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Whitfield H, Rodriguez RF, Shipton ML, Li AW, Riley AM, Potter BV, Hemmings AM, Brearley CA. Crystal Structure and Enzymology of Solanum tuberosum Inositol Tris/Tetrakisphosphate Kinase 1 ( StITPK1). Biochemistry 2024; 63:42-52. [PMID: 38146842 PMCID: PMC10765375 DOI: 10.1021/acs.biochem.3c00404] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2023] [Revised: 11/30/2023] [Accepted: 11/30/2023] [Indexed: 12/27/2023]
Abstract
Inositol phosphates and their pyrophosphorylated derivatives are responsive to the phosphate supply and are agents of phosphate homeostasis and other aspects of physiology. It seems likely that the enzymes that interconvert these signals work against the prevailing milieu of mixed populations of competing substrates and products. The synthesis of inositol pyrophosphates is mediated in plants by two classes of ATP-grasp fold kinase: PPIP5 kinases, known as VIH, and members of the inositol tris/tetrakisphosphate kinase (ITPK) family, specifically ITPK1/2. A molecular explanation of the contribution of ITPK1/2 to inositol pyrophosphate synthesis and turnover in plants is incomplete: the absence of nucleotide in published crystal structures limits the explanation of phosphotransfer reactions, and little is known of the affinity of potential substrates and competitors for ITPK1. Herein, we describe a complex of ADP and StITPK1 at 2.26 Å resolution and use a simple fluorescence polarization approach to compare the affinity of binding of diverse inositol phosphates, inositol pyrophosphates, and analogues. By simple HPLC, we reveal the novel catalytic capability of ITPK1 for different inositol pyrophosphates and show Ins(3,4,5,6)P4 to be a potent inhibitor of the inositol pyrophosphate-synthesizing activity of ITPK1. We further describe the exquisite specificity of ITPK1 for the myo-isomer among naturally occurring inositol hexakisphosphates.
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Affiliation(s)
- Hayley
L. Whitfield
- School
of Biological Sciences, University of East
Anglia, Norwich Research Park, Norwich NR4 7TJ, U.K.
| | - Raquel Faba Rodriguez
- School
of Biological Sciences, University of East
Anglia, Norwich Research Park, Norwich NR4 7TJ, U.K.
- School
of Chemistry, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, U.K.
| | - Megan L. Shipton
- Medicinal
Chemistry & Drug Discovery, Department of Pharmacology, University of Oxford, Mansfield Road, Oxford OX1 3QT, U.K.
| | - Arthur W.H. Li
- School
of Biological Sciences, University of East
Anglia, Norwich Research Park, Norwich NR4 7TJ, U.K.
- School
of Chemistry, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, U.K.
| | - Andrew M. Riley
- Medicinal
Chemistry & Drug Discovery, Department of Pharmacology, University of Oxford, Mansfield Road, Oxford OX1 3QT, U.K.
| | - Barry V.L. Potter
- Medicinal
Chemistry & Drug Discovery, Department of Pharmacology, University of Oxford, Mansfield Road, Oxford OX1 3QT, U.K.
| | - Andrew M. Hemmings
- School
of Biological Sciences, University of East
Anglia, Norwich Research Park, Norwich NR4 7TJ, U.K.
- School
of Chemistry, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, U.K.
- College
of Food Science and Technology, Shanghai
Ocean University, Shanghai 201306, China
| | - Charles A. Brearley
- School
of Biological Sciences, University of East
Anglia, Norwich Research Park, Norwich NR4 7TJ, U.K.
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2
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Ricaña CL, Dick RA. Inositol Phosphates and Retroviral Assembly: A Cellular Perspective. Viruses 2021; 13:v13122516. [PMID: 34960784 PMCID: PMC8703376 DOI: 10.3390/v13122516] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2021] [Revised: 12/09/2021] [Accepted: 12/11/2021] [Indexed: 12/13/2022] Open
Abstract
Understanding the molecular mechanisms of retroviral assembly has been a decades-long endeavor. With the recent discovery of inositol hexakisphosphate (IP6) acting as an assembly co-factor for human immunodeficiency virus (HIV), great strides have been made in retroviral research. In this review, the enzymatic pathways to synthesize and metabolize inositol phosphates (IPs) relevant to retroviral assembly are discussed. The functions of these enzymes and IPs are outlined in the context of the cellular biology important for retroviruses. Lastly, the recent advances in understanding the role of IPs in retroviral biology are surveyed.
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An ATP-responsive metabolic cassette comprised of inositol tris/tetrakisphosphate kinase 1 (ITPK1) and inositol pentakisphosphate 2-kinase (IPK1) buffers diphosphosphoinositol phosphate levels. Biochem J 2021; 477:2621-2638. [PMID: 32706850 PMCID: PMC7115839 DOI: 10.1042/bcj20200423] [Citation(s) in RCA: 24] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2020] [Revised: 06/29/2020] [Accepted: 07/06/2020] [Indexed: 12/27/2022]
Abstract
Inositol polyphosphates are ubiquitous molecular signals in metazoans, as are their pyrophosphorylated derivatives that bear a so-called ‘high-energy’ phosphoanhydride bond. A structural rationale is provided for the ability of Arabidopsis inositol tris/tetrakisphosphate kinase 1 to discriminate between symmetric and enantiomeric substrates in the production of diverse symmetric and asymmetric myo-inositol phosphate and diphospho-myo-inositol phosphate (inositol pyrophosphate) products. Simple tools are applied to chromatographic resolution and detection of known and novel diphosphoinositol phosphates without resort to radiolabeling approaches. It is shown that inositol tris/tetrakisphosphate kinase 1 and inositol pentakisphosphate 2-kinase comprise a reversible metabolic cassette converting Ins(3,4,5,6)P4 into 5-InsP7 and back in a nucleotide-dependent manner. Thus, inositol tris/tetrakisphosphate kinase 1 is a nexus of bioenergetics status and inositol polyphosphate/diphosphoinositol phosphate metabolism. As such, it commands a role in plants that evolution has assigned to a different class of enzyme in mammalian cells. The findings and the methods described will enable a full appraisal of the role of diphosphoinositol phosphates in plants and particularly the relative contribution of reversible inositol phosphate hydroxykinase and inositol phosphate phosphokinase activities to plant physiology.
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Abstract
The multitudinous inositol phosphate family elicits a wide range of molecular effects that regulate countless biological responses. In this review, I provide a methodological viewpoint of the manner in which key advances in the field of inositol phosphate research were made. I also note some of the considerable challenges that still lie ahead.
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Affiliation(s)
- Stephen B Shears
- Laboratory of Signal Transduction, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC, USA.
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5
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ITPK1 mediates the lipid-independent synthesis of inositol phosphates controlled by metabolism. Proc Natl Acad Sci U S A 2019; 116:24551-24561. [PMID: 31754032 PMCID: PMC6900528 DOI: 10.1073/pnas.1911431116] [Citation(s) in RCA: 46] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Inositol phosphates (IPs) are a class of signaling molecules regulating cell physiology. The best-characterized IP, the calcium release factor IP3, is generated by phospholipase C hydrolysis of phosphoinositides lipids. For historical and technical reasons, IPs synthesis is believed to originate from the lipid-generated IP3. While this is true in yeast, our work has demonstrated that other organisms use a “soluble” (nonlipid) route to synthesize IPs. This soluble pathway depends on the metabolic status of the cells, and is under the control of the kinase ITPK1, which phosphorylates inositol monophosphate likely generated from glucose. The data shed light on the evolutionary origin of IPs, signaling and tightening the link between these small molecules and basic metabolism. Inositol phosphates (IPs) comprise a network of phosphorylated molecules that play multiple signaling roles in eukaryotes. IPs synthesis is believed to originate with IP3 generated from PIP2 by phospholipase C (PLC). Here, we report that in mammalian cells PLC-generated IPs are rapidly recycled to inositol, and uncover the enzymology behind an alternative “soluble” route to synthesis of IPs. Inositol tetrakisphosphate 1-kinase 1 (ITPK1)—found in Asgard archaea, social amoeba, plants, and animals—phosphorylates I(3)P1 originating from glucose-6-phosphate, and I(1)P1 generated from sphingolipids, to enable synthesis of IP6. We also found using PAGE mass assay that metabolic blockage by phosphate starvation surprisingly increased IP6 levels in a ITPK1-dependent manner, establishing a route to IP6 controlled by cellular metabolic status, that is not detectable by traditional [3H]-inositol labeling. The presence of ITPK1 in archaeal clades thought to define eukaryogenesis indicates that IPs had functional roles before the appearance of the eukaryote.
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Wilson MSC, Saiardi A. Importance of Radioactive Labelling to Elucidate Inositol Polyphosphate Signalling. Top Curr Chem (Cham) 2017; 375:14. [PMID: 28101851 PMCID: PMC5396384 DOI: 10.1007/s41061-016-0099-y] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2016] [Accepted: 12/21/2016] [Indexed: 01/09/2023]
Abstract
Inositol polyphosphates, in their water-soluble or lipid-bound forms, represent a large and multifaceted family of signalling molecules. Some inositol polyphosphates are well recognised as defining important signal transduction pathways, as in the case of the calcium release factor Ins(1,4,5)P3, generated by receptor activation-induced hydrolysis of the lipid PtdIns(4,5)P2 by phospholipase C. The birth of inositol polyphosphate research would not have occurred without the use of radioactive phosphate tracers that enabled the discovery of the “PI response”. Radioactive labels, mainly of phosphorus but also carbon and hydrogen (tritium), have been instrumental in the development of this research field and the establishment of the inositol polyphosphates as one of the most important networks of regulatory molecules present in eukaryotic cells. Advancements in microscopy and mass spectrometry and the development of colorimetric assays have facilitated inositol polyphosphate research, but have not eliminated the need for radioactive experimental approaches. In fact, such experiments have become easier with the cloning of the inositol polyphosphate kinases, enabling the systematic labelling of specific positions of the inositol ring with radioactive phosphate. This approach has been valuable for elucidating their metabolic pathways and identifying specific and novel functions for inositol polyphosphates. For example, the synthesis of radiolabelled inositol pyrophosphates has allowed the discovery of a new protein post-translational modification. Therefore, radioactive tracers have played and will continue to play an important role in dissecting the many complex aspects of inositol polyphosphate physiology. In this review we aim to highlight the historical importance of radioactivity in inositol polyphosphate research, as well as its modern usage.
