Benzodiazepine diazepam regulates cell surface ß1-adrenergic receptor density in human monocytes.

Downregulation of cell surface ß-adrenergic receptors (ß-AR) is an important adaptive response that prevents deleterious effects of receptor overstimulation. Various factors including reactive oxygen species cause ß-AR downregulation. In this study, we evaluated the effects of ligands of the peripheral benzodiazepine receptor (PBR), a key protein in regulating oxidative stress, on surface density of endogenous ß1-and ß2-ARs in highly differentiated cells such as human monocytes, which express both ß-AR subtypes. ß-AR expression in human monocytes was evaluated by flow cytometry, qPCR and western blotting. Monocyte treatment with ß-AR agonist isoproterenol did not change surface ß1-AR density while downregulating surface ß2-AR density. This effect was antagonized by the ß-blocker propranolol. An opposite response was observed with benzodiazepine diazepam that led to a time-dependent reduction in ß1-AR density. In particular, while no significant downregulation was observed after 3 h of treatment, only 63% of ß1-ARs were still present on the cell surface after 48 h of treatment with diazepam at 1 µM. Treatment with the PBR antagonist PK11195, but not with propranolol, antagonized the effects of diazepam. No change in ß1-AR-mRNA or protein levels was observed at any time after diazepam treatment. We also found that diazepam did not affect Gs-protein or ß-arrestin-2 recruitment for both ß-ARs in engineered fibroblasts, further suggesting that diazepam activity on ß1-AR density is mediated by PBR. Finally, no sex-related differences were found. Collectively, these results indicate that monocyte ß1-ARs are resistant to catecholamine-mediated downregulation and suggest that PBR plays an important role in regulating ß1-AR density.

A xanthophyll-derived apocarotenoid regulates carotenogenesis in tomato chromoplasts.

Carotenoids possess important biological functions that make them essential components of the human diet. ß-Carotene and some other carotenoids have vitamin A activity while lutein and zeaxanthin, typically referred to as the macular pigments, are involved in good vision and in delaying the onset of age-related eye diseases. In order to create a zeaxanthin-producing tomato fruit, two transgenic lines, one with a high ß-carotene cyclase activity and the other with a high ß-carotene hydroxylase activity, have been genetically crossed. Ripe fruits from the resulting progeny contained significant levels of violaxanthin, antheraxanthin, and xanthophyll esters. However, their zeaxanthin content was not as high as expected, and the total level of carotenoids was only 25% of the carotenoids found in ripe fruits of the comparator line. Targeted transcript analysis and apocarotenoids determinations indicated that transcriptional regulation of the pathway or degradation of synthesized carotenoids were not responsible for the low carotenoid content of hybrid fruits which instead appeared to result from a substantial reduction of carotenoid biosynthesis. Notably, the content of an unidentified hydroxylated cyclic (C13) apocarotenoid was 13 times higher in the hybrid fruits than in the control fruits. Furthermore, a GC-MS-based metabolite profiling demonstrated a perturbation of carotenogenesis in ripening hybrid fruits compatible with a block of the pathway. Moreover, carotenoid profiling on leaf, fruit, and petal samples from a set of experimental lines carrying the hp3 mutation, in combination with the two transgenes, indicated that the carotenoid biosynthesis in petal and fruit chromoplasts could be regulated. Altogether the data were consistent with the hypothesis of the regulation of the carotenoid pathway in tomato chromoplasts through a mechanism of feedback inhibition mediated by a xanthophyll-derived apocarotenoid. This chromoplast-specific post-transcriptional mechanism was disclosed in transgenic fruits of HU hybrid owing to the abnormal production of zeaxanthin and antheraxanthin, the more probable precursors of the apocarotenoid signal. A model describing the regulation of carotenoid pathway in tomato chromoplasts is presented.

Crosstalk between ß2- and α2-Adrenergic Receptors in the Regulation of B16F10 Melanoma Cell Proliferation.

