Effects of transformation with the v-src oncogene on inositol phosphate metabolism in rat-1 fibroblasts. D-myo-inositol 1,4,5,6-tetrakisphosphate is increased in v-src-transformed rat-1 fibroblasts and can be synthesized from D-myo-inositol 1,3,4-trisphosphate in cytosolic extracts

Deep Learning Approach for Predicting the Therapeutic Usages of Unani Formulas towards Finding Essential Compounds

The use of herbal medicines in recent decades has increased because their side effects are considered lower than conventional medicine. Unani herbal medicines are often used in Southern Asia. These herbal medicines are usually composed of several types of medicinal plants to treat various diseases. Research on herbal medicine usually focuses on insight into the composition of plants used as ingredients. However, in the present study, we extended to the level of metabolites that exist in the medicinal plants. This study aimed to develop a predictive model of the Unani therapeutic usage based on its constituent metabolites using deep learning and data-intensive science approaches. Furthermore, the best prediction model was then utilized to extract important metabolites for each therapeutic usage of Unani. In this study, it was observed that the deep neural network approach provided a much better prediction model than other algorithms including random forest and support vector machine. Moreover, according to the best prediction model using the deep neural network, we identified 118 important metabolites for nine therapeutic usages of Unani.

The Methyl-CpG-Binding Domain 2 and 3 Proteins and Formation of the Nucleosome Remodeling and Deacetylase Complex

The Nucleosome Remodeling and Deacetylase (NuRD) complex uniquely combines both deacetylase and remodeling enzymatic activities in a single macromolecular complex. The methyl-CpG-binding domain 2 and 3 (MBD2 and MBD3) proteins provide a critical structural link between the deacetylase and remodeling components, while MBD2 endows the complex with the ability to selectively recognize methylated DNA. Hence, NuRD combines three major arms of epigenetic gene regulation. Research over the past few decades has revealed much of the structural basis driving formation of this complex and started to uncover the functional roles of NuRD in epigenetic gene regulation. However, we have yet to fully understand the molecular and biophysical basis for methylation-dependent chromatin remodeling and transcription regulation by NuRD. In this review, we discuss the structural information currently available for the complex, the role MBD2 and MBD3 play in forming and recruiting the complex to methylated DNA, and the biological functions of NuRD.

Tyrosine phosphorylation of HDAC3 by Src kinase mediates proliferation of HER2-positive breast cancer cells

The role of histone deacetylase 3 (HDAC3) is to repress the expression of various genes by eliminating acetyl group from histone. Thus, the regulation of HDAC3 activity is essential to maintain cellular homeostasis. In this study, we found that HDAC3 interacts with c-Src kinase. However, the interaction between HDAC3 and c-Src was previously reported, it has still been ambiguous whether c-Src phosphorylates HDAC3 and affects the function of HDAC3. First, we confirmed that HDAC3 directly binds to c-Src, and c-Src identified to interact with C-terminal domain (277-428 a.a.) of HDAC3. c-Src also phosphorylated three tyrosine sites of HDAC3 at tyrosine 325, 328, and 331. Importantly, wild-type c-Src increases HDAC3 activity, but not mutant c-Src^K298M (kinase inactive form). When these tyrosine residues are all substituted for alanine residues, the deacetylase activity of mutant HDAC3 was abolished. In addition, a proliferation of HER2-positive breast cancer cells expressing phosphorylation deficient mutant HDAC3 is decreased in comparison with control cells. Thus, our findings suggested that phosphorylation of HDAC3 by c-Src kinase regulates the HDAC3 activity and the proliferation of breast cancer cells.

Transcriptional coregulators: fine-tuning metabolism

Metabolic homeostasis requires that cellular energy levels are adapted to environmental cues. This adaptation is largely regulated at the transcriptional level, through the interaction between transcription factors, coregulators, and the basal transcriptional machinery. Coregulators, which function as both metabolic sensors and transcriptional effectors, are ideally positioned to synchronize metabolic pathways to environmental stimuli. The balance between inhibitory actions of corepressors and stimulatory effects of coactivators enables the fine-tuning of metabolic processes. This tight regulation opens therapeutic opportunities to manage metabolic dysfunction by directing the activity of cofactors toward specific transcription factors, pathways, or cells/tissues, thereby restoring whole-body metabolic homeostasis.

