Recovery of upland acid grasslands after successful Pteridium aquilinum control: Long-term effectiveness of cutting, repeated herbicide treatment and bruising.

There is a clear need for the development of management strategies to control dominant, perennial weeds and restore semi-natural communities and an important part of this is to know how long control treatments take to be effective and how long they last after treatments stop. Here, we report the results from a 17-year long experiment where we compared the effects of five control treatments on dense Pteridium aquilinum (L. Kuhn) relative to an untreated experimental-control in Derbyshire, UK. The experiment was run in two phases. In Phase 1 (2005-2012) we controlled the P. aquilinum by cutting and bruising, both twice and thrice annually, and a herbicide treatment (asulam in year 1, followed by annual spot-re-treatment of all emergent fronds). In Phase 2 (2012-2021) all treatments were stopped, and the vegetation was allowed to develop naturally. Between 2005 and 2021 we monitored P. aquilinum performance annually and full plant species composition at intervals. Here, we concentrate on analysing the Phase 2 data where we used regression approaches to model individual species responses through time and unconstrained ordination to compare treatment effects on the entire species composition over both Phases. Remote sensing was also used to assess edge invasion in 2018. At the end of Phase 1, a good reduction of P. aquilinum and restoration of acid-grassland was achieved for the asulam and cutting treatments, but not for bruising. In Phase 2, P. aquilinum increased through time in all treated plots but the asulam and cutting ones maintained a much lower P. aquilinum performance for nine years on all measures assessed. There was a reduction in species richness and richness fluctuations, especially in graminoid species. However, multivariate analysis showed that the asulam and cutting treatments were stationed some distance from the untreated and bruising treatments with no apparent sign of reversions suggesting an Alternative Stable State had been created, at least over this nine-year period. P. aquilinum reinvasion was mainly from plot edges. The use of repeated P. aquilinum control treatments, either through an initial asulam spray with annual follow-up spot-spraying or cutting twice or thrice annually for eight years gave good P. aquilinum control and helped restore an acid-grassland community. Edge reinvasion was detected, and it is recommended that either whole-patch control be implemented or treatments should be continued around patch edges.

Investigating diagnosis, treatment, and burden of disease in patients with ankylosing spondylitis in Central Eastern Europe and the United States: a real-world study.

INTRODUCTION/OBJECTIVES: Ankylosing spondylitis (AS) is a chronic inflammatory immune-mediated condition. We compared AS diagnosis, treatment, and burden in Central Eastern European countries (CEE), where this has been less researched, and the United States (US) from a real-world perspective. METHODS: Point-in-time survey of rheumatologists and their AS patients was conducted in the US (Apr-Oct 2018) and CEE (Aug-Nov 2019) via physician- and patient-completed record forms, including clinical and patient-reported outcomes. Statistical analysis included descriptive statistics, t-tests, Fisher's exact tests, and generalized linear models. RESULTS: In total, 487 patients were recruited from 88 rheumatologists in the US and 922 patients from 126 rheumatologists in CEE. Time from onset of symptoms to final AS diagnosis was longer in CEE than the US (4.2 vs 2.7 years, p < 0.05). At diagnosis, a greater use of conventional synthetic disease-modifying antirheumatic drugs (DMARDs) and injected steroids was reported in CEE vs the US (43.7% vs 27.6%, p < 0.05; 19.3% vs 8.7%, p < 0.05). 22.9% of US patients received a biologic DMARD at diagnosis vs 10% of CEE patients (p < 0.05). At current consultation, biologic DMARD use in CEE was lower vs the US (27.9% vs 71.0%, p < 0.05). CEE vs US patients had greater disease activity (mean Bath Ankylosing Spondylitis Disease Activity Index 4.2 vs 3.1, p < 0.05) and worse quality of life (QoL; mean Ankylosing Spondylitis Quality of Life Questionnaire score 6.2 vs 8.4, p < 0.05). CONCLUSIONS: AS patients in CEE vs the US faced slower diagnosis and worse access to biologics, disease activity, and QoL. Whether early access to biologics can improve symptoms, QoL, and daily activities in AS patients in CEE remains to be seen. Key Points • The study provided evidence on the real-world approach to the diagnosis, treatment, and burden of axSpA (axial spondyloarthritis) in CEE compared with the US. • The study reported patients in CEE experienced longer delays in diagnosis and poorer access to biologics than in the US. • This may have resulted in higher disease activity, greater levels of pain, and poorer outcomes, as reported by patients with axSpA in CEE.

