Aplindore (DAB-452), a high affinity selective dopamine D2 receptor partial agonist

The pharmacology of aplindore (DAB-452) was characterized in CHO-K1 cells stably transfected with the human dopamine D(2) receptor short isoform (CHO-D(2s)) and in a behavioral model for post-synaptic agonism in rats. In [(3)H]-spiperone competition binding studies, aplindore showed high affinity for dopamine D(2) and D(3) receptors and low affinity for the dopamine D(4), serotonin (5-HT)(1A), 5-HT(2) receptors and the alpha1-adrenoceptor. The high potency partial agonist activity of aplindore was demonstrated in [(35)S]guanosine 5'-O-(3-thiotriphosphate) ([(35)S]GTPgammaS) binding, extracellular signal-regulated kinase (ERK)-phosphorylation and intracellular calcium flux assay using fluorometric plate reader ([Ca(2+)](i)-FLIPR) format. The [Ca(2+)](i)-FLIPR assay was conducted with CHO-D(2S) receptor cells also stably expressing chimeric G(alphaq/o)-proteins. In all assay modalities, the potencies and intrinsic activities of aplindore were lower than dopamine and higher than aripiprazole. In contrast to the [(35)S]GTPgammaS binding and ERK-phosphorylation assays, the [Ca(2+)](i)-FLIPR assay was able to detect the low partial agonist activity of SDZ 208-912. In unilaterally 6-hydroxydopamine (6-OHDA) lesioned rats, aplindore induced contralateral turning, which was blocked by the dopamine D(2) receptor antagonist raclopride. The dopamine D(2) receptor selective partial agonist profile of aplindore suggests that it should be effective for the treatment of dopaminergic-based disorders, such as schizophrenia and Parkinson's disease.

Two Glucose-sensing Pathways Converge on Rgt1 to Regulate Expression of Glucose Transporter Genes in Saccharomyces cerevisiae

The yeast Saccharomyces cerevisiae deploys two different types of glucose sensors on its cell surface that operate in distinct glucose signaling pathways: the glucose transporter-like Snf3 and Rgt2 proteins and the Gpr1 receptor that is coupled to Gpa2, a G-protein alpha subunit. The ultimate target of the Snf3/Rgt2 pathway is Rgt1, a transcription factor that regulates expression of HXT genes encoding glucose transporters. We have found that the cAMP-dependent protein kinase A (PKA), which is activated by the Gpr1/Gpa2 glucose-sensing pathway and by a glucose-sensing pathway that works through Ras1 and Ras2, catalyzes phosphorylation of Rgt1 and regulates its function. Rgt1 is phosphorylated in vitro by all three isoforms of PKA, and this requires several serine residues located in PKA consensus sequences within Rgt1. PKA and the consensus serine residues of Rgt1 are required for glucose-induced removal of Rgt1 from the HXT promoters and for induction of HXT expression. Conversely, overexpression of the TPK genes led to constitutive expression of the HXT genes. The PKA consensus phosphorylation sites of Rgt1 are required for an intramolecular interaction that is thought to regulate its DNA binding activity. Thus, two different glucose signal transduction pathways converge on Rgt1 to regulate expression of glucose transporters.

Activation of the phosphatidylinositol 3-kinase Vps34 by a G protein alpha subunit at the endosome

In the yeast Saccharomyces cerevisiae, the G protein beta gamma subunits are essential for pheromone signaling. The Galpha subunit Gpa1 can also promote signaling, but the effectors in this pathway are not well characterized. To identify candidate Gpa1 effectors, we expressed the constitutively active Gpa1(Q323L) mutant in each of nearly 5000 gene-deletion strains and measured mating-specific responses. Our analysis reveals a requirement for both the catalytic (Vps34) and regulatory (Vps15) subunits of the sole phosphatidylinositol 3-kinase in yeast. We demonstrate that Gpa1 is present at endosomes, where it interacts directly with both Vps34 and Vps15 and stimulates increased production of phosphatidylinositol 3-phosphate. Notably, Vps15 binds to GDP-bound Gpa1 and is predicted to have a seven-WD repeat structure similar to that of known G protein beta subunits. These findings reveal two new components of the pheromone signaling pathway. More remarkably, these proteins appear to comprise a preformed effector-G beta subunit assembly and function at the endosome rather than at the plasma membrane.

