Engineering therapeutic antibodies targeting G-protein-coupled receptors

Neuroanatomical distribution of fluorophores within adult RXFP3 Cre-tdTomato/YFP mouse brain

Relaxin-family peptide 3 receptor (RXFP3) is activated by relaxin-3 in the brain to influence arousal and related functions, such as feeding and stress responses. Two transgenic mouse lines have recently been developed that co-express different fluorophores within RXFP3-expressing neurons: either yellow fluorescent protein (YFP; RXFP3-Cre/YFP mice) or tdTomato (RXFP3-Cre/tdTomato mice). To date, the characteristics of neurons that express RXFP3-associated fluorophores in these mice have only been investigated in the bed nucleus of the stria terminalis and the hypothalamic arcuate nucleus. To better determine the utility of these fluorophore-expressing mice for further research, we characterised the neuroanatomical distribution of fluorophores throughout the brain of these mice and compared this to the published distribution of Rxfp3 mRNA (detected by in situ hybridisation) in wildtype mice. Coronal sections of RXFP3-Cre/YFP (n = 8) and RXFP3-Cre/tdTomato (n = 8) mouse brains were imaged, and the density of fluorophore-expressing cells within various brain regions/nuclei was qualitatively assessed. Comparisons with our previously reported RXFP3 mRNA distribution revealed that of 212 brain regions that contained either fluorophore or RXFP3 mRNA, approximately half recorded densities that were within two qualitative measurements of each other (on a 9-point scale), including hippocampal dentate gyrus and amygdala subregions. However, many brain areas with likely non-authentic, false-positive, or false-negative fluorophore expression were also detected, including the cerebellum. Therefore, this study provides a guide to which brain regions should be prioritized for future study of RXFP3 in these mice, to better understand the neuroanatomy and function of this intriguing, neuronal peptide receptor.

Repurposing an endogenous degradation domain for antibody-mediated disposal of cell-surface proteins

The exquisite specificity of antibodies can be harnessed to effect targeted degradation of membrane proteins. Here, we demonstrate targeted protein removal utilising a protein degradation domain derived from the endogenous human protein Proprotein Convertase Subtilisin/Kexin type 9 (PCSK9). Recombinant antibodies genetically fused to this domain drive the degradation of membrane proteins that undergo constitutive internalisation and recycling, including the transferrin receptor and the human cytomegalovirus latency-associated protein US28. We term this approach PACTAC (PCSK9-Antibody Clearance-Targeting Chimeras).

Generation and characterization of nanobodies targeting GPCR

G protein-coupled receptors (GPCRs) are a large family of cell membrane proteins that are important targets for drug discovery. Nanobodies, also known as VHH (variable domains of heavy chain-only antibodies, HcAbs) antibodies, are small antibody fragments derived from camelids that have gained significant attention as potential therapeutics for targeting GPCRs due to their advantages over conventional antibodies. However, there are challenges in developing nanobodies targeting GPCRs, among which epitope accessibility is the most significant because the cell membrane partially shields the GPCR surface. We developed a universal protocol for making nanobodies targeting GPCRs using the cell membrane extract of GPCR-overexpressing HEK293 cells as the llama/alpaca immunization antigen. We constructed an immune VHH library and identified nanobodies by phage display bio-panning. The monoclonal nanobodies were recombinantly expressed in Escherichia coli (E. coli) and purified to characterize their binding potency.

Systematic Evaluation of Protein-Small Molecule Hybrids on the Yeast Surface

Protein-small molecule hybrids are structures that have the potential to combine the inhibitory properties of small molecules and the specificities of binding proteins. However, achieving such synergies is a substantial engineering challenge with fundamental principles yet to be elucidated. Recent work has demonstrated the power of the yeast display-based discovery of hybrids using a combination of fibronectin-binding domains and thiol-mediated conjugations to introduce small-molecule warheads. Here, we systematically study the effects of expanding the chemical diversity of these hybrids on the yeast surface by investigating a combinatorial set of fibronectins, noncanonical amino acid (ncAA) substitutions, and small-molecule pharmacophores. Our results show that previously discovered thiol-fibronectin hybrids are generally tolerant of a range of ncAA substitutions and retain binding functions to carbonic anhydrases following click chemistry-mediated assembly of hybrids with diverse linker structures. Most surprisingly, we identified several cases where replacement of a potent acetazolamide warhead with a substantially weaker benzenesulfonamide warhead still resulted in the assembly of multiple functional hybrids. In addition to these unexpected findings, we expanded the throughput of our system by validating a 96-well plate-based format to produce yeast-displayed hybrid conjugates in parallel. These efficient explorations of hybrid chemical diversity demonstrate that there are abundant opportunities to expand the functions of protein-small molecule hybrids and elucidate principles that dictate their efficient discovery and design.

