Chimeric antigens displaying GPR65 extracellular loops on a soluble scaffold enabled the discovery of antibodies, which recognized native receptor

GPR65 is a proton-sensing G-protein coupled receptor associated with multiple immune-mediated inflammatory diseases, whose function is relatively poorly understood. With few reagents commercially available to probe the biology of receptor, generation of an anti-GPR65 monoclonal antibody was desired. Using soluble chimeric scaffolds, such as ApoE3, displaying the extracellular loops of GPR65, together with established phage display technology, native GPR65 loop-specific antibodies were identified. Phage-derived loop-binding antibodies recognized the wild-type native receptor to which they had not previously been exposed, generating confidence in the use of chimeric soluble proteins to act as efficient surrogates for membrane protein extracellular loop antigens. This technique provides promise for the rational design of chimeric antigens in facilitating the discovery of specific antibodies to GPCRs.

Deciphering the role of glycosaminoglycans in GPCR signaling

G protein-coupled receptors (GPCR) and glycosaminoglycans (GAGs) are two essential components of the cell surface that regulate physiological processes in the body. GPCRs are the most extensive family of transmembrane receptors that control cellular responses to extracellular stimuli, while GAGs are polysaccharides that contribute to the function of the extracellular matrix (ECM). Due to their proximity to the plasma membrane, GAGs participate in signal transduction by interacting with various extracellular molecules and cell surface receptors. GAGs can directly interact with certain GPCRs or their ligands (chemokines, peptide hormones and neuropeptides, structural proteins, and enzymes) from the glutamate receptor family, the rhodopsin receptor family, the adhesion receptor family, and the secretin receptor family. These interactions have recently become an emerging topic, providing a new avenue for understanding how GPCR signaling is regulated. This review discusses our current state of knowledge about the role of GAGs in GPCR signaling and function.

The polybasic region in Gαi proteins: Relevant or not? Insights from Gαi3 research

Heterotrimeric G proteins are responsible for signal transduction from G-protein-coupled receptors (GPCRs) to intracellular effectors. This process is only possible when G proteins are located on the inner side of the cell membrane due to the specific localization of GPCR receptors. The Gα subunit is directed to the cell membrane through several signals, including modification by fatty acid moieties, interaction with the Gβγ complex, and, as observed in some Gα proteins, the presence of basic amino acid residues in the N-terminal region. In this work, we focused on investigating the influence of the polybasic region on the localization and function of a representative member of the Gαi family, Gαi3. Through the use of confocal microscopy and fluorescence lifetime microscopy, we showed that, in the case of this protein, neutralizing the positive charge does not significantly affect its abundance in the cell membrane. However, it does affect its spatial arrangement concerning the dopamine D2 receptor and influences inhibitory effect of Gαi3 on intracellular cAMP production triggered by D2 receptor stimulation. Moreover, in this work, we have shown, for the first time, that nonlipidated Gαi3 binds to negatively charged lipids through electrostatic interactions, and membrane fluidity plays a significant role in this interaction.

Melanin-concentrating hormone receptor 1 is discarded by exosomes after internalization

Melanin-concentrating hormone (MCH) receptor 1 (MCHR1), a G protein-coupled receptor, is poised for interaction with its ligands on the plasma membrane. Analyses of MCHR1 knockout mice suggest that this receptor could be a therapeutic target for the treatment of appetite disorders, glucose metabolism, psychiatric disorders, and inflammation. Binding of MCH to MCHR1 initiates calcium signaling, which is subsequently attenuated through receptor internalization. However, the ultimate destiny of the receptor post-internalization remains unexplored. In this study, we report the extracellular secretion of MCHR1 via exosomes. The recruitment of MCHR1 to exosomes occurs subsequent to its internalization, which is induced by stimulation with the ligand MCH. Although a highly glycosylated form of MCHR1, potentially representing a mature form, is selectively recruited to exosomes, the MCHR1 transferred into other cells does not exhibit functionality. The truncation of MCHR1 at the C-terminus not only impairs its response to MCH but also hinders its recruitment to exosomes. These findings imply that functional MCHR1 could be secreted extracellularly via exosomes, a process that may represent a mechanism for the termination of intracellular MCHR1 signaling.

Novel pharmacological targets for GABAergic dysfunction in ADHD

Attention deficit/hyperactivity disorder (ADHD) is a neurodevelopment disorder that affects approximately 5% of the population. The disorder is characterized by impulsivity, hyperactivity, and deficits in attention and cognition, although symptoms vary across patients due to the heterogenous and polygenic nature of the disorder. Stimulant medications are the standard of care treatment for ADHD patients, and their effectiveness has led to the dopaminergic hypothesis of ADHD in which deficits in dopaminergic signaling, especially in cortical brain regions, mechanistically underly ADHD pathophysiology. Despite their effectiveness in many individuals, almost one-third of patients do not respond to stimulant treatments and the long-term negative side effects of these medications remain unclear. Emerging clinical evidence is beginning to highlight an important role of dysregulated excitatory/inhibitory (E/I) balance in ADHD. These deficits in E/I balance are related to functional abnormalities in glutamate and Gamma-Aminobutyric Acid (GABA) signaling in the brain, with increasing emphasis placed on GABAergic interneurons driving specific aspects of ADHD pathophysiology. Recent genome-wide association studies (GWAS) have also highlighted how genes associated with GABA function are mutated in human populations with ADHD, resulting in the generation of several new genetic mouse models of ADHD. This review will discuss how GABAergic dysfunction underlies ADHD pathophysiology, and how specific receptors/proteins related to GABAergic interneuron dysfunction may be pharmacologically targeted to treat ADHD in subpopulations with specific comorbidities and symptom domains. This article is part of the Special Issue on "PFC circuit function in psychiatric disease and relevant models".

Wnt pathway inhibition with the porcupine inhibitor LGK974 decreases trabecular bone but not fibrosis in a murine model with fibrotic bone

G protein-coupled receptors (GPCRs) mediate a wide spectrum of physiological functions, including the development, remodeling, and repair of the skeleton. Fibrous dysplasia (FD) of the bone is characterized by fibrotic, expansile bone lesions caused by activating mutations in GNAS. There are no effective therapies for FD. We previously showed that ColI(2.3)+/Rs1+ mice, in which Gs-GPCR signaling was hyper-activated in osteoblastic cell lineages using an engineered receptor strategy, developed a fibrotic bone phenotype with trabecularization that could be reversed by normalizing Gs-GPCR signaling, suggesting that targeting the Gs-GPCR or components of the downstream signaling pathway could serve as a promising therapeutic strategy for FD. The Wnt signaling pathway has been implicated in the pathogenesis of FD-like bone, but the specific Wnts and which cells produce them remain largely unknown. Single-cell RNA sequencing on long-bone stromal cells of 9-wk-old male ColI(2.3)+/Rs1+ mice and littermate controls showed that fibroblastic stromal cells in ColI(2.3)+/Rs1+ mice were expanded. Multiple Wnt ligands were up- or downregulated in different cellular populations, including in non-osteoblastic cells. Treatment with the porcupine inhibitor LGK974, which blocks Wnt signaling broadly, induced partial resorption of the trabecular bone in the femurs of ColI(2.3)+/Rs1+ mice, but no significant changes in the craniofacial skeleton. Bone fibrosis remained evident after treatment. Notably, LGK974 caused significant bone loss in control mice. These results provide new insights into the role of Wnt and Gs-signaling in fibrosis and bone formation in a mouse model of Gs-GPCR pathway overactivation.

