title: The Significance of the Bifunctional Kinase/Phosphatase Activities of Diphosphoinositol Pentakisphosphate Kinases (PPIP5Ks) for Coupling Inositol Pyrophosphate Cell Signaling to Cellular Phosphate Homeostasis.
abstract: Proteins responsible for Pihomeostasis are critical for all life. InSaccharomyces cerevisiae, extracellular [Pi] is "sensed" by the inositol-hexakisphosphate kinase (IP6K) that synthesizes the intracellular inositol pyrophosphate 5-diphosphoinositol 1,2,3,4,6-pentakisphosphate (5-InsP7) as follows: during a period of Pistarvation, there is a decline in cellular [ATP]; the unusually low affinity of IP6Ks for ATP compels 5-InsP7levels to fall in parallel (Azevedo, C., and Saiardi, A. (2017)Trends. Biochem. Sci.42, 219-231. Hitherto, such Pisensing has not been documented in metazoans. Here, using a human intestinal epithelial cell line (HCT116), we show that levels of both 5-InsP7and ATP decrease upon [Pi] starvation and subsequently recover during Pireplenishment. However, a separate inositol pyrophosphate, 1,5-bisdiphosphoinositol 2,3,4,6-tetrakisphosphate (InsP8), reacts more dramatically (i.e.with a wider dynamic range and greater sensitivity). To understand this novel InsP8response, we characterized kinetic properties of the bifunctional 5-InsP7kinase/InsP8phosphatase activities of full-length diphosphoinositol pentakisphosphate kinases (PPIP5Ks). These data fulfil previously published criteria for any bifunctional kinase/phosphatase to exhibit concentration robustness, permitting levels of the kinase product (InsP8in this case) to fluctuate independently of varying precursor (i.e.5-InsP7) pool size. Moreover, we report that InsP8phosphatase activities of PPIP5Ks are strongly inhibited by Pi(40-90% within the 0-1 mm range). For PPIP5K2, Pisensing by InsP8is amplified by a 2-fold activation of 5-InsP7kinase activity by Piwithin the 0-5 mm range. Overall, our data reveal mechanisms that can contribute to specificity in inositol pyrophosphate signaling, regulating InsP8turnover independently of 5-InsP7, in response to fluctuations in extracellular supply of a key nutrient.
authors.affiliation: From the Laboratory of Signal Transduction, NIEHS, National Institutes of Health, Research Triangle Park, North Carolina, 27709.
authors.forename: Chunfang
authors.initials: C
authors.lastname: Gu
authors.affiliation: From the Laboratory of Signal Transduction, NIEHS, National Institutes of Health, Research Triangle Park, North Carolina, 27709.
authors.forename: Hoai-Nghia
authors.initials: HN
authors.lastname: Nguyen
authors.affiliation: Department of Chemistry, University of Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland.
authors.forename: Alexandre
authors.initials: A
authors.lastname: Hofer
authors.affiliation: Institute of Organic Chemistry, Albert Ludwigs University, Albertstrasse 21, 79104 Freiburg, Germany, and.
authors.forename: Henning J
authors.initials: HJ
authors.lastname: Jessen
authors.affiliation: Division of Cardiology, McAllister Heart Institute, University of North Carolina, Chapel Hill, North Carolina 27599.
authors.forename: Xuming
authors.initials: X
authors.lastname: Dai
authors.affiliation: From the Laboratory of Signal Transduction, NIEHS, National Institutes of Health, Research Triangle Park, North Carolina, 27709.
authors.forename: Huanchen
authors.initials: H
authors.lastname: Wang
authors.affiliation: From the Laboratory of Signal Transduction, NIEHS, National Institutes of Health, Research Triangle Park, North Carolina, 27709, shears@niehs.nih.gov.
authors.forename: Stephen B
authors.initials: SB
authors.lastname: Shears
mesh_terms: D017766:Acid Anhydride Hydrolases / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D045325:HCT116 Cells; D057809:HEK293 Cells; D006706:Homeostasis; D006801:Humans; D007295:Inositol Phosphates / Q000378:metabolism*; D017856:Phosphotransferases (Phosphate Group Acceptor) / Q000378:metabolism*; D015398:Signal Transduction
chemical_list: D007295:Inositol Phosphates; C079849:1-diphosphoinositol pentakisphosphate; C010251:inositol-1-pyrophosphate; D000255:Adenosine Triphosphate; D017856:Phosphotransferases (Phosphate Group Acceptor); C519580:PPIP5K1 protein, human; C562140:PPIP5K2 protein, human; D017766:Acid Anhydride Hydrolases; C116368:diphosphoinositol polyphosphate phosphohydrolase
keywords: inositol phosphate; metabolism; phosphatase; signal transduction; signaling