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Philip W. Majerus - One of the best experts on this subject based on the ideXlab platform.

  • regulation of pi 3 k akt signalling and cellular transformation by Inositol Polyphosphate 4 phosphatase 1
    EMBO Reports, 2009
    Co-Authors: Ivan Ivetac, Philip W. Majerus, Rajendra Gurung, Lauren C. Binge, Sandra Hakim, Kristy A Horan, David A Sheffield, Tony Tiganis, Christina Anne Mitchell
    Abstract:

    Akt is a crucial phosphoinositide 3-kinase (PI(3)K) effector that regulates cell proliferation and survival. PI(3)K-generated signals, PtdIns(3,4,5)P3 and PtdIns(3,4)P2, direct Akt plasma membrane engagement. Pathological Akt plasma membrane association promotes oncogenesis. PtdIns(3,4)P2 is degraded by Inositol Polyphosphate 4-phosphatase-1 (4-ptase-1) forming PtdIns(3)P; however, the role of 4-ptase-1 in regulating the activation and function of Akt is unclear. In mouse embryonic fibroblasts lacking 4-ptase-1 (−/−MEFs), the Akt-pleckstrin homology (PH) domain was constitutively membrane-associated both in serum-starved and agonist-stimulated cells, in contrast to +/+MEFs, in which it was detected only at the plasma membrane following serum stimulation. Epidermal growth factor (EGF) stimulation resulted in increased Ser473 and Thr308-Akt phosphorylation and activation of Akt-dependent signalling in −/−MEFs, relative to +/+MEFs. Significantly, loss of 4-ptase-1 resulted in increased cell proliferation and decreased apoptosis. SV40-transformed −/−MEFs showed increased anchorage-independent cell growth and formed tumours in nude mice. This study provides the first evidence, to our knowledge, that 4-ptase-1 controls the activation of Akt and thereby cell proliferation, survival and tumorigenesis.

  • The Inositol Polyphosphate 5-phosphatase Ocrl associates with endosomes that are partially coated with clathrin
    Proceedings of the National Academy of Sciences, 2004
    Co-Authors: Alexander Ungewickell, Michael Ward, Ernst J. Ungewickell, Philip W. Majerus
    Abstract:

    The subcellular localization of Ocrl, the Inositol Polyphosphate 5-phosphatase that is mutated in Lowe syndrome, was investigated by fluorescence microscopy. Ocrl was localized to endosomes and Golgi membranes along with clathrin, giantin, the mannose 6-phosphate receptor, transferrin, and the early endosomal antigen 1 endosomal marker in fixed cells. The endosomal localization of Ocrl was confirmed by live-cell time-lapse microscopy in which we monitored the dynamics of Ocrl on endosomes. GST binding assays show that Ocrl interacts with the clathrin terminal domain and the clathrin adaptor protein AP-2. Our findings suggest a role for Ocrl in endosomal receptor trafficking and sorting.

  • phosphoinositide specific Inositol Polyphosphate 5 phosphatase iv inhibits akt protein kinase b phosphorylation and leads to apoptotic cell death
    Journal of Biological Chemistry, 2002
    Co-Authors: Marina V Kisseleva, Li Cao, Philip W. Majerus
    Abstract:

    Abstract Phosphoinositide-specific Inositol Polyphosphate 5- phosphatase IV has the affinity for PI(3,4,5)P3 (K m = 0.65 μM) that is approximately 10-fold greater than the other Inositol Polyphosphate 5-phosphatases, which use this substrate including SHIP, OCRL, and 5ptase II, suggesting that it may be important in controlling intracellular levels of this metabolite. We created cell lines stably expressing the enzyme to study its effect on cell function. We found that overexpression of 5ptase IV in 293 cells caused the rapid depletion of both PI(4,5)P2 and PI(3,4,5)P3 in cells with corresponding increases in the products, PI(4)P and PI(3,4)P2, changing the balance of two phosphoInositol products of phosphoinositide 3-kinase, PI(3,4)P2 and PI(3,4,5)P3, in the cell. One of the targets of these phosphoinositides is the serine/threonine kinase Akt, which plays an important role in the control of apoptosis. We were able to address the relative roles of PI(3,4)P2 and PI(3,4,5)P3 in the activation of Akt by selective depletion of these phosphoinositides in cells stably transfected with 5ptase IV and Inositol Polyphosphate 4-phosphatase (4ptase I). In cells transfected with 4ptase I, the level of PI(3,4)P2 was reduced, and PI(3,4,5)P3 was increased. Expression of the two enzymes had the opposite effect on the phosphorylation of Akt in response to stimulation with growth factors or heat shock. Akt phosphorylation was inhibited in cells expressing 5ptase IV but increased in 4ptase I cells and correlated with the intracellular level of PI(3,4,5)P3 and not that of PI(3,4)P2. The inhibition of Akt phosphorylation in cells expressing 5ptase IV makes them highly susceptible to FAS-induced apoptosis, whereas overexpressing of the 4ptase I protects cells from apoptosis. Our results place 5ptase IV as a relevant biological regulator of PI3K/Akt pathway in cells.

