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PubMed1985

[Phosphoinositide metabolism in essential and experimental hypertension].

The metabolism of phosphoinositides, a class of membrane lipids that appears to be intimately involved in the regulation by the membrane of the intracellular Ca2+ level, has been reported to be modified in the erythrocyte of the spontaneously hypertensive rat (SHR and SHR/SP). In order to elucidate the link between the phosphoinositide alteration and hypertension, the metabolism of phosphoinositides was studied in human essential hypertension and in Sabra rats under various patho-physiological conditions. Experiments were performed in vitro on isolated ghost membranes by measuring the radioactivity incorporated into triphosphoinositides (PI-P2) and diphosphoinositides (PI-P) following the incubation of membranes with [gamma 32P]-ATP. 32P-PI-P2, in moderate untreated essential hypertensive controls (n = 31) was higher than in normotensives (n = 30) (1.18 +/- 0.06 vs 0.92 +/- 0.04, 32P nmol/15 min/mg prot, p less than 0.005); 32P-PI-P2 and 32P-PI-P in hypertensive patients treated with beta-blocking agents (n = 20) did not differ from the values observed in untreated hypertensives. In Sabra rats, 32P-PI-P2 values were 0.79 +/- 0.03 and 1.32 +/- 0.08 for SbN and SbH, respectively (8-11 animals per group); difference was significant. 32P-PI-P values varied similarly. Both 32P-PI-P2 and 32P-PI-P did not change significantly when animals were fed a high sodium diet or were injected with DOCA, though such treatments rose the blood pressure. Our data indicate that the modification of phosphoinositide metabolism that we observed both in rat and human hypertension is not a consequence of the blood pressure elevation, but may be considered as an intrinsic membrane defect. Changes in the phosphoinositide metabolism may therefore be associated with the functional and structural alterations concerning the transmembrane Na+ and Ca2+ fluxes which may be of pathogenic importance.

Adult↗

PubMed1986

Effects of lithium on phosphoinositide metabolism in vivo.

All of the known pathways for metabolizing the phospholipase C (EC 3.1.4.10) products of phosphoinositide metabolism eventually lead to myo-inositol monophosphates and products that are hydrolyzed by myo-inositol 1-phosphatase (EC 3.1.3.25). That enzyme is inhibited by lithium (Ki about 1 mM). In animals treated with LiCl, elevations of myo-inositol 1-phosphate (1-IP) occur in brain that appear to result from endogenous neural activity for they are diminished by the anesthetics halothane and pentobarbital. Lithium is thus a useful tool for assessing endogenous in vivo cerebral phosphoinositide metabolism. The 1-IP elevation is also useful for revealing in vivo central nervous system (CNS) receptor activity that is stimulated by endogenous or exogenous processes such as the effects of centrally acting drugs and of seizures. Stimulation of the CNS in the presence of lithium causes myo-inositol to be sequestered in 1-IP in proportion to the amount of stimulation. Thus if the inositol level falls sufficiently resynthesis of the phosphoinositides may be compromised and receptor response to stimuli may be reduced. Evidence for such an occurrence would support the theory that this is one mechanism by which lithium acts in the therapy of manic illness. We extended our efforts to identify such a lowering of phosphoinositide levels to mice where cerebral metabolism can be halted more rapidly than in rats. However, the only change detected was a small elevation in phosphatidylinositol 4-phosphate. We were successful, however, in causing all of the phosphoinositides to be reduced in rat cerebral cortex by pilocarpine stimulation after lithium treatment, a procedure that causes seizures. The same procedure causes the largest reduction in cortical myo-inositol levels that we have observed, and thus may represent the point where the inositol decrement is sufficient to interfere with resynthesis of the lipids.

Animals↗

PubMed1986

Regulation of serotonin-stimulated phosphoinositide hydrolysis: relation to the serotonin 5-HT-2 binding site.