GPR84 in physiology-Many functions in many tissues

Members of the GPCR superfamily have a wide variety of physiological roles and are therefore valuable targets for developing effective medicines. However, within this superfamily are receptors that are less well characterized and remain orphans, including GPR84. This receptor is stimulated by ligands derived from dietary nutrients, specifically medium chain fatty acids (C9-14), and novel synthetic agonists. There are data demonstrating the role of GPR84 in inflammatory pathways, in addition to emerging data suggesting a key role for GPR84 as a nutrient-sensing GPCR involved in metabolism by sensing energy load via nutrient exposure and subsequent signalling leading to modulation of food intake. Exploring GPR84 pharmacology, its localization and what drives its expression has revealed multiple roles for this receptor. Here, we will reflect on these various roles of GRP84 demonstrated thus far, primarily by exploring data from pre-clinical and clinical studies in various physiological systems, with a specific focus on the gastrointestinal tract. LINKED ARTICLES: This article is part of a themed issue GPR84 Pharmacology. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v181.10/issuetoc.

Function and regulation of GPR84 in human neutrophils

Human neutrophils are components of the innate immune system and are the most abundant white blood cells in the circulation. They are professional phagocytes and express several G protein-coupled receptors (GPCRs), which are essential for proper neutrophil functions. So far, the two formyl peptide receptors, FPR1 and FPR2, have been the most extensively studied group of neutrophil GPCRs, but recently, a new group, the free fatty acid (FFA) receptors, has attracted growing attention. Neutrophils express two FFA receptors, GPR84 and FFA2, which sense medium- and short-chain fatty acids respectively, and display similar activation profiles. The exact pathophysiological role of GPR84 is not yet fully understood, but it is generally regarded as a pro-inflammatory receptor that mediates neutrophil activation. In this review, we summarize current knowledge of how GPR84 affects human neutrophil functions and discuss the regulatory mechanisms that control these responses, focusing on the similarities and differences in comparison to the two FPRs and FFA2. LINKED ARTICLES: This article is part of a themed issue GPR84 Pharmacology. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v181.10/issuetoc.

Molecular Determinant Underlying Selective Coupling of Primary G-Protein by Class A GPCRs

G-protein-coupled receptors (GPCRs) transmit downstream signals predominantly via G-protein pathways. However, the conformational basis of selective coupling of primary G-protein remains elusive. Histamine receptors H2R and H3R couple with Gs- or Gi-proteins respectively. Here, three cryo-EM structures of H2R-Gs and H3R-Gi complexes are presented at a global resolution of 2.6-2.7 Å. These structures reveal the unique binding pose for endogenous histamine in H3R, wherein the amino group interacts with E2065.46 of H3R instead of the conserved D1143.32 of other aminergic receptors. Furthermore, comparative analysis of the H2R-Gs and H3R-Gi complexes reveals that the structural geometry of TM5/TM6 determines the primary G-protein selectivity in histamine receptors. Machine learning (ML)-based structuromic profiling and functional analysis of class A GPCR-G-protein complexes illustrate that TM5 length, TM5 tilt, and TM6 outward movement are key determinants of the Gs and Gi/o selectivity among the whole Class A family. Collectively, the findings uncover the common structural geometry within class A GPCRs that determines the primary Gs- and Gi/o-coupling selectivity.

Alared: Solvatochromic and Fluorogenic Red Amino Acid for Ratiometric Live-cell Imaging of Bioactive Peptides

To fill the need for environmentally sensitive fluorescent unnatural amino acids able to operate in the red region of the spectrum, we have designed and synthesized Alared, a red solvatochromic and fluorogenic amino acid derived from the Nile Red chromophore. The new unnatural amino acid can be easily integrated into bioactive peptides using classical solid-phase peptide synthesis. The fluorescence quantum yield and the emission maximum of Alared-labeled peptides vary in a broad range depending on the peptide's environment, making Alared a powerful reporter of biomolecular interactions. Due to its red-shifted absorption and emission spectra, Alared-labeled peptides could be followed in living cells with minimal interference from cellular autofluorescence. Using ratiometric fluorescence microscopy, we were able to track the fate of the Alared-labeled peptide agonists of the apelin G protein-coupled receptor upon receptor activation and internalization. Due to its color-shifting environmentally sensitive emission, Alared allowed for distinguishing the fractions of peptides that are specifically bound to the receptor or unspecifically bound to different cellular membranes.

Deciphering a GPCR-lncRNA-miRNA Nexus: Identification of an Aberrant Therapeutic Target in Ovarian Cancer

Ovarian cancer ranks as a leading cause of mortality among gynecological malignancies, primarily due to the lack of early diagnostic tools, effective targeted therapy, and clear understanding of disease etiology. Previous studies have identified the pivotal role of Lysophosphatidic acid (LPA)-signaling in ovarian cancer pathobiology. Our earlier transcriptomic analysis identified Urothelial Carcinoma Associated-1 (UCA1) as an LPA-stimulated long non-coding RNA (lncRNA). In this study, we elucidate the tripartite interaction between LPA-signaling, UCA1, and let-7 miRNAs in ovarian cancer progression. Results show that the elevated expression of UCA1 enhances cell proliferation, invasive migration, and therapy resistance in high-grade serous ovarian carcinoma cells, whereas silencing UCA1 reverses these oncogenic phenotypes. UCA1 expression inversely correlates with survival outcomes and therapy response in ovarian cancer clinical samples, underscoring its prognostic significance. Mechanistically, UCA1 sequesters let-7 miRNAs, effectively neutralizing their tumor-suppressive functions involving key oncogenes such as Ras and c-Myc. More significantly, intratumoral delivery of UCA1-specific siRNAs inhibits the growth of cisplatin-refractory ovarian cancer xenografts, demonstrating the therapeutic potential of targeting LPAR-UCA1-let-7 axis in ovarian cancer. Thus, our results identify LPAR-UCA1-let-7 axis as a novel avenue for targeted treatment strategies.

Characterization of myoinhibitory peptide signaling system and its implication in larval metamorphosis and spawning behavior in Pacific abalone

Myoinhibitory peptides (MIPs) affect various physiological functions, including juvenile hormone signaling, muscle contraction, larval development, and reproduction in invertebrates. Although MIPs are ligands for MIP and/or sex peptide receptors (MIP/SPRs) in diverse arthropods and model organisms belonging to Lophotrochozoa, the MIP signaling system has not yet been fully investigated in mollusks. In this study, we identified the MIP signaling system in the Pacific abalone Haliotis discus hannai (Hdh). Similar to the invertebrate MIPs, a total of eight paracopies of MIPs (named Hdh-MIP1 to Hdh-MIP8), harboring a WX5-7Wamide motif, except for Hdh-MIP2, were found in the Hdh-MIP precursor. Furthermore, we characterized a functional Hdh-MIPR, which responded to the Hdh-MIPs, except for Hdh-MIP2, possibly linked with the PKC/Ca2+ and PKA/cAMP signaling pathways. Hdh-MIPs delayed larval metamorphosis but increased the spawning behavior. These results suggest that the Hdh-MIP signaling system provides insights into the unique function of MIP in invertebrates.