Inositol based non-viral vectors for transgene expression in human cervical carcinoma and hepatoma cell lines

Myo-Inositol (INO) is a biomolecule with crucial functions in many aspects. In this study, hyperbranched copolymers for gene delivery were synthesized based on inositol and low molecular weight polyethylenimine. The capacity of INO-PEIs to load plasmid DNA and their biocompatibility was demonstrated. A tumor target ligand, folic acid (FA), which was widely used for drug delivery systems, was subsequently conjugated to INO-PEIs and resulted in INO-PEI-FA copolymers. The polymers were then evaluated on their activity to mediate transgene expression in mammalian cell lines. As indicated, INO-PEIs were able to mediate efficient transgene expression, which was particularly noticeable in carcinoma cell line HeLa. INO-PEI-FA further improved the efficiency in HepG2. Distribution of INO-PEI-FA polymers in non-carcinoma NIH 3T3 and carcinoma HeLa cell lines was discussed.

Differential transcriptomic analysis of spontaneous lung tumors in B6C3F1 mice: comparison to human non-small cell lung cancer

Lung cancer is the leading cause of cancer-related death in people and is mainly due to environmental factors such as smoking and radon. The National Toxicology Program (NTP) tests various chemicals and mixtures for their carcinogenic hazard potential. In the NTP chronic bioassay using B6C3F1 mice, the incidence of lung tumors in treated and control animals is second only to the liver tumors. In order to study the molecular mechanisms of chemically induced lung tumors, an understanding of the genetic changes that occur in spontaneous lung (SL) tumors from untreated control animals is needed. The authors have evaluated the differential transcriptomic changes within SL tumors compared to normal lungs from untreated age-matched animals. Within SL tumors, several canonical pathways associated with cancer (eukaryotic initiation factor 2 signaling, RhoA signaling, PTEN signaling, and mammalian target of rapamycin signaling), metabolism (Inositol phosphate metabolism, mitochondrial dysfunction, and purine and pyramidine metabolism), and immune responses (FcγR-mediated phagocytosis, clathrin-mediated endocytosis, interleukin 8 signaling, and CXCR4 signaling) were altered. Meta-analysis of murine SL tumors and human non-small cell lung cancer transcriptomic data sets revealed a high concordance. These data provide important information on the differential transcriptomic changes in murine SL tumors that will be critical to our understanding of chemically induced lung tumors and will aid in hazard analysis in the NTP 2-year carcinogenicity bioassays.

Structure of HDAC3 bound to co-repressor and inositol tetraphosphate

Histone deacetylase enzymes (HDACs) are emerging cancer drug targets. They regulate gene expression by removing acetyl groups from lysine residues in histone tails, resulting in chromatin condensation. The enzymatic activity of most class I HDACs requires recruitment into multi-subunit co-repressor complexes, which are in turn recruited to chromatin by repressive transcription factors. Here we report the structure of a complex between an HDAC and a co-repressor, namely, human HDAC3 with the deacetylase activation domain (DAD) from the human SMRT co-repressor (also known as NCOR2). The structure reveals two remarkable features. First, the SMRT-DAD undergoes a large structural rearrangement on forming the complex. Second, there is an essential inositol tetraphosphate molecule--D-myo-inositol-(1,4,5,6)-tetrakisphosphate (Ins(1,4,5,6)P(4))--acting as an 'intermolecular glue' between the two proteins. Assembly of the complex is clearly dependent on the Ins(1,4,5,6)P(4), which may act as a regulator--potentially explaining why inositol phosphates and their kinases have been found to act as transcriptional regulators. This mechanism for the activation of HDAC3 appears to be conserved in class I HDACs from yeast to humans, and opens the way to novel therapeutic opportunities.

Defining signal transduction by inositol phosphates

Ins(1,4,5)P(3) is a classical intracellular messenger: stimulus-dependent changes in its levels elicits biological effects through its release of intracellular Ca(2+) stores. The Ins(1,4,5)P(3) response is "switched off" by its metabolism to a range of additional inositol phosphates. These metabolites have themselves come to be collectively described as a signaling "family". The validity of that latter definition is critically examined in this review. That is, we assess the strength of the hypothesis that Ins(1,4,5)P(3) metabolites are themselves "classical" signals. Put another way, what is the evidence that the biological function of a particular inositol phosphate depends upon stimulus dependent changes in its levels? In this assessment, examples of an inositol phosphate acting as a cofactor (i.e. its function is not stimulus-dependent) do not satisfy our signaling criteria. We conclude that Ins(3,4,5,6)P(4) is, to date, the only Ins(1,4,5)P(3) metabolite that has been validated to act as a second messenger.