The hypothesis that serotonin (5-HT)-stimulated phosphoinositide hydrolysis is mediated by the 5-HT-2 binding site in cerebral cortex was tested by comparing antagonist Kd values determined by Schild analyses with Ki values at the 5-HT-2 binding site. A significant correlation was found between Kd values and Ki values at competing for 3H-ketanserin binding (R = 0.98), suggesting that the phosphoinositide-linked receptor and the 5-HT-2 site are identical. The 5-HT-2-mediated phosphoinositide response was then used as a measure of 5-HT-2 receptor sensitivity after in vivo treatments that alter the availability of 5-HT. Chronic treatment with the 5-HT-2 antagonist mianserin resulted in a significant decrease (52%) in the density of 5-HT-2 binding sites and a significant decrease (49%) in the maximal phosphoinositide hydrolysis response to 5-HT. Depletion of 5-HT levels with para-chlorophenylalanine or chemical denervation of serotonergic neurons with 5,7-dihydroxytryptamine had no significant effect upon 5-HT-2 receptor density or upon the phosphoinositide response to 5-HT. These data suggest that changes or lack of changes in 5-HT-2 receptor density following in vivo manipulations reflect the functional state of the receptor.

5,7-Dihydroxytryptamine↗

PubMed1987

Developmental changes in muscarinic receptor-stimulated phosphoinositide metabolism in rat brain.

Muscarinic receptor-stimulated phosphoinositide hydrolysis was investigated in rat brain during ontogeny by measuring the accumulation of [3H]inositol phosphates ([3H]InsPs) in cerebral cortex slices at various ages. Experiments with carbachol and acetylcholine showed that [3H]InsPs accumulation was maximal in 7-day-old rats (1477 +/- 98% of basal) and lowest in adult (75 days) rats (428 +/- 24% of basal). No differences were found in the EC50 values for both cholinergic agonists. This effect appeared to be mediated by the M1-muscarinic receptor subtype as it was blocked by pirenzepine with Ki = 29.1 +/- 7.1 nM (adults) and 87.9 +/- 18.2 nM (7-day-old rats). Incorporation of [3H]inositol into phospholipid decreased from day 3 to adulthood; however, when data of [3H]InsPs release were corrected for the incorporation at a given age, the highest stimulation by cholinergic agonists was still observed in 7-day-old rats. Among the other neurotransmitters tested (norepinephrine, histamine and serotonin), all known to stimulate phosphoinositide metabolism, none had the same developmental profile of [3H]InsPs accumulation as cholinergic agonists. In contrast to carbachol- and acetylcholine-stimulated phosphoinositide hydrolysis, the density of muscarinic binding sites, measured by [3H]quinuclidinyl benzilate binding, increased from day 3 to day 75. Acetylcholinesterase activity also increased during development. The dissociation of receptor binding sites from receptor-stimulated phosphoinositide metabolism suggests the presence of a more effective receptor-effector coupling at specific times of neonatal development, particularly 1 week. Furthermore, the fact that maximal stimulation of phosphoinositide hydrolysis coincides with the period of brain growth spurt in the rats suggests that this system in the cerebral cortex might be involved in the processes of cell division and differentiation.

Acetylcholine↗

PubMed1987

Relative efficacies of piperazines at the phosphoinositide hydrolysis-linked serotonergic (5-HT-2 and 5-HT-1c) receptors.

Serotonin (5-HT)-stimulated phosphoinositide hydrolysis is mediated by the 5-HT-2 receptor in rat cerebral cortex and by the 5-HT-1c receptor in rat choroid plexus. These systems were used to determine relative efficacies of piperazine derivatives at the 5-HT-2 and 5-HT-1c receptors. Both quipazine and 6-chloro-2-[1-piperazinyl]-pyrazine (MK-212) stimulated phosphoinositide hydrolysis in cerebral cortex, and these effects were blocked by ketanserin. The maximum responses to these agonists were 80% of the maximum response to 5-HT. m-Trifluoromethylphenylpiperazine (TFMPP), m-chlorophenylpiperazine (MCPP) and 1-(1-naphthyl)-piperazine (1-NP) did not stimulate phosphoinositide hydrolysis in cerebral cortex at concentrations that blocked the effect of 5-HT. In the choroid plexus, TFMPP and MCPP, as well as MK-212 and quipazine, increased phosphoinositide hydrolysis and mianserin blocked these effects. MK-212 had an efficacy which was equal to that of 5-HT, whereas quipazine, MCPP and TFMPP were partial agonists in the choroid plexus. 1-NP did not stimulate phosphoinositide hydrolysis in choroid plexus but completely blocked the effect 5-HT. On the basis of these data, we conclude that quipazine and MK-212 are partial agonists at 5-HT-2 receptors in cerebral cortex, whereas 1-NP, TFMPP and MCPP are pure antagonists of the cortical 5-HT-2 receptor. However, TFMPP and MCPP as well as quipazine and MK-212 are agonists at the 5-HT-1c receptor, while 1-NP is a pure antagonist of the 5-HT-1c receptor in choroid plexus.