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Affiliation(s)
- Miranda S C Wilson
- Medical Research Council Laboratory for Molecular Cell Biology, University College London, Gower Street, London, WC1E 6BT, UK
| | - Adolfo Saiardi
- Medical Research Council Laboratory for Molecular Cell Biology, University College London, Gower Street, London, WC1E 6BT, UK.
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Thota SG, Bhandari R. The emerging roles of inositol pyrophosphates in eukaryotic cell physiology. J Biosci 2016; 40:593-605. [PMID: 26333405 DOI: 10.1007/s12038-015-9549-x] [Citation(s) in RCA: 55] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Inositol pyrophosphates are water soluble derivatives of inositol that contain pyrophosphate or diphosphate moieties in addition to monophosphates. The best characterised inositol pyrophosphates, are IP7 (diphosphoinositol pentakisphosphate or PP-IP5), and IP8 (bisdiphosphoinositol tetrakisphosphate or (PP)2-IP4). These energy-rich small molecules are present in all eukaryotic cells, from yeast to mammals, and are involved in a wide range of cellular functions including apoptosis, vesicle trafficking, DNA repair, osmoregulation, phosphate homeostasis, insulin sensitivity, immune signalling, cell cycle regulation, and ribosome synthesis. Identified more than 20 years ago, there is still only a rudimentary understanding of the mechanisms by which inositol pyrophosphates participate in these myriad pathways governing cell physiology and homeostasis. The unique stereochemical and bioenergetic properties these molecules possess as a consequence of the presence of one or two pyrophosphate moieties in the vicinity of densely packed monophosphates are likely to form the molecular basis for their participation in multiple signalling and metabolic pathways. The aim of this review is to provide first time researchers in this area with an introduction to inositol pyrophosphates and a comprehensive overview on their cellular functions.
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Affiliation(s)
- Swarna Gowri Thota
- Laboratory of Cell Signalling, Centre for DNA Fingerprinting and Diagnostics, Hyderabad 500 001, India
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The maternal ITPK1 gene polymorphism is associated with neural tube defects in a high-risk Chinese population. PLoS One 2014; 9:e86145. [PMID: 24465924 PMCID: PMC3896452 DOI: 10.1371/journal.pone.0086145] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2013] [Accepted: 12/05/2013] [Indexed: 01/05/2023] Open
Abstract
Background Epidemiological surveys and animal studies have revealed that inositol metabolism is associated with NTDs, but the mechanisms are not clear. Inositol 1,3,4-trisphosphate 5/6-kinase (ITPK1) is a pivotal regulatory enzyme in inositol metabolic pathway. The objective was to assess the potential impact of the maternal ITPK1 genotypes on the inositol parameter and on the NTD risk in a NTD high-risk area in China. Methodology/Results A case-control study of pregnant women affected with NTDs (n = 200) and controls (n = 320) was carried out. 13 tag SNPs of ITPK1 were selected and genotyped by the Sequenom MassArray system. We found that 4 tag SNPs were statistically significant in spina bifida group (P<0.05). MACH was used to impute the un-genotyped SNPs in ITPK1 locus and showed that 3 meaningful SNPs in the non-coding regions were significant. We also predicted the binding capacity of transcription factors in the positive SNPs using the bioinformatics method and found that only rs3783903 was located in the conserved sequence of activator protein-1 (AP-1). To further study the association between biochemical values and genotypes, maternal plasma inositol hexakisphosphate (IP6) levels were also assessed using LC-MS. The maternal plasma IP6 concentrations in the spina bifida subgroup were 7.1% lower than control (136.67 vs. 147.05 ng mL−1, P<0.05), and significantly lower in rs3783903 GG genotype than others (P<0.05). EMSA showed a different allelic binding capacity of AP-1 in rs3783903, which was affected by an A→G exchange. The RT-PCR suggested the ITPK1 expression was decreased significantly in mutant-type of rs3783903 compared with wild-type in the 60 healthy pregnancies (P<0.05). Conclusions/Significance These results suggested that the maternal rs3783903 of ITPK1 might be associated with spina bifida, and the allele G of rs3783903 might affect the binding of AP-1 and the decrease of maternal plasma IP6 concentration in this Chinese population.
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Development of low phytate rice by RNAi mediated seed-specific silencing of inositol 1,3,4,5,6-pentakisphosphate 2-kinase gene (IPK1). PLoS One 2013; 8:e68161. [PMID: 23844166 PMCID: PMC3699528 DOI: 10.1371/journal.pone.0068161] [Citation(s) in RCA: 78] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2012] [Accepted: 05/30/2013] [Indexed: 02/03/2023] Open
Abstract
Phytic acid (InsP6) is considered to be the major source of phosphorus and inositol phosphates in most cereal grains. However, InsP6 is not utilized efficiently by monogastric animals due to lack of phytase enzyme. Furthermore, due to its ability to chelate mineral cations, phytic acid is considered to be an antinutrient that renders these minerals unavailable for absorption. In view of these facts, reducing the phytic acid content in cereal grains is a desired goal for the genetic improvement of several crops. In the present study, we report the RNAi-mediated seed-specific silencing (using the Oleosin18 promoter) of the IPK1 gene, which catalyzes the last step of phytic acid biosynthesis in rice. The presence of the transgene cassette in the resulting transgenic plants was confirmed by molecular analysis, indicating the stable integration of the transgene. The subsequent T4 transgenic seeds revealed 3.85-fold down-regulation in IPK1 transcripts, which correlated to a significant reduction in phytate levels and a concomitant increase in the amount of inorganic phosphate (Pi). The low-phytate rice seeds also accumulated 1.8-fold more iron in the endosperm due to the decreased phytic acid levels. No negative effects were observed on seed germination or in any of the agronomic traits examined. The results provide evidence that silencing of IPK1 gene can mediate a substantial reduction in seed phytate levels without hampering the growth and development of transgenic rice plants.
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Abstract
Phosphoinositides (PIs) make up only a small fraction of cellular phospholipids, yet they control almost all aspects of a cell's life and death. These lipids gained tremendous research interest as plasma membrane signaling molecules when discovered in the 1970s and 1980s. Research in the last 15 years has added a wide range of biological processes regulated by PIs, turning these lipids into one of the most universal signaling entities in eukaryotic cells. PIs control organelle biology by regulating vesicular trafficking, but they also modulate lipid distribution and metabolism via their close relationship with lipid transfer proteins. PIs regulate ion channels, pumps, and transporters and control both endocytic and exocytic processes. The nuclear phosphoinositides have grown from being an epiphenomenon to a research area of its own. As expected from such pleiotropic regulators, derangements of phosphoinositide metabolism are responsible for a number of human diseases ranging from rare genetic disorders to the most common ones such as cancer, obesity, and diabetes. Moreover, it is increasingly evident that a number of infectious agents hijack the PI regulatory systems of host cells for their intracellular movements, replication, and assembly. As a result, PI converting enzymes began to be noticed by pharmaceutical companies as potential therapeutic targets. This review is an attempt to give an overview of this enormous research field focusing on major developments in diverse areas of basic science linked to cellular physiology and disease.
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Affiliation(s)
- Tamas Balla
- Section on Molecular Signal Transduction, Program for Developmental Neuroscience, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA.
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Regulation of inositol 1,3,4-trisphosphate 5/6-kinase (ITPK1) by reversible lysine acetylation. Proc Natl Acad Sci U S A 2012; 109:2290-5. [PMID: 22308441 DOI: 10.1073/pnas.1119740109] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The enzyme inositol 1,3,4-trisphosphate 5/6-kinase (ITPK1) catalyzes the rate-limiting step in the formation of higher phosphorylated forms of inositol in mammalian cells. Because it sits at a key regulatory point in the inositol metabolic pathway, its activity is likely to be regulated. We have previously shown that ITPK1 is phosphorylated, a posttranslational modification used by cells to regulate enzyme activity. We show here that ITPK1 is modified by acetylation of internal lysine residues. The acetylation sites, as determined by mass spectrometry, were found to be lysines 340, 383, and 410, which are all located on the surface of this protein. Overexpression of the acetyltransferases CREB-binding protein or p300 resulted in the acetylation of ITPK1, whereas overexpression of mammalian silent information regulator 2 resulted in the deacetylation of ITPK1. Functionally, ITPK1 acetylation regulates its stability. CREB-binding protein dramatically decreased the half-life of ITPK1. We further found that ITPK1 acetylation down-regulated its enzyme activity. HEK293 cells stably expressing acetylated ITPK1 had reduced levels of the higher phosphorylated forms of inositol, compared with the levels seen in cells expressing unacetylated ITPK1. These results demonstrate that lysine acetylation alters both the stability as well as the activity of ITPK1 in cells.
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Affiliation(s)
- Philip W Majerus
- Division of Hematology, Washington University Medical School, St Louis, Missouri 63110, USA.
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Abstract
Lipid-derived inositol phosphates (InsPs) comprise a family of second messengers that arise through the action of six classes of InsP kinases, generally referred to as IPKs. Genetic studies have indicated that InsPs play critical roles in embryonic development, but the mechanisms of action for InsPs in mammalian cellular function are largely unknown. This chapter outlines a method for manipulating cellular InsP profiles through the coexpression of a constitutively active G protein and various IPKs. It provides a mechanism by which the metabolism of a variety of InsPs can be upregulated, enabling the evaluation of the effects of these InsPs on cellular functions.
