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

Metabolic profiling of Mytilus coruscus mantle in response of shell repairing under acute acidification

Mytilus coruscus is an economically important marine bivalve mollusk found in the Yangtze River estuary, which experiences dramatic pH fluctuations due to seasonal freshwater input and suffer from shell fracture or injury in the natural environment. In this study, we used intact-shell and damaged-shell M. coruscus and performed metabolomic analysis, free amino acids analysis, calcium-positive staining, and intracellular calcium level tests in the mantle to investigate whether the mantle-specific metabolites can be induced by acute sea-water acidification and understand how the mantle responds to acute acidification during the shell repair process. We observed that both shell damage and acute acidification induced alterations in phospholipids, amino acids, nucleotides, organic acids, benzenoids, and their analogs and derivatives. Glycylproline, spicamycin, and 2-aminoheptanoic acid (2-AHA) are explicitly induced by shell damage. Betaine, aspartate, and oxidized glutathione are specifically induced by acute acidification. Our results show different metabolic patterns in the mussel mantle in response to different stressors, which can help elucidate the shell repair process under ocean acidification. furthermore, metabolic processes related to energy supply, cell function, signal transduction, and amino acid synthesis are disturbed by shell damage and/or acute acidification, indicating that both shell damage and acute acidification increased energy consumption, and disturb phospholipid synthesis, osmotic regulation, and redox balance. Free amino acid analysis and enzymatic activity assays partially confirmed our findings, highlighting the adaptation of M. coruscus to dramatic pH fluctuations in the Yangtze River estuary.

Insulin potentiates bradykinin-induced inositol 1,4,5-triphosphate in neonatal rat cardiomyocytes

This study investigated whether cross-talk between insulin and the bradykinin receptor exists to modulate bradykinin-induced increase in inositol 1,4,5-triphosphate (IP3) in neonatal rat cardiomyocytes. Treatment of the cultures with 1, 2, and 20 nM of insulin for 90 min before adding bradykinin increased the IP3 response to the same bradykinin dose to 372.0 +/- 17.8, 413.7 +/- 17.7, and 457.3 +/- 18.2 pmol/mg protein, respectively. Tyrphostine A23 and genistein (tyrosine kinase inhibitors) decreased the bradykinin (10 nM)-induced IP3 production potentiated by 2 nM insulin from 400.7 +/- 19.4 pmol/mg protein to 297.3 +/- 42.4 and 314.3 +/- 37.5 pmol/mg protein, respectively. Administration of 100 nM N-(6-aminohexyl)-5-chloro-naphthalenesulfonamide (W7, a calmodulin antagonist) significantly increased the bradykinin (10 nM)-induced IP3 production from 311.7 +/- 13.0 pmol/mg protein in the absence of insulin to 457.8 +/- 19.9, 578.2 +/- 25.9, and 665.2 +/- 16.0 pmol/mg protein in the presence of 1, 2, and 20 nM insulin, respectively. These results demonstrate that cross-talk between the insulin receptor and the bradykinin signaling system may exist in neonatal rat cardiomyocytes. Tyrosine kinase appears to play an important role in the cross-talking. Calmodulin controls the IP3 response to bradykinin by a negative feedback mechanism.

The second messenger binding site of inositol 1,4,5-trisphosphate 3-kinase is centered in the catalytic domain and related to the inositol trisphosphate receptor site

A segment of inositol 1,4,5-trisphosphate 3-kinase responsible for inositol 1,4,5-trisphosphate (InsP(3)) binding was characterized and confirmed by three different approaches employing the fully active expressed catalytic domain of the enzyme. Part of this moiety was protected from limited tryptic proteolysis by InsP(3). Sequencing of two fragments of 16 and 21 kDa, generated in the absence or presence of InsP(3), respectively, identified segment Glu-271 to Arg-305 as being protected. 15 monoclonal antibodies, all binding to epitopes within this region, inhibited enzyme activity and interfered with inositol phosphate binding. Detailed enzyme kinetic parameters of 32 site-directed mutants revealed residues Arg-276 and Lys-303 in this segment and Arg-322, located nearby, as directly involved in and five other closely neighbored residues, all located within a segment of 73 amino acids, as also influencing InsP(3) binding. Part of this region is similar in sequence to an InsP(3) binding segment in InsP(3) receptors. Combined with the finding that mutants influencing only ATP binding all lie outside this region, these data indicate that an InsP(3) binding core domain is inserted between two segments acting together in ATP binding and phosphate transfer.