Animals↗

PubMed1995

Regulation of phosphoinositide-3-kinase by G protein beta gamma subunits in a rat osteosarcoma cell line.

Rat osteosarcoma 17/2.8 cells (Ros 17/2.8 cells) were labeled with [32P]PO4(2-), and their levels of inositol lipids were determined after stimulation with thrombin. Thrombin stimulated a pertussis toxin-sensitive rapid accumulation of phosphatidylinositol-3,4,5-trisphosphate [PtdIns(3,4,5)P3] with lesser increases in levels of phosphatidylinositol-3,4-bisphosphate [PtdIns(3,4)P2] and phosphatidylinositol-3-phosphate [PtdIns3P] that were slower in onset. Ros 17/2.8 cell homogenates contained phosphatase activities that hydrolyzed PtdIns(3,4,5)P3 to PtdIns(3,4)P2 and PtdIns3P. Phosphoinositide-3-kinase activity was determined in Ros 17/2.8 cell homogenates using exogenously provided PtdIns(4,5)P2. Guanosine-5'-3-O-(thio)triphosphate caused an approximately 3-fold increase in phosphoinositide-3-kinase activity in a manner that was blocked by high concentrations of guanosine-5'-2-O-(thio)diphosphate. Purified bovine brain G protein beta gamma subunits also increased phosphoinositide-3-kinase activity modestly in Ros 17/2.8 cell homogenates. Ros 17/2.8 cell homogenates contained phosphatase activities that sequentially dephosphorylated PtdIns(3,4,5)P3 to PtdIns(3,4)P2 and PtdIns3P. Two peaks of phosphoinositide-3-kinase activity were resolved by anion exchange chromatography of a Ros 17/2.8 cell cytosolic extract. The later elution of these was selectively activated by beta gamma subunits (16-fold activation with 16 microM beta gamma subunits). Half-maximal effects of the beta gamma subunits were observed at a concentration of 0.6 microM, and activation was blocked by preincubation of the beta gamma subunits with an excess of recombinant Gi alpha 2. beta gamma Subunits did not activate the p85 alpha/p110 beta form of phosphoinositide-3-kinase purified from sf9 cells after expression with the use of baculovirus vectors.

Animals↗

PubMed1995

[Changes in the phosphoinositide metabolism in the blood and tissues of benign and malignant uterine tumors].

Measurements of phosphoinositide levels in the blood, immunocompetent cells, and tumors of 105 patients with uterine myomas, 24 patients with cancer of the corpus uteri, and 17 ones with uterine sarcoma showed that the parameters of phosphoinositide metabolism in the blood of patients with tumors of the uterus reliably differed from those in healthy women. The content of phosphatidylinosites and other phosphoinositide fractions in patients with uterine myomas reliably differed from those in patients with malignant tumors of the uterus, this permitting the use of such measurements in the differential diagnosis. Phosphoinositide mechanism of development of tumors of the uterus is discussed, which is related to the "new" phosphoinositides and secondary messengers directly participating in transfer of cell growth signals.

Adult↗

PubMed1996

Cholinergic stimulation of AP-1 and NF kappa B transcription factors is differentially sensitive to oxidative stress in SH-SY5Y neuroblastoma: relationship to phosphoinositide hydrolysis.

