A novel nuclear-localized protein with special adenylate kinase properties from Caenorhabditis elegans

hCINAP alleviates senescence by regulating MDM2 via p14ARF and the HDAC1/CoREST complex

Cellular senescence is a major process affected by multiple signals and coordinated by a complex signal response network. Identification of novel regulators of cellular senescence and elucidation of their molecular mechanisms will aid in the discovery of new treatment strategies for aging-related diseases. In the present study, we identified human coilin-interacting nuclear ATPase protein (hCINAP) as a negative regulator of aging. Depletion of cCINAP significantly shortened the lifespan of Caenorhabditis elegans and accelerated primary cell aging. Moreover, mCINAP deletion markedly promoted organismal aging and stimulated senescence-associated secretory phenotype in the skeletal muscle and liver from mouse models of radiation-induced senescence. Mechanistically, hCINAP functions through regulating MDM2 status by distinct mechanisms. On the one hand, hCINAP decreases p53 stability by attenuating the interaction between p14ARF and MDM2; on the other hand, hCINAP promotes MDM2 transcription via inhibiting the deacetylation of H3K9ac in the MDM2 promoter by hindering the HDAC1/CoREST complex integrity. Collectively, our data demonstrate that hCINAP is a negative regulator of aging and provide insight into the molecular mechanisms underlying the aging process.

Regulation of Adenine Nucleotide Metabolism by Adenylate Kinase Isozymes: Physiological Roles and Diseases

Adenylate kinase (AK) regulates adenine nucleotide metabolism and catalyzes the ATP + AMP ⇌ 2ADP reaction in a wide range of organisms and bacteria. AKs regulate adenine nucleotide ratios in different intracellular compartments and maintain the homeostasis of the intracellular nucleotide metabolism necessary for growth, differentiation, and motility. To date, nine isozymes have been identified and their functions have been analyzed. Moreover, the dynamics of the intracellular energy metabolism, diseases caused by AK mutations, the relationship with carcinogenesis, and circadian rhythms have recently been reported. This article summarizes the current knowledge regarding the physiological roles of AK isozymes in different diseases. In particular, this review focused on the symptoms caused by mutated AK isozymes in humans and phenotypic changes arising from altered gene expression in animal models. The future analysis of intracellular, extracellular, and intercellular energy metabolism with a focus on AK will aid in a wide range of new therapeutic approaches for various diseases, including cancer, lifestyle-related diseases, and aging.

MoFap7, a ribosome assembly factor, is required for fungal development and plant colonization of Magnaporthe oryzae

Fap7, an important ribosome assembly factor, plays a vital role in pre-40S small ribosomal subunit synthesis in Saccharomyces cerevisiae via its ATPase activity. Currently, the biological functions of its homologs in filamentous fungi remain elusive. Here, MoFap7, a homologous protein of ScFap7, was identified in the rice blast fungus Magnaporthe oryzae, which is a devastating fungal pathogen in rice and threatens food security worldwide. ΔMofap7 mutants exhibited defects in growth and development, conidial morphology, appressorium formation and infection, and were sensitive to oxidative stress. In addition, site-directed mutagenesis analysis confirmed that the conserved Walker A motif and Walker B motif in MoFap7 are essential for the biological functions of M. oryzae. We further analyzed the regulation mechanism of MoFap7 in pathogenicity. MoFap7 was found to interact with MoMst50, a regulator functioning in the MAPK Pmk1 signaling pathway, that participates in modulating plant penetration and cell-to-cell invasion by regulating the phosphorylation of MoPmk1. Moreover, MoFap7 interacted with the GTPases MoCdc42 and MoRac1 to control growth and conidiogenesis. Taken together, the results of this study provide novel insights into MoFap7-mediated orchestration of the development and pathogenesis of filamentous fungi.