Cascaded amplifying circuit enables sensitive detection of fungal pathogens

The rapid and accurate detection of fungal pathogens is of utmost importance in the fields of healthcare, food safety, and environmental monitoring. In this study, we implemented a cascaded amplifying circuit in Saccharomyces cerevisiae to improve the G protein-coupled receptor (GPCR) mediated fungal detection. The GPCR signaling pathway was coupled with the galactose-regulated (GAL) system and a positive feedback loop was implemented to enhance the performance of yeast biosensor. We systematically compared four generations of biosensors for detecting the mating pheromone of Candida albicans, and the best biosensor exhibited the limit of detection (LOD) as low as 0.25 pM and the limit of quantification (LOQ) of 1 pM after 2 h incubation. Subsequently, we developed a betaxanthin-based colorimetric module for the easy visualization of signal outputs, and the resulting biosensors can give reliable naked-eye readouts. In summary, we demonstrated that cascaded amplifying circuits could substantially improve the engineered yeast biosensors with a better sensitivity and signal output magnitude, which will pave the way for their real-world applications in public health.

Non-canonical adrenergic neuromodulation of motoneuron intrinsic excitability through β-receptors in wild-type and ALS mice

Altered neuronal excitability and synaptic inputs to motoneurons are part of the pathophysiology of Amyotrophic Lateral Sclerosis. The cAMP/PKA pathway regulates both of them but therapeutic interventions at this level are limited by the lack of knowledge about suitable pharmacological entry points. Here we used transcriptomics on microdissected and in situ motoneurons to reveal the modulation of PKA-coupled receptorome in SOD1(G93A) ALS mice, vs WT, demonstrating the dysregulation of multiple PKA-coupled GPCRs, in particular on vulnerable MNs, and the relative sparing of β-adrenergic receptors. In vivo MN electrophysiology showed that β2/β3 agonists acutely increase excitability, in particular the input/output relationship, demonstrating a non-canonical adrenergic neuromodulation mediated by β2/β3 receptors both in WT and SOD1 mice. The excitability increase corresponds to the upregulation of immediate-early gene expression and dysregulation of ion channels transcriptome. However the β2/β3 neuromodulation is submitted to a strong homeostasis, since a ten days delivery of β2/β3 agonists results in an abolition of the excitability increase. The homeostatic response is largely caused by a substantial downregulation of PKA-coupled GPCRs in MNs from WT and SOD1 mice. Thus, β-adrenergic receptors are physiologically involved in the regulation of MN excitability and transcriptomics, but, intriguingly, a strong homeostatic response is triggered upon chronic pharmacologic intervention.

GPCR kinase subtype requirements for arrestin-2 and -3 translocation to the cannabinoid CB1 receptor and the consequences on G protein signalling

Arrestins are key negative regulators of G Protein-Coupled Receptors (GPCRs) through mediation of G protein desensitisation and receptor internalisation. Arrestins can also contribute to signal transduction by scaffolding downstream signalling effectors for activation. GPCR kinase (GRK) enzymes phosphorylate the intracellular C-terminal domain, or intracellular loop regions of GPCRs to promote arrestin interaction. There are seven different GRK subtypes, which may uniquely phosphorylate the C-terminal tail in a type of 'phosphorylation barcode,' potentially differentially contributing to arrestin translocation and arrestin-dependent signalling. Such contributions may be exploited to develop arrestin-biased ligands. Here, we examine the effect of different GRK subtypes on the ability to promote translocation of arrestin-2 and arrestin-3 to the cannabinoid CB1 receptor (CB1) with a range of ligands. We find that most GRK subtypes (including visual GRK1) can enhance arrestin-2 and -3 translocation to CB1, and that GRK-dependent changes in arrestin-2 and arrestin-3 translocation were broadly shared for most agonists tested. GRK2/3 generally enhanced arrestin translocation more than the other GRK subtypes, with some small differences between ligands. We also explore the interplay between G protein activity and GRK2/3-dependent arrestin translocation, highlighting that high-efficacy G protein agonists will cause GRK2/3 dependent arrestin translocation. This study supports the hypothesis that arrestin-biased ligands for CB1 must engage GRK5/6 rather than GRK2/3, and G protein-biased ligands must have inherently low efficacy.

The biased apelin receptor agonist, MM07, reverses Sugen/hypoxia-induced pulmonary arterial hypertension as effectively as the endothelin antagonist macitentan

Introduction: Pulmonary arterial hypertension (PAH) is characterised by endothelial dysfunction and pathological vascular remodelling, resulting in the occlusion of pulmonary arteries and arterioles, right ventricular hypertrophy, and eventually fatal heart failure. Targeting the apelin receptor with the novel, G protein-biased peptide agonist, MM07, is hypothesised to reverse the developed symptoms of elevated right ventricular systolic pressure and right ventricular hypertrophy. Here, the effects of MM07 were compared with the clinical standard-of-care endothelin receptor antagonist macitentan. Methods: Male Sprague-Dawley rats were randomised and treated with either normoxia/saline, or Sugen/hypoxia (SuHx) to induce an established model of PAH, before subsequent treatment with either saline, macitentan (30 mg/kg), or MM07 (10 mg/kg). Rats were then anaesthetised and catheterised for haemodynamic measurements, and tissues collected for histopathological assessment. Results: The SuHx/saline group presented with significant increases in right ventricular hypertrophy, right ventricular systolic pressure, and muscularization of pulmonary arteries compared to normoxic/saline controls. Critically, MM07 was as at least as effective as macitentan in significantly reversing detrimental structural and haemodynamic changes after 4 weeks of treatment. Discussion: These results support the development of G protein-biased apelin receptor agonists with improved pharmacokinetic profiles for use in human disease.

Frizzleds act as dynamic pharmacological entities

The Frizzled family of transmembrane receptors (FZD1-10) belongs to the class F of G protein-coupled receptors (GPCRs). FZDs bind to and are activated by Wingless/Int1 (WNT) proteins. The WNT/FZD signaling system regulates crucial aspects of developmental biology and stem-cell regulation. Dysregulation of WNT/FZD communication can lead to developmental defects and diseases such as cancer and fibrosis. Recent insight into the activation mechanisms of FZDs has underlined that protein dynamics and conserved microswitches are essential for FZD-mediated information flow and build the basis for targeting these receptors pharmacologically. In this review, we summarize recent advances in our understanding of FZD activation, and how novel concepts merge and collide with existing dogmas in the field.

Intracellular pathways of calcitonin gene-related peptide-induced relaxation of human coronary arteries: A key role for Gβγ subunit instead of cAMP

BACKGROUND AND PURPOSE

Calcitonin gene-related peptide (CGRP) is a potent vasodilator. While its signalling is assumed to be mediated via increases in cAMP, this study focused on elucidating the actual intracellular signalling pathways involved in CGRP-induced relaxation of human isolated coronary arteries (HCA).

EXPERIMENTAL APPROACH

HCA were obtained from heart valve donors (27 M, 25 F, age 54 ± 2 years). Concentration-response curves to human α-CGRP or forskolin were constructed in HCA segments, incubated with different inhibitors of intracellular signalling pathways, and intracellular cAMP levels were measured with and without stimulation.