Change to ecosystem properties through changing the dominant species: Impact of Pteridium aquilinum-control and heathland restoration treatments on selected soil properties.

It is well known that soils are influenced by the plant species that grow in them. Here we consider the effects of management-induced changes to plant communities and their soils during restoration within a 20-year manipulative experiment where the aim was to change a late-successional community dominated by the weed, Pteridium aquilinum, to an earlier-successional grass-heath one. The ecological restoration treatments altered the above- and below-ground components of the community substantially. Untreated plots maintained a dense Pteridium cover with little understory vegetation, cutting treatments produce significant reductions of Pteridium, whereas herbicide (asulam) produced significant immediate reductions in Pteridium but regressed towards the untreated plots within 10 years. Thereafter, all asulam-treated plots were re-treated in year 11, and then were spot-sprayed annually. Both cutting and asulam treatments reduced frond density to almost zero and resulted in a grass-heath vegetation. There was also a massive change in biomass distribution, untreated plots had a large above-ground biomass/necromass that was much reduced where Pteridium was controlled. Below-ground in treated plots, there was a replacement of the substantive Pteridium rhizome mass with a much greater root mass of other species. The combined effects of Pteridium-control and restoration treatment, reduced soil total C and N as and available P concentrations, but increased soil pH and available N. Soil biological activity was also affected with a reduction in soil N mineralization rate, but an increased soil-root respiration. Multivariate analysis showed a clear trend along a pH/organic matter gradient, with movement along it correlated to management intensity from the untreated plots with low pH/high organic matter and treated plots with to a higher pH/lower organic matter in the sequence asulam treatment, cut once per year to cut twice per year. The role that these changed soil conditions might have in restricting Pteridium recovery are discussed.

Evidence for validity of a national physician and patient-reported, cross-sectional survey in China and UK: the Disease Specific Programme.

OBJECTIVE: Diabetes represents a significant challenge for Chinese healthcare providers. Healthcare decision-making is generally based on many data sources, including randomised controlled and real-world studies; however, good-quality data from Chinese diabetes patients are scarce. We performed an initial validation to assess the representativeness of one source of real-world data-the Diabetes Adelphi Disease Specific Programme (DSP) in China. SETTING: China, UK. PARTICIPANTS: The Chinese DSP included 2060 patients with previously diagnosed type 2 diabetes mellitus (T2DM) sampled by 200 physicians. The reference Chinese population comprised 238 639 patients with previously diagnosed T2DM. The UK DSP contained 1481 patients with T2DM sampled by 125 physicians; the reference UK population comprised 289 patients with diabetes. PRIMARY AND SECONDARY OUTCOMES: The primary outcome was comparison of unweighted China DSP and reference data for sex, body mass index (BMI), blood pressure (BP), patients achieving glycosylated haemoglobin (HbA1c)<7%, total cholesterol, coronary heart disease and dyslipidaemia. The secondary outcome was comparison of weighted UK DSP and reference data for BMI, BP, mean HbA1c, total cholesterol, smoking and insulin status. RESULTS: Comparison of unweighted China DSP and reference data revealed statistical equivalence for BMI, systolic BP, proportion of patients achieving HbA1c <7%, total cholesterol, coronary heart disease and dyslipidaemia. Sex, age, diabetes duration, diastolic BP and mean HbA1c level were not equivalent, although differences were generally small. Weighting of data did not substantially affect the results. A similar pattern was observed for UK data. CONCLUSIONS: This study provides evidence that the methodology used for the China and UK parts of the Diabetes DSP produces representative samples that are comparable with other independent sources of patient treatment outcomes data, which may ultimately inform public health decision-making. Although this method could be used in other countries, the current validation applies to UK and China. Further research is required for other countries.

