Nm23/NDP kinases in human male germ cells: role in spermiogenesis and sperm motility?

Nucleoside diphosphate (NDP) kinases, responsible for the synthesis of nucleoside triphosphates and produced by the nm23 genes, are involved in numerous regulatory processes associated with proliferation, development, and differentiation. Their possible role in providing the GTP/ATP required for sperm function is unknown. Testis biopsies and ejaculated sperm were examined by immunohistochemical and immunofluorescence microscopy using specific antibodies raised against Nm23-H5, specifically expressed in testis germinal cells and the ubiquitous NDP kinases A to D. Nm23-H5 was present in sperm extract, together with the ubiquitous A and B NDP kinases (but not the C and D isoforms) as shown by Western blotting. Nm23-H5 was located in the flagella of spermatids and spermatozoa, adjacent to the central pair and outer doublets of axonemal microtubules. High levels of NDP kinases A and B were observed at specific locations in postmeiotic germinal cells. NDP kinase A was transiently located in round spermatid nuclei and became asymmetrically distributed in the cytoplasm at the nuclear basal pole of elongating spermatids. The distribution of NDP kinase B was reminiscent of the microtubular structure of the manchette. In ejaculated spermatozoa, the proteins presented specific locations in the head and flagella. Nm23/NDP kinase isoforms may have specific functions in the phosphotransfer network involved in spermiogenesis and flagellar movement.

A distinct repertoire of autoantibodies in hepatocellular carcinoma identified by proteomic analysis

Chronic infections with hepatitis B (HBV) and hepatitis C (HCV) viruses are major risk factors for hepatocellular carcinoma (HCC). We have utilized a proteomic approach to determine whether a distinct repertoire of autoantibodies can be identified in HCC. Sera from 37 patients with HCC and 31 subjects chronically infected with HBV or HCV without HCC were investigated. Sera from 116 patients with other cancers, three patients with systemic lupus erythematosus, and 24 healthy subjects were utilized as controls. We report the identification of eight proteins, for each of which autoantibodies were detected in sera from more than 10% of patients with HCC but not in sera from healthy individuals (p < 0.05). Autoantibodies to four of these proteins were detected at a comparable frequency in sera from patients with chronic hepatitis. The other four proteins, which consisted of calreticulin isoforms, cytokeratin 8, nucleoside diphosphate kinase A, and F(1)-ATP synthase beta-subunit, induced autoantibodies among patients with HCC, independently of their HBV/HCV status. Calreticulin, and a novel truncated form of calreticulin (Crt32) we have identified, most commonly elicited autoantibodies among patients with HCC (27%). We conclude that a distinct repertoire of autoantibodies is associated with HCC that may have utility in early diagnosis of HCC among high risk subjects with chronic hepatitis.

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.

Expression of nm23-H1 in prostatic intraepithelial neoplasia and adenocarcinoma

The product of the nm23-H1 gene has been reported to be related to the metastatic potential of several tumors. Although several studies have characterized the expression of the nm23-H1 gene product in prostatic adenocarcinoma, little is known of the expression of this protein in prostatic intraepithelial neoplasia (PIN), a putative precancerous lesion. The authors used immunohistochemistry to examine the expression of the nm23-H1 protein in PIN as well as benign and malignant prostatic tissue. A monoclonal antibody to nm23-H1 (Novocastra, Newcastle upon Tyne, UK, clone 37.6) and a biotin/strepavidin detection system were used for antigen localization. Weak to moderate immunostaining was consistently detected in the benign glandular epithelium of 28 radical prostatectomy specimens. In contrast, strong immunostaining was detected in the glandular epithelium in PIN lesions of 19 radical prostatectomy specimens examined. Strong immunostaining was also frequently detected in the malignant cells of 39 localized prostatic adenocarcinomas, as well as 7 metastatic lesions. These findings show a phenotypic similarity of PIN to prostatic adenocarcinoma with respect to nm23-H1 expression. Furthermore, strong expression of nm23-H1 likely represents an early event in the development of prostatic adenocarcinoma.