  • Inositol Polyphosphate 4-phosphatase type I regulates cell growth downstream of transcription factor GATA-1
    Proceedings of the National Academy of Sciences of the United States of America, 2000
    Co-Authors: Paresh Vyas, Philip W. Majerus, F A Norris, R Joseph, Stuart H Orkin
    Abstract:

    Megakaryocytes lacking transcription factor GATA-1 fail to complete maturation in vivo and hyperproliferate. To define how GATA-1 regulates megakaryocyte cell growth we searched for mRNA transcripts expressed in primary wild-type, but not GATA-1 − , megakaryocytes. One differentially expressed transcript encodes Inositol Polyphosphate 4-phosphatase type I (4-Ptase I). This enzyme hydrolyses phosphatidylInositol 3,4-bisphosphate and also has lesser activity against soluble analogues of this lipid, Inositol 3,4-bisphosphate and Inositol 1,3,4-triphosphate. Reintroduction of 4-Ptase I into both primary GATA-1 − and wild-type megakaryocytes significantly retards cell growth, suggesting that absence of 4-Ptase I may contribute to the hyperproliferative phenotype of GATA-1 − megakaryocytes. Overexpression of 4-Ptase I also markedly reduces growth of NIH 3T3 fibroblasts. Taken together, these data indicate that 4-Ptase I is a regulator of cell proliferation.

  • The isolation and characterization of a cDNA encoding phospholipid-specific Inositol Polyphosphate 5-phosphatase.
    Journal of Biological Chemistry, 2000
    Co-Authors: Marina V Kisseleva, Monita P. Wilson, Philip W. Majerus
    Abstract:

    Abstract We report the cDNA cloning and characterization of a novel human Inositol Polyphosphate 5-phosphatase (5-phosphatase) that has substrate specificity unlike previously described members of this large gene family. All previously described members hydrolyze water soluble Inositol phosphates. This enzyme hydrolyzes only lipid substrates, phosphatidylInositol 3,4,5-trisphosphate and phosphatidylInositol 4,5-bisphosphate. The cDNA isolated comprises 3110 base pairs and predicts a protein product of 644 amino acids and M r = 70,023. We designate this 5-phosphatase as type IV. It is a highly basic protein (pI = 8.8) and has the greatest affinity toward phosphatidylInositol 3,4,5-trisphosphate of known 5-phosphatases. TheK m is 0.65 μm, 1/10 that of SHIP (5.95 μm), another 5-phosphatase that hydrolyzes phosphatidylInositol 3,4,5-trisphosphate. The activity of 5-phosphatase type IV is sensitive to the presence of detergents in the in vitro assay. Thus the enzyme hydrolyzes lipid substrates in the absence of detergents or in the presence of n-octyl β-glucopyranoside or Triton X-100, but not in the presence of cetyltriethylammonium bromide, the detergent that has been used in other studies of the hydrolysis of phosphatidylInositol 4,5-bisphosphate. Remarkably SHIP, a 5-phosphatase previously characterized as hydrolyzing only substrates with d-3 phosphates, also readily hydrolyzed phosphatidylInositol 4,5-bisphosphate in the presence of n-octyl β-glucopyranoside but not cetyltriethylammonium bromide. We used antibodies prepared against a peptide predicted by the cDNA to identify the 5-phosphatase type IV enzyme in human tissues and find that it is highly expressed in the brain as determined by Western blotting. We also performed Western blotting of mouse tissues and found high levels of expression in the brain, testes, and heart with lower levels of expression in other tissues. mRNA was detected in many tissues and cell lines as determined by Northern blotting.

Christina Anne Mitchell - One of the best experts on this subject based on the ideXlab platform.

  • regulation of ptdins 3 4 5 p3 akt signalling by Inositol Polyphosphate 5 phosphatases
    Biochemical Society Transactions, 2016
    Co-Authors: Matthew J Eramo, Christina Anne Mitchell
    Abstract:

