Activation by calmodulin of inositol-1,4,5-trisphosphate 3-kinase in guinea pig peritoneal macrophages

D-myo-inositol 1,4,5-trisphosphate analogues substituted at the 3-hydroxyl group

D-myo-Inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) analogues derived at 3-OH with a bulky substituent were chemically synthesized and structural features of vicinity surrounding the 3-OH of Ins(1,4,5)P3, recognized by metabolic enzymes and by the receptor were explored. 3-Benzoyl-, 3-methylbenzoyl- and 3-para-aminobenzoyl-Ins(1,4,5)P3 inhibited the dephosphorylation of [3H]Ins(1,4,5)P3 by the 5-phosphatase present in erythrocyte ghosts, but the potency varied. The inhibitory potency for the former two compounds was slightly lower than that for Ins(1,4,5)P3, while that for the latter compound was higher. Transfer of the amino group to the meta-position of the benzoyl group led to a less potent analogue. In an assay of [3H]Ins(1,4,5)P3 3-kinase at a low Ca2+ concentration, catalyzed by rat brain cytosol, 3-meta-aminobenzoyl-Ins(1,4,5)P3 was the most potent among compounds examined, including Ins(1,4,5)P3 in inhibiting the phosphorylation, whereas both 3-benzoyl- and 3-methylbenzoyl-Ins(1,4,5)P3 at concentrations up to 30 microM, were without effect. All analogues examined were effective in inhibiting [3H]Ins(1,4,5)P3 binding to purified Ins(1,4,5)P3 receptor, but all 3-derived analogues were less potent and 3-benzoyl-Ins(1,4,5)P3 was the least potent. It would thus appear that the space in the vicinity surrounding the 3-hydroxyl group of Ins(1,4,5)P3 is sterically restrictive with regard to recognition by metabolic enzymes and the receptor, whereas the amino group providing arms for either the electrostatic interaction or the hydrogen bond, makes the analogues more potent.

Protein kinase C activity does not mediate the inhibitory effect of carbachol on chloride secretion by T84 cells

Carbachol induces calcium-dependent chloride secretion and activates protein kinase C in T84 cells. However, prolonged stimulation with carbachol or direct activation of protein kinase C inhibits subsequent calcium-dependent chloride secretion. Furthermore, the ability of carbachol to elevate inositol tetrakisphosphate levels may be linked to inhibition of chloride secretion. Here we demonstrate that protein kinase C activation increases levels of inositol tetrakisphosphates (1,3,4,6- and 3,4,5,6-isomers) in T84 colonic epithelia. Furthermore, this corresponds to an inhibition of chloride secretion. However, protein kinase C is unlikely to mediate the analogous effects of carbachol. Neither the ability of carbachol to inhibit calcium-dependent chloride secretion nor its effects on inositol 3,4,5,6-tetrakisphosphate levels were reversed by staurosporine. Carbachol also has quantitatively and qualitatively different effects on inositol tetrakisphosphate isomers than protein kinase C activators. Thus protein kinase C activity can increase levels of various inositol tetrakisphosphate isomers within T84 cells but does not mediate carbachol-induced increases in these putative messengers. These data further support the hypothesis that inositol 3,4,5,6-tetrakisphosphate is a negative second messenger, uncoupling epithelial chloride secretion from changes in intracellular calcium.

The metabolism of D-myo-inositol 1,4,5-trisphosphate and D-myo-inositol 1,3,4,5-tetrakisphosphate by porcine skeletal muscle