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King J, Keim M, Teo R, Weening KE, Kapur M, McQuillan K, Ryves J, Rogers B, Dalton E, Williams RSB, Harwood AJ. Genetic control of lithium sensitivity and regulation of inositol biosynthetic genes. PLoS One 2010; 5:e11151. [PMID: 20567601 PMCID: PMC2887444 DOI: 10.1371/journal.pone.0011151] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2010] [Accepted: 03/30/2010] [Indexed: 12/12/2022] Open
Abstract
Lithium (Li(+)) is a common treatment for bipolar mood disorder, a major psychiatric illness with a lifetime prevalence of more than 1%. Risk of bipolar disorder is heavily influenced by genetic predisposition, but is a complex genetic trait and, to date, genetic studies have provided little insight into its molecular origins. An alternative approach is to investigate the genetics of Li(+) sensitivity. Using the social amoeba Dictyostelium, we previously identified prolyl oligopeptidase (PO) as a modulator of Li(+) sensitivity. In a link to the clinic, PO enzyme activity is altered in bipolar disorder patients. Further studies demonstrated that PO is a negative regulator of inositol(1,4,5)trisphosphate (IP(3)) synthesis, a Li(+) sensitive intracellular signal. However, it was unclear how PO could influence either Li(+) sensitivity or risk of bipolar disorder. Here we show that in both Dictyostelium and cultured human cells PO acts via Multiple Inositol Polyphosphate Phosphatase (Mipp1) to control gene expression. This reveals a novel, gene regulatory network that modulates inositol metabolism and Li(+) sensitivity. Among its targets is the inositol monophosphatase gene IMPA2, which has also been associated with risk of bipolar disorder in some family studies, and our observations offer a cellular signalling pathway in which PO activity and IMPA2 gene expression converge.
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Affiliation(s)
- Jason King
- School of Biosciences, Cardiff University, Cardiff, United Kingdom
| | - Melanie Keim
- School of Biosciences, Cardiff University, Cardiff, United Kingdom
| | - Regina Teo
- School of Biosciences, Cardiff University, Cardiff, United Kingdom
| | - Karin E. Weening
- School of Biosciences, Cardiff University, Cardiff, United Kingdom
| | - Mridu Kapur
- School of Biosciences, Cardiff University, Cardiff, United Kingdom
| | - Karina McQuillan
- School of Biosciences, Cardiff University, Cardiff, United Kingdom
| | - Jonathan Ryves
- School of Biosciences, Cardiff University, Cardiff, United Kingdom
| | - Ben Rogers
- School of Biosciences, Cardiff University, Cardiff, United Kingdom
| | - Emma Dalton
- School of Biosciences, Cardiff University, Cardiff, United Kingdom
| | - Robin S. B. Williams
- School of Biological Sciences, Royal Holloway, University of London, Egham, Surrey, United Kingdom
| | - Adrian J. Harwood
- School of Biosciences, Cardiff University, Cardiff, United Kingdom
- * E-mail:
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Monserrate JP, York JD. Inositol phosphate synthesis and the nuclear processes they affect. Curr Opin Cell Biol 2010; 22:365-73. [DOI: 10.1016/j.ceb.2010.03.006] [Citation(s) in RCA: 86] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2010] [Revised: 03/03/2010] [Accepted: 03/04/2010] [Indexed: 01/30/2023]
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Expression of inositol 1,3,4-trisphosphate 5/6-kinase (ITPK1) and its role in neural tube defects. ACTA ACUST UNITED AC 2009; 50:365-72. [PMID: 19914276 DOI: 10.1016/j.advenzreg.2009.10.017] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
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Neural tube defects in mice with reduced levels of inositol 1,3,4-trisphosphate 5/6-kinase. Proc Natl Acad Sci U S A 2009; 106:9831-5. [PMID: 19482943 DOI: 10.1073/pnas.0904172106] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Inositol 1,3,4-trisphosphate 5/6-kinase (ITPK1) is a key regulatory enzyme at the branch point for the synthesis of inositol hexakisphosphate (IP(6)), an intracellular signaling molecule implicated in the regulation of ion channels, endocytosis, exocytosis, transcription, DNA repair, and RNA export from the nucleus. IP(6) also has been shown to be an integral structural component of several proteins. We have generated a mouse strain harboring a beta-galactosidase (betagal) gene trap cassette in the second intron of the Itpk1 gene. Animals homozygous for this gene trap are viable, fertile, and produce less ITPK1 protein than wild-type and heterozygous animals. Thus, the gene trap represents a hypomorphic rather than a null allele. Using a combination of immunohistochemistry, in situ hybridization, and betagal staining of mice heterozygous for the hypomorphic allele, we found high expression of Itpk1 in the developing central and peripheral nervous systems and in the paraxial mesoderm. Examination of embryos resulting from homozygous matings uncovered neural tube defects (NTDs) in some animals and axial skeletal defects or growth retardation in others. On a C57BL/6 x 129(P2)Ola background, 12% of mid-gestation embryos had spina bifida and/or exencephaly, whereas wild-type animals of the same genetic background had no NTDs. We conclude that ITPK1 is required for proper development of the neural tube and axial mesoderm.
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Stiles AR, Qian X, Shears SB, Grabau EA. Metabolic and signaling properties of an Itpk gene family in Glycine max. FEBS Lett 2008; 582:1853-8. [PMID: 18474240 PMCID: PMC2515385 DOI: 10.1016/j.febslet.2008.04.054] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2008] [Revised: 04/28/2008] [Accepted: 04/29/2008] [Indexed: 11/21/2022]
Abstract
We have cloned and characterized four Itpk genes from soybean. All four recombinant Itpk proteins showed canonical Ins(1,3,4)P3 5/6-kinase activity, but a kinetic analysis raised questions about its biological significance. Instead, we provide evidence that one alternative biological role for soybean Itpks is to interconvert the Cl(-) channel inhibitor, Ins(3,4,5,6)P4, and its metabolic precursor, Ins(1,3,4,5,6)P5, within a substrate cycle. The soybean Itpks also phosphorylated Ins(3,4,6)P3 to Ins(1,3,4,6)P4 which was further phosphorylated to Ins(1,3,4,5,6)P5 by soybean Ipk2. Thus, soybean Itpks may participate in an inositol lipid-independent pathway of InsP6 synthesis.
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Affiliation(s)
| | | | - Stephen B. Shears
- Department of Plant Pathology, Physiology and Weed Science, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061 (A.R.S, E.A.G);, Laboratory of Signal Transduction, National Institute of Environmental Health Sciences, NIH, DHSS, Research Triangle Park, NC 27709 (X.Q., S.B.S.)
| | - Elizabeth A. Grabau
- Department of Plant Pathology, Physiology and Weed Science, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061 (A.R.S, E.A.G);, Laboratory of Signal Transduction, National Institute of Environmental Health Sciences, NIH, DHSS, Research Triangle Park, NC 27709 (X.Q., S.B.S.)
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Saiardi A, Cockcroft S. Human ITPK1: a reversible inositol phosphate kinase/phosphatase that links receptor-dependent phospholipase C to Ca2+-activated chloride channels. Sci Signal 2008; 1:pe5. [PMID: 18272466 DOI: 10.1126/stke.14pe5] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Inositol 3,4,5,6-tetrakisphosphate [Ins(3,4,5,6)P4] is an inhibitor of the conductance of the Ca(2+)-activated chloride channels in the plasma membrane. These ion channels are required for salt and fluid secretion from epithelial cells, for cell volume homeostasis, and for electrical excitability in neurons and smooth muscle. The enzyme ITPK1 (inositol 1,3,4-triphosphate 5/6 kinase) is the source of Ins(3,4,5,6)P4. It can phosphorylate both Ins(1,3,4)P3 at the 5 or 6 positions and Ins(3,4,5,6)P4 at the 1 position and can also dephosphorylate Ins(1,3,4,5,6)P5 to Ins(3,4,5,6)P4. A study now shows that these various enzyme activities manifested by ITPK1 provide a molecular mechanism that allows the receptor-activated changes in phospholipase C activity and consequent increases in the concentration of Ins(1,3,4)P3 to regulate the abundance of Ins(3,4,5,6)P4. ITPK1 sequesters a tightly bound nucleotide that can accept a phosphate from, or donate a phosphate directly to, an inositol polyphosphate without the nucleotide being released in the bulk medium. This phenomenon of "intersubstrate" transfer is found only in the human enzyme, which can use Ins(1,3,4)P3 to promote increased cellular concentrations of Ins(3,4,5,6)P4.
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Affiliation(s)
- Adolfo Saiardi
- Medical Research Council Cell Biology Unit and Laboratory of Molecular Cell Biology, University College London, London, UK
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Otto JC, Kelly P, Chiou ST, York JD. Alterations in an inositol phosphate code through synergistic activation of a G protein and inositol phosphate kinases. Proc Natl Acad Sci U S A 2007; 104:15653-8. [PMID: 17895383 PMCID: PMC1994134 DOI: 10.1073/pnas.0705729104] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
In mammals, many cellular stimuli evoke a response through G protein activation of phospholipase C, which results in the lipid-derived production of inositol 1,4,5-trisphosphate (IP(3)). Although it is well established that IP(3) is converted to numerous inositol phosphates (IPs) and pyrophosphates (PP-IPs) through the action of up to six classes of inositol phosphate kinases (IPKs), it is not clear that these metabolites are influenced by G protein signaling. Here we report that activation of Galpha(q) leads to robust stimulation of IP(3) to IP(8) metabolism. To expose flux through these pathways, genetic perturbation was used to alter IP homeostasis. Coupled expression of a constitutively active Galpha(q)QL and one or more IPK gene products synergistically generated dramatic changes in the patterns of intracellular IP messengers. Many distinct IP profiles were observed through the expression of different combinations of IPKs, including changes in previously unappreciated pools of IP(5) and IP(6), two molecules widely viewed as stable metabolites. Our data link the activation of a trimeric G protein to a plethora of metabolites downstream of IP(3) and provide a framework for suggesting that cells possess the machinery to produce an IPK-dependent IP code. We imply, but do not prove, that agonist-induced alterations in such a code would theoretically be capable of enhancing signaling complexity and specificity. The essential roles for IPKs in organism development and cellular adaptation are consistent with our hypothesis that such an IP code may be relevant to signaling pathways.