Adrenergic receptors (AR) belong to the G protein-coupled receptor superfamily and regulate migration and proliferation in various cell types. The objective of this study was to evaluate whether ß-AR stimulation affects the antiproliferative action of α2-AR agonists on B16F10 cells and, if so, to determine the relative contribution of ß-AR subtypes. Using pharmacological approaches, evaluation of Ki-67 expression by flow cytometry and luciferase-based cAMP assay, we found that treatment with isoproterenol, a ß-AR agonist, increased cAMP levels in B16F10 melanoma cells without affecting cell proliferation. Propranolol inhibited the cAMP response to isoproterenol. In addition, stimulation of α2-ARs with agonists such as clonidine, a well-known antihypertensive drug, decreased cancer cell proliferation. This effect on cell proliferation was suppressed by treatment with isoproterenol. In turn, the suppressive effects of isoproterenol were abolished by the treatment with either ICI 118,551, a ß2-AR antagonist, or propranolol, suggesting that isoproterenol effects are mainly mediated by the ß2-AR stimulation. We conclude that the crosstalk between the ß2-AR and α2-AR signaling pathways regulates the proliferative activity of B16F10 cells and may therefore represent a therapeutic target for melanoma therapy.

Prokineticin receptors interact unselectively with several G protein subtypes but bind selectively to ß-arrestin 2.

Prokineticin 1 (pk1) and prokineticin 2 (pk2) interact with two structurally related G-protein coupled receptors, prokineticin receptor 1 (PKR1) and prokineticin receptor 2 (PKR2). Cellular signalling studies show that the activated receptors can evoke Ca2+-mobilization, pertussis toxin-sensitive ERK phosphorylation, and intracellular cAMP accumulation, which suggests the partecipation of several G protein subtypes, such as Gq/11, Gi/o and Gs. However, direct interactions with these transduction proteins have not been studied yet. Here we measured by bioluminescence resonance energy transfer (BRET) the association of PKR1 and PKR2 with different heterotrimeric Gα proteins in response to pk1 and pk2 activation. Using host-cell lines carrying gene deletions of Gαq/11 or Gαs, and pertussis toxin treatment to abolish the receptor interactions with Gαi/o, we determined that both receptors could couple with comparable efficiency to Gq/11 and Gi/o, but far less efficiently to Gs or other pertussis toxin-insensitive G proteins. We also used BRET methodology to assess the association of prokineticin receptors with ß-arrestin isoforms. Fluorescent versions of the isoforms were transfected both in HEK293 cells and in double KO ß-arrestin 1/2 mouse fibroblasts, to study receptor interaction with the reconstituted individual ß-arrestins without background expression of the endogenous genes. Both receptors formed stable BRET-emitting complexes with ß-arrestin 2 but not with ß-arrestin 1, indicating strong selectivity for the former. In all the studied transducer interactions and in both receptors, pk2 was more potent than pk1 in promoting receptor binding to transduction proteins.

Vasopressin receptor 2 mutations in the nephrogenic syndrome of inappropriate antidiuresis show different mechanisms of constitutive activation for G protein coupled receptors.

Vasopressin receptor 2 (V2R) mutations causing the nephrogenic syndrome of inappropriate antidiuresis (NSIAD) can generate two constitutively active receptor phenotypes. One type results from residue substitutions in several V2R domains and is sensitive to vaptan inverse agonists. The other is only caused by Arg 137 replacements and is vaptan resistant. We compared constitutive and agonist-driven interactions of the vaptan-sensitive F229V and vaptan-resistant R137C/L V2R mutations with ß-arrestin 1, ß-arrestin 2, and Gαs, using null fibroblasts reconstituted with individual versions of the ablated transduction protein genes. F229V displayed very high level of constitutive activation for Gs but not for ß-arrestins, and enhanced or normal responsiveness to agonists and inverse agonists. In contrast, R137C/L mutants exhibited maximal levels of constitutive activation for ßarrestin 2 and Gs, minimal levels for ß-arrestin 1, but a sharp decline of ligands sensitivity at all transducer interactions. The enhanced constitutive activity and reduced ligand sensitivity of R137 mutants on cAMP signaling persisted in cells lacking ß-arrestins, indicating that these are intrinsic molecular properties of the mutations, not the consequence of altered receptor trafficking. The results suggest that the two groups of NSIAD mutations represent two distinct molecular mechanisms of constitutive activation in GPCRs.

