Phospholipase Cbeta serves as a coincidence detector through its Ca2+ dependency for triggering retrograde endocannabinoid signal

Endocannabinoids mediate retrograde signal and modulate transmission efficacy at various central synapses. Although endocannabinoid release is induced by either depolarization or activation of G(q/11)-coupled receptors, it is markedly enhanced by the coincidence of depolarization and receptor activation. Here we report that this coincidence is detected by phospholipase Cbeta1 (PLCbeta1) in hippocampal neurons. By measuring cannabinoid-sensitive synaptic currents, we found that the receptor-driven endocannabinoid release was dependent on physiological levels of intracellular Ca(2+) concentration ([Ca(2+)](i)), and markedly enhanced by depolarization-induced [Ca(2+)](i) elevation. Furthermore, we measured PLC activity in intact neurons by using exogenous TRPC6 channel as a biosensor for the PLC product diacylglycerol and found that the receptor-driven PLC activation exhibited similar [Ca(2+)](i) dependence to that of endocannabinoid release. Neither endocannabinoid release nor PLC activation was induced by receptor activation in PLCbeta1 knockout mice. We therefore conclude that PLCbeta1 serves as a coincidence detector through its Ca(2+) dependency for endocannabinoid release in hippocampal neurons.

Single and repeated stress-induced modulation of phospholipase C catalytic activity and expression: role in LH behavior

PI-PLC, a critical enzyme of the phosphoinositide (PI) signaling pathway, mediates many physiological functions in the brain, including cellular plasticity. Stress-induced learned helplessness (LH) in animals serves as a model of behavioral depression. Recently, we observed that repeated stress prolongs the duration of LH behavior in rats, enabling us to compare neurobiologic abnormalities in acute and chronic depression. Here we examine whether LH behavior is associated with alterations in phospholipase C (PLC), and whether repetition of inescapable shock has similar or dissimilar effects on PLC to those of the single-stress paradigm. Rats were exposed to inescapable shock either once on day 1, or twice, on days 1 and 7. Rats were tested for escape latency on days 2 and 4 after day 1 inescapable shock or on days 2, 8, and 14 after day 1 and 7 inescapable shock. PI-PLC activity and mRNA and protein expression of three different PLC isozymes were determined in the frontal cortex and hippocampus. Higher escape latencies were observed in LH rats tested on day 2 after single inescapable shock and on day 14 after repeated inescapable shock. Single inescapable shock reduced PI-PLC activity in the frontal cortex and hippocampus of LH rats. On the other hand, repeated inescapable shock not only reduced PI-PLC activity in these brain areas of LH rats but also selectively decreased the expression of PLC beta1 and PLC gamma1 isozymes. Our results suggest different responsiveness at the level of PI-PLC after single vs repeated stress, and that reductions in PLC may be critical in the pathophysiology of depression and other stress-related disorders.

C5a differentially stimulates the ERK1/2 and p38 MAPK phosphorylation through independent signaling pathways to induced chemotactic migration in RAW264.7 macrophages

We elucidate the roles of various protein kinases involved in complement 5a (C5a)-induced cell migration. Results showed that extracellular signal-regulated kinase1/2 (ERK1/2), p38 mitogen-activated protein kinase (p38 MAPK) and phosphatidylinositol 3-kinase (P13K) were necessary for C5a-induced migration, whereas protein kinase C and c-Jun N-terminal kinase (JNK) were nonessential. C5a-induced migration was also suppresses by phospholipase C (PLC) inhibitor U73122 and pertussis toxin (PTX). We found that C5a-induced, time-dependent (1) ERK1/2 phosphorylation was markedly diminished by PTX, U73122, P13K inhibitors wortmannin and LY294002 and ERK1/2 inhibitor PD98059; (2) Akt phosphorylation was also attenuated by the above inhibitors except PD98059; (3) p38 MAPK phosphorylation was only affected by PTX. Furthermore, C5a also stimulated PLCbeta(2) membrane translocation in a time-dependent manner that occurred early prior to Akt phosphorylation and could be abolished only by PTX and U73122. These results suggest that C5a, through the activation of PTX-sensitive G protein, to differentially stimulate ERK1/2 and p38 MAPK phosphorylation and evoke cell migration. That is, ERK1/2 but not p38 MAPK phosphorylation is down stream of P13K/Akt and modulated by PLC. Additionally, beta(2) isoform may be one of the participates in C5a signal and acts more upstream of P13K/Akt.

Illumination of the melanopsin signaling pathway

In mammals, a small population of intrinsically photosensitive retinal ganglion cells (ipRGCs) plays a key role in the regulation of nonvisual photic responses, such as behavioral responses to light, pineal melatonin synthesis, pupillary light reflex, and sleep latency. These ipRGCs also express melanopsin (Opn4), a putative opsin-family photopigment that has been shown to play a role in mediating these nonvisual photic responses. Melanopsin is required for the function of this inner retinal pathway, but its precise role in generating photic responses has not yet been determined. We found that expression of melanopsin in Xenopus oocytes results in light-dependent activation of membrane currents through the Galpha(q)/Galpha(11) G protein pathway, with an action spectrum closely matching that of melanopsin-expressing ipRGCs and of behavioral responses to light in mice lacking rods and cones. When coexpressed with arrestins, melanopsin could use all-trans-retinaldehyde as a chromophore, which suggests that it may function as a bireactive opsin. We also found that melanopsin could activate the cation channel TRPC3, a mammalian homolog of the Drosophila phototransduction channels TRP and TRPL. Melanopsin therefore signals more like an invertebrate opsin than like a classical vertebrate rod-and-cone opsin.

The relative role of PLCbeta and PI3Kgamma in platelet activation

Stimulation of platelet G protein-coupled receptors results in the cleavage of phosphatidylinositol 4,5-trisphosphate (PIP(2)) into inositol 1,4,5-trisphosphate and 1,2-diacylglycerol by phospholipase C (PLCbeta). It also results in the phosphorylation of PIP2 by the gamma isoform of phosphatidylinositol 3-kinase (PI3Kgamma) to synthesize phosphatidylinositol 3,4,5-trisphosphate. To understand the role of PIP2 in platelet signaling, we evaluated knock-out mice lacking 2 isoforms of PLCbeta (PLCbeta2 and PLCbeta3) or lacking the G(betagamma)-activated isoform of PI3K (PI3Kgamma). Both knock-out mice were unable to form stable thrombi in a carotid injury model. To provide a functional explanation, knock-out platelets were studied ex vivo. PLCbeta2/beta3-/- platelets failed to assemble filamentous actin, had defects in both secretion and mobilization of intracellular calcium, and were unable to form stable aggregates following low doses of agonists. Platelets lacking PI3Kgamma disaggregated following low-dose adenosine diphosphate (ADP) and had a mildly impaired ability to mobilize intracellular calcium. Yet, they exhibited essentially normal actin assembly and secretion. Remarkably, both PLCbeta2/beta3-/- and PI3Kgamma-/- platelets spread more slowly upon fibrinogen. These results suggest substantial redundancy in platelet signaling pathways. Nonetheless, the diminished ability of knock-out platelets to normally spread after adhesion and to form stable thrombi in vivo suggests that both PLCbeta2/beta3 and PI3Kgamma play vital roles in platelet cytoskeletal dynamics.

Defective sarcolemmal phospholipase C signaling in diabetic cardiomyopathy

Phospholipase C (PLC) activity is known to influence cardiac function. This study was undertaken to examine the status of PLC beta3 in the cardiac cell plasma membrane (sarcolemma, SL) in an experimental model of chronic diabetes. SL membrane was isolated from diabetic rat hearts at 8 weeks after a single i.v. injection of streptozotocin (65 mg/kg body weight). The total SL PLC was decreased in diabetes and was associated with a decrease in SL PLC beta3 activity, which immunofluorescence in frozen diabetic left ventricular tissue sections revealed to be due to a decrease in PLC beta3 protein abundance. In contrast, the SL abundance of Gqalpha was significantly increased during diabetes. These changes were associated with a loss of contractile function (+/- dP/dt). A 2-week insulin treatment of 6-week diabetic animals partially normalized all of these parameters. These findings suggest a defect in PLC beta3-mediated signaling processes may contribute to the cardiac dysfunction seen during diabetes.

eNOS, nNOS, cGMP and protein kinase G mediate the inhibitory effect of pancreastatin, a chromogranin A-derived peptide, on growth and proliferation of hepatoma cells

Pancreastatin (PST), a chromogranin A-derived peptide, has an anti-insulin metabolic effect and inhibits growth and proliferation by producing nitric oxide (NO) in HTC rat hepatoma cells. When NO production is blocked, a proliferative effect prevails due to the activation a Galphaq/11-phospholipase C-beta (PLC-beta) pathway, which leads to an increase in [Ca2+]i, protein kinase C (PKC) and mitogen-activated protein kinase (MAPK) activation. The aim of the present study was to investigate the NO synthase (NOS) isoform that mediates these effects of PST on HTC hepatoma cells and the possible roles of cyclic GMP (cGMP) and cGMP-dependent protein kinase. DNA and protein synthesis in response to PST were measured as [3H]-thymidine and [3H]-leucine incorporation in the presence of various pharmacological inhibitors: N-monomethyl-L-arginine (NMLA, nonspecific NOS inhibitor), L-NIO (endothelial nitric oxide synthase (eNOS) inhibitor), espermidine (neuronal nitric oxide synthase (nNOS) inhibitor), LY83583 (guanylyl cyclase inhibitor), and KT5823 (protein kinase G inhibitor, (PKG)). L-NIO, similarly to NMLA, reverted the inhibitory effect of PST on hepatoma cell into a stimulatory effect on growth and proliferation. Nevertheless, espermidine also prevented the inhibitory effect of PST, but there was no stimulation of growth and proliferation. When guanylyl cyclase activity was blocked, there was again a reversion of the inhibitory effect into a stimulatory action, suggesting that the effect of NO was mediated by the production of cGMP. PKG inhibition prevented the inhibitory effect of PST, but there was no stimulatory effect. Therefore, the inhibitory effect of PST on growth and proliferation of hepatoma cells may be mainly mediated by eNOS activation. In turn, the effect of NO may be mediated by cGMP, whereas other pathways in addition to PKG activation seem to mediate the inhibition of DNA and protein synthesis by PST in HTC hepatoma cells.