Adenylate Kinase: A Ubiquitous Enzyme Correlated with Medical Conditions

Adenylate kinase is a small, usually monomeric, enzyme found in every living thing due to its crucial role in energetic metabolism. This paper outlines the most relevant data about adenylate kinases isoforms, and the connection between dysregulation or mutation of human adenylate kinase and medical conditions. The following datadases were consulted: National Centre for Biotechnology Information, Protein Data Bank, and Mouse Genomic Informatics. The SmartBLAST tool, EMBOSS Needle Program, and Clustal Omega Program were used to analyze the best protein match, and to perform pairwise sequence alignment and multiple sequence alignment. Human adenylate kinase genes are located on different chromosomes, six of them being on the chromosomes 1 and 9. The adenylate kinases' intracellular localization and organ distribution explain their dysregulation in many diseases. The cytosolic isoenzyme 1 and the mitochondrial isoenzyme 2 are the main adenylate kinases that are integrated in the vast network of inflammatory modulators. The cytosolic isoenzyme 5 is correlated with limbic encephalitis and Leu673Pro mutation of the isoenzyme 7 leads to primary male infertility due to impairment of the ciliary function. The impairment of the mitochondrial isoenzymes 2 and 4 is demonstrated in neuroblastoma or glioma. The adenylate kinases are disease modifier that can assess the risk of diseases where oxidative stress plays a crucial role in pathogenesis like metabolic syndrome or neurodegenerative diseases. Because adenylate kinases has ATP as substrate, they are integrated in the global network of energetic process of any organism therefore are valid target for new pharmaceutical compounds.

Human secreted stabilin-1-interacting chitinase-like protein aggravates the inflammation associated with rheumatoid arthritis and is a potential macrophage inflammatory regulator in rodents

OBJECTIVE

To study the relationship between the human secreted protein stabilin-1-interacting chitinase-like protein (SI-CLP) and rheumatoid arthritis (RA).

METHODS

The expression of SI-CLP in peripheral blood mononuclear cells (PBMCs) and synovial fluid from patients with RA and the effects of cytokines on SI-CLP expression were examined by Western blotting. Fluorescence-activated cell sorting analysis was performed to investigate the binding between SI-CLP and cells. Bone marrow-derived macrophages were isolated from wild-type and SI-CLP(-/-) mice, and real-time quantitative polymerase chain reaction was performed to detect the levels of messenger RNA for cytokines or SI-CLP in SI-CLP- or cytokine-treated macrophages. Histologic studies were conducted to evaluate inflammation and the expression of interleukin-12 (IL-12), IL-13, and SI-CLP in lesions. Enzyme-linked immunosorbent assays were used to detect the cytokine levels in bone marrow-derived macrophages. Rats or mice with collagen-induced arthritis (CIA) and SI-CLP(-/-) mice were used to study the function of SI-CLP in RA.

RESULTS

SI-CLP expression was increased in PBMCs and detectable in synovial fluid from patients with RA. Administration of SI-CLP to rats with CIA aggravated arthritis-associated inflammation. SI-CLP was specifically attached to the surface protein of macrophages, which elevated the expression of IL-1β, IL-6, IL-12, and IL-13 in macrophages and mouse bone marrow-derived macrophages, up-regulating ERK phosphorylation. Moreover, SI-CLP was up-regulated by both IL-12 and IL-13 through JNK and JAK/STAT signaling, respectively. Knockout of SI-CLP resulted in a decrease in the expression of IL-1β, IL-6, IL-12, and IL-13 and lower susceptibility to CIA compared with wild-type mice. SI-CLP treatment also aggravated arthritis-related inflammation in wild-type and SI-CLP(-/-) mice.

CONCLUSION

SI-CLP functions as a regulator of the inflammatory response by macrophages. The decrease in inflammation-associated cytokine levels resulting from SI-CLP knockout may explain the lower susceptibility to CIA in SI-CLP(-/-) mice.

Molecular and functional characterization of a Trypanosoma cruzi nuclear adenylate kinase isoform

Trypanosoma cruzi, the etiological agent of Chagas' disease, is an early divergent eukaryote in which control of gene expression relies mainly in post-transcriptional mechanisms. Transcription levels are globally up and down regulated during the transition between proliferating and non-proliferating life-cycle stages. In this work we characterized a nuclear adenylate kinase isoform (TcADKn) that is involved in ribosome biogenesis. Nuclear adenylate kinases have been recently described in a few organisms, being all related to RNA metabolism. Depending on active transcription and translation, TcADKn localizes in the nucleolus or the cytoplasm. A non-canonical nuclear localization signal was mapped towards the N-terminal of the protein, being the phosphate-binding loop essential for its localization. In addition, TcADKn nuclear exportation depends on the nuclear exportation adapter CRM1. TcADKn nuclear shuttling is governed by nutrient availability, oxidative stress and by the equivalent in T. cruzi of the mammalian TOR (Target of Rapamycin) pathway. One of the biological functions of TcADKn is ribosomal 18S RNA processing by direct interaction with ribosomal protein TcRps14. Finally, TcADKn expression is regulated by its 3′ UTR mRNA. Depending on extracellular conditions, cells modulate protein translation rates regulating ribosome biogenesis and nuclear adenylate kinases are probably key components in these processes.