    The phosphoinositide 3-kinase (PI3K) generated lipid signals, PtdIns(3,4,5) P 3 and PtdIns(3,4) P 2, are both required for the maximal activation of the serine/threonine kinase proto-oncogene Akt. The Inositol Polyphosphate 5-phosphatases (5-phosphatases) hydrolyse the 5-position phosphate from the Inositol head group of PtdIns(3,4,5) P 3 to yield PtdIns(3,4) P 2. Extensive work has revealed several 5-phosphatases inhibit PI3K-driven Akt signalling, by decreasing PtdIns(3,4,5) P 3 despite increasing cellular levels of PtdIns(3,4) P 2. The roles that 5-phosphatases play in suppressing cell proliferation and transformation are slow to emerge; however, the 5-phosphatase PIPP [proline-rich Inositol Polyphosphate 5-phosphatase; Inositol Polyphosphate 5-phosphatase ( INPP5J )] has recently been identified as a putative tumour suppressor in melanoma and breast cancer and SHIP1 [SH2 (Src homology 2)-containing Inositol phosphatase 1] inhibits haematopoietic cell proliferation. INPP5E regulates cilia stability and INPP5E mutations have been implicated ciliopathy syndromes. This review will examine 5-phosphatase regulation of PI3K/Akt signalling, focussing on the role PtdIns(3,4,5) P 3 5-phosphatases play in developmental diseases and cancer. * 3AC, : 3-a-aminocholestane; 5-phosphatases, : Inositol Polyphosphate 5-phosphatases; AURKA, : aurora kinase A; BJAB, : human B-cell lymphoma cell line; BMMC, : bone marrow-derived mast cells; CHO, : Chinese hamster ovary; EGF, : epidermal growth factor; ENU, : N -ethyl- N -nitrosourea; ER, : estrogen receptor; FoxO, : forkhead box, class O; GLUT4, : glucose transporter type 4; Gpr161, : G-protein-coupled receptor 161; HEK, : human embryonic kidney; IGF-1, : insulin-like growth factor-1; IL-3, : interleukin-3; LPS, : lipopolysaccharide; MEF, : mouse embryonic fibroblast; MM, : multiple myeloma; mTORC, : mammalian target of rapamycin complex; NFAT, : nuclear factor of activated T cells; OCRL, : oculocerebrorenal syndrome of Lowe; Pak1, : P21-activated kinase 1; PDK1, : phosphoinositide-dependent kinase 1; PH, : pleckstrin homology; 1PIE, : (2-phenyl-benzo[ h ]quinolin-4-yl)-[2]piperidyl-methanol hydrochloride; 2PIQ, : 1-[(chlorophenyl)methyl]-2-methyl-5-(methylthio)-1H-indole-3-ethanamine hydrochloride; 6PTQ, : (2-adamantan-1-yl-6,8-dichloro-quinolin-4-yl)-pyridin-2-yl-methanol hydrochloride; PI3K, : phosphoinositide 3-kinase; PIPP, : proline-rich Inositol Polyphosphate 5-phosphatase; PRAS40, : proline-rich Akt substrate of 40 kDa; PTEN, : phosphatase and tensin homologue deleted on chromosome 10; PyMT, : polyoma middle T; Rheb, : Ras homologue enriched in brain; RhoGAP, : Rho GTP-ase activating protein; SAG, : smoothened agonist; Shh, : sonic hedgehog; SHIP, : SH2-containing Inositol phosphatase; SKICH, : SKIP carboxy homology; SKIP, : skeletal muscle- and kidney-enriched Inositol phosphatase; TNFα, : tumour necrosis factor α; TSC, : tuberous sclerosis; TULP3, : Tubby-like protein 3

  • Inositol Polyphosphate 5-phosphatases; new players in the regulation of cilia and ciliopathies
    FEBS Letters, 2012
    Co-Authors: Sarah E Conduit, Jennifer M Dyson, Christina Anne Mitchell
    Abstract:

    Phosphoinositides regulate numerous cellular events via the recruitment and activation of multiple lipid-binding effector proteins. The precise temporal and spatial regulation of phosphoinositide signals by the co-ordinated activities of phosphoinositide kinases and phosphatases is essential for homeostasis and development. Mutations in two Inositol Polyphosphate 5-phosphatases, INPP5E and OCRL, cause the cerebrorenal syndromes of Joubert and Lowe's, respectively. INPP5E and OCRL exhibit overlapping phosphoinositide substrate specificity and subcellular localisation, including an association with the primary cilia. Here, we review recent studies that identify a new role for these enzymes in the regulation of primary cilia function. Joubert syndrome has been extensively linked to primary cilia defects, and Lowe's may represent a new class of 'ciliopathy associated' syndromes.

  • regulation of pi 3 k akt signalling and cellular transformation by Inositol Polyphosphate 4 phosphatase 1
    EMBO Reports, 2009
    Co-Authors: Ivan Ivetac, Philip W. Majerus, Rajendra Gurung, Lauren C. Binge, Sandra Hakim, Kristy A Horan, David A Sheffield, Tony Tiganis, Christina Anne Mitchell
    Abstract:

    Akt is a crucial phosphoinositide 3-kinase (PI(3)K) effector that regulates cell proliferation and survival. PI(3)K-generated signals, PtdIns(3,4,5)P3 and PtdIns(3,4)P2, direct Akt plasma membrane engagement. Pathological Akt plasma membrane association promotes oncogenesis. PtdIns(3,4)P2 is degraded by Inositol Polyphosphate 4-phosphatase-1 (4-ptase-1) forming PtdIns(3)P; however, the role of 4-ptase-1 in regulating the activation and function of Akt is unclear. In mouse embryonic fibroblasts lacking 4-ptase-1 (−/−MEFs), the Akt-pleckstrin homology (PH) domain was constitutively membrane-associated both in serum-starved and agonist-stimulated cells, in contrast to +/+MEFs, in which it was detected only at the plasma membrane following serum stimulation. Epidermal growth factor (EGF) stimulation resulted in increased Ser473 and Thr308-Akt phosphorylation and activation of Akt-dependent signalling in −/−MEFs, relative to +/+MEFs. Significantly, loss of 4-ptase-1 resulted in increased cell proliferation and decreased apoptosis. SV40-transformed −/−MEFs showed increased anchorage-independent cell growth and formed tumours in nude mice. This study provides the first evidence, to our knowledge, that 4-ptase-1 controls the activation of Akt and thereby cell proliferation, survival and tumorigenesis.