Intermittent ß-adrenergic blockade downregulates the gene expression of ß-myosin heavy chain in the mouse heart.

Expression of the ß-myosin heavy chain (ß-MHC), a major component of the cardiac contractile apparatus, is tightly regulated as even modest increases can be detrimental to heart under stress. In healthy hearts, continuous inhibition of ß-adrenergic tone upregulates ß-MHC expression. However, it is unknown whether the duration of the ß-adrenergic inhibition and ß-MHC expression are related. Here, we evaluated the effects of intermittent ß-blockade on cardiac ß-MHC expression. To this end, the ß-blocker propranolol, at the dose of 15mg/kg, was administered once a day in mice for 14 days. This dosing schedule caused daily drug-free periods of at least 6 h as evidenced by propranolol plasma concentrations and cardiac ß-adrenergic responsiveness. Under these conditions, ß-MHC expression decreased by about 75% compared to controls. This effect was abolished in mice lacking ß1- but not ß2-adrenergic receptors (ß-AR) indicating that ß-MHC expression is regulated in a ß1-AR-dependent manner. In ß1-AR knockout mice, the baseline ß-MHC expression was fourfold higher than in wild-type mice. Also, we evaluated the impact of intermittent ß-blockade on ß-MHC expression in mice with systolic dysfunction, in which an increased ß-MHC expression occurs. At 3 weeks after myocardial infarction, mice showed systolic dysfunction and upregulation of ß-MHC expression. Intermittent ß-blockade decreased ß-MHC expression while attenuating cardiac dysfunction. In vitro studies showed that propranolol does not affect ß-MHC expression on its own but antagonizes catecholamine effects on ß-MHC expression. In conclusion, a direct relationship occurs between the duration of the ß-adrenergic inhibition and ß-MHC expression through the ß1-AR.

ß-blockers Reverse Agonist-Induced ß2-AR Downregulation Regardless of Their Signaling Profile.

Altered ß-adrenergic receptor (ß-AR) density has been reported in cells, animals, and humans receiving ß-blocker treatment. In some cases, ß-AR density is upregulated, but in others, it is unaffected or even reduced. Collectively, these results would imply that changes in ß-AR density and ß-blockade are not related. However, it has still not been clarified whether the effects of ß-blockers on receptor density are related to their ability to activate different ß-AR signaling pathways. To this aim, five clinically relevant ß-blockers endowed with inverse, partial or biased agonism at the ß2-AR were evaluated for their effects on ß2-AR density in both human embryonic kidney 293 (HEK293) cells expressing exogenous FLAG-tagged human ß2-ARs and human lymphocytes expressing endogenous ß2-ARs. Cell surface ß2-AR density was measured by enzyme-linked immunosorbent assay (ELISA) and flow cytometry. Treatment with propranolol, carvedilol, pindolol, sotalol, or timolol did not induce any significant change in surface ß2-AR density in both HEK293 cells and human lymphocytes. On the contrary, treatment with the ß-AR agonist isoproterenol reduced the number of cell surface ß2-ARs in the tested cell types without affecting ß2-AR-mRNA levels. Isoproterenol-induced effects on receptor density were completely antagonized by ß-blocker treatment. In conclusion, the agonistic activity of ß-blockers does not exert an important effect on short-term regulation of ß2-AR density.

Gain-of-function mutations of the V2 vasopressin receptor in nephrogenic syndrome of inappropriate antidiuresis (NSIAD): a cell-based assay to assess constitutive water reabsorption.