Characterizing pharmacological ligands to study the long-chain fatty acid receptors GPR40/FFA1 and GPR120/FFA4.

The free fatty acid receptors (FFA) 1 (previously designated GPR40) and FFA4 (previously GPR120) are two GPCRs activated by saturated and unsaturated longer-chain free fatty acids. With expression patterns and functions anticipated to directly or indirectly promote insulin secretion, provide homeostatic control of blood glucose and improve tissue insulin sensitivity, both receptors are being studied as potential therapeutic targets for the control of type 2 diabetes. Furthermore, genetic and systems biology studies in both humans and mouse models link FFA4 receptors to diabetes and obesity. Although activated by the same group of free fatty acids, FFA1 and FFA4 receptors are not closely related and, while the basis of recognition of fatty acids by FFA1 receptors is similar to that of the short-chain fatty acid receptors FFA2 and FFA3, the amino acid residues involved in endogenous ligand recognition by FFA4 receptors are more akin to those of the sphingosine 1 phosphate receptor S1P1 . Screening and subsequent medicinal chemistry programmes have developed a number of FFA1 receptor selective agonists that are effective in promoting insulin secretion in a glucose concentration-dependent manner, and in lowering blood glucose levels. However, the recent termination of Phase III clinical trials employing TAK-875/fasiglifam has caused a setback and raises important questions over the exact nature and mechanistic causes of the problems. Progress in the identification and development of highly FFA4 receptor-selective pharmacological tools has been less rapid and several issues remain to be clarified to fully validate this receptor as a therapeutic target. Despite this, the ongoing development of a range of novel ligands offers great opportunities to further unravel the contributions of these receptors.

Factors affecting the foraging behaviour of the European shag: implications for seabird tracking studies.

Seabird tracking has become an ever more popular tool to aid environmental procedures such as the designation of marine protected areas and environmental impact assessments. However, samples used are usually small and little consideration is given to experimental design and sampling protocol. European shags Phalacrocorax aristotelis were tracked using GPS technology over three breeding seasons and the following foraging trip characteristics: trip duration, trip distance, maximum distance travelled from the colony, size of area used and direction travelled from colony were determined for each foraging trip. The effect of sex, year of study, breeding site, number and age of chicks and the timing of tracking on foraging behaviour were investigated using a General Estimation Equation model. A range of sampling scenarios reflecting likely field sampling were also tested to compare how foraging behaviour differed depending on composition of the sample of birds tracked. Trip distance, trip duration, maximum distance travelled and size of area used were all significantly affected by the breeding site, and the number of chicks a tracked adult was raising. The effect of sex was also seen when examining trip distance, trip duration and the maximum distance travelled. The direction travelled on a foraging trip was also significantly affected by breeding site. This study highlights the importance of sampling regime and the influence that year, sex, age, number of chicks and breeding site can have on the foraging trip characteristics for this coastal feeding seabird. Given the logistical and financial constraints in tracking large numbers of individuals, this study identifies the need for researchers to consider the composition of their study sample to ensure any identified foraging areas are as representative as possible of the whole colony's foraging area.

The three α1-adrenoceptor subtypes show different spatio-temporal mechanisms of internalization and ERK1/2 phosphorylation.

