Exploring a role for heteromerization in GPCR signalling specificity

The critical involvement of GPCRs (G-protein-coupled receptors) in nearly all physiological processes, and the presence of these receptors at the interface between the extracellular and the intracellular milieu, has positioned these receptors as pivotal therapeutic targets. Although a large number of drugs targeting GPCRs are currently available, significant efforts have been directed towards understanding receptor properties, with the goal of identifying and designing improved receptor ligands. Recent advances in GPCR pharmacology have demonstrated that different ligands binding to the same receptor can activate discrete sets of downstream effectors, a phenomenon known as ‘ligand-directed signal specificity’, which is currently being explored for drug development due to its potential therapeutic advantage. Emerging studies suggest that GPCR responses can also be modulated by contextual factors, such as interactions with other GPCRs. Association between different GPCR types leads to the formation of complexes, or GPCR heteromers, with distinct and unique signalling properties. Some of these heteromers activate discrete sets of signalling effectors upon activation by the same ligand, a phenomenon termed ‘heteromer-directed signalling specificity’. This has been shown to be involved in the physiological role of receptors and, in some cases, in disease-specific dysregulation of a receptor effect. Hence targeting GPCR heteromers constitutes an emerging strategy to select receptor-specific responses and is likely to be useful in achieving specific beneficial therapeutic effects.

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Alteration of circadian machinery in monocytes underlies chronic kidney disease-associated cardiac inflammation and fibrosis

Nature Communications ◽

10.1038/s41467-021-23050-x ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Yuya Yoshida ◽

Naoya Matsunaga ◽

Takaharu Nakao ◽

Kengo Hamamura ◽

Hideaki Kondo ◽

...

Keyword(s):

Chronic Kidney Disease ◽

Kidney Disease ◽

Clock Genes ◽

Serum Levels ◽

Serum Retinol ◽

Cardiac Inflammation ◽

Physiological Processes ◽

G Protein Coupled ◽

Clock Protein

AbstractDysfunction of the circadian clock has been implicated in the pathogenesis of cardiovascular disease. The CLOCK protein is a core molecular component of the circadian oscillator, so that mice with a mutated Clock gene (Clk/Clk) exhibit abnormal rhythms in numerous physiological processes. However, here we report that chronic kidney disease (CKD)-induced cardiac inflammation and fibrosis are attenuated in Clk/Clk mice even though they have high blood pressure and increased serum angiotensin II levels. A search for the underlying cause of the attenuation of heart disorder in Clk/Clk mice with 5/6 nephrectomy (5/6Nx) led to identification of the monocytic expression of G protein-coupled receptor 68 (GPR68) as a risk factor of CKD-induced inflammation and fibrosis of heart. 5/6Nx induces the expression of GPR68 in circulating monocytes via altered CLOCK activation by increasing serum levels of retinol and its binding protein (RBP4). The high-GPR68-expressing monocytes have increased potential for producing inflammatory cytokines, and their cardiac infiltration under CKD conditions exacerbates inflammation and fibrosis of heart. Serum retinol and RBP4 levels in CKD patients are also sufficient to induce the expression of GPR68 in human monocytes. Our present study reveals an uncovered role of monocytic clock genes in CKD-induced heart failure.

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The Role of Prokineticin 2 in Oxidative Stress and in Neuropathological Processes

Frontiers in Pharmacology ◽

10.3389/fphar.2021.640441 ◽

2021 ◽

Vol 12 ◽

Author(s):

Roberta Lattanzi ◽

Cinzia Severini ◽

Daniela Maftei ◽

Luciano Saso ◽

Aldo Badiani

Keyword(s):