Molecular characterization of a G protein alpha-subunit-encoding gene from Mucor circinelloides

Genes encoding the Galpha subunit were cloned from Mucor circinelloides, a zygomycete dimorphic fungus. There are at least four genes that encode for Galpha subunits, gpa1, gpa2, gpa3, and gpa4. The genes gpa1 and gpa3 were isolated and characterized, and their predicted products showed 36%-67% identity with Galpha subunits from diverse fungi. Northern blot analysis of gpa3 showed that it is present in spores and constitutively expressed during mycelium development and during yeast-mycelium and mycelium-yeast transitions. However, during yeast cell growth, decreased levels of mRNA were observed. Sequence analysis of gpa3 cDNA revealed that Gpa3 encodes a polypeptide of 356 amino acids with a calculated molecular mass of 40.8 kDa. The deduced sequence of Gpa3 protein contains all the consensus regions of Galpha subunits of the Galpha(i/o/t) subfamily except the cysteine near the C terminus for potential ADP-ribosylation by pertussis toxin. This cDNA was expressed in Escherichia coli and purified by affinity chromatography. Based on its electrophoretic mobility in SDS-PAGE, the molecular mass of the His6-tagged Gpa3 was 45 kDa. The recombinant protein was recognized by a polyclonal antibody against a fragment of a human Galpha(i/o/t). Furthermore, the recombinant Gpa3 was ADP-ribosylated by activated cholera toxin and [32P]NAD but not by pertussis toxin. These results indicate that in M. circinelloides the Galpha subunit Gpa3 is expressed constitutively during differentiation.

Mechanism of action and structural requirements of constrained peptide inhibitors of RGS proteins

Regulators of G-protein signaling (RGS) accelerate guanine triphosphate hydrolysis by Galpha-subunits and profoundly inhibit signaling by G protein-coupled receptors. The distinct expression patterns and pathophysiologic regulation of RGS proteins suggest that inhibitors may have therapeutic potential. We previously reported the design of a constrained peptide inhibitor of RGS4 (1: Ac-Val-Lys-[Cys-Thr-Gly-Ile-Cys]-Glu-NH2, S-S) based on the structure of the Galphai switch 1 region but its mechanism of action was not established. In the present study, we show that 1 inhibits RGS4 by mimicking and competing for binding with the switch 1 region of Galphai and that peptide 1 shows selectivity for RGS4 and RGS8 versus RGS7. Structure-activity relationships of analogs related to 1 are described that illustrate key features for RGS inhibition. Finally, we demonstrate activity of the methylene dithioether-bridged peptide inhibitor, 2, to modulate muscarinic receptor-regulated potassium currents in atrial myocytes. These data support the proposed mechanism of action of peptide RGS inhibitors, demonstrate their action in native cells, and provide a starting point for the design of RGS inhibitor drugs.

Quantitative assessment of olfactory receptors activity in immobilized nanosomes: a novel concept for bioelectronic nose

We describe how mammalian olfactory receptors (ORs) could be used as sensing elements of highly specific and sensitive bioelectronic noses. An OR and an appropriate G(alpha) protein were co-expressed in Saccharomyces cerevisiae cells from which membrane nanosomes were prepared, and immobilized on a sensor chip. By Surface Plasmon Resonance, we were able to quantitatively evaluate OR stimulation by an odorant, and G protein activation. We demonstrate that ORs in nanosomes discriminate between odorant ligands and unrelated odorants, as in whole cells. This assay also provides the possibility for quantitative assessment of the coupling efficiency of the OR with different G(alpha) subunits, without the interference of the cellular transduction pathway. Our findings will be useful to develop a new generation of electronic noses for detection and discrimination of volatile compounds, particularly amenable to micro- and nano-sensor formats.