  • the role of the Inositol Polyphosphate 5 phosphatases in cellular function and human disease
    Biochemical Journal, 2009
    Co-Authors: Lisa M Ooms, Rajendra Gurung, Parvin Rahman, Kristy Amanda Horan, Gillian Seaton, Dharini S Kethesparan, Christina Anne Mitchell
    Abstract:

    Phosphoinositides are membrane-bound signalling molecules that regulate cell proliferation and survival, cytoskeletal reorganization and vesicular trafficking by recruiting effector proteins to cellular membranes. Growth factor or insulin stimulation induces a canonical cascade resulting in the transient phosphorylation of PtdIns(4,5)P2 by PI3K (phosphoinositide 3-kinase) to form PtdIns(3,4,5)P3, which is rapidly dephosphorylated either by PTEN (phosphatase and tensin homologue deleted on chromosome 10) back to PtdIns(4,5)P2, or by the 5-ptases (Inositol Polyphosphate 5-phosphatases), generating PtdIns(3,4)P2. The 5-ptases also hydrolyse PtdIns(4,5)P2, forming PtdIns4P. Ten mammalian 5-ptases have been identified, which share a catalytic mechanism similar to that of the apurinic/apyrimidinic endonucleases. Gene-targeted deletion of 5-ptases in mice has revealed that these enzymes regulate haemopoietic cell proliferation, synaptic vesicle recycling, insulin signalling, endocytosis, vesicular trafficking and actin polymerization. Several studies have revealed that the molecular basis of Lowe's syndrome is due to mutations in the 5-ptase OCRL (oculocerebrorenal syndrome of Lowe). Futhermore, the 5-ptases SHIP [SH2 (Src homology 2)-domain-containing Inositol phosphatase] 2, SKIP (skeletal muscle- and kidney-enriched Inositol phosphatase) and 72-5ptase (72 kDa 5-ptase)/Type IV/Inpp5e (Inositol Polyphosphate 5-phosphatase E) are implicated in negatively regulating insulin signalling and glucose homoeostasis in specific tissues. SHIP2 polymorphisms are associated with a predisposition to insulin resistance. Gene profiling studies have identified changes in the expression of various 5-ptases in specific cancers. In addition, 5-ptases such as SHIP1, SHIP2 and 72-5ptase/Type IV/Inpp5e regulate macrophage phagocytosis, and SHIP1 also controls haemopoietic cell proliferation. Therefore the 5-ptases are a significant family of signal-modulating enzymes that govern a plethora of cellular functions by regulating the levels of specific phosphoinositides. Emerging studies have implicated their loss or gain of function in human disease.

  • the Inositol Polyphosphate 5 phosphatase pipp is a novel regulator of phosphoinositide 3 kinase dependent neurite elongation
    Molecular Biology of the Cell, 2005
    Co-Authors: Lisa M Ooms, Megan Victoria Astle, Clare G Fedele, Ivan Ivetac, V Cheung, Richard B Pearson, Meredith J Layton, Ariel Forrai, Harshal Hanumant Nandurkar, Christina Anne Mitchell
    Abstract:

    The spatial activation of phosphoinositide 3-kinase (PI3-kinase) signaling at the axon growth cone generates phosphatidylInositol 3,4,5 trisphosphate (PtdIns(3,4,5)P3), which localizes and facilitates Akt activation and stimulates GSK-3beta inactivation, promoting microtubule polymerization and axon elongation. However, the molecular mechanisms that govern the spatial down-regulation of PtdIns(3,4,5)P3 signaling at the growth cone remain undetermined. The Inositol Polyphosphate 5-phosphatases (5-phosphatase) hydrolyze the 5-position phosphate from phosphatidylInositol 4,5 bisphosphate (PtdIns(4,5)P2) and/or PtdIns(3,4,5)P3. We demonstrate here that PIPP, an uncharacterized 5-phosphatase, hydrolyzes PtdIns(3,4,5)P3 forming PtdIns(3,4)P2, decreasing Ser473-Akt phosphorylation. PIPP is expressed in PC12 cells, localizing to the plasma membrane of undifferentiated cells and the neurite shaft and growth cone of NGF-differentiated neurites. Overexpression of wild-type, but not catalytically inactive PIPP, in PC12 cells inhibited neurite elongation. Targeted depletion of PIPP using RNA interference (RNAi) resulted in enhanced neurite differentiation, associated with neurite hyperelongation. Inhibition of PI3-kinase activity prevented neurite hyperelongation in PIPP-deficient cells. PIPP targeted-depletion resulted in increased phospho-Ser473-Akt and phospho-Ser9-GSK-3beta, specifically at the neurite growth cone, and accumulation of PtdIns(3,4,5)P3 at this site, associated with enhanced microtubule polymerization in the neurite shaft. PIPP therefore inhibits PI3-kinase-dependent neurite elongation in PC12 cells, via regulation of the spatial distribution of phospho-Ser473-Akt and phospho-Ser9-GSK-3beta signaling.