Characterization of myo-inositol hexakisphosphate deposits from larval Echinococcus granulosus

The abundant metabolite myo-inositol hexakisphosphate (InsP6) can form vesicular deposits with cations, a widespread phenomenon in plants also found in the cestode parasite, Echinococcus granulosus. In this organism, the deposits are exocytosed, accumulating in a host-exposed sheath of extracellular matrix termed the laminated layer. The formation and mobilization of InsP6 deposits, which involve precipitation and solubilization reactions, respectively, cannot yet be rationalized in quantitative chemical terms, as the solids involved have not been formally described. We report such a description for the InsP6 deposits from E. granulosus, purified as the solid residue left by mild alkaline digestion of the principal mucin component of the laminated layer. The deposits are largely composed of the compound Ca5H2L.16H2O (L representing fully deprotonated InsP6), and additionally contain Mg2+ (6-9% molar ratio with respect to Ca2+), but not K+. Calculations employing recently available chemical constants show that the precipitation of Ca5H2L.16H2O is predicted by thermodynamics in secretory vesicle-like conditions. The deposits appear to be similar to microcrystalline solids when analysed under the electron microscope; we estimate that each crystal comprises around 200 InsP6 molecules. We calculate that the deposits increase, by three orders of magnitude, the surface area available for adsorption of host proteins, a salient ability of the laminated layer. The major inositol phosphate in the deposits, other than InsP6, is myo-inositol (1,2,4,5,6) pentakisphosphate, or its enantiomer, inositol (2,3,4,5,6) pentakisphosphate. The compound appears to be a subproduct of the intracellular pathways leading to the synthesis and vesicular accumulation of InsP6, rather than arising from extracellular hydrolysis of InsP6.

A role for rat inositol polyphosphate kinases rIPK2 and rIPK1 in inositol pentakisphosphate and inositol hexakisphosphate production in rat-1 cells

Over 30 inositol polyphosphates are known to exist in mammalian cells; however, the majority of them have uncharacterized functions. In this study we investigated the molecular basis of synthesis of highly phosphorylated inositol polyphosphates (such as inositol tetrakisphosphate, inositol pentakisphosphate (IP5), and inositol hexakisphosphate (IP6)) in rat cells. We report that heterologous expression of rat inositol polyphosphate kinases rIPK2, a dual specificity inositol trisphosphate/inositol tetrakisphosphate kinase, and rIPK1, an IP5 2-kinase, were sufficient to recapitulate IP6 synthesis from inositol 1,4,5-trisphosphate in mutant yeast cells. Overexpression of rIPK2 in Rat-1 cells increased inositol 1,3,4,5,6-pentakisphosphate (I(1,3,4,5,6)P5) levels about 2-3-fold compared with control. Likewise in Rat-1 cells, overexpression of rIPK1 was capable of completely converting I(1,3,4,5,6)P5 to IP6. Simultaneous overexpression of both rIPK2 and rIPK1 in Rat-1 cells increased both IP5 and IP6 levels. To reduce IPK2 activity in Rat-1 cells, we introduced vector-based short interference RNA against rIPK2. Cells harboring the short interference RNA had a 90% reduction of mRNA levels and a 75% decrease of I(1,3,4,5,6)P5. These data confirm the involvement of IPK2 and IPK1 in the conversion of inositol 1,4,5-trisphosphate to IP6 in rat cells. Furthermore these data suggest that rIPK2 and rIPK1 act as key determining steps in production of IP5 and IP6, respectively. The ability to modulate the intracellular inositol polyphosphate levels by altering IPK2 and IPK1 expression in rat cells will provide powerful tools to study the roles of I(1,3,4,5,6)P5 and IP6 in cell signaling.