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Affiliation(s)
- James C. Otto
- *Howard Hughes Medical Institute
- Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, NC 27710
| | - Patrick Kelly
- Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, NC 27710
| | - Shean-Tai Chiou
- *Howard Hughes Medical Institute
- Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, NC 27710
| | - John D. York
- *Howard Hughes Medical Institute
- Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, NC 27710
- To whom all correspondence should be addressed. E-mail:
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Abstract
Wnt3a stimulates lymphoid enhancer factor/T-cell factor protein-sensitive transcription, i.e. the canonical pathway, in mouse F9 embryonal tetratocarcinoma cells expressing rat Frizzled-1. We explored the potential roles for inositol polyphosphates as mediators of Wnt signaling in the canonical path-way. Wnt3a triggers G-protein-linked phosphatidylinositol signaling, transiently generating inositol polyphosphates, especially inositol pentakisphosphate (IP(5)) accumulation. Knock-down of Galpha(q) abolishes, whereas expression of the Q209L constitutively active mutant of Galpha(q) mimics, the effects of Wnt3a on IP(5) generation and downstream signaling. Phospholipase Cbeta-1 and Cbeta-3 mediate the G protein signal to the level of phosphatidylinositol signaling. Knock-down and inhibitor studies of the enzymes responsible for generating IP(5) reveal inositol 1,4,5-trisphosphate 3-kinase and inositol polyphosphate multikinase as key mediators in the production of IP(5). Wnt3a stimulation of the canonical pathway requires accumulation of IP(5), which acts to inhibit the activity of glycogen synthase kinase-3beta, whereas stimulating casein kinase 2. Blockade of Wnt3a stimulation of IP(5) generation blocks beta-catenin accumulation, activation of lymphoid enhancer factor/T-cell factor protein-sensitive transcription, and promotion of primitive endoderm formation in response to Wnt3a. Phosphatidylinositol signaling mediates Wnt3a action in the canonical pathway, acting to generate inositol pentakisphosphate, a key second messenger of Wnt3a.
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Affiliation(s)
- Yuan Gao
- Department of Physiology and Biophysics, Diabetes and Metabolic Disease Research Center, School of Medicine, Health Sciences Center, State University of New York, Stony Brook, New York 11794-8661, USA
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Fridy PC, Otto JC, Dollins DE, York JD. Cloning and characterization of two human VIP1-like inositol hexakisphosphate and diphosphoinositol pentakisphosphate kinases. J Biol Chem 2007; 282:30754-62. [PMID: 17690096 DOI: 10.1074/jbc.m704656200] [Citation(s) in RCA: 93] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Eukaryotes possess numerous inositol phosphate (IP) and diphosphoinositol phosphate (PP-IPs or inositol pyrophosphates) species that act as chemical codes important for intracellular signaling pathways. Production of IP and PP-IP molecules occurs through several classes of evolutionarily conserved inositol phosphate kinases. Here we report the characterization of a human inositol hexakisphosphate (IP6) and diphosphoinositol pentakisphosphate (PP-IP5 or IP7) kinase with similarity to the yeast enzyme Vip1, a recently identified IP6/IP7 kinase (Mulugu, S., Bai, W., Fridy, P. C., Bastidas, R. J., Otto, J. C., Dollins, D. E., Haystead, T. A., Ribeiro, A. A., and York, J. D. (2007) Science 316, 106-109). Recombinant human VIP1 exhibits in vitro IP6 and IP7 kinase activities and restores IP7 synthesis when expressed in mutant yeast. Expression of human VIP1 in HEK293T cells engineered to produce high levels of IP7 results in dramatic increases in bisdiphosphoinositol tetrakisphosphate (PP2-IP4 or IP8). Northern blot analysis indicates that human VIP1 is expressed in a variety of tissues and is enriched in skeletal muscle, heart, and brain. The subcellular distribution of tagged human VIP1 is indicative of a cytoplasmic non-membrane localization pattern. We also characterized human and mouse VIP2, an additional gene product with nearly 90% similarity to VIP1 in the kinase domain, and observed both IP6 and IP7 kinase activities. Our data demonstrate that human VIP1 and VIP2 function as IP6 and IP7 kinases that act along with the IP6K/Kcs1-class of kinases to convert IP6 to IP8 in mammalian cells, a process that has been found to occur in response to various stimuli and signaling events.
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Affiliation(s)
- Peter C Fridy
- Department of Pharmacology, Duke University Medical Center, Durham, North Carolina, 27710, USA
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Sweetman D, Stavridou I, Johnson S, Green P, Caddick SEK, Brearley CA. Arabidopsis thaliana inositol 1,3,4-trisphosphate 5/6-kinase 4 (AtITPK4) is an outlier to a family of ATP-grasp fold proteins from Arabidopsis. FEBS Lett 2007; 581:4165-71. [PMID: 17698066 DOI: 10.1016/j.febslet.2007.07.046] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2007] [Revised: 07/16/2007] [Accepted: 07/19/2007] [Indexed: 10/23/2022]
Abstract
The Arabidopsis genome encodes a family of inositol 1,3,4-trisphosphate 5/6-kinases which form a subgroup of a larger group of ATP-grasp fold proteins. An analysis of the inositol 1,3,4-trisphosphate 5/6-kinase family might, ultimately, be best rewarded by detailed comparison of related enzymes in a single genome. The enzyme encoded by At2G43980, AtITPK4; is an outlier to its family. At2G43980 is expressed in male and female organs of young and mature flowers. AtITPK4 differs from other family members in that it does not display inositol 3,4,5,6-tetrakisphosphate 1-kinase activity; rather, it displays inositol 1,4,5,6-tetrakisphosphate and inositol 1,3,4,5-tetrakisphosphate isomerase activity.
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Affiliation(s)
- Dylan Sweetman
- School of Biological Sciences, University of East Anglia, Earlham Road, Norwich, Norfolk, UK
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Seeds AM, Frederick JP, Tsui MMK, York JD. Roles for inositol polyphosphate kinases in the regulation of nuclear processes and developmental biology. ACTA ACUST UNITED AC 2007; 47:10-25. [PMID: 17467778 PMCID: PMC3258027 DOI: 10.1016/j.advenzreg.2006.12.019] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Affiliation(s)
| | | | | | - John D. York
- To whom correspondence should be addressed: Department of Pharmacology and Cancer Biology, Howard Hughes Medical Institute, Duke University Medical Center, DUMC 3813, Durham, NC 27710, Tel: 919-681-6414, Fax: 919-668-0991, E-mail:
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25
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Otto JC, Mulugu S, Fridy PC, Chiou ST, Armbruster BN, Ribeiro AA, York JD. Biochemical analysis of inositol phosphate kinases. Methods Enzymol 2007; 434:171-85. [PMID: 17954248 DOI: 10.1016/s0076-6879(07)34010-x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Lipid-derived inositol phosphates (IPs) are a complex group of second messengers generated by the sequential phosphorylation of inositol 1,4,5-trisphosphate (IP(3)). Synthetic pathways leading from IP(3) to the formation of inositol tetrakisphosphate IP(4), inositol pentakisphosphate IP(5), inositol hexakisphosphate IP(6), and inositol pyrophosphates PP-IPs have been elucidated in eukaryotes from yeast to human. Studies have attributed a variety of cellular functions to IPs, highlighting the importance of understanding how the pathways for their synthesis are regulated. This chapter summarizes experimental techniques for the biochemical characterization of the key inositol phosphate kinases IPKs necessary for producing the diverse array of IP species.
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Affiliation(s)
- James C Otto
- Howard Hughes Medical Institute, Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, North Carolina, USA
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Affiliation(s)
- Victor Raboy
- USDA-ARS and University of Idaho, Aberdeen, Idaho 83210, USA
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York JD. Regulation of nuclear processes by inositol polyphosphates. Biochim Biophys Acta Mol Cell Biol Lipids 2006; 1761:552-9. [PMID: 16781889 DOI: 10.1016/j.bbalip.2006.04.014] [Citation(s) in RCA: 132] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2006] [Accepted: 04/18/2006] [Indexed: 11/18/2022]
Abstract
Inositide signaling pathways represent a multifaceted ensemble of cellular switches capable of regulating a number of processes, for example, intracellular calcium release, membrane trafficking, chemotaxis, ion channel activity and several nuclear functions. Over 30 inositide messengers are found in eukaryotic cells that may be grouped into two classes: (1) inositol lipids, phosphatidylinositols or phosphoinositides (PIPs) and (2) water-soluble inositol polyphosphates (IPs). This review will focus on inositol polyphosphate kinases (IPK) and inositol pyrophosphate synthases (IPS) responsible for the cellular production of IP(4), IP(5) IP(6) and PP-IPs. Of interest, IPK and IPS proteins localize, in part, within the nucleus and their activities are necessary for proper regulation of gene expression, mRNA export, DNA repair and telomere maintenance. The breadth of nuclear processes regulated and the evolutionary conservation of the genes involved in their synthesis have sparked renewed interest in inositide messengers derived from sequential phosphorylation of inositol 1,4,5-trisphosphate.
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Affiliation(s)
- John D York
- Departments of Pharmacology and Cancer Biology and of Biochemistry, Howard Hughes Medical Institute, Duke University Medical Center, Box 3813, Durham, NC 27710, USA.
