Publications

• Integration of inositol phosphate signaling pathways via human ITPK1.

  Chamberlain P.P., Qian X., Stiles A.R., Cho J., Jones D.H., Lesley S.A., Grabau E.A., Shears S.B., Spraggon G.

  Inositol 1,3,4-trisphosphate 5/6-kinase (ITPK1) is a reversible, poly-specific inositol phosphate kinase that has been implicated as a modifier gene in cystic fibrosis. Upon activation of phospholipase C at the plasma membrane, inositol 1,4,5-trisphosphate enters the cytosol and is inter-converted ... >> More

  Inositol 1,3,4-trisphosphate 5/6-kinase (ITPK1) is a reversible, poly-specific inositol phosphate kinase that has been implicated as a modifier gene in cystic fibrosis. Upon activation of phospholipase C at the plasma membrane, inositol 1,4,5-trisphosphate enters the cytosol and is inter-converted by an array of kinases and phosphatases into other inositol phosphates with diverse and critical cellular activities. In mammals it has been established that inositol 1,3,4-trisphosphate, produced from inositol 1,4,5-trisphosphate, lies in a branch of the metabolic pathway that is separate from inositol 3,4,5,6-tetrakisphosphate, which inhibits plasma membrane chloride channels. We have determined the molecular mechanism for communication between these two pathways, showing that phosphate is transferred between inositol phosphates via ITPK1-bound nucleotide. Intersubstrate phosphate transfer explains how competing substrates are able to stimulate each others' catalysis by ITPK1. We further show that these features occur in the human protein, but not in plant or protozoan homologues. The high resolution structure of human ITPK1 identifies novel secondary structural features able to impart substrate selectivity and enhance nucleotide binding, thereby promoting intersubstrate phosphate transfer. Our work describes a novel mode of substrate regulation and provides insight into the enzyme evolution of a signaling mechanism from a metabolic role. << Less

  J. Biol. Chem. 282:28117-28125(2007) [PubMed] [EuropePMC]

  This publication is cited by 4 other entries.

• 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.

  Sweetman D., Stavridou I., Johnson S., Green P., Caddick S.E., Brearley C.A.

  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 ... >> More

  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. << Less

  FEBS Lett. 581:4165-4171(2007) [PubMed] [EuropePMC]

  This publication is cited by 2 other entries.

• Isolation of inositol 1,3,4-trisphosphate 5/6-kinase, cDNA cloning and expression of the recombinant enzyme.

  Wilson M.P., Majerus P.W.

  Inositol 1,3,4-trisphosphate 5/6-kinase was purified 12,900-fold from calf brain using chromatography on heparin-agarose and affinity elution with inositol hexakisphosphate. The final preparation contained proteins of 48 and 36-38 kDa. All of these proteins had the same amino-terminal sequence and ... >> More

  Inositol 1,3,4-trisphosphate 5/6-kinase was purified 12,900-fold from calf brain using chromatography on heparin-agarose and affinity elution with inositol hexakisphosphate. The final preparation contained proteins of 48 and 36-38 kDa. All of these proteins had the same amino-terminal sequence and were enzymatically active. The smaller species represent proteolysis products with carboxyl-terminal truncation. The Km of the enzyme for inositol 1,3,4-trisphosphate was 80 nM with a Vmax of 60 nmol of product/min/mg of protein. The amino acid sequence of the tryptic peptide HSKLLARPAGGLVGERTCNAXP matched the protein sequence encoded by a human expressed sequence tag clone (GB T09063) at 16 of 22 residues. The expressed sequence tag clone was used to screen a human fetal brain cDNA library to obtain a cDNA clone of 1991 base pairs (bp) that predicts a protein of 46 kDa. The clone encodes the amino-terminal amino acid sequence obtained from the purified calf brain preparation, suggesting that it represents its human homologue. The cDNA was expressed as a fusion protein in Escherichia coli and was found to have inositol 1,3,4-trisphosphate 5/6-kinase activity. Remarkably, both the purified calf brain and recombinant proteins produced both inositol 1,3,4,6-tetrakisphosphate and inositol 1,3,4,5-tetrakisphosphate as products in a ratio of 2.3-5:1. This finding proves that a single kinase phosphorylates inositol in both the D5 and D6 positions. Northern blot analysis identified a transcript of 3.6 kilobases in all tissues with the highest levels in brain. The composite cDNA isolated contains 3054 bp with a poly(A) tail, suggesting that 500-600 bp of 5' sequence remains to be identified. << Less

  J. Biol. Chem. 271:11904-11910(1996) [PubMed] [EuropePMC]

  This publication is cited by 2 other entries.