Loss of association between activated Galpha q and Gbetagamma disrupts receptor-dependent and receptor-independent signaling

The G protein subunit, betagamma, plays an important role in targeting alpha subunits to the plasma membrane and is essential for binding and activation of the heterotrimer by heptahelical receptors. Mutation of residues in the N-terminal alpha-helix of alpha s and alpha q that contact betagamma in the crystal structure of alpha i reduces binding between alpha and betagamma, inhibits plasma membrane targeting and palmitoylation of the alpha subunit, and results in G proteins that fail to couple receptor activation to stimulation of effector. Overexpression of betagamma can recover this loss of signaling through Gs but not Gq. In fact, a single mutation (I25A) in alpha q can block alpha q-mediated generation of inositol phosphates. Function is not recovered by betagamma overexpression nor myristoylation directed plasma membrane localization. Introduction of a Q209L activating mutation with I25A results in a constitutively active alpha q as expected, but surprisingly a R183C activating mutation does not result in constitutive activity when present with I25A. Examination of binding between alpha and betagamma via a pull down assay shows that the N-terminal betagamma-binding mutations inhibit alpha-betagamma binding significantly more than the R183C or Q209L activating mutations do. Moreover, introduction of the I25A mutation into alpha q RC disrupts co-immunoprecipitation with PLCbeta1. Taken together, results presented here suggest that alpha-betagamma binding is necessary at a point downstream from receptor activation of the heterotrimeric G protein for signal transduction by alpha q.

Determination of the activation volume of PLCbeta by Gbeta gamma-subunits through the use of high hydrostatic pressure

Activation of phospholipase Cbeta (PLCbeta) by G-proteins results in increased intracellular Ca(2+) and activation of protein kinase C. We have previously found that activated PLCbeta-Gbetagamma complex can be rapidly deactivated by Galpha(GDP) subunits without dissociation, which led to the suggestion that Galpha(GDP) binds to PLCbeta-Gbeta gamma and perturbs the activating interaction without significantly affecting the PLCbeta-Gbeta gamma binding energy. Here, we have used high pressure fluorescence spectroscopy to determine the volume change associated with this interaction. Since PLCbeta and G-protein subunits associate on membrane surfaces, we worked under conditions where the membrane surface properties are not expected to change. We also determined the pressure range in which the proteins remain membrane bound: PLCbeta binding was stable throughout the 1-2000 bars range, Gbeta gamma binding was stable only at high membrane concentrations, whereas Galpha(s)(GDP) dissociated from membranes above 1 kbar. High pressure dissociated PLCbeta-Gbeta gamma with a DeltaV = 34 +/- 5 ml/mol. This same volume change is obtained for a peptide derived from Gbeta which also activates PLCbeta. In the presence of Galpha(s)(GDP), the volume change associated with PLCbeta-Gbeta gamma interaction is reduced to 25 +/- 1 ml/mol. These results suggest that activation of PLCbeta by Gbeta gamma is conferred by a small (i.e., 3-15 ml/mol) volume element.

Glutamate regulation of DARPP-32 phosphorylation in neostriatal neurons involves activation of multiple signaling cascades

Dopamine- and cAMP-regulated phosphoprotein of 32 kDa (DARPP-32) plays a central role in medium spiny neurons in the neostriatum in the integration of various neurotransmitter signaling pathways. In its Thr-34-phosphorylated form, it acts as a potent protein phosphatase-1 inhibitor, and, in its Thr-75-phosphorylated form, it acts as a cAMP-dependent kinase inhibitor. Here, we investigated glutamate-dependent signaling cascades in mouse neostriatal slices by analyzing the phosphorylation of DARPP-32 at Thr-34 and Thr-75. Treatment with glutamate (5 mM) caused a complex change in DARPP-32 Thr-34 phosphorylation. An initial rapid increase in Thr-34 phosphorylation was NMDA/alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/metabotropic glutamate-5 receptor-dependent and was mediated through activation of a neuronal nitric oxide synthase/nitric oxide/cGMP/cGMP-dependent kinase signaling cascade. A subsequent decrease in phosphorylation was attributable to activation of an NMDA/AMPA receptor/Ca2+/protein phosphatase-2B signaling cascade. This decrease was followed by rephosphorylation via a pathway involving metabotropic glutamate-5 receptor/phospholipase C and extracellular receptor kinase signaling cascade. Treatment with glutamate initially decreased Thr-75 phosphorylation through activation of NMDA/AMPA receptor/Ca2+/protein phosphatase-2A signaling. Thereafter, glutamate slowly increased Thr-75 phosphorylation through activation of metabotropic glutamate-1 receptor/phospholipase C signaling. Our analysis of DARPP-32 phosphorylation in the neostriatum revealed that glutamate activates at least five different signaling cascades with different time dependencies, resulting in complex regulation of protein kinase and protein phosphatase activities.

Disruption of the mouse phospholipase C-beta1 gene in a beta-lactoglobulin transgenic line affects viability, growth, and fertility in mice

A recessive insertional mutation was identified in one line of transgenic mice for the caprine beta-lactoglobulin (betaLG) gene. High mortality after birth, a significant reduction in postnatal growth and adult body size, changes in the morphometric features of the head, and infertility are the most prominent phenotypic traits of the mutant animals. Molecular cloning and sequencing of the transgene insertion site showed that 22 copies of the betaLG transgene are inserted in an intronic region of the phospholipase C-beta1 (PLC-beta1) gene, which plays a pivotal role in modulating different cellular functions. As a result of the insertional mutation (PLC-beta1(betaLG) mutation), a hybrid messenger RNA (mRNA) between the mouse PLC-beta1 and the goat betaLG genes is transcribed. The tissue-specific pattern of expression of this hybrid mRNA in PLC-beta1(betaLG) homozygotes is equivalent to that of the endogenous PLC-beta1 mRNA in nontransgenic animals, which is reported for the first time in this species, but expression levels are significantly reduced. Although the hybrid PLCbeta1-betaLG mRNA contains all the essential information to produce a PLCbeta1 protein that could be activated, this protein was not detected by Western blot. The PLC-beta1(betaLG) mouse model described here represents a useful tool to investigate the role of the PLC-beta1 gene in the molecular mechanisms underlying growth and fertility.

The guanine nucleotide exchange factor p63RhoGEF, a specific link between Gq/11-coupled receptor signaling and RhoA

The monomeric GTPase RhoA, which is a key regulator of numerous cellular processes, is activated by a variety of G protein-coupled receptors, through either G12 or G(q) family proteins. Here we report that p63RhoGEF, a recently identified RhoA-specific guanine nucleotide exchange factor, enhances the Rho-dependent gene transcription induced by agonist-stimulated G(q/11)-coupled receptors (M3-cholinoceptor, histamine H1 receptor) or GTPase-deficient mutants of G alpha(q) and G alpha11. We further demonstrate that active G alpha(q) or G alpha11, but not G alpha12 or G alpha13, strongly enhances p63RhoGEF-induced RhoA activation by direct protein-protein interaction with p63RhoGEF at its C-terminal half. Moreover, the activation of p63RhoGEF by G alpha(q/11) occurs independently of and in competition to the activation of the canonical G alpha(q/11) effector phospholipase C beta. Therefore, our results elucidate a new signaling pathway by which G alpha(q/11)-coupled receptors specifically induce Rho signaling through a direct interaction of activated G alpha(q/11) subunits with p63RhoGEF.

Phospholipase Cβ2 Binds to and Inhibits Phospholipase Cδ1

Phospholipase Cbeta (PLCbeta) isoforms, which are under the control of Galphaq and Gbetagamma subunits, generate Ca2+ signals induced by a broad array of extracellular agonists, whereas PLCdelta isoforms depend on a rise in cytosolic Ca2+ for their activation. Here we find that PLCbeta2 binds strongly to PLCdelta1 and inhibits its catalytic activity in vitro and in living cells. In vitro, this PLC complex can be disrupted by increasing concentrations of free Gbetagamma subunits. Such competition has consequences for signaling, because in HEK293 cells PLCbeta2 suppresses elevated basal [Ca2+] and inositol phosphates levels and the sustained agonist-induced elevation of Ca2+ levels caused by PLCdelta1. Also, expression of both PLCs results in a synergistic release of [Ca2+] upon stimulation in A10 cells. These results support a model in which PLCbeta2 suppresses the basal catalytic activity of PLCdelta1, which is relieved by binding of Gbetagamma subunits to PLCbeta2 allowing for amplified calcium signals.