We analyzed the kinetic and spatial patterns characterizing activation of the MAP kinases ERK 1 and 2 (ERK1/2) by the three α1-adrenoceptor (α1-AR) subtypes in HEK293 cells and the contribution of two different pathways to ERK1/2 phosphorylation: protein kinase C (PKC)-dependent ERK1/2 activation and internalization-dependent ERK1/2 activation. The different pathways of phenylephrine induced ERK phosphorylation were determined by western blot, using the PKC inhibitor Ro 31-8425, the receptor internalization inhibitor concanavalin A and the siRNA targeting ß-arrestin 2. Receptor internalization properties were studied using CypHer5 technology and VSV-G epitope-tagged receptors. Activation of α1A- and α1B-ARs by phenylephrine elicited rapid ERK1/2 phosphorylation that was directed to the nucleus and inhibited by Ro 31-8425. Concomitant with phenylephrine induced receptor internalization α1A-AR, but not α1B-AR, produced a maintained and PKC-independent ERK phosphorylation, which was restricted to the cytosol and inhibited by ß-arrestin 2 knockdown or concanavalin A treatment. α1D-AR displayed constitutive ERK phosphorylation, which was reduced by incubation with prazosin or the selective α1D antagonist BMY7378. Following activation by phenylephrine, α1D-AR elicited rapid, transient ERK1/2 phosphorylation that was restricted to the cytosol and not inhibited by Ro 31-8425. Internalization of the α1D-AR subtype was not observed via CypHer5 technology. The three α1-AR subtypes present different spatio-temporal patterns of receptor internalization, and only α1A-AR stimulation translates to a late, sustained ERK1/2 phosphorylation that is restricted to the cytosol and dependent on ß-arrestin 2 mediated internalization.

Predicting small molecule fluorescent probe localization in living cells using QSAR modeling. 1. Overview and models for probes of structure, properties and function in single cells.

Small molecule fluorochromes (synonyms: biosensors, chemosensors, fluorescent probes, vital stains) are widely used to investigate the structure, composition, physicochemical properties and biological functions of living cells, tissues and organisms. Selective entry and accumulation within particular cells and cellular structures are key processes for achieving these diverse objectives. Despite the complexities, probes routinely are applied using standard protocols, often without experimenter awareness of what factors that control accumulation and localization. The mechanisms of many such selective accumulations, however, now are known. Moreover, the influence of physicochemical properties of probes on their uptake and localization often can be defined numerically, hence predicted, using quantitative structure activity relations (QSAR) models with its required numerical structure parameters (or "descriptors"). The state of the art of this approach is described. Available QSAR models are summarized for uptake into cells and localization in the cytosol, endoplasmic reticulum, generic biomembranes, Golgi apparatus, lipid droplets, lysosomes/endosomes, mitochondria, eukaryotic nuclei (histones and DNA), plasma membrane, and ribosomal RNA (cytoplasmic and nucleolar). Integration of such core models to both aid understanding and troubleshooting of current fluorescent probes and to assist the design of novel probes is outlined and illustrated using case examples. Limitations and generic problems arising with this approach and comments on application of such approaches to xenobiotics other than probes, e.g., drugs and herbicides, together with a brief note about an alternative approach to prediction, are given.

Physiological employment standards I. Occupational fitness standards: objectively subjective?

This paper examines the processes involved in the establishment of a minimum occupational fitness standard, with particular reference to the interplay that inevitably occurs between objective measurements and subjective decisions. The areas considered include: the determination of the critical task on which to base a standard; establishing minimum acceptable performance and methods of best practice for the execution of these tasks; determining the physical demands of a task and a reasonable relative workload; producing the final standard. Finally, the impact of the subjective component of the development of an occupational fitness standard on its defensibility is discussed. It is concluded that all standards involve some subjective aspects; the extent of these could be reduced by further research. In the meantime, it would be prudent for those developing standards to detail the rationale, methods and evidence by which subjective decisions were reached, to provide an audit trail for subsequent investigation.

Health-related quality of life and healthcare resource use in European patients with plaque psoriasis: an association independent of observed disease severity.