Nephrogenic syndrome of inappropriate antidiuresis (NSIAD) is a recently identified chromosome X-linked disease associated with gain-of-function mutations of the V2 vasopressin receptor (V2R), a G-protein-coupled receptor. It is characterized by inability to excrete a free water load, hyponatremia, and undetectable vasopressin-circulating levels. Hyponatremia can be quite severe in affected male children. To gain a deeper insight into the functional properties of the V2R active mutants and how they might translate into the pathological outcome of NSIAD, in this study, we have expressed the wild-type V2R and three constitutively active V2R mutants associated with NSIAD (R137L, R137C, and the F229V) in MCD4 cells, a cell line derived from renal mouse collecting duct, stably expressing the vasopressin-sensitive water channel aquaporin-2 (AQP2). Our findings indicate that in cells expressing each active mutant, AQP2 was constitutively localized to the apical plasma membrane in the absence of vasopressin stimulation. In line with these observations, under basal conditions, osmotic water permeability in cells expressing the constitutively active mutants was significantly higher compared to that of cells expressing the wild-type V2R. Our findings demonstrate a direct link between activating mutations of the V2R and the perturbation of water balance in NSIAD. In addition, this study provides a useful cell-based assay system to assess the functional consequences of newly discovered activating mutations of the V2R on water permeability in kidney cells and to screen the effect of drugs on the mutated receptors.

The road to astaxanthin production in tomato fruit reveals plastid and metabolic adaptation resulting in an unintended high lycopene genotype with delayed over-ripening properties.

Tomato fruit are an important nutritional component of the human diet and offer potential to act as a cell factory for speciality chemicals, which are often produced by chemical synthesis. In the present study our goal was to produce competitive levels of the high value ketocarotenoid, astaxanthin, in tomato fruit. The initial stage in this process was achieved by expressing the 4, 4' carotenoid oxygenase (crtW) and 3, 3' hydroxylase (crtZ) from marine bacteria in tomato under constitutive control. Characterization of this genotype showed a surprising low level production of ketocarotenoids in ripe fruit but over production of lycopene (~3.5 mg/g DW), accompanied by delayed ripening. In order to accumulate these non-endogenous carotenoids, metabolite induced plastid differentiation was evident as well as esterification. Metabolomic and pathway based transcription studies corroborated the delayed onset of ripening. The data also revealed the importance of determining pheno/chemotype inheritance, with ketocarotenoid producing progeny displaying loss of vigour in the homozygous state but stability and robustness in the hemizygous state. To iteratively build on these data and optimize ketocarotenoid production in this genotype, a lycopene ß-cyclase was incorporated to avoid precursor limitations and a more efficient hydroxylase was introduced. These combinations resulted in the production of astaxanthin (and ketocarotenoid esters) in ripe fruit at ~3 mg/g DW. Based on previous studies, this level of product formation represents an economic competitive value in a Generally Regarded As Safe (GRAS) matrix that requires minimal downstream processing.

CRISPR/Cas9 editing of carotenoid genes in tomato.

CRISPR/Cas9 technology is rapidly spreading as genome editing system in crop breeding. The efficacy of CRISPR/Cas9 in tomato was tested on Psy1 and CrtR-b2, two key genes of carotenoid biosynthesis. Carotenoids are plant secondary metabolites that must be present in the diet of higher animals because they exert irreplaceable functions in important physiological processes. Psy1 and CrtR-b2 were chosen because their impairment is easily detectable as a change of fruit or flower color. Two CRISPR/Cas9 constructs were designed to target neighboring sequences on the first exon of each gene. Thirty-four out of forty-nine (69%) transformed plants showed the expected loss-of-function phenotypes due to the editing of both alleles of a locus. However, by including the seven plants edited only at one of the two homologs and showing a normal phenotype, the editing rate reaches the 84%. Although none chimeric phenotype was observed, the cloning of target region amplified fragments revealed that in the 40% of analyzed DNA samples were present more than two alleles. As concerning the type of mutation, it was possible to identify 34 new different alleles across the four transformation experiments. The sequence characterization of the CRISPR/Cas9-induced mutations showed that the most frequent repair errors were the insertion and the deletion of one base. The results of this study prove that the CRISPRCas9 system can be an efficient and quick method for the generation of useful mutations in tomato to be implemented in breeding programs.