Liposome-mediated transfection of mature taste cells

The introduction and expression of exogenous DNA in neurons is valuable for analyzing a range of cellular and molecular processes in the periphery, e.g., the roles of transduction-related proteins, the impact of growth factors on development and differentiation, and the function of promoters specific to cell type. However, sensory receptor cells, particularly chemosensory cells, have been difficult to transfect. We have successfully introduced plasmids expressing green and Discosoma Red fluorescent proteins (GFP and DsRed) into rat taste buds in primary culture. Transfection efficiency increased when delaminated taste epithelium was redigested with fresh protease, suggesting that a protective barrier of extracellular matrix surrounding taste cells may normally be present. Because taste buds are heterogeneous aggregates of cells, we used alpha-gustducin, neuronal cell adhesion molecule (NCAM), and neuronal ubiquitin carboxyl terminal hydrolase (PGP9.5), markers for defined subsets of mature taste cells, to demonstrate that liposome-mediated transfection targets multiple taste cell types. After testing eight commercially available lipids, we identified one, Transfast, that is most effective on taste cells. We also demonstrate the effectiveness of two common "promiscuous" promoters and one promoter that taste cells use endogenously. These studies should permit ex vivo strategies for studying development and cellular function in taste cells.

Metabotropic glutamate receptor/phospholipase C pathway: A vulnerable target to Creutzfeldt-Jakob disease in the cerebral cortex

Glutamate is the main excitatory neurotransmitter in the cerebral cortex. Altered glutamatergic transmission has been suggested as having a central role in many neurodegenerative diseases. Metabotropic glutamate receptors (mGluRs) are coupled to intracellular signal transduction via G proteins, and they mediate slower responses than ionotropic glutamate receptors. Group I mGluRs are positively coupled to phospholipase C beta1 (PLCbeta1). Creutzfeldt-Jakob disease (CJD) is a human transmissible spongiform encephalopathy associated with a dysfunction in the membrane glycoprotein PrP which is converted into an abnormal isoform, with a predominant beta-sheet structure, that is pathogenic and partially resistant to protease digestion. Proteins associated with the signal transduction of group I mGluRs were examined in the frontal cortex (area 8) of 12 cases with sCJD and four age-matched controls, by means of gel electrophoresis and Western blotting of total homogenates. Densitometric analysis of the bands demonstrated decreased expression levels of PLCbeta1 and PLCgamma, a non-related phospholipase which is a substrate of tyrosine kinase, in CJD cases when compared with controls. Novel protein kinase C delta (nPKCdelta) has also been found to be significantly decreased in CJD cases. However, no modifications in mGluR1 cPKCalpha expression levels are found in CJD when compared with controls. No modifications in PLCbeta1 solubility in PBS-, deoxycholate- and sodium dodecylsulphate-soluble fractions have been observed in CJD when compared with controls. Finally, no interactions between PLCbeta1 and PrP, as revealed by immunoprecipitation assays, have been found in CJD and controls. The present results show, for the first time, reduced expression levels of phospholipases, particularly PLCbeta1, which may interfere with group I mGluR signaling in the cerebral cortex in CJD. These abnormalities are not the result of abnormal PLC solubility or interactions with PrP. Selective involvement of group I mGluRs may have functional effects on glutamatergic transmission modulation and processing in CJD.

Fluorescence Studies Suggest a Role for α-Synuclein in the Phosphatidylinositol Lipid Signaling Pathway

Alpha-synuclein plays a key role in the pathogenesis of many neurodegenerative diseases. To date, its cellular role has yet to be determined, although it has been proposed to be connected to calcium and G protein-mediated dopamine signaling. Alpha-synuclein is known to bind strongly to model membrane surfaces where it may interact with other membrane-associated proteins. Here, we find that the membrane association of alpha-synuclein is enhanced by the presence of phosphatidylinositol 4,5-bisphosphate [PI(4,5)P(2)] and Ca(2+). We also find that alpha-synuclein interacts with high affinity with the G protein-regulated enzyme phospholipase Cbeta(2) (PLCbeta(2)), which catalyzes the hydrolysis of PI(4,5)P(2). Binding of alpha-synuclein to PLCbeta(2) reduces its catalytic activity by 50%, but causes its level of activation by Gbetagamma subunits to increase from 4- to 24-fold. This effect is greatly reduced for A53T alpha-synuclein, which is a mutant associated with familial Parkinson's disease. PI(4,5)P(2) hydrolysis by PLCbeta(2) results in an increase in the intracellular Ca(2+) concentration, and we find that in cultured cells the presence of alpha-synuclein results in a 6-fold enhancement in the release of Ca(2+) from intracellular stores in response to agents that release Gbetagamma subunits relative to controls. Alpha-synuclein also enhances the increase in the level of inositol phosphates seen upon G protein stimulation, suggesting that it also may interact with PLCbeta(2) in cells. Given that Ca(2+) and dopamine regulation are mediated through PLCbeta and G protein signals, our results suggest that alpha-synuclein may play a role in inositol phospholipid signaling.

Regulatory interactions between the amino terminus of G-protein betagamma subunits and the catalytic domain of phospholipase Cbeta2

We previously identified a 10-amino acid region from the Y domain of phospholipase Cbeta2 (PLCbeta2) that associates with G-protein betagamma subunits (Sankaran, B., Osterhout, J., Wu, D., and Smrcka, A. V. (1998) J. Biol. Chem. 273, 7148-7154). We mapped the site for cross-linking of a synthetic peptide (N20K) corresponding to this Y domain region to Cys(25) within the amino-terminal coiled-coil domain of Gbetagamma (Yoshikawa, D. M., Bresciano, K., Hatwar, M., and Smrcka, A. V. (2001) J. Biol. Chem. 276, 11246-11251). Here, further experiments with a series of variable length cross-linking agents refined the site of N20K binding to within 4.4-6.7 angstroms of Cys(25). A mutant within the amino terminus of the Gbeta subunit, Gbeta(1)(23-27)gamma(2), activated PLCbeta2 more effectively than wild type, with no significant change in the EC(50), indicating that this region is directly involved in the catalytic regulation of PLCbeta2. This mutant was deficient in cross-linking to N20K, suggesting that a binding site for the peptide had been eliminated. Surprisingly, N20K could still inhibit Gbeta(1)(23-27)gamma(2)-dependent activation of PLC, suggesting a second N20K binding site. Competition analysis with a peptide that binds to the Galpha subunit switch II binding surface of Gbetagamma indicates a second N20K binding site at this surface. Furthermore, mutations to the N20K region within the Y-domain of full-length PLCbeta2 inhibited Gbetagamma-dependent regulation of the enzyme, providing further evidence for aGbetagamma binding site within the catalytic domain of PLCbeta2. The data support a model with two modes of PLC binding to Gbetagamma through the catalytic domain, where interactions with the amino-terminal coiled-coil domain are inhibitory, and interactions with the Galpha subunit switch II binding surface are stimulatory.

Reconstitution of chemotactic peptide-induced nicotinamide adenine dinucleotide phosphate (reduced) oxidase activation in transgenic COS-phox cells

A whole-cell-based reconstitution system was developed to study the signaling mechanisms underlying chemoattractant-induced activation of NADPH oxidase. This system takes advantage of the lack of formyl peptide receptor-mediated response in COS-phox cells expressing gp91(phox), p22(phox), p67(phox), and p47(phox), which respond to phorbol ester and arachidonic acid with O()(2) production. By exogenous expression of signaling molecules enriched in neutrophils, we have identified several critical components for fMLP-induced NADPH oxidase activation. Expression of PKCdelta, but not PKCalpha, -betaII, and -zeta, is necessary for the COS-phox cells to respond to fMLP. A role of PKCdelta in neutrophil NADPH oxidase was confirmed based on the ability of fMLP to induce PKCdelta translocation and the sensitivity of fMLP-induced O()(2) production to rottlerin, a PKCdelta-selective inhibitor. Optimal reconstitution also requires phospholipase C-beta2 and PI3K-gamma. We found that formyl peptide receptor could use the endogenous Rac1 as well as exogenous Rac1 and Rac2 for NADPH oxidase activation. Exogenous expression of p40(phox) potentiated fMLP-induced O()(2) production and raised the level of O()(2) in unstimulated cells. Collectively, these results provide first direct evidence for reconstituting fMLP-induced O()(2) production in a nonhemopoietic cell line, and demonstrate the requirement of multiple signaling components for optimal activation of NADPH oxidase by a chemoattractant.

