Differential expression of nm23 genes in adult mouse dorsal root ganglia

The mitochondrial nucleoside diphosphate kinase (NDPK-D/NME4), a moonlighting protein for cell homeostasis

Mitochondrial nucleoside diphosphate kinase (NDPK-D; synonyms: NME4, NM23-H4) represents the major mitochondrial NDP kinase. The homohexameric complex emerged as a protein with multiple functions in bioenergetics and phospholipid signaling. It occurs at different but precise mitochondrial locations and can affect among other mitochondrial shapes and dynamics, as well as the specific elimination of defective mitochondria or cells via mitophagy or apoptosis. With these various functions in cell homeostasis, NDPK-D/NME4 adds to the group of so-called moonlighting (or gene sharing) proteins.

Regulation of heterotrimeric G-protein signaling by NDPK/NME proteins and caveolins: an update

Heterotrimeric G proteins are pivotal mediators of cellular signal transduction in eukaryotic cells and abnormal G-protein signaling plays an important role in numerous diseases. During the last two decades it has become evident that the activation status of heterotrimeric G proteins is both highly localized and strongly regulated by a number of factors, including a receptor-independent activation pathway of heterotrimeric G proteins that does not involve the classical GDP/GTP exchange and relies on nucleoside diphosphate kinases (NDPKs). NDPKs are NTP/NDP transphosphorylases encoded by the nme/nm23 genes that are involved in a variety of cellular events such as proliferation, migration, and apoptosis. They therefore contribute, for example, to tumor metastasis, angiogenesis, retinopathy, and heart failure. Interestingly, NDPKs are translocated and/or upregulated in human heart failure. Here we describe recent advances in the current understanding of NDPK functions and how they have an impact on local regulation of G-protein signaling.

Nucleoside Diphosphate Kinase-C Suppresses cAMP Formation in Human Heart Failure

BACKGROUND

Chronic heart failure (HF) is associated with altered signal transduction via β-adrenoceptors and G proteins and with reduced cAMP formation. Nucleoside diphosphate kinases (NDPKs) are enriched at the plasma membrane of patients with end-stage HF, but the functional consequences of this are largely unknown, particularly for NDPK-C. Here, we investigated the potential role of NDPK-C in cardiac cAMP formation and contractility.

METHODS

Real-time polymerase chain reaction, (far) Western blot, immunoprecipitation, and immunocytochemistry were used to study the expression, interaction with G proteins, and localization of NDPKs. cAMP levels were determined with immunoassays or fluorescent resonance energy transfer, and contractility was determined in cardiomyocytes (cell shortening) and in vivo (fractional shortening).

RESULTS

NDPK-C was essential for the formation of an NDPK-B/G protein complex. Protein and mRNA levels of NDPK-C were upregulated in end-stage human HF, in rats after long-term isoprenaline stimulation through osmotic minipumps, and after incubation of rat neonatal cardiomyocytes with isoprenaline. Isoprenaline also promoted translocation of NDPK-C to the plasma membrane. Overexpression of NDPK-C in cardiomyocytes increased cAMP levels and sensitized cardiomyocytes to isoprenaline-induced augmentation of contractility, whereas NDPK-C knockdown decreased cAMP levels. In vivo, depletion of NDPK-C in zebrafish embryos caused cardiac edema and ventricular dysfunction. NDPK-B knockout mice had unaltered NDPK-C expression but showed contractile dysfunction and exacerbated cardiac remodeling during long-term isoprenaline stimulation. In human end-stage HF, the complex formation between NDPK-C and Gα_i2 was increased whereas the NDPK-C/Gα_s interaction was decreased, producing a switch that may contribute to an NDPK-C-dependent cAMP reduction in HF.

CONCLUSIONS

Our findings identify NDPK-C as an essential requirement for both the interaction between NDPK isoforms and between NDPK isoforms and G proteins. NDPK-C is a novel critical regulator of β-adrenoceptor/cAMP signaling and cardiac contractility. By switching from Gα_s to Gα_i2 activation, NDPK-C may contribute to lower cAMP levels and the related contractile dysfunction in HF.

