Physiological regulation of G protein-linked signaling

Insulin induces IRS2-dependent and GRK2-mediated β2AR internalization to attenuate βAR signaling in cardiomyocytes

The counter-regulatory effects of insulin and catecholamines on carbohydrate and lipid metabolism are well studied, whereas the details of insulin regulation of β adrenergic receptor (βAR) signaling pathway in heart remain unknown. Here, we characterize a novel signaling pathway of insulin receptor (IR) to G protein-coupled receptor kinase 2 (GRK2) in the heart. Insulin stimulates recruitment of GRK2 to β2AR, which induces β2AR phosphorylation at the GRK sites of serine 355/356 and subsequently β2AR internalization. Insulin thereby suppresses βAR-induced cAMP-PKA activities and contractile response in neonatal and adult mouse cardiomyocytes. Deletion of insulin receptor substrate 2 (IRS2) disrupts the complex of IR and GRK2, which attenuates insulin-mediated β2AR phosphorylation at the GRK sites and β2AR internalization, and the counter-regulation effects of insulin on βAR signaling. These data indicate the requirements of IRS2 and GRK2 for insulin to stimulate counter-regulation of βAR via β2AR phosphorylation and internalization in cardiomyocytes.

Fluorosed mouse ameloblasts have increased SATB1 retention and Gαq activity

Dental fluorosis is characterized by subsurface hypomineralization and increased porosity of enamel, associated with a delay in the removal of enamel matrix proteins. To investigate the effects of fluoride on ameloblasts, A/J mice were given 50 ppm sodium fluoride in drinking water for four weeks, resulting serum fluoride levels of 4.5 µM, a four-fold increase over control mice with no fluoride added to drinking water. MicroCT analyses showed delayed and incomplete mineralization of fluorosed incisor enamel as compared to control enamel. A microarray analysis of secretory and maturation stage ameloblasts microdissected from control and fluorosed mouse incisors showed that genes clustered with Mmp20 appeared to be less downregulated in maturation stage ameloblasts of fluorosed incisors as compared to control maturation ameloblasts. One of these Mmp20 co-regulated genes was the global chromatin organizer, special AT-rich sequence-binding protein-1 (SATB1). Immunohistochemical analysis showed increased SATB1 protein present in fluorosed ameloblasts compared to controls. In vitro, exposure of human ameloblast-lineage cells to micromolar levels of both NaF and AlF₃ led to a significantly increase in SATB1 protein content, but not levels of Satb1 mRNA, suggesting a fluoride-induced mechanism protecting SABT1 from degradation. Consistent with this possibility, we used immunohistochemistry and Western blot to show that fluoride exposed ameloblasts had increased phosphorylated PKCα both in vivo and in vitro. This kinase is known to phosphorylate SATB1, and phosphorylation is known to protect SATB1 from degradation by caspase-6. In addition, production of cellular diacylglycerol (DAG) was significantly increased in fluorosed ameloblasts, suggesting that the increased phosphorylation of SATB1 may be related to an effect of fluoride to enhance Gαq activity of secretory ameloblasts.

Probing the stoichiometry of β2-adrenergic receptor phosphorylation by targeted mass spectrometry

Background

Protein phosphorylation of G-protein-coupled receptors (GPCR) is central to the myriad of functions that these ubiquitous receptors perform in biology. Although readily addressable with the use of phospho-specific antibodies, analysis phosphorylation at the level of stoichiometry requires receptor isolation and advanced proteomics. We chose two key sites of potential phosphorylation of human beta2-adrenergic receptor (β2AR residues S355 and S356) to ascertain the feasibility of applying targeted mass spectrometry to establishing the stoichiometry of the phosphorylation.

Method

We stimulated HEK293 cells stably expressing Flag-tagged β2AR-eGFP with 10 μM beta-adrenergic agonist (isoproterenol) and made use of proteomics and targeted mass spectrometry (MS) to quantify the molar ration of phosphorylation on S355 and S356 versus non-phosphorylated receptor in agonist-treated cells.

Results

Phosphorylation of either S355 or S356 residue occurred only for agonist-occupied β2AR. The results demonstrated that pS356 is the dominant site of protein phosphorylation. The abundance of the p356 was 8.6-fold more than that of pS355. Calculation of the molar ratio of phosphorylated (pS355 plus pS356) versus non-phosphorylated receptor reveals that at high occupancy of the receptor only 12.4% of the β2AR is phosphorylated at these sites.

Conclusions

Application of advanced proteomics and use of the most sensitive targeted MS strategy makes possible the detection and quantification of phosphorylation of very low abundance peptide digests of β2AR. Establishing the stoichiometry of two key sites of agonist-stimulated phosphorylation with β2AR is an essential first-step to global analysis of the stoichiometry of GPCR phosphorylation.

Coronin 1 regulates cognition and behavior through modulation of cAMP/protein kinase A signaling

The evolutionarily conserved protein coronin 1 is needed for activating the cyclic AMP signaling pathway in the brain and is important for cognition and behavior.

Cognitive and behavioral disorders are thought to be a result of neuronal dysfunction, but the underlying molecular defects remain largely unknown. An important signaling pathway involved in the regulation of neuronal function is the cyclic AMP/Protein kinase A pathway. We here show an essential role for coronin 1, which is encoded in a genomic region associated with neurobehavioral dysfunction, in the modulation of cyclic AMP/PKA signaling. We found that coronin 1 is specifically expressed in excitatory but not inhibitory neurons and that coronin 1 deficiency results in loss of excitatory synapses and severe neurobehavioral disabilities, including reduced anxiety, social deficits, increased aggression, and learning defects. Electrophysiological analysis of excitatory synaptic transmission in amygdala revealed that coronin 1 was essential for cyclic–AMP–protein kinase A–dependent presynaptic plasticity. We further show that upon cell surface stimulation, coronin 1 interacted with the G protein subtype Gαs to stimulate the cAMP/PKA pathway. The absence of coronin 1 or expression of coronin 1 mutants unable to interact with Gαs resulted in a marked reduction in cAMP signaling. Strikingly, synaptic plasticity and behavioral defects of coronin 1–deficient mice were restored by in vivo infusion of a membrane-permeable cAMP analogue. Together these results identify coronin 1 as being important for cognition and behavior through its activity in promoting cAMP/PKA-dependent synaptic plasticity and may open novel avenues for the dissection of signal transduction pathways involved in neurobehavioral processes.

Memory and behavior depend on the proper transduction of signals in the brain, but the underlying molecular mechanisms remain largely unknown. Coronin 1 is a member of a highly conserved family of proteins, and although its gene lies in a chromosome region associated with neurobehavioral dysfunction in mice and men, it has never been directly ascribed a specific function in the brain. Here we show that coronin 1 plays an important role in cognition and behavior by regulating the cyclic AMP (cAMP) signaling pathway. We find that when cell surface receptors are activated, coronin 1 stimulates cAMP production and activation of protein kinase A. Coronin 1 deficiency resulted in severe functional defects at excitatory synapses. Furthermore, in both mice and humans, deletion or mutation of coronin 1 causes severe neurobehavioral defects, including social deficits, increased aggression, and learning disabilities. Strikingly, treatment with a membrane-permeable analogue of cAMP restored synaptic plasticity and behavioral defects in mice lacking coronin 1. Together this work not only shows a critical role for coronin 1 in neurobehavior but also defines a role for the coronin family in regulating the transmission of signals within cells.