• The pathway of myo-inositol 1,3,4-trisphosphate phosphorylation in liver. Identification of myo-inositol 1,3,4-trisphosphate 6-kinase, myo-inositol 1,3,4-trisphosphate 5-kinase, and myo-inositol 1,3,4,6-tetrakisphosphate 5-kinase.

  Shears S.B.

  Inositol 1,3,4-trisphosphate (Ins(1,3,4)P3) metabolism has been studied in liver homogenates and in 100,000 x g supernatant and particulate fractions. When liver homogenates were incubated in an "intracellular" medium containing 5 mM MgATP, equal proportions of Ins(1,3,4)P3 were dephosphorylated a ... >> More

  Inositol 1,3,4-trisphosphate (Ins(1,3,4)P3) metabolism has been studied in liver homogenates and in 100,000 x g supernatant and particulate fractions. When liver homogenates were incubated in an "intracellular" medium containing 5 mM MgATP, equal proportions of Ins(1,3,4)P3 were dephosphorylated and phosphorylated. Two inositol tetrakisphosphate (InsP4) products and an inositol pentakisphosphate (InsP5) were detected. The InsP4 isomers were unequivocally identified as inositol 1,3,4,5-tetrakisphosphate (Ins(1,3,4,5)P4) and inositol 1,3,4,6-tetrakisphosphate (Ins(1,3,4,6)P4) by high performance liquid chromatography separation of inositol phosphates, periodate oxidation, alkaline hydrolysis, and stereo-specific polyol dehydrogenase. Ins(1,3,4)P3 5-kinase is a novel enzyme activity and accounted for 16% of the total Ins(1,3,4)P3 phosphorylation. Ins(1,3,4,6)P4 was also shown to be further phosphorylated to inositol 1,3,4,5,6-pentakisphosphate (Ins(1,3,4,5,6)P5) by a kinase not previously known to occur in liver. About 75% of Ins(1,3,4)P3 kinase activities were soluble and were partly purified by anion-exchange fast protein liquid chromatography. The two Ins(1,3,4)P3 kinase activities eluted as a single peak that was well resolved from Ins(1,3,4)P3 phosphatase, Ins(1,3,4,6)P4 5-kinase, and Ins(1,3,4,5)P4 5-phosphatase activities. A further novel observation was that 10 microM Ins(1,3,4,5)P4 inhibited Ins(1,3,4)P3 kinase activities by 60%. << Less

  J Biol Chem 264:19879-19886(1989) [PubMed] [EuropePMC]

  This publication is cited by 1 other entry.

• L-myo-inositol 1,4,5,6-tetrakisphosphate (3-hydroxy)kinase.

  Stephens L.R., Hawkins P.T., Morris A.J., Downes P.C.

  Homogenates of primary-cultured murine bone macrophages contain an enzyme capable of synthesizing myo-[3H]inositol pentakisphosphate from myo-[3H]inositol tetrakisphosphate fractions derived from myo-[3H]inositol-labelled mouse macrophages and chick erythrocytes. D-myo-inositol 1,3,4,5-tetrakis[32 ... >> More