In soluble and particulate extracts from muscle D-myo-inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] and D-myo-inositol 1,3,4,5-tetrakisphosphate [Ins(1,3,4,5)P4] are metabolised stepwise to inositol. Ins(1,4,5)P3 is rapidly dephosphorylated to D-myo-inositol 1,4-bisphosphate then to D-myo-inositol 4-phosphate and finally inositol. In soluble extracts Ins(1,3,4,5)P4 is dephosphorylated to D-myo-inositol 1,3,4-trisphosphate then sequentially to D-myo-inositol 3,4-bisphosphate, D-myo-inositol 3-phosphate and inositol, while in particulate extracts D-myo-inositol 1,3-bisphosphate is the predominant inositol bisphosphate formed. Dephosphorylation of these inositol polyphosphates is Mg2+ dependent and inhibited by D-2,3-bisphosphoglyceric acid. Ins(1,4,5)P3 is also phosphorylated to form Ins(1,3,4,5)P4 in soluble extracts by Ins(1,4,5)P3 3-kinase. Ins(1,4,5)P3 3-kinase activity is Mg2+ and ATP dependent and is stimulated by Ca2+ and calmodulin. Particulate (sarcotubular) inositol polyphosphate 5-phosphatase (5-phosphatase) is found in membranes which are intimately involved in excitation-contraction coupling and the generation of the primary Ca2+ signal of muscle cells. Particulate 5-phosphatase had the highest specific activity in the transverse-tubule membrane, when compared to the terminal cisternae and longitudinal-tubule membranes of the sarcoplasmic reticulum. Particulate Ins(1,3,4,5)P4-3-phosphatase activity was also detected after fractionation of solubilised sarcotubular membranes by DEAE-Sephacel. Particulate 5-phosphatase activity was purified 25,600-fold to a specific activity of 25.6 mumol Ins(1,4,5)P3 hydrolysed.min-1.mg protein-1, after DEAE-Sephacel and novel affinity chromatography using D-2,3-bisphosphoglycerate/agarose and Sepharose-4B-immobilised Ins(1,4,5)P3-analog matrices. Purified particulate 5-phosphatase had apparent Km of 46.3 microM and 1.9 microM and Vmax of 115 and 0.046 mumol substrate hydrolysed.min-1.mg protein-1, for Ins(1,4,5)P3 and Ins(1,3,4,5)P4, respectively. In contrast, purified soluble type I 5-phosphatase had apparent Km of 8.9 microM and 1.1 microM and Vmax of 3.55 and 0.13 mumol substrate hydrolysed.min-1.mg protein-1, for Ins(1,4,5P3 and Ins(1,3,4,5)P4, respectively. As in other cells, muscle 5-phosphatases have a lower affinity, but a higher capacity to metabolise Ins(1,4,5)P3 than Ins(1,3,4,5)P4. Soluble type I 5-phosphatase may have a functional role in the metabolism of both inositol polyphosphates, while particulate 5-phosphatase may primarily metabolise Ins(1,4,5)P3. Purified Ins(1,4,5)P3 3-kinase had an apparent Km of 0.42 microM and a Vmax of 4.12 nmol Ins(1,4,5)P3 phosphorylated.min-1.mg protein-1. The profile of inositol polyphosphate metabolism in muscle is similar to that reported in other tissues.(ABSTRACT TRUNCATED AT 400 WORDS)

The role of phosphoinositide metabolism in Ca2+ signalling of skeletal muscle cells

1. The mobilization of Ca2+ from intracellular stores by D-myo-inositol 1,4,5-triphosphate[Ins(1,4,5)P3] is now widely accepted as the primary link between plasma membrane receptors that stimulate phospholipase C and the subsequent increase in intracellular free Ca2+ that occurs when such receptors are activated (Berridge, 1993). Since the observations of Volpe et al. (1985) which showed that Ins(1,4,5)P3 could induce Ca2+ release from isolated terminal cisternae membranes and elicit contracture of chemically skinned muscle fibres, research has focused on the role of Ins(1,4,5)P3 in the generation of SR Ca2+ transients and in the mechanism of excitation-contraction coupling (EC-coupling). 2. The mechanism of signal transduction at the triadic junction during EC-coupling is unknown. Asymmetric charge movement and mechanical coupling between highly specialized triadic proteins has been proposed as the primary mechanism for voltage-activated generation of SR Ca2+ signals and subsequent contraction. Ins(1,4,5)P3 has also been proposed as the major signal transduction molecule for the generation of the primary Ca2+ transient produced during EC-coupling. 3. Investigations on the generation of Ca2+ transients by Ins(1,4,5)P3 have been conducted on ion channels incorporated into lipid bilayers, skinned and intact fibres and isolated membrane vesicles. Ins(1,4,5)P3 induces SR Ca2+ release and the enzymes responsible for its synthesis and degradation are present in muscle tissue. However, the sensitivity of the Ca2+ release mechanism to Ins(1,4,5)P3 is highly dependent on experimental conditions and on membrane potential. 4. While Ins(1,4,5)P3 may not be the major signal transduction molecule for the generation of the primary Ca2+ signal produced during voltage-activated contraction, this inositol polyphosphate may play a functional role as a modulator of EC-coupling and/or of the processes of myoplasmic Ca2+ regulation occurring on a time scale of seconds, during the events of contraction.