Pain Perception ◽

G Protein Coupled Receptors ◽

Cellular Processes ◽

Prokineticin 2 ◽

Physiological Processes ◽

Pathological Conditions ◽

Double Function ◽

The Central Nervous System ◽

G Protein Coupled

The prokineticin (PK) family, prokineticin 1 and Bv8/prokineticin 2 (PROK2), initially discovered as regulators of gastrointestinal motility, interacts with two G protein-coupled receptors, PKR1 and PKR2, regulating important biological functions such as circadian rhythms, metabolism, angiogenesis, neurogenesis, muscle contractility, hematopoiesis, immune response, reproduction and pain perception. PROK2 and PK receptors, in particular PKR2, are widespread distributed in the central nervous system, in both neurons and glial cells. The PROK2 expression levels can be increased by a series of pathological insults, such as hypoxia, reactive oxygen species, beta amyloid and excitotoxic glutamate. This suggests that the PK system, participating in different cellular processes that cause neuronal death, can be a key mediator in neurological/neurodegenerative diseases. While many PROK2/PKRs effects in physiological processes have been documented, their role in neuropathological conditions is not fully clarified, since PROK2 can have a double function in the mechanisms underlying to neurodegeneration or neuroprotection. Here, we briefly outline the latest findings on the modulation of PROK2 and its cognate receptors following different pathological insults, providing information about their opposite neurotoxic and neuroprotective role in different pathological conditions.

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Modulation of voltage-dependent Ca2+ conductance by changing Cl- concentration in rat lactotrophs

AJP Cell Physiology ◽

10.1152/ajpcell.1997.272.4.c1178 ◽

1997 ◽

Vol 272 (4) ◽

pp. C1178-C1185 ◽

Cited By ~ 65

Author(s):

L. Garcia ◽

M. Fahmi ◽

N. Prevarskaya ◽

B. Dufy ◽

P. Sartor

Keyword(s):

Carboxylic Acid ◽

Fluorescence Probe ◽

Physiological Role ◽

Feedback Mechanism ◽

Pituitary Cells ◽

Physiological Processes ◽

Voltage Dependent ◽

Ca2 Channels ◽

Cl Conductance

In pituitary cells, voltage-dependent Ca2+ channels play an important role in such physiological processes as exocytosis, secretion, the cell cycle, and proliferation. Thus mechanisms that modulate voltage-dependent Ca2+ channel activity participate indirectly in regulating intracellular Ca2+ concentration. We have shown a new modulating mechanism for voltage-dependent Ca2+ channels by demonstrating that Ca2+ influx is influenced by Cl-. To evaluate the role of Cl- on Ca2+ conductance coupling, we first measured the intracellular Cl- concentration of rat lactotrophs using the Cl(-)-sensitive fluorescence probe sulfopropylquinolinium by simple microspectrofluorometry or combined with electrophysiology. We found an average intracellular Cl- concentration of rat lactotrophs of approximately 60 mM (n = 39). Using the whole cell tight-seal recording technique, we showed that a reduction in external Cl- concentration ([Cl-]o) and a decrease in Cl- conductances affected Ca2+ conductance as measured by Ba2+ movement through the Ca2+ channels (I(Ba)). Low [Cl-]o (39 mM) induced a decrease in Ca2+ entry via voltage-gated Ca2+ channels (-27.75 +/- 4% of normalized I(Ba)). Similarly, blockade of the Cl- conductance by 1 mM 9-anthracene carboxylic acid induced a decrease in I(Ba) (-26 +/- 6% of normalized I(Ba)). This modulation of I(Ba) was inhibited by 24-h pretreatment of the cells with pertussis toxin (1 microg/ml), suggesting that changes in Cl- concentration induced by low [Cl-]o and 9-anthracene carboxylic acid interfered with the phosphorylation of G proteins involved in Ca2+ channel activation. These results suggest a feedback mechanism based on constant interaction between Ca2+ and Cl-. Finally, they also emphasize the physiological role of Cl- in rat lactotrophs.