John D. York - One of the best experts on this subject based on the ideXlab platform.

  • generation of phytate free seeds in arabidopsis through disruption of Inositol Polyphosphate kinases
    Proceedings of the National Academy of Sciences of the United States of America, 2005
    Co-Authors: Jill Stevensonpaulik, Robert J Bastidas, Sheantai Chiou, Roy A Frye, John D. York
    Abstract:

    Phytate (Inositol hexakisphosphate, IP6) is a regulator of intracellular signaling, a highly abundant animal antinutrient, and a phosphate store in plant seeds. Here, we report a requirement for Inositol Polyphosphate kinases, AtIPK1 and AtIPK2β, for the later steps of phytate synthesis in Arabidopsis thaliana. Coincident disruption of these kinases nearly ablates seed phytate without accumulation of phytate precursors, increases seed-free phosphate by 10-fold, and has normal seed yield. Additionally, we find a requirement for Inositol tetrakisphosphate (IP4)/Inositol pentakisphosphate (IP5) 2-kinase activity in phosphate sensing and root hair elongation. Our results define a commercially viable strategy for the genetic engineering of phytate-free grain and provide insights into the role of Inositol Polyphosphate kinases in phosphate signaling biology.

  • molecular definition of a novel Inositol Polyphosphate metabolic pathway initiated by Inositol 1 4 5 trisphosphate 3 kinase activity in saccharomyces cerevisiae
    Journal of Biological Chemistry, 2005
    Co-Authors: Andrew M Seeds, Robert J Bastidas, John D. York
    Abstract:

    The production of Inositol Polyphosphate (IPs) and pyrophosphates (PP-IPs) from Inositol 1,4,5-trisphosphate (I(1,4,5)P3) requires the 6-/3-/5-kinase activity of Ipk2 (also known as Arg82 and Inositol Polyphosphate multikinase). Here, we probed the distinct roles for I(1,4,5)P3 6- versus 3-kinase activities in IP metabolism and cellular functions reported for Ipk2. Expression of either I(1,4,5)P3 6- or 3-kinase activity rescued growth of ipk2-deficient yeast at high temperatures, whereas only 6-kinase activity enabled growth on ornithine as the sole nitrogen source. Analysis of IP metabolism revealed that the 3-kinase initiated the synthesis of novel pathway consisting of over eleven IPs and PP-IPs. This pathway was present in wild-type and ipk2 null cells, albeit at low levels as compared with Inositol hexakisphosphate synthesis. The primary route of synthesis was: I(1,4,5)P3 --> I(1,3,4,5)P4 --> I(1,2,3,4,5)P5 --> PP-IP4 --> PP2-IP3 and required Kcs1 (or possibly Ipk2), Ipk1, a novel Inositol pyrophosphate synthase, and then Kcs1 again, respectively. Mutation of kcs1 ablated this pathway in ipk2 null cells and overexpression of Kcs1 in ipk2 mutant cells phenocopied IP3K expression, confirming it harbors a novel 3-kinase activity. Our work provides a revised genetic map of IP metabolism in yeast and evidence for dosage compensation between IPs and PP-IPs downstream of I(1,4,5)P3 in the regulation of nucleocytoplasmic processes.

  • a role for rat Inositol Polyphosphate kinases ripk2 and ripk1 in Inositol pentakisphosphate and Inositol hexakisphosphate production in rat 1 cells
    Journal of Biological Chemistry, 2005
    Co-Authors: Makoto Fujii, John D. York
    Abstract:

    Abstract Over 30 Inositol Polyphosphates are known to exist in mammalian cells; however, the majority of them have uncharacterized functions. In this study we investigated the molecular basis of synthesis of highly phosphorylated Inositol Polyphosphates (such as Inositol tetrakisphosphate, Inositol pentakisphosphate (IP5), and Inositol hexakisphosphate (IP6)) in rat cells. We report that heterologous expression of rat Inositol Polyphosphate kinases rIPK2, a dual specificity Inositol trisphosphate/Inositol tetrakisphosphate kinase, and rIPK1, an IP5 2-kinase, were sufficient to recapitulate IP6 synthesis from Inositol 1,4,5-trisphosphate in mutant yeast cells. Overexpression of rIPK2 in Rat-1 cells increased Inositol 1,3,4,5,6-pentakisphosphate (I(1,3,4,5,6)P5) levels about 2–3-fold compared with control. Likewise in Rat-1 cells, overexpression of rIPK1 was capable of completely converting I(1,3,4,5,6)P5 to IP6. Simultaneous overexpression of both rIPK2 and rIPK1 in Rat-1 cells increased both IP5 and IP6 levels. To reduce IPK2 activity in Rat-1 cells, we introduced vector-based short interference RNA against rIPK2. Cells harboring the short interference RNA had a 90% reduction of mRNA levels and a 75% decrease of I(1,3,4,5,6)P5. These data confirm the involvement of IPK2 and IPK1 in the conversion of Inositol 1,4,5-trisphosphate to IP6 in rat cells. Furthermore these data suggest that rIPK2 and rIPK1 act as key determining steps in production of IP5 and IP6, respectively. The ability to modulate the intracellular Inositol Polyphosphate levels by altering IPK2 and IPK1 expression in rat cells will provide powerful tools to study the roles of I(1,3,4,5,6)P5 and IP6 in cell signaling.