Divergent syntheses of all possible optically active regioisomers of myo-inositol tris- and tetrakisphosphates

Since the discovery of D-myo-inositol 1,4,5-trisphosphate, which plays a pivotal role as a second messenger in transmembrane signaling, the scope of the phosphoinositide-based signaling processes has been continually expanding. However, the clear understanding of the molecular signal transduction mechanisms including the functions of newly found IP(n) is still lacking. As a continuing effort to our previously reported syntheses of all possible 39 optically inactive regioisomers of myo-inositol phosphates (IP(n); n = 1-6), we synthesized all possible optically active regioisomers of myo-IP(3) and myo-IP(4) using chiral IBz(3)s and IBz(2)s, respectively. A series of procedures involving CRL-catalyzed enzymatic resolution of racemic 1,2:5,6-di-O-isopropylidene-myo-inositol and base-catalyzed benzoyl migration in tri- and dibenzoyl-isopropylidene-myo-inositol afforded eight enantiomeric pairs of IBz(3) and six enantiomeric pairs of IBz(2), respectively. Phosphorylation of these intermediates by the phosphitylation and oxidation procedure gave the target products.

Back in the water: the return of the inositol phosphates

Following the discovery of inositol-1,4,5-trisphosphate as a second messenger, many other inositol phosphates were discovered in quick succession, with some understanding of their synthesis pathways and a few guesses at their possible functions. But then it all seemed to go comparatively quiet, with an explosion of interest in the inositol lipids. Now the water-soluble phase is once again becoming a focus of interest. Old and new data point to a new vista of inositol phosphates, with functions in many diverse aspects of cell biology, such as ion-channel physiology, membrane dynamics and nuclear signalling.

The versatility of inositol phosphates as cellular signals

Cells from across the phylogenetic spectrum contain a variety of inositol phosphates. Many different functions have been ascribed to this group of compounds. However, it is remarkable how frequently several of these different inositol phosphates have been linked to various aspects of signal transduction. Therefore, this review assesses the evidence that inositol phosphates have evolved into a versatile family of second messengers.

Alterations of signal transduction pathways involved in 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced malignant transformation of human cells in culture

Effects of signal transduction pathways in TCDD-induced neoplastic transformation of human cells were assessed with respect to PLC-coupled signaling pathways, adenylyl cyclase-mediated responses and PKC isozyme expressions. A lower stimulation of the intracellular free calcium levels with exposure to extracellular ATP or histamine was observed in the transformed cells, as compared to the parental cells. While the steady-state level of IP3 was higher in the transformed cells, the magnitude of stimulation of IP3 generation by ATP or histamine was significantly lower in the transformed cells than the parental cells. These results indicate that a downregulation PLC-coupled signaling pathways may be involved in the TCDD-induced transformation of human cells. While the steady-state levels of cAMP accumulation were similar between the two cell lines, treatment of PGE2, a potent differentiation inducer, stimulated a higher accumulation of cAMP in the parental cells but isoproterenol, a typical beta-adrenergic agonist, did not induce a significant difference between the two cell lines. These results suggest that desensitization of cAMP-mediated response to extracellular signals including differentiation signals may be associated with a possible mechanism of the carcinogenesis. Elevated expression of PKC-alpha, -gamma, -zeta, -epsilon, -lambda, and -tau were observed in TCDD-transformed cells, indicating a possible association of altered expression of PKC isozymes with TCDD-induced transformation of human cells. The present study demonstrates that alterations of signal transduction pathways are involved in the TCDD-induced transformation of human cells and provides a valuable basis to investigate effects of signaling pathway as a possible mechanism of TCDD-induced carcinogenesis in human cells.

D-myo-Inositol 1,4,5,6-tetrakisphosphate produced in human intestinal epithelial cells in response to Salmonella invasion inhibits phosphoinositide 3-kinase signaling pathways

Several inositol-containing compounds play key roles in receptor-mediated cell signaling events. Here, we describe a function for a specific inositol polyphosphate, D-myo-inositol 1,4,5,6-tetrakisphosphate [Ins(1,4,5,6)P4], that is produced acutely in response to a receptor-independent process. Thus, infection of intestinal epithelial cells with the enteric pathogen Salmonella, but not with other invasive bacteria, induced a multifold increase in Ins(1,4,5,6)P4 levels. To define a specific function of Ins(1,4,5,6)P4, a membrane-permeant, hydrolyzable ester was used to deliver it to the intracellular compartment, where it antagonized epidermal growth factor (EGF)-induced inhibition of calcium-mediated chloride (Cl-) secretion (CaMCS) in intestinal epithelia. This EGF function is likely mediated through a phosphoinositide 3-kinase (PtdIns3K)-dependent mechanism because the EGF effects are abolished by wortmannin, and three different membrane-permeant esters of the PtdIns3K product phosphatidylinositol 3,4,5-trisphosphate mimicked the EGF effect on CaMCS. We further demonstrate that Ins(1,4,5,6)P4 antagonized EGF signaling downstream of PtdIns3K because Ins(1,4,5, 6)P4 interfered with the PtdInsP3 effect on CaMCS without affecting PtdIns3K activity. Thus, elevation of Ins(1,4,5,6)P4 in Salmonella-infected epithelia may promote Cl- flux by antagonizing EGF inhibition mediated through PtdIns3K and PtdInsP3.