Infection with Trypanosoma cruzi produces a condition known as Chagas disease which affects at least 17 million people. Adenylate kinases, so called myokinases, are involved in a wide variety of processes, mainly related to their role in nucleotide interconversion and energy management. Recently, nuclear isoforms have been described in several organisms. This “atypical” isoform in terms of primary structure was associated to ribosomes biogenesis in yeast and to Cajal body organization in humans. Moreover nuclear adenylate kinases are essential for maintaining cellular homeostasis. In this manuscript we characterized T. cruzi nuclear adenylate kinase (TcADKn). TcADKn localizes in the nucleolus or cell cytoplasm. Nuclear shuttling mechanisms were also studied for the first time, being dependent on nutrient availability, oxidative stress and by the equivalent of the mammalian TOR pathway in T. cruzi. Furthermore we characterized the signals involved in nuclear importation and exportation processes. In addition, TcADKn expression levels are regulated at an mRNA level, being its 3′UTR involved in this process. These findings are the first steps in the understanding of ribosome processing in trypanosomatids.

hCINAP is a novel regulator of ribosomal protein-HDM2-p53 pathway by controlling NEDDylation of ribosomal protein S14

The tumor-suppressor p53 provides a critical brake on tumor development. HDM2 (human double-minute 2), a p53 E3 ubiquitin ligase, is the principal cellular antagonist of p53. Mounting evidence has suggested that ribosomal proteins (RPs) modulate HDM2-p53 as a novel pathway for regulating p53 signaling. However, the upstream regulators that mediate RP-HDM2-p53 circuits remain poorly understood. Here we identify human coilin-interacting nuclear ATPase protein (hCINAP) as an interacting partner of ribosomal protein S14 (RPS14). RPS14 stabilized and activated p53 by inhibiting HDM2-mediated p53 polyubiquitination and degradation. More importantly, RPS14 was specifically modified with NEDD8 and hCINAP inhibited RPS14 NEDDylation by recruiting NEDD8-specific protease 1. The decrease in RPS14 NEDDylation led to reduced stability and incorrect localization of RPS14, thereby attenuating the interaction between RPS14 and HDM2. Free HDM2 stimulated p53 polyubiquitination and degradation. In conclusion, we demonstrate that hCINAP acts as a novel regulator of RPS14-HDM2-p53 by regulating the interaction between RPS14 and HDM2 through the control of RPS14 NEDDylation. These findings suggest that hCINAP is an important regulator of RP-HDM2-p53 pathway and a potential anticancer drug target.

Identification of a novel nuclear-localized adenylate kinase 6 from Arabidopsis thaliana as an essential stem growth factor

Adenylate kinase (AK; EC 2.7.4.3) is highly conserved across a wide range of organisms, including Saccharomyces cerevisiae, Caenorhabditis elegans, Drosophila melanogaster, Arabidopsis thaliana, and Homo sapiens. While AK6 orthologs play important roles in the growth of yeast and worms, the physiological function of AK6 in A. thaliana is still unknown. In this study, we first cloned and expressed Arabidopsis adenylate kinase 6 (AAK6). Enzyme assays revealed that AAK6 has characteristic adenylate kinase properties, with ATP as the preferred phosphate donor and AMP as the best phosphate acceptor. A subcellular localization assay demonstrated that AAK6 had a predominant nuclear localization. Through biochemical purification and mass spectrometry analysis, a putative homolog of the S. cerevisiae Rps14 protein was identified as a partner of AAK6. Most importantly, we observed that aak6 T-DNA insertion mutants had decreased stem growth compared with wild-type plants. These data indicate that AAK6 exhibits adenylate kinase activity and is an essential growth factor in Arabidopsis.

Adenylate kinase 2 (AK2) promotes cell proliferation in insect development

Background

Adenylate kinase 2 (AK2) is a phosphotransferase that catalyzes the reversible reaction 2ADP(GDP) ↔ ATP(GTP) + AMP and influences cellular energy homeostasis. However, the role of AK2 in regulating cell proliferation remains unclear because AK2 has been reported to be involved in either cell proliferation or cell apoptosis in different cell types of various organisms.