  • molecular and biochemical characterization of two plant Inositol Polyphosphate 6 3 5 kinases
    Journal of Biological Chemistry, 2002
    Co-Authors: Jill Stevensonpaulik, Audrey R Odom, John D. York
    Abstract:

    Despite the high deposition of Inositol hexakisphosphate (IP6), 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, IP6 synthesis occurs through the sequential phosphorylation of I(1,4,5)P3 by two gene products, Ipk2 and Ipk1, a IP3/IP4 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 AtIpk2α and AtIpk2β that are encoded by distinct genes on chromosome 5 and that are ubiquitously expressed in mature tissue. The primary structures of AtIpk2α and AtIpk2β are 70% identical to each other and 12–18% identical to Ipk2s from yeast and mammals. Similar to yeast Ipk2, purified recombinant AtIpk2α and AtIpk2β have 6-/3-kinase activities that sequentially phosphorylate I(1,4,5)P3 to generate I(1,3,4,5,6)P5 predominantly via an I(1,4,5,6)P4 intermediate. While I(1,3,4,5)P4is a substrate for the plant Ipk2s, it does not appear to be a detectable product of the IP3 reaction. Additionally, we report that the plant and yeast Ipk2 have a novel 5-kinase activity toward I(1,3,4,6)P4 and I(1,2,3,4,6)P5, which would allow these proteins to participate in at least two proposed pathways in the synthesis of IP6. Heterologous expression of either plant isoform in an ipk2 mutant yeast strain restores IP4 and IP5 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.

  • SPECIFICITY DETERMINANTS IN PHOSPHOINOSITIDE DEPHOSPHORYLATION: CRYSTAL STRUCTURE OF AN ARCHETYPAL Inositol Polyphosphate 5-PHOSPHATASE
    Cell, 2001
    Co-Authors: Yosuke Tsujishita, John D. York, Shuling Guo, Leslie E. Stolz, James H. Hurley
    Abstract:

    Inositol Polyphosphate 5-phosphatases are central to intracellular processes ranging from membrane trafficking to Ca(2+) signaling, and defects in this activity result in the human disease Lowe syndrome. The 1.8 resolution structure of the Inositol Polyphosphate 5-phosphatase domain of SPsynaptojanin bound to Ca(2+) and Inositol (1,4)-bisphosphate reveals a fold and an active site His and Asp pair resembling those of several Mg(2+)-dependent nucleases. Additional loops mediate specific Inositol Polyphosphate contacts. The 4-phosphate of Inositol (1,4)-bisphosphate is misoriented by 4.6 compared to the reactive geometry observed in the apurinic/apyrimidinic endonuclease 1, explaining the dephosphorylation site selectivity of the 5-phosphatases. Based on the structure, a series of mutants are described that exhibit altered substrate specificity providing general determinants for substrate recognition.

Seyun Kim - One of the best experts on this subject based on the ideXlab platform.

  • Inositol Polyphosphate multikinase mediates extinction of fear memory
    NATL ACAD SCIENCES, 2019
    Co-Authors: Jina Park, Seung Ju Park, Emanuela Santini, Francesco Longo, Richa Tyagi, Seyun Kim, Seulgi Lee, Mihyun Bae, Jin-hee Han, Eric Klann
    Abstract:

    Inositol Polyphosphate multikinase (IPMK), the key enzyme for the biosynthesis of higher Inositol Polyphosphates and phosphatidylInositol 3,4,5-trisphosphate, also acts as a versatile signaling player in regulating tissue growth and metabolism. To elucidate neurobehavioral functions of IPMK, we generated mice in which IPMK was deleted from the excitatory neurons of the postnatal forebrain. These mice showed no deficits in either novel object recognition or spatial memory. IPMK conditional knockout mice formed cued fear memory normally but displayed enhanced fear extinction. Signaling analyses revealed dysregulated expression of neural genes accompanied by selective activation of the mechanistic target of rapamycin (mTOR) regulatory enzyme p85 S6 kinase 1 (S6K1) in the amygdala following fear extinction. The IPMK mutants also manifested facilitated hippocampal long-term potentiation. These findings establish a signaling action of IPMK that mediates fear extinction. © 2019 National Academy of Sciences. All Rights Reserve

  • the expanding significance of Inositol Polyphosphate multikinase as a signaling hub
    Molecules and Cells, 2017
    Co-Authors: Eunha Kim, Hyoungjoon Ahn, Mingyu Kim, Haein Lee, Seyun Kim
    Abstract:

    The Inositol Polyphosphates are a group of multifunctional signaling metabolites whose synthesis is catalyzed by a family of Inositol kinases that are evolutionarily conserved from yeast to humans. Inositol Polyphosphate multikinase (IPMK) was first identified as a subunit of the arginine-responsive transcription complex in budding yeast. In addition to its role in the production of Inositol tetrakis- and pentakisphosphates (IP4 and IP5), IPMK also exhibits phosphatidylInositol 3-kinase (PI3-kinase) activity. Through its PI3-kinase activity, IPMK activates Akt/PKB and its downstream signaling pathways. IPMK also regulates several protein targets non-catalytically via protein-protein interactions. These non-catalytic targets include cytosolic signaling factors and transcription factors in the nucleus. In this review, we highlight the many known functions of mammalian IPMK in controlling cellular signaling networks and discuss future challenges related to clarifying the unknown roles IPMK plays in physiology and disease.