Nucleoside diphosphate kinase B-activated intermediate conductance potassium channels are critical for neointima formation in mouse carotid arteries

OBJECTIVE

Vascular smooth muscle cells (VSMC) proliferation is a hallmark of atherosclerosis and vascular restenosis. The intermediate conductance Ca(2+)-activated K(+) (SK4) channel is required for pathological VSMC proliferation. In T lymphocytes, nucleoside diphosphate kinase B (NDPKB) has been implicated in SK4 channel activation. We thus investigated the role of NDPKB in the regulation of SK4 currents (ISK4) in proliferating VSMC and neointima formation.

APPROACH AND RESULTS

Function and expression of SK4 channels in VSMC from injured mouse carotid arteries were assessed by patch-clamping and real-time polymerase chain reaction. ISK4 was detectable in VSMC from injured but not from uninjured arteries correlating with the occurrence of the proliferative phenotype. Direct application of NDPKB to the membrane of inside-out patches increased ISK4, whereas NDPKB did not alter currents in VSMC obtained from injured vessels of SK4-deficient mice. The NDPKB-induced increase in ISK4 was prevented by protein histidine phosphatase 1, but not an inactive protein histidine phosphatase 1 mutant indicating that ISK4 is regulated via histidine phosphorylation in proliferating VSMC; moreover, genetic NDPKB ablation reduced ISK4 by 50% suggesting a constitutive activation of ISK4 in proliferating VSMC. In line, neointima formation after wire injury of the carotid artery was substantially reduced in mice deficient in SK4 channels or NDPKB.

CONCLUSIONS

NDPKB to SK4 signaling is required for neointima formation. Constitutive activation of SK4 by NDPKB in proliferating VSMC suggests that targeting this interaction via, for example, activation of protein histidine phosphatase 1 may provide clinically meaningful effects in vasculoproliferative diseases such as atherosclerosis and post angioplasty restenosis.

The many isoforms of human adenylate kinases

Adenine nucleotides are involved in a variety of cellular metabolic processes, including nucleic acid synthesis and repair, formation of coenzymes, energy transfer, cell and ciliary motility, hormone secretion, gene expression regulation and ion-channel control. Adenylate kinases are abundant phosphotransferases that catalyze the interconversion of adenine nucleotides and thus regulate the adenine nucleotide ratios in different intracellular compartments. Nine different adenylate kinase isoenzymes have been identified and characterized so far in human tissues, named AK1 to AK9 according to their order of discovery. Adenylate kinases differ in molecular weight, tissue distribution, subcellular localization, substrate and phosphate donor specificity and kinetic properties. The preferred substrate and phosphate donor of all adenylate kinases are AMP and ATP respectively, but some members of the family can phosphorylate other substrates and use other phosphate donors. In addition to their nucleoside monophosphate kinase activity, adenylate kinases were found to possess nucleoside diphosphate kinase activity as they are able to phosphorylate both ribonucleoside and deoxyribonucleoside diphosphates to their corresponding triphosphates. Nucleoside analogues are structural analogues of natural nucleosides, used in the treatment of cancer and viral infections. They are inactive prodrugs that are dependent on intracellular phosphorylation to their pharmacologically active triphosphate form. Novel data presented in this review confirm the role of adenylate kinases in the activation of deoxyadenosine and deoxycytidine nucleoside analogues.