A simple statistical method for estimating type-II (cluster-specific) functional divergence of protein sequences

Predicting functional amino acid residues in silico is important for comparative genomics. In this paper, we focus on the issue of how to statistically identify cluster-specific amino acid residues that are related to the functional divergence after gene duplication. We approach this problem using a framework based on site-specific shift of amino acid property (type-II functional divergence), as opposed to site-specific shift of evolutionary rate (type-I functional divergence). An efficient statistical procedure is implemented to facilitate the development of phylogenomic database for cluster-specific residues of large-scale protein families. Our method has the following features: 1) statistical testing of the type-II functional divergence and 2) the site-specific Bayesian profile to measure how amino acid residues contribute to type-II (cluster-specific) functional divergence. Consequently, one may obtain the posterior probability for "functional" cluster-specific residues. Case studies are presented and indicate that radical cluster-specific residues are responsible for most of inferred type-II functional divergence, whereas conserved cluster-specific residues appear less than even those imperfect radical cluster-specific residues to this type of functional divergence.

Differential roles of Arabidopsis heterotrimeric G-protein subunits in modulating cell division in roots

Signaling through heterotrimeric G proteins is conserved in diverse eukaryotes. Compared to vertebrates, the simpler repertoire of G-protein complex and accessory components in Arabidopsis (Arabidopsis thaliana) offers a unique advantage over all other multicellular, genetic-model systems for dissecting the mechanism of G-protein signal transduction. One of several biological processes that the G-protein complex regulates in Arabidopsis is cell division. We determined cell production rate in the primary root and the formation of lateral roots in Arabidopsis to define individually the types of modulatory roles of the respective G-protein alpha- and beta-subunits, as well as the heterotrimer in cell division. The growth rate of the root is in part a consequence of cell cycle maintenance in the root apical meristem (RAM), while lateral root production requires meristem formation by founder pericycle cells. Thus, a comparison of these two parameters in various genetic backgrounds enabled dissection of the role of the G-protein subunits in modulation of cell division, both in maintenance and initiation. Cell production rates were determined for the RAM and lateral root formation in gpa1 (Arabidopsis G-protein alpha-subunit) and agb1 (Arabidopsis G-protein beta-subunit) single and double mutants, and in transgenic lines overexpressing GPA1 or AGB1 in agb1 or gpa1 mutant backgrounds, respectively. We found in the RAM that the heterotrimeric complex acts as an attenuator of cell proliferation, whereas the GTP-bound form of the Galpha-subunit's role is a positive modulator. In contrast, for the formation of lateral roots, the Gbetagamma-dimer acts largely independently of the Galpha-subunit to attenuate cell division. These results suggest that Arabidopsis heterotrimeric G-protein subunits have differential and opposing roles in the modulation of cell division in roots.

Identification of a second-site suppressor mutation of the GTPase defect associated with McCune-Albright syndrome: a model using the yeast heterotrimeric G protein, GPA1

McCune-Albright syndrome (MAS) causes a variety of bone and endocrine abnormalities due to the post-zygotic mutation of the alpha subunit of the stimulatory G-protein Gsalpha. This mutation causes signal-independent activity of the G-protein in the affected cells. We report the development of a system to study the effects of MAS mutations using Saccharomyces cerevisiae, wherein activation of the yeast G-protein pathway results in growth arrest in a genetically recessive fashion. We introduced the MAS mutation into the analogous site in the yeast Galpha gene, GPA1 and randomly mutated the gene to produce intragenic suppressors. Yeast with normal and mutated G-protein genes were induced to lose the normal gene, and mutations able to intragenically suppress the constitutive activity of the MAS mutation were identified based on their ability to form colonies. We report one mutation in GPA1, also in the active site, that is an intragenic suppressor of the MAS defect.

New roles for Galpha and RGS proteins: communication continues despite pulling sisters apart

Large G protein alpha subunits and their attendant regulators of G-protein signaling (RGS) proteins control both intercellular signaling and asymmetric cell divisions by distinct pathways. The classical pathway, found throughout higher eukaryotic organisms, mediates intercellular communication via hormone binding to G-protein-coupled receptors (GPCRs). Recent studies have led to the discovery of GPCR-independent activation of Galpha subunits by the guanine nucleotide exchange factor RIC-8 in both asymmetric cell division and synaptic vesicle priming in metazoan organisms. Protein-protein interactions and protein function in each pathway are driven through the cycle of GTP binding and hydrolysis by the Galpha subunit. This review builds a conceptual framework for understanding RIC-8-mediated pathways by comparison with the mechanism of classical G-protein activation and inhibition in GPCR signaling.

