNA distribution

Nm23 has been identified as a gene family encoding different isoforms of the nucleoside diphosphate kinase. This protein is a key enzyme in the control of cellular concentrations of nucleoside triphosphates. Moreover, it has been shown to play important roles in various cellular functions such as differentiation and metastasis. In the present study, a second cDNA for nucleoside diphosphate kinase A (Nm23-M1) was isolated from a cDNA library of mouse embryonic stem cells. This clone encodes the same putative 152 aminoacids long protein as an already published cDNA but is longer in both its 5' and 3' untranslated regions. Tissue and cellular distribution of nm23-M1 mRNA was investigated by using Northern blot analysis and in situ hybridization. Nm23-M1 transcripts were found to be widely distributed throughout the mouse central nervous system with prominent expression in several restricted areas. No differences were noticed between the distribution of long and short transcripts. Furthermore, a similar pattern of expression was described in the central nervous system for nm23-M2 mRNA, encoding a second isoform of the nucleoside diphosphate kinase. However, the transcript of this isoform displayed a wider distribution and was expressed in all organs analysed by northern blotting. The possible involvement of nm23-M1 in differentiation of mouse nervous system is further discussed.

Identification of novel mRNA transcripts of the nm23-M1 gene that are modulated during mouse embryo development and are differently expressed in adult murine tissues

The nm23-M1, a putative metastasis-suppressor gene, and its homologs are involved in development and differentiation. We have shown previously that in vitro neuronal cell proliferation and differentiation can be modulated by nm23-M1 expression levels. In the present study, by the yeast two-hybrid system, we have shown that, at the onset of mouse tissue differentiation, the Nm23-M1 protein forms either homodimers, or heterodimers with Nm23-M2. Furthermore, we have isolated two cDNA variants of the nm23-M1 gene in the 3'-untranslated region (UTR). The two variants related to novel mRNA transcripts that are modulated in mouse embryo and are differently expressed in adult murine tissues.

An integrated approach to proteome analysis: identification of proteins associated with cardiac hypertrophy

Hypertrophy of cardiac myocytes is a primary response of the heart to overload, and is an independent predictor of heart failure and death. Distinct cellular phenotypes are associated with hypertrophy resulting from different causes. These phenotypes have been described by others at the molecular level by analysis of gene transcription patterns. An alternative approach is the analysis of large-scale protein expression patterns (the proteome) by two-dimensional polyacrylamide gel electrophoresis. Realization of this goal requires the ability to rigorously analyze complex 2D gel images, efficiently digest individual gel isolated proteins (especially those expressed at low levels), and analyze the resulting peptides with high sensitivity for rapid database searches. We have undertaken to improve the technology and experimental approaches to these challenges in order to effectively study a cell culture model for cardiac hypertrophy. The 2D gel patterns for cell lysates from multiple samples of cardiac myocytes with or without phenylephrine-induced hypertrophy were analyzed and spots which changed in abundance with statistical significance were located. Eleven such spots were identified using improved procedures for in-gel digestion of silver-stained proteins and high-sensitivity mass spectrometry. The incorporation of low levels of sodium dodecyl sulfate into the digestion buffer improved peptide recovery. The combination of matrix-assisted laser desorption mass spectrometry for initial measurements and capillary liquid chromatography-ion trap mass spectrometry for peptide sequence determination yielded efficient protein identification. The integration of 2D gel image analysis and routine identification of proteins present in gels at the subpicomole level represents a general model for proteome studies relating genomic sequence with protein expression patterns.

Three different genes encode NM23/nucleoside diphosphate kinases in Xenopus laevis

Nucleoside diphosphate kinases (NDPKs) catalyse the phosphorylation of nucleoside diphosphates. In mammals, the functional enzyme is a hexamer composed of different amounts of two homologous acidic (A) and basic (B) subunits encoded by separate genes. In prokaryotes and invertebrate eukaryotes, only one cytoplasmic enzyme has been isolated. Other genes encoding chloroplastic and mitochondrial forms as well as related proteins have been cloned. Here, we show that in Xenopus laevis, as in mammals, the cytoplasmic NDPK is encoded by several homologous genes. With Xenopus laevis being a pseudotetraploid species, each monomer is encoded by two genes. The amino acid sequences are very similar, and all the differences concern amino acids located at the outer surface of the hexameric enzyme. The Xenopus genes share 82-87% identity with their human counterparts. Interestingly, in vitro, the Xenopus X1 enzyme binds to a specific nuclease hypersensitive element (NHE) of the human c-myc promoter, as does its human counterpart. X1 also binds to a single-stranded (CT)(n) dinucleotide repeat. The NHE is present in the coding strand of a pyrimidine-rich region of the 3' non-coding sequence of the Xenopus NDPK genes. We propose that NDPK is indeed able to bind to its own mRNA and prevent polyadenylation at the normal position. This could provide an autoregulatory translation mechanism. A phylogenetic tree of the vertebrate NDPK sequences supports the idea that in amphibians, as in mammals, gene duplication has resulted in functional diversification.