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Sweetman D, Johnson S, Caddick S, Hanke D, Brearley C. Characterization of an Arabidopsis inositol 1,3,4,5,6-pentakisphosphate 2-kinase (AtIPK1). Biochem J 2006; 394:95-103. [PMID: 16223361 PMCID: PMC1386007 DOI: 10.1042/bj20051331] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The metabolic pathway(s) by which plants synthesize InsP6 (inositol 1,2,3,4,5,6-hexakisphosphate) remains largely undefined [Shears (1998) Biochim. Biophys. Acta 1436, 49-67], while the identities of the genes that encode enzymes catalysing individual steps in these pathways are, with the notable exception of myo-inositol phosphate synthase and ZmIpk [Shi, Wang, Wu, Hazebroek, Meeley and Ertl (2003) Plant Physiol. 131, 507-515], unidentified. A yeast enzyme, ScIPK1, catalyses the synthesis of InsP6 by 2-phosphorylation of Ins(1,3,4,5,6)P5 (inositol 1,3,4,5,6-pentakisphosphate). A human orthologue, HsIPK1, is able to substitute for yeast ScIPK1, restoring InsP6 production in a Saccharomyces cerevisiae mutant strain lacking the ScIPK1 open reading frame (ScIpk1Delta). We have identified an Arabidopsis genomic sequence, AtIPK1, encoding an Ins(1,3,4,5,6)P5 2-kinase. Inclusion of the AtIPK1 protein in alignments of amino acid sequences reveals that human and Arabidopis kinases are more similar to each other than to the S. cerevisiae enzyme, and further identifies an additional motif. Recombinant AtIPK1 protein expressed in Escherichia coli catalysed the synthesis of InsP6 from Ins(1,3,4,5,6)P5. The enzyme obeyed Michaelis-Menten kinetics with an apparent V(max) of 35 nmol x min(-1) x (mg of protein)(-1) and a K(m) for Ins(1,3,4,5,6)P5 of 22 microM at 0.4 mM ATP. RT (reverse transcriptase)-PCR analysis of AtIPK1 transcripts revealed that AtIPK1 is expressed in siliques, leaves and cauline leaves. In situ hybridization experiments further revealed strong expression of AtIPK1 in male and female organs of flower buds. Expression of AtIPK1 protein in an ScIpk1Delta mutant strain restored InsP6 production and rescued the temperature-sensitive growth phenotype of the yeast.
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Affiliation(s)
- Dylan Sweetman
- *School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, U.K
| | - Sue Johnson
- *School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, U.K
| | | | - David E. Hanke
- †Department of Plant Sciences, University of Cambridge, Cambridge CB2 3EA, U.K
| | - Charles A. Brearley
- *School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, U.K
- To whom correspondence may be addressed (email )
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29
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Yang L, Reece J, Gabriel SE, Shears SB. Apical localization of ITPK1 enhances its ability to be a modifier gene product in a murine tracheal cell model of cystic fibrosis. J Cell Sci 2006; 119:1320-8. [PMID: 16537650 DOI: 10.1242/jcs.02836] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
A new aspect of research into the pathogenesis of cystic fibrosis (CF) is a genetics-based search for ;modifier genes' that may affect the severity of CF lung disease. Using an alternative, cell biological approach, we show that ITPK1 should be considered a modifier gene. ITPK1 synthesizes an intracellular signal, inositol (3,4,5,6)-tetrakisphosphate [Ins(3,4,5,6)P4]. A bio-activatable, cell-permeable analogue of Ins(3,4,5,6)P4 inhibited Ca2+-dependent secretion of Cl- from polarized monolayers of immortalized mouse tracheal epithelial cells (MTEs). Analysis by high-pressure liquid chromatography showed endogenous Ins(3,4,5,6)P4 levels in CF MTEs were approximately 60% below those in wild-type MTEs (P<0.03). This adaptation, which improves purinergic activation of Ca2+-dependent Cl- secretion in CF MTEs, was exceptionally specific; there was no effect upon the cellular levels of all the other inositol phosphate signals. Real-time PCR provided the explanation: the level of ITPK1 expression in wild-type MTEs was twice as high as that in CF MTEs (P<0.002). The biological impact of this differential gene expression is amplified by ITPK1 being concentrated at the apical membrane of MTEs, which we discovered following confocal immunofluorescence microscopy. Compartmentalization of Ins(3,4,5,6)P4 synthesis adjacent to its site of action will enhance its regulatory capacity.
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Affiliation(s)
- Ling Yang
- Inositol Signaling Section, and N.I.E.H.S. / N.I.H. / D.H.S.S., Research Triangle Park, NC 27709, USA
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Caldwell KK, Sosa M, Buckley CT. Identification of mitogen-activated protein kinase docking sites in enzymes that metabolize phosphatidylinositols and inositol phosphates. Cell Commun Signal 2006; 4:2. [PMID: 16445858 PMCID: PMC1379644 DOI: 10.1186/1478-811x-4-2] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2005] [Accepted: 01/30/2006] [Indexed: 12/18/2022] Open
Abstract
BACKGROUND Reversible interactions between the components of cellular signaling pathways allow for the formation and dissociation of multimolecular complexes with spatial and temporal resolution and, thus, are an important means of integrating multiple signals into a coordinated cellular response. Several mechanisms that underlie these interactions have been identified, including the recognition of specific docking sites, termed a D-domain and FXFP motif, on proteins that bind mitogen-activated protein kinases (MAPKs). We recently found that phosphatidylinositol-specific phospholipase C-gamma1 (PLC-gamma1) directly binds to extracellular signal-regulated kinase 2 (ERK2), a MAPK, via a D-domain-dependent mechanism. In addition, we identified D-domain sequences in several other PLC isozymes. In the present studies we sought to determine whether MAPK docking sequences could be recognized in other enzymes that metabolize phosphatidylinositols (PIs), as well as in enzymes that metabolize inositol phosphates (IPs). RESULTS We found that several, but not all, of these enzymes contain identifiable D-domain sequences. Further, we found a high degree of conservation of these sequences and their location in human and mouse proteins; notable exceptions were PI 3-kinase C2-gamma, PI 4-kinase type IIbeta, and inositol polyphosphate 1-phosphatase. CONCLUSION The results indicate that there may be extensive crosstalk between MAPK signaling and signaling pathways that are regulated by cellular levels of PIs or IPs.
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Affiliation(s)
- Kevin K Caldwell
- Department of Neurosciences University of New Mexico Health Sciences Center Albuquerque, NM 87131 USA
| | - Marcos Sosa
- Department of Neurosciences University of New Mexico Health Sciences Center Albuquerque, NM 87131 USA
| | - Colin T Buckley
- Department of Neurosciences University of New Mexico Health Sciences Center Albuquerque, NM 87131 USA
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31
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Riley AM, Deleu S, Qian X, Mitchell J, Chung SK, Adelt S, Vogel G, Potter BVL, Shears SB. On the contribution of stereochemistry to human ITPK1 specificity: Ins(1,4,5,6)P4 is not a physiologic substrate. FEBS Lett 2005; 580:324-30. [PMID: 16376887 DOI: 10.1016/j.febslet.2005.12.016] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2005] [Accepted: 12/06/2005] [Indexed: 11/17/2022]
Abstract
Ins(1,4,5,6)P4, a biologically active cell constituent, was recently advocated as a substrate of human Ins(3,4,5,6)P4 1-kinase (hITPK1), because stereochemical factors were believed relatively unimportant to specificity [Miller, G.J., Wilson, M.P., Majerus, P.W. and Hurley, J.H. (2005) Specificity determinants in inositol polyphosphate synthesis: crystal structure of inositol 1,3,4-triphosphate 5/6-kinase. Mol. Cell. 18, 201-212]. Contrarily, we provide three examples of hITPK1 stereospecificity. hITPK1 phosphorylates only the 1-hydroxyl of both Ins(3,5,6)P3 and the meso-compound, Ins(4,5,6)P3. Moreover, hITPK1 has >13,000-fold preference for Ins(3,4,5,6)P4 over its enantiomer, Ins(1,4,5,6)P4. The biological significance of hITPK1 being stereospecific, and not physiologically phosphorylating Ins(1,4,5,6)P4, is reinforced by our demonstrating that Ins(1,4,5,6)P4 is phosphorylated (K(m) = 0.18 microM) by inositolphosphate-multikinase.
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Affiliation(s)
- Andrew M Riley
- Wolfson Laboratory for Medicinal Chemistry, Department of Pharmacy and Pharmacology, University of Bath, Claverton Down, Bath BA2 7AY, UK
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Verbsky J, Majerus PW. Increased levels of inositol hexakisphosphate (InsP6) protect HEK293 cells from tumor necrosis factor (alpha)- and Fas-induced apoptosis. J Biol Chem 2005; 280:29263-8. [PMID: 15967797 DOI: 10.1074/jbc.m503366200] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The overexpression of inositol 1,3,4-trisphosphate 5/6-kinase has recently been shown to protect HEK293 cells from tumor necrosis factor alpha (TNF(alpha))-induced apoptosis. This overexpression leads to an increase in the levels of both inositol 1,3,4,5,6-pentakisphosphate (InsP5) and inositol 1,2,3,4,5,6-hexakisphosphate (InsP6). Cells that overexpress InsP5 2-kinase have increased levels of InsP6 and are also protected from TNFalpha-induced apoptosis; furthermore, cells that express an RNA interference construct to the 2-kinase are deficient in InsP6 and are sensitized to TNFalpha-induced apoptosis. Therefore the protective effect of 5/6-kinase on TNFalpha-mediated apoptosis is due to an increase of InsP6 or to a metabolite derived from InsP6. Furthermore, we find that the InsP6 also protects from Fas-mediated apoptosis. No effect was seen in the endocytic rate of transferrin receptor, caspase 8 activity, or TNF receptor number at the cell surface. Cells that overexpress 2-kinase do show an increase in the amount of receptor-interacting protein (RIP), while cells with reduced InsP6 levels show relatively less RIP, providing a possible mechanism for the effect on apoptosis.