Metabolism of inositol-1,4,5-trisphosphate in the taste organ of the channel catfish, Ictalurus punctatus

1. The metabolism of inositol-1,4,5-trisphosphate was studied in the taste organ (barbel) of the channel catfish, Ictalurus punctatus. 2. Homogenates of epithelial barbel scrapings were incubated with [3H]-1,4,5-IP3, whose dephosphorylation or phosphorylation was assayed under first-order conditions by measuring the production of either [3H]-1,4-IP2 (representing the activity of IP3-5-phosphatase) or [3H]-1,3,4,5-IP4 (representing the activity of IP3-3-kinase). 3. Both enzymes were predominantly cytosolic, magnesium-dependent and maximally active at pH 6.4. For IP3-phosphatase, Km = 6 microM and Vmax = 10.5 nmol/min/mg. For IP3-kinase, Km = 0.23 microM and Vmax = 0.05 nmol/min/mg. 4. Neither enzyme was significantly affected by the presence of taste stimuli (amino acids), GTP gamma S, cAMP or phorbol esters. 5. In the presence of physiological levels of free calcium (0.05-12 microM) IP3-phosphatase was moderately activated whereas IP3-kinase was moderately inhibited. 6. IP3-phosphatase was moderately activated by Mn2+, unaffected by LiCl, and strongly inhibited by 2,3-diphosphoglycerate, Na-pyrophosphate, CdCl2, HgCl2, CuCl2, FeCl3 and ZnSO4 7. IP3-kinase was strongly activated by 2,3-diphosphoglycerate, Na-pyrophosphate, CdCl2, HgCl2, FeCl3 and LiCl and inhibited by ZnSO4 and Mn2+. 8. IP3-kinase was significantly activated in a calcium-dependent manner by exogenously-added phosphatidylcholine and sphingomyelin, and to a lesser extent by diacylglycerol. IP3-phosphatase was unaffected by exogenously-added lipids. 9. IP3-phosphatase may participate in taste transduction since calculations based on the first-order rate constant (6.9 sec-1) indicate that it is capable of dephosphorylating basal levels of IP3 with a half-life of 0.1 sec.

Ultrastructural localization of inositol 1,4,5-trisphosphate 3-kinase in rat cerebellar cortex

Subcellular localization of inositol 1,4,5-trisphosphate 3-kinase in the rat cerebellar cortex was studied immunohistochemically using a monoclonal antibody. Electron microscopy revealed intense immunoreactivity in the dendritic spines of Purkinje cells forming synapses with the parallel fibers, climbing fibers and recurrent collaterals of Purkinje cell axons. The labelling was associated with the hypolemmal cisternae, surrounding matrix and plasmalemma including the postsynaptic densities. Weaker immunoreactivity was present in the dendritic spines of basket cells and in certain segments of Purkinje cell recurrent collaterals. The postsynaptic regions of the dendritic trunks of Purkinje and basket cells were negative. These results indicate that inositol 1,4,5-trisphosphate 3-kinase is distributed amongst the spines of various synaptic relations with different electrophysiological properties, and that axon terminals of certain cell types are another functional site for the enzyme.

Regulation of the metabolism of 1,2-diacylglycerols and inositol phosphates that respond to receptor activation

This review assimilates information on the regulation of the metabolism of those inositol phosphates and diacylglycerols that respond to receptor activation. Particular emphasis is placed on the regulation of specific enzymes, the occurrence of isoenzymes, and metabolic compartmentalization; the overall aim is to demonstrate the significance of these activities in relation to the physiological impact of the various cell signalling processes.