RESULTS

Adenylyl cyclase (AC) inhibitors SQ22536 + DDA and MDL-12330A, and PKA inhibitors Rp-8-Br-cAMPs and H89, did not inhibit CGRP-induced relaxation of HCA, nor did the guanylyl cyclase inhibitor ODQ, PKG inhibitor KT5823, EPAC1/2 inhibitor ESI09, potassium channel blockers TRAM-34 + apamin, iberiotoxin or glibenclamide, or the Gαq inhibitor YM-254890. Phosphodiesterase inhibitors induced a concentration-dependent decrease in the response to KCl but did not potentiate relaxation to CGRP. Relaxation to forskolin was not blocked by PKA or AC inhibitors, although AC inhibitors significantly inhibited the increase in cAMP. Inhibition of Gβγ subunits using gallein significantly inhibited the relaxation to CGRP in human coronary arteries.

CONCLUSION

While CGRP signalling is generally assumed to act via cAMP, the CGRP-induced vasodilation in HCA was not inhibited by targeting this intracellular signalling pathway at different levels. Instead, inhibition of Gβγ subunits did inhibit the relaxation to CGRP, suggesting a different mechanism of CGRP-induced relaxation than generally believed.

Pharmacological characterization of seven human histamine H3 receptor isoforms

The histamine H3 receptor (H3R) regulates as a presynaptic G protein-coupled receptor the release of histamine and other neurotransmitters in the brain, and is consequently a potential therapeutic target for neuronal disorders. The human H3R encodes for seven splice variants that vary in the length of intracellular loop 3 and/or the C-terminal tail but are all able to induce heterotrimeric Gi protein signaling. The last two decades H3R drug discovery and lead optimization has been exclusively focused on the 445 amino acids-long reference isoform H3R-445. In this study, we pharmacologically characterized for the first time all seven H3R isoforms by determining their binding affinities for reference histamine H3 receptor agonists and inverse agonists. The H3R-453, H3R-415, and H3R-413 isoforms display similar binding affinities for all ligands as the H3R-445. However, increased agonist binding affinities were observed for the three shorter isoforms H3R-329, H3R-365, and H3R-373, whereas inverse agonists such as the approved anti-narcolepsy drug pitolisant (Wakix®) displayed significantly decreased binding affinities for the latter two isoforms. This opposite change in binding affinity of agonist versus inverse agonists on H3R-365 and H3R-373 is associated with their higher constitutive activity in a cAMP biosensor assay as compared to the other five isoforms. The observed differences in pharmacology between longer and shorter H3R isoforms should be considered in future drug discovery programs.

Discovery of a Photoaffinity Probe that Captures the Active Conformation of the Cannabinoid CB2 Receptor

The cannabinoid receptor type 2 (CB2R) is a G protein-coupled receptor with therapeutic potential for the treatment of inflammatory disorders. Fluorescent probes are desirable to study its receptor localization, expression and occupancy. Previously, we have reported a photoaffinity probe LEI-121 that stabilized the inactive conformation of the CB2R. Here, we report the structure-based design of a novel bifunctional probe that captures the active conformation of the CB2R upon irradiation with light. An alkyne handle was incorporated to visualize the receptor using click-chemistry with fluorophore-azides. These probes may hold promise to study different receptor conformations in relation to their cellular localization and function.

Discovery of potential TAAR1 agonist targeting neurological and psychiatric disorders: An in silico approach

Trace amine-associated receptor 1 (TAAR1) is a G-protein-coupled receptor which is primarily expressed in the brain. It is activated by trace amines which play a role in regulating neurotransmitters like dopamine, serotonin and norepinephrine. TAAR1 agonists have potential applications in the treatment of neurological and psychiatric disorders, especially schizophrenia. In this study, we have used a structure-based virtual screening approach to identify potential TAAR1 agonist(s). We have modelled the structure of TAAR1 and predicted the binding pocket. Further, molecular docking of a few well-known antipsychotic drugs was carried out with TAAR1 model, which showed key interactions with the binding pocket. From screening a library of 5 million compounds from the Enamine REAL Database using structure-based virtual screening method, we shortlisted 12 compounds which showed good docking score, glide energy and interactions with the key residues. One lead compound (Z31378290) was finally selected. The lead compound showed promising binding affinity and stable interactions with TAAR1 during molecular dynamics simulations and demonstrated better van der Waals and binding energy than the known agonist, ulotaront. Our findings suggest that the lead compound may serve as a potential TAAR1 agonist, offering a promising avenue for the development of new therapies for neurological and psychiatric disorders.

Imaging flow cytometry of tumoroids: A new method for studying GPCR expression

Fluorescence confocal microscopy is commonly used to analyze the regulation membrane proteins expression such as G protein-coupled receptors (GPCRs). With this approach, the internal movement of GPCRs within the cell can be observed with a high degree of resolution. However, these microscopy techniques led to complex and time-consuming analysis and did not allow a large population of events to be sampled. A recent approach termed imaging flow cytometry (IFC), which combines flow cytometry and fluorescence microscopy, had two main advantages to study the regulation of GPCRs expression such as orexins receptors (OXRs): the ability (1) to analyze large numbers of cells and; (2) to visualize cell integrity and fluorescent markers localization. Here, we compare these two technologies using the orexin A (OxA) ligand coupled to rhodamine (OxA-rho) to investigate anti-tumoral OX1R expression in human digestive cancers. IFC has been adapted for cancer epithelial adherent cells and also to 3D cell culture tumoroids which partially mimic tumoral structures. In the absence of specific antibody, expression of OX1R is examined in the presence of OxA-rho. 2D-culture of colon cancer cells HT-29 exhibits a maximum level of OX1R internalization induced by OxA with 19% ± 3% colocalizing to early endosomes. In 3D-culture of HT-29 cells, internalization of OX1R/OxA-rho reached its maximum at 60 min, with 30.7% ± 6.4% of OX1R colocalizing with early endosomes. This is the first application of IFC to the analysis of the expression of a native GPCR, OX1R, in both 2D and 3D cultures of adherent cancer cells.

In silico identification of a biarylamine acting as agonist at human β3 adrenoceptors and exerting BRL37344-like effects on mouse metabolism

Human β3-adrenoceptor (β3AR) agonists were considered potential agents for the treatment of metabolic disorders. However, compounds tested as β3AR ligands have shown marked differences in pharmacological profile in rodent and human species, although these compounds remain attractive as they were successfully repurposed for the therapy of urinary incontinence. In this work, some biarylamine compounds were designed and tested in silico as potential β3AR agonists on 3-D models of mouse or human β3ARs. Based on the theoretical results, we identified, synthesized and tested a biarylamine compound (polibegron). In CHO-K1 cells expressing the human β3AR, polibegron and the β3AR agonist BRL 37344 were partial agonists for stimulating cAMP accumulation (50 and 57% of the response to isoproterenol, respectively). The potency of polibegron was 1.71- and 4.5-fold higher than that of isoproterenol and BRL37344, respectively. These results indicate that polibegron acts as a potent, but partial, agonist at human β3ARs. In C57BL/6N mice with obesity induced by a high-fat diet, similar effects of the equimolar intraperitoneal administration of polibegron and BRL37344 were observed on weight, visceral fat and plasma levels of glucose, cholesterol and triglycerides. Similarities and differences between species related to ligand-receptor interactions can be useful for drug designing.