G-protein-coupled receptor GPR161 is overexpressed in breast cancer and is a promoter of cell proliferation and invasion

Triple-negative breast cancer (TNBC) accounts for 20% of breast cancer in women and lacks an effective targeted therapy. Therefore, finding common vulnerabilities in these tumors represents an opportunity for more effective treatment. Despite the growing appreciation of G-protein-coupled receptor (GPCR)-mediated signaling in cancer pathogenesis, very little is known about the role GPCRs play in TNBC. Using genomic information of human breast cancer, we have discovered that the orphan GPCR, G-protein-coupled receptor 161 (GPR161) is overexpressed specifically in TNBC and correlates with poor prognosis. Knockdown of GPR161 impairs proliferation of human basal breast cancer cell lines. Overexpression of GPR161 in human mammary epithelial cells increases cell proliferation, migration, intracellular accumulation of E-cadherin, and formation of multiacinar structures in 3D culture. GPR161 forms a signaling complex with the scaffold proteins β-arrestin 2 and Ile Gln motif containing GTPase Activating Protein 1, a regulator of mammalian target of rapamycin complex 1 and E-cadherin. Consistently, GPR161 amplified breast tumors and cells overexpressing GPR161 activate mammalian target of rapamycin signaling and decrease Ile Gln motif containing GTPase Activating Protein 1 phosphorylation. Thus, we identify the orphan GPCR, GPR161, as an important regulator and a potential drug target for TNBC.

Molecular cloning and expression of the gene for G protein alpha subunit induced by bisphenol A in marine polychaete Perinereis aibuhitensis

A G protein alpha subunit gene named Pa Gα was isolated from the marine polychaete Perinereis aibuhitensis. The full-length cDNA of Pa Gα was 1832 bp and contained a 205 bp 5' untranslated region (5'UTR), a 565 bp 3' UTR and a 1062 bp open reading frame encoding 353 amino acid residues. The deduced protein sequence of Pa Gα showed 73% homology with the Gα protein of Dipolydora quadrilobata. Tissue-specific expression induced by exposure to bisphenol A (BPA) in P. aibuhitensis was detected by real-time PCR, which showed BPA induced expression of the Pa Gα gene, and the level of transcription was related positively to the concentration of BPA and the length of exposure time. With increasing concentration of BPA and length of exposure time, the level of mRNA transcription was raised gradually, but the level of increasing expression of Pa Gα mRNA induced by exposure to BPA varied significantly among different tissues.

Phospholipase C-β1 and β4 contribute to non-genetic cell-to-cell variability in histamine-induced calcium signals in HeLa cells

A uniform extracellular stimulus triggers cell-specific patterns of Ca(2+) signals, even in genetically identical cell populations. However, the underlying mechanism that generates the cell-to-cell variability remains unknown. We monitored cytosolic inositol 1,4,5-trisphosphate (IP3) concentration changes using a fluorescent IP3 sensor in single HeLa cells showing different patterns of histamine-induced Ca(2+) oscillations in terms of the time constant of Ca(2+) spike amplitude decay and the Ca(2+) oscillation frequency. HeLa cells stimulated with histamine exhibited a considerable variation in the temporal pattern of Ca(2+) signals and we found that there were cell-specific IP3 dynamics depending on the patterns of Ca(2+) signals. RT-PCR and western blot analyses showed that phospholipase C (PLC)-β1, -β3, -β4, -γ1, -δ3 and -ε were expressed at relatively high levels in HeLa cells. Small interfering RNA-mediated silencing of PLC isozymes revealed that PLC-β1 and PLC-β4 were specifically involved in the histamine-induced IP3 increases in HeLa cells. Modulation of IP3 dynamics by knockdown or overexpression of the isozymes PLC-β1 and PLC-β4 resulted in specific changes in the characteristics of Ca(2+) oscillations, such as the time constant of the temporal changes in the Ca(2+) spike amplitude and the Ca(2+) oscillation frequency, within the range of the cell-to-cell variability found in wild-type cell populations. These findings indicate that the heterogeneity in the process of IP3 production, rather than IP3-induced Ca(2+) release, can cause cell-to-cell variability in the patterns of Ca(2+) signals and that PLC-β1 and PLC-β4 contribute to generate cell-specific Ca(2+) signals evoked by G protein-coupled receptor stimulation.

Role of regulator of G protein signaling proteins in bone

Regulators of G protein signaling (RGS) proteins are a family with more than 30 proteins that all contain an RGS domain. In the past decade, increasing evidence has indicated that RGS proteins play crucial roles in the regulation of G protein coupling receptors (GPCR), G proteins, and calcium signaling during cell proliferation, migration, and differentiation in a variety of tissues. In bone, those proteins modulate bone development and remodeling by influencing various signaling pathways such as GPCR-G protein signaling, Wnt, calcium oscillations and PTH. This review summarizes the recent advances in the understanding of the regulation of RGS gene expression, as well as the functions and mechanisms of RGS proteins, especially in regulating GPCR-G protein signaling, Wnt signaling, calcium oscillations signaling and PTH signaling during bone development and remodeling. This review also highlights the regulation of different RGS proteins in osteoblasts, chondrocytes and osteoclasts. The knowledge from the recent advances of RGS study summarized in the review would provide the insights into new therapies for bone diseases.

Anti-platelet activity of a three-finger toxin (3FTx) from Indian monocled cobra (Naja kaouthia) venom

A low molecular weight anti-platelet peptide (6.9 kDa) has been purified from Naja kaouthia venom and was named KT-6.9. MALDI-TOF/TOF mass spectrometry analysis revealed the homology of KT-6.9 peptide sequence with many three finger toxin family members. KT-6.9 inhibited human platelet aggregation process in a dose dependent manner. It has inhibited ADP, thrombin and arachidonic acid induced platelet aggregation process in dose dependent manner, but did not inhibit collagen and ristocetin induced platelet aggregation. Strong inhibition (70%) of the ADP induced platelet aggregation by KT-6.9 suggests competition with ADP for its receptors on platelet surface. Anti-platelet activity of KT-6.9 was found to be 25 times stronger than that of anti-platelet drug clopidogrel. Binding of KT-6.9 to platelet surface was confirmed by surface plasma resonance analysis using BIAcore X100. Binding was also observed by a modified sandwich ELISA method using anti-KT-6.9 antibodies. KT-6.9 is probably the first 3 FTx from Indian monocled cobra venom reported as a platelet aggregation inhibitor.

Harnessing the genome for characterization of G-protein coupled receptors in cancer pathogenesis

G-protein coupled receptors (GPCRs) mediate numerous physiological processes and represent the targets for a vast array of therapeutics for diseases ranging from depression to hypertension to reflux. Despite the recognition that GPCRs can act as oncogenes and tumour suppressors by regulating oncogenic signalling networks, few drugs targeting GPCRs are utilized in cancer therapy. Recent large-scale genome-wide analyses of multiple human tumours have uncovered novel GPCRs altered in cancer. However, work aiming to determine which GPCRs from these lists are the drivers of tumourigenesis, and hence valid therapeutic targets, comprises a formidable challenge. The present review highlights recent studies providing evidence that GPCRs are relevant targets for cancer therapy through their effects on known cancer signalling pathways, tumour progression, invasion and metastasis, and the microenvironment. Furthermore, the review also explores how genomic analysis is beginning to highlight GPCRs as therapeutic targets in the age of personalized medicine.