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New thoughts on the role of the βγ subunit in G protein signal transduction

Biochemistry and Cell Biology ◽

10.1139/o00-075 ◽

2000 ◽

Vol 78 (5) ◽

pp. 537-550 ◽

Cited By ~ 1

Author(s):

Barbara Vanderbeld ◽

Gregory M Kelly

Keyword(s):

Signal Transduction ◽

G Protein ◽

G Proteins ◽

G Protein Coupled Receptors ◽

Limited Information ◽

Α Subunit ◽

Downstream Effectors ◽

Receptor Signal ◽

G Protein Coupled

Heterotrimeric G proteins are involved in numerous biological processes, where they mediate signal transduction from agonist-bound G-protein-coupled receptors to a variety of intracellular effector molecules and ion channels. G proteins consist of two signaling moieties: a GTP-bound α subunit and a βγ heterodimer. The βγ dimer, recently credited as a significant modulator of G-protein-mediated cellular responses, is postulated to be a major determinant of signaling fidelity between G-protein-coupled receptors and downstream effectors. In this review we have focused on the role of βγ signaling and have included examples to demonstrate the heterogeneity in the heterodimer composition and its implications in signaling fidelity. We also present an overview of some of the effectors regulated by βγ and draw attention to the fact that, although G proteins and their associated receptors play an instrumental role in development, there is rather limited information on βγ signaling in embryogenesis.Key words: G protein, βγ subunit, G-protein-coupled receptor, signal transduction, adenylyl cyclase.

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Targeted disruption of G protein-coupled bile acid receptor 1 (Gpbar1/M-Bar) in mice

Journal of Endocrinology ◽

10.1677/joe.1.06546 ◽

2006 ◽

Vol 191 (1) ◽

pp. 197-205 ◽

Cited By ~ 170

Author(s):

Takaharu Maruyama ◽

Kenichi Tanaka ◽

Jun Suzuki ◽

Hiroyuki Miyoshi ◽

Naomoto Harada ◽

...

Keyword(s):

Bile Acid ◽

G Protein ◽

Physiological Role ◽

Wild Type ◽

Fat Accumulation ◽

Acid Receptor ◽

Bile Acid Receptor ◽

The Impact ◽

G Protein Coupled

G protein-coupled bile acid receptor 1 (Gpbar1/M-Bar) is a novel G protein-coupled receptor for bile acid. Tissue distribution and cell-type specificity of Gpbar1 mRNA suggest a potential role for the receptor in the endocrine system; however, the precise physiological role of Gpbar1 still remains to be elucidated. To investigate the role of Gpbar1 in vivo, the Gpbar1 gene was disrupted in mice. In homozygous mice, total bile acid pool size was significantly decreased by 21–25% compared with that of the wild-type mice, suggesting that Gpbar1 contributes to bile acid homeostasis. In order to assess the impact of Gpbar1 deficiency in bile acid homeostasis more precisely, Gpbar1 homozygous mice were fed a high-fat diet for 2 months. As a result, female Gpbar1 homozygous mice showed significant fat accumulation with body weight gain compared with that of the wild-type mice. These findings were also observed in heterozygous mice to the same extent. Although the precise mechanism for fat accumulation in female Gpbar1 homozygous mice remains to be addressed, these data indicate that Gpbar1 is a potential new player in energy homeostasis. Thus, Gpbar1-deficient mice are useful in elucidating new physiological roles for Gpbar1.

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Data Supporting a New Physiological Role for Brain Apelin in the Regulation of Hypothalamic Oxytocin Neurons in Lactating Rats

Endocrinology ◽

10.1210/en.2011-0206 ◽

2011 ◽

Vol 152 (9) ◽

pp. 3492-3503 ◽

Cited By ~ 14

Author(s):

Laurence Bodineau ◽

Christopher Taveau ◽

Hong-Hanh Lê Quan Sang ◽

Guillaume Osterstock ◽

Isabelle Queguiner ◽

...