The molecular phylogeny of a nematode-specific clade of heterotrimeric G-protein alpha-subunit genes

In animal olfactory systems, odorant molecules are detected by olfactory receptors (ORs). ORs are part of the G-protein-coupled receptor (GPCR) superfamily. Heterotrimeric guanine nucleotide binding G-proteins (G-proteins) relay signals from GPCRs to intracellular effectors. G-proteins are comprised of three peptides. The G-protein alpha subunit confers functional specificity to G-proteins. Vertebrate and insect Galpha-subunit genes are divided into four subfamilies based on functional and sequence attributes. The nematode Caenorhabditis elegans contains 21 Galpha genes, 14 of which are exclusively expressed in sensory neurons. Most individual mammalian cells express multiple distinct GPCR gene products, however, individual mammalian and insect olfactory neurons express only one functional odorant OR. By contrast C. elegans expresses multiple ORs and multiple Galpha subunits within each olfactory neuron. Here we show that, in addition to having at least one member of each of the four mammalian Galpha gene classes, C. elegans and other nematodes also possess two lineage-specific Galpha gene expansions, homologues of which are not found in any other organisms examined. We hypothesize that these novel nematode-specific Galpha genes increase the functional complexity of individual chemosensory neurons, enabling them to integrate odor signals from the multiple distinct ORs expressed on their membranes. This neuronal gene expansion most likely occurred in nematodes to enable them to compensate for the small number of chemosensory cells and the limited emphasis on cephalization during nematode evolution.

Ric-8B promotes functional expression of odorant receptors

Odorants are detected by a large family of odorant receptors (ORs) expressed in the nose. The information provided by the ORs is transmitted to specific regions of the brain, leading to odorant perception. The determination of the odorant specificities of the different ORs will contribute to the understanding of how odorants are discriminated by the olfactory system. However, to date only a few ORs have been linked to odorants they recognize, because ORs are poorly expressed on the cell surface of heterologous cells. Here we show that Ric-8B, a putative guanine nucleotide exchange factor for Galphaolf, promotes efficient heterologous expression of ORs. Our results also show that Ric-8B enhances accumulation of Galphaolf at the cell periphery, indicating that it promotes functional OR expression by improving the efficiency of OR coupling to Galphaolf. Expression systems containing Galphaolf and Ric-8B should contribute to the functional characterization of ORs.

Mutation R238E in transducin-alpha yields a GTPase and effector-deficient, but not dominant-negative, G-protein alpha-subunit

PURPOSE

Certain forms of inherited and light-induced retinal degenerations are believed to involve excessive phototransduction signaling. A dominant-negative mutant of the visual G-protein, transducin, would represent a major tool in designing potential therapeutical strategies for this group of visual diseases. We thought to further investigate a novel mutant of the transducin-alpha subunit, R238E, that was recently reported to be a dominant-negative inhibitor of the rhodopsin/transducin/PDE visual system.

METHODS

The R238E substitution was introduced into a tranducin-like chimeric Gtalpha*-subunit. The nucleotide-bound state of the Gtalpha*R238E mutant was assessed using the trypsin-protection assay. The ability of the Gtalpha*R238E mutant to interact with Gtbetagamma, couple to photoexcited rhodopsin (R*), and undergo R*-stimulated guanine nucleotide exchange was examined by a GTPgammaS binding assay. The GTPase activity of the mutant Gtalpha* and its interaction with RGS proteins was characterized in the steady-state and single turnover measurements of GTP hydrolysis. A binding assay utilizing the fluorescently-labeled gamma-subunit of PDE6 (Pgamma) was employed to monitor the effector function of Gtalpha*R238E.

RESULTS

The Gtalpha*R238E mutant bound GDP and was capable of the AlF4--induced activational conformational change. The capacity of Gtalpha*R238E to couple to R* in the presence of Gtbetagamma was similar to that of Gtalpha*. However, the mutant GTPase activity was markedly impaired. This defect was further exacerbated by the diminished interactions of Gtalpha*R238E with the GAP proteins, RGS9 and RGS16. Another consequence of the mutation was the reduction in Gtalpha*R238E's affinity for Pgamma.

CONCLUSIONS

Transducin mutant Gtalpha*R238E exists in a nucleotide-bound state and is fully capable of activational coupling to R*. This mutation results in a significant impairment of Gtalpha*'s ability to hydrolyze GTP and interact with the inhibitory subunit of PDE6. This phenotype is entirely inconsistent with that of a dominant-negative inhibitor as recently reported.