Mitochondrial cardiolipin/phospholipid trafficking: the role of membrane contact site complexes and lipid transfer proteins

Historically, cellular trafficking of lipids has received much less attention than protein trafficking, mostly because its biological importance was underestimated, involved sorting and translocation mechanisms were not known, and analytical tools were limiting. This has changed during the last decade, and we discuss here some progress made in respect to mitochondria and the trafficking of phospholipids, in particular cardiolipin. Different membrane contact site or junction complexes and putative lipid transfer proteins for intra- and intermembrane lipid translocation have been described, involving mitochondrial inner and outer membrane, and the adjacent membranes of the endoplasmic reticulum. An image emerges how cardiolipin precursors, remodeling intermediates, mature cardiolipin and its oxidation products could migrate between membranes, and how this trafficking is involved in cardiolipin biosynthesis and cell signaling events. Particular emphasis in this review is given to mitochondrial nucleoside diphosphate kinase D and mitochondrial creatine kinases, which emerge to have roles in both, membrane junction formation and lipid transfer.

The NME gene family in zebrafish oogenesis and early development

After the recent report of the expression of several nme genes in the zebrafish gonads, the present study aimed at further analyzing the expression of nme genes in the ovary with special attention for the nme transcripts that are maternally inherited and could thus participate in the determination of oocyte developmental competence. The expression levels of all groups I and II nme genes were characterized by QPCR in a panel of zebrafish tissues. The nme genes exhibiting an ovarian expression were subsequently monitored throughout oogenesis and early development, and their expression sites characterized using in situ hybridization. Here, we show that nme2b1, nme3, nme4, and nme6 are highly expressed in the ovary and present in the zebrafish oocyte throughout oogenesis. While the four transcripts are maternally inherited, nme3 and nme6 display a typical maternal profile and are detected in the zebrafish early embryo. In contrast to nme3, nme6, abundance exhibits a sharp decrease during early embryogenesis. After zygotic genome activation, we observed an increased expression of nme2b1, nme2b2, nme3, and nme6. The present study provides a comprehensive overview of the expression of nme family members during zebrafish oogenesis and early development. In addition, the maternal origin of two nme transcripts in the early embryo is reported here for the first time in any vertebrate species. Together, our observations suggest an important role of the nme family in oocyte and embryo development in vertebrates.

Developmental function of Nm23/awd: a mediator of endocytosis

The metastasis suppressor gene Nm23 is highly conserved from yeast to human, implicating a critical developmental function. Studies in cultured mammalian cells have identified several potential functions, but many have not been directly verified in vivo. Here, we summarize the studies on the Drosophila homolog of the Nm23 gene, named a bnormal w ing d iscs (awd), which shares 78% amino acid identity with the human Nm23-H1 and H2 isoforms. These studies confirmed that awd gene encodes a nucleoside diphosphate kinase, and provided strong evidence of a role for awd in regulating cell differentiation and motility via regulation of growth factor receptor signaling. The latter function is mainly mediated by control of endocytosis. This review provides a historical account of the discovery and subsequent analyses of the awd gene. We will also discuss the possible molecular function of the Awd protein that underlies the endocytic function.

The NM23 family in development

The NM23 (non-metastatic 23) family is almost universally conserved across all three domains of life: eubacteria, archaea and eucaryotes. Unicellular organisms possess one NM23 ortholog, whilst vertebrates possess several. Gene multiplication through evolution has been accompanied by structural and functional diversification. Many NM23 orthologs are nucleoside diphosphate kinases (NDP kinases), but some more recently evolved members lack NDP kinase activity and/or display other functions, for instance, acting as protein kinases or transcription factors. These members display overlapping but distinct expression patterns during vertebrate development. In this review, we describe the functional differences and similarities among various NM23 family members. Moreover, we establish orthologous relationships through a phylogenetic analysis of NM23 members across vertebrate species, including Xenopus laevis and zebrafish, primitive chordates and several phyla of invertebrates. Finally, we summarize the involvement of NM23 proteins in development, in particular neural development. Carcinogenesis is a process of misregulated development, and NM23 was initially implicated as a metastasis suppressor. A more detailed understanding of the evolution of the family and its role in vertebrate development will facilitate elucidation of the mechanism of NM23 involvement in human cancer.