  • Inositol Polyphosphate multikinase is a coactivator for serum response factor-dependent induction of immediate early genes
    Proceedings of the National Academy of Sciences of the United States of America, 2013
    Co-Authors: Eunha Kim, Richa Tyagi, Jina Park, Joo Young Lee, Young-ran Kim, Jiyoon Beon, Po Yu Chen, Ji-young Cha, Solomon H. Snyder, Seyun Kim
    Abstract:

    Inositol Polyphosphate multikinase (IPMK) is a notably pleiotropic protein. It displays both Inositol phosphate kinase and phosphatidylInositol kinase catalytic activities. Noncatalytically, IPMK stabilizes the mammalian target of rapamycin complex 1 and acts as a transcriptional coactivator for CREB-binding protein/E1A binding protein p300 and tumor suppressor protein p53. Serum response factor (SRF) is a major transcription factor for a wide range of immediate early genes. We report that IPMK, in a noncatalytic role, is a transcriptional coactivator for SRF mediating the transcription of immediate early genes. Stimulation by serum of many immediate early genes is greatly reduced by IPMK deletion. IPMK stimulates expression of these genes, an influence also displayed by catalytically inactive IPMK. IPMK acts by binding directly to SRF and thereby enhancing interactions of SRF with the serum response element of diverse genes.

  • Inositol Polyphosphate multikinase signaling in the regulation of metabolism
    Annals of the New York Academy of Sciences, 2012
    Co-Authors: Joo Young Lee, Jina Park, Young-ran Kim, Seyun Kim
    Abstract:

    Inositol phosphates (IPs) act as signaling messengers to regulate various cellular processes such as growth. Inositol Polyphosphate multikinase (IPMK) generates Inositol tetrakis- and pentakisphosphates (IP4 and IP5), acting as a key enzyme for Inositol Polyphosphate biosynthesis. IPMK was initially discovered as an essential subunit of the arginine-sensing transcription complex in budding yeast. In mammals, IPMK is also known as a physiologically important phosphatidylInositol 3 kinase (PI3K) that forms phosphatidylInositol 3,4,5-trisphosphate (PIP3), which activates Akt/PKB and stimulates its signaling. Acting in a catalytically independent fashion, IPMK mediates the activation of mammalian target of rapamycin (mTOR) in response to essential amino acids. In addition, IPMK binds and modulates AMP-activated protein kinase (AMPK) signaling pathways, including those involved in hypothalamic control of food intake. These recent findings strongly suggest that IPMK is a versatile player in insulin-, nutrient-, and energy-mediated metabolism signaling networks. Agents that control IPMK functions may provide novel therapeutics in metabolic syndromes such as obesity and diabetes.

  • Inositol Polyphosphate multikinase an emerging player for the central action of amp activated protein kinase
    Biochemical and Biophysical Research Communications, 2012
    Co-Authors: Megan J Dailey, Seyun Kim
    Abstract:

    AMP-activated protein kinase (AMPK) is an essential enzyme indispensable for energy sensing and metabolic homeostasis at both the cellular and whole-body levels. Phosphorylation of AMPK, a key step for its activation, is known to be regulated by upstream kinases such as liver kinase B1 (LKB1) and calmodulin-dependent protein kinase kinase-beta (CaMKKβ). Recent evidence shows that Inositol Polyphosphate multikinase (IPMK), which possesses both Inositol phosphate kinase and lipid Inositol kinase activities, can physiologically regulate AMPK signaling in cultured cells and in the arcuate nucleus. IPMK-mediated regulation of AMPK occurs through the dynamic protein interactions of IPMK with AMPK in response to glucose availability. Here we review and discuss a novel role for the hypothalamic IPMK signaling in the control of AMPK and central energy homeostasis.

S Snyder - One of the best experts on this subject based on the ideXlab platform.

  • Inositol Polyphosphate multikinase mediates extinction of fear memory
    Proceedings of the National Academy of Sciences of the United States of America, 2019
    Co-Authors: Jina Park, Seung Ju Park, Emanuela Santini, Eric Klann, Francesco Longo, Richa Tyagi, S Snyder
    Abstract:

    Inositol Polyphosphate multikinase (IPMK), the key enzyme for the biosynthesis of higher Inositol Polyphosphates and phosphatidylInositol 3,4,5-trisphosphate, also acts as a versatile signaling player in regulating tissue growth and metabolism. To elucidate neurobehavioral functions of IPMK, we generated mice in which IPMK was deleted from the excitatory neurons of the postnatal forebrain. These mice showed no deficits in either novel object recognition or spatial memory. IPMK conditional knockout mice formed cued fear memory normally but displayed enhanced fear extinction. Signaling analyses revealed dysregulated expression of neural genes accompanied by selective activation of the mechanistic target of rapamycin (mTOR) regulatory enzyme p85 S6 kinase 1 (S6K1) in the amygdala following fear extinction. The IPMK mutants also manifested facilitated hippocampal long-term potentiation. These findings establish a signaling action of IPMK that mediates fear extinction.