Transcriptional activation of c-Fos by constitutively active Galpha(16)QL through a STAT1-dependent pathway

Hematopoietic restrictive Galpha(16) has long been known to stimulate phospholipase Cbeta (PLCbeta) and induce mitogen-activated protein kinase (MAPK) phosphorylation. Recently, we have demonstrated that Galpha(16) is capable of inducing the phosphorylation and transcriptional activation of transcription factors, such as signal transducer and activator of transcription 3 (STAT3) and nuclear factor kappaB (NFkappaB). However, the downstream signaling regulation by Galpha(16) has not yet been documented. In the present study, we have determined the signaling mechanism by which constitutively active Galpha(16) mediates c-Fos transcriptional activation in human embryonic kidney (HEK) 293 cells. Overexpression of constitutively active Galpha(16), Galpha(16)QL, resulted in the stimulation of c-Fos transcriptional activation in HEK 293 cells. The participation of PLCbeta, c-Src/Janus kinase 2 (JAK2) and extracellular signal-regulated kinase (ERK) signaling pathways in Galpha(16)QL-induced c-Fos transcriptional activation was demonstrated by the use of their specific inhibitors. However, c-Jun N terminal kinase (JNK), p38 MAPK and phosphatidylinositol-3 kinase (PI3K) were not required. Interestingly, the dominant negative mutant of STAT1, but not STAT3, suppressed c-Fos transcriptional activation induced by Galpha(16)QL, implying that STAT1 was involved in this signaling mechanism. To further examine the role of STAT1 in the signaling pathway of Galpha(16), we demonstrated that Galpha(16)QL was able to induce STAT1 activation. Also, stimulation of adenosine A1 receptor-coupled Galpha(16) was shown to induce ERK and STAT1 phosphorylations in a concentration-dependent manner. Using selective inhibitors, PLCbeta, c-Src/JAK and ERK, but not JNK, p38 MAPK and PI3K, were shown to be involved in Galpha(16)QL-induced STAT1 activation. Collectively, our results demonstrate for the first time that stimulation of Galpha(16) can lead to STAT1-dependent c-Fos transcriptional activation via PLCbeta, c-Src/JAK and ERK pathways.

The plastid protein THYLAKOID FORMATION1 and the plasma membrane G-protein GPA1 interact in a novel sugar-signaling mechanism in Arabidopsis

Mutations in genes encoding components of the heterotrimeric G-protein complex were previously shown to confer altered sensitivity to increased levels of D-glucose. This suggests that G-protein coupling may be a novel sugar-signaling mechanism in Arabidopsis thaliana. THYLAKOID FORMATION1 (THF1) is here demonstrated in vivo as a Galpha interaction partner that functions downstream of the plasma membrane-delimited heterotrimeric G-protein (GPA1) in a D-glucose signaling pathway. THF1 is a plastid protein localized to both the outer plastid membrane and the stroma. Contact between root plastidic THF1 and GPA1 at the plasma membrane occurs at sites where the plastid membrane abuts the plasma membrane, as demonstrated by Förster resonance energy transfer (FRET). A probable role for THF1 in sugar signaling is demonstrated by both biochemical and genetic evidence. Root growth in the thf1-1 null mutant is hypersensitive to exogenous D-glucose, and THF1-overexpressing roots are resistant to inhibition of growth rate by high D-glucose. Additionally, THF1 levels are rapidly degraded by D-glucose but not L-glucose. The interaction between THF1 and GPA1 has been confirmed by in vitro and in vivo coimmunoprecipitation, FRET analysis, and genetic epistasis and provides evidence of a sugar-signaling mechanism between plastids and the plasma membrane.