Oxidative stress appears to contribute to neuronal dysfunction in a number of neurodegenerative conditions, notably including Alzheimer's disease, in which cholinergic receptor-linked signal transduction activity is severely impaired. To test whether oxidative stress could contribute to deficits in cholinergic signaling, responses to carbachol were measured in human neuroblastoma SH-SY5Y cells exposed to H2O2. DNA binding activities of two transcription factors that are respondent to oxidative conditions, AP-1 and NF kappa B, were measured in nuclear extracts. H2O2 and carbachol individually induced dose- and time-dependent increases in AP-1 and NF kappa B. In contrast, when given together, H2O2 concentration dependently (30-300 microM) inhibited the increase after carbachol in AP-1. Carbachol's stimulation of NF kappa B was not inhibited except with a high concentration (300 microM) of H2O2, which was associated with impaired activation of protein kinase C. Lower concentrations of H2O2 (30-300 microM) inhibited carbachol-induced [3H]phosphoinositide hydrolysis, and this inhibition correlated (r = 0.95) with the inhibition of carbachol-induced AP-1. Activation [3H]phosphoinositide hydrolysis by the calcium ionophore ionomycin was unaffected by H2O2, indicating that phospholipase C and phosphoinositides were impervious to this treatment. In contrast, activation with NaF of G-proteins coupled to phospholipase C was concentration dependently inhibited by H2O2, indicating impaired G-protein function. These effects of H2O2 are similar to signaling impairments reported in Alzheimer's disease brain, which involve deficits in receptor- and G-protein-stimulated phosphoinositide hydrolysis, but not phospholipase C activity. Thus, these findings indicate that oxidative stress may contribute to impaired phosphoinositide signaling in neurological disorders in which oxidative stress occurs, and that oxidative stress can differentially influence transcription factors activated by cholinergic stimulation.

Carbachol↗

PubMed1996

Dependence on intracellular pH and Mg2+ of metabolic compartmentation of phosphoinositides in human erythrocytes.

Effects of intracellular pH and Mg2+ on turnover and extent of metabolic compartmentation of phosphomonoester groups of phosphoinositides and phosphatidate were investigated in human erythrocytes by short-term and equilibrium labeling with [32P]Pi under steady-state conditions. At pH 6.7, the specific radio-activities of phosphoinositides reached apparent equilibrium values, in the range of 70% of that ATP-gamma-P after long-term labelling. At pH 7.2, these values were in the range of 40-50% of that ATP-gamma-P. This demonstrates a decreased accessibility of phosphoinositides to enzymatic phosphorylation and dephosphorylation at the transition from acidic to normal incubation conditions. These changes were more pronounced at pH 7.8. High intracellular [Mg2+] initially activated the turnover of phosphoinositides at pH 7.2. The activation changed into an inhibition and an increase of metabolic compartmentation after three hours preincubation of erythrocytes at high [Mg2+]. The long-term Mg2+ effects are reversible to a great extent by a subsequent re-reduction of [Mg2+]. In conclusion, deprotonation of phosphoinositides by low [H+] or high intracellular [Mg2+] at normal pH induces a decreased accessibility for their specific lipid kinases and phosphatases. This effect may be the result of lateral phase separation of acidic phospholipids as a consequence of divalent cation complexation under both experimental conditions, high pH and high [Mg2+] at normal pH.

Erythrocytes↗

PubMed1997

4-Methylhomoibotenic acid activates a novel metabotropic glutamate receptor coupled to phosphoinositide hydrolysis.

Metabotropic glutamate receptors (mGluRs) are a family of glutamate receptors that are coupled to a variety of second messenger systems through GTP-binding proteins. Of the eight subtypes cloned to date, mGluR1 and mGluR5 are coupled to phosphoinositide hydrolysis in expression systems, and both are activated by the glutamate analogue 1-aminocyclopentane-1S,3R-dicarboxylic acid. Previously, we provided evidence that in rat cortical slices, 4-bromohomoibotenic acid (BrHI) and 4-methylhomoibotenic acid (MHI) activate a 1-aminocyclopentane-1S,3R-dicarboxylic acid-insensitive phosphoinositide hydrolysis-coupled mGluR. We further examine these compounds in expression systems. In a stable cell line expressing mGluR1a, BrHI is a weak partial agonist whereas MHI has no agonist activity. In Xenopus oocytes expressing mGluR1a or mGluR5a, BrHI is a weak agonist at mGluR5a whereas MHI is without effect on either receptor. Both BrHI and MHI have weak agonist activity at mGluRs 4a and 7a expressed in stable BHK cell lines whereas neither compound had any activity on BHK cells expressing mGluR2. Finally, we found that the novel mGluR antagonist LY341495 completely blocked the activation of mGluR1 and mGluR5 and blocked the phosphoinositide hydrolysis response to DHPG in rat cortical slices. In contrast, LY341495 did not block the phosphoinositide hydrolysis response to MHI in rat cortical slices. This provides further evidence that the phosphoinositide hydrolysis response to MHI in rat cortical slices is due to activation of a novel receptor that is distinct from the previously cloned mGluRs.