Inositol 1,4,5-trisphosphate affinity chromatography

Inositol 1,4,5-trisphosphate (IP3) affinity columns were made by coupling IP3 analogs to a supporting matrix. Sepharose 4B. IP3 5-phosphatase activity. IP3 3-kinase activity and IP3 binding activity from rat brain were absorbed on the IP3 columns. and were eluted by increasing KC1 concentration. This purification procedure increased the specific activities of these parameters 5-200-fold. Thus Sepharose 4B immobilized IP3 analogs can specifically interact with IP3-binding proteins, demonstrating that IP3 affinity columns are a good method for purifying such proteins. Furthermore, our results suggest that IP3 analogs can be linked to other molecules to make useful derivatives without loss of their biological activities.

Ca2+/calmodulin independent inositol 1,4,5-trisphosphate 3-kinase activity in guinea pig peritoneal macrophages

1. The Ca2+/calmodulin (CaM) independent activity of inositol 1,4,5-trisphosphate (InsP3) 3-kinase in macrophages could be separated from the dependent activity by serial column chromatography, gel filtration, Orange A and DEAE-5PW. 2. An InsP3 analog which has an aminobenzoyl group on the 2nd carbon of the inositol ring inhibited the conversion of [3H]InsP3 to [3H]InsP4 (inositol 1,3,4,5-tetrakisphosphate) in a dose-dependent manner. The concentration required for half-maximal inhibition (IC50) with the Ca2+/CaM independent enzyme activity was also dependent on the free Ca2+ concentration, as with the dependent activity. 3. These results suggest that a conformational change in the enzyme occurs in response to a change in free Ca2+ concentration, and thus the potency to recognize the InsP3 analog would change, even when the Ca2+/CaM independent enzyme activity was used.

Fibroblasts transformed with v-src show enhanced formation of an inositol tetrakisphosphate

The tyrosine kinase pp60v-src, encoded by the v-src oncogene, seems to regulate phosphatidylinositol metabolism. The effect of pp60v-src on control points in inositol phosphate production was examined by measuring the amounts of inositol polyphosphates in Rat-1 cells expressing wild-type or mutant forms of the protein. Expression of v-src-resulted in a five- to sevenfold elevation in the steady-state amount of an isomer of inositol tetrakisphosphate, whereas the concentrations of inositol trisphosphates or other inositol tetrakisphosphates were not affected. The activity of a key enzyme in the formation of inositol tetrakisphosphates, inositol (1,4,5)-trisphosphate 3-kinase, was increased six- to eightfold in cytosolic extracts prepared from the v-src-transformed cells, suggesting that this enzyme may be one target for the pp60v-src kinase and that it may participate in the synthesis of novel, higher order inositol phosphates.

Mode of activation of bovine brain inositol 1,4,5-trisphosphate 3-kinase by calmodulin and calcium

The effect of Ca2+ and calmodulin (CaM) on the activation of purified bovine brain Ins(1,4,5)P3 kinase was quantified and interpreted according to the model of sequential equilibria generally used for other calmodulin-stimulated systems. Two main conclusions can be drawn. (i) CaM.Ca3 and CaM.Ca4 together are the biologically active species in vitro, as is the case for the great majority of other calmodulin targets. (ii) These species bind in a non-co-operative way to the enzyme with an affinity constant of 8.23 x 10(9) M-1, i.e. approx 10-fold higher than for most calmodulin-activated target enzymes. The dose-response curve of the activation of Ins(1,4,5)P3 kinase by calmodulin is not significantly impaired by melittin and trifluoperazine, whereas under very similar assay conditions the half-maximal activation of bovine brain cyclic AMP phosphodiesterase requires over 30-50-fold higher concentrations of CaM when 1 microM melittin or 20 microM-trifluoperazine is present in the assay medium. Similarly, 1 microM of the anti-calmodulin peptides seminalplasmin and gramicidin S, as well as 20 microM of N-(6-aminohexyl)-5-chloro-1-naphthalene-sulphonamide (W7), do not inhibit the activation process. These data suggest that binding and activation of Ins(1,4,5)P3 kinase require surface sites of calmodulin which are different from those involved in the binding of most other target enzymes or of model peptides.

