The pathway of myo-inositol 1,3,4-trisphosphate dephosphorylation in liver.
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ABSTRACT:
SUBMITTER: Shears SB
PROVIDER: S-EPMC1148648 | biostudies-other | 1987 Dec
REPOSITORIES: biostudies-other
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Project description:We have augmented our previous studies [Storey, Shears, Kirk & Michell (1984) Nature (London) 312, 374-376] on the subcellular location and properties of Ins(1,4,5)P3 (inositol 1,4,5-trisphosphate) phosphatases in rat liver and human erythrocytes. We also investigate Ins(1,3,4)P3 (inositol 1,3,4-trisphosphate) metabolism by rat liver. Membrane-bound and cytosolic Ins(1,4,5)P3 phosphatases both attack the 5-phosphate. The membrane-bound enzyme is located on the inner face of the plasma membrane, and there is little or no activity associated with Golgi apparatus. Cytosolic Ins(1,4,5)P3 5-phosphatase (Mr 77,000) was separated by gel filtration from Ins(1,4)P2 (inositol 1,4-bisphosphate) and inositol 1-phosphate phosphatases (Mr 54,000). Ins(1,4,5)P3 5-phosphatase activity in hepatocytes was unaffected by treatment of the cells with insulin, vasopressin, glucagon or dibutyryl cyclic AMP. Ins(1,4,5)P3 5-phosphatase activity in cell homogenates was unaffected by changes in [Ca2+] from 0.1 to 2 microM. After centrifugation of a liver homogenate at 100,000 g, Ins(1,3,4)P3 phosphatase activity was largely confined to the supernatant. The sum of the activities in the supernatant and the pellet exceeded that in the original homogenate. When these fractions were recombined, Ins(1,3,4)P3 phosphatase activity was restored to that observed in unfractionated homogenate. Ins(1,3,4)P3 was produced from Ins(1,3,4,5)P4 (inositol 1,3,4,5-tetrakisphosphate) and was metabolized to a novel InsP2 that was the 3,4-isomer. Ins(1,3,4)P3 phosphatase activity was not changed by 50 mM-Li+ or 0.07 mM-Ins(1,4)P2 alone, but when added together these agents inhibited Ins(1,3,4)P3 metabolism. In Li+-treated and vasopressin-stimulated hepatocytes, Ins(1,4)P2 may reach concentrations sufficient to inhibit Ins(1,3,4)P3 metabolism, with little effect on Ins(1,4,5)P3 hydrolysis.
| S-EPMC1147718 | biostudies-other
Project description:d-myo-Inositol 1,4,5-trisphosphate receptors (IP3Rs) are Ca2+ channels activated by the intracellular messenger inositol 1,4,5-trisphosphate (IP3, 1). The glyconucleotide adenophostin A (AdA, 2) is a potent agonist of IP3Rs. A recent synthesis of d-chiro-inositol adenophostin (InsAdA, 5) employed suitably- protected chiral building blocks and replaced the d-glucose core by d-chiro-inositol. An alternative approach to fully chiral material is now reported using intrinsic sugar chirality to avoid early isomer resolution, involving the coupling of a protected and activated racemic myo-inositol derivative to a d-ribose derivative. Diastereoisomer separation was achieved after trans-isopropylidene group removal, and the absolute ribose-inositol conjugate stereochemistry assigned with reference to the earlier synthesis. Optimization of stannylene-mediated regiospecific benzylation was explored using the model 1,2-O-isopropylidene-3,6-di-O-benzyl-myo-inositol and conditions successfully transferred to one conjugate diastereoisomer with 3:1 selectivity. However, only roughly 1:1 regiospecificity was achieved on the required diastereoisomer. The regioisomers were successfully separated and transformed subsequently to InsAdA after amination, pan-phosphorylation, and deprotection. InsAdA from this synthetic route bound with greater affinity than AdA to IP3R1 and was more potent in releasing Ca2+ from intracellular stores through IP3Rs. It is the most potent full agonist of IP3R1 and was equipotent with material from the fully chiral synthetic route.