Multiple transcripts for rat nucleoside diphosphate kinase alpha isoform are structurally categorized into two groups that exhibit cell-specific expression and distinct translation potential

Rat nucleoside diphosphate (NDP) kinase is composed of two isoforms (alpha and beta) encoded by independent genes. The mRNAs are expressed ubiquitously; however, the level of expression is tissue-dependent and is also up- or down-regulated under certain conditions, including growth stimulation, differentiation, and tumor metastasis. To address the regulatory mechanisms of gene expression for the rat NDP kinase major isoform alpha (an nm23-H2/PuF homologue), we identified the transcription initiation sites in detail by RNase protection and 5'-rapid amplification of DNA ends and located the core promoter region by chloramphenicol acetyltransferase assay. The transcripts, initiated from an extraordinarily wide range of sites, were categorized into two groups; one transcribed from an upstream region was spliced in the untranslated region (group 1), whereas the other initiated in the downstream region was not (group 2). RNase protection demonstrated that the group 1 mRNA was the dominant form present in all tissues except heart and skeletal muscle. In situ hybridization revealed cell-specific expression of these mRNA species. Furthermore, they differed in the translational efficiency (the group 2 alpha > beta > the group 1 alpha). These findings suggest that the regulation of the NDP kinase expression at both transcriptional and posttranscriptional steps could be fundamentally governed by the selection of transcription initiation sites.

Site-directed mutagenesis of nm23-H1. Mutation of proline 96 or serine 120 abrogates its motility inhibitory activity upon transfection into human breast carcinoma cells

We report the first correlation of Nm23 sequence and its tumor metastasis-suppressive capacity using site-directed mutagenesis and an in vitro tumor cell motility assay. MDA-MB-435 human breast carcinoma cells were transfected with a control expression vector (pCMVBamneo), the vector containing the wild type nm23-H1, or the nm23-H1 vector encoding mutations at the following amino acids: serine 44, a phosphorylation site; proline 96, the k-pn mutation in the Drosophila nm23 homolog that causes developmental defects; histidine 118, involved in Nm23's nucleoside diphosphate kinase activity; and serine 120, a site of mutation in human neuroblastomas and phosphorylation. The wild type nm23-H1 transfectants were 44-98% less motile to serum and 86-99% less motile to autotaxin than control vector transfectants. The proline 96 k-pn, serine 120 to glycine, and to a lesser extent serine 120 to alanine mutant nm23-H1-transfected cell lines exhibited motility levels at or above the control transfectants, indicating that these mutations can abrogate the motility-suppressive phenotype of nm23-H1. No effect was observed on cellular proliferation, nor were the serine 44 to alanine nm23-H1 mutant transfectants motile, demonstrating the specificity of the data. The data identify the first structural motifs of nm23-H1 that influence its metastasis suppressive effect and suggest complex biochemical associations or activities in the Nm23 suppressive pathway.

Transducin-mediated, isoform-specific interaction of recombinant rat nucleoside diphosphate kinases with bleached bovine retinal rod outer segment membranes

The properties of the binding of recombinant rat nucleoside diphosphate (NDP) kinase isoforms alpha and beta (NDP kinase alpha and beta, respectively) to bleached bovine retinal rod outer segment (ROS) membranes were investigated. It was found that: (1) both NDP kinase isoforms interacted with ROS membranes in a pH-, cation- and GTPgammaS-dependent manner; (2) the retinal G-protein transducin was an obligatory factor for the interaction; (3) the apparent affinity of NDP kinase alpha for ROS membranes was about 100-fold higher than that of NDP kinase beta; and (4) an alpha-isoform-specific peptide, corresponding to the sequence of the N-terminal third (variable region), had the ability to displace bovine NDP kinase from ROS membranes. The results suggest the possible involvement of NDP kinases in cellular regulation via interaction with G-proteins and provide a structural basis for the possible differential roles of mammalian NDP kinase isoforms in the cell.