Activation of PLC-delta1 by Gi/o-coupled receptor agonists

The mechanism of phospholipase (PLC)-delta activation by G protein-coupled receptor agonists was examined in rabbit gastric smooth muscle. Ca(2+) stimulated an eightfold increase in PLC-delta1 activity in permeabilized muscle cells. Treatment of dispersed or cultured muscle cells with three G(i/o)-coupled receptor agonists (somatostatin, delta-opioid agonist [D-Pen(2),D-Pen(5)]enkephalin, and A(1) agonist cyclopentyl adenosine) caused delayed increase in phosphoinositide (PI) hydrolysis (8- to 10-fold) that was strongly inhibited by overexpression of dominant-negative PLC-delta1(E341R/D343R; 65-76%) or constitutively active RhoA(G14V). The response coincided with capacitative Ca(2+) influx and was not observed in the absence of extracellular Ca(2+), but was partly inhibited by nifedipine (16-30%) and strongly inhibited by SKF-96365, a blocker of store-operated Ca(2+) channels. Treatment of the cells with a G(q/13)-coupled receptor agonist, CCK-8, caused only transient, PLC-beta1-mediated PI hydrolysis. Unlike G(i/o)-coupled receptor agonists, CCK-8 activated RhoA and stimulated RhoA:PLC-delta1 association. Inhibition of RhoA activity with C3 exoenzyme or by overexpression of dominant-negative RhoA(T19N) or Galpha(13) minigene unmasked a delayed increase in PI hydrolysis that was strongly inhibited by coexpression of PLC-delta1(E341R/D343R) or by SKF-96365. Agonist-independent capacitative Ca(2+) influx induced by thapsigargin stimulated PI hydrolysis (8-fold), which was partly inhibited by nifedipine ( approximately 25%) and strongly inhibited by SKF-96365 ( approximately 75%) and in cells expressing PLC-delta1(E341R/D343R). Agonist-independent Ca(2+) release or Ca(2+) influx via voltage-gated Ca(2+) channels stimulated only moderate PI hydrolysis (2- to 3-fold), which was abolished by PLC-delta1 antibody or nifedipine. We conclude that PLC-delta1 is activated by G(i/o)-coupled receptor agonists that do not activate RhoA. The activation is preferentially mediated by Ca(2+) influx via store-operated Ca(2+) channels.

Signaling complex formation of phospholipase Cβ4 with metabotropic glutamate receptor type 1α and 1,4,5-trisphosphate receptor at the perisynapse and endoplasmic reticulum in the mouse brain

Upon activation of cell surface receptors coupled to the Gq subclass of G proteins, phospholipase C (PLC) beta hydrolyses membrane phospholipid to yield a pair of second messengers, inositol 1,4,5-trisphosphate (IP3) and 1,2-diacylglycerol. PLCbeta4 has been characterized as the isoform enriched in cerebellar Purkinje cells (PCs) and the retina and involved in motor and visual functions. Here we examined cellular and subcellular distributions of PLCbeta4 in adult mouse brains. Immunohistochemistry showed that high levels of PLCbeta4 were detected in the somatodendritic domain of neuronal populations expressing the metabotropic glutamate receptor (mGluR) type 1alpha, including olfactory periglomerular cells, neurons in the bed nucleus anterior commissure, thalamus, substantia nigra, inferior olive, and unipolar brush cells and PCs in the cerebellum. Low to moderate levels were detected in many other mGluR1alpha-positive neurons and in a few mGluR1alpha-negative neurons. In PCs, immunogold electron microscopy localized PLCbeta4 to the perisynapse, at which mGluR1alpha is concentrated, and to the smooth endoplasmic reticulum in dendrites and spines, an intracellular Ca2+ store gated by IP3 receptors. In the cerebellum, immunoblot demonstrated its concentrated distribution in the post-synaptic density and microsomal fractions, where mGluR1alpha and type 1 IP3 receptor were also greatly enriched. Furthermore, PLCbeta4 formed coimmunoprecipitable complexes with mGluR1alpha, type 1 IP3 receptor and Homer 1. These results suggest that PLCbeta4 is preferentially localized in the perisynapse and smooth endoplasmic reticulum as a component of the physically linked phosphoinositide signaling complex. This close molecular relationship might provide PLCbeta4 with a high-fidelity effector function to mediate various neuronal responses under physiological and pathophysiological conditions.

The sweet and the bitter of mammalian taste

The discovery of two families of mammalian taste receptors has provided important insights into taste recognition and taste perception. Recent studies have examined the receptors and signaling pathways that mediate sweet, bitter, and amino acid taste detection in mammals. These studies demonstrate that taste cells are selectively tuned to different taste modalities and clarify the logic of taste coding in the periphery.

?-Gustducin immunoreactivity in the airways

The G-protein subunit alpha-gustducin is a marker of chemoreceptive cells. In the present study, we examined the immunohistochemical localization of alpha-gustducin in rat airway epithelium both by light and electron microscopy. alpha-Gustducin immunoreactivity was found in solitary cells that presented ultrastructural features of chemoreceptor cells, i.e. flask-shaped or pear-shaped, with an apical process with thin microvilli protruding into the lumen. The immunostaining was mainly concentrated in the apical process and along the basolateral cell surface. To investigate whether alpha-gustducin-immunoreactive cells represented a distinct cell subset in rat airways, we performed double-label immunocytochemistry with antibodies to protein gene groduct (PGP) 9.5, a marker of neuroendocrine cells, and to phospholipase C beta2 (PLCbeta2), a component of the bitter signalling pathway. alpha-Gustducin-immunoreactive cells were present in a subset of PGP-9.5-immunoreactive elements, although not all alpha-gustducin-positive cells expressed PGP 9.5 labelling. In addition, a subset of alpha-gustducin-expressing cells colocalized PLCbeta2. This work thus demonstrates that solitary alpha-gustducin-immunoreactive cells exist throughout the airways and represent a specialized cell type with morphological and immunohistochemical characteristics of chemoreceptor cells.

Influence of membrane components in the binding of proteins to membrane surfaces

We have quantified the enhancement of membrane binding of activated and deactivated Galpha(s) and Galpha(q) subunits, Gbetagamma subunits, and phospholipase Cbeta(2) by lipid rafts and by the presence of membrane-associated protein partners. Membrane binding studies show that lipid rafts do not affect the intrinsic membrane affinity of Galpha(q)(GDP) and Galpha(s)(GDP), supporting the idea that these proteins partition evenly between the domains. Visualization of lipid rafts on monolayers by use of a probe that does not enter raft domains shows that neither activated nor deactivated Galpha(q)(GDP) subunits distribute evenly between the raft and nonraft domains, contrary to previous suggestions. Membrane binding of deactivated Galpha(q) and Galpha(s)(GDP) became weaker when Gbetagamma subunits were present, in contrast with the behavior predicted by thermodynamics. However, activated Galpha subunits and phospholipase Cbeta(2) were recruited to membrane surfaces by protein partners by predicted amounts. Our studies suggest that the anomalous behavior seen for deactivated Galpha subunits in the presence of Gbetagamma subunits may be due to conformational changes in the N-terminus and/or occlusion of a portion of its membrane interaction region by Gbetagamma. Even though membrane recruitment was clearly observed for one protein partner, the presence of a second partner of lower affinity did not further promote membrane binding. For these proteins, the formation of larger protein complexes with very high membrane affinities is unlikely.

G16-mediated activation of nuclear factor kappaB by the adenosine A1 receptor involves c-Src, protein kinase C, and ERK signaling

The G(i)-linked adenosine A1 receptor has been shown to mediate anti-inflammatory actions, possibly via modulation of the transcription factor nuclear factor-kappaB (NFkappaB). Here we demonstrate that an adenosine A1 agonist, N(6)-cyclohexyladenosine (CHA), activated IKKalpha/beta phosphorylation through PTX-insensitive G proteins in human lymphoblastoma Reh cells. To delineate the mechanism of action, different PTX-insensitive G proteins were expressed in human embryonic kidney 293 cells. Only Galpha(16) supported the CHA-induced IKK phosphorylation and NFkappaB-driven luciferase activity in time-dependent, dose-dependent, and PTX-insensitive manners. Gbetagamma subunits also modulated IKK/NFkappaB, as indicated by the stimulatory actions of Gbeta(1)gamma(2) and the abrogation of CHA-induced response by transducin. The participation of phospholipase Cbeta, protein kinase C, and calmodulin-dependent kinase II in CHA-induced IKK/NFkappaB activation were demonstrated by employing specific inhibitors and dominant-negative mutants. Inhibition of c-Src and numerous intermediates along the extracellular signal-regulated (ERK) kinase cascade including Ras, Raf-1 kinase, and MEK1/2 abolished the CHA-induced IKK/NFkappaB activation. Although c-Jun N-terminal kinase and p38 MAPK were also activated by CHA, they were not required for the IKK/NFkappaB regulation. Similar results were obtained using Reh cells. These data suggest that the G(16)-mediated activation of IKK/NFkappaB by CHA required a complex signaling network composed of multiple intermediates.

Characterization of the GRK2 binding site of Galphaq

Heterotrimeric guanine nucleotide-binding proteins (G proteins) transmit signals from membrane bound G protein-coupled receptors (GPCRs) to intracellular effector proteins. The G(q) subfamily of Galpha subunits couples GPCR activation to the enzymatic activity of phospholipase C-beta (PLC-beta). Regulators of G protein signaling (RGS) proteins bind to activated Galpha subunits, including Galpha(q), and regulate Galpha signaling by acting as GTPase activating proteins (GAPs), increasing the rate of the intrinsic GTPase activity, or by acting as effector antagonists for Galpha subunits. GPCR kinases (GRKs) phosphorylate agonist-bound receptors in the first step of receptor desensitization. The amino termini of all GRKs contain an RGS homology (RH) domain, and binding of the GRK2 RH domain to Galpha(q) attenuates PLC-beta activity. The RH domain of GRK2 interacts with Galpha(q/11) through a novel Galpha binding surface termed the "C" site. Here, molecular modeling of the Galpha(q).GRK2 complex and site-directed mutagenesis of Galpha(q) were used to identify residues in Galpha(q) that interact with GRK2. The model identifies Pro(185) in Switch I of Galpha(q) as being at the crux of the interface, and mutation of this residue to lysine disrupts Galpha(q) binding to the GRK2-RH domain. Switch III also appears to play a role in GRK2 binding because the mutations Galpha(q)-V240A, Galpha(q)-D243A, both residues within Switch III, and Galpha(q)-Q152A, a residue that structurally supports Switch III, are defective in binding GRK2. Furthermore, GRK2-mediated inhibition of Galpha(q)-Q152A-R183C-stimulated inositol phosphate release is reduced in comparison to Galpha(q)-R183C. Interestingly, the model also predicts that residues in the helical domain of Galpha(q) interact with GRK2. In fact, the mutants Galpha(q)-K77A, Galpha(q)-L78D, Galpha(q)-Q81A, and Galpha(q)-R92A have reduced binding to the GRK2-RH domain. Finally, although the mutant Galpha(q)-T187K has greatly reduced binding to RGS2 and RGS4, it has little to no effect on binding to GRK2. Thus the RH domain A and C sites for Galpha(q) interaction rely on contacts with distinct regions and different Switch I residues in Galpha(q).