| S-EPMC7116374 | biostudies-literature
Project description:d-myo-Inositol 1,4,5-trisphosphate receptors (IP3Rs) are Ca2+ channels activated by the intracellular messenger inositol 1,4,5-trisphosphate (IP3, 1). The glyconucleotide adenophostin A (AdA, 2) is a potent agonist of IP3Rs. A recent synthesis of d-chiro-inositol adenophostin (InsAdA, 5) employed suitably protected chiral building blocks and replaced the d-glucose core by d-chiro-inositol. An alternative approach to fully chiral material is now reported using intrinsic sugar chirality to avoid early isomer resolution, involving the coupling of a protected and activated racemic myo-inositol derivative to a d-ribose derivative. Diastereoisomer separation was achieved after trans-isopropylidene group removal and the absolute ribose-inositol conjugate stereochemistry assigned with reference to the earlier synthesis. Optimization of stannylene-mediated regiospecific benzylation was explored using the model 1,2-O-isopropylidene-3,6-di-O-benzyl-myo-inositol and conditions successfully transferred to one conjugate diastereoisomer with 3:1 selectivity. However, only roughly 1:1 regiospecificity was achieved on the required diastereoisomer. The conjugate regioisomers of benzyl derivatives 39 and 40 were successfully separated and 39 was transformed subsequently to InsAdA after amination, pan-phosphorylation, and deprotection. InsAdA from this synthetic route bound with greater affinity than AdA to IP3R1 and was more potent in releasing Ca2+ from intracellular stores through IP3Rs. It is the most potent full agonist of IP3R1 known and .equipotent with material from the fully chiral synthetic route.
| S-EPMC7659177 | biostudies-literature
Project description:Dephosphorylation of 1D-myo-inositol 1,4-bisphosphate [Ins(1,4)P2] in rat liver is catalysed by a cytosolic phosphatase that removes the 1-phosphate group. The Km for Ins(1,4)P2 is approx. 17 microM. Li+ (100 mM) causes 50% inhibition of Ins(1,4)P2 phosphatase activity when activity is measured at the very low substrate concentration of 10 nM, but on raising the substrate concentration to 100 microM there is a greater than 10-fold increase in sensitivity to Li+, suggesting that Li+ acts mainly, but not entirely, as an uncompetitive inhibitor of Ins(1,4)P2 phosphatase. In addition, rat liver cytosol shows Li+-sensitive phosphatase activity against 1D-myo-inositol 1-,3- and 4-monophosphates. The Ins(1,4)P2 1-phosphatase and inositol monophosphatase activities all share an apparent Mr of 47 x 10(3), as determined by gel-filtration chromatography. However, the Ins(1,4)P2 1-phosphatase is more sensitive to inactivation by heat, and can be separated from inositol monophosphatase activity by anion-exchange chromatography. We conclude that rat liver cytosol contains an Ins(1,4)P2 1-phosphatase that is distinct from, but in many ways similar to, inositol monophosphatase.
| S-EPMC1135135 | biostudies-other
Project description:Dephosphorylation of inositol 1,3,4,5-tetrakisphosphate [Ins(1,3,4,5)P4] was measured in both the soluble and the particulate fractions of rat brain homogenates. Analysis of the hydrolysis of [4,5-32P]Ins(1,3,4,5)P4 showed that for both fractions the 5-phosphate of Ins(1,3,4,5)P4 was removed and inositol 1,3,4-trisphosphate [Ins(1,3,4)P3] was specifically produced. In the soluble fraction, Ins(1,3,4)P3 was further hydrolysed at the 1-phosphate position to inositol 3,4-bisphosphate[Ins(3,4)P2]. DEAE-cellulose chromatography of the soluble fraction separated the phosphatase activities into three peaks. The first hydrolysed both Ins(1,3,4,5)P4 and inositol 1,4,5-trisphosphate, the second inositol 1-phosphate and the third Ins(1,3,4)P3 and inositol 1,4-bisphosphate, [Ins(1,4)P2]. Further purification of the third peak on either Sephacryl S-200 or Blue Sepharose could not dissociate these two activities [i.e. with Ins(1,4)P2 and Ins(1,3,4)P3 as substrates]. The dephosphorylation of Ins(1,3,4)P3 could be inhibited by the addition of Li+.
| S-EPMC1148459 | biostudies-other
Project description: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.
| S-EPMC3289378 | biostudies-literature
Project description: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.