A M1 muscarinic acetylcholine receptor-specific positive allosteric modulator VU0486846 reduces neurogliosis in female Alzheimer's mice

Alzheimer's disease (AD) is the most prevalent type of dementia, disproportionately affecting females, who make up nearly 60% of diagnosed cases. In AD patients, the accumulation of beta-amyloid (Aβ) in the brain triggers a neuroinflammatory response driven by neuroglia, worsening the condition. We have previously demonstrated that VU0486846, an orally available positive allosteric modulator (PAM) targeting M1 muscarinic acetylcholine receptors, enhances cognitive function and reduces Aβ pathology in female APPswe/PSEN1ΔE9 (APP/PS1) mice. However, it remained unclear whether these improvements were linked to a decrease in neuroglial activation. To investigate, we treated nine-month-old APP/PS1 and wildtype mice with VU0486846 for 8 weeks and analyzed brain slices for markers of microglial activation (ionized calcium binding adaptor molecule 1, Iba1) and astrocyte activation (Glial fibrillary acidic protein, GFAP). We find that VU0486846 reduces the presence of Iba1-positive microglia and GFAP-positive astrocytes in the hippocampus of female APP/PS1 mice and limits the recruitment of these cells to remaining Aβ plaques. This study sheds light on an additional mechanism through which novel M1 mAChR PAMs exhibit disease-modifying effects by reducing neuroglial activation and underscore the potential of these ligands for the treatment of AD, especially in females.

Butyrate as a promising therapeutic target in cancer: From pathogenesis to clinic (Review)

Cancer is one of the leading causes of mortality worldwide. The etiology of cancer has not been fully elucidated yet, and further enhancements are necessary to optimize therapeutic efficacy. Butyrate, a short‑chain fatty acid, is generated through gut microbial fermentation of dietary fiber. Studies have unveiled the relevance of butyrate in malignant neoplasms, and a comprehensive understanding of its role in cancer is imperative for realizing its full potential in oncological treatment. Its full antineoplastic effects via the activation of G protein‑coupled receptors and the inhibition of histone deacetylases have been also confirmed. However, the underlying mechanistic details remain unclear. The present study aimed to review the involvement of butyrate in carcinogenesis and its molecular mechanisms, with a particular emphasis on its association with the efficacy of tumor immunotherapy, as well as discussing relevant clinical studies on butyrate as a therapeutic target for neoplastic diseases to provide new insights into cancer treatment.

Fluorine-19 labeling of the tryptophan residues in the G protein-coupled receptor NK1R using the 5-fluoroindole precursor in Pichia pastoris expression

In NMR spectroscopy of biomolecular systems, the use of fluorine-19 probes benefits from a clean background and high sensitivity. Therefore, 19F-labeling procedures are of wide-spread interest. Here, we use 5-fluoroindole as a precursor for cost-effective residue-specific introduction of 5-fluorotryptophan (5F-Trp) into G protein-coupled receptors (GPCRs) expressed in Pichia pastoris. The method was successfully implemented with the neurokinin 1 receptor (NK1R). The 19F-NMR spectra of 5F-Trp-labeled NK1R showed one well-separated high field-shifted resonance, which was assigned by mutational studies to the "toggle switch tryptophan". Residue-selective labeling thus enables site-specific investigations of this functionally important residue. The method described here is inexpensive, requires minimal genetic manipulation and can be expected to be applicable for yeast expression of GPCRs at large.

Preassembly of specific Gβγ subunits at GABAB receptors through auxiliary KCTD proteins accelerates channel gating

GABAB receptors (GBRs) are G protein-coupled receptors for GABA, the main inhibitory neurotransmitter in the brain. GBRs regulate fast synaptic transmission by gating Ca2+ and K+ channels via the Gβγ subunits of the activated G protein. It has been demonstrated that auxiliary GBR subunits, the KCTD proteins, shorten onset and rise time and increase desensitization of receptor-induced K+ currents. KCTD proteins increase desensitization of K+ currents by scavenging Gβγ from the channel, yet the mechanism responsible for the rapid activation of K+ currents has remained elusive. In this study, we demonstrate that KCTD proteins preassemble Gβγ at GBRs. The preassembly obviates the need for diffusion-limited G protein recruitment to the receptor, thereby accelerating G protein activation and, as a result, K+ channel activation. Preassembly of Gβγ at the receptor relies on the interaction of KCTD proteins with a loop protruding from the seven-bladed propeller of Gβ subunits. The binding site is shared between Gβ1 and Gβ2, limiting the interaction of KCTD proteins to these particular Gβ isoforms. Substituting residues in the KCTD binding site of Gβ1 with those from Gβ3 hinders the preassembly of Gβγ with GBRs, delays onset and prolongs rise time of receptor-activated K+ currents. The KCTD-Gβ interface, therefore, represents a target for pharmacological modulation of channel gating by GBRs.

Computational Characterization of Membrane Proteins as Anticancer Targets: Current Challenges and Opportunities

Cancer remains a leading cause of mortality worldwide and calls for novel therapeutic targets. Membrane proteins are key players in various cancer types but present unique challenges compared to soluble proteins. The advent of computational drug discovery tools offers a promising approach to address these challenges, allowing for the prioritization of "wet-lab" experiments. In this review, we explore the applications of computational approaches in membrane protein oncological characterization, particularly focusing on three prominent membrane protein families: receptor tyrosine kinases (RTKs), G protein-coupled receptors (GPCRs), and solute carrier proteins (SLCs). We chose these families due to their varying levels of understanding and research data availability, which leads to distinct challenges and opportunities for computational analysis. We discuss the utilization of multi-omics data, machine learning, and structure-based methods to investigate aberrant protein functionalities associated with cancer progression within each family. Moreover, we highlight the importance of considering the broader cellular context and, in particular, cross-talk between proteins. Despite existing challenges, computational tools hold promise in dissecting membrane protein dysregulation in cancer. With advancing computational capabilities and data resources, these tools are poised to play a pivotal role in identifying and prioritizing membrane proteins as personalized anticancer targets.

Exploring Diverse Signaling Mechanisms of G Protein-Coupled Receptors through Structural Biology

Recent advancements in structural biology have facilitated the elucidation of complexes involving G protein-coupled receptors (GPCRs) and their associated signal transducers, including G proteins and arrestins. A comprehensive analysis of these structures provides profound insights into the dynamics of signaling mechanisms. These structural revelations can potentially guide the development of drugs to minimize side effects through targeted and selective signaling. Understanding the binding modes of different signal-selective ligands is imperative for future drug research and development. Here, we conduct a comparative examination of the structural details of various GPCR-signal transducer complexes and delve into the molecular basis of the currently proposed signal selectivity.