  • huntington s disease neural dysfunction linked to Inositol Polyphosphate multikinase
    Proceedings of the National Academy of Sciences of the United States of America, 2015
    Co-Authors: Ishrat Ahmed, Richa Tyagi, Risheng Xu, Bindu D Paul, Maged M Harraz, Juan I Sbodio, Jonathan C Grima, Lauren K Albacarys, Maimon E Hubbi, S Snyder
    Abstract:

    Huntington’s disease (HD) is a progressive neurodegenerative disease caused by a glutamine repeat expansion in mutant huntingtin (mHtt). Despite the known genetic cause of HD, the pathophysiology of this disease remains to be elucidated. Inositol Polyphosphate multikinase (IPMK) is an enzyme that displays soluble Inositol phosphate kinase activity, lipid kinase activity, and various noncatalytic interactions. We report a severe loss of IPMK in the striatum of HD patients and in several cellular and animal models of the disease. This depletion reflects mHtt-induced impairment of COUP-TF-interacting protein 2 (Ctip2), a striatal-enriched transcription factor for IPMK, as well as alterations in IPMK protein stability. IPMK overexpression reverses the metabolic activity deficit in a cell model of HD. IPMK depletion appears to mediate neural dysfunction, because intrastriatal delivery of IPMK abates the progression of motor abnormalities and rescues striatal pathology in transgenic murine models of HD.

  • Inositol Polyphosphate multikinase is a coactivator of p53 mediated transcription and cell death
    Science Signaling, 2013
    Co-Authors: Risheng Xu, Adele M Snowman, Bindu D Paul, Scott M Vandiver, Jing Xu, S Snyder
    Abstract:

    The tumor suppressor protein p53 is a critical stress response transcription factor that induces the expression of genes leading to cell cycle arrest, apoptosis, and tumor suppression. We found that mammalian Inositol Polyphosphate multikinase (IPMK) stimulated p53-mediated transcription by binding to p53 and enhancing its acetylation by the acetyltransferase p300 independently of its Inositol phosphate and lipid kinase activities. Genetic or RNA interference (RNAi)–mediated knockdown of IPMK resulted in decreased activation of p53, decreased recruitment of p53 and p300 to target gene promoters, abrogated transcription of p53 target genes, and enhanced cell viability. Additionally, blocking the IPMK-p53 interaction decreased the extent of p53-mediated transcription. These results suggest that IPMK acts as a transcriptional coactivator for p53 and that it is an integral part of the p53 transcriptional complex facilitating cell death.

  • amp activated protein kinase is physiologically regulated by Inositol Polyphosphate multikinase
    Proceedings of the National Academy of Sciences of the United States of America, 2012
    Co-Authors: Sookhee Bang, Megan J Dailey, Yong Chen, Timothy H Moran, S Snyder
    Abstract:

    The AMP-activated kinase (AMPK) senses the energy status of cells and regulates fuel availability, whereas hypothalamic AMPK regulates food intake. We report that Inositol Polyphosphate multikinase (IPMK) regulates glucose signaling to AMPK in a pathway whereby glucose activates phosphorylation of IPMK at tyrosine 174 enabling the enzyme to bind to AMPK and regulate its activation. Thus, refeeding fasted mice rapidly and markedly stimulates transcriptional enhancement of IPMK expression while down-regulating AMPK. Also, AMPK is up-regulated in mice with genetic depletion of hypothalamic IPMK. IPMK physiologically binds AMPK, with binding enhanced by glucose treatment. Regulation by glucose of phospho-AMPK in hypothalamic cell lines is prevented by blocking AMPK-IPMK binding. These findings imply that IPMK inhibitors will be beneficial in treating obesity and diabetes.

  • amino acid signaling to mtor mediated by Inositol Polyphosphate multikinase
    Cell Metabolism, 2011
    Co-Authors: David Maag, Adam C Resnick, Anutosh Chakraborty, Michael A Koldobskiy, Roxanne K Barrow, Adele M Snowman, Krishna R Juluri, Micah J Maxwell, S Snyder
    Abstract:

    mTOR complex 1 (mTORC1; mammalian target of rapamycin [mTOR] in complex with raptor) is a key regulator of protein synthesis and cell growth in response to nutrient amino acids. Here we report that Inositol Polyphosphate multikinase (IPMK), which possesses both Inositol phosphate kinase and lipid kinase activities, regulates amino acid signaling to mTORC1. This regulation is independent of IPMK's catalytic function, instead reflecting its binding with mTOR and raptor, which maintains the mTOR-raptor association. Thus, IPMK appears to be a physiologic mTOR cofactor, serving as a determinant of mTORC1 stability and amino acid-induced mTOR signaling. Substances that block IPMK-mTORC1 binding may afford therapeutic benefit in nutrient amino acid-regulated conditions such as obesity and diabetes.