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Affiliation(s)
- John Verbsky
- Department of Internal Medicine, Division of Hematology, Washington University School of Medicine, St. Louis, MO 63110, USA
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33
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Miller GJ, Wilson MP, Majerus PW, Hurley JH. Specificity determinants in inositol polyphosphate synthesis: crystal structure of inositol 1,3,4-trisphosphate 5/6-kinase. Mol Cell 2005; 18:201-12. [PMID: 15837423 DOI: 10.1016/j.molcel.2005.03.016] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2005] [Revised: 03/10/2005] [Accepted: 03/18/2005] [Indexed: 01/08/2023]
Abstract
Inositol hexakisphosphate and other inositol high polyphosphates have diverse and critical roles in eukaryotic regulatory pathways. Inositol 1,3,4-trisphosphate 5/6-kinase catalyzes the rate-limiting step in inositol high polyphosphate synthesis in animals. This multifunctional enzyme also has inositol 3,4,5,6-tetrakisphosphate 1-kinase and other activities. The structure of an archetypal family member, from Entamoeba histolytica, has been determined to 1.2 A resolution in binary and ternary complexes with nucleotide, substrate, and product. The structure reveals an ATP-grasp fold. The inositol ring faces ATP edge-on such that the 5- and 6-hydroxyl groups are nearly equidistant from the ATP gamma-phosphate in catalytically productive phosphoacceptor positions and explains the unusual dual site specificity of this kinase. Inositol tris- and tetrakisphosphates interact via three phosphate binding subsites and one solvent-exposed site that could in principle be occupied by 18 different substrates, explaining the mechanisms for the multiple specificities and catalytic activities of this enzyme.
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Affiliation(s)
- Gregory J Miller
- Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, United States Department of Health and Human Services, Bethesda, Maryland 20892, USA
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Shears SB, Yang L, Qian X. Cell signaling by a physiologically reversible inositol phosphate kinase/phosphatase. ACTA ACUST UNITED AC 2005; 44:265-77. [PMID: 15581495 DOI: 10.1016/j.advenzreg.2004.02.002] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Affiliation(s)
- Stephen B Shears
- Laboratory of Signal Transduction, Inositol Signaling Section, National Institute of Environmental Health Sciences, NIH/DHHS, Research Triangle Park, NC 27709, USA.
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35
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Verbsky JW, Chang SC, Wilson MP, Mochizuki Y, Majerus PW. The pathway for the production of inositol hexakisphosphate in human cells. J Biol Chem 2004; 280:1911-20. [PMID: 15531582 DOI: 10.1074/jbc.m411528200] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The yeast and Drosophila pathways leading to the production of inositol hexakisphosphate (InsP(6)) have been elucidated recently. The in vivo pathway in humans has been assumed to be similar. Here we show that overexpression of Ins(1,3,4)P(3) 5/6-kinase in human cell lines results in an increase of inositol tetrakisphosphate (InsP(4)) isomers, inositol pentakisphosphate (InsP(5)) and InsP(6), whereas its depletion by RNA interference decreases the amounts of these inositol phosphates. Expression of Ins(1,3,4,6)P(4) 5-kinase does not increase the amount of InsP(5) and InsP(6), although its depletion does block InsP(5) and InsP(6) production, showing that it is necessary for production of InsP(5) and InsP(6). Expression of Ins(1,3,4,5,6)P(5) 2-kinase increases the amount of InsP(6) by depleting the InsP(5) in the cell, and depletion of 2-kinase decreases the amount of InsP(6) and causes an increase in InsP(5). These results are consistent with a pathway that produces InsP(6) through the sequential action of Ins(1,3,4)P(3) 5/6-kinase, Ins(1,3,4,6)P(4) 5-kinase, and Ins(1,3,4,5,6)P5 2-kinase to convert Ins(1,3,4)P(3) to InsP(6). Furthermore, the evidence implicates 5/6-kinase as the rate-limiting enzyme in this pathway.
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Affiliation(s)
- John W Verbsky
- Department of Internal Medicine, Division of Hematology, Washington University School of Medicine, St. Louis, Missouri 63110, USA
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36
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González B, Schell MJ, Letcher AJ, Veprintsev DB, Irvine RF, Williams RL. Structure of a human inositol 1,4,5-trisphosphate 3-kinase: substrate binding reveals why it is not a phosphoinositide 3-kinase. Mol Cell 2004; 15:689-701. [PMID: 15350214 DOI: 10.1016/j.molcel.2004.08.004] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2004] [Revised: 06/29/2004] [Accepted: 07/01/2004] [Indexed: 11/30/2022]
Abstract
Mammalian cells produce a variety of inositol phosphates (InsPs), including Ins(1,4,5)P3 that serves both as a second messenger and as a substrate for inositol polyphosphate kinases (IPKs), which further phosphorylate it. We report the structure of an IPK, the human Ins(1,4,5)P3 3-kinase-A, both free and in complexes with substrates and products. This enzyme catalyzes transfer of a phosphate from ATP to the 3-OH of Ins(1,4,5)P3, and its X-ray crystal structure provides a template for understanding a broad family of InsP kinases. The catalytic domain consists of three lobes. The N and C lobes bind ATP and resemble protein and lipid kinases, despite insignificant sequence similarity. The third lobe binds inositol phosphate and is a unique four-helix insertion in the C lobe. This lobe embraces all of the phosphates of Ins(1,4,5)P3 in a positively charged pocket, explaining the enzyme's substrate specificity and its inability to phosphorylate PtdIns(4,5)P2, the membrane-resident analog of Ins(1,4,5)P3.
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Affiliation(s)
- Beatriz González
- MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, United Kingdom
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37
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Shears SB. How versatile are inositol phosphate kinases? Biochem J 2004; 377:265-80. [PMID: 14567754 PMCID: PMC1223885 DOI: 10.1042/bj20031428] [Citation(s) in RCA: 148] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2003] [Revised: 10/14/2003] [Accepted: 10/20/2003] [Indexed: 01/31/2023]
Abstract
This review assesses the extent and the significance of catalytic versatility shown by several inositol phosphate kinases: the inositol phosphate multikinase, the reversible Ins(1,3,4) P (3)/Ins(3,4,5,6) P (4) kinase, and the kinases that synthesize diphosphoinositol polyphosphates. Particular emphasis is placed upon data that are relevant to the situation in vivo. It will be shown that catalytic promiscuity towards different inositol phosphates is not typically an evolutionary compromise, but instead is sometimes exploited to facilitate tight regulation of physiological processes. This multifunctionality can add to the complexity with which inositol signalling pathways interact. This review also assesses some proposed additional functions for the catalytic domains, including transcriptional regulation, protein kinase activity and control by molecular 'switching', all in the context of growing interest in 'moonlighting' (gene-sharing) proteins.
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Affiliation(s)
- Stephen B Shears
- Inositol Signaling Section, Laboratory of Signal Transduction, NIEHS/NIH/DHSS Research Triangle Park, NC 27709, USA.
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38
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Abstract
myo-Inositol-1,2,3,4,5,6-hexakisphosphate (Ins P(6)) was first described as an abundant form of phosphorus in plant seeds and other plant tissues and dubbed "phytic acid". Subsequently it was found to be a common constituent in eukaryotic cells, its metabolism a basic component of cellular housekeeping. In addition to phosphate, myo-inositol (Ins) and mineral storage and retrieval in plant organs and tissues, other roles for Ins P(6) include service as a major metabolic pool in Ins phosphate and pyrophosphate pathways involved in signaling and regulation; possibly as an effector or ligand in these processes; as a form of energy currency and in ATP regeneration; in RNA export and DNA repair; and as an anti-oxidant. The relatively recent demonstration that pyrophosphate-containing derivatives of Ins P(6) can function as phosphate donors in the regeneration of ATP is reminiscent of the proposal, made four decades ago in studies of seed development, that Ins P(6) itself may serve in this function. Studies of Ins P(6) in non-plant systems rarely include the consideration that this compound might represent a significant fraction of cellular P; cellular phosphate nutrition has been viewed as either not interesting or of little importance. However, there may be few fundamental differences among diverse eukaryotes in both the metabolic pathways involving Ins P(6) and the spectrum of possible roles for it and its metabolites.
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Affiliation(s)
- Victor Raboy
- USDA-ARS, 1691 South 2700 West, Aberdeen, ID 83210, USA.
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Sun Y, Mochizuki Y, Majerus PW. Inositol 1,3,4-trisphosphate 5/6-kinase inhibits tumor necrosis factor-induced apoptosis. J Biol Chem 2003; 278:43645-53. [PMID: 12925536 DOI: 10.1074/jbc.m300674200] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Tumor necrosis factor receptor 1 (TNF-R1) signaling elicits a wide range of biological responses, including inflammation, proliferation, differentiation, and apoptosis. TNF-R1 activates both caspase-mediated apoptosis and NF-kappaB transcription of anti-apoptotic factors. We now report a link between the TNF-R1 and inositol phosphate signaling pathways. We observed that overexpression of inositol 1,3,4-trisphosphate 5/6-kinase (5/6-kinase) inhibited apoptosis induced by TNFalpha. The anti-apoptotic effect by 5/6-kinase is not attributable to NF-kappaB activation, as no changes were detected in the levels of NF-kappaB DNA binding, IkappaBalpha degradation, or anti-apoptotic factors, such as x-linked inhibitor of apoptosis protein. Decreased expression of 5/6-kinase by RNA interference rendered HeLa cells more susceptible to TNFalpha-induced apoptosis. Overexpression of 5/6-kinase in human embryonic kidney 293 cells inhibited TNFalpha-induced activation of caspases-8, -3, and -9, BID, and poly(ADP-ribose) polymerase. However, 5/6-kinase did not protect against Fas-, etoposide-, or cycloheximide-induced apoptosis. Further, 5/6-kinase protected against apoptosis induced by the overexpression of TNF-R1-associated death domain but not Fas-associated death domain. Therefore, we suggest that 5/6-kinase modifies TNFalpha-induced apoptosis by interfering with the activation of TNF-R1-associated death domain.