Systematic errors in detecting biased agonism: Analysis of current methods and development of a new model-free approach.

Discovering biased agonists requires a method that can reliably distinguish the bias in signalling due to unbalanced activation of diverse transduction proteins from that of differential amplification inherent to the system being studied, which invariably results from the non-linear nature of biological signalling networks and their measurement. We have systematically compared the performance of seven methods of bias diagnostics, all of which are based on the analysis of concentration-response curves of ligands according to classical receptor theory. We computed bias factors for a number of ß-adrenergic agonists by comparing BRET assays of receptor-transducer interactions with Gs, Gi and arrestin. Using the same ligands, we also compared responses at signalling steps originated from the same receptor-transducer interaction, among which no biased efficacy is theoretically possible. In either case, we found a high level of false positive results and a general lack of correlation among methods. Altogether this analysis shows that all tested methods, including some of the most widely used in the literature, fail to distinguish true ligand bias from "system bias" with confidence. We also propose two novel semi quantitative methods of bias diagnostics that appear to be more robust and reliable than currently available strategies.

Pharmacological characterization of tachykinin tetrabranched derivatives.

BACKGROUND AND PURPOSE: Peptide welding technology (PWT) is a novel chemical strategy that allows the synthesis of multibranched peptides with high yield, purity and reproducibility. Using this technique, we have synthesized and pharmacologically characterized the tetrabranched derivatives of the tachykinins, substance P (SP), neurokinin A (NKA) and B (NKB). EXPERIMENTAL APPROACH: The following in vitro assays were used: calcium mobilization in cells expressing human recombinant NK receptors, BRET studies of G-protein - NK1 receptor interaction, guinea pig ileum and rat urinary bladder bioassays. Nociceptive behavioural response experiments were performed in mice following intrathecal injection of PWT2-SP. KEY RESULTS: In calcium mobilization studies, PWT tachykinin derivatives behaved as full agonists at NK receptors with a selectivity profile similar to that of the natural peptides. NK receptor antagonists display similar potency values when tested against PWT2 derivatives and natural peptides. In BRET and bioassay experiments PWT2-SP mimicked the effects of SP with similar potency, maximal effects and sensitivity to aprepitant. After intrathecal administration in mice, PWT2-SP mimicked the nociceptive effects of SP, but with higher potency and a longer-lasting action. Aprepitant counteracted the effects of PWT2-SP in vivo. CONCLUSIONS AND IMPLICATIONS: The present study has shown that the PWT technology can be successfully applied to the peptide sequence of tachykinins to generate tetrabranched derivatives characterized with a pharmacological profile similar to the native peptides. In vivo, PWT2-SP displayed higher potency and a marked prolongation of action, compared with SP.

Elevation of lutein content in tomato: a biochemical tug-of-war between lycopene cyclases.