Chronic morphine-induced loss of the facilitative interaction between vasoactive intestinal polypeptide and delta-opioid: involvement of protein kinase C and phospholipase Cbetas

This laboratory recently demonstrated a multiplicative interaction between the pelvic visceral afferent transmitter vasoactive intestinal polypeptide (VIP) and the delta-opioid receptor (DOR)-selective agonist [D-Pen2,5] enkephalin (DPDPE) to regulate cAMP levels in spinal cord [Brain Res. 959 (2003) 103]. Although DOR activation is required for the manifestation of the VIP-DPDPE facilitative interaction, its relevance to opioid antinociception remains unclear. The current study investigates whether or not the VIP-DPDPE facilitation of cAMP formation is subject to tolerance formation, a hallmark characteristic of opioid antinociception. Chronic morphine exposure abolishes the VIP-DPDPE facilitative interaction, consistent with its relevance to DOR antinociception. However, acute in vitro inhibition of protein kinase C (PKC) reinstates the VIP-DPDPE multiplicative interaction characteristic of opioid naïve spinal tissue. This suggests that its chronic morphine-induced loss requires a PKC phosphorylation. PKC phosphorylation negatively modulates phospholipase C (PLC)beta, enzymes intimately associated with phosphoinositide turnover and calcium trafficking. These are essential determinants of acute and chronic opioid effects. Accordingly, the effect of chronic morphine on their state of phosphorylation was also investigated. Central nervous system opioid tolerance is associated with the reciprocal phosphorylation (regulation) of two PLCbeta isoforms, PLCbeta1 and PLCbeta3. However, although chelerythrine reinstates the chronic morphine-induced loss of the multiplicative VIP-DPDPE interaction, it does not alter the associated changes in PLCbeta phosphorylation, possibly indicating different time courses of restitution of function and/or involvement of different kinases for different components of tolerance. These results could provide a mechanistic rubric for understanding positive modulation of opioid antinociception by afferent transmission.

Identification of a novel site within G protein alpha subunits important for specificity of receptor-G protein interaction

Several domains of G protein alpha subunits are implicated in the control of receptor-G protein coupling specificity. Among these are the extreme N-and C-termini, the alpha4/beta6-loops, and the loop linking the N-terminal alpha-helix to the beta1-strand of the ras-like domain. In this study, we illustrate that single-point mutations of a highly conserved glycine residue within the linker I region of the Galpha(q) subunit confers upon the mutant Galpha(q) the ability to be activated by Galpha(i)- and Galpha(s) -coupled receptors, as evidenced by guanosine 5'-O-(3-[(35)S]thio)triphosphate binding and inositol phosphate turnover assays. The mutations did not affect expression of Galpha(q) proteins nor their ability to stimulate phospholipase Cbeta. It is noteworthy that both mutant and wild-type Galpha(q) proteins are indistinguishable in their ability to reconstitute a functional Gq-PLCbeta-calcium signaling pathway when cotransfected with the Galpha(q)-coupled neurokinin 1 or muscarinic M3 receptor into mouse embryonic fibroblasts derived from Galpha(q/11) knockout mice. On a three-dimensional model of the receptor-G protein complex, the highly conserved linker I region connecting the helical and the GTPase domain of the Galpha protein is inaccessible to the intracellular surface of the receptors. Our data indicate that receptor-G protein coupling specificity is not exclusively governed by direct receptor-G protein interaction and that it even bypasses the requirement of the extreme C terminus of Galpha, a well accepted receptor recognition domain, suggesting a novel allosteric mechanism for G protein-coupled receptor-G protein selectivity.

Association analysis of two candidate phospholipase genes that map to the chromosome 15q15.1-15.3 region associated with reading disability

Molecular genetic studies have suggested a reading disability (RD, dyslexia) susceptibility locus on chromosome 15q. We have previously mapped this locus by association to the region surrounding D15S994. Very little is known about the neurobiological processes involved in RD, and therefore selecting positional candidate genes for analysis based upon function is difficult. Nevertheless we were able to identify two functional candidates based upon existing hypotheses. Both were phospholipase genes, phospholipase C beta 2 (PLCB2) and phospholipase A2, group IVB (cytosolic; PLA2G4B). D15S944 is located within PLCB2 and is 1.6 Mb from PLA2G4B. We examined each gene for association using a mixed direct and indirect association approach, a case (n = 164)/control (n = 174) sample, and a partially overlapping sample of 178 RD parent-proband trios from South Wales and England. Mutation analysis revealed 14 sequence variants in PLCB2 and 33 variants in PLA2G4B. All non-synonymous SNPs were genotyped as were SNPs across each gene with maximum distance between SNPs of 6 kb. Case-control analyses revealed modest evidence (0.01 < P < 0.05) for association between a single variant in PLCB2 and two variants in PLA2G4B. However, association was not confirmed in the family based sample. As the latter sample has previously generated replicated significant evidence for association between RD and markers/haplotypes surrounding D15S944, it should have sufficient power to detect association to variants in susceptibility gene itself. We conclude that neither gene accounts for the association signal we previously observed. As these are the only clear cut functional candidate genes in the region, identification of the putative susceptibility locus for RD on 15q will require more methodical non-hypothesis driven positional cloning approaches.

Possible involvement of group I mGluRs in neuroprotective effect of theanine

We investigated the molecular mechanism underlying the neuroprotective effect of theanine, a green tea component, using primary cultured rat cortical neurons, focusing on group I metabotropic glutamate receptors (mGluRs). Theanine and a group I mGluR agonist, DHPG, inhibited the delayed death of neurons caused by brief exposure to glutamate, and this effect of theanine was abolished by group I mGluR antagonists. Although the administration of glutamate alone decreased the neuronal expression of phospholipase C (PLC)-beta1 and -gamma1, which are linked to group I mGluRs, their expression was equal to the control levels on cotreatment with theanine. Treatment with theanine or DHPG alone for 5-7 days resulted in increased expression of PLC-beta1 and -gamma1, and the action of theanine was completely abolished by group I mGluR antagonists. These findings indicate that group I mGluRs might be involved in neuroprotective effect of theanine by increasing the expression levels of PLC-beta1 and -gamma1.

Phospholipase-C beta1 is predominantely expressed in the granular layer of rat cerebellar cortex

The beta1 isoform of phospholipase-C is exclusively present in the nucleus of several hematopoietic and non-hematopoietic cell lines and primary cells of different species. When present, it represents the key enzyme for initiating the nuclear phospholipid breakdown that is involved in the cellular response to proliferating and differentiating stimuli. We have studied the expression of this enzyme isoform in the rat cerebellar cortex. We demonstrate that phospholipase-C beta1 (PLCbeta1) is predominantly expressed in the neurons of the granular layer, while it is virtually absent in the molecular and Purkinje cell layers of rat cerebellar cortex. This pattern of expression is partially different from that of the mouse cerebellar cortex, where not only granular cells, but also Purkinje cells express PLCbeta1. The high level of synaptic inputs that converge on granular cells may imply a constantly active nuclear phospholipid metabolism that may not be strictly required for the appropriate cellular responses of the other cell types of rat cerebellar cortex.

Identification and characterization of a specific sensory epithelium in the rat larynx

A specific laryngeal sensory epithelium (SLSE), which includes arrays of solitary chemoreceptor cells, is described in the supraglottic region of the rat. Two plates of SLSE were found, one on each side of the larynx. The first plate was located in the ventrolateral wall of the larynx, and the second was located in the interarytenoidal region. In SLSE, immunoblotting showed the presence of alpha-gustducin and phospholipase C beta2 (PLCbeta2), which are two markers of chemoreceptor cells. At immunocytochemistry, laryngeal immunoreactivity for alpha-gustducin was localized mainly in solitary chemosensory cells. Double-label immunocytochemistry using confocal microscopy demonstrated that alpha-gustducin-expressing cells in large part colocalize type III IP3 receptor (IP3R3), another key molecule in bitter taste perception. However, some IP3R3-expressing cells do not colocalize alpha-gustducin. At ultrastructural immunocytochemistry, these cells showed packed apical microvilli, clear cytoplasmic vesicles, and cytoneural junctions. SLSE was characterized by high permeability to a tracer due to poorly developed junctional contacts between superficial cells. Junctions were short in length and showed little contact with the terminal web. Ultrastructural analysis showed deep pits among the superficial cells. In SLSE, high density of intraepithelial nerve fibers was found. The lamina propria of the SLSE appeared thicker than that in other supraglottic regions. It was characterized by the presence of a well-developed subepithelial nerve plexus. The immunocytochemical and ultrastructural data suggested that SLSE is a chemoreceptor located in an optimal position for detecting substances entering the larynx from the pharynx or the trachea.