The mammalian Nm23/NDPK family: from metastasis control to cilia movement

Nucleoside diphosphate kinases (NDPK) are encoded by the NME genes, also called NM23. They catalyze the transfer of gamma-phosphate from nucleoside triphosphates to nucleoside diphosphates by a ping-pong mechanism involving the formation of a high energy phospho-histidine intermediate [1, 2]. Besides their known functions in the control of intracellular nucleotide homeostasis, they are involved in multiple physiological and pathological cellular processes such as differentiation, development, metastastic dissemination or cilia functions. Over the past 15 years, ten human genes have been discovered encoding partial, full length, and/or tandemly repeated Nm23/NDPK domains, with or without N-or C-terminal extensions and/or additional domains. These genes encode proteins exhibiting different functions at various tissular and subcellular localizations. Most of these genes appear late in evolution with the emergence of the vertebrate lineage. This review summarizes the present knowledge on these multitalented proteins.

The mammalian Nm23/NDPK family: from metastasis control to cilia movement

Nucleoside diphosphate kinases (NDPK) are encoded by the NME genes, also called NM23. They catalyze the transfer of gamma-phosphate from nucleoside triphosphates to nucleoside diphosphates by a ping-pong mechanism involving the formation of a high energy phospho-histidine intermediate [1, 2]. Besides their known functions in the control of intracellular nucleotide homeostasis, they are involved in multiple physiological and pathological cellular processes such as differentiation, development, metastastic dissemination or cilia functions. Over the past 15 years, ten human genes have been discovered encoding partial, full length, and/or tandemly repeated Nm23/NDPK domains, with or without N-or C-terminal extensions and/or additional domains. These genes encode proteins exhibiting different functions at various tissular and subcellular localizations. Most of these genes appear late in evolution with the emergence of the vertebrate lineage. This review summarizes the present knowledge on these multitalented proteins.

Interaction of NDPK-D with cardiolipin-containing membranes: Structural basis and implications for mitochondrial physiology

Nucleoside diphosphate kinases (NDPKs/Nm23), responsible for intracellular di- and tri-phosphonucleoside homeostasis, play multi-faceted roles in cellular energetic, signaling, proliferation, differentiation and tumor invasion. The mitochondrial NDPK-D, the NME4 gene product, is a peripheral protein of the inner membrane. Several new aspects of the interaction of NDPK-D with the inner mitochondrial membrane have been recently characterized. Surface plasmon resonance analysis using recombinant NDPK-D and different phospholipid liposomes showed that NDPK-D interacts electrostatically with anionic phospholipids, with highest affinity observed for cardiolipin, a phospholipid located mostly in the mitochondrial inner membrane. Mutation of the central arginine (R90) in a surface exposed cationic RRK motif unique to NDPK-D strongly reduced phospholipid interaction in vitro and in vivo. Stable expression of NDPK-D proteins in HeLa cells naturally almost devoid of this isoform revealed a tight functional coupling of NDPK-D with oxidative phosphorylation that depends on the membrane-bound state of the enzyme. Owing to its symmetrical hexameric structure exposing membrane binding motifs on two opposite sides, NDPK-D could bridge liposomes containing anionic phospholipids and promote lipid transfer between them. In vivo, NDPK-D could induce intermembrane contacts and facilitate lipid movements between mitochondrial membranes. Most of these properties are reminiscent to those of the mitochondrial creatine kinase. We review here the common properties of both kinases and we discuss their potential roles in mitochondrial functions such as energy production, apoptosis and mitochondrial dynamics.

Direct binding of cytosolic NDP kinases to membrane lipids is regulated by nucleotides

In spite of their complete lack of any structural features that characterize membrane proteins, cytosolic nucleoside-diphosphate kinases (NDPKs) have been found repeatedly to associate with membranes. In some instances the recruitment of cytosolic NDPKs to membranes was attributed to interactions with peripheral or integral membrane proteins, but in many cases the mechanism underlying the association of NDPKs with membranes remained unknown. We show here that cytosolic NDPKs bind directly to membrane lipids in a dynamic process that is controlled by its substrates, nucleoside tri- and diphosphates, and can be fully reconstituted with chemically defined, protein-free phospholipids and recombinant NDPK, or with purified NDPK. Our results uncover a novel mechanism for the reversible targeting of soluble NDPKs to membranes, where they may act as a reservoir of high energy phosphate, supporting the operation of membrane-based processes that utilize nucleotides other than ATP, such as intracellular traffic and phospholipid biosynthesis.