Expression, purification, and regulation of two isoforms of the inositol 1,4,5-trisphosphate 3-kinase

The level of inositol 1,4,5-trisphosphate in the cytoplasm is tightly regulated by two enzymes, the inositol 1,4,5,5-phosphatase and the inositol 1,4,5-trisphosphate 3-kinase. Two isoforms of the inositol 1,4,5-trisphosphate 3-kinase have been identified, the A form and the B form. The regulatory properties of the two isoforms were compared following overexpression and purification of the proteins from a v-src transformed mammalian cell line. The highly purified, recombinant inositol 1,4,5-trisphosphate 3-kinases were differentially regulated by calcium/calmodulin and via phosphorylation by protein kinase C or the cyclic AMP-dependent protein kinase. Both enzymes had similar affinities for inositol 1,4, 5-trisphosphate (Km 2-5 mu M). Calcium/calmodulin stimulated the activity of isoform A about 2.5-fold, whereas the activity of isoform B was increased 20-fold. The cyclic AMP-dependent protein kinase phosphorylated the inositol 1,4,5-trisphosphate 3-kinase A to the extent of 0.9 mol/mol and isoform B to 1 mol/mol. Protein kinase C phosphorylated isoform A to the extent of 2 mol/mol and isoform B to 2.7 mol/mol. Phosphorylation of isoform A by the cyclic AMP-dependent protein kinase caused a 2.5-fold increase in its activity when assayed in the absence of calcium/calmodulin, whereas phosphorylation by protein kinase C decreased activity by 72%. The activity of isoform B in the absence of calcium/calmodulin was not affected by phosphorylation using either kinase. When assayed in the presence of calcium/calmodulin, phosphorylation of isoform A by the cyclic AMP-dependent protein kinase increased activity 1.5-fold, whereas phosphorylation of isoform B decreased activity by 45%. Phosphorylation of either isoform A or B by protein kinase C resulted in a 70% reduction of calcium/calmodulin-stimulated activity. Differential expression and regulation of the two inositol 1,4,5-trisphosphate 3-kinase isoforms provides multiple mechanisms for regulating the cytosolic level of inositol 1,4,5-trisphosphate in cells.

Binding and activity of the nine possible regioisomers of myo-inositol tetrakisphosphate at the inositol 1,4,5-trisphosphate receptor

All 9 racemic regioisomers (15 enantiomerically) of myo-inositol tetrakisphosphates (IP4s): DL-Ins(1,2,4,5)P4 [A], DL-Ins(1,2,4,6)P4 [B], Ins(1,2,3,5)P4 [C], Ins(1,3,4,6)P4 [D], Ins(2,4,5,6)P4 [E], DL-Ins(1,3,4,5)P4 [F], DL-Ins(1,2,5,6)P4 [G], DL-Ins(1,2,3,4)P4 [H] and DL-Ins(1,4,5,6)P4 [I] [Chung S-K., Chang Y-T. Synthesis of all possible regioisomers of myo-inositol tetrakisphosphate. J Chem Soc Chem Commun 1995; 11-13] were investigated for their ability to bind to the D-myo-inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] receptor in bovine adrenal cortical membranes, and for their ability to mobilize 45Ca2+ from Ins(1,4,5)P3-sensitive Ca2+ stores in permeabilized Chinese hamster ovary (CHO) cells. DL-Ins(1,2,4,5)P4 (Ki = 11 nM) bound to Ins(1,4,5)P3 receptors with an affinity only 2-fold lower than Ins(1,4,5)P3 (Ki = 6 nM). Ins(1,2,3,5)P4, Ins(1,3,4,6)P4, Ins(2,4,5,6)P4, DL-Ins(1,3,4,5)P4, DL-Ins(1,2,3,4)P4 and DL-Ins(1,4,5,6)P4 bound with affinities of between 0.4-0.7 microM. DL-Ins(1,2,4,6)P4 and DL-Ins(1,2,5,6)P4 bound to the Ins(1,4,5)P3 receptor with low affinity (approximately 2-3 microM). All but one of the IP4s mediated release of 45Ca2+ from stores of permeabilized CHO cells with a similar rank order of potency as that for Ins(1,4,5)P3 receptor binding, being between 16-fold and 50-fold less potent at releasing 45Ca2+ compared with their apparent binding affinities to the Ins(1,4,5)P3 receptor. The notable exception was Ins(1,2,3,5)P4, which showed an approximately 200-fold lower potency compared with its affinity for the Ins(1,4,5)P3 receptor. Ins(1,2,3,5)P4 may be a useful lead compound for the rational design of novel synthetic Ins(1,4,5)P3 analogues possessing structure-activity profiles with relatively high binding affinity, but low intrinsic efficacy, and hence partial agonists and antagonists at the Ins(1,4,5)P3 receptor.