G-protein complex mutants are hypersensitive to abscisic acid regulation of germination and postgermination development

Abscisic acid (ABA) plays regulatory roles in a host of physiological processes throughout plant growth and development. Seed germination, early seedling development, stomatal guard cell functions, and acclimation to adverse environmental conditions are key processes regulated by ABA. Recent evidence suggests that signaling processes in both seeds and guard cells involve heterotrimeric G proteins. To assess new roles for the Arabidopsis (Arabidopsis thaliana) Galpha subunit (GPA1), the Gbeta subunit (AGB1), and the candidate G-protein-coupled receptor (GCR1) in ABA signaling during germination and early seedling development, we utilized knockout mutants lacking one or more of these components. Our data show that GPA1, AGB1, and GCR1 each negatively regulates ABA signaling in seed germination and early seedling development. Plants lacking AGB1 have greater ABA hypersensitivity than plants lacking GPA1, suggesting that AGB1 is the predominant regulator of ABA signaling and that GPA1 affects the efficacy of AGB1 execution. GCR1 acts upstream of GPA1 and AGB1 for ABA signaling pathways during germination and early seedling development: gcr1 gpa1 double mutants exhibit a gpa1 phenotype and agb1 gcr1 and agb1 gcr1 gpa1 mutants exhibit an agb1 phenotype. Contrary to the scenario in guard cells, where GCR1 and GPA1 have opposite effects on ABA signaling during stomatal opening, GCR1 acts in concert with GPA1 and AGB1 in ABA signaling during germination and early seedling development. Thus, cell- and tissue-specific functional interaction in response to a given signal such as ABA may determine the distinct pathways regulated by the individual members of the G-protein complex.

Chemical genetics reveals an RGS/G-protein role in the action of a compound

We report here on a chemical genetic screen designed to address the mechanism of action of a small molecule. Small molecules that were active in models of urinary incontinence were tested on the nematode Caenorhabditis elegans, and the resulting phenotypes were used as readouts in a genetic screen to identify possible molecular targets. The mutations giving resistance to compound were found to affect members of the RGS protein/G-protein complex. Studies in mammalian systems confirmed that the small molecules inhibit muscarinic G-protein coupled receptor (GPCR) signaling involving G-αq (G-protein alpha subunit). Our studies suggest that the small molecules act at the level of the RGS/G-αq signaling complex, and define new mutations in both RGS and G-αq, including a unique hypo-adapation allele of G-αq. These findings suggest that therapeutics targeted to downstream components of GPCR signaling may be effective for treatment of diseases involving inappropriate receptor activation.

The authors have utilized Caenorhabditis elegans, and yeast genetics, combined with mammalian tissue and cell culture experiments to investigate the mechanism of action of a unique set of small molecules. These molecules are active in tissue models of urinary incontinence and allow for increased bladder filling. In the course of studying sensitivity and resistance to these compounds, Fitzgerald et al. uncovered novel alleles of RGS and Gq proteins. Further characterization of one such allele identified that its action conferred a hypo-adaptive phenotype on yeast during pheromone signaling assays. Their data as a whole indicate that these small molecules are able to diminish signaling from G-protein coupled receptors (GPCR) downstream of the receptors themselves. Since GPCR signaling is very important in many diseases in humans, the novel mechanism of these compounds may offer new ways to treat human disease.

Different signalling pathways involving a Galpha protein, cAMP and a MAP kinase control germination of Botrytis cinerea conidia

Conidial germination of the grey mould fungus Botrytis cinerea was found to be induced by different chemical and physical signals, namely the amount and quality of nutrients as well as the hydrophobicity and rigidity of the surface. A B. cinerea Deltabcg3 mutant disrupted in the Galpha3 subunit of the heterotrimeric G protein was specifically defective in germination induced by carbon sources. A similar germination defect of an adenylate cyclase mutant, and the complementing effect of cAMP addition to conidia of these mutants confirmed the involvement of cAMP. In contrast, a Deltabmp1 MAP kinase mutant was delayed in carbon source-induced germination, but completely unable to germinate on hydrophobic surfaces. Based on these data, it is proposed that the germination response of B. cinerea conidia is controlled by three signalling pathways: Germination induction by rich media is weakly dependent on BMP1; induction by carbon sources requires BCG3, cAMP and BMP1; and induction by contact to hydrophobic surfaces is absolutely dependent on BMP1. Other defects of the Deltabcg3 mutant, such as low conidiation, excessive formation of sclerotia and delayed host infection, were also restored by cAMP. Microscopical studies of germling growth and differentiation on host cuticles revealed that the delayed infection of the Deltabcg3 mutant was due to a surface sensing defect leading to a reduced penetration. Thus, in addition to their role in germination, Galpha3, cAMP as well as BMP1 are required also for proper host surface recognition and penetration ability of germinated conidia.