Phytochrome regulates phosphorylation of a protein with characteristics of a nucleoside diphosphate kinase in the crude membrane fraction from stem sections of etiolated pea seedlings

The molecular mechanism of light signal perception via phytochrome was analysed using the third internodes of etiolated pea seedlings irradiated with red or red followed by far-red light. A crude membrane fraction prepared from the tissue was labelled by [gamma-32P]ATP at 4 x 10(-8) M for 15 s at 0 degree C, and the proteins were separated by two-dimensional gel electrophoresis. The phosphorylation of a protein with a molecular mass of about 15 kDa in the crude membrane fraction increased with an increase in the intensity of red light irradiation (10, 50 and 100 mumol m-2 s-1) for 20 s. Successive irradiation with red light (100 mumol m-2 s-1 for 20 s) and subsequent irradiation with far-red light reduced the phosphorylation of the protein, depending on the intensity of the far-red light (from 0.1 to 8 mumol m-2 s-1 for 180 s). A plasma membrane purified from the crude membrane fraction from red light irradiated tissue showed a rapid phosphorylation of the 15 kDa protein by 4 x 10(-8) M [gamma-32P]ATP at 0 degree C for 7 s, and subsequent addition of ATP, GTP, ADP or GDP at 10(-5) or 10(-6) M efficiently removed the phosphoryl group of the 15 kDa protein. The 15 kDa protein was autophosphorylated in the gel following separation by sodium dodecylsulphate (SDS) polyacrylamide gel electrophoresis. The partially purified 15 kDa protein included nucleoside diphosphate kinase (NDP kinase) activity, as well as cross-reactivity with an antibody specific to rat NDP kinase as assayed by immunostaining and crossreactivity with an antibody specific to ricet NDP kinase as assayed by immunoprecipitation.

Neutralizing antibodies to nucleoside diphosphate kinase inhibit the enzyme in vitro and in vivo: evidence for two distinct mechanisms of activation of atrial currents by ATPgammaS

Nucleoside diphosphate kinase (NDPK) participates in multiple cellular functions, yet the molecular mechanisms of its involvement are often unknown, given that there are no specific inhibitors for the enzyme from vertebrates. We developed antibodies against NDPK by immunization of rabbits with the enzyme from bullfrog skeletal muscle. The antibodies specifically recognized the enzyme from frog tissues, and cross-reacted with NDPK from Xenopus. In contrast to mammalian NDPK, the amphibian enzyme elicited antibodies that inhibit potently its catalytic function. We utilized the inhibitory properties of these immunoglobulins to examine the role of NDPK on the ATPgammaS-induced stimulation of Ca2+ and K+ currents of cardiac myocytes. Injection of NDPK-neutralizing Fab fragments into atrial cells reduced considerably the effect of ATPgammaS on muscarinic K+ currents, but not on Ca2+ currents. Therefore, ATPgammaS increases calcium and potassium currents of atrial cells by two distinct mechanisms. NDPK is essential for the conversion of ATPgammaS into GTPgammaS which leads to muscarinic K+ channel activation but not for the stimulation of Ca2+ currents by ATPgammaS. The results demonstrate that antibodies to frog NDPK block the activity of the enzyme in vivo and in vitro, and can be used to determine the relevance of NDPK and its catalytic activity to the function of vertebrate cells.

Purification and characterization of a soluble nucleoside diphosphate kinase in Trypanosoma cruzi