BACKGROUND: Healthcare resource utilization (HCRU) by patients with plaque psoriasis increases with skin lesion severity; however, the relationship between patient quality of life (QoL), which correlates only weakly with clinical severity, and HCRU is less understood. AIM: To evaluate the relationship between QoL, HCRU and employment in European patients with plaque psoriasis. METHODS: Patients (n = 897) were recruited in five European countries. Data were analysed by group according to the Dermatology Life Quality Index (DLQI): ≤ 10 (better QoL) and > 10 (worse QoL). RESULTS: Mean numbers of primary dermatologist visits and hospitalizations were significantly higher for patients with DLQI > 10. Likewise, significantly more patients with worse QoL reported employment disadvantages. Significant differences were maintained even after adjusting for age, gender and body surface area affected. CONCLUSIONS: In patients with plaque psoriasis, poorer QoL is associated with increased HCRU, independent of clinical severity. This suggests that QoL, in addition to skin lesion severity, should be considered in predicting the economic burden of disease.

Angiotensin1-9 antagonises pro-hypertrophic signalling in cardiomyocytes via the angiotensin type 2 receptor.

The renin­angiotensin system (RAS) regulates blood pressure mainly via the actions of angiotensin (Ang)II, generated via angiotensin converting enzyme (ACE). The ACE homologue ACE2 metabolises AngII to Ang1-7, decreasing AngII and increasing Ang1-7, which counteracts AngII activity via the Mas receptor. However, ACE2 also converts AngI to Ang1-9, a poorly characterised peptide which can be further converted to Ang1-7 via ACE. Ang1-9 stimulates bradykinin release in endothelium and has antihypertrophic actions in the heart, attributed to its being a competitive inhibitor of ACE, leading to decreased AngII, rather than increased Ang1-7. To date no direct receptor-mediated effects of Ang1-9 have been described. To further understand the role of Ang1-9 in RAS function we assessed its action in cardiomyocyte hypertrophy in rat neonatal H9c2 and primary adult rabbit left ventricular cardiomyocytes, compared to Ang1-7. Cardiomyocyte hypertrophy was stimulated with AngII or vasopressin, significantly increasing cell size by approximately 1.2-fold (P < 0.05) as well as stimulating expression of the hypertrophy gene markers atrial natriuretic peptide, brain natriuretic peptide, ß-myosin heavy chain and myosin light chain (2- to 5-fold, P < 0.05). Both Ang1-9 and Ang1-7 were able to block hypertrophy induced by either agonist (control, 186.4 µm; AngII, 232.8 µm; AngII+Ang1-7, 198.3 µm; AngII+Ang1-9, 195.9 µm; P < 0.05). The effects of Ang1-9 were not inhibited by captopril, supporting previous evidence that Ang1-9 acts independently of Ang1-7. Next, we investigated receptor signalling via angiotensin type 1 and type 2 receptors (AT1R, AT2R) and Mas. The AT1R antagonist losartan blocked AngII-induced, but not vasopressin-induced, hypertrophy. Losartan did not block the antihypertrophic effects of Ang1-9, or Ang1-7 on vasopressin-stimulated cardiomyocytes. The Mas antagonist A779 efficiently blocked the antihypertrophic effects of Ang1-7, without affecting Ang1-9. Furthermore, Ang1-7 activity was also inhibited in the presence of the bradykinin type 2 receptor antagonist HOE140, without affecting Ang1-9. Moreover, we observed that the AT2R antagonist PD123,319 abolished the antihypertrophic effects of Ang1-9, without affecting Ang1-7, suggesting Ang1-9 signals via the AT2R. Radioligand binding assays demonstrated that Ang1-9 was able to bind the AT2R (pKi = 6.28 ± 0.1). In summary, we ascribe a direct biological role for Ang1-9 acting via the AT2R. This has implications for RAS function and identifying new therapeutic targets in cardiovascular disease.

ß-Arrestin 1 inhibits the GTPase-activating protein function of ARHGAP21, promoting activation of RhoA following angiotensin II type 1A receptor stimulation.