[Importance of heterotrimeric G proteins in prostate cancer molecular biology]

OBJECTIVE

To deep in the knowledge of the involvement of G-protein alphas and alphai subunits in human prostate cancer.

METHODS

Prostate tissue from 9 patients undergoing radical prostatectomy for prostate cancer and 5 controls undergoing cystoprostatectomy for bladder carcinoma. G-protein alphas and alphai subunits were studied for expression (mRNA by RT-PCR and protein by Western-blot), functionality (adenylyl cyclase activity, AC) and possibility of mutations (analysis with restriction enzymes and cDNA sequentiation).

RESULTS

At mRNA level, the expression of alphas, alphai1, alphai2 y alphai3 was detected in healthy and cancerous tissues. At protein level, the expression of alphas y alphai1,2 diminished (25% and 40%, respectively) in prostate cancer. The expression of alphai3/0 also diminished, whereas that of beta subunit was not modified. Basal AC activity in adenocarcinoma membranes was 40% inferior to the control. Digestion with restriction enzymes Eag I or AlwN I did not allow to locate mutations in alphas. However, digestion at alphai2 level with BstU I enzyme served to observe a change of Gln205 (CAG triplet) to Pro (CCG).

CONCLUSIONS

The functionality and expression of heterotrimeric G proteins are selectively modified in human prostate adenocarcinoma, occurring in addition some punctual mutation. The observed substitution of Gln205 by Pro may result in a low GTPase activity for alphai2 that, therefore, is stabilized in its active form.

Parietal-eye phototransduction components and their potential evolutionary implications

The parietal-eye photoreceptor is unique because it has two antagonistic light signaling pathways in the same cell-a hyperpolarizing pathway maximally sensitive to blue light and a depolarizing pathway maximally sensitive to green light. Here, we report the molecular components of these two pathways. We found two opsins in the same cell: the blue-sensitive pinopsin and a previously unidentified green-sensitive opsin, which we name parietopsin. Signaling components included gustducin-alpha and Galphao, but not rod or cone transducin-alpha. Single-cell recordings demonstrated that Go mediates the depolarizing response. Gustducin-alpha resembles transducin-alpha functionally and likely mediates the hyperpolarizing response. The parietopsin-Go signaling pair provides clues about how rod and cone phototransduction might have evolved.

Conditional ablation of mature olfactory sensory neurons mediated by diphtheria toxin receptor

The vertebrate olfactory epithelium provides an excellent model system to study the regulatory mechanisms of neurogenesis and neuronal differentiation due to its unique ability to generate new sensory neurons throughout life. The replacement of olfactory sensory neurons is stimulated when damage occurs in the olfactory epithelium. In this study, transgenic mice, with a transgene containing human diphtheria toxin receptor under the control of the olfactory marker protein promoter (OMP-DTR), were generated in which the mature olfactory sensory neurons could be specifically ablated when exposed to diphtheria toxin. Following diphtheria toxin induced neuronal ablation, we observed increased numbers of newly generated growth associated protein 43 (GAP43)-positive immature olfactory sensory neurons. OMP-positive neurons were continuously produced from the newly generated GAP43-positive cells. The expression of the signal transduction components adenylyl cyclase type III and the G-protein alpha subunit G(alpha olf) was sensitive to diphtheria toxin exposure and their levels decreased dramatically preceding the disappearance of the OMP-positive sensory neurons. These data validate the hypothesis that OMP-DTR mice can be used as a tool to ablate the mature olfactory sensory neurons in a controlled fashion and to study the regulatory mechanisms of the neuronal replacement.