Proteomic analysis of NK92-MI cells activated by neuropeptide substance P

Substance P (SP) has been well known by its immunoregulatory properties on the functions of NK cells. However, the changes of molecules involved in the signaling pathways and effects of these molecules of NK92-MI cells activated by SP remain unclear. In this study, we explored the global changes in cellular protein expression of NK92-MI cells activated by SP by 2D-PAGE analysis. Subsequently, we demonstrated that 40 protein spots showed more than 2-fold changes, which displayed marked alterations with statistic significance (p<0.05) between the testing group and control group. Compared with the control we also found that 16 proteins were up-regulated and 24 proteins were down-regulated among the 40 differentially expressed protein spots in the NK92-MI cells activated by SP. In addition 21 differentially expressed proteins were identified by MS/MS, suggesting that those proteins may play important roles in the process of activation of NK92-MI cells by SP. Moreover, the protein Rho GDI-2, Protein DJ-1 and alpha-enolase were reconfirmed by western blotting. Taken together, these findings may provide a new insight into better understanding at the molecular mechanisms of activation of NK92-MI cells by SP.

Non-traditional roles of G protein-coupled receptors in basic cell biology

G protein-coupled receptors (GPCRs) are key signaling proteins that regulate how cells interact with their environment. Traditional signaling cascades involving GPCRs have been well described and are well established and very important clinical targets. With the development of more recent technologies, hints about the involvement of GPCRs in fundamental cell biological processes are beginning to emerge. In this review, we give a basic introduction to GPCR signaling and highlight some less well described roles of GPCRs, including in cell division and membrane trafficking, which may occur through canonical and non-canonical signaling pathways.

Increased intracellular magnesium attenuates β-adrenergic stimulation of the cardiac Ca(V)1.2 channel

Increases in intracellular Mg²⁺ (Mg²⁺_i), as observed in transient cardiac ischemia, decrease L-type Ca²⁺ current of mammalian ventricular myocytes (VMs). However, cardiac ischemia is associated with an increase in sympathetic tone, which could stimulate L-type Ca²⁺ current. Therefore, the effect of Mg²⁺_i on L-type Ca²⁺ current in the context of increased sympathetic tone was unclear. We tested the impact of increased Mg²⁺_i on the β-adrenergic stimulation of L-type Ca²⁺ current. Exposure of acutely dissociated adult VMs to higher Mg²⁺_i concentrations decreased isoproterenol stimulation of the L-type Ca²⁺ current from 75 ± 13% with 0.8 mM Mg²⁺_i to 20 ± 8% with 2.4 mM Mg²⁺_i. We activated this signaling cascade at different steps to determine the site or sites of Mg²⁺_i action. Exposure of VMs to increased Mg²⁺_i attenuated the stimulation of L-type Ca²⁺ current induced by activation of adenylyl cyclase with forskolin, inhibition of cyclic nucleotide phosphodiesterases with isobutylmethylxanthine, and inhibition of phosphoprotein phosphatases I and IIA with calyculin A. These experiments ruled out significant effects of Mg²⁺_i on these upstream steps in the signaling cascade and suggested that Mg²⁺_i acts directly on Ca_V1.2 channels. One possible site of action is the EF-hand in the proximal C-terminal domain, just downstream in the signaling cascade from the site of regulation of Ca_V1.2 channels by protein phosphorylation on the C terminus. Consistent with this hypothesis, Mg²⁺_i had no effect on enhancement of Ca_V1.2 channel activity by the dihydropyridine agonist (S)-BayK8644, which activates Ca_V1.2 channels by binding to a site formed by the transmembrane domains of the channel. Collectively, our results suggest that, in transient ischemia, increased Mg²⁺_i reduces stimulation of L-type Ca²⁺ current by the β-adrenergic receptor by directly acting on Ca_V1.2 channels in a cell-autonomous manner, effectively decreasing the metabolic stress imposed on VMs until blood flow can be reestablished.

Gene expression changes of interconnected spared cortical neurons 7 days after ischemic infarct of the primary motor cortex in the rat

After cortical injury resulting from stroke, some recovery can occur and may involve spared areas of the cerebral cortex reorganizing to assume functions previously controlled by the damaged cortical areas. No studies have specifically assessed gene expression changes in remote neurons with axonal processes that terminate in the infarcted tissue, i.e., the subset of neurons most likely to be involved in regenerative processes. By physiologically identifying the primary motor area controlling forelimb function in adult rats (caudal forelimb area = CFA), and injecting a retrograde tract-tracer, we labeled neurons within the non-primary motor cortex (rostral forelimb area = RFA) that project to CFA. Then, 7 days after a CFA infarct (n = 6), we used laser capture microdissection techniques to harvest labeled neurons in RFA. Healthy, uninjured rats served as controls (n = 6). Biological interactions and functions of gene profiling were investigated by Affymetrix Microarray, and Ingenuity Pathway Analysis. A total of 143 up- and 128 down-regulated genes showed significant changes (fold change ≥1.3 and p < 0.05). The canonical pathway, "Axonal Guidance Signaling," was overrepresented (p value = 0.002). Significantly overrepresented functions included: branching of neurites, organization of cytoskeleton, dendritic growth and branching, organization of cytoplasm, guidance of neurites, development of cellular protrusions, density of dendritic spines, and shape change (p = 0.000151-0.0487). As previous studies have shown that spared motor areas are important in recovery following injury to the primary motor area, the results suggest that these gene expression changes in remote, interconnected neurons may underlie reorganization and recovery mechanisms.

Assaying embryotoxicity in the test tube: current limitations of the embryonic stem cell test (EST) challenging its applicability domain

Testing for embryotoxicity in vitro is an attractive alternative to animal experimentation. The embryonic stem cell test (EST) is such a method, and it has been formally validated by the European Centre for the Validation of Alternative Methods. A number of recent studies have underscored the potential of this method. However, the EST performed well below the 78% accuracy expected from the validation study using a new set of chemicals and pharmaceutical compounds, and also of toxicity criteria, tested to enlarge the database of the validated EST as part of the Work Package III of the ReProTect Project funded within the 6th Framework Programme of the European Union. To assess the performance and applicability domain of the EST we present a detailed review of the substances and their effects in the EST being nitrofen, ochratoxin A, D-penicillamine, methylazoxymethanol, lovastatin, papaverine, warfarin, β-aminopropionitrile, dinoseb, furosemide, doxylamine, pravastatin, and metoclopramide. By delineation of the molecular mechanisms of the substances we identify six categories of reasons for misclassifications. Some of these limitations might also affect other in vitro methods assessing embryotoxicity. Substances that fall into these categories need to be included in future validation sets and in validation guidelines for embryotoxicity testing. Most importantly, we suggest conceivable improvements and additions to the EST which will resolve most of the limitations.