Animals↗

PubMed1998

Phosphoinositide metabolism and Ca2+ oscillation.

The main pathways of hydrolysis and synthesis of phosphoinositides, metabolism of inositol phosphates and their role in animal and human cells are reviewed. Mechanisms of regulation of phospholipase C and other key enzymes of phosphoinositide metabolism by hormones and growth factors are discussed. The mechanisms of regulation of metabolism and cellular activity by second messengers formed during activation of phosphoinositide hydrolysis are considered. Special attention is given to the regulation of cytoplasmic Ca2+ level by inositol phosphates. The review summarizes data on formation and possible biological role of inositol phosphates and phosphoinositides containing phosphate at position 3. The role of phosphoinositides in the interaction of cellular membranes with proteins of the cytoskeleton is considered.

Animals↗

PubMed2006

Phosphoinositide-specific phospholipase C (PI-PLC) beta1 and nuclear lipid-dependent signaling.

Over the last years, evidence has suggested that phosphoinositides, which are involved in the regulation of a large variety of cellular processes both in the cytoplasm and in the plasma membrane, are present also within the nucleus. A number of advances has resulted in the discovery that phosphoinositide-specific phospholipase C signalling in the nucleus is involved in cell growth and differentiation. Remarkably, the nuclear inositide metabolism is regulated independently from that present elsewhere in the cell. Even though nuclear inositol lipids hydrolysis generates second messengers such as diacylglycerol and inositol 1,4,5-trisphosphate, it is becoming increasingly clear that in the nucleus polyphosphoinositides may act by themselves to influence pre-mRNA splicing and chromatin structure. Among phosphoinositide-specific phospholipase C, the beta(1) isoform appears to be one of the key players of the nuclear lipid signaling. This review aims at highlighting the most significant and up-dated findings about phosphoinositide-specific phospholipase C beta(1) in the nucleus.

Animals↗

PubMed1998

Lipid products of phosphoinositide 3-kinase and phosphatidylinositol 4',5'-bisphosphate are both required for ADP-dependent platelet spreading.

We have shown previously that ADP released upon platelet adhesion mediated by alphaIIb beta3 integrin triggers accumulation of phosphatidylinositol 3',4'-bisphosphate (PtdIns-3,4-P2) (Gironcel, D. , Racaud-Sultan, C., Payrastre, B., Haricot, M., Borchert, G., Kieffer, N., Breton, M., and Chap, H. (1996) FEBS Lett. 389, 253-256). ADP has also been involved in platelet spreading. Therefore, in order to study a possible role of phosphoinositide 3-kinase in platelet morphological changes following adhesion, human platelets were pretreated with specific phosphoinositide 3-kinase inhibitors LY294002 and wortmannin. Under conditions where PtdIns-3, 4-P2 synthesis was totally inhibited (25 microM LY294002 or 100 nM wortmannin), platelets adhered to the fibrinogen matrix, extended pseudopodia, but did not spread. Moreover, addition of ADP to the medium did not reverse the inhibitory effects of phosphoinositide 3-kinase inhibitors on platelet spreading. Although synthetic dipalmitoyl PtdIns-3,4-P2 and dipalmitoyl phosphatidylinositol 3',4', 5'-trisphosphate restored only partially platelet spreading, phosphatidylinositol 4',5'-bisphosphate (PtdIns-4,5-P2) was able to trigger full spreading of wortmannin-treated adherent platelets. Following 32P labeling of intact platelets, the recovery of [32P]PtdIns-4,5-P2 in anti-talin immunoprecipitates from adherent platelets was found to be decreased upon treatment by wortmannin. These results suggest that the lipid products of phosphoinositide 3-kinase are required but not sufficient for ADP-induced spreading of adherent platelets and that PtdIns-4,5-P2 could be a downstream messenger of this signaling pathway.