Biochemical pharmacology of adenylyl cyclases in cancer

Globally, despite extensive research and pharmacological advancement, cancer remains one of the most common causes of mortality. Understanding the signaling pathways involved in cancer progression is essential for the discovery of new drug targets. The adenylyl cyclase (AC) superfamily comprises glycoproteins that regulate intracellular signaling and convert ATP into cyclic AMP, an important second messenger. The present review highlights the involvement of ACs in cancer progression and suppression, broken down for each specific mammalian AC isoform. The precise mechanisms by which ACs contribute to cancer cell proliferation and invasion are not well understood and are variable among cancer types; however, AC overactivation, along with that of downstream regulators, presents a potential target for novel anticancer therapies. The expression patterns of ACs in numerous cancers are discussed. In addition, we highlight inhibitors of AC-related signaling that are currently under investigation, with a focus on possible anti-cancer strategies. Recent discoveries with small molecules regarding more direct modulation AC activity are also discussed in detail. A more comprehensive understanding of different components in AC-related signaling could potentially lead to the development of novel therapeutic strategies for personalized oncology and might enhance the efficacy of chemoimmunotherapy in the treatment of various cancers.

Opsin expression varies across larval development and taxa in pteriomorphian bivalves

Introduction

Many marine organisms have a biphasic life cycle that transitions between a swimming larva with a more sedentary adult form. At the end of the first phase, larvae must identify suitable sites to settle and undergo a dramatic morphological change. Environmental factors, including photic and chemical cues, appear to influence settlement, but the sensory receptors involved are largely unknown. We targeted the protein receptor, opsin, which belongs to large superfamily of transmembrane receptors that detects environmental stimuli, hormones, and neurotransmitters. While opsins are well-known for light-sensing, including vision, a growing number of studies have demonstrated light-independent functions. We therefore examined opsin expression in the Pteriomorphia, a large, diverse clade of marine bivalves, that includes commercially important species, such as oysters, mussels, and scallops.

Methods

Genomic annotations combined with phylogenetic analysis show great variation of opsin abundance among pteriomorphian bivalves, including surprisingly high genomic abundance in many species that are eyeless as adults, such as mussels. Therefore, we investigated the diversity of opsin expression from the perspective of larval development. We collected opsin gene expression in four families of Pteriomorphia, across three distinct larval stages, i.e., trochophore, veliger, and pediveliger, and compared those to adult tissues.

Results

We found larvae express all opsin types in these bivalves, but opsin expression patterns are largely species-specific across development. Few opsins are expressed in the adult mantle, but many are highly expressed in adult eyes. Intriguingly, opsin genes such as retinochrome, xenopsins, and Go-opsins have higher levels of expression in the later larval stages when substrates for settlement are being tested, such as the pediveliger.

Conclusion

Investigating opsin gene expression during larval development provides crucial insights into their intricate interactions with the surroundings, which may shed light on how opsin receptors of these organisms respond to various environmental cues that play a pivotal role in their settlement process.

Direct interrogation of context-dependent GPCR activity with a universal biosensor platform

G protein-coupled receptors (GPCRs) are the largest family of druggable proteins encoded in the human genome, but progress in understanding and targeting them is hindered by the lack of tools to reliably measure their nuanced behavior in physiologically relevant contexts. Here, we developed a collection of compact ONE vector G-protein Optical (ONE-GO) biosensor constructs as a scalable platform that can be conveniently deployed to measure G-protein activation by virtually any GPCR with high fidelity even when expressed endogenously in primary cells. By characterizing dozens of GPCRs across many cell types like primary cardiovascular cells or neurons, we revealed insights into the molecular basis for G-protein coupling selectivity of GPCRs, pharmacogenomic profiles of anti-psychotics on naturally occurring GPCR variants, and G-protein subtype signaling bias by endogenous GPCRs depending on cell type or upon inducing disease-like states. In summary, this open-source platform makes the direct interrogation of context-dependent GPCR activity broadly accessible.

Interaction modes of human orexin 2 receptor with selective and nonselective antagonists studied by NMR spectroscopy

Orexin neuropeptides have many physiological roles in the sleep-wake cycle, feeding behavior, reward demands, and stress responses by activating cognitive receptors, the orexin receptors (OX1R and OX2R), distributed in the brain. There are only subtle differences between OX1R and OX2R in the orthosteric site, which has hindered the rational development of subtype-selective antagonists. In this study, we utilized solution-state NMR to capture the structural plasticity of OX2R labeled with 13CH3-ε-methionine in complex with antagonists. Mutations in the orthosteric site allosterically affected the intracellular tip of TM6. Ligand exchange experiments with the subtype-selective EMPA and the nonselective suvorexant identified three methionine residues that were substantially perturbed. The NMR spectra suggested that the suvorexant-bound state exhibited more structural plasticity than the EMPA-bound state, which has not been foreseen from the close similarity of their crystal structures, providing insights into dynamic features to be considered in understanding the ligand recognition mode.

The association of GNB5 with Alzheimer disease revealed by genomic analysis restricted to variants impacting gene function

Disease-associated variants identified from genome-wide association studies (GWASs) frequently map to non-coding areas of the genome such as introns and intergenic regions. An exclusive reliance on gene-agnostic methods of genomic investigation could limit the identification of relevant genes associated with polygenic diseases such as Alzheimer disease (AD). To overcome such potential restriction, we developed a gene-constrained analytical method that considers only moderate- and high-risk variants that affect gene coding sequences. We report here the application of this approach to publicly available datasets containing 181,388 individuals without and with AD and the resulting identification of 660 genes potentially linked to the higher AD prevalence among Africans/African Americans. By integration with transcriptome analysis of 23 brain regions from 2,728 AD case-control samples, we concentrated on nine genes that potentially enhance the risk of AD: AACS, GNB5, GNS, HIPK3, MED13, SHC2, SLC22A5, VPS35, and ZNF398. GNB5, the fifth member of the heterotrimeric G protein beta family encoding Gβ5, is primarily expressed in neurons and is essential for normal neuronal development in mouse brain. Homozygous or compound heterozygous loss of function of GNB5 in humans has previously been associated with a syndrome of developmental delay, cognitive impairment, and cardiac arrhythmia. In validation experiments, we confirmed that Gnb5 heterozygosity enhanced the formation of both amyloid plaques and neurofibrillary tangles in the brains of AD model mice. These results suggest that gene-constrained analysis can complement the power of GWASs in the identification of AD-associated genes and may be more broadly applicable to other polygenic diseases.

Inhibition of a novel Dickkopf-1-LDL receptor-related proteins 5 and 6 axis prevents diabetic cardiomyopathy in mice

BACKGROUND AND AIMS

Anti-hypertensive agents are one of the most frequently used drugs worldwide. However, no blood pressure-lowering strategy is superior to placebo with respect to survival in diabetic hypertensive patients. Previous findings show that Wnt co-receptors LDL receptor-related proteins 5 and 6 (LRP5/6) can directly bind to several G protein-coupled receptors (GPCRs). Because angiotensin II type 1 receptor (AT1R) is the most important GPCR in regulating hypertension, this study examines the possible mechanistic association between LRP5/6 and their binding protein Dickkopf-1 (DKK1) and activation of the AT1R and further hypothesizes that the LRP5/6-GPCR interaction may affect hypertension and potentiate cardiac impairment in the setting of diabetes.

METHODS

The roles of serum DKK1 and DKK1-LRP5/6 signalling in diabetic injuries were investigated in human and diabetic mice.