A soluble nucleoside diphosphate kinase (NDP kinase) was purified and characterized in epimastigote forms of Trypanosoma cruzi. The enzyme was purified by affinity chromatography on Blue-agarose and Q-Sepharose columns and by FPLC on a Superose 12 column. A membrane-associated NDP kinase was identified which accounts for 30% of total enzymatic activity. Western blot analysis of the soluble NDP kinase revealed a 16.5-kDa monomer recognized by polyclonal antibodies to NDP kinase from Dictyostelium discoideum, Candida albicans or human. Most of the T. cruzi NDP kinase is found in the cell as a hexamer composed of 16.5-kDa monomers. The Km values of the enzyme for ATP, GDP and dTDP were 0.2 +/- 0.008 mM, 0.125 +/- 0.012 mM and 0.4 +/- 0.009 mM, respectively. The parasite enzyme was stable, remained active at 65 degrees C and was found to tolerate up to 2.5 M urea. The 16.5-kDa subunit was phosphorylated with [gamma-32P]ATP or thiophosphorylated with [35S]GTP gamma S. The incubation of the 32P-labelled phosphoenzyme with unlabelled nucleoside 5'-diphosphates resulted in the formation of 32P-labelled nucleoside 5'-triphosphates without strict base specificity, indicating that the reaction mechanism of the T. cruzi enzyme is the same as reported for other NDP kinases. When the phosphoenzyme was incubated with a mixture of nucleoside 5'-diphosphates, GTP was preferentially formed.

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.

Microinjection of an nm23 specific antibody inhibits cell division in rat embryo fibroblasts

Expression of the nm23/NDP-K gene correlates with reduced metastasis in some tumors and with increased proliferation in both nontransformed and transformed cells in culture. Decreased nm23/NDP-K expression results in mitotic arrest in neuroblasts of developing Drosophila. In order to better understand the biological role(s) of nm23 in non-transformed cells, an nm23-specific antibody was introduced into rat embryo fibroblasts and effects on DNA synthesis and cell cycle progression were analyzed. Microinjection of the nm23 antibody inhibited cell division with no apparent effect on DNA synthesis. Control experiments revealed that the survival of cells injected with the nm23 antibody was similar to that of control antibody injected cells in the absence of cell division. These results suggest that in mammalian fibroblasts, as in Drosophila, nm23 expression may be necessary for progression through the cell cycle.

Expression of nm23/NDP kinase proteins on the cell surface

We determined whether proteins encoded by the nm23/nucleoside diphosphate (NDP) kinase gene, a potential metastasis-suppressor gene, are expressed on the cell surface. Monoclonal antibodies (mAb) specific for nm23-H1 or H2 proteins were prepared using the corresponding fusion proteins with glutathione S-transferase (GST) as immunogens. mAb H1-229 was specifically reactive with nm23-H1 protein, whereas mAb H2-439 was specific for nm23-H2 protein in immunoprecipitation and immunoblotting. mAb H1-229 was reactive with most human hematopoietic and some non-hematopoietic cell lines in flow cytometry. On the other hand, mAb H2-439 was reactive with only a limited number of cell lines. Based upon the surface expression of nm23/NDP kinase, cells were classified as nm23-H1+H2-, nm23-H1+H2+ or nm23-H1-H2-. No cell lines with nm23-H1-H2+ were found among those examined. The specificity of flow cytometry analysis was confirmed in the murine myeloma line NS-1 transfected with either the nm23-H1 or H2 genes. Both mAbs were reactive only to NS-1 transfected with the corresponding nm23 genes. Immunoprecipitation and SDS-PAGE analysis identified 20.5- and 18-kDa proteins with mAb H1-229 or H2-439, respectively, in cellular extracts of 125I-surface labeled NS-1 transfected with the corresponding genes. The presence of nm23/NDP kinase on the cell surface indicates an extracellular role for these proteins in addition to their reported intracellular functions.

Molecular cloning and functional expression of the second mouse nm23/NDP kinase gene, nm23-M2

A new murine cDNA of nm23/NDP kinase was isolated. A RT-PCR product was obtained from the normal mouse liver mRNA with primers designed for the human nm23-H2 gene. The product was used as a probe to screen a cDNA library from the murine melanoma cell line, B16, and two clones containing the entire open reading frame were obtained. It was predicted that the DNA sequence encoded 152 amino acids which was 98% identical to the nm23-H2 protein. The entire nm23-M1 and -M2 gene-coding regions were translated as fusion proteins with a glutathione S-transferase. These fusion proteins displayed NDP kinase activities.