Keyword(s):

Direct Action ◽

Physiological Role ◽

Double Immunofluorescence ◽

Endogenous Ligand ◽

Electrophysiological Measurements ◽

Apelin Receptor ◽

Immunofluorescence Labeling ◽

G Protein Coupled

Apelin is a bioactive peptide identified as the endogenous ligand of the human orphan G protein-coupled receptor APJ in 1998. The present data show that apelin modulates the activity of magnocellular and parvocellular oxytocin (OXY) neurons in the lactating rat. A combination of in situ hybridization and immunohistochemistry demonstrated the presence of apelin receptor mRNA in hypothalamic OXY neurons. Double immunofluorescence labeling then revealed the colocalization of apelin with OXY in about 20% of the hypothalamic OXY-positive neurons. Intracerebroventricular apelin administration inhibited the activity of magnocellular and parvocellular OXY neurons, as shown by measuring the c-fos expression in OXY neurons or by direct electrophysiological measurements of the electrical activity of these neurons. This effect was correlated with a decrease in the amount of milk ejected. Thus, apelin inhibits the activity of OXY neurons through a direct action on apelin receptors expressed by these neurons in an autocrine and paracrine manner. In conclusion, these findings highlight the inhibitory role of apelin as an autocrine/paracrine peptide acting on OXY neurons during breastfeeding.

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The role of integrins αv in the pathogenesis of oral squamous cell carcinoma

Advances in molecular oncology ◽

10.17650/2313-805x-2018-5-4-86-93 ◽

2019 ◽

Vol 5 (4) ◽

pp. 86-93

Author(s):

G. M. Tuguzbaeva ◽

V. N. Pavlov

Keyword(s):

Squamous Cell Carcinoma ◽

Oral Squamous Cell Carcinoma ◽

Cell Carcinoma ◽

Squamous Cell ◽

Physiological Role ◽

Normal Epithelium ◽

Molecular Oncology ◽

Physiological Processes ◽

Integrin Family

The initiation of carcinoma progression is attributed to significant disorders in the synthesis of macromolecules that affect physiological processes in the epithelial cells of oral mucosa. It is known that the integrin family receptors are crucial for regenerative and reparative functions of the normal epithelium. In addition to their well-established physiological role, some types of integrins are the major determinants of malignant transformations. In particular, the results of recent studies in molecular oncology reveal the importance of αv integrins in the pathogenesis of carcinomas, including oral squamous cell carcinoma. This review aims to analyse the significance of αv integrins in the key processes of malignant growth and metastasis of oral squamous cell carcinoma. The prospects of using αv integrins as prognostic molecular markers and targets for developing novel diagnostic and therapeutic methods in the management of oral cancer are discussed.

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Shedding light on the role of CX3CR1 in the pathogenesis of schizophrenia

Pharmacological Reports ◽

10.1007/s43440-021-00269-5 ◽

2021 ◽

Author(s):

Katarzyna Chamera ◽

Magdalena Szuster-Głuszczak ◽

Agnieszka Basta-Kaim

Keyword(s):

Experimental Studies ◽

Physiological Processes ◽

Unique System ◽

The Family ◽

Inflammatory Processes ◽

The Central Nervous System ◽

G Protein Coupled ◽

The Brain ◽

Brain Homeostasis

AbstractSchizophrenia has a complex and heterogeneous molecular and clinical picture. Over the years of research on this disease, many factors have been suggested to contribute to its pathogenesis. Recently, the inflammatory processes have gained particular interest in the context of schizophrenia due to the increasing evidence from epidemiological, clinical and experimental studies. Within the immunological component, special attention has been brought to chemokines and their receptors. Among them, CX3C chemokine receptor 1 (CX3CR1), which belongs to the family of seven-transmembrane G protein-coupled receptors, and its cognate ligand (CX3CL1) constitute a unique system in the central nervous system. In the view of regulation of the brain homeostasis through immune response, as well as control of microglia reactivity, the CX3CL1–CX3CR1 system may represent an attractive target for further research and schizophrenia treatment. In the review, we described the general characteristics of the CX3CL1–CX3CR1 axis and the involvement of this signaling pathway in the physiological processes whose disruptions are reported to participate in mechanisms underlying schizophrenia. Furthermore, based on the available clinical and experimental data, we presented a guide to understanding the implication of the CX3CL1–CX3CR1 dysfunctions in the course of schizophrenia.