Rice heterotrimeric G-protein gamma subunits (RGG1 and RGG2) are differentially regulated under abiotic stress

Heterotrimeric G-proteins (α, β and γ subunits) are primarily involved in diverse signaling processes by transducing signals from an activated transmembrane G-protein coupled receptor (GPCR) to appropriate downstream effectors within cells. The role of α and β G-protein subunits in salinity and heat stress has been reported but the regulation of γ subunit of plant G-proteins in response to abiotic stress has not heretofore been described. In the present study we report the isolation of full-length cDNAs of two isoforms of Gγ [RGG1(I), 282 bp and RGG2(I), 453 bp] from rice (Oryza sativa cv Indica group Swarna) and described their transcript regulation in response to abiotic stresses. Protein sequence alignment and pairwise comparison of γ subunits of Indica rice [RGG(I)] with other known plant G-protein γ subunits demonstrated high homology to barley (HvGs) while soybean (GmG2) and Arabidopsis (AGG1) were least related. The numbers of the exons and introns were found to be similar between RGG1(I) and RGG2(I), but their sizes were different. Analyses of promoter sequences of RGG(I) confirmed the presence of stress-related cis-regulatory signature motifs suggesting their active and possible independent roles in abiotic stress signaling. The transcript levels of RGG1(I) and RGG2(I) were upregulated following NaCl, cold, heat and ABA treatments. However, in drought stress only RGG1(I) was upregulated. Strong support by transcript profiling suggests that γ subunits play a critical role via cross talk in signaling pathways. These findings provide first direct evidence for roles of Gγ subunits of rice G-proteins in regulation of abiotic stresses. These findings suggest the possible exploitation of γ subunits of G-protein machinery for promoting stress tolerance in plants.

Inhibition and Termination of Physiological Responses by GTPase Activating Proteins

Physiological processes are strictly organized in space and time. However, in cell physiology research, more attention is given to the question of space rather than to time. To function as a signal, environmental changes must be restricted in time; they need not only be initiated but also terminated. In this review, we concentrate on the role of one specific protein family involved in biological signal termination. GTPase activating proteins (GAPs) accelerate the endogenously low GTP hydrolysis rate of monomeric guanine nucleotide-binding proteins (GNBPs), limiting thereby their prevalence in the active, GTP-bound form. We discuss cases where defective or excessive GAP activity of specific proteins causes significant alteration in the function of the nervous, endocrine, and hemopoietic systems, or contributes to development of infections and tumors. Biochemical and genetic data as well as observations from human pathology support the notion that GAPs represent vital elements in the spatiotemporal fine tuning of physiological processes.

G protein-coupled receptors in the hypothalamic paraventricular and supraoptic nuclei--serpentine gateways to neuroendocrine homeostasis

G protein-coupled receptors (GPCRs) are the largest family of transmembrane receptors in the mammalian genome. They are activated by a multitude of different ligands that elicit rapid intracellular responses to regulate cell function. Unsurprisingly, a large proportion of therapeutic agents target these receptors. The paraventricular nucleus (PVN) and supraoptic nucleus (SON) of the hypothalamus are important mediators in homeostatic control. Many modulators of PVN/SON activity, including neurotransmitters and hormones act via GPCRs--in fact over 100 non-chemosensory GPCRs have been detected in either the PVN or SON. This review provides a comprehensive summary of the expression of GPCRs within the PVN/SON, including data from recent transcriptomic studies that potentially expand the repertoire of GPCRs that may have functional roles in these hypothalamic nuclei. We also present some aspects of the regulation and known roles of GPCRs in PVN/SON, which are likely complemented by the activity of 'orphan' GPCRs.

GPCRs regulate the assembly of a multienzyme complex for purine biosynthesis

G protein-coupled receptors (GPCRs) transmit exogenous signals to the nucleus, promoting a myriad of biological responses via multiple signaling pathways in both healthy and cancerous cells. However, little is known about the response of cytosolic metabolic pathways to GPCR-mediated signaling. Here we applied fluorescent live-cell imaging and label-free dynamic mass redistribution assays to study whether purine metabolism is associated with GPCR signaling. Through a library screen of GPCR ligands in conjunction with live-cell imaging of a metabolic multienzyme complex for de novo purine biosynthesis, the purinosome, we demonstrated that the activation of endogenous Gα(i)-coupled receptors correlates with purinosome assembly and disassembly in native HeLa cells. Given the implications of GPCRs in mitogenic signaling and of the purinosome in controlling metabolic flux via de novo purine biosynthesis, we hypothesize that regulation of purinosome assembly and disassembly may be one of the downstream events of mitogenic GPCR signaling in human cancer cells.

Boolean modeling of transcriptome data reveals novel modes of heterotrimeric G-protein action

Classical mechanisms of heterotrimeric G-protein signaling are observed to function in regulation of the transcriptome. Conversely, many theoretical regulatory modes of the G-protein are not manifested in the transcriptomes we investigate.

A new mechanism of G-protein signaling is revealed, in which the β subunit regulates gene expression identically in the presence or absence of the α subunit.

We find evidence of cross-talk between G-protein-mediated and hormone-mediated transcriptional regulation.

We find evidence of system specificity in G-protein signaling.

Heterotrimeric G-proteins, composed of α, β, and γ subunits, participate in a wide range of signaling pathways in eukaryotes (Morris and Malbon, 1999). According to the typical, mammalian paradigm, in its inactive state, the G-protein exists as an associated heterotrimer. G-protein signaling begins with ligand binding that results in a conformational change in a G-protein-coupled receptor (GPCR). Once activated by the GPCR, the Gα separates from the associated Gβγ dimer and the freed Gα and Gβγ proteins can then interact with downstream effector molecules, alone or in combination, to transduce the signal. Subsequent to signal propagation, Gα re-associates with the Gβγ dimer to reform the G-protein complex.

There are several classical routes for signal propagation through heterotrimeric G-proteins that have been categorized in mammalian systems (Marrari et al, 2007; Dupre et al, 2009). One route, which we designate classical I, requires the presence of both subunits, and can invoke one of two distinct mechanisms. In one mechanism, on GPCR activation, freed Gα and Gβγ each interact with downstream effectors to elicit the downstream response. In a related mechanism, Gα but not Gβγ interacts with downstream effectors, but the Gβγ dimer is nevertheless required to facilitate coupling of Gα with the relevant GPCR (Marrari et al, 2007). In a second route, which we designate classical II, it is solely the Gβγ dimer that interacts with downstream effectors; in this case, sequestration of Gβγ within the heterotrimer prevents signal propagation. In addition, a few non-classical G-protein regulatory modes have also been implicated in some systems, for example signaling by the intact heterotrimer in yeast (Klein et al, 2000; Frank et al, 2005). Observations such as these lead to a fundamental question, namely, which of all the theoretical regulatory modes of G-protein signaling are realized biologically. Our study answers this question in the context of the model plant Arabidopsis thaliana, and in addition analyzes the manner in which G-protein signaling couples with signaling by the plant hormone abscisic acid. The Arabidopsis genome encodes only one canonical Gα subunit, GPA1, and one canonical Gβ subunit, AGB1, and knockout mutants are available for each of these, allowing clear dissection of Gα- and Gβ-related phenotypes.