Proliferation-related expression of p19/nm23 nucleoside diphosphate kinase

High level expression of the nm23-H1 gene, which encodes for a nucleoside diphosphate kinase, has been found to correlate with diminished metastasis in some tumors but not in others. We have previously identified the protein product of the nm23-H1 gene in two-dimensional electrophoretic gels and have designated it p19/nm23. In neuroblastoma, higher levels of p19/nm23, which are associated with amplification of the N-myc oncogene, large tumor mass, and metastasis, were observed in advanced stage tumors compared with limited stage disease. Because of the variable expression of nm23-H1 in different tumors, we have investigated the relationship between amounts of the protein and cell proliferation. The levels of p19/nm23 were compared between resting and mitotically stimulated normal human PBLs and in leukemia cells. The amount of p19/nm23 increased in normal lymphocytes in response to mitotic stimulation and paralleled the increase in DNA synthesis. In leukemia cells obtained from patients with different subtypes of acute leukemia, p19/nm23 levels were also increased relative to resting normal lymphocytes. Treatment of mitotically stimulated lymphocytes with cyclosporin, which inhibits proliferation, blocked the increase in p19/nm23; treatment of the leukemia cell line HL-60 with dimethylsulfoxide, which induces terminal differentiation, resulted in diminished levels of p19/nm23. Our data therefore provide evidence that nm23-H1 expression is related to cell proliferative activity.

Nucleoside diphosphate kinase from human erythrocytes. Structural characterization of the two polypeptide chains responsible for heterogeneity of the hexameric enzyme

Human erythrocyte nucleoside-diphosphate kinase (NDP kinase) is a hexameric enzyme consisting of two kinds of polypeptide chains, A and B. By random association (A6, A5B...AB5, B6) these polypeptides form isoenzymes differing in their isoelectric point. Chains A and B of NDP kinase were purified by ion-exchange chromatography under denaturing conditions. Upon mixing and renaturation, the isozymic pattern of NDP kinase obtained by conventional methods was restored. Antibodies raised against purified chains showed significant cross-reactivity, both in immunoblot experiments and activity inhibition studies. Sequence determination showed that both chains consisted of 152 amino acid residues corresponding to Mr or 17,143 (chain A) and 17,294 (chain B), respectively. There was high homology between the two sequences (88% identity). The phosphorylation site on the enzyme is located at His-118. Chain A was identical with human Nm23 protein, which has been reported as a potential suppressor protein in tumor metastasis and chain B was identical with Nm23-H2 protein.

A Drosophila gene that is homologous to a mammalian gene associated with tumor metastasis codes for a nucleoside diphosphate kinase

The product of the abnormal wing discs (awd) gene of Drosophila is 78% identical to the product of the nm23 gene of mammals, which is differentially expressed in certain metastatic tumors. We present evidence that the awd gene codes for a nucleoside diphosphate kinase (NDP kinase) and that this Awd/NDP kinase is microtubule associated. Neuroblasts in Drosophila larvae homozygous for a null mutation in the awd gene are arrested in metaphase, indicating that microtubule-associated Awd/NDP kinase plays a critical role in spindle microtubule polymerization.

Effects of chemical modification of lysine, tyrosine and tryptophan residues in pea seed nucleoside diphosphate kinase and inhibition of the enzyme with antibodies

Pea seed nucleoside diphosphate kinase (NDP kinase) is an oligomeric, tetrameric enzyme which has been shown to be phosphorylated by its substrate ATP, presumably forming an 1-phosphohistidine at its active site. Recently has also a reactive lysine residue been demonstrated at the active site. In the present investigation nitration of a tyrosine residue is shown to inactivate the enzyme. There seems only to be a slight structural change in the enzyme on modification of these essential lysine and tyrosine residues, since double diffusion experiments with an inhibitory antiserum shows no difference in reactivity between the native enzyme and the modified enzyme. It is also found that modification of all tryptophan residues in the enzyme reduces the enzyme activity only to a small degree, indication that these hydrophobic amino acid residues are not directly involved in the catalytic process.