Possible binding sites for inositol 1,4,5-trisphosphate in macrophages

We reported that an arylazide derivative of inositol 1,4,5-trisphosphate (InsP3) caused irreversible InsP3-induced Ca2+ release from saponin-permeabilized macrophages after photoirradiation. To determine the specific receptors for InsP3, presumably present on the endoplastic reticulum, we synthesized isotope-labeled arylazide derivatives of InsP3; InsP3 was coupled with p-azidobenzoyl [3H]beta-alanine (InsP3-[3H]AB beta A) or p-[125I]azidosalicyl beta-alanine (InsP3-[125I]AS beta A). We report here that three proteins may be associated with the Ca2+ releasing mechanism, in photoirradiated saponin-permeabilized macrophages and in the microsomal fraction.

Inositol phosphates: proliferation, metabolism and function

After the initial discovery of receptor-linked generation of inositol(1,4,5)trisphosphate (Ins(1,4,5)P3) it was generally assumed that Ins(1,4,5)P3 and its proposed breakdown products inositol(1,4)bisphosphate (Ins(1,4)P2) and Ins1P, along with cyclic inositol monophosphate, were the only inositol phosphates found in significant amounts in animal cells. Since then, three levels of complexity have been introduced. Firstly, Ins(1,4,5)P3 can be phosphorylated to Ins(1,3,4,5)P4, and the subsequent metabolism of these two compounds has been found to be intricate and probably different between various tissues. The functions of Ins(1,4,5)P3 and Ins(1,3,4,5)P4 are almost certainly to regulate cytosolic Ca2+ concentrations, but the reasons for the labyrinth of the metabolic pathways after their deactivation by a specific 5-phosphatase remain obscure. Secondly, inositol pentakis- and hexakisphosphates have been found in many animal cells other than avian erythrocytes. It has been shown that their synthesis pathway is entirely separate from the inositol phosphates discussed above, both in terms of many of the isomers involved and probably in the subcellular localization; some possible functions of InsP5 and InsP6 are discussed here. Thirdly, cyclic inositol polyphosphates have been reported in stimulated tissues; the evidence for their occurrence in vivo and their possible physiological significance are also discussed.

Ca2+/calmodulin-sensitive inositol 1,4,5-trisphosphate 3-kinase in rat and bovine brain tissues

Inositol 1,4,5-trisphosphate (Ins P3) 3-kinase catalyzes the ATP-dependent phosphorylation of Ins P3 to Inositol 1,3,4,5-tetrakisphosphate (Ins P4). Ca2+/calmodulin (CaM)-sensitivity of Ins P3 3-kinase was measured in the crude soluble fraction from rat brain and different anatomic regions of bovine brain. Kinase activity was inhibited in the presence of EGTA (free Ca2+ below 1 nM) as compared to Ca2+ (10 microM free Ca2+) or Ca2+ (10 microM free Ca2+) and CaM (1 microM). Ca2+-sensitivity was also seen for the cAMP phosphodiesterase measured under the same assay conditions, but was not for the Ins P3 5-phosphatase. DEAE-cellulose chromatography of the soluble fraction of rat brain or bovine cerebellum resolved a Ca2+/CaM-sensitive Ins P3 3-kinase (maximal stimulation at 1 microM Ins P3 substrate level was 2.0-3.0 fold).

Purification and characterization of inositol 1,4,5-trisphosphate 3-kinase from pig aortic smooth muscle

Inositol 1,4,5-trisphosphate (InsP3) 3-kinase, which phosphorylates InsP3 to form inositol 1,3,4,5-tetrakisphosphate, was purified to apparent homogeneity by (NH4)2SO4 fractionation and sequential chromatographic steps on DEAE-sepharose, calmodulin-Affi-Gel and DEAE-5PW h.p.l.c. The purified enzyme had a specific activity of 24.4 nmol of inositol tetrakisphosphate formed/min per mg of protein, which represented a purification of approx. 195-fold with a 0.29% recovery, compared with the cytosol fraction of the muscle. SDS/polyacrylamide-gel electrophoresis showed a single protein-staining band of Mr 93,000. Moreover, the major protein peak, of Mr 84,000, was detected by TSK gel G3000SW gel-permeation chromatography of the purified sample. As this value was approximately consistent with the Mr determined by SDS/polyacrylamide-gel-electrophoretic analysis, the InsP3 3-kinase might be a monomeric enzyme. The purified enzyme had a Km for InsP3 of 0.4 microM, with an optimum pH range of 5.8-7.7. The enzyme was maximally activated by calmodulin, with a stoichiometry of 1:1.