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Affiliation(s)
- Young Sun
- Department of Internal Medicine, Division of Hematology, Washington University School of Medicine, St. Louis, Missouri 63110, USA
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Dewaste V, Moreau C, De Smedt F, Bex F, De Smedt H, Wuytack F, Missiaen L, Erneux C. The three isoenzymes of human inositol-1,4,5-trisphosphate 3-kinase show specific intracellular localization but comparable Ca2+ responses on transfection in COS-7 cells. Biochem J 2003; 374:41-9. [PMID: 12747803 PMCID: PMC1223573 DOI: 10.1042/bj20021963] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2002] [Revised: 04/24/2003] [Accepted: 05/15/2003] [Indexed: 12/16/2022]
Abstract
Inositol 1,4,5-trisphosphate [Ins(1,4,5) P3] 3-kinase catalyses the phosphorylation of InsP3 to inositol 1,3,4,5-tetrakisphosphate. cDNAs encoding three human isoenzymes of InsP3 3-kinase (A, B and C) have been reported previously [Choi, Kim, Lee, Moon, Sim, Kim, Chung and Rhee (1990) Science 248, 64-66; Dewaste, Pouillon, Moreau, Shears, Takazawa and Erneux (2000) Biochem. J. 352, 343-351; Dewaste, Roymans, Moreau and Erneux (2002) Biochem. Biophys. Res. Commun. 291, 400-405; Takazawa, Perret, Dumont and Erneux (1991) Biochem. Biophys. Res. Commun. 174, 529-535]. The localization of InsP3 3-kinase isoenzymes fused at their N-terminus to the green fluorescent protein has been studied by confocal microscopy. The A isoform appeared to associate with the cytoskeleton, whereas the C isoform was totally cytoplasmic. The B isoform had a more complex localization: it appeared in the plasma membrane, cytoskeleton and in the endoplasmic reticulum. The three human isoenzymes of InsP3 3-kinase can thus be distinguished by their N-terminal sequence, sensitivity to Ca2+/calmodulin and localization on transfection in COS-7 cells. We have compared the cytosolic Ca2+ responses induced by ATP in COS-7 cells transfected with the three isoenzymes. Cells expressing high levels of any of the three isoforms no longer respond to ATP, whereas cells expressing low levels of each enzyme showed a reduced response consisting of one to three Ca2+ spikes in response to 100 microM ATP. These effects were seen only in wild-type InsP3 3-kinase-transfected cells. 3-Kinase-dead mutant cells behaved as vector-transfected cells. The results highlight the potential role of the three isoforms of InsP3 3-kinase as direct InsP3 metabolizing enzymes and direct regulators of Ca2+ responses to extracellular signals.
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Affiliation(s)
- Valérie Dewaste
- Institute of Interdisciplinary Research, Université Libre de Bruxelles, Campus Erasme, Bldg. C, 808 route de Lennik, B-1070 Brussels, Belgium
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41
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Nalaskowski MM, Bertsch U, Fanick W, Stockebrand MC, Schmale H, Mayr GW. Rat inositol 1,4,5-trisphosphate 3-kinase C is enzymatically specialized for basal cellular inositol trisphosphate phosphorylation and shuttles actively between nucleus and cytoplasm. J Biol Chem 2003; 278:19765-76. [PMID: 12649294 DOI: 10.1074/jbc.m211059200] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The calcium-liberating second messenger inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) is converted to inositol 1,3,4,5-tetrakisphosphate (Ins(1,3,4,5)P4) by Ins(1,4,5)P3 3-kinases (IP3Ks) that add a fourth phosphate group to the 3-position of the inositol ring. Two isoforms of IP3Ks (named A and B) from different vertebrate species have been well studied. Recently the cloning and examination of a human full-length cDNA encoding a novel isoform, termed human IP3K-C (HsIP3K-C), has been reported. In the present study we report the cloning of a full-length cDNA encoding a rat homologue of HsIP3K-C with a unique mRNA expression pattern, which differs remarkably from the tissue distribution of HsIP3K-C. Of the rat tissues examined, rat IP3K-C (RnIP3K-C) is mainly present in heart, brain, and testis and shows the strongest expression in an epidermal tissue, namely tongue epithelium. RnIP3K-C has a calculated molecular mass of approximately 74.5 kDa and shows an overall identity of approximately 75% with HsIP3K-C. A bacterially expressed, enzymatically active and Ca2+-calmodulin-regulated fragment of this isoform displays remarkable enzymatic properties like a very low Km for Ins(1,4,5)P3 ( approximately 0.2 microm), substrate inhibition by high concentrations of Ins(1,4,5)P3, allosteric product activation by Ins(1,3,4,5)P4 in absence of Ca2+-calmodulin (Ka(app) 0.52 microm), and the ability to efficiently phosphorylate a second InsP3 substrate, inositol 2,4,5-trisphosphate, to inositol 2,4,5,6-tetrakisphosphate in the presence of Ins(1,3,4,5)P4. Furthermore, the RnIP3K-C fused with a fluorescent protein tag is actively transported into and out of the nucleus when transiently expressed in mammalian cells. A leucine-rich nuclear export signal and an uncharacterized nuclear import activity are localized in the N-terminal domain of the protein and determine its nucleocytoplasmic shuttling. These findings point to a particular role of RnIP3K-C in nuclear inositol trisphosphate phosphorylation and cellular growth.
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Affiliation(s)
- Marcus M Nalaskowski
- Institute for Cellular Signal Transduction, University Hospital Hamburg-Eppendorf, Martinistrasse 52, Germany
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42
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Shi J, Wang H, Wu Y, Hazebroek J, Meeley RB, Ertl DS. The maize low-phytic acid mutant lpa2 is caused by mutation in an inositol phosphate kinase gene. PLANT PHYSIOLOGY 2003; 131:507-15. [PMID: 12586875 PMCID: PMC166827 DOI: 10.1104/pp.014258] [Citation(s) in RCA: 96] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/06/2002] [Revised: 10/11/2002] [Accepted: 11/06/2002] [Indexed: 05/18/2023]
Abstract
Reduced phytic acid content in seeds is a desired goal for genetic improvement in several crops. Low-phytic acid mutants have been used in genetic breeding, but it is not known what genes are responsible for the low-phytic acid phenotype. Using a reverse genetics approach, we found that the maize (Zea mays) low-phytic acid lpa2 mutant is caused by mutation in an inositol phosphate kinase gene. The maize inositol phosphate kinase (ZmIpk) gene was identified through sequence comparison with human and Arabidopsis Ins(1,3,4)P(3) 5/6-kinase genes. The purified recombinant ZmIpk protein has kinase activity on several inositol polyphosphates, including Ins(1,3,4)P(3), Ins(3,5,6)P(3), Ins(3,4,5,6)P(4), and Ins(1,2,5,6)P(4). The ZmIpk mRNA is expressed in the embryo, the organ where phytic acid accumulates in maize seeds. The ZmIpk Mutator insertion mutants were identified from a Mutator F(2) family. In the ZmIpk Mu insertion mutants, seed phytic acid content is reduced approximately 30%, and inorganic phosphate is increased about 3-fold. The mutants also accumulate myo-inositol and inositol phosphates as in the lpa2 mutant. Allelic tests showed that the ZmIpk Mu insertion mutants are allelic to the lpa2. Southern-blot analysis, cloning, and sequencing of the ZmIpk gene from lpa2 revealed that the lpa2-1 allele is caused by the genomic sequence rearrangement in the ZmIpk locus and the lpa2-2 allele has a nucleotide mutation that generated a stop codon in the N-terminal region of the ZmIpk open reading frame. These results provide evidence that ZmIpk is one of the kinases responsible for phytic acid biosynthesis in developing maize seeds.
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Affiliation(s)
- Jinrui Shi
- Pioneer Hi-Bred International, P.O. Box 1004, Johnston, Iowa 50131, USA.
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43
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Sun Y, Wilson MP, Majerus PW. Inositol 1,3,4-trisphosphate 5/6-kinase associates with the COP9 signalosome by binding to CSN1. J Biol Chem 2002; 277:45759-64. [PMID: 12324474 DOI: 10.1074/jbc.m208709200] [Citation(s) in RCA: 83] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The COP9 signalosome (CSN) is a complex of eight proteins first identified as a repressor of plant photomorphogenesis. A protein kinase activity associated with the COP9 signalosome has been reported but not identified; we present evidence for inositol 1,3,4-trisphosphate 5/6-kinase (5/6-kinase) as a protein kinase associated with the COP9 signalosome. We have shown that 5/6-kinase exists in a complex with the eight-component COP9 signalosome both when purified from bovine brain and when transfected into HEK 293 cells. 5/6-kinase phosphorylates the same substrates as those of the COP9 signalosome, including IkappaBalpha, p53, and c-Jun but fails to phosphorylate several other substrates, including c-Jun 1-79, which are not substrates for the COP9-associated kinase. Both the COP9 signalosome- associated kinase and 5/6-kinase are inhibited by curcumin. The association of 5/6-kinase with the COP9 signalosome is through an interaction with CSN1, which immunoprecipitates with 5/6-kinase. In addition, the inositol kinase activity of 5/6-kinase is inhibited when in a complex with CSN1. We propose that 5/6-kinase is the previously described COP9 signalosome-associated kinase.