Inhibition of porcine brain inositol 1,3,4-trisphosphate kinase by inositol polyphosphates, other polyol phosphates, polyanions and polycations

We have partially purified an enzyme activity that phosphorylates inositol 1,3,4-trisphosphate from porcine brain, rat liver and bovine testis by FPLC chromatography on Q-Sepharose anion-exchange resin and Heparin-agarose. The products of this reaction were inositol 1,3,4,6-tetrakisphosphate and inositol 1,3,4,5-tetrakisphosphate. The same enzyme appears to be responsible for both 6-kinase and 5-kinase activities against inositol 1,3,4-trisphosphate (the 6-kinase: 5-kinase activity ratio is approximately 4 to 1), has a pH optimum of approximately 6.8 and requires Mg2+ for activity. The Km values of the enzyme for inositol 1,3,4-trisphosphate and ATP were approximately 0.5 microM and approximately 100 microM, respectively. Inositol 3,4,5,6-tetrakisphosphate, inositol 1,3,4,6-tetrakisphosphate and inositol 1,3,4,5-tetrakisphosphate are all competitive inhibitors with K(i) values of 0.4 microM, 3 microM and 5 microM, respectively, well within their likely intracellular concentration ranges: they inhibited 6-kinase and 5-kinase activities equally. 2,3-Bisphosphoglycerate and spermine were also competitive inhibitors, with K(i) values of 0.8 mM an 12 mM, respectively. Dextran sulphate was a non-competitive inhibitor with a Ki of approximately 15 microM, and poly-L-lysine (IC50 approximately 200 microM), polyvinylsulphate (IC50 approximately 250 microM) and heparin (IC50 approximately 2 mg/ml) also inhibited. Inhibition by these compounds suggests that inositol 3,4,5,6-tetrakisphosphate (and to a lesser extent inositol 1,3,4,5-tetrakisphosphate and other naturally occurring intracellular ions) may restrict the synthesis of inositol 1,3,4,6-tetrakisphosphate and hence regulate the rate of inositol penta- and hexakisphosphate synthesis from receptor-generated inositol phosphates.

Differential localization and pH dependency of phosphoinositide 1,4,5-IP3, 1,3,4,5-IP4 and IP6 receptors in rat and human brains

It is well established that the inositol lipids mediate signal transduction in several cellular populations. Many neurotransmitters, hormones and growth factors act at plasma membrane receptors to induce the hydrolysis of phosphatidylinositols and hence the generation of various inositol phosphates (IP). The best known member of this family is 1,4,5-IP3, which is associated with the release of Ca2+ from intracellular pools. It has also been proposed that two others inositides, 1,3,4,5-IP4 and IP6, may be involved in Ca2+ homeostasis. In order to study the possible relevance of these various inositides in neuronal tissues, we have localized the respective receptors in rat and human brain under both acidic and basic pH conditions. In the hippocampal formation, [3H]1,3,4,5-IP4 binding sites are concentrated in the hilus and the molecular layer while a clearly different pattern of distribution is seen for [3H]1,4,5-IP3, its highest concentration of labelling being concentrated in the oriens and radiatum laminae. This contrasting profile of distribution is also observed in other brain areas such as the caudate-putamen, the septo-hippocampal area, and the molecular and granular layers of the cerebellum. Moreover, while highest amounts of specific [3H]1,4,5-IP3 binding are obtained at pH 8.5, the opposite is found for [3H]1,3,4,5-IP4, with high binding levels seen under acidic conditions. [3H]IP6 binding sites are broadly distributed with specific labelling concentrated in areas enriched with neuronal perikarya such as the granular cell layer of the dentate gyrus, the pyramidal cell layers of the hippocampus and the granular cell layer of the cerebellum.(ABSTRACT TRUNCATED AT 250 WORDS)