The role of inositol 1,4,5-trisphosphate 5-phosphatase in inositol signaling in the CNS of larval Manduca sexta

Production of inositol 1,4,5-trisphosphate (IP3) in cells results in the mobilization of intracellular calcium. Therefore, the dynamics of IP3 metabolism is important for calcium dependent processes in cells. This report investigates the coupling of mAChRs to the inositol lipid pathway in the CNS of the larval Manduca sexta. Stimulation of intact abdominal ganglia prelabeled with [3H]-inositol using a muscarinic agonist, oxotremorine-M (oxo-M), increased total inositol phosphate levels in a dose dependent manner (EC50 = 4.23 microM). These inositol phosphates consisted primarily of inositol 1,4-bisphosphate (IP2) and inositol monophosphate (IP1). Similarly, when nerve cord homogenates were provided with [3H]-phosphatidylinositol 4,5-bisphosphate ([3H]-PIP2) (10-13 microM) the predominant products were IP2 and IP1. In contrast, incubation of purified membranes with 1 mM oxo-M in the presence of 100 microM GTP gamma S and [3H]-PIP2 increased IP3 levels, suggesting that the direct activation of phospholipase C (PLC) by mAChRs occurs in a membrane delimited process. Together, these results suggest that in the intact nerve cord and in crude homogenates, a cytosolic 5-phosphatase quickly metabolizes IP3 to produce to IP2 and IP1. This enzyme was kinetically characterized using IP3 (Km = 43.7 microM, Vmax = 864 pmoles/min/mg) and IP4 (Km = 0.93 microM; Vmax = 300pmoles/min/mg) as substrates. The enzyme activity can be potently inhibited by two IP thiol compounds; IP3S3 (1,4,6) and IP3S3 (2,3,5), that show complex binding kinetics (Hill numbers < 1) and can distinguish different forms of the 5-phosphatase in purified membranes. These two inhibitors could be very useful tools to determine the role of the inositol lipid pathway in neuroexcitability.

Simulations of the effects of inositol 1,4,5-trisphosphate 3-kinase and 5-phosphatase activities on Ca2+ oscillations

Inositol 1,4,5-trisphosphate (Ins-1,4,5-P3) is responsible for Ca2+ mobilization in response to external stimulation in many cell types. The latter phenomenon often occurs as repetitive Ca2+ spikes. In this study, the effect of the two Ins-1,4,5-P3 metabolizing enzymes (Ins-1,4,5-P3 3-kinase and 5-phosphatase) on the temporal pattern of Ca2+ oscillations has been investigated. On the basis of the well-documented Ins-1,4,5-P3 3-kinase stimulation by the Ca2+/calmodulin complex and of the experimentally-determined kinetic characteristics of these enzymes, we predict that 5-phosphatase primarily controls the levels of Ins-1,4,5-P3 and, thereby, the occurrence and frequency of Ca2+ oscillations. Consequently, the model reproduces the experimental observation performed in Chinese hamster ovary cells that 5-phosphatase overexpression has a much more pronounced effect on the pattern of Ca2+ oscillations than 3-kinase overexpression. We also investigated, in more detail, under which conditions a similar effect could be observed in other cell types expressing various Ins-1,4,5-P3 3-kinase activities.

Differential induction of inositol phosphate metabolism by three adipokinetic hormones

Many (in)vertebrates simultaneously release several structurally and functionally related hormones; however, the relevance of this phenomenon is poorly understood. In the locust e.g. each of three adipokinetic hormones (AKHs) is capable of controlling mobilization of carbohydrate and lipid from fat body stores, but it is unclear why three AKHs coexist. We now demonstrate disparities in the signal transduction of these hormones. Massive doses of the AKHs stimulated total inositol phosphate (InsPn) production in the fat body biphasicly, but time courses were different. Inhibition of phospholipase C (PLC) resulted in attenuation of both InsPn synthesis and glycogen phosphorylase activation. The AKHs evoked differential formation of individual [3H]InsPn isomers (InsP(1-6)), the effect being most pronounced for InsP3. 40 nM of AKH-I and -III induced a substantial rise in total InsPn and [3H]InsP3 at short incubations, whereas the AKH-II effect was negligible. At a more physiological dose of 4 nM, the AKHs equally enhanced Ins(1,4,5)P3 levels. The InsP3 effect was most prolonged for AKH-III. These subtle differences in InsPn metabolism, together with earlier findings on differences between the AKHs, support the hypothesis that each AKH exerts specific biological functions in the overall syndrome of energy mobilization during flight.