G-protein-coupled receptor 1, G-protein Galpha-subunit 1, and prephenate dehydratase 1 are required for blue light-induced production of phenylalanine in etiolated Arabidopsis

Different classes of plant hormones and different wavelengths of light act through specific signal transduction mechanisms to coordinate higher plant development. A specific prephenate dehydratase protein (PD1) was discovered to have a strong interaction with the sole canonical G-protein Galpha-subunit (GPA1) in Arabidopsis (Arabidopsis thaliana). PD1 is a protein located in the cytosol, present in etiolated seedlings, with a specific role in blue light-mediated synthesis of phenylpyruvate and subsequently of phenylalanine (Phe). Insertion mutagenesis confirms that GPA1 and the sole canonical G-protein-coupled receptor (GCR1) in Arabidopsis also have a role in this blue light-mediated event. In vitro analyses indicate that the increase in PD1 activity is the direct and specific consequence of its interaction with activated GPA1. Because of their shared role in the light-mediated synthesis of phenylpyruvate and Phe, because they are iteratively interactive, and because activated GPA1 is directly responsible for the activation of PD1; GCR1, GPA1, and PD1 form all of or part of a signal transduction mechanism responsible for the light-mediated synthesis of phenylpyruvate, Phe, and those metabolites that derive from that Phe. Data are also presented to confirm that abscisic acid can act through the same pathway. An additional outcome of the work is the confirmation that phenylpyruvate acts as the intermediate in the synthesis of Phe in etiolated plants, as it commonly does in bacteria and fungi.

Effects of polymorphisms in β1-adrenoceptor and α-subunit of G protein on heart rate and blood pressure during exercise test. The Finnish Cardiovascular Study

We tested whether the Arg389Gly and Ser49Gly polymorphisms of the β1-adrenergic receptor gene ADRB1 and the T393C polymorphism of the G protein α-subunit gene GNAS1 modulate heart rate (HR) and blood pressure responses during an exercise stress test. The study population comprised 890 participants (563 men and 327 women, mean age 58.1 ± 12.6 yr) of the Finnish Cardiovascular Study. Their HR, systolic (SAP), and diastolic arterial pressures (DAP) at rest, during exercise, and 4 min after the test were measured and analyzed by repeated-measurement ANOVA (RANOVA). Genotypes were detected by TaqMan 5′ nuclease assay. In all subjects, and in men and women separately, the T393C of GNAS1 was the only polymorphism with genotype × time interaction in HR over the three study phases ( P = 0.04, RANOVA). None of the polymorphisms presented genotype × time interaction in SAP or DAP responses ( P > 0.10, RANOVA). In all subjects at rest, the Ser49Gly polymorphism of ADRB1 tended ( P = 0.06, ANOVA) to differentiate HR. Arg389Gly polymorphism of ADRB1 affected maximal SAP during exercise ( P = 0.04, ANOVA) and the change in SAP from rest to maximal ( P = 0.03, ANOVA). Arg389 homozygotes, particularly men, were less likely to have ventricular extrasystoles during the exercise (odds ratio = 0.68, 95% confidence interval = 0.51–0.91, P = 0.009, and odds ratio = 0.60, 95% confidence interval = 0.42–0.86, P = 0.006, respectively) than did Gly389 carriers. In conclusion, polymorphisms examined appear to have modulatory effects on hemodynamics in a clinical exercise test setting. However, the effects in absolute numbers were minor and clinically possibly insignificant.

Heterotrimeric G proteins facilitate Arabidopsis resistance to necrotrophic pathogens and are involved in jasmonate signaling

Heterotrimeric G proteins have been previously linked to plant defense; however a role for the Gbetagamma dimer in defense signaling has not been described to date. Using available Arabidopsis (Arabidopsis thaliana) mutants lacking functional Galpha or Gbeta subunits, we show that defense against the necrotrophic pathogens Alternaria brassicicola and Fusarium oxysporum is impaired in Gbeta-deficient mutants while Galpha-deficient mutants show slightly increased resistance compared to wild-type Columbia ecotype plants. In contrast, responses to virulent (DC3000) and avirulent (JL1065) strains of Pseudomonas syringae appear to be independent of heterotrimeric G proteins. The induction of a number of defense-related genes in Gbeta-deficient mutants were severely reduced in response to A. brassicicola infection. In addition, Gbeta-deficient mutants exhibit decreased sensitivity to a number of methyl jasmonate-induced responses such as induction of the plant defensin gene PDF1.2, inhibition of root elongation, seed germination, and growth of plants in sublethal concentrations of methyl jasmonate. In all cases, the behavior of the Galpha-deficient mutants is coherent with the classic heterotrimeric mechanism of action, indicating that jasmonic acid signaling is influenced by the Gbetagamma functional subunit but not by Galpha. We hypothesize that Gbetagamma acts as a direct or indirect enhancer of the jasmonate signaling pathway in plants.