Abscisic acid (ABA) is a major plant hormone, which inhibits growth and promotes tolerance of abiotic stresses such as drought, salinity, and cold. ABA signaling is known to interact with heterotrimeric G-protein signaling in both developmental and stress responses in a complex manner, causing, for example, ABA hyposensitivity of guard cell stomatal opening in gpa1 and agb1 single mutants as well as agb1 gpa1 double mutants (Fan et al, 2008), but ABA hypersensitivity of the inhibition of seed germination and post-germination seedling development in the same mutants (Pandey et al, 2006). These experimental observations implicate G-proteins as one of the components of ABA signaling, but to date no systematic study has been conducted in either plant or metazoan systems to define the co-regulatory modes of a G-protein and a hormone.

In this study, we conduct genome-wide gene expression profiling in G-protein subunit mutants of A. thaliana guard cells and leaves, with or without treatment with ABA. By introducing one or more mediators acting downstream of the G-protein and ABA to control transcript levels, we propose nine G-protein/ABA signaling pathways including ABA-independent G-protein signaling pathways, G-protein-independent ABA signaling pathways, and seven distinct ABA–G-protein-coupled signaling pathways (Figure 1). We develop a Boolean modeling framework to systematically enumerate 14 possible theoretical regulatory modes of the G-protein and 142 co-regulatory modes of the G-protein and ABA, and then use a pattern matching approach to associate target genes with theoretical regulatory modes.

Our analysis shows that the G-protein regulatory mode that requires the presence of both Gα and Gβγ subunits (consistent with classical I mechanisms), is well represented in both guard cells and leaves. The G-protein regulatory mode that requires a freed Gβγ subunit (classical II G-protein regulatory mechanism) is well supported in guard cells and somewhat less so in leaves. In addition, a G-protein regulatory mode representing a non-classical regulatory mechanism is prevalent in guard cells but less so in leaves (Figure 5). In this regulatory mode, signaling by Gβ(γ) occurs, and this signaling is not regulated in any way by Gα.

By relating the target genes with the nine proposed G-protein/ABA signaling pathways, we are able to gauge the plausibility of regulatory modes of the G-protein and ABA at the pathway level. We find that G-protein-independent ABA signaling pathways are prevalent in both guard cells and leaves. The existence of an ABA-independent regulatory activity of the G-protein is well supported in guard cells, but not supported in leaves. Additive regulation by G-protein signaling plus G-protein-independent ABA signaling is rare in both guard cells and leaves. In addition, combinatorial cross-talk between G-protein signaling and ABA signaling and additive cross-talk between ABA–G-protein signaling and G-protein-independent ABA signaling are observed in both guard cells and leaves. Our transcriptome analysis indicates that in some cases, ABA definitely does not influence G-protein signaling, though it may do so in some other cases.

To investigate whether previously observed hypersensitivity or hyposensitivity of developmental and dynamic transient responses to ABA in G-protein mutants is recapitulated at the level of transcriptional regulation, we compare gene regulation by ABA in guard cells and leaves of the G-protein mutants versus wild type. We find that in guard cells, equal ABA hyposensitivity of all mutants combined is significant, although hyposensitivity in individual mutants is not. There is also a separate group of genes in guard cells that show ABA hypersensitivity in the gpa1 mutant, suggesting complex interactions between ABA and G-protein signaling in gene regulation in this cell type. In leaves, ABA hyposensitivity of gene expression in the three individual mutants and equal hyposensitivity in all mutants are strongly supported. In addition, several of the functional categories identified by our analysis of G-protein regulatory modes have been implicated in previous physiological analyses of G-protein mutants, providing validation to the biological interpretation of our results.

In summary, by conducting a genome-wide gene expression profiling study in G-protein subunit mutants of A. thaliana guard cells and leaves and developing a Boolean modeling framework, we systematically evaluate the biological utilization of mechanisms of G-protein regulatory action and reveal novel regulatory modes of the G-protein. The results generate empirical evidence and insights regarding molecular events of G-protein signaling and response at the physiological level in both plants and mammals.

Heterotrimeric G-proteins mediate crucial and diverse signaling pathways in eukaryotes. Here, we generate and analyze microarray data from guard cells and leaves of G-protein subunit mutants of the model plant Arabidopsis thaliana, with or without treatment with the stress hormone, abscisic acid. Although G-protein control of the transcriptome has received little attention to date in any system, transcriptome analysis allows us to search for potentially uncommon yet significant signaling mechanisms. We describe the theoretical Boolean mechanisms of G-protein × hormone regulation, and then apply a pattern matching approach to associate gene expression profiles with Boolean models. We find that (1) classical mechanisms of G-protein signaling are well represented. Conversely, some theoretical regulatory modes of the G-protein are not supported; (2) a new mechanism of G-protein signaling is revealed, in which Gβ regulates gene expression identically in the presence or absence of Gα; (3) guard cells and leaves favor different G-protein modes in transcriptome regulation, supporting system specificity of G-protein signaling. Our method holds significant promise for analyzing analogous ‘switch-like' signal transduction events in any organism.

Drug-induced regulation of target expression

Drug perturbations of human cells lead to complex responses upon target binding. One of the known mechanisms is a (positive or negative) feedback loop that adjusts the expression level of the respective target protein. To quantify this mechanism systems-wide in an unbiased way, drug-induced differential expression of drug target mRNA was examined in three cell lines using the Connectivity Map. To overcome various biases in this valuable resource, we have developed a computational normalization and scoring procedure that is applicable to gene expression recording upon heterogeneous drug treatments. In 1290 drug-target relations, corresponding to 466 drugs acting on 167 drug targets studied, 8% of the targets are subject to regulation at the mRNA level. We confirmed systematically that in particular G-protein coupled receptors, when serving as known targets, are regulated upon drug treatment. We further newly identified drug-induced differential regulation of Lanosterol 14-alpha demethylase, Endoplasmin, DNA topoisomerase 2-alpha and Calmodulin 1. The feedback regulation in these and other targets is likely to be relevant for the success or failure of the molecular intervention.

P2Y2 receptor-Gq/11 signaling at lipid rafts is required for UTP-induced cell migration in NG 108-15 cells

Lipid rafts, formed by sphingolipids and cholesterol within the membrane bilayer, are believed to have a critical role in signal transduction. P2Y(2) receptors are known to couple with G(q) family G proteins, causing the activation of phospholipase C (PLC) and an increase in intracellular Ca(2+) ([Ca(2+)](i)) levels. In the present study, we investigated the involvement of lipid rafts in P2Y(2) receptor-mediated signaling and cell migration in NG 108-15 cells. When NG 108-15 cell lysates were fractionated by sucrose density gradient centrifugation, Galpha(q/11) and a part of P2Y(2) receptors were distributed in a fraction where the lipid raft markers, cholesterol, flotillin-1, and ganglioside GM1 were abundant. Methyl-beta-cyclodextrin (CD) disrupted not only lipid raft markers but also Galpha(q/11) and P2Y(2) receptors in this fraction. In the presence of CD, P2Y(2) receptor-mediated phosphoinositide hydrolysis and [Ca(2+)](i) elevation were inhibited. It is noteworthy that UTP-induced cell migration was inhibited by CD or the G(q/11)-selective inhibitor YM254890 [(1R)-1-{(3S,6S,9S,12S,18R,21S,22R)-21-acetamido-18-benzyl-3-[(1R)-1-methoxyethyl]-4,9,10,12,16, 22-hexamethyl-15-methylene-2,5,8,11,14,17,-20-heptaoxo-1,19-dioxa-4,7,10,13,16-pentaazacyclodocosan-6-yl}-2-methylpropyl rel-(2S,3R)-2-acetamido-3-hydroxy-4-methylpentanoate]. Moreover CD and YM254890 completely inhibited Rho-A activation. Downstream of Rho-A signaling, stress fiber formation and phosphorylation of cofilin were also inhibited by CD or YM254890. However, UTP-induced phosphorylation of cofilin was not affected by the expression of p115-regulator of G protein signaling, which inhibits the G(12/13) signaling pathway. This implies that UTP-induced Rho-A activation was relatively regulated by the G(q/11) signaling pathway. These results suggest that lipid rafts are critical for P2Y(2) receptor-mediated G(q/11)-PLC-Ca(2+) signaling and this cascade is important for cell migration in NG 108-15 cells.