Nucleoside diphosphate kinase from Pseudomonas aeruginosa: characterization of the gene and its role in cellular growth and exopolysaccharide alginate synthesis

We report the cloning and determination of the nucleotide sequence of the gene encoding nucleoside diphosphate kinase (Ndk) from Pseudomonas aeruginosa. The amino acid sequence of Ndk was highly homologous with other known bacterial and eukaryotic Ndks (39.9 to 58.3% amino acid identity). We have previously reported that P. aeruginosa strains with mutations in the genes algR2 and algR2 algH produce extremely low levels of Ndk and, as a consequence, are defective in their ability to grow in the presence of Tween 20, a detergent that inhibits a kinase which can substitute for Ndk. Hyperexpression of ndk from the clone pGWS95 in trans in the P. aeruginosa algR2 and algR2 algH double mutant restored Ndk production to levels which equalled or exceeded wild-type levels and enabled these strains to grow in the presence of Tween 20. Hyperexpression of ndk from pGWS95 in the P. aeruginosa algR2 mutant also restored alginate production to levels that were approximately 60% of wild type. Nucleoside diphosphate kinase activity was present in both the cytosolic and membrane-associated fractions of P. aeruginosa. The cytosolic Ndk was non-specific in its transfer activity of the terminal phosphate from ATP to other nucleoside diphosphates. However, the membrane form of Ndk was more active in the transfer of the terminal phosphate from ATP to GDP resulting in the predominant formation of GTP. We report in this work that pyruvate kinase and Ndk form a complex which alters the specificity of Ndk substantially to GTP. The significance of GTP in signal transduction events within the cell and in the production of GDP-mannose, an essential alginate precursor, clearly indicates the importance of Ndk in cellular processes as well as in alginate synthesis.

Cloning and functional analysis of the ndk1 gene encoding nucleoside-diphosphate kinase in Schizosaccharomyces pombe

We cloned the ndk1 gene encoding a subunit of nucleoside-diphosphate kinase (NDK) from Schizosaccharomyces pombe, by using polymerase chain reaction. The deduced ndk1 gene product has 151 amino acid residues and is approximately 60% identical with both Saccharomyces cerevisiae and mammalian NDKs. The gene product exhibited NDK activity and cross-reacted with antibodies raised against rat NDK. Disruption of ndk1 greatly reduced the cellular NDK activity but caused no obvious phenotype in cell growth and sexual development of the organism. However, a mutated allele of ndk1 could inhibit sexual development in a dominant-negative manner. This allele carried a point mutation in cysteine 116, which locates next to the putative active center histidine 117, and the mutant gene product showed no NDK activity. Gene expression inducible in response to mating pheromone signaling was decreased in cells carrying the dominant-negative allele. Cases have been reported in higher eukaryotes in which NDK appears to play a more sophisticated role than a simple catalyst in cell physiology, and the results of this study suggest that S. pombe NDK may also perform such a role in regulation of sexual development in the fission yeast.

Nucleoside diphosphate kinase from the parasitic nematode Brugia malayi

Using a reverse transcription-polymerase chain reaction (RT-PCR) procedure that exploited the presence of a conserved 22-nucleotide spliced leader (SL) sequence that is trans-spliced to the 5' end of nematode transcripts, a novel Brugia malayi (Bm) infective-stage SL cDNA expression library was constructed and characterized. The library was immunoscreened with rabbit anti-infective-stage antibodies (Ab) and an immunodominant clone, BmG4-7, was identified and characterized. BmG4-7 contained a full-length cDNA that had significant sequence similarity to nucleoside diphosphate kinase (NDK)-encoding sequences reported from a number of species, including Drosophila melanogaster and humans. BmNDK was found to be constitutively transcribed during all stages of parasite development. An anti-BmNDK Ab was used to immunostain a Western blot of extracts from adult and larval parasites. The Ab specifically recognized a 17.5-kDa molecule in all of the parasite extracts. Molecular modeling of the BmNDK showed several regions surrounding the conserved catalytic site that may be important in the design of drugs specific for the disruption of NTP synthesis in filarial parasites.