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Demonstration and characterization of motilin-binding sites in the rabbit cerebellum

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.1997.272.5.g994 ◽

1997 ◽

Vol 272 (5) ◽

pp. G994-G999 ◽

Cited By ~ 6

Author(s):

I. Depoortere ◽

T. L. Peeters

Keyword(s):

Binding Sites ◽

Molecular Layer ◽

Physiological Role ◽

Scatchard Analysis ◽

Affinity Binding ◽

Lower Affinity ◽

Erythromycin A ◽

G Protein Coupled

This is the first report on central motilin receptors. Autoradiography on cerebellar slices revealed specific motilin-binding sites in the molecular layer of the cortex. Scatchard analysis of cold saturation studies showed the existence of a high-(pKd,hi = 9.07 +/- 0.09, where pKd is the negative logarithm of the dissociation constant) and a low-affinity binding site (pKd,lo = 6.56 +/- 0.09). Similar affinities were found with rabbit motilin and with the porcine (po) antagonist [Phe3, Leu13]po-motilin. Feline and canine motilin had a markedly lower affinity for the low-affinity site (pKd,lo = 5.29 and 4.58, respectively); chicken motilin had a lower affinity for both sites (pKd,hi = 8.36, pKd,lo = 3.97). Erythromycin A and its derivative N-trimethyl erythromycin A cnol ether also bound to cerebellar motilin receptors (pKd,hi = 7.29 and 8.91, respectively). Structure-activity studies with motilin fragments and the potency ranking of agonists suggest that a novel subtype receptor of motilin may exist in the brain. Guanosine 5'-O-(3-thiotriphosphate) (0.1 mM) reduced the number and the affinity for the high-affinity binding sites, which is evidence for G protein-coupled receptors. Our findings open new perspectives for the study of the physiological role of motilin.

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Engineering of chimeric peptides as antagonists for the G protein-coupled receptor, RXFP4

Scientific Reports ◽

10.1038/s41598-019-53707-z ◽

2019 ◽

Vol 9 (1) ◽

Cited By ~ 1

Author(s):

Praveen Praveen ◽

Ross A. D. Bathgate ◽

Mohammed Akhter Hossain

Keyword(s):

Physiological Role ◽

Disulfide Bridges ◽

Antagonist Activity ◽

Partial Agonism ◽

Relaxin Family ◽

Specific Antagonist ◽

Chimeric Peptides ◽

Further Development ◽

G Protein Coupled

AbstractInsulin-like peptide 5 (INSL5) is a very important pharma target for treating human conditions such as anorexia and diabetes. However, INSL5 with two chains and three disulfide bridges is an extremely difficult peptide to assemble by chemical or recombinant means. In a recent study, we were able to engineer a simplified INSL5 analogue 13 which is a relaxin family peptide receptor 4 (RXFP4)-specific agonist. To date, however, no RXFP4-specific antagonist (peptide or small molecule) has been reported in the literature. The focus of this study was to utilize the non-specific RXFP3/RXFP4 antagonist ΔR3/I5 as a template to rationally design an RXFP4 specific antagonist. Unexpectedly, we demonstrated that ΔR3/I5 exhibited partial agonism at RXFP4 when expressed in CHO cells which is associated with only partial antagonism of INSL5 analogue activation. In an attempt to improve RXFP4 specificity and antagonist activity we designed and chemically synthesized a series of analogues of ΔR3/I5. While all the chimeric analogues still demonstrated partial agonism at RXFP4, one peptide (Analogue 17) exhibited significantly improved RXFP4 specificity. Importantly, analogue 17 has a simplified structure which is more amenable to chemical synthesis. Therefore, analogue 17 is an ideal template for further development into a specific high affinity RXFP4 antagonist which will be an important tool to probe the physiological role of RXFP4/INSL5 axis.

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