Activation of the small GTPase RhoA following angiotensin II stimulation is known to result in actin reorganization and stress fiber formation. Full activation of RhoA, by angiotensin II, depends on the scaffolding protein ß-arrestin 1, although the mechanism behind its involvement remains elusive. Here we uncover a novel partner and function for ß-arrestin 1, namely, in binding to ARHGAP21 (also known as ARHGAP10), a known effector of RhoA activity, whose GTPase-activating protein (GAP) function it inhibits. Using yeast two-hybrid screening, a peptide array, in vitro binding studies, truncation analyses, and coimmunoprecipitation techniques, we show that ß-arrestin 1 binds directly to ARHGAP21 in a region that transects the RhoA effector GAP domain. Moreover, we show that the level of a complex containing ß-arrestin 1 and ARHGAP21 is dynamically increased following angiotensin stimulation and that the kinetics of this interaction modulates the temporal activation of RhoA. Using information gleaned from a peptide array, we developed a cell-permeant peptide that serves to inhibit the interaction of these proteins. Using this peptide, we demonstrate that disruption of the ß-arrestin 1/ARHGAP21 complex results in a more active ARHGAP21, leading to less-efficient signaling via the angiotensin II type 1A receptor and, thereby, attenuation of stimulated stress fiber formation.

GPR35 as a Novel Therapeutic Target.

G protein-coupled receptors (GPCRs) remain the best studied class of cell surface receptors and the most tractable family of proteins for novel small molecule drug discovery. Despite this, a considerable number of GPCRs remain poorly characterized and in a significant number of cases, endogenous ligand(s) that activate them remain undefined or are of questionable physiological relevance. GPR35 was initially discovered over a decade ago but has remained an "orphan" receptor. Recent publications have highlighted novel ligands, both endogenously produced and synthetic, which demonstrate significant potency at this receptor. Furthermore, evidence is accumulating which highlights potential roles for GPR35 in disease and therefore, efforts to characterize GPR35 more fully and develop it as a novel therapeutic target in conditions that range from diabetes and hypertension to asthma are increasing. Recently identified ligands have shown marked species selective properties, indicating major challenges for future drug development. As we begin to understand these issues, the continuing efforts to identify novel agonist and antagonist ligands for GPR35 will help to decipher its true physiological relevance; translating multiple assay systems in vitro, to animal disease systems in vivo and finally to man.

The risk of psoriatic arthritis remains constant following initial diagnosis of psoriasis among patients seen in European dermatology clinics.

BACKGROUND: Estimates of psoriatic arthritis (PsA) prevalence among psoriasis patients vary widely (5-40%). The time to development of PsA in patients with plaque psoriasis also remains unclear. OBJECTIVES: To examine whether length of time since diagnosis of psoriasis affects risk of developing PsA, and to assess differences in quality of life (QoL), work-related issues, comorbidities and healthcare resource utilization (HCRU) for patients with PsA vs. psoriasis. METHODS: This large cross-sectional observational study was conducted in the UK, Italy, France, Spain and Germany in 2006. Dermatologists who actively treated patients with psoriasis recruited 10 consecutive patients with psoriasis. Presence of PsA, body surface area (BSA) affected with psoriasis and HCRU were recorded; patients completed EUROQoL (EQ5D) and employment disadvantages questionnaires. RESULTS: Patients with psoriasis (n = 1560) included 126 with PsA. Ninety per cent of these patients with PsA were seen by dermatologists who involved a rheumatologist in the care of their patients with PsA. Survival analysis indicated that the incidence of PsA among psoriasis patients remained constant (74 per 1000 person-years), while the prevalence increased with time since diagnosis of psoriasis, reaching 20.5% after 30 years. In addition, those with high BSA currently affected by psoriasis were more likely to have developed PsA (P < 0.028). PsA patients reported reduced QoL compared with psoriasis patients (EQ5D score: 0.56 vs. 0.82: P < 0.0005), as well as more work problems. PsA patients were more likely to be hospitalized (0.27 +/- 0.84 vs. 0.14 +/- 0.71 per year; P < 0.0005) and have additional comorbidities than those without PsA. CONCLUSIONS: The incidence of PsA was constant after initial diagnosis of psoriasis, leading to a higher prevalence of concomitant PsA over time. PsA is associated with decreased QoL and increased work-related problems, HCRU and comorbidities. Dermatologists should screen for PsA in their patients, especially long-standing patients who did not initially present with PsA.