Point mutations in awdKpn which revert the prune/Killer of prune lethal interaction affect conserved residues that are involved in nucleoside diphosphate kinase substrate binding and catalysis

The awd gene of Drosophila melanogaster encodes a nucleoside diphosphate kinase. Killer of prune (Kpn) is a mutation in the awd gene which substitutes Ser for Pro at position 97 and causes dominant lethality in individuals that do not have a functional prune gene. This lethality is not due to an inadequate amount of nucleoside diphosphate (NDP) kinase activity. In order to understand why the prune/Killer of prune combination is lethal, even in the presence of an adequate NDP kinase specific activity level, and to understand the biochemical basis for the conditional lethality of the awdKpn mutation, we generated second site mutations which revert this lethal interaction. All of the 12 revertants we recovered are second site mutations of the awdKpn gene. Three revertants have deletions of the awdKpn protein coding region. Two revertants have substitutions of the initiator methionine and do not accumulate KPN protein. Seven revertants have amino acid substitutions of conserved residues that are likely to affect the active site: five of these have no enzymatic activity and two have a very low level of specific activity. These data suggest that an altered NDP kinase activity is involved in the mechanism underlying the conditional lethality of the awdKpn mutation.

Inhibitory action of nm23 proteins on induction of erythroid differentiation of human leukemia cells

We recently identified a differentiation inhibitory factor (I-factor) in mouse myeloid leukemia M1 cells as a murine homolog of the human nm23-H2 gene product. nm23 genes encode proteins that participate in tumor metastasis regulation and in various fundamental cellular processes, although their mechanisms of action are still unknown. Although all nm23 proteins contain nucleoside diphosphate (NDP) kinase activity, it has not been established that the enzyme activity mediated the various functions of nm23 proteins. In the present experiment, we examined the effect of nm23 proteins on various differentiation induction systems of human leukemic cells including HL-60, U937, HEL/S, KU812F, K562, and HEL cells. Native human erythrocyte NDP kinase protein inhibited the induction of erythroid differentiation of HEL, KU812 and K562 cells, but not the induction of monocytic or granulocytic differentiation of HL-60, U937 and HEL/S cells. The erythroid differentiation of HEL cells was inhibited by recombinant human nm23-H1, -H2, mouse nm23-M1, and -M2 proteins. Moreover, both the mutant nm23-H2His protein and truncated nm23-H2 protein containing N-terminal (1-60) peptide, which do not have NDP kinase activity, also inhibited erythroid differentiation of HEL cells. These results suggest that (1) the differentiation inhibitory activity of I-factor/nm23 protein is not restricted to monocytic differentiation of M1 cells, (2) the inhibitory activity is exhibited without species specificity, and (3) the differentiation inhibitory activity of the nm23/NDP kinase protein is independent of its enzyme activity and requires the presence of N-terminal peptides.

A new function of Nm23/NDP kinase as a differentiation inhibitory factor, which does not require it's kinase activity

We recently identified a differentiation inhibiting factor (I-factor) in mouse myeloid leukemia M1 cells as a murine homolog of nm23-H2/nucleoside diphosphate kinase (NDPK)-B gene product. We examined the I-factor activities of several authentic nm23/NDPK proteins, i.e. recombinant rat NDPK alpha and beta, recombinant mouse nm23-M1 and -M2, and recombinant human nm23-H1 and -H2 containing a mutant nm23-H2His protein lacing NDPK activity. Almost all these nm23/NDPK proteins showed I-factor activity. Moreover, to understand the active domain exhibiting I-factor activity of nm23-H2 protein lacking NDPK activity, we have investigated the I-factor activities of some truncated nm23-H2 proteins. The truncated nm23-H2 protein containing N-terminal peptide 1-60 retained the I-factor activity. These results provide the first evidence for a function of nm23/NDPK as a differentiation inhibiting factor in leukemic cells, that is independent of its NDPK activity and dependent on the presence of N-terminal peptide.