Changes in the gene expression of specific G-protein subunits correlate with morphine insensitivity in streptozotocin-induced diabetic rats

Several animal and human studies have shown a decreased analgesic potency of morphine in diabetic subjects. Since G-protein subunits have an important role in morphine effects at the cellular level and the exact mechanism(s) of diabetes-induced morphine insensitivity has not been fully clarified yet, the present study was designed to determine the changes in the levels of G(alphai), G(alphas), G(beta) mRNAs and proteins involved in this phenomenon. All experiments were carried out on male Wistar rats. The tail-flick test was used to assess the nociceptive threshold. Diabetes was induced by injection of 50 mg/kg (i.p.) streptozotocin. Four weeks after diabetes induction, the dorsal half of the lumbar spinal cord was assayed for the expression of G-protein subunits using semiquantitative RT-PCR and immunoblotting. The antinociceptive effect of intrathecal morphine (5, 10 and 15 microg i.t.) was significantly reduced in diabetic rats and these effects were reversed with insulin replacement. In diabetic animals, a significant increase in the mRNA levels of G(alphai) (23.5%) was observed in the dorsal portion of the lumbar spinal cord. The mRNA level of G(alphas) and G(beta) did not change. Following diabetes a significant decrease in the protein levels of G(alphai) was induced. In contrast, no significant changes were observed in the protein level of G(alphas) and G(beta). In diabetic animals that received insulin, levels of G(alphai) mRNA and protein were close to those in control rats. In conclusion, our results demonstrate that the expression pattern of the cellular components involved in morphine analgesia changes in diabetic animals. This may be, at least partly, responsible for diabetes-induced morphine insensitivity.

Role of transient receptor potential vanilloid 2 in LPS-induced cytokine production in macrophages

There is considerable evidence indicating that intracellular Ca2+ participates as a second messenger in TLR4-dependent signaling. However, how intracellular free Ca2+ concentrations ([Ca2+]i) is increased in response to LPS and how they affect cytokine production are poorly understood. Here we examined the role of transient receptor potential (TRP), a major Ca2+ permeation pathway in non-excitable cells, in the LPS-induced cytokine production in macrophages. Pharmacologic experiments suggested that TRPV family members, but neither TRPC nor TRPM family members, are involved in the LPS-induced TNFalpha and IL-6 production in RAW264 macrophages. RT-PCR and immunoblot analyses showed that TRPV2 is the sole member of TRPV family expressed in macrophages. ShRNA against TRPV2 inhibited the LPS-induced TNFalpha and IL-6 production as well as IkappaBalpha degradation. Experiments using BAPTA/AM and EGTA, and Ca2+ imaging suggested that the LPS-induced increase in [Ca2+]i involves both the TRPV2-mediated intracellular and extracellular Ca2+ mobilizations. BAPTA/AM abolished LPS-induced TNFalpha and IL-6 production, while EGTA only partially suppressed LPS-induced IL-6 production, but not TNFalpha production. These data indicate that TRPV2 is involved in the LPS-induced Ca2+ mobilization from intracellular Ca2+ store and extracellular Ca2+. In addition to Ca2+ mobilization through the IP3-receptor, TRPV2-mediated intracellular Ca2+ mobilization is involved in NFkappaB-dependent TNFalpha and IL-6 expression, while extracellular Ca2+ entry is involved in NFkappaB-independent IL-6 production.

Aminergic control and modulation of honeybee behaviour

Biogenic amines are important messenger substances in the central nervous system and in peripheral organs of vertebrates and of invertebrates. The honeybee, Apis mellifera, is excellently suited to uncover the functions of biogenic amines in behaviour, because it has an extensive behavioural repertoire, with a number of biogenic amine receptors characterised in this insect.In the honeybee, the biogenic amines dopamine, octopamine, serotonin and tyramine modulate neuronal functions in various ways. Dopamine and serotonin are present in high concentrations in the bee brain, whereas octopamine and tyramine are less abundant. Octopamine is a key molecule for the control of honeybee behaviour. It generally has an arousing effect and leads to higher sensitivity for sensory inputs, better learning performance and increased foraging behaviour. Tyramine has been suggested to act antagonistically to octopamine, but only few experimental data are available for this amine. Dopamine and serotonin often have antagonistic or inhibitory effects as compared to octopamine.Biogenic amines bind to membrane receptors that primarily belong to the large gene-family of GTP-binding (G) protein coupled receptors. Receptor activation leads to transient changes in concentrations of intracellular second messengers such as cAMP, IP(3) and/or Ca(2+). Although several biogenic amine receptors from the honeybee have been cloned and characterised more recently, many genes still remain to be identified. The availability of the completely sequenced genome of Apis mellifera will contribute substantially to closing this gap.In this review, we will discuss the present knowledge on how biogenic amines and their receptor-mediated cellular responses modulate different behaviours of honeybees including learning processes and division of labour.

Live cell optical sensing for high throughput applications

Live cell optical sensing employs label-free optical biosensors to non-invasively measure stimulus-induced dynamic mass redistribution (DMR) in live cells within the sensing volume of the biosensor. The resultant DMR signal is an integrated cellular response, and reflects cell signaling mediated through the cellular target(s) with which the stimulus intervenes. This article describes the uses of live cell optical sensing for probing cell biology and ligand pharmacology, with an emphasis of resonant waveguide grating biosensor cellular assays for high throughput applications.

Gbetagamma-mediated growth and developmental control in Aspergillus fumigatus

The roles of the Gbetagamma subunits of the opportunistic human pathogen Aspergillus fumigatus were investigated. The predicted AfuSfaD (Gbeta) protein consists of 353 amino acids and shows 94-98% similarity with other Aspergillus Gbeta subunits. AfuGpgA consists of 90 amino acids showing 95-98% identity with other fungal G-protein gamma subunits. The deletion (Delta) of AfusfaD or AfugpgA resulted in severe impairment in vegetative growth, conidial germination and conidial trehalose breakdown. While the total number of conidia produced by DeltaAfusfaD and DeltaAfugpgA strains on solid medium was only about 1% of wild type, the growth-adjusted conidiation levels were twofold higher than those of wild type. Enhanced formation of conidiophores and elevated AfubrlA mRNA levels were observable in DeltaAfusfaD or DeltaAfugpgA strains in liquid submerged culture. Moreover, overexpression of AfusfaD or AfugpgA caused reduced levels of submerged culture conidiation, indicating that Gbetagamma is involved in negative regulation of conidiation. Gliotoxin and other metabolites were not detected in the chloroform extracts of DeltaAfusfaD and DeltaAfugpgA culture filtrates. Northern blot analyses revealed that, while AfulaeA mRNA levels unchanged, accumulation of gliZ mRNA was delayed by DeltaAfusfaD or DeltaAfugpgA. A model summarizing the roles of AfusfaD and AfugpgA in A. fumigatus is presented.