Novel inositol containing phospholipids and phosphates: their synthesis and possible new roles in cellular signalling

Details of the widely employed PtdIns(4,5)P2 hydrolysis receptor-stimulated signalling pathway continue to be elucidated rapidly. However, it has recently become apparent that numerous other inositol lipids and phosphates are widespread and are likely to have important cellular functions. In this review, we focus particularly on three rapidly progressing areas: the synthesis and possible functions of 3-phosphorylated inositol lipids, particularly phosphatidylinositol 3,4,5-trisphosphate; the roles of inositol 1,4,5-trisphosphate and inositol 1,3,4,5-tetrakisphosphate in coordinating intracellular Ca2+ mobilization and Ca2+ influx in stimulated cells; and the metabolism and possible functions of other inositol polyphosphates and of inositol polyphosphate pyrophosphates.

Inositol phosphates and cell signaling: new views of InsP5 and InsP6

Ins(1,3,4,5,6)P5 and InsP6 comprise the bulk of the inositol phosphate content of mammalian cells, but their intracellular functions are unknown. Until recently it seemed that these compounds were metabolically lethargic; this has diverted attention away from their possible role in short-term regulation of physiological processes. Interest in the idea that these polyphosphates play more dynamic roles is now increasing, following recent demonstrations that they are precursors of several inositol phosphates that turnover rapidly.

Okadaic acid inhibits angiotensin II stimulation of Ins(1,4,5)P3 and calcium signalling in rat hepatocytes

OKA2 and CL-A significantly inhibit the ability of angiotensin II, ATP and vasopressin to raise [Ca2+]i in rat hepatocytes, with a partial inhibition of the initial spike, and a complete inhibition of the following plateau. In contrast, the [Ca2+]i response to thapsigargin, which releases intracellular calcium stores through a mechanism independent of inositol phosphates, is much less affected. The ability of angiotensin II to stimulate Ins(1,4,5)P3 production is also reduced by OKA, with kinetics consistent with the inhibited [Ca2+]i response. Since OKA and CL-A are potent and selective inhibitors of phosphoprotein phosphatases, these results provide further evidence that agonist-stimulated Ins(1,4,5)P3 signalling can be inhibited by protein phosphorylation.

Phosphoinositides and cell growth

The findings described above illustrate how the src kinase can influence several new pathways of inositol phosphate metabolism, both at the membrane level with the production of novel D-3 phosphoinositides and the activation of PI-3 kinase, and at the cytosolic level by altering the expression of certain inositol polyphosphates, in particular Ins(1,4,5,6)P4. At present, it is difficult to speculate on the role these phenomena play in cellular transformation by src, since the functions of D-3 phosphoinositides and most inositol polyphosphates are unclear. There is evidence, however, that these new pathways of phosphoinositide metabolism occur in response to other types of cellular stimulations besides src transformation. Novel D-3 phosphoinositides are expressed in a variety of nonneoplastic cells, including human platelets treated with thrombin, smooth muscle cells and stimulated neutrophils. In addition, unusual InsP4 isomers such as D/L-Ins(1,4,5,6)P4 are found in chicken erythrocytes, murine macrophages, AR4-2J rat pancreatoma cells and adrenal glomerulosa cells, to name only a few. Recently, associations have been reported between PI-3 kinases and cytoskeletal elements in thrombin- stimulated platelets, and between activated ras proteins in rat liver epithelial cells. The latter discovery is particularly intriguing since GTP-binding proteins such as ras are known to influence cell shape and serve as downstream effector proteins in the signal transduction pathways of numerous growth factor receptors. Thus, one function of novel phosphoinositides and their metabolites may lie at the level of cytoskeletal and cell shape regulation. Clearly, additional roles for phosphoinositides exist in cells besides their traditional use as precursors for the generation of Ins(1,4,5)P3 and diacylglycerol.(ABSTRACT TRUNCATED AT 250 WORDS)