A third type of nucleoside diphosphate kinase from spinach leaves: purification, characterization and amino-acid sequence

A third type of nucleoside diphosphate kinase (NDP kinase III), distinct from the previously described NDP kinases I and II (Nomura et al. (1991) Biochim. Biophys. Acta 1077, 47-55), was purified from spinach leaves to electrophoretic homogeneity. NDP kinase III was judged by SDS-PAGE and by gel filtration to have molecular masses of 17 kDa and 102 kDa, respectively, suggesting that it is composed of six subunits similarly to the other spinach isoforms, NDP kinases I and II. Amino-acid sequence analysis revealed the primary structure of NDP kinase III to be comprised of 153 amino-acid residues, the sequence of which exhibited 61% and 53% homology with those of NDP kinases I and II, respectively. In the reaction catalyzed by the three isoforms, the order of Km as phosphate acceptor was determined as GDP << ADP for NDP kinase III, different from those observed for NDP kinase I (ADP << GDP) and for NDP kinase II (GDP = ADP). These results suggest that the three isoforms may have distinct roles in regulating intracellular 5'-di- and 5'-triphosphonucleotide levels in spinach leaves.

NM23 gene expression correlates with cell growth rate and S-phase

Two human NM23 genes have been identified: NM23.H1 and NM23.H2 coding for the A and B subunit of a nucleoside diphosphate kinase (NDPK), respectively. NM23.H1 gene has been proposed as a suppressor of metastatic ability in tumor cells, NM23.H2 is identical to the c-myc transcription factor, PuF. The NM23 coding sequence is strongly preserved through different species. Indirect evidence of various types has been accumulated and seems to support an implication of NM23 in cell proliferation. This report shows that the NM23 gene expression is strictly related to the growth state of the cells. Two different in vitro systems (human peripheral blood lymphocytes and human breast epithelial cell line MCF-10A) and one in vivo (human primary infiltrating ductal breast carcinomas) system have been investigated. The mRNA is present in PHA-stimulated peripheral blood lymphocytes, whereas it is nearly undetectable in their resting counterparts. The level of the NM23 gene expression parallels the fraction of cells incorporating thymidine (S-phase) in neoplastic mammary tissues. In synchronously cycling MCF-10A cells NM23.H1 mRNA reaches a maximum abundance in the S-phase and is absent or only present at very low levels during G0/G1 phase, whereas NM23.H2 is present in growth-arrested cells but is upregulated following serum growth stimulation.

Nm23/nucleoside diphosphate kinase: toward a structural and biochemical understanding of its biological functions

The nm23 gene, a putative metastasis suppressor gene, was originally identified by its reduced expression in highly metastatic K-1735 murine melanoma cell lines, as compared to related, low metastatic melanoma cell lines. Transfection of nm23 cDNA has been reported to suppress malignant progression in Drosophila and mammalian cells. Highly conserved homologues of nm23 have been found in organisms ranging from the prokaryote Myxococcus xanthus to Drosophila, where the gene is involved in normal development and differentiation. The product of the nm23 gene exhibits a nucleoside diphosphate kinase activity, yet the nucleoside diphosphate kinase activity of Nm23 does not correlate with its apparent biological functions. We review recent cellular, genetic, biochemical and X-ray crystallographic data to formulate and evaluate hypotheses concerning the molecular mechanism of nm23 action.

A copy-number-controlled expression vector for the fission yeast Schizosaccharomyces pombe

A novel expression vector for the fission yeast Schizosaccharomyces pombe carries the neomycin-resistance-encoding gene regulated by the SV40 early promoter, and its copy number is controlled by the level of Geneticin (G418). Foreign gene expression is driven by the human cytomegalovirus (hCMV) promoter which is transcriptionally active in S. pombe. Moreover, the vector expresses foreign genes at high levels, due to the 5'-untranslated region (5'-UTR) containing an A + T-rich sequence of about 50 nucleotides located between the TATA box of the hCMV promoter and the start codon. Recombinant human lipocortin I was produced at levels of up to 50% of the total soluble protein in the presence of 100-200 micrograms/ml of G418 in the media. Southern and Northern blotting showed that this high level of expression was due to an increase in copy number induced by G418, the high transcriptional activity of the hCMV promoter and the high translational efficiency of the 5'-UTR. We modified the vector into an 'ATG vector', named pTL2M, that maintains the 5'-UTR optimized for gene expression and into which any foreign gene, whose exact sequence is known, can be easily inserted.