Transformation of Rat-1 fibroblasts with the v-src oncogene induces inositol 1,4,5-trisphosphate 3-kinase expression

Transformation of Rat-1 fibroblasts with the v-src oncogene leads to a 6- to 8-fold enhancement of the activity of the Ins(1,4,5)P3 3-kinase in cytosolic extracts [Johnson, Wasilenko, Mattingly, Weber and Garrison (1989) Science 246, 121-124]. This study confirms these results using another v-src-transformed Rat-1 cell line (B31 cells) and investigates the molecular mechanism by which pp60v-src activates Ins(1,4,5)P3 3-kinase. The mRNA and protein levels for two rat isoforms of Ins(1,4,5)P3 3-kinase were determined in the v-src-transformed cell line. Both the mRNA and protein levels for isoform A were elevated in v-src-transformed Rat-1 cells while those for isoform B were not significantly affected. Moreover, stable expression of either form of Ins(1,4,5)P3 3-kinase in the B31 v-src-transformed Rat-1 cell line did not result in tyrosine phosphorylation of Ins(1,4,5)P3 3-kinase A or B. These results suggest that at least one mechanism by which the v-src oncogene increases the activity of the Ins(1,4,5)P3 3-kinase in the Rat-1 transformed fibroblast is by increasing the level of expression of Ins(1,4,5)P3 3-kinase A.

Insect adipokinetic hormone stimulates inositol phosphate metabolism: roles for both Ins(1,4,5)P3 and Ins(1,3,4,5)P4 in signal transduction?

Adipokinetic hormones (AKHs) control the mobilization of energy reserves from the insect fat body as fuels for flight activity. As a part of our investigations on AKH signal transduction, we demonstrate in this study that the inositol lipid cycle may be involved in the action of AKH-I on fat body of the migratory locust. We show that [3H]inositol is incorporated into fat body phosphoinositides in vitro, whose hydrolysis leads to the formation of the following inositol phosphates (InsPs): Ins(1 and/or 3)P, Ins(4)P, Ins(1,3)P2, Ins(1,4)P2, Ins(3,4)P3, Ins(1,3,4)P3, Ins(1,4,5)P3 and Ins(1,3,4,5)P4. AKH stimulates the formation of these isomers, eliciting an increase in radioactivity of total InsPs already after 1 min. Mass measurements show that Ins(1,4,5)P3 levels are substantially enhanced by AKH, which is indicative of hormonal activation of phospholipase C. In cell-free tissue preparations, Ins(1,4,5)P3 is metabolized through dephosphorylation as well as further phosphorylation. Ins(1,3,4,5)P4 is dephosphorylated primarily to Ins(1,3,4)P3, although the ability for its reconversion to Ins(1,4,5)P3 suggests that in vivo Ins(1,3,4,5)P4 may function as a rapidly mobilizable pool for Ins(1,4,5)P3 generation. Metabolic pathways for the conversion of InsPs to inositol in the locust fat body are proposed.

D-myo-inositol 1,4,5-trisphosphate analogues modified at the 3-position inhibit phosphatidylinositol 3-kinase

Several natural and unnatural inositol phosphates and analogues were analyzed for their ability to inhibit the in vitro phosphatidylinositol 3-kinase (PI 3-kinase) activity immunoprecipitated from a leukemic T cell line by a p85 monoclonal antibody. A 3-position ring-modified analogue of D-myo-inositol 1,4,5-trisphosphate (Ins(1,4,5)P3), L-chiro-inositol 2,3,5-trisphosphate (L-chiro-Ins(2,3,5)P3) and its phosphorothioate analogue, L-chiro-inositol 2,3,5-trisphosphorothioate, as well as the analogue benzene 1,2,4-trisphosphate induced reversible inhibition of PI 3-kinase activity, which correlated with decreased Vmax but unchanged Km values for PI 3-kinase. Other inositol phosphates, including D- and L-Ins(1,4,5)P3, D-myo-inositol 1,3,4,5-tetrakisphosphate, the enantiomers of myo-inositol 1,3,4-trisphosphate, DL-myo-inositol 1,4,6-trisphosphate (DL-Ins(1,4,6)P3), and DL-scyllo-inositol 1,2,4-trisphosphate (DL-scyllo-Ins(1,2,4)P3), did not inhibit PI 3-kinase activity under identical conditions. L-chiro-Ins(2,3,5)P3 closely resembles Ins(1,4,5)P3 and D-Ins(1,4,6)P3 except for a difference in the orientation of a single hydroxyl group at either the equivalent 3-OH or 2-OH position of Ins(1,4,5)P3, respectively. Similarly, L-chiro-Ins(2,3,5)P3 resembles D-scyllo-Ins(1,2,4)P3, but has a different orientation of both the equivalent 3-OH and 2-OH positions. Since Ins(1,4,5)P3, DL-Ins(1,4,6)P3, and DL-scyllo-Ins(1,2,4)P3 did not inhibit PI 3-kinase activity, this suggests that the orientation of the two hydroxyl groups at the 2- and 3-positions plays a pivotal role in the inhibitory action of inositol phosphate analogues on PI 3-kinase activity. Thus, inositol phosphate analogues inter alia are shown for the first time to inhibit PI 3-kinase and may be useful tools for determining the function of PI 3-kinase and its substrate binding specificities.