Nucleotide-dependent self-assembly of Nucleoside Diphosphate Kinase (NDPK) in vitro

In addition to their role in nucleotide homeostasis, members of the Nucleoside Diphosphate Kinase (NDPK) family have been implicated in tumor metastasis, cell migration and vesicle trafficking. Although its role in most cases depends on nucleotide catalysis, a precise understanding of how the catalytic activity of NDPK supports its function in diverse processes is lacking. Here we report that wild type, but not catalytically inactive (H118C) NDPKB, undergoes dynamic self-assembly into ordered 20-25 nm diameter filaments in vitro. Self-assembly is nucleoside triphosphate dependent, GTP being most effective at promoting polymer formation. In addition, polymerization appears to depend on formation of the phosphoryl-Histidine intermediate of the enzyme, suggesting a previously unappreciated conformational change in NDPK during its catalytic cycle. We hypothesize that the observed nucleotide-dependent self-assembly property of NDPKB may reflect a key feature of NDPK enzymes that enables their function in diverse processes.

Nucleoside diphosphate kinase B (NDKB) scaffolds endoplasmic reticulum membranes in vitro

The mechanisms that structure the mammalian endoplasmic reticulum (ER) network are not fully understood. Here we show that salt extraction of semi-intact normal rat kidney (NRK) fibroblasts and subsequent incubation of the extracted cells with ATP resulted in dramatic ER network retraction. Under these conditions, addition of a single protein, Nucleoside Diphosphate Kinase B (NDKB), was sufficient to reverse the retraction and to promote ER network extension. The underlying mechanism of membrane extension involved direct lipid binding, as NDKB bound phosphatidylinositol (PtdIns)(4)P, PtdIns(4,5)P(2) and phosphatidic acid (PA); binding to these anionic lipids required clusters of basic residues on the surface of the NDKB hexamer; and amino acid changes in NDKB that blocked lipid binding also blocked ER network extension. Remarkably, purified NDKB transformed a uniform population of synthetic lipid vesicles into extensive membrane networks, and this also required its phospholipid-binding activity. Altogether these results identify a protein sufficient to scaffold extended membrane networks, and suggest a possible role for NDKB-like proteins, as well as phosphoinositides and/or acidic phospholipids, in modulating ER network morphogenesis.

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.

Nm23H2 facilitates coat protein complex II assembly and endoplasmic reticulum export in mammalian cells

The cytosolic coat protein complex II (COPII) mediates vesicle formation from the endoplasmic reticulum (ER) and is essential for ER-to-Golgi trafficking. The minimal machinery for COPII assembly is well established. However, additional factors may regulate the process in mammalian cells. Here, a morphological COPII assembly assay using purified COPII proteins and digitonin-permeabilized cells has been applied to demonstrate a role for a novel component of the COPII assembly pathway. The factor was purified and identified by mass spectrometry as Nm23H2, one of eight isoforms of nucleoside diphosphate kinase in mammalian cells. Importantly, recombinant Nm23H2, as well as a catalytically inactive version, promoted COPII assembly in vitro, suggesting a noncatalytic role for Nm23H2. Consistent with a function for Nm23H2 in ER export, Nm23H2 localized to a reticular network that also stained for the ER marker calnexin. Finally, an in vivo role for Nm23H2 in COPII assembly was confirmed by isoform-specific knockdown of Nm23H2 by using short interfering RNA. Knockdown of Nm23H2, but not its most closely related isoform Nm23H1, resulted in diminished COPII assembly at steady state and reduced kinetics of ER export. These results strongly suggest a previously unappreciated role for Nm23H2 in mammalian ER export.