Modulation of alpha2-adrenoceptor functions by heterotrimeric Galphai protein isoforms

Subtype diversity of heterotrimeric G proteins and G protein-coupled receptors enables a wide spectrum of signal transduction. However, the significance of isoforms within receptor or G protein subfamilies has not been fully elucidated. In the present study, we have tested whether alpha(2)-adrenoceptors require specific Galpha isoforms for their function in vivo. In particular, we analyzed the role of the highly homologous Galpha(i) isoforms, Galpha(i1), Galpha(i2), and Galpha(i3), in typical alpha(2)-adrenoceptor-controlled functions. Mice with targeted deletions in the genes encoding Galpha(i1), Galpha(i2), or Galpha(i3) were used to test the effects of alpha(2)-adrenoceptor stimulation by the agonist medetomidine. The alpha(2)-adrenoceptor agonist medetomidine inhibited [(3)H]norepinephrine release from isolated prefrontal brain cortex or cardiac atria tissue specimens with similar potency and efficacy in tissues from wild-type or Galpha(i)-deficient mice. In vivo, bradycardia, hypotension, induction of sleep, antinociception, and hypothermia induced by alpha(2)-adrenoceptor activation did not differ between wild-type and Galpha(i)-knockout mice. However, the effects of the alpha(2)-agonists medetomidine or 5-bromo-6-(2-imidazolin-2-ylamino)quin-oxaline tartrate (UK14,304) on spontaneous locomotor activity or anesthetic sparing were reduced or absent, respectively, in mice lacking Galpha(i2). In microdissected locus coeruleus neurons or postganglionic sympathetic neurons from stellate ganglia, all three Galpha(i) subunits were expressed as determined by quantitative reverse transcription-polymerase chain reaction, with Galpha(i1) and Galpha(i2) dominating over Galpha(i3). Functional redundancy of the highly homologous Galpha(i) isoforms may predominate over specificity to regulate distinct intracellular pathways downstream of alpha(2)-adrenoceptors in vivo. In contrast, inhibition of locomotor activity and anesthetic sparing may be elicited by a specific coupling of alpha(2A)-adrenoceptors via the Galpha(i2) isoform to intracellular pathways.

Resonant waveguide grating biosensor for whole-cell GPCR assays

Current drug discovery campaigns for G protein-coupled receptors (GPCRs) heavily rely on assay technologies that use artificial cell systems tailored to a point-of-contact readout and as a consequence are mostly pathway biased. Recently, we have developed label-free optical biosensor cellular assays that are capable of examining systems cell biology of endogenous receptors and systems cell pharmacology of GPCR ligands in both physiologically and disease relevant environments. We have shown that these biosensor assays enable high-throughput screening of pathway-biased ligands acting on endogenous beta(2)-adrenergic receptor in cells. These biosensor cellular assays hold the potential to reduce attrition rates in drug discovery and development process.

Functional and Molecular Alterations in T Cells Induced by CCL5

To delineate whether, and the extent to which, CCL5 could impact T cell function we examined cytokine production and proliferative ability following CCL5 treatment in vitro. We report a decreased ability of splenic T cells to produce IFN-? and TNF-a as well as proliferate in response to crosslinking with antibody to CD3 after 72, but not 24 hours of CCL5 exposure. To identify a mechanism by which CCL5 modulated T cell function, we examined T cell receptor translocation and lipid raft clustering. After exposure to CCL5, T cells were less efficient at translocating the TCR and clustering lipid rafts. Since TCR translocation and lipid raft clustering are required for creation of an immunological synapse, these data suggest that extended exposure to CCL5 may impact T cell effector function by modulating the ability to create a functional immunological synapse.

Neuronostatin inhibits cardiac contractile function via a protein kinase A- and JNK-dependent mechanism in murine hearts

Neuronostatin, a newly identified peptide hormone sharing the same precursor with somatostatin, exerts multiple pharmacological effects in gastrointestinal tract, hypothalamus, and cerebellum. However, the cardiovascular effect of neuronostatin is unknown. The aim of this study was to elucidate the impact of neuronostatin on cardiac contractile function in murine hearts and isolated cardiomyocytes. Short-term exposure of neuronostatin depressed left ventricular developed pressure (LVDP), maximal velocity of pressure development (+/-dP/dt), and heart rate in Langendorff heart preparation. Consistently, neuronostatin inhibited peak shortening (PS) and maximal velocity of shortening/relengthening (+/-dL/dt) without affecting time-to-PS (TPS) and time-to-90% relengthening (TR(90)) in cardiomyocytes. The neuronostatin-elicited cardiomyocyte mechanical responses were mimicked by somatostatin, the other posttranslational product of preprosomatostatin. Furthermore, the neuronostatin-induced cardiomyocyte mechanical effects were ablated by the PKA inhibitor H89 (1 microM) and the Jun N-terminal kinase (JNK) inhibitor SP600125 (20 microM). The PKC inhibitor chelerythrine (1 microM) failed to alter neuronostatin-induced cardiomyocyte mechanical responses. To the contrary, chelerythrine, but not H89, abrogated somatostatin-induced cardiomyocyte contractile responses. Our results also showed enhanced c-fos and c-jun expression in response to neuronostatin exposure (0.5 to 2 h). Taken together, our data suggest that neuronostatin is a peptide hormone with overt cardiac depressant action. The neuronostatin-elicited cardiac contractile response appears to be mediated, at least in part, through a PKA- and/or JNK-dependent mechanism.

Whole proteome identification of plant candidate G-protein coupled receptors in Arabidopsis, rice, and poplar: computational prediction and in-vivo protein coupling

Computational prediction and in vivo protein coupling experiments identify candidate plant G-protein coupled receptors in Arabidopsis, rice and poplar.

Background

The classic paradigm of heterotrimeric G-protein signaling describes a heptahelical, membrane-spanning G-protein coupled receptor that physically interacts with an intracellular Gα subunit of the G-protein heterotrimer to transduce signals. G-protein coupled receptors comprise the largest protein superfamily in metazoa and are physiologically important as they sense highly diverse stimuli and play key roles in human disease. The heterotrimeric G-protein signaling mechanism is conserved across metazoa, and also readily identifiable in plants, but the low sequence conservation of G-protein coupled receptors hampers the identification of novel ones. Using diverse computational methods, we performed whole-proteome analyses of the three dominant model plant species, the herbaceous dicot Arabidopsis thaliana (mouse-eared cress), the monocot Oryza sativa (rice), and the woody dicot Populus trichocarpa (poplar), to identify plant protein sequences most likely to be GPCRs.

Results

Our stringent bioinformatic pipeline allowed the high confidence identification of candidate G-protein coupled receptors within the Arabidopsis, Oryza, and Populus proteomes. We extended these computational results through actual wet-bench experiments where we tested over half of our highest ranking Arabidopsis candidate G-protein coupled receptors for the ability to physically couple with GPA1, the sole Gα in Arabidopsis. We found that seven out of eight tested candidate G-protein coupled receptors do in fact interact with GPA1. We show through G-protein coupled receptor classification and molecular evolutionary analyses that both individual G-protein coupled receptor candidates and candidate G-protein coupled receptor families are conserved across plant species and that, in some cases, this conservation extends to metazoans.