Increased expression of nucleoside diphosphate kinases/nm23 in human diploid fibroblasts transformed by SV40 large T antigen or 60Co irradiation

When the expression levels of nucleoside diphosphate (NDP) kinase/nm23 were examined in four human normal diploid fibroblast cell lines in comparison with their corresponding immortalized cells transformed by SV40 large T antigen or 60Co irradiation, mRNA levels of the two isoforms (NDP kinase A/nm23-H1, NDP kinase B/nm23-H2) were increased in the immortalized cell lines. The increase was found to be associated with increased translation products. Furthermore, the cell extracts prepared from these immortalized cell lines demonstrated slightly higher enzyme activity than those from their normal counterparts. Neither the growth state nor the in vitro aging largely affected their expression in a normal cell line (TIG-3) examined. The results suggest possible involvement of NDP kinases/nm23 in acquiring an infinite growth property of these cells.

High-level expression of human lipocortin I in the fission yeast Schizosaccharomyces pombe using a novel expression vector

We have developed a novel expression system that allows the fission yeast, Schizosaccharomyces pombe, to be used for the efficient overproduction of heterologous proteins. As an example of the utility of this system, human lipocortin I was expressed to 50 percent of soluble protein, and 150 mg of highly purified material was obtained from 10 grams of wet cell paste. Expression of lipocortin I was driven by the human cytomegalovirus (hCMV) promoter in a vector that also contains a neomycin resistance gene (neo) under the control of the SV40 early promoter, permitting selection for increasing copy-number with increasing concentrations of the antibiotic G418. The purified protein was equivalent to its native counterpart with respect to antigenicity and biochemical properties such as phospholipase A2 inhibition, actin binding and N-terminal acetylation. We have also used this system to produce comparable amounts of other proteins including rat arginase, rat NDP-kinase and human interleukin-6.

Recombinant rat nucleoside diphosphate kinase isoforms (alpha and beta): purification, properties and application to immunological detection of native isoforms in rat tissues

We previously demonstrated that at least two isoforms of nucleoside diphosphate (NDP) kinase, the products of two different tandemly arrayed genes, are present in rat. To understand the physiological role of each isoform, some biochemical properties of recombinant rat NDP kinase alpha- and beta-isoforms, produced in large amount, were studied. cDNAs of the two isoforms were inserted in an expression vector pET3b and recombinant enzymes were overproduced in Escherichia coli. Their primary structures were different from the native enzymes in that the latter suffer from modification of the NH2-terminal end. The two recombinant isoforms were purified from the cell lysate to apparent homogeneity by ammonium sulfate fractionation followed by three successive column chromatographies. Despite their extreme similarity in the amino-acid sequences, the two showed somewhat different enzymic properties in terms of di- and triphosphate nucleotide substrate specificity. They showed similar mobilities on SDS-PAGE as expected from their calculated molecular weight (alpha-isoform, 17,283 versus beta-isoform, 17,192) but differed in isoelectric point (alpha-isoform, pI 6.7; beta-isoform, pI 7.8) and heat stability. Polyclonal antibody which reacted with both isoforms and alpha-isoform-specific monoclonal antibodies differentially recognized native enzymes from rat tissues after the tissue extracts were separated by isoelectric focusing gel electrophoresis under a denaturation condition. The results showed that the alpha-isoform, though its amount varied from one tissue to another, was the major form in rat tissues examined compared with the beta-isoform which was detectable in brain and testis. There was no preference in their subcellular localization when examined with myelin, synaptosomal supernatant and total homogenate fractions from the rat cerebrum and cerebellum.

Adenosine 5'-diphosphate binding and the active site of nucleoside diphosphate kinase

The X-ray structure of nucleoside diphosphate kinase (NDP kinase) from the slime mold Dictyostelium discoideum has been determined to 2.2-A resolution and refined to an R-factor of 0.19 with and without bound ADP-Mg2+. The nucleotide binds near His 122, a residue which becomes phosphorylated during the catalytic cycle. The mode of binding is different from that observed in other phosphokinases, and it involves no glycine-rich sequence. The adenine base makes only nonpolar contacts with the protein. It points outside, explaining the lack of specificity of NDP kinase toward the base. The ribose 2'- and 3'-hydroxyls and the pyrophosphate moiety are H-bonded to polar side chains. A Mg2+ ion bridges the alpha- to the beta-phosphate which approaches the imidazole group of His 122 from the N delta side. The geometry at the active site in the ADP-Mg2+ complex suggests a mechanism for catalysis whereby the gamma-phosphate of a nucleoside triphosphate can be transferred onto His 122 with a minimum of atomic motion.