Adenosine Diphosphate↗

PubMed2006

Evidence from bioinformatics, expression and inhibition studies of phosphoinositide-3 kinase signalling in Giardia intestinalis.

BACKGROUND: Giardia intestinalis is a parasitic protozoan and major cause of diarrhoeal disease. Disease transmission is dependent on the ability of the parasite to differentiate back and forth between an intestine-colonising trophozoite and an environmentally-resistant infective cyst. Our current understanding of the intracellular signalling mechanisms that regulate parasite replication and differentiation is limited, yet such information could suggest new methods of disease control. Phosphoinositide-3 kinase (PI3K) signalling pathways have a central involvement in many vital eukaryotic processes, such as regulation of cell growth, intracellular membrane trafficking and cell motility. Here we present evidence for the existence of functional PI3K intracellular signalling pathways in G. intestinalis. RESULTS: We have identified and characterised two genes, Gipi3k1 and Gipi3k2, which encode putative PI3Ks. Both genes are expressed in trophozoites and encysting cells, suggesting a possible role of GiPI3K1 and GiPI3K2 in regulating giardial growth and differentiation. Extensive nucleotide and amino acid sequence characterisation predicts that both encoded PI3Ks are functional as indicated by the presence of highly conserved structural domains and essential catalytic residues. The inhibitory effect of the PI3K inhibitor LY294002 on trophozoite proliferation also supports their functionality. Phylogenetic analysis supports the identity of GiPI3K1 as a Class I isoform and GiPI3K2 as a Class III isoform. In addition, giardial genes encoding putative homologues of phosphoinositide-metabolising enzymes such as PTEN, MTM, PIPkin and PI 5-phosphatase as well as downstream effectors with phosphoinositide-binding domains have been identified, placing GiPI3K1 and GiPI3K2 in a broader signalling context. Compared with twenty-six PI3Ks from other organisms, GiPI3K1 and GiPI3K2 are unique in that they contain large insertions within their highly conserved kinase domains. The function of these insertions is unknown; however we show here that they are not intron-derived and would probably not hinder substrate binding. These insertions may represent a plausible drug target. CONCLUSION: G. intestinalis encodes and expresses two putative PI3Ks, at least one of which appears to be required during normal parasite proliferation. The identification of Class I and Class III but not Class II isoforms suggests that both extracellularly-initiated signalling (Class I-regulated) and intracellular vesicle trafficking (Class III-regulated) might be controlled by PI3Ks in G. intestinalis. The presence of genes encoding putative homologues of phosphoinositide-metabolising enzymes and downstream effectors in the G. intestinalis genome further suggests that the overall architecture of PI3K signalling may be comparable with pathways present in other better-studied organisms.

Amino Acid Sequence↗

PubMed1992

Regulation of D-3 phosphoinositides during T cell activation via the T cell antigen receptor/CD3 complex and CD2 antigens.

An immediate consequence of T cell activation via the T cell receptor (TcR)/CD3 complex and CD2 antigen is the hydrolysis of phosphatidylinositol-(4,5)-bisphosphate and the generation of inositol-(1,4,5)-trisphosphate and diacylglycerol which then regulate intracellular calcium and protein kinase C. Changes in cellular levels of phosphoinositides phosphorylated on the D-4 and D-5 position during T cell activation have been well documented. Recently it has been proposed that phosphoinositides phosphorylated on the D-3 position of the inositol ring by a novel phosphoinositide (PI) 3 kinase may also be important in cell activation. In the present study we have examined the levels and regulation of D-3 phosphoinositides in T cells activated by the TcR/CD3 complex and CD2 antigens. The data show the existence of phosphatidylinositol-(3)-monophosphate [PtdIns(3)P], phosphatidylinositol-(3,4)-bisphosphate [PtdIns(3,4)P2] and phosphatidylinositol-(3,4,5)-trisphosphate [PtdIns(3,4,5)P3] in T cells. Activation of the TcR/CD3 complex or CD2 antigen results in modulation of PtdIns(3,4)P2 and a putative PtdIns(3,4,5)P3 in T cells but does not change levels of PtdIns(3)P. These data provide the first evidence that lipid products of a PI3 kinase exist in T cells.