Differential expression of the nm23 genes in the developing human trophoblast

NDP kinases are the non-specific enzymes which catalyse the synthesis of the NTPs through a transfer reaction using ATP as phosphoryl donor. In addition to their enzymatic activity, they display other not yet explained functions related to cell growth, differentiation and apoptosis, embryonic development, tumour progression and metastasis. In this study, the expression patterns of the three highly related NDP kinases A, B and C isoforms were investigated in the developing human trophoblast. Both NDP kinase A and B were found to be primarily present in the villous and extravillous cytotrophoblasts, while NDP kinase C was found almost exclusively in the syncytiotrophoblast layer. This suggests that NDP kinase A and B could be a marker for the mononuclear stage of differentiation of villous trophoblasts, while NDP kinase C could be a marker of the syncytiotrophoblast layer.

SwoHp, a nucleoside diphosphate kinase, is essential in Aspergillus nidulans

The temperature-sensitive swoH1 mutant of Aspergillus nidulans was previously identified in a screen for mutants with defects in polar growth. In the present work, we found that the swoH1 mutant swelled, lysed, and did not produce conidia during extended incubation at the restrictive temperature. When shifted from the permissive to the restrictive temperature, swoH1 showed the temperature-sensitive swelling phenotype only after 8 h at the higher temperature. The swoH gene was mapped to chromosome II and cloned by complementation of the temperature-sensitive phenotype. The sequence showed that swoH encodes a homologue of nucleoside diphosphate kinases (NDKs) from other organisms. Deletion experiments showed that the swoH gene is essential. A hemagglutinin-SwoHp fusion complemented the mutant phenotype, and the purified fusion protein possessed phosphate transferase activity in thin-layer chromatography assays. Sequencing of the mutant allele showed a predicted V83F change. Structural modeling suggested that the swoH1 mutation would lead to perturbation of the NDK active site. Crude cell extracts from the swoH1 mutant grown at the permissive temperature had approximately 20% of the NDK activity seen in the wild type and did not show any decrease in activity when assayed at higher temperatures. Though the data are not conclusive, the lack of temperature-sensitive NDK activity in the swoH1 mutant raises the intriguing possibility that the SwoH NDK is required for growth at elevated temperatures rather than for polarity maintenance.

Receptor activation regulates cortical, but not vesicular localization of NDP kinase

We used immunofluorescence techniques to determine the localization of nucleoside diphosphate (NDP) kinase in NIH-3T3 fibroblasts. We found that cytoplasmic NDP kinase can be separated into two populations according to subcellular localization and response to extracellular stimuli. Specifically, within minutes of stimulation of resting fibroblasts with serum, growth factors or bombesin, a portion of NDP kinase becomes associated with membrane ruffles and lamellipodia. Another pool of NDP kinase accumulates independently of stimulation around intracellular vesicles. Transfection of cells with activated Rac mimics, whereas expression of dominant negative Rac inhibits, the effects of extracellular stimulation on the translocation of NDP kinase to the cell cortex. Neither Rac mutant affects the vesicle-associated pool. Association of NDP kinase with vesicles depends on microtubule integrity and is disrupted by nocodazole. In cell-free assays NDP kinase binds tightly to membrane vesicles associated with taxol-stabilized microtubules. Binding of NDP kinase to this fraction is reduced by ATP and abolished by GTP, as well as guanine nucleotides that are NDP kinase substrates. Thus, the localization of the two NDP kinase pools identified here is regulated independently by distinct cellular components: the appearance of cortical NDP kinase is a consequence of Rac activation, whereas vesicular NDP kinase is responsive to microtubule dynamics and nucleotides, in particular GTP. These results suggest that in fibroblasts NDP kinase participates in Rac-related cortical events and in GTP-dependent processes linked to intracellular vesicle trafficking.

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.