Lutein is becoming increasingly important in preventive medicine due to its possible role in maintaining good vision and in preventing age-related maculopathy. Average daily lutein intake in developed countries is often below suggested daily consumption levels, and lutein supplementation could be beneficial. Lutein is also valuable in the food and feed industries and is emerging in nutraceutical and pharmaceutical markets. Currently, lutein is obtained at high cost from marigold petals, and synthesis alternatives are thus desirable. Tomato constitutes a promising starting system for production as it naturally accumulates high levels of lycopene. To develop tomato for lutein synthesis, the tomato Red Setter cultivar was transformed with the tomato lycopene ε-cyclase-encoding gene under the control of a constitutive promoter, and the HighDelta (HD) line, characterised by elevated lutein and δ-carotene content in ripe fruits, was selected. HD was crossed to the transgenic HC line and to RS(B) with the aim of converting all residual fruit δ-carotene to lutein. Fruits of both crosses were enriched in lutein and presented unusual carotenoid profiles. The unique genetic background of the crosses used in this study permitted an unprecedented analysis of the role and regulation of the lycopene cyclase enzymes in tomato. A new defined biochemical index, the relative cyclase activity ratio, was used to discern post-transcriptional regulation of cyclases, and will help in the study of carotenoid biosynthesis in photosynthetic plant species and particularly in those, like tomato, that have been domesticated for the production of food, feed or useful by-products.

Cell contact-dependent functional selectivity of ß2-adrenergic receptor ligands in stimulating cAMP accumulation and extracellular signal-regulated kinase phosphorylation.

Activation of ß(2)-adrenegic receptor (ß(2)-AR) leads to an increase in intracellular cAMP and activation of ERK. These two signals are activated by the interaction of the receptor with different transducer partners. We showed that the intrinsic activities of ß(2)-AR ligands for stimulating cAMP production and ERK phosphorylation responses in HEK-293 cells were not correlated. The lack of correlation resulted mainly from the discrepancy between the intrinsic activities of two groups of ligands for these two responses: The first group consisted of clenbuterol, cimaterol, procaterol, and terbutaline which acted as full agonists for cAMP production but displayed very weak effect on ERK phosphorylation. The second group comprised adrenaline and noradrenaline which displayed higher intrinsic activity for the ERK phosphorylation than for the cAMP response. Thus, both groups behaved as functionally selective ligands. The functional selectivity of the first group was observable only in adherent cells when confluence was approximately 100%. When cell-cell contact was minimized either by decreasing the density of the adherent cells or by bringing the cells into suspension, the first group of ligands gained the ability to stimulate ERK phosphorylation without a change in their effect on cAMP production. In contrast, selectivity of the second group was independent of the adherence state of the cells. Our results show that the inherent "bias" of ligands in coupling a G protein-coupled receptor to different transducers may not always be revealed as functional selectivity when there is a "cross-talk" between the signaling pathways activated by the same receptor.

Propranolol enhances cell cycle-related gene expression in pressure overloaded hearts.

BACKGROUND AND PURPOSE: Cell cycle regulators are regarded as essential for cardiomyocyte hypertrophic growth. Given that the ß-adrenoceptor antagonist propranolol blunts cardiomyocyte hypertrophic growth, we determined whether propranolol alters the expression of cell cycle-related genes in mouse hearts subjected to pressure overload. EXPERIMENTAL APPROACH: Pressure overload was induced by transverse aortic constriction (TAC), whereas the expression levels of 84 cell cycle-related genes were assayed by real-time PCR. Propranolol (80 mg·kg(-1) ·day(-1) ) was administered in drinking water for 14 days. KEY RESULTS: Two weeks after surgery, TAC caused a 46% increase in the left ventricular weight-to-body weight (LVW/BW) ratio but no significant changes in cell cycle gene expression. Propranolol, at plasma concentrations ranging from 10 to 140 ng·mL(-1) , blunted the LVW/BW ratio increase in TAC mice, while significantly increasing expression of 10 cell cycle genes including mitotic cyclins and proliferative markers such as Ki67. This increase in cell cycle gene expression was paralleled by a significant increase in the number of Ki67-positive non-cardiomyocyte cells as revealed by immunohistochemistry and confocal microscopy. ß-Adrenoceptor signalling was critical for cell cycle gene expression changes, as genetic deletion of ß-adrenoceptors also caused a significant increase in cyclins and Ki67 in pressure overloaded hearts. Finally, we found that metoprolol, a ß(1) -adrenoceptor antagonist, failed to enhance cell cycle gene expression in TAC mice. CONCLUSIONS AND IMPLICATIONS: Propranolol treatment enhances cell cycle-related gene expression in pressure overloaded hearts by increasing the number of cycling non-cardiomyocyte cells. These changes seem to occur via ß(2) -adrenoceptor-mediated mechanisms.