Antigens, Differentiation, T-Lymphocyte↗

PubMed1993

Ligation of CD28 receptor by B7 induces formation of D-3 phosphoinositides in T lymphocytes independently of T cell receptor/CD3 activation.

The co-stimulatory role of B7/CD28 interactions is important in promoting T cell activation. Very little is known about the intracellular events that follow CD28 engagement although recent evidence has implicated coupling of CD28 to a protein tyrosine kinase signal transduction pathway. In this study we have investigated the putative role of D-3 phosphoinositides as mediators of CD28 receptor signaling, since phosphoinositide (PI) 3-kinase, the enzyme responsible for D-3 phosphoinositide formation, is a known substrate for protein tyrosine kinases associated with certain T cell surface receptors such as CD4 and interleukin-2 receptor. The lipid products of PI 3-kinase activity have been suggested to play a role in mitogenic signaling and growth regulation in other cells. Chinese hamster ovary cells (CHO) previously transfected with B7 cDNA, induced time-dependent elevation above basal levels of phosphatidylinositol(3,4)-bisphosphate (PtdIns(3,4)P2) and PtdIns(3,4,5)P3, while parental CHO cells that did not express B7 had no effect on these lipids. Moreover, the elevation of these same lipids by CD3 ligation was potentiated in an additive manner by CHO-B7+ but not by CHO-B7- cells. CHO-B7+ and CHO-B7- cells did not activate phospholipase C as evidenced by their inability to modulate basal or CD3-induced changes in the levels of phosphatidic acid or D-4 and D-5 phosphoinositides. These data imply that PI 3-kinase but not phospholipase C, may be an important signal transduction molecule with respect to CD28-mediated co-stimulation and T cell activation following ligation by B7.

Animals↗

PubMed1995

Inhibition of CD28-mediated T cell costimulation by the phosphoinositide 3-kinase inhibitor wortmannin.

T lymphocyte activation requires at least two signals, one via the antigen-specific T cell receptor and a second via the surface molecule CD28 which provides signals critical to interleukin-2 (IL-2) production and T cell proliferation. We have previously shown (Ward S. G., Westwick, J., Hall N. and Sansom D. M. Eur. J. Immunol. 1993. 23: 2572) that CD28 stimulates phosphoinositide (PI) 3-kinase activity, indicating that D-3 phosphoinositides may act as mediators of CD28-induced T cell costimulation. Here, we report that immunoprecipitation of CD28 molecules from Jurkat cells stimulated with the CD28-ligand B7, results in a ligand-dependent association of CD28 with PI 3-kinase. This association correlates with the appearance of PI 3-kinase enzymatic activity in CD28 immunoprecipitates and the formation of D-3 phosphoinositides. Consistent with the hypothesis that D-3 phosphoinositides are important mediators of CD28 signaling, treatment of T cells with the PI 3-kinase inhibitor wortmannin, inhibited both T cell proliferation and production of IL-2, but not the response of T cells to exogenous IL-2. Hence, abrogation of PI 3-kinase activity by wortmannin, appears sufficient to disrupt the costimulatory pathway utilized by CD28, indicating a central role for this enzyme in the CD28 signaling pathway.

Androstadienes↗

PubMed1992

Different fatty-acid profiles in phosphoinositides from human fibroblastic meningiomas with or without chromosome 22 monosomy.

The fatty-acid composition of phosphoinositides derived from 13 human fibroblastic meningiomas, divided according to the presence or the absence of monosomy of chromosome 22, was analyzed. Phosphoinositides were separated into their 3 main components: phosphatidylinositol, phosphatidylinositol-4-phosphate, and phosphatidylinositol-4,5-bisphosphate. In all the tumors, regardless of cytogenetic differences, remarkable differences were detected between phosphatidylinositol and phosphatidylinositol-4-phosphate or phosphatidylinositol-4,5-bisphosphate. In meningiomas with 22 monosomy, there was a significant decrease in the relative amount of arachidonate in all the phosphoinositide fractions; this situation might determine diminished down-regulation of the corresponding diacylglycerol, derived by the phospholipase-C-stimulated hydrolysis of phosphoinositides, and, consequently, different protein-kinase-C stimulation.

Chromosome Aberrations↗