Results

This study reports AK2 promotion of cell proliferation using the lepidopteran insect Helicoverpa armigera and its epidermal cell line HaEpi as models. Western blot analysis indicates that AK2 constitutively expresses in various tissues during larval development. Immunocytochemistry analysis indicates that AK2 localizes in the mitochondria. The recombinant expressed AK2 in E. coli promotes cell growth and viability of HaEpi cell line by 3-(4, 5-Dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay. AK2 knockdown in larvae by RNA interference causes larval growth defects, including body weight decrease and development delay. AK2 knockdown in larvae also decreases the number of circulating haemocytes. The mechanism for such effects might be the suppression of gene transcription involved in insect development caused by AK2 knockdown.

Conclusion

These results show that AK2 regulates cell growth, viability, and proliferation in insect growth and development.

hCINAP is an atypical mammalian nuclear adenylate kinase with an ATPase motif: structural and functional studies

Human coilin interacting nuclear ATPase protein (hCINAP) directly interacts with coilin, a marker protein of Cajal Bodies (CBs), nuclear organelles involved in the maturation of small nuclear ribonucleoproteins UsnRNPs and snoRNPs. hCINAP has previously been designated as an adenylate kinase (AK6), but is very atypical as it exhibits unusually broad substrate specificity, structural features characteristic of ATPase/GTPase proteins (Walker motifs A and B) and also intrinsic ATPase activity. Despite its intriguing structure, unique properties and cellular localization, the enzymatic mechanism and biological function of hCINAP have remained poorly characterized. Here, we offer the first high-resolution structure of hCINAP in complex with the substrate ADP (and dADP), the structure of hCINAP with a sulfate ion bound at the AMP binding site, and the structure of the ternary complex hCINAP-Mg(2+) ADP-Pi. Induced fit docking calculations are used to predict the structure of the hCINAP-Mg(2+) ATP-AMP ternary complex. Structural analysis suggested a functional role for His79 in the Walker B motif. Kinetic analysis of mutant hCINAP-H79G indicates that His79 affects both AK and ATPase catalytic efficiency and induces homodimer formation. Finally, we show that in vivo expression of hCINAP-H79G in human cells is toxic and drastically deregulates the number and appearance of CBs in the cell nucleus. Our findings suggest that hCINAP may not simply regulate nucleotide homeostasis, but may have broader functionality, including control of CB assembly and disassembly in the nucleus of human cells.

ATP binding to hemoglobin response gene 1 protein is necessary for regulation of the mating type locus in Candida albicans

HBR1 (hemoglobin response gene 1) is an essential gene in Candida albicans that positively regulates mating type locus MTLα gene expression and thereby regulates cell type-specific developmental genes. Hbr1p contains a phosphate-binding loop (P-loop), a highly conserved motif characteristic of ATP- and GTP-binding proteins. Recombinant Hbr1p was isolated in an oligomeric state that specifically bound ATP with K(d) ∼2 μM. ATP but not ADP, AMP, GTP, or dATP specifically protected Hbr1p from proteolysis by trypsin. Site-directed mutagenesis of the highly conserved P-loop lysine (K22Q) and the less conserved glycine (G19S) decreased the binding affinity for soluble ATP and ATP immobilized through its γ-phosphate. ATP bound somewhat more avidly than ATPγS to wild type and mutant Hbr1p. Although Hbr1p exhibits sequence motifs characteristic of adenylate kinases, and adenylate kinase and ATPase activities have been reported for the apparent human ortholog of Hbr1p, assays for adenylate kinase activity, autophosphorylation, and ATPase activity proved negative. Overexpression of wild type but not the mutant forms of Hbr1p restored MTlα2 expression in an HBR1/hbr1 mutant, indicating that ATP binding to the P-loop is necessary for this function of Hbr1p.

Depletion of hCINAP by RNA interference causes defects in Cajal body formation, histone transcription, and cell viability

hCINAP is a highly conserved and ubiquitously expressed protein in eukaryotic organisms and its overexpression decreases the average number of Cajal bodies (CBs) with diverse nuclear functions. Here, we report that hCINAP is associated with important components of CBs. Depletion of hCINAP by RNA interference causes defects in CB formation and disrupts subcellular localizations of its components including coilin, survival motor neurons protein, spliceosomal small nuclear ribonucleoproteins, and nuclear protein ataxia-telangiectasia. Moreover, knockdown of hCINAP expression results in marked reduction of histone transcription, lower levels of U small nuclear RNAs (U1, U2, U4, and U5), and a loss of cell viability. Detection of increased caspase-3 activities in hCINAP-depleted cells indicate that apoptosis is one of the reasons for the loss of viability. Altogether, these data suggest that hCINAP is essential for the formation of canonical CBs, histone transcription, and cell viability.