Divergent agonist selectivity in activating ß1- and ß2-adrenoceptors for G-protein and arrestin coupling.

The functional selectivity of adrenergic ligands for activation of ß1- and ß2-AR (adrenoceptor) subtypes has been extensively studied in cAMP signalling. Much less is known about ligand selectivity for arrestin-mediated signalling pathways. In the present study we used resonance energy transfer methods to compare the ability of ß1- and ß2-ARs to form a complex with the G-protein ß-subunit or ß-arrestin-2 in response to a variety of agonists with various degrees of efficacy. The profiles of ß1-/ß2-AR selectivity of the ligands for the two receptor-transducer interactions were sharply different. For G-protein coupling, the majority of ligands were more effective in activating the ß2-AR, whereas for arrestin coupling the relationship was reversed. These data indicate that the ß1-AR interacts more efficiently than ß2-AR with arrestin, but less efficiently than ß2-AR with G-protein. A group of ligands exhibited ß1-AR-selective efficacy in driving the coupling to arrestin. Dobutamine, a member of this group, had 70% of the adrenaline (epinephrine) effect on arrestin via ß1-AR, but acted as a competitive antagonist of adrenaline via ß2-AR. Thus the structure of such ligands appears to induce an arrestin-interacting form of the receptor only when bound to the ß1-AR subtype.

Characterization of P450 carotenoid beta- and epsilon-hydroxylases of tomato and transcriptional regulation of xanthophyll biosynthesis in root, leaf, petal and fruit.

The pathway of carotenoids starts with the synthesis of phytoene and proceeds along a single path up to lycopene which can be transformed to ß-carotene by the action of lycopene ß-cyclase or to α-carotene through the sequential action of lycopene ε-cyclase and lycopene ß-cyclase. All xanthophylls are produced from these two cyclic precursors following two hydroxylation steps. ß,ß-Xanthophyll biosynthesis requires hydroxylases belonging to the so-called 'non-heme di-iron' group while the biosynthesis of lutein involves enzymes belonging to the vast group of P450 monooxygenases with different enzymatic specificity due to the distinct rings of α-carotene. Here we report on the isolation and functional characterization of tomato CYP97A29 and CYP97C11 genes encoding the P450 carotenoid ß- and ε-hydroxylases. Through a reverse transcription-quantitative real-time PCR analysis of the two P450 and nine other carotenoid biosynthetic genes it was possible to highlight the transcriptional patterns of the 11 genes in root, leaf, petal and fruit at three stages of development and ripening. Finally, the characterization of the two P450 carotenoid (A29 and C11) hydroxylases was complemented by an in planta analysis through the use of transgenic plants. Results of this study have permitted us to model the lutein synthesis in leaf and in fruit of tomato.

Overexpression of CrtR-b2 (carotene beta hydroxylase 2) from S. lycopersicum L. differentially affects xanthophyll synthesis and accumulation in transgenic tomato plants.