RESULTS

Blood pressure up-regulation positively correlated with serum DKK1 elevations in humans. Notably, LRP5/6 physically and functionally interacted with AT1R. The loss of membrane LRP5/6 caused by injection of a recombinant DKK1 protein or conditional LRP5/6 deletions resulted in AT1R activation and hypertension, as well as β-arrestin1 activation and cardiac impairment, possibly because of multiple GPCR alterations. Importantly, unlike commonly used anti-hypertensive agents, administration of the anti-DKK1 neutralizing antibody effectively prevented diabetic cardiac impairment in mice.

CONCLUSIONS

These findings establish a novel DKK1-LRP5/6-GPCR pathway in inducing diabetic injuries and may resolve the long-standing conundrum as to why elevated blood DKK1 has deleterious effects. Thus, monitoring and therapeutic elimination of blood DKK1 may be a promising strategy to attenuate diabetic injuries.

19F-NMR studies of the impact of different detergents and nanodiscs on the A2A adenosine receptor

For the A2A adenosine receptor (A2AAR), a class A G-protein-coupled receptor (GPCR), reconstituted in n-dodecyl-β-D-maltoside (DDM)/‌‌‌‌‌cholesteryl hemisuccinate (CHS) mixed micelles, previous 19F-NMR studies revealed the presence of multiple simultaneously populated conformational states. Here, we study the influence of a different detergent, lauryl maltose neopentyl glycol (LMNG) in mixed micelles with CHS, and of lipid bilayer nanodiscs on these conformational equilibria. The populations of locally different substates are pronouncedly different in DDM/‌‌‌‌‌CHS and LMNG/‌‌‌‌‌CHS micelles, whereas the A2AAR conformational manifold in LMNG/‌‌‌‌‌CHS micelles is closely similar to that in the lipid bilayer nanodiscs. Considering that nanodiscs represent a closer match of the natural lipid bilayer membrane, these observations support that LMNG/‌‌‌‌‌CHS micelles are a good choice for reconstitution trials of class A GPCRs for NMR studies in solution.

Non-canonical G protein signaling

The original paradigm of classical - also referred to as canonical - cellular signal transduction of heterotrimeric G proteins (G protein) is defined by a hierarchical, orthograde interaction of three players: the agonist-activated G protein-coupled receptor (GPCR), which activates the transducing G protein, that in turn regulates its intracellular effectors. This receptor-transducer-effector concept was extended by the identification of regulators and adapters such as the regulators of G protein signaling (RGS), receptor kinases like βARK, or GPCR-interacting arrestin adapters that are integrated into this canonical signaling process at different levels to enable fine-tuning. Finally, the identification of atypical signaling mechanisms of classical regulators, together with the discovery of novel modulators, added a new and fascinating dimension to the cellular G protein signal transduction. This heterogeneous group of accessory G protein modulators was coined "activators of G protein signaling" (AGS) proteins and plays distinct roles in canonical and non-canonical G protein signaling pathways. AGS proteins contribute to the control of essential cellular functions such as cell development and division, intracellular transport processes, secretion, autophagy or cell movements. As such, they are involved in numerous biological processes that are crucial for diseases, like diabetes mellitus, cancer, and stroke, which represent major health burdens. Although the identification of a large number of non-canonical G protein signaling pathways has broadened the spectrum of this cellular communication system, their underlying mechanisms, functions, and biological effects are poorly understood. In this review, we highlight and discuss atypical G protein-dependent signaling mechanisms with a focus on inhibitory G proteins (Gi) involved in canonical and non-canonical signal transduction, review recent developments and open questions, address the potential of new approaches for targeted pharmacological interventions.

Orphan peptide and G protein-coupled receptor signalling in alcohol use disorder

Neuropeptides and G protein-coupled receptors (GPCRs) have long been, and continue to be, one of the most popular target classes for drug discovery in CNS disorders, including alcohol use disorder (AUD). Yet, orphaned neuropeptide systems and receptors (oGPCR), which have no known cognate receptor or ligand, remain understudied in drug discovery and development. Orphan neuropeptides and oGPCRs are abundantly expressed within the brain and represent an unprecedented opportunity to address brain function and may hold potential as novel treatments for disease. Here, we describe the current literature regarding orphaned neuropeptides and oGPCRs implicated in AUD. Specifically, in this review, we focus on the orphaned neuropeptide cocaine- and amphetamine-regulated transcript (CART), and several oGPCRs that have been directly implicated in AUD (GPR6, GPR26, GPR88, GPR139, GPR158) and discuss their potential and pitfalls as novel treatments, and progress in identifying their cognate receptors or ligands.

The perspective of cAMP/cGMP signaling and cyclic nucleotide phosphodiesterases in aortic aneurysm and dissection

Aortic aneurysm (AA) and dissection (AD) are aortic diseases caused primarily by medial layer degeneration and perivascular inflammation. They are lethal when the rupture happens. Vascular smooth muscle cells (SMCs) play critical roles in the pathogenesis of medial degeneration, characterized by SMC loss and elastin fiber degradation. Many molecular pathways, including cyclic nucleotide signaling, have been reported in regulating vascular SMC functions, matrix remodeling, and vascular structure integrity. Intracellular cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) are second messengers that mediate intracellular signaling transduction through activating effectors, such as protein kinase A (PKA) and PKG, respectively. cAMP and cGMP are synthesized by adenylyl cyclase (AC) and guanylyl cyclase (GC), respectively, and degraded by cyclic nucleotide phosphodiesterases (PDEs). In this review, we will discuss the roles and mechanisms of cAMP/cGMP signaling and PDEs in AA/AD formation and progression and the potential of PDE inhibitors in AA/AD, whether they are beneficial or detrimental. We also performed database analysis and summarized the results showing PDEs with significant expression changes under AA/AD, which should provide rationales for future research on PDEs in AA/AD.

State-dependent dynamics of extramembrane domains in the β2 -adrenergic receptor

G protein-coupled receptors (GPCRs) are membrane-bound signaling proteins that play an essential role in cellular signaling processes. Due to their intrinsic function of transmitting internal signals in response to external cues, these receptors are adapted to be highly dynamic in nature. The β2 -adrenergic receptor (β2 AR) is a representative member of the family that has been extensively analyzed in terms of its structure and activation. Although the structure of the transmembrane domain has been characterized in the different functional states of the receptor, the conformational dynamics of the extramembrane domains, especially the intrinsically disordered regions are still emerging. In this study, we analyze the state-dependent dynamics of extramembrane domains of β2 AR using atomistic molecular dynamics simulations. We introduce a parameter, the residue excess dynamics that allows us to better quantify receptor dynamics. Using this measure, we show that the dynamics of the extramembrane domains are sensitive to the receptor state. Interestingly, the ligand-bound intermediateR ' state shows the maximal dynamics compared to either the active R*G or inactive R states. Ligand binding appears to be correlated with high residue excess dynamics that are dampened upon G protein coupling. The intracellular loop-3 (ICL3) domain has a tendency to flip towards the membrane upon ligand binding, which could contribute to receptor "priming." We highlight an important ICL1-helix-8 interplay that is broken in the ligand-bound state but is retained in the active state. Overall, our study highlights the importance of characterizing the functional dynamics of the GPCR loop domains.

Neuromodulation and the toolkit for behavioural evolution: can ecdysis shed light on an old problem?