GPCR theme editorial.

This themed section of BJP includes 11 reviews on the biology of G-protein coupled receptors (GPCRs) and the drug targets that these present, 21 research papers on the pharmacology of a range of GPCRs and Commentaries on four of the papers. Areas reviewed include molecular interactions, particular in respect of hetero-dimerisation between receptors and other membrane-located proteins and other key signalling molecules including cAMP and G12/13 proteins and recently de-orphanised receptors including the Neuromedins U & S and the Free Fatty Acid receptors FFA2 & FFA3. The research papers cover the pharmacology of a range of agents acting at GPCRs, including adrenoceptors, purinoceptors, 5HT, opioid, cannabinoid & PAR-2 receptors. A group of papers is concerned with the interesting and rapidly developing pharmacology of drugs acting at beta(2)-adrenoceptors. The reach of GPCRs is illustrated by the range of physiological systems and therapeutic applications involved, including pain, cancer, cardiovascular, gastrointestinal, visual and respiratory and central nervous systems.

Co-expression of mu and delta opioid receptors as receptor-G protein fusions enhances both mu and delta signalling via distinct mechanisms.

Mu and delta opioid receptors (MORs and DORs) were co-expressed as fusion proteins between a receptor and a pertussis insensitive mutant Galpha(i/o) protein in human embryonic kidney 293 cells. Signalling efficiency was then monitored following inactivation of endogenous Galpha(i/o) proteins by pertussis toxin. Co-expression resulted in increased delta opioid signalling which was insensitive to the mu specific antagonist d-Phe-Cys-Tyr-d-Trp-Arg-Thr-Pen-Thr-NH2. Under these conditions, mu opioid signalling was also increased and insensitive to the delta specific antagonist Tic-deltorphin. In this latter case, however, no G protein activation was observed in the presence of the delta specific inverse agonist N,N(CH3)2-Dmt-Tic-NH2. When a MOR fused to a non-functional Galpha subunit was co-expressed with the DOR-Galpha protein fusion, delta opioid signalling was not affected whereas mu opioid signalling was restored. Altogether our results suggest that increased delta opioid signalling is due to enhanced DOR coupling to its tethered Galpha subunit. On the other hand, our data indicate that increased mu opioid signalling requires an active conformation of the DOR and also results in activation of the Galpha subunit fused the DOR.

A day in the life of a G protein-coupled receptor: the contribution to function of G protein-coupled receptor dimerization.

G protein-coupled receptors are one of the most actively studied families of proteins. However, despite the ubiquity of protein dimerization and oligomerization as a structural and functional motif in biology, until the last decade they were generally considered as monomeric, non-interacting polypeptides. For the metabotropic glutamate-like group of G protein-coupled receptors, it is now firmly established that they exist and function as dimers or, potentially, even within higher-order structures. Despite some evidence continuing to support the view that rhodopsin-like G protein-coupled receptors are predominantly monomers, many recent studies are consistent with the dimerization/oligomerization of such receptors. Key roles suggested for dimerization of G protein-coupled receptors include control of protein maturation and cell surface delivery and providing the correct framework for interactions with both hetero-trimeric G proteins and arrestins to allow signal generation and its termination. As G protein-coupled receptors are the most targeted group of proteins for the development of therapeutic small molecule medicines, recent indications that hetero-dimerization between co-expressed G protein-coupled receptors may be a common process offers the potential for the development of more selective and tissue restricted medicines. However, many of the key experiments have, so far, been limited to model cell systems. Priorities for the future include the generation of tools and reagents able to identify unequivocally potential G protein-coupled receptor hetero-dimers in native tissues and detailed analyses of the influence of hetero-dimerization on receptor function and pharmacology.