Phospholipase C-beta 2 as a mammalian taste signaling marker is expressed in the multiple gustatory tissues of medaka fish, Oryzias latipes

Phospholipase C-beta 2 (PLC-beta 2) is a key enzyme in mammalian taste signal transduction. To analyze the taste system in fishes at molecular level, we cloned mfplc-beta 2 as a medaka fish homologue of PLC-beta 2. In situ hybridization analysis revealed that mfplc-beta 2 is expressed in the lip and branchial region where chemosensory tissues are distributed. Immunohistochemical detection of nerve fibers near the mfplc-beta 2 positive cells suggests the characteristic of peripheral sensory cells. These results suggest that mfplc-beta 2 is expressed in the gustatory sensory cells of medaka. This may provide a molecular basis for the taste reception at multiple tissues in fish species.

Selective serotonin reuptake inhibitor disrupts organization of thalamocortical somatosensory barrels during development

To further investigate the role of the transiently expressed serotonin (5-HT) transporter (5-HTT) in the development of thalamic fibers projecting to cortical barrels and the potential developmental changes in neuronal circuitry caused by a selective serotonin reuptake inhibitor (SSRI), paroxetine (5 mg/kg, twice daily, s.c.) or saline was administered to rat pups from postnatal day 0 (P0) to P8. Pups were perfused on P8 for 5-HT immunostaining (-im) to confirm the 5-HT uptake blockade, and 5-HTT-im and phospholipase C-beta1 (PLC-beta1)-im to label the thalamic afferents to barrels and barrel cells respectively. Paroxetine treatment completely blocked 5-HT uptake into the thalamocortical fibers as indicated by the negative 5-HT-im in cortical barrel areas. Organization of thalamic afferents to barrels, indicated by 5-HTT-im or PLC-beta1, was altered in paroxetine-treated pups in the following manners: (1) segregation of thalamocortical fibers was partially disrupted and thalamocortical fibers corresponding to anterior snouts and row A mystacial vibrissae were fused; (2) sizes of the unfused thalamocortical fiber patches related to the long caudal vibrissae in rows B, C, D and E were significantly decreased without changes in the brain weights and cortical areas representing these vibrissae; and (3) thalamocortical fibers corresponding to C4 and D4 vibrissae tended to be closer to each other along the arc while the relative positions of thalamocortical fibers related to the rest of the vibrissae were normal. Our study demonstrated that 5-HTT plays an important role in the refinement, but not the formation, of barrel-like clusters of thalamocortical fibers and that the development of neural circuitry in rodent somatosensory cortex was affected by exposure to a SSRI during thalamocortical synaptic formation.

NHERF2 specifically interacts with LPA2 receptor and defines the specificity and efficiency of receptor-mediated phospholipase C-beta3 activation

Lysophosphatidic acid (LPA) activates a family of cognate G protein-coupled receptors and is involved in various pathophysiological processes. However, it is not clearly understood how these LPA receptors are specifically coupled to their downstream signaling molecules. This study found that LPA(2), but not the other LPA receptor isoforms, specifically interacts with Na(+)/H(+) exchanger regulatory factor2 (NHERF2). In addition, the interaction between them requires the C-terminal PDZ domain-binding motif of LPA(2) and the second PDZ domain of NHERF2. Moreover, the stable expression of NHERF2 potentiated LPA-induced phospholipase C-beta (PLC-beta) activation, which was markedly attenuated by either a mutation in the PDZ-binding motif of LPA(2) or by the gene silencing of NHERF2. Using its second PDZ domain, NHERF2 was found to indirectly link LPA(2) to PLC-beta3 to form a complex, and the other PLC-beta isozymes were not included in the protein complex. Consistently, LPA(2)-mediated PLC-beta activation was specifically inhibited by the gene silencing of PLC-beta3. In addition, NHERF2 increases LPA-induced ERK activation, which is followed by cyclooxygenase-2 induction via a PLC-dependent pathway. Overall, the results suggest that a ternary complex composed of LPA(2), NHERF2, and PLC-beta3 may play a key role in the LPA(2)-mediated PLC-beta signaling pathway.

Signal transducer and activator of transcription 3 activation by the delta-opioid receptor via Galpha14 involves multiple intermediates

The hematopoietic-specific Galpha14 links a variety of G protein-coupled receptors to phospholipase Cbeta (PLCbeta) stimulation. Recent studies reveal that several Galpha subunits are capable of activating signal transducer and activator of transcription (STAT) proteins. In the present study, we investigated the mechanism by which Galpha14 mediates receptor-induced stimulation of STAT3. In human embryonic kidney 293 cells, coexpression of Galpha14 with delta-opioid receptor supported [D-Pen2, D-Pen5]enkephalin (DPDPE)-induced STAT3 phosphorylations at both Tyr705 and Ser727 in a pertussis toxin-insensitive manner. The constitutively active Galpha4QL mutant also induced STAT3 phosphorylations at these sites and promoted STAT3-dependent luciferase activity. Requirements for PLCbeta, protein kinase C (PKC), and calmodulin-dependent kinase II (CaMKII) in Galpha14QL-induced STAT3 activation were demonstrated by their respective inhibitors as well as by coexpression of their dominant-negative mutants. Inhibition of c-Src and Janus kinase 2 and 3 activities abolished STAT3 activation induced by Galpha14QL, but no physical association between Galpha14QL and c-Src could be detected by coimmunoprecipitation. Various intermediates along the extracellular signal-regulated kinase signaling cascade were apparently required for Galpha14QL-induced STAT3 activation; they included Ras/Rac1, Raf-1, and mitogen-activated protein kinase kinase-1/2. In contrast, functional blockade of c-Jun N-terminal kinase, p38 mitogen-activated protein kinase, and phosphatidylinositol-3 kinase had no effect on Galpha14QL-induced responses. PLCbeta, PKC, and CaMKII were shown to be involved in Galpha14QL-mediated c-Src phosphorylation. Similar results were obtained with human erythro-leukemia cells upon DPDPE treatment. These results demonstrate for the first time that Galpha14 activation can lead to STAT3 stimulation via a complex signaling network involving multiple intermediates.

Origins of Delays in Monolayer Kinetics: Phospholipase A2 Paradigm

The interfacial kinetic paradigm is adopted to model the kinetic behavior of pig pancreatic phospholipase A(2) (PLA2) at the monolayer interface. A short delay of about a minute to the onset of the steady state is observed under all monolayer reaction progress conditions, including the PLA2-catalyzed hydrolysis of didecanoylphosphatidyl-choline (PC10) and -glycerol (PG10) monolayers as analyzed in this paper. This delay is independent of enzyme concentration and surface pressure and is attributed to the equilibration time by stationary diffusion of the enzyme added to the stirred subphase to the monolayer through the intervening unstirred aqueous layer. The longer delays of up to several hours, seen with the PC10 monolayers at >15 mN/m, are influenced by surface pressure as well as enzyme concentration. Virtually all features of the monolayer reaction progress are consistent with the assumption that the product accumulates in the substrate monolayer, although the products alone do not spread as a compressible monolayer. These results rule out models that invoke slow "activation" of PLA2 on the monolayer. The observed steady-state rate on monolayers after the delays is <1% of the rate observed with micellar or vesicles substrates of comparable substrate. Together these results suggest that the monolayer steady-state rate includes contributions from steps other than those of the interfacial turnover cycle. Additional considerations that provide understanding of the pre-steady-state behaviors and other nonideal effects at the surface are also discussed.

Targeted mutagenesis of the farnesylation site of Drosophila Ggammae disrupts membrane association of the G protein betagamma complex and affects the light sensitivity of the visual system

Activation of phototransduction in the compound eye of Drosophila is mediated by a heterotrimeric G protein that couples to the effector enzyme phospholipase Cbeta. The gamma subunit of this G protein (Ggammae) as well as gamma subunits of vertebrate transducins contain a carboxyl-terminal CAAX motif (C, cysteine; A, aliphatic amino acid; X, any amino acid) with a consensus sequence for protein farnesylation. To examine the function of Ggammae farnesylation, we mutated the farnesylation site and overexpressed the mutated Ggammae in Drosophila. Mass spectrometry of overexpressed Ggammae subunits revealed that nonmutated Ggammae is modified by farnesylation, whereas the mutated Ggammae is not farnesylated. In the transgenic flies, mutated Ggammae forms a dimeric complex with Gbetae, with the consequence that the fraction of non-membrane-bound Gbetagamma is increased. Thus, farnesylation of Ggammae facilitates the membrane attachment of the Gbetagamma complex. We also expressed human Ggammarod in Drosophila photoreceptors. Despite similarities in the primary structure between the transducin gamma subunit and Drosophila Ggammae, we observed no interaction of human Ggammarod with Drosophila Gbetae. This finding indicates that human Ggammarod and Drosophila Ggammae provide different interfaces for the interaction with Gbeta subunits. Electroretinogram recordings revealed a significant loss of light sensitivity in eyes of transgenic flies that express mutated Ggammae. This loss in light sensitivity reveals that post-translational farnesylation is a critical step for the formation of membrane-associated Galphabetagamma required for transmitting light activation from rhodopsin to phospholipase Cbeta.