Plant chloroplasts are enriched in xanthophylls which participate in photosynthesis as light-absorbing pigments and as dissipaters of excess light. In comparison, chromoplasts have evolved the capacity to synthesize and store brightly coloured carotenoid pigments to give flowers and fruits the power to attract pollinators and fruit dispersers. The best performing accumulator of xanthophylls in tomato is the petal chromoplast in contrast to the fruit chromoplast which only seems able to store carotenes. We have generated genetically engineered tomato lines carrying the tomato CrtR-b2 transgene with the aim of forcing the fruit to accumulate beta-xanthophylls. Both chloroplast- and chromoplast-containing tissues of hemizygous transgenic plants were found to contain elevated xanthophyll contents as a direct consequence of the increased number of CrtR-b2 transcripts. Hemizygous transgenic leaves contained fourfold more violaxanthin than control leaves. Developing fruits were yellow instead of green since they lacked chlorophyll a, and their violaxanthin and neoxanthin contents were seven- and threefold higher, respectively, than those of the control. Ripe fruits of hemizygous transgenic plants contained free violaxanthin and significant amounts of esterified xanthophylls. Esterified xanthophylls were present also in ripe fruits of control and homozygous plants. However, in transgenic homozygous plants, we observed a reduction in transcript content in most tissues, particularly in petals, due to a post-transcriptional gene silencing process. These findings demonstrate that tomato fruit chromoplasts can accumulate xanthophylls with the same sequestration mechanism (esterification) as that exploited by chromoplasts of the tomato petal and pepper fruit. This study on transgenic plants overexpressing an important carotenoid gene (CrtR-b2) provides an interesting model for future investigations on perturbations in beta-carotene-derived xanthophyll synthesis which in turn may provide insights into the molecular mechanisms controlling carotenoid metabolism in tomato.

Morphine-like opiates selectively antagonize receptor-arrestin interactions.

The addictive potential of opioids may be related to their differential ability to induce G protein signaling and endocytosis. We compared the ability of 20 ligands (sampled from the main chemical classes of opioids) to promote the association of mu and delta receptors with G protein or beta-arrestin 2. Receptor-arrestin binding was monitored by bioluminescence resonance energy transfer (BRET) in intact cells, where pertussis toxin experiments indicated that the interaction was minimally affected by receptor signaling. To assess receptor-G protein coupling without competition from arrestins, we employed a cell-free BRET assay using membranes isolated from cells expressing luminescent receptors and fluorescent Gbeta(1). In this system, the agonist-induced enhancement of BRET (indicating shortening of distance between the two proteins) was G alpha-mediated (as shown by sensitivity to pertussis toxin and guanine nucleotides) and yielded data consistent with the known pharmacology of the ligands. We found marked differences of efficacy for G protein and arrestin, with a pattern suggesting more restrictive structural requirements for arrestin efficacy. The analysis of such differences identified a subset of structures showing a marked discrepancy between efficacies for G protein and arrestin. Addictive opiates like morphine and oxymorphone exhibited large differences both at delta and mu receptors. Thus, they were effective agonists for G protein coupling but acted as competitive enkephalins antagonists (delta) or partial agonists (mu) for arrestin. This arrestin-selective antagonism resulted in inhibition of short and long term events mediated by arrestin, such as rapid receptor internalization and down-regulation.

Pharmacological profile of NOP receptors coupled with calcium signaling via the chimeric protein G alpha qi5.

In this study, the Galpha(qi5) protein was used to force the human nociceptin/orphanin FQ (N/OFQ) peptide (NOP) receptor to signal through the Ca(2+) pathway in CHO cells. [Ca(2+)](i) levels were monitored using the fluorometer FlexStation II and the Ca(2+) dye Fluo 4 AM. Concentration response curves were generated with a panel of full and partial agonists, while NOP antagonists were assessed in inhibition-response curves. The following rank order of potency of antagonists was measured: SB - 612111 > J - 113397 = Trap - 101 > or = UFP - 101 > [Nphe1]N/OF Q(1 - 13)NH2 >> naloxone, which is superimposable to literature findings. The rank order of potency of full and partial agonists is also similar to that obtained in previous studies with the exception of a panel of ligands (UFP-112, Ro 64-6198, ZP120, UFP-113) whose potency was relatively low in the Galpha(qi5)-NOP receptor calcium assay. Interestingly, these NOP ligands are characterized by slow kinetic of interaction with the NOP receptor, as demonstrated by bioassay experiments. These results demonstrated that the FlexStation II-Galpha(qi5)-NOP receptor calcium assay represents an adequate and useful screening for NOP receptor ligands, particularly for antagonists.