Conclusion

Our computational and wet-bench results provide the first step toward understanding the diversity, conservation, and functional roles of plant candidate G-protein coupled receptors.

Role of beta-adrenoceptor signaling in skeletal muscle: implications for muscle wasting and disease

The importance of beta-adrenergic signaling in the heart has been well documented, but it is only more recently that we have begun to understand the importance of this signaling pathway in skeletal muscle. There is considerable evidence regarding the stimulation of the beta-adrenergic system with beta-adrenoceptor agonists (beta-agonists). Although traditionally used for treating bronchospasm, it became apparent that some beta-agonists could increase skeletal muscle mass and decrease body fat. These so-called "repartitioning effects" proved desirable for the livestock industry trying to improve feed efficiency and meat quality. Studying beta-agonist effects on skeletal muscle has identified potential therapeutic applications for muscle wasting conditions such as sarcopenia, cancer cachexia, denervation, and neuromuscular diseases, aiming to attenuate (or potentially reverse) the muscle wasting and associated muscle weakness, and to enhance muscle growth and repair after injury. Some undesirable cardiovascular side effects of beta-agonists have so far limited their therapeutic potential. This review describes the physiological significance of beta-adrenergic signaling in skeletal muscle and examines the effects of beta-agonists on skeletal muscle structure and function. In addition, we examine the proposed beneficial effects of beta-agonist administration on skeletal muscle along with some of the less desirable cardiovascular effects. Understanding beta-adrenergic signaling in skeletal muscle is important for identifying new therapeutic targets and identifying novel approaches to attenuate the muscle wasting concomitant with many diseases.

Post-adrenalectomy changes in the gene expression of specific G-protein subunits involved in morphine sensitization

There are some reports indicating that adrenalectomy significantly potentiates morphine-induced analgesia. Since G-protein subunits have an important role in morphine effects at the cellular level and the exact mechanism(s) of adrenalectomy-induced morphine sensitization has not yet been clarified, the present study was designed to determine the changes in the levels of Galphai/o, Galphas, Gbeta mRNA involved in this phenomenon. All experiments were carried out on male Wistar rats. The tail-flick test was used to assess the nociceptive threshold and corticosterone levels were measured by radioimmunoassay as a marker of HPA function. The dorsal half of the lumbar spinal cord was assayed for the expression of G-protein subunits using semiquantitative PCR normalized to beta-actin gene expression. Results showed that morphine not only in 3 mg/kg, but also in a sub-effective dose (2 mg/kg) could affect the nociceptive threshold and induce an analgesic response in adrenalectomized (ADX) rats while 2 mg/kg morphine did not demonstrate analgesic properties in sham-operated animals. These effects were reversed with corticosterone replacement. Morphine increased plasma corticosterone concentration in a dose-dependent manner in sham-operated rats. Following adrenalectomy a significant increase in the mRNA levels of Galphai/o (79%) and Gbeta (96%) was observed in the dorsal portion of the lumbar spinal cord. In contrast, no significant changes were observed in the mRNA level of Galphas. In conclusion, our results demonstrate that the levels of the cellular components involved in morphine analgesia significantly increase in ADX animals. This may be at least partly responsible for adrenalectomy-induced morphine sensitization.

Membranes: a meeting point for lipids, proteins and therapies

Membranes constitute a meeting point for lipids and proteins. Not only do they define the entity of cells and cytosolic organelles but they also display a wide variety of important functions previously ascribed to the activity of proteins alone. Indeed, lipids have commonly been considered a mere support for the transient or permanent association of membrane proteins, while acting as a selective cell/organelle barrier. However, mounting evidence demonstrates that lipids themselves regulate the location and activity of many membrane proteins, as well as defining membrane microdomains that serve as spatio-temporal platforms for interacting signalling proteins. Membrane lipids are crucial in the fission and fusion of lipid bilayers and they also act as sensors to control environmental or physiological conditions. Lipids and lipid structures participate directly as messengers or regulators of signal transduction. Moreover, their alteration has been associated with the development of numerous diseases. Proteins can interact with membranes through lipid co-/post-translational modifications, and electrostatic and hydrophobic interactions, van der Waals forces and hydrogen bonding are all involved in the associations among membrane proteins and lipids. The present study reviews these interactions from the molecular and biomedical point of view, and the effects of their modulation on the physiological activity of cells, the aetiology of human diseases and the design of clinical drugs. In fact, the influence of lipids on protein function is reflected in the possibility to use these molecular species as targets for therapies against cancer, obesity, neurodegenerative disorders, cardiovascular pathologies and other diseases, using a new approach called membrane-lipid therapy.

Effects of single administration of morphine on G-protein mRNA level in the presence and absence of inflammation in the rat spinal cord

Antinociceptive potency of opioids is greater against various noxious stimuli in animals with peripheral inflammation. Opioid agonists stimulate activation of G-protein-coupled receptor. Changes in the resting levels of G-protein subtypes could have an effect on intracellular signalling pathways. The present study was designed to investigate the effects of analgesic morphine treatment on the level G-protein subunits mRNA in the presence and absence of inflammation. Our results showed that the carrageenan administration increased G-protein subunits. Administration of analgesic dose of morphine alone and in the presence of inflammation induced different alterations in the levels of G-protein mRNA. Taken together, the results obtained using real time RT-PCR suggested that G-protein genes expression levels following the acute administration of morphine between animals with and without inflammation could influence, at least in part, analgesic responsiveness.

Galphaz negatively regulates insulin secretion and glucose clearance

Relatively little is known about the in vivo functions of the alpha subunit of the heterotrimeric G protein Gz (Galphaz). Clues to one potential function recently emerged with the finding that activation of Galphaz inhibits glucose-stimulated insulin secretion in an insulinoma cell line (Kimple, M. E., Nixon, A. B., Kelly, P., Bailey, C. L., Young, K. H., Fields, T. A., and Casey, P. J. (2005) J. Biol. Chem. 280, 31708-31713). To extend this study in vivo, a Galphaz knock-out mouse model was utilized to determine whether Galphaz function plays a role in the inhibition of insulin secretion. No differences were discovered in the gross morphology of the pancreatic islets or in the islet DNA, protein, or insulin content between Galphaz-null and wild-type mice. There was also no difference between the insulin sensitivity of Galphaz-null mice and wild-type controls, as measured by insulin tolerance tests. Galphaz-null mice did, however, display increased plasma insulin concentrations and a corresponding increase in glucose clearance following intraperitoneal and oral glucose challenge as compared with wild-type controls. The increased plasma insulin observed in Galphaz-null mice is most likely a direct result of enhanced insulin secretion, since pancreatic islets isolated from Galphaz-null mice exhibited significantly higher glucose-stimulated insulin secretion than those of wild-type mice. Finally, the increased insulin secretion observed in Galphaz-null islets appears to be due to the relief of a tonic inhibition of adenylyl cyclase, as cAMP production was significantly increased in Galphaz-null islets in the absence of exogenous stimulation. These findings indicate that Galphaz may be a potential new target for therapeutics aimed at ameliorating beta-cell dysfunction in Type 2 diabetes.