  Homogenates of primary-cultured murine bone macrophages contain an enzyme capable of synthesizing myo-[3H]inositol pentakisphosphate from myo-[3H]inositol tetrakisphosphate fractions derived from myo-[3H]inositol-labelled mouse macrophages and chick erythrocytes. D-myo-inositol 1,3,4,5-tetrakis[32P]-phosphate present in the same incubations was not phosphorylated. Since the myo-[3H]inositol-labelled tetrakisphosphate fractions used as substrates consist of a mixture of L-myo-inositol 1,4,5,6-tetrakisphosphate (60-85%) and a periodate-resistant tetrakisphosphate(s) whose characteristics are consistent with those of D-myo-inositol 1,3,4,5-tetrakisphosphate (the preceding paper [Stephens, Hawkins, Carter, Chahwala, Morris, Whetton & Downes (1988) Biochem. J. 249, 271-282] ), these data suggest the existence of a kinase that phosphorylates L-myo-inositol 1,4,5,6-tetrakisphosphate to give a myo-inositol pentakisphosphate. A similar activity was identified in homogenates of rat cerebrum, liver, heart and parotid gland. D-myo-Inositol 1,3,4,5-tetrakis[32P]phosphate in the same incubations was not a substrate. The activity was almost entirely soluble in all the tissues investigated and was found at its greatest specific activity in brain cytosol. The activity was purified 120-fold from a rat brain homogenate by (NH4)2SO4 fractionation and anion-exchange chromatography. The activity was clearly distinct from D-myo-inositol 1,4,5-trisphosphate (3-hydroxy)kinase. Incubation of this partially purified preparation with L-myo-[3H]inositol 1,4,5,6-tetrakisphosphate from chick erythrocytes and [gamma-32P]ATP resulted in the formation of L-myo-[3H]-inositol [1-32P]1,3,4,5,6-pentakisphosphate. The enzyme is therefore identified as an L-myo-inositol 1,4,5,6-tetrakisphosphate (3-hydroxy)kinase. << Less

  Biochem J 249:283-292(1988) [PubMed] [EuropePMC]

• An Entamoeba histolytica inositol 1,3,4-trisphosphate 5/6-kinase has a novel 3-kinase activity.

  Field J., Wilson M.P., Mai Z., Majerus P.W., Samuelson J.

  Mol. Biochem. Parasitol. 108:119-123(2000) [PubMed] [EuropePMC]

  This publication is cited by 2 other entries.

• Metabolism of D-myo-inositol 1,3,4,5-tetrakisphosphate by rat liver, including the synthesis of a novel isomer of myo-inositol tetrakisphosphate.

  Shears S.B., Parry J.B., Tang E.K., Irvine R.F., Michell R.H., Kirk C.J.

  1. We have studied the metabolism of Ins(1,3,4,5)P4 (inositol 1,3,4,5-tetrakisphosphate) by rat liver homogenates incubated in a medium resembling intracellular ionic strength and pH. 2. Ins(1,3,4,5)P4 was dephosphorylated to a single inositol trisphosphate product, Ins(1,3,4)P3 (inositol 1,3,4-tr ... >> More

  1. We have studied the metabolism of Ins(1,3,4,5)P4 (inositol 1,3,4,5-tetrakisphosphate) by rat liver homogenates incubated in a medium resembling intracellular ionic strength and pH. 2. Ins(1,3,4,5)P4 was dephosphorylated to a single inositol trisphosphate product, Ins(1,3,4)P3 (inositol 1,3,4-trisphosphate), the identity of which was confirmed by periodate degradation, followed by reduction and dephosphorylation to yield altritol. 3. The major InsP2 (inositol bisphosphate) product was inositol 3,4-bisphosphate [Shears, Storey, Morris, Cubitt, Parry, Michell & Kirk (1987) Biochem. J. 242, 393-402]. Small quantities of a second InsP2 product was also detected in some experiments, but its isomeric configuration was not identified. 4. The Ins(1,3,4,5)P4 5-phosphatase activity was primarily associated with plasma membranes. 5. ATP (5 mM) decreased the membrane-associated Ins(1,4,5)P3 5-phosphatase and Ins(1,3,4,5)P4 5-phosphatase activities by 40-50%. This inhibition was imitated by AMP, adenosine 5'-[beta gamma-imido]triphosphate, adenosine 5'-[gamma-thio]triphosphate or PPi, but not by adenosine or Pi. A decrease in [ATP] from 7 to 3 mM halved the inhibition of Ins(1,3,4,5)P4 5-phosphatase activity, but the extent of inhibition was not further decreased unless [ATP] less than 0.1 mM. 6. Ins(1,3,4,5)P4 5-phosphatase was insensitive to 50 mM-Li+, but was inhibited by 5 mM-2,3-bisphosphoglycerate. 7. The Ins(1,3,4,5)P4 5-phosphatase activity was unchanged by cyclic AMP, GTP, guanosine 5'-[beta gamma-imido]triphosphate or guanosine 5'-[gamma-thio]triphosphate, or by increasing [Ca2+] from 0.1 to 1 microM. 8. Ins(1,3,4)P3 was phosphorylated in an ATP-dependent manner to an isomer of InsP4 that was partially separable on h.p.l.c. from Ins(1,3,4,5)P4. The novel InsP4 appears to be Ins(1,3,4,6)P4. Its metabolic fate and function are not known. << Less

  Biochem J 246:139-147(1987) [PubMed] [EuropePMC]

• Metabolism of inositol 1,3,4-trisphosphate to a new tetrakisphosphate isomer in angiotensin-stimulated adrenal glomerulosa cells.