The geneticist Thomas Dobzhansky famously declared: 'Nothing in biology makes sense except in the light of evolution'. A key evolutionary adaptation of Metazoa is directed movement, which has been elaborated into a spectacularly varied number of behaviours in animal clades. The mechanisms by which animal behaviours have evolved, however, remain unresolved. This is due, in part, to the indirect control of behaviour by the genome, which provides the components for both building and operating the brain circuits that generate behaviour. These brain circuits are adapted to respond flexibly to environmental contingencies and physiological needs and can change as a function of experience. The resulting plasticity of behavioural expression makes it difficult to characterize homologous elements of behaviour and to track their evolution. Here, we evaluate progress in identifying the genetic substrates of behavioural evolution and suggest that examining adaptive changes in neuromodulatory signalling may be a particularly productive focus for future studies. We propose that the behavioural sequences used by ecdysozoans to moult are an attractive model for studying the role of neuromodulation in behavioural evolution.

Heterotrimeric G protein signaling without GPCRs: The Gα-binding-and-activating (GBA) motif

Heterotrimeric G proteins (Gαβγ) are molecular switches that relay signals from 7-transmembrane receptors located at the cell surface to the cytoplasm. The function of these receptors is so intimately linked to heterotrimeric G proteins that they are named G protein-coupled receptors (GPCRs), showcasing the interdependent nature of this archetypical receptor-transducer axis of transmembrane signaling in eukaryotes. It is generally assumed that activation of heterotrimeric G protein signaling occurs exclusively by the action of GPCRs, but this idea has been challenged by the discovery of alternative mechanisms by which G proteins can propagate signals in the cell. This review will focus on a general principle of G protein signaling that operates without the direct involvement of GPCRs. The mechanism of G protein signaling reviewed here is mediated by a class of G protein regulators defined by containing an evolutionarily conserved sequence named the Gα-binding-and-activating (GBA) motif. Using the best characterized proteins with a GBA motif as examples, Gα-interacting vesicle-associated protein (GIV)/Girdin and dishevelled-associating protein with a high frequency of leucine residues (DAPLE), this review will cover (i) the mechanisms by which extracellular cues not relayed by GPCRs promote the coupling of GBA motif-containing regulators with G proteins, (ii) the structural and molecular basis for how GBA motifs interact with Gα subunits to facilitate signaling, (iii) the relevance of this mechanism in different cellular and pathological processes, including cancer and birth defects, and (iv) strategies to manipulate GBA-G protein coupling for experimental therapeutics purposes, including the development of rationally engineered proteins and chemical probes.

Blockade of vasoactive intestinal peptide receptor 2 (VIPR2) signaling suppresses cyclin D1-dependent cell-cycle progression in MCF-7 cells

Vasoactive intestinal peptide (VIP) receptor 2 (VIPR2) is a G protein-coupled receptor that binds to Gαs, Gαi, and Gαq proteins to regulate various downstream signaling molecules, such as protein kinase A (PKA), phosphatidylinositol 3-kinase (PI3K), and phospholipase C. In this study, we examined the role of VIPR2 in cell cycle progression. KS-133, a newly developed VIPR2-selective antagonist peptide, attenuated VIP-induced cell proliferation in MCF-7 cells. The percentage of cells in the S-M phase was decreased in MCF-7 cells treated with KS-133. KS-133 in the presence of VIP decreased the phosphorylation of extracellular signal-regulated kinase (ERK), AKT, and glycogen synthase kinase-3β (GSK3β), resulting in a decrease in cyclin D1 levels. In MCF-7 cells stably-expressing VIPR2, KS-133 decreased PI3K activity and cAMP levels. Treatment with the ERK-specific kinase (MEK) inhibitor U0126 and the class I PI3K inhibitor ZSTK474 decreased the percentage of cells in the S phase. KS-133 reduced the percentage of cells in the S phase more than treatment with U0126 or ZSTK474 alone and did not affect the effect of the mixture of these inhibitors. Our findings suggest that VIPR2 signaling regulates cyclin D1 levels through the cAMP/PKA/ERK and PI3K/AKT/GSK3β pathways, and mediates the G1/S transition to control cell proliferation.

Transient cAMP production drives rapid and sustained spiking in brainstem parabrachial neurons to suppress feeding

Brief stimuli can trigger longer-lasting brain states. G-protein-coupled receptors (GPCRs) could help sustain such states by coupling slow-timescale molecular signals to neuronal excitability. Brainstem parabrachial nucleus glutamatergic (PBNGlut) neurons regulate sustained brain states such as pain and express Gs-coupled GPCRs that increase cAMP signaling. We asked whether cAMP in PBNGlut neurons directly influences their excitability and effects on behavior. Both brief tail shocks and brief optogenetic stimulation of cAMP production in PBNGlut neurons drove minutes-long suppression of feeding. This suppression matched the duration of prolonged elevations in cAMP, protein kinase A (PKA) activity, and calcium activity in vivo and ex vivo, as well as sustained, PKA-dependent increases in action potential firing ex vivo. Shortening this elevation in cAMP reduced the duration of feeding suppression following tail shocks. Thus, molecular signaling in PBNGlut neurons helps prolong neural activity and behavioral states evoked by brief, salient bodily stimuli.

CMV-encoded GPCRs in infection, disease, and pathogenesis

G protein coupled receptors (GPCRs) are seven-transmembrane domain proteins that modulate cellular processes in response to external stimuli. These receptors represent the largest family of membrane proteins, and in mammals, their signaling regulates important physiological functions, such as vision, taste, and olfaction. Many organisms, including yeast, slime molds, and viruses encode GPCRs. Cytomegaloviruses (CMVs) are large, betaherpesviruses, that encode viral GPCRs (vGPCRs). Human CMV (HCMV) encodes four vGPCRs, including UL33, UL78, US27, and US28. Each of these vGPCRs, as well as their rodent and primate orthologues, have been investigated for their contributions to viral infection and disease. Herein, we discuss how the CMV vGPCRs function during lytic and latent infection, as well as our understanding of how they impact viral pathogenesis.

Evaluating conserved domains and motifs of decapod gonadotropin-releasing hormone G protein-coupled receptor superfamily

G protein-coupled receptors (GPCRs) are an ancient family of signal transducers that are both abundant and consequential in metazoan endocrinology. The evolutionary history and function of the GPCRs of the decapod superfamilies of gonadotropin-releasing hormone (GnRH) are yet to be fully elucidated. As part of which, the use of traditional phylogenetics and the recycling of a diminutive set of mis-annotated databases has proven insufficient. To address this, we have collated and revised eight existing and three novel GPCR repertoires for GnRH of decapod species. We developed a novel bioinformatic workflow that included clustering analysis to capture likely GnRH receptor-like proteins, followed by phylogenetic analysis of the seven transmembrane-spanning domains. A high degree of conservation of the sequences and topology of the domains and motifs allowed the identification of species-specific variation (up to ~70%, especially in the extracellular loops) that is thought to be influential to ligand-binding and function. Given the key functional role of the DRY motif across GPCRs, the classification of receptors based on the variation of this motif can be universally applied to resolve cryptic GPCR families, as was achieved in this work. Our results contribute to the resolution of the evolutionary history of invertebrate GnRH receptors and inform the design of bioassays in their deorphanization and functional annotation.