| S-EPMC2701051 | biostudies-literature
Project description:A complete separation of myo-inositol 1,4,5-[4,5-(32)P]trisphosphate prepared from human erythrocytes, and myo-[2-3H]inositol 1,3,4-trisphosphate prepared from carbachol-stimulated rat parotid glands [Irvine, Letcher, Lander & Downes (1984) Biochem. J. 223, 237-243], was achieved by anion-exchange high-performance liquid chromatography. This separation technique was then used to study the metabolism of these two isomers of inositol trisphosphate in carbachol-stimulated rat parotid glands. Fragments of glands were pre-labelled with myo-[2-3H]inositol, washed, and then stimulated with carbachol. At 5s after stimulation a clear increase in inositol 1,4,5-trisphosphate was detected, with no significant increase in inositol 1,3,4-trisphosphate. After this initial lag however, inositol 1,3,4-phosphate rose rapidly; by 15s it predominated over inositol 1,4,5-trisphosphate, and continued to rise so that after 15 min it was at 10-20 times the radiolabelling level of the 1,4,5-isomer. In contrast, after the initial rapid rise (maximal within 15s), inositol 1,4,5-trisphosphate levels declined to near control levels after 1 min and then rose again very gradually over the next 15 min. When a muscarinic blocker (atropine) was added after 15 min of carbachol stimulation, inositol 1,4,5-trisphosphate levels dropped to control levels within 2-3 min, whereas inositol 1,3,4-trisphosphate levels took at least 15 min to fall, consistent with the kinetics observed earlier for total parotid inositol trisphosphates [Downes & Wusteman (1983) Biochem. J. 216, 633-640]. Phosphatidylinositol bisphosphate (PtdInsP2) from stimulated and control cells were degraded chemically to inositol trisphosphate to seek evidence for 3H-labelled PtdIns(3,4)P2. No evidence could be obtained that a significant proportion of PtdInsP2 was this isomer; in control tissues it must be less than 5% of the total PtdInsP2 radiolabelled by myo-[2-3H]inositol. These data indicate that, provided that inositol 1,4,5-trisphosphate is studied independently of inositol 1,3,4-trisphosphate, the former shows metabolic characteristics consistent with its proposed role as a second messenger for calcium mobilization. The metabolic profile of inositol 1,3,4-trisphosphate is entirely different, and its function and source remain unclear.
| S-EPMC1145084 | biostudies-other
Project description:Fatty liver is the most common type of liver disease, affecting nearly one third of the US population and more than half a billion people worldwide. Abnormalities in ER calcium handling and mitochondrial function each have been implicated in abnormal lipid droplet formation. Here we show that the type 1 isoform of the inositol 1,4,5-trisphosphate receptor (InsP3R1) specifically links ER calcium release to mitochondrial calcium signaling and lipid droplet formation in hepatocytes. Moreover, liver-specific InsP3R1 knockout mice have impaired mitochondrial calcium signaling, decreased hepatic triglycerides, reduced lipid droplet formation and are resistant to development of fatty liver. Patients with non-alcoholic steatohepatitis, the most malignant form of fatty liver, have increased hepatic expression of InsP3R1 and the extent of ER-mitochondrial co-localization correlates with the degree of steatosis in human liver biopsies.ConclusionInsP3R1 plays a central role in lipid droplet formation in hepatocytes and the data suggest that it is involved in the development of human fatty liver disease.
| S-EPMC5613674 | biostudies-literature
Project description:The inositol trisphosphate liberated on stimulation of guinea-pig hepatocytes, pancreatic acinar cells and dimethyl sulphoxide-differentiated human myelomonocytic HL-60 leukaemia cells is composed of two isomers, the 1,4,5-trisphosphate and the 1,3,4-trisphosphate. Inositol 1,4,5-trisphosphate was released rapidly, with no measurable latency on hormone stimulation, and, consistent with its proposed role as an intracellular messenger for Ca2+ mobilization, there was good temporal correlation between its formation and Ca2+-mediated events in these tissues. There was a definite latency before an increase in the formation of inositol 1,3,4-trisphosphate could be detected. In all of these tissues, however, it formed a substantial proportion of the total inositol trisphosphate by 1 min of stimulation. In guinea-pig hepatocytes, where inositol trisphosphate increases for at least 30 min after hormone application, inositol 1,3,4-trisphosphate made up about 90% of the total inositol trisphosphate by 5-10 min. In pancreatic acinar cells, pretreatment with 20 mM-Li+ caused an increase in hormone-induced inositol trisphosphate accumulation. This increase was accounted for by a rise in inositol 1,3,4-trisphosphate; inositol 1,4,5-trisphosphate was unaffected. This finding is consistent with the observation that Li+ has no effect on Ca2+-mediated responses in these cells. The role, if any, of inositol 1,3,4-trisphosphate in cellular function is unknown.
| S-EPMC1152864 | biostudies-other