G-protein-coupled receptors: an update.

The receptors that couple to G proteins (GPCR) and which span the cell membranes seven times (7-TM receptors) were the focus of a symposium in Stockholm 2006. The ensemble of GPCR has now been mapped in several animal species. They remain a major focus of interest in drug development, and their diverse physiological and pathophysiological roles are being clarified, i.a. by genetic targeting. Recent developments hint at novel levels of complexity. First, many, if not all, GPCRs are part of multimeric ensembles, and physiology and pharmacology of a given GPCR may be at least partly guided by the partners it was formed together with. Secondly, at least some GPCRs may be constitutively active. Therefore, drugs that are inverse agonists may prove useful. Furthermore, the level of activity may vary in such a profound way between cells and tissues that this could offer new ways of achieving specificity of drug action. Finally, it is becoming increasingly clear that some of these receptors can signal via novel types of pathways, and hence that 'GPCRs' may not always be G-protein-coupled. Thus there are many challenges for the basic scientist and the drug industry.

The role of GPCR dimerisation/oligomerisation in receptor signalling.

A wide range of techniques have been employed to examine the quaternary structure of G-protein-coupled receptors (GPCRs). Although it is well established that homo-dimerisation is common, recent studies have sought to explore the physical basis of these interactions and the role of dimerisation in signal transduction. Growing evidence hints at the existence of higher-order organisation of individual GPCRs and the potential for hetero-dimerisation between pairs of co-expressed GPCRs. Here we consider how both homo-dimerisation/oligomerisation and hetero-dimerisation can regulate signal transduction through GPCRs and the potential consequences of this for function of therapeutic medicines that target GPCRs. Hetero-dimerisation is not the sole means by which co-expressed GPCRs may regulate the function of one another. Heterologous desensitisation may be at least as important and we also consider if this can be the basis for physiological antagonism between pairs of co-expressed GPCRs. Although there may be exceptions (Meyer et al. 2006), a great deal of recent evidence has indicated that most G-protein-coupled receptors (GPCRs) do not exist as monomers but rather as dimers or, potentially, within higher-order oligomers (Milligan 2004b; Park et al. 2004). Support for such models has been provided by a range of studies employing different approaches, including co-immunoprecipitation of differentially epitope-tagged but co-expressed forms of the same GPCR, co-operativity in ligand binding and a variety of resonance energy transfer techniques (Milligan and Bouvier 2005). Only for the photon receptor rhodopsin has the organisational structure of a GPCR been studied in situ. The application of atomic force microscopy to murine rod outer segment discs indicated that rhodopsin is organised in a series of parallel arrays of dimers (Liang et al. 2003) and based on this, molecular models were constructed to try to define and interpret regions of contact between the monomers (Fotiadis et al. 2004). Only for relatively few other GPCRs are details of the molecular basis of dimerisation available but within this limited data set, recent studies on the dopamine D2 receptor suggest a means by which information on the binding of an agonist can be transmitted between the two elements of the dimer via the dimer interface (Guo et al. 2005). Although the availability of cDNAs encoding molecularly defined GPCRs has allowed high-throughput screening for ligands that modulate GPCR function, this is performed almost exclusively in heterologous cell lines transfected to express only the specific GPCR of interest. Given that the human genome contains some 400-450 genes encoding non-chemosensory GPCRs, it is clear that any individual cell of the body may express a considerable number of GPCRs. Interactions between these, either via hetero-dimerisation, via heterologous desensitisation or via the integration of downstream signals can potentially alter the pharmacology, sensitivity and function of receptor agonists and hence produce varied responses. In this article, we will use specific examples to consider the role of homo-dimerisation/oligomerisation in GPCR function and whether either direct hetero-dimerisation or heterologous desensitisation between pairs of co-expressed GPCRs affects the function of the receptor pairs.