  Balla T., Guillemette G., Baukal A.J., Catt K.J.

  Angiotensin stimulates rapid and prominent increases in inositol polyphosphates and their metabolites in bovine glomerulosa cells labeled with [3H]inositol. In addition to the early formation of inositol 1,4,5-trisphosphate (Ins-1,4,5-P3) and inositol 1,3,4-trisphosphate (Ins-1,3,4-P3), as well as ... >> More

  Angiotensin stimulates rapid and prominent increases in inositol polyphosphates and their metabolites in bovine glomerulosa cells labeled with [3H]inositol. In addition to the early formation of inositol 1,4,5-trisphosphate (Ins-1,4,5-P3) and inositol 1,3,4-trisphosphate (Ins-1,3,4-P3), as well as their intermediate product, inositol 1,3,4,5-tetrakisphosphate (Ins-1,3,4,5-P4), delayed increases in two new InsP4 isomers were consistently observed by high resolution high performance liquid chromatography. Studies on the metabolism of purified Ins-1,3,4,5-P4 preparations, labeled with [3H]inositol and 32P to monitor sites of dephosphorylation, were performed in permeabilized glomerulosa cells. In addition to rapid degradation of Ins-1,3,4,5-P3 to Ins-1,3,4-P3 and then to Ins-3,4-P2, there was delayed formation of one of the putative InsP4 isomers observed during AII stimulation in intact cells. The kinetics of formation of the new InsP4 isomer, and the lack of phosphate in its 5 position based on isotope ratios, were consistent with its origin from Ins-1,3,4-P3. This was confirmed by the conversion of [3H]Ins-1,3,4-P3 to the new InsP4 isomer in permeabilized cells by a kinase distinct from that which phosphorylates Ins-1,4,5-P3. These results have demonstrated that the dephosphorylation sequence of Ins-1,4,5-P3 metabolism is accompanied by a complex cycle of higher phosphorylations with formation of new intermediates of potential significance in cellular regulation. << Less

  J Biol Chem 262:9952-9955(1987) [PubMed] [EuropePMC]

• Multitasking in signal transduction by a promiscuous human Ins(3,4,5,6)P(4) 1-kinase/Ins(1,3,4)P(3) 5/6-kinase.

  Yang X., Shears S.B.

  We describe a human cDNA encoding 1-kinase activity that inactivates Ins(3,4,5,6)P(4), an inhibitor of chloride-channel conductance that regulates epithelial salt and fluid secretion, as well as membrane excitability. Unexpectedly, we further discovered that this enzyme has alternative positional ... >> More

  We describe a human cDNA encoding 1-kinase activity that inactivates Ins(3,4,5,6)P(4), an inhibitor of chloride-channel conductance that regulates epithelial salt and fluid secretion, as well as membrane excitability. Unexpectedly, we further discovered that this enzyme has alternative positional specificity (5/6-kinase activity) towards a different substrate, namely Ins(1,3,4)P(3). Kinetic data from a recombinant enzyme indicate that Ins(1,3,4)P(3) (K(m)=0.3 microM; V(max)=320 pmol/min per microg) and Ins(3,4,5,6)P(4) (K(m)=0.1 microM; V(max)=780 pmol/min per microg) actively compete for phosphorylation in vivo. This competition empowers the kinase with multitasking capability in several key aspects of inositol phosphate signalling. << Less

  Biochem. J. 351:551-555(2000) [PubMed] [EuropePMC]

• Regulation of Ins(3,4,5,6)P(4) signaling by a reversible kinase/phosphatase.

  Ho M.W.Y., Yang X., Carew M.A., Zhang T., Hua L., Kwon Y.-U., Chung S.-K., Adelt S., Vogel G., Riley A.M., Potter B.V.L., Shears S.B.

  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 ... >> More

  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. << Less

  Curr. Biol. 12:477-482(2002) [PubMed] [EuropePMC]

  This publication is cited by 3 other entries.