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Affiliation(s)
- Young Sun
- Department of Internal Medicine, Division of Hematology, Washington University School of Medicine, Saint Louis, Missouri 63110, USA
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44
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Chang SC, Miller AL, Feng Y, Wente SR, Majerus PW. The human homolog of the rat inositol phosphate multikinase is an inositol 1,3,4,6-tetrakisphosphate 5-kinase. J Biol Chem 2002; 277:43836-43. [PMID: 12223481 DOI: 10.1074/jbc.m206134200] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We have demonstrated that the human homolog of the rat inositol phosphate multikinase is an inositol 1,3,4,6-tetrakisphosphate 5-kinase (InsP(4) 5-kinase). The cDNA of the human gene contained a putative open reading frame of 1251 bp encoding 416 amino acids with 83.6% identity compared with the rat protein. The substrate specificity of the recombinant human protein demonstrated preference for Ins(1,3,4,6)P(4) with a catalytic efficiency (V(max)/K(m)) 43-fold greater than that of Ins(1,3,4,5)P(4) and 2-fold greater than that of Ins(1,4,5)P(3). The apparent V(max) was 114 nmol of Ins(1,3,4,5,6)P(5) formed/min/mg of protein, and the apparent K(m) was 0.3 microm Ins(1,3,4,6)P(4). The functional homolog in yeast is Ipk2p, and ipk2-null yeast strains do not synthesize Ins(1,3,4,5,6)P(5) or InsP(6). Synthesis of these compounds was restored by transformation with wild-type yeast IPK2 but not with human InsP(4) 5-kinase. Thus the human gene does not complement for the loss of the yeast gene because yeast cells do not contain the substrate Ins(1,3,4,6)P(4), and the reaction of the human protein with Ins(1,3,4,5)P(4) is insufficient to effect rescue or synthesis of InsP(5) and InsP(6). Therefore the major activity of human InsP(4) 5-kinase is phosphorylation at the D-5 position, and the pathways for synthesis of Ins(1,3,4,5,6)P(5) in yeast versus humans are different.
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Affiliation(s)
- Shao-Chun Chang
- Department of Internal Medicine, Division of Hematology, Washington University School of Medicine, St. Louis, Missouri 63110, USA
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45
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Stevenson-Paulik J, Odom AR, York JD. Molecular and biochemical characterization of two plant inositol polyphosphate 6-/3-/5-kinases. J Biol Chem 2002; 277:42711-8. [PMID: 12226109 DOI: 10.1074/jbc.m209112200] [Citation(s) in RCA: 111] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Despite the high deposition of inositol hexakisphosphate (IP(6)), also known as phytate or phytin, in certain plant tissues little is known at the molecular level about the pathway(s) involved in its production. In budding yeast, IP(6) synthesis occurs through the sequential phosphorylation of I(1,4,5)P(3) by two gene products, Ipk2 and Ipk1, a IP(3)/IP(4) dual-specificity 6-/3-kinase and an inositol 1,3,4,5,6-pentakisphosphate 2-kinase, respectively. Here we report the identification and characterization of two inositol polyphosphate kinases from Arabidopsis thaliana, designated AtIpk2alpha and AtIpk2beta that are encoded by distinct genes on chromosome 5 and that are ubiquitously expressed in mature tissue. The primary structures of AtIpk2alpha and AtIpk2beta are 70% identical to each other and 12-18% identical to Ipk2s from yeast and mammals. Similar to yeast Ipk2, purified recombinant AtIpk2alpha and AtIpk2beta have 6-/3-kinase activities that sequentially phosphorylate I(1,4,5)P(3) to generate I(1,3,4,5,6)P(5) predominantly via an I(1,4,5,6)P(4) intermediate. While I(1,3,4,5)P(4) is a substrate for the plant Ipk2s, it does not appear to be a detectable product of the IP(3) reaction. Additionally, we report that the plant and yeast Ipk2 have a novel 5-kinase activity toward I(1,3,4,6)P(4) and I(1,2,3,4,6)P(5), which would allow these proteins to participate in at least two proposed pathways in the synthesis of IP(6). Heterologous expression of either plant isoform in an ipk2 mutant yeast strain restores IP(4) and IP(5) production in vivo and rescues its temperature-sensitive growth defects. Collectively our results provide a molecular basis for the synthesis of higher inositol polyphosphates in plants through multiple routes and indicate that the 6-/3-/5-kinase activities found in plant extracts may be encoded by the IPK2 gene class.
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Affiliation(s)
- Jill Stevenson-Paulik
- Department of Pharmacology and Cancer Biology, Howard Hughes Medical Institute, Duke University Medical Center, Durham, North Carolina 27710, USA
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Verbsky JW, Wilson MP, Kisseleva MV, Majerus PW, Wente SR. The synthesis of inositol hexakisphosphate. Characterization of human inositol 1,3,4,5,6-pentakisphosphate 2-kinase. J Biol Chem 2002; 277:31857-62. [PMID: 12084730 DOI: 10.1074/jbc.m205682200] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The enzyme(s) responsible for the production of inositol hexakisphosphate (InsP(6)) in vertebrate cells are unknown. In fungal cells, a 2-kinase designated Ipk1 is responsible for synthesis of InsP(6) by phosphorylation of inositol 1,3,4,5,6-pentakisphosphate (InsP(5)). Based on limited conserved sequence motifs among five Ipk1 proteins from different fungal species, we have identified a human genomic DNA sequence on chromosome 9 that encodes human inositol 1,3,4,5,6-pentakisphosphate 2-kinase (InsP(5) 2-kinase). Recombinant human enzyme was produced in Sf21 cells, purified, and shown to catalyze the synthesis of InsP(6) or phytic acid in vitro. The recombinant protein converted 31 nmol of InsP(5) to InsP(6)/min/mg of protein (V(max)). The Michaelis-Menten constant for InsP(5) was 0.4 microM and for ATP was 21 microM. Saccharomyces cerevisiae lacking IPK1 do not produce InsP(6) and show lethality in combination with a gle1 mutant allele. Here we show that expression of the human InsP(5) 2-kinase in a yeast ipk1 null strain restored the synthesis of InsP(6) and rescued the gle1-2 ipk1-4 lethal phenotype. Northern analysis on human tissues showed expression of the human InsP(5) 2-kinase mRNA predominantly in brain, heart, placenta, and testis. The isolation of the gene responsible for InsP(6) synthesis in mammalian cells will allow for further studies of the InsP(6) signaling functions.
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Affiliation(s)
- John W Verbsky
- Department of Internal Medicine, Washington University School of Medicine, St. Louis, Missouri 63110, USA
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47
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Ho MWY, Yang X, Carew MA, Zhang T, Hua L, Kwon YU, Chung SK, Adelt S, Vogel G, Riley AM, Potter BVL, Shears SB. Regulation of Ins(3,4,5,6)P(4) signaling by a reversible kinase/phosphatase. Curr Biol 2002; 12:477-82. [PMID: 11909533 DOI: 10.1016/s0960-9822(02)00713-3] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Regulation of Cl(-) channel conductance by Ins(3,4,5,6)P(4) provides receptor-dependent control over salt and fluid secretion, cell volume homeostasis, and electrical excitability of neurones and smooth muscle. Ignorance of how Ins(3,4,5,6)P(4) is synthesized has long hindered our understanding of this signaling pathway. We now show Ins(3,4,5,6)P(4) synthesis by Ins(1,3,4,5,6)P(5) 1-phosphatase activity by an enzyme previously characterized as an Ins(3,4,5,6)P(4) 1-kinase. Rationalization of these phenomena with a ligand binding model unveils Ins(1,3,4)P(3) as not simply an alternative kinase substrate, but also an activator of Ins(1,3,4,5,6)P(5) 1-phosphatase. Stable overexpression of the enzyme in epithelial monolayers verifies its physiological role in elevating Ins(3,4,5,6)P(4) levels and inhibiting secretion. It is exceptional for a single enzyme to catalyze two opposing signaling reactions (1-kinase/1-phosphatase) under physiological conditions. Reciprocal coordination of these opposing reactions offers an alternative to general doctrine that intracellular signals are regulated by integrating multiple, distinct phosphatases and kinases.
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Affiliation(s)
- Melisa W Y Ho
- Inositide Signaling Group, Laboratory of Signal Transduction and National Institute of Environmental Health Sciences, Research Triangle Park, NC 27709, USA
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48
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Wilson MP, Sun Y, Cao L, Majerus PW. Inositol 1,3,4-trisphosphate 5/6-kinase is a protein kinase that phosphorylates the transcription factors c-Jun and ATF-2. J Biol Chem 2001; 276:40998-1004. [PMID: 11533064 DOI: 10.1074/jbc.m106605200] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Phosphorylation of inositol 1,3,4-trisphosphate by inositol 1,3,4-trisphosphate 5/6-kinase is the first committed step in the formation of higher phosphorylated forms of inositol. We have shown that the eight proteins called the COP9 signalosome complex copurify with calf brain 5/6-kinase. Because the complex has been shown to phosphorylate c-Jun in vitro, we tested both the complex and 5/6-kinase and found that both are able to phosphorylate c-Jun and ATF-2 on serine/threonine residues. These findings establish a link between two major signal transduction systems: the inositol phosphates and the stress response system.
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Affiliation(s)
- M P Wilson
- Washington University School of Medicine, Department of Internal Medicine, St. Louis, Missouri 63110, USA.
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York JD, Guo S, Odom AR, Spiegelberg BD, Stolz LE. An expanded view of inositol signaling. ADVANCES IN ENZYME REGULATION 2001; 41:57-71. [PMID: 11384737 DOI: 10.1016/s0065-2571(00)00025-x] [Citation(s) in RCA: 77] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Affiliation(s)
- J D York
- Howard Hughes Medical Institute, Departments of Pharmacology and Cancer Biology, and of Biochemistry, Duke University Medical Center, DUMC 3813, Durham NC 27710, USA.
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Abstract
Following the discovery of inositol-1,4,5-trisphosphate as a second messenger, many other inositol phosphates were discovered in quick succession, with some understanding of their synthesis pathways and a few guesses at their possible functions. But then it all seemed to go comparatively quiet, with an explosion of interest in the inositol lipids. Now the water-soluble phase is once again becoming a focus of interest. Old and new data point to a new vista of inositol phosphates, with functions in many diverse aspects of cell biology, such as ion-channel physiology, membrane dynamics and nuclear signalling.
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Affiliation(s)
- R F Irvine
- Department of Pharmacology, Tennis Court Road, Cambridge CB2 1QJ, UK.
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