Adenylate kinase and AMP signaling networks: metabolic monitoring, signal communication and body energy sensing

Adenylate kinase and downstream AMP signaling is an integrated metabolic monitoring system which reads the cellular energy state in order to tune and report signals to metabolic sensors. A network of adenylate kinase isoforms (AK1-AK7) are distributed throughout intracellular compartments, interstitial space and body fluids to regulate energetic and metabolic signaling circuits, securing efficient cell energy economy, signal communication and stress response. The dynamics of adenylate kinase-catalyzed phosphotransfer regulates multiple intracellular and extracellular energy-dependent and nucleotide signaling processes, including excitation-contraction coupling, hormone secretion, cell and ciliary motility, nuclear transport, energetics of cell cycle, DNA synthesis and repair, and developmental programming. Metabolomic analyses indicate that cellular, interstitial and blood AMP levels are potential metabolic signals associated with vital functions including body energy sensing, sleep, hibernation and food intake. Either low or excess AMP signaling has been linked to human disease such as diabetes, obesity and hypertrophic cardiomyopathy. Recent studies indicate that derangements in adenylate kinase-mediated energetic signaling due to mutations in AK1, AK2 or AK7 isoforms are associated with hemolytic anemia, reticular dysgenesis and ciliary dyskinesia. Moreover, hormonal, food and antidiabetic drug actions are frequently coupled to alterations of cellular AMP levels and associated signaling. Thus, by monitoring energy state and generating and distributing AMP metabolic signals adenylate kinase represents a unique hub within the cellular homeostatic network.

Conjugated polyelectrolyte based real-time fluorescence assay for adenylate kinase

Addition of adenosine 5'-triphosphate (ATP) to a solution of the anionic conjugated polyelectrolyte PPECO2 and copper(II) ion (Cu2+) recovers the Cu2+-quenched fluorescence of PPECO(2) to a significantly greater extent compared with the addition of adenosine 5'-diphosphate (ADP) or adenosine 5'-monophosphate (AMP) at the same concentration levels. Taking advantage of the differential response of the PPECO2-Cu2+ system to ATP, ADP and AMP, we have developed fluorescence turn-off and turn-on assays that monitor the catalytic activity of adenylate kinase (ADK) in the equilibrium transphosphorylation reaction (ATP + AMP <--> 2ADP). The fluorescence turn-on and turn-off assays monitor the forward and reverse transphosphorylation reactions, respectively. The forward assay operates with ATP substrate present at the submillimolar concentration range and offers a straightforward and rapid detection of ADK catalytic activity with the enzyme present in the nanomolar range, in either end-point or real-time formats. The real-time fluorescence intensity from PPECO2 can be converted to substrate (ATP) concentration in the forward reaction assay by using an ex-situ calibration curve, allowing ADK catalyzed reaction rates and kinetic parameters to be determined. ADK activation by Mg2+ and inhibition by Ag+ and product are analyzed using the optimized assay system. Non-specific interactions are observed between the assay complex and other proteins, but the signal response to the ADK assay is demonstrated to mainly arise from the specific enzyme catalyzed transphosphorylation reaction.

Identification of a novel nuclear-localized adenylate kinase from Drosophila melanogaster

As a step to further understand the role of adenylate kinase (AK) in the energy metabolism network, we identified, purified, and characterized a previously undescribed adenylate kinase in Drosophila melanogaster. The cDNA encodes a 175-amino acid protein, which shows 47.85% identity in 163 amino acids to human AK6. The recombinant protein was successfully expressed in Escherichia coli BL21(DE3) strain. Characterization of this protein by enzyme activity assay showed adenylate kinase activity. AMP and CMP were the preferred substrates, and UMP can also be phosphorylated to some extent, with ATP as the best phosphate donor. Subcellular localization study showed a predominantly nuclear localization. Therefore, based on the substrate specificity, the specific nuclear localization in the cell, and the sequence similarity with human AK6, we named this novel adenylate kinase identified from the fly DAK6.