Action of Pasteurella multocida toxin depends on the helical domain of Galphaq

Pasteurella multocida produces a 146-kDa protein toxin (PMT), which activates multiple cellular signal transduction pathways, resulting in the activation of phospholipase Cbeta, RhoA, Jun kinase, and extracellular signal-regulated kinase. Using Galpha(q)/Galpha(11) -deficient cells, it was shown that the PMT-induced pleiotropic effects are mediated by Galpha(q) but not by the highly related Galpha(11) protein (Zywietz, A., Gohla, A., Schmelz, M., Schultz, G., and Offermanns, S. (2001) J. Biol. Chem. 276, 3840-3845). Here we studied the molecular basis of the unique specificity of PMT to distinguish between Galpha(q) and/or Galpha(11). Infection of Galpha(q) -deficient cells with retrovirus-encoding Galpha(q) caused reconstitution of PMT-induced activation of phospholipase Cbeta, whereas Galpha(11) -encoding virus did not reconstitute PMT activity. Chimeras between Galpha(q) and/or Galpha(11) revealed that a peptide region of Galpha(q), covering amino acid residues 105-113, is essential for the action of PMT to activate phospholipase Cbeta. Exchange of glutamine 105 or asparagine 109 of Galpha(11), which are located in the all-helical domain of the Galpha subunit, with the equally positioned histidines of Galpha(q), renders Galpha(11) capable of transmission PMT-induced phospholipase Cbeta activation. The data indicate that the all-helical domain of Galpha(q) is essential for the action of PMT and suggest an essential functional role of this domain in signal transduction via G(q) proteins.

Specific molecular alterations in the norpA-encoded phospholipase C of Drosophila and their effects on electrophysiological responses in vivo

A large number of mutants in the norpA gene, which encodes the phospholipase C (PLC) involved in Drosophila phototransduction, is available for the investigation of the effects of specific amino acid substitutions in PLC on biochemical and electrophysiological properties of these mutants. Of the 47 norpA mutants screened for PLC protein content, all but one (H43) displayed drastically decreased amounts of the protein suggesting that almost any mutational alteration has a deleterious effect on the integrity of the protein. Three new amino acids were identified in the catalytic domains X and Y that are important for PLC catalytic activity and the generation of photoreceptor responses (ERG). One of them was found substituted in H43, which showed a low specific PLC activity, a pronounced decrease in ERG sensitivity, and a wild-type-like response termination time. The response termination times obtained from three mutants was found to be approximately inversely proportional to the amount of PLC. In addition, we show that (i) the specific PLC activity is a key factor determining the photoreceptor sensitivity; (ii) the catalytic activity and response termination are separable functions of PLC; and (iii) a mutation in the putative G alpha-interacting C2 domain causes a preferentially strong defect in latency.

Delay fear conditioning modifies phospholipase C-β1a signaling in the hippocampus and frontal cortex

The use of the single-trial fear conditioning paradigm allows for control over the exact moment when an animal is exposed to a learning event, making it possible to study both the initial neurobiological changes that are associated with learning and changes that take place over long periods of time. In the present study, we performed detailed analyses of the alterations in phosphatidylinositol-specific phospholipase C-beta1a (PLC-beta1a) levels and enzyme activities in subcellular fractions prepared from the hippocampal formation (HPF) and medial frontal cortex (MFC) 1, 3, 5, 7, 24, and 72 h following single-trial fear conditioning. We observed tissue- and time-dependent changes in both PLC-beta1a enzyme activity and anti-PLC-beta1a immunoreactivity in each subcellular fraction. Based on these observations, we hypothesize that changes in PLC-beta1a catalytic activity and subcellular distribution play important roles in neuronal signaling processes that are required for fear-conditioned learning and memory.

Distinctive G protein-dependent signaling in smooth muscle by sphingosine 1-phosphate receptors S1P1and S1P2

We examined expression of sphingosine 1-phosphate (S1P) receptors and sphingosine kinase (SPK) in gastric smooth muscle cells and characterized signaling pathways mediating S1P-induced 20-kDa myosin light chain (MLC20) phosphorylation and contraction. RT-PCR demonstrated expression of SPK1 and SPK2 and S1P1and S1P2receptors. S1P activated Gq, G13, and all Giisoforms and stimulated PLC-β1, PLC-β3, and Rho kinase activities. PLC-β activity was partially inhibited by pertussis toxin (PTX), Gβ or Gαqantibody, PLC-β1 or PLC-β3 antibody, and by expression of Gαqor Gαiminigene, and was abolished by a combination of antibodies or minigenes. S1P-stimulated Rho kinase activity was partially inhibited by expression of Gα13or Gαqminigene and abolished by expression of both. S1P stimulated Ca2+release that was inhibited by U-73122 and heparin and induced concentration-dependent contraction of smooth muscle cells (EC501 nM). Initial contraction and MLC20phosphorylation were abolished by U-73122 and MLC kinase (MLCK) inhibitor ML-9. Initial contraction was also partially inhibited by PTX and Gαqor Gβ antibody and abolished by a combination of both antibodies. In contrast, sustained contraction and MLC20phosphorylation were partially inhibited by a PKC or Rho kinase inhibitor (bisindolylmaleimide and Y-27632) and abolished by a combination of both inhibitors but not affected by U-73122 or ML-9. These results indicate that S1P induces 1) initial contraction mediated by S1P2and S1P1involving concurrent activation of PLC-β1 and PLC-β3 via Gαqand Gβγi, respectively, resulting in inositol 1,4,5-trisphosphate-dependent Ca2+release and MLCK-mediated MLC20phosphorylation, and 2) sustained contraction exclusively mediated by S1P2involving activation of RhoA via Gαqand Gα13, resulting in Rho kinase- and PKC-dependent MLC20phosphorylation.

Stimulation by Parathyroid Hormone of a NHERF-1-assembled Complex Consisting of the Parathyroid Hormone I Receptor, Phospholipase Cβ, and Actin Increases Intracellular Calcium in Opossum Kidney Cells

Parathyroid hormone (PTH) binds its cognate G-protein-coupled receptor (PTH1R) and signals through both adenylyl cyclase and phospholipase C (PLC). C-terminal determinants of the PTH1R interact with the Na+/H+ exchanger regulatory factor 1 (NHERF-1) by binding the first of two PDZ (psd95, discs-large, ZO-1) domains. Compared with wild-type opossum kidney (OK) cells, OKH cells, a sub-clone, do not display PTH-mediated increases of [Ca2+]i and express NHERF-1 at markedly lower levels. Stable expression of NHERF-1 in the OKH parent (OKH-N1) restores the PTH-mediated increase of [Ca2+]i that arises from an influx of extracellular calcium and is both PLC-dependent and pertussis toxin-sensitive. From a morphological perspective, NHERF-1 and the PTH1R co-localize to apical patches of OKH-N1 cells, an expression pattern that is absent in OKH cells and depends on a direct NHERF-1-PTH1R interaction in OKH-N1 cells. Actin and PLCbeta1 and -beta3 co-localize with NHERF-1 and the PTH1R in OKH-N1 cell apical patches. Actin is also an integral component of the NHERF-1-assembled complex because cytochalasin D disrupts apical localization of both NHERF-1 and the PTH1R and inhibits the PTH-mediated increase of [Ca2+]i. Expression of the first PDZ domain of NHERF-1 acts as a dominant-negative interactor by blocking apical localization of the PTH1R and inhibiting PTH-elicited increases of [Ca2+]i. Thus, NHERF-1 assembles a signaling complex in the apical domains of OK cells that contains the PTH1R, PLCbeta, and the actin cytoskeleton. Disruption of this complex blocks the PTH mediated increases of intracellular calcium.

Inositide-specific phospholipase c β1 gene deletion in the progression of myelodysplastic syndrome to acute myeloid leukemia

Myelodysplastic syndrome (MDS) is an adult hematological disease that evolves into acute myeloid leukemia (AML) in about 30% of the cases. The availability of a highly specific probe moved us to perform in patients affected with MDS/AML, associated with normal karyotype, painting and fluorescence in situ hybridization (FISH) analysis aimed to check the inositide-specific phospholipase C (PI-PLC) beta1 gene, a player in the control of some checkpoints of the cell cycle. Here we present a preliminary observation in which FISH analysis disclosed in a small group of MDS/AML patients with normal karyotype the monoallelic deletion of the PI-PLCbeta1 gene. On the contrary, PI-PLC beta4, another gene coding for a signaling molecule, located on 20p12.3 at a distance as far as less than 1Mb from PI-PLCbeta1, is unaffected in MDS patients with the deletion of PI-PLC beta1 gene, hinting at an interstitial deletion. The MDS patients, bearing the deletion, rapidly evolved to AML. The data suggest the possible involvement of PI-PLCbeta1 in the progression of the disease and pave the way for a larger investigation aimed at identifying a possible high-risk group among MDS patients with a normal karyotype.

Splicing of the period gene 3'-terminal intron is regulated by light, circadian clock factors, and phospholipase C

The daily timing of circadian ( congruent with 24-h) controlled activity in many animals exhibits seasonal adjustments, responding to changes in photoperiod (day length) and temperature. In Drosophila melanogaster, splicing of an intron in the 3' untranslated region of the period (per) mRNA is enhanced at cold temperatures, leading to more rapid daily increases in per transcript levels and earlier "evening" activity. Here we show that daily fluctuations in the splicing of this intron (herein referred to as dmpi8) are regulated by the clock in a manner that depends on the photoperiod (day length) and temperature. Shortening the photoperiod enhances dmpi8 splicing and advances its cycle, whereas the amplitude of the clock-regulated daytime decline in splicing increases as temperatures rise. This suggests that at elevated temperatures the clock has a more pronounced role in maintaining low splicing during the day, a mechanism that likely minimizes the deleterious effects of daytime heat on the flies by favoring nocturnal activity during warm days. Light also has acute inhibitory effects, rapidly decreasing the proportion of dmpi8-spliced per transcript, a response that does not require a functional clock. Our results identify a novel nonphotic role for phospholipase C (no-receptor-potential-A [norpA]) in the temperature regulation of dmpi8 splicing.

Morphologic characterization of rat taste receptor cells that express components of the phospholipase C signaling pathway

Rat taste buds contain three morphologically distinct cell types that are candidates for taste transduction. The physiologic roles of these cells are, however, not clear. Inositol 1,4,5-triphosphate (IP(3)) has been implicated as an important second messenger in bitter, sweet, and umami taste transductions. Previously, we identified the type III IP(3) receptor (IP(3)R3) as the dominant isoform in taste receptor cells. In addition, a recent study showed that phospholipase Cbeta(2) (PLCbeta(2)) is essential for the transduction of bitter, sweet, and umami stimuli. IP(3)R3 and PLCbeta(2) are expressed in the same subset of cells. To identify the taste cell types that express proteins involved in PLC signal transduction, we used 3,3'diaminobenzidine tetrahydrochloride immunoelectron microscopy and fluorescence microscopy to identify cells with IP(3)R3. Confocal microscopy was used to compare IP(3)R3 or PLCbeta(2) immunoreactivity with that of some known cell type markers such as serotonin, protein gene-regulated product 9.5, and neural cell adhesion molecule. Here we show that a large subset of type II cells and a small subset of type III cells display IP(3)R3 immunoreactivity within their cytoplasm. These data suggest that type II cells are the principal transducers of bitter, sweet, and umami taste transduction. However, we did not observe synapses between type II taste cells and nerve fibers. Interestingly, we observed subsurface cisternae of smooth endoplasmic reticulum at the close appositions between the plasma membrane of type II taste cells and nerve processes. We speculate that some type II cells may communicate to the nervous system via subsurface cisternae of smooth endoplasmic reticulum in lieu of conventional synapses.

AHNAK-mediated activation of phospholipase C-gamma1 through protein kinase C

We have recently shown that phospholipase C-gamma (PLC-gamma) is activated by the central repeated units (CRUs) of the AHNAK protein in the presence of arachidonic acid. Here we demonstrate that four central repeated units (4 CRUs) of AHNAK act as a scaffolding motif networking PLC-gamma and PKC-alpha. Specifically, 4 CRUs of AHNAK bind and activate PKC-alpha, which in turn stimulates the release of arachidonic acid near where PLC-gamma1 is localized. Moreover, 4 CRUs of AHNAK interacted with PLC-gamma and the concerted action of 4 CRUs with arachidonic acid stimulated PLC-gamma activity. Stimulation of NIH3T3 cells expressing 4 CRUs of AHNAK with phorbol 12-myristate 13-acetate resulted in the increased generation of total inositol phosphates (IP(T)) and mobilization of the intracellular calcium. Phorbol 12-myristate 13-acetate-dependent generation of IP(T) was completely blocked in NIH3T3 cells depleted of PLC-gamma1 by RNA interference. Furthermore, bradykinin, which normally stimulated the PLC-beta isozyme resulting in the generation of a monophasic IP(T) within 30 s in NIH3T3 cells, led to a biphasic pattern for generation of IP(T) in NIH3T3 cells expressing 4 CRUs of AHNAK. The secondary activation of PLC is likely because of the scaffolding activity of AHNAK, which is consistent with the role of 4 CRUs as a molecular linker between PLC-gamma and PKC-alpha.

Role of Gαq in smooth muscle cell proliferation

BACKGROUND

G protein-linked receptors are involved in the processes that lead to intimal hyperplasia. This study examined the role of Galphaq signaling pathways in vascular smooth muscle cell (SMC) proliferation in vitro.

METHODS

Rat pulmonary artery SMCs were cultured in vitro. Standard assays of cellular DNA synthesis, proliferation, phospholipase C-beta (PLCbeta) activation, and extracellular signal-regulated kinase (ERK1/2) phosphorylation were used to study the response to angiotensin II (a specific Galphaq agonist; 0.1-100 micromol/L) in the presence and absence of GP-2A (a competitive Galphaq inhibitor; 10 micromol/L) and the PLCbeta inhibitor U73122 (10micromol/L).

RESULTS

Angiotensin II induced SMC DNA synthesis and cell proliferation. DNA synthesis was inhibited by both Galphaq inhibitor, GP-2A, and PLCbeta inhibitor U73122, in a dose-dependent manner (66% +/- 7% of angiotensin II alone at 10 micromol/L for GP-2A [P <.05] and 63% +/- 6% for U73122). GP-2A completely inhibited angiotensin II-induced Galphaq-mediated PLCbeta phosphorylation. Activation of ERK1/2 by angiotensin II was significantly reduced by GP-2A (P <.05) and by PLCbeta inhibition (P <.05).

CONCLUSION

Inhibition of Galphaq decreases PLCbeta and ERK1/2 phosphorylation, leading to decreased SMC proliferation in vitro. Understanding specific signal transduction pathways will be an integral component of anti-restenosis therapy.Clinical Relevance The universal response of a blood vessel to injury is chronic wound healing, which includes the development of intimal hyperplasia and subsequent remodeling of the vessel wall. This can lead to luminal narrowing in as many as 30% of patients undergoing angioplasty. Neointimal formation is the principal cause of in-stent recurrent stenosis. Intimal hyperplasia is in part produced by smooth muscle cell (SMC) proliferation. Understanding the keys to the proliferation of SMCs will enable therapies to be developed that may inhibit the initial development of intimal hyperplasia. Whereas in the past many studies focused on the multiple mechanical, humoral, and cellular elements that induce SMC proliferation, molecular therapeutics focuses on key choke points within the cell that can be used to inhibit proliferation. One of these key choke points is signal transduction. Galphaq is one of the ubiquitous signal transduction proteins on the membrane of SMCs. Inhibiting G proteins, such as Galphaq, would enable interference with a significant amount of the mechanical, humeral, and cellular elements that produce SMC proliferation, and thus decrease the development of intimal hyperplasia. The present study identifies and begins to map out the role of Galphaq in SMC proliferation and investigates the possible use of a small peptide in its inhibition. Other data suggest that inhibition of other G proteins will also decrease intimal hyperplasia. This is therefore a fertile area for the development of therapeutics to inhibit intimal hyperplasia. The direct relevance to the clinician is that this study identifies a transduction pathway that may be inhibited, and points in the direction of a possible molecular therapeutic target that would be beneficial as an adjunct to angioplasty or as part of a drug-eluding stent regimen.

Purification of phospholipase C beta and phospholipase C epsilon from Sf9 cells

Phosphatidylinositol-specific phospholipase C (PLC) enzymes catalyze hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2) generating diacylglycerol (DAG) and inositol 1,4,5-triphosphate (IP(3)). The PLC beta isoforms of PLCs are activated by G proteins after hormone or neurotransmitter stimulation of G protein-coupled receptors (GPCR). PLC epsilon is a recently identified PLC isoform that is activated by Ras and G beta gamma subunit although the physiological role of this enzyme is not well understood. Methods for purification of PLC beta and PLC epsilon from Sf9 cells are described. In the case of hexahistidine (6-His)-tagged PLC beta the purification involves two steps, affinity chromatography with Ni-NTA agarose followed by heparin Sepharose chromatography. 6-His-tagged PLC epsilon can be purified in a single step with nickel nitrilotriacetic acid-agarose (Ni-NTA) affinity chromatography.

Assay for G protein-dependent activation of phospholipase C beta using purified protein components

The activity of mammalian phosphoinositide-specific phospholipase C beta (PLC beta) is regulated by the alpha q family of G protein alpha subunits and by beta gamma subunits thought to be released from Gi. Interactions between G protein subunits and PLC beta can be assayed by measuring the stimulation of PLC beta enzymatic activity on reconstituting the purified G protein subunits with purified PLC beta on artificial phospholipid vesicles containing the substrate, phosphatidylinositol-4,5-bisphosphate (PIP2). These vesicles are doped with [3H]-inositol PIP2 and the rate of hydrolysis is determined by quantitating the amount of [3H]-inositol triphosphate (IP3) released from the vesicle into the aqueous phase. This assay provides a relatively simple method for assessing the activity PLC activity and its ability to be regulated by beta gamma and alpha(q) subunits. It can also be used to assess the functionality of the components after modification by mutagenesis, chemical modification, or in the presence of competing molecules.

Seasonal behavior in Drosophila melanogaster requires the photoreceptors, the circadian clock, and phospholipase C

Drosophila melanogaster locomotor activity responds to different seasonal conditions by thermosensitive regulation of splicing of a 3' intron in the period mRNA transcript. Here we demonstrate that the control of locomotor patterns by this mechanism is primarily light-dependent at low temperatures. At warmer temperatures, when it is vitally important for the fly to avoid midday desiccation, more stringent regulation of splicing is observed, requiring the light input received through the visual system during the day and the circadian clock at night. During the course of this study, we observed that a mutation in the no-receptor-potential-A(P41) (norpA(P41)) gene, which encodes phospholipase-C, generated an extremely high level of 3' splicing. This cannot be explained simply by the mutation's effect on the visual pathway and suggests that norpA(P41) is directly involved in thermosensitivity.