Monoclonal antibody targeting mu-opioid receptor attenuates morphine tolerance via enhancing morphine-induced receptor endocytosis

Morphine is a frequently used analgesic that activates the mu-opioid receptor (MOR), which has prominent side effects of tolerance. Although the inefficiency of morphine in inducing the endocytosis of MOR underlies the development of morphine tolerance, currently, there is no effective therapy to treat morphine tolerance. In the current study, we aimed to develop a monoclonal antibody (mAb) precisely targeting MOR and to determine its therapeutic efficacy on morphine tolerance and the underlying molecular mechanisms. We successfully prepared a mAb targeting MOR, named 3A5C7, by hybridoma technique using a strategy of deoxyribonucleic acid immunization combined with cell immunization, and identified it as an immunoglobulin G mAb with high specificity and affinity for MOR and binding ability to antigens with spatial conformation. Treatment of two cell lines, HEK293T and SH-SY5Y, with 3A5C7 enhanced morphine-induced MOR endocytosis via a G protein-coupled receptor kinase 2 (GRK2)/β-arrestin2-dependent mechanism, as demonstrated by immunofluorescence staining, flow cytometry, Western blotting, coimmunoprecipitation, and small interfering ribonucleic acid (siRNA)-based knockdown. This mAb also allowed MOR recycling from cytoplasm to plasma membrane and attenuated morphine-induced phosphorylation of MOR. We established an in vitro morphine tolerance model using differentiated SH-SY5Y cells induced by retinoic acid. Western blot, enzyme-linked immunosorbent assays, and siRNA-based knockdown revealed that 3A5C7 mAb diminished hyperactivation of adenylate cyclase, the in vitro biomarker of morphine tolerance, via the GRK2/β-arrestin2 pathway. Furthermore, in vivo hotplate test demonstrated that chronic intrathecal administration of 3A5C7 significantly alleviated morphine tolerance in mice, and withdrawal jumping test revealed that both chronic and acute 3A5C7 intrathecal administration attenuated morphine dependence. Finally, intrathecal electroporation of silencing short hairpin RNA illustrated that the in vivo anti-tolerance and anti-dependence efficacy of 3A5C7 was mediated by enhanced morphine-induced MOR endocytosis via GRK2/β-arrestin2 pathway. Collectively, our study provided a therapeutic mAb, 3A5C7, targeting MOR to treat morphine tolerance, mediated by enhancing morphine-induced MOR endocytosis. The mAb 3A5C7 demonstrates promising translational value to treat clinical morphine tolerance.

Concerted Antibody and Antigen Discovery by Differential Whole-cell Phage Display Selections and Multi-omic Target Deconvolution

Monoclonal antibody (mAb)-based biologics are well established treatments of cancer. Antibody discovery campaigns are typically directed at a single target of interest, which inherently limits the possibility of uncovering novel antibody specificities or functionalities. Here, we present a target-unbiased approach for antibody discovery that relies on generating mAbs against native target cell surfaces via phage display. This method combines a previously reported method for improved whole-cell phage display selections with next-generation sequencing analysis to efficiently identify mAbs with the desired target cell reactivity. Applying this method to multiple myeloma cells yielded a panel of >50 mAbs with unique sequences and diverse reactivities. To uncover the identities of the cognate antigens recognized by this panel, representative mAbs from each unique reactivity cluster were used in a multi-omic target deconvolution approach. From this, we identified and validated three cell surface antigens: PTPRG, ICAM1, and CADM1. PTPRG and CADM1 remain largely unstudied in the context of multiple myeloma, which could warrant further investigation into their potential as therapeutic targets. These results highlight the utility of optimized whole-cell phage display selection methods and could motivate further interest in target-unbiased antibody discovery workflows.

CCR6 as a Potential Target for Therapeutic Antibodies for the Treatment of Inflammatory Diseases

The CC chemokine receptor 6 (CCR6) is a G protein-coupled receptor (GPCR) involved in a wide range of biological processes. When CCR6 binds to its sole ligand CCL20, a signaling network is produced. This pathway is implicated in mechanisms related to many diseases, such as cancer, psoriasis, multiple sclerosis, HIV infection or rheumatoid arthritis. The CCR6/CCL20 axis plays a fundamental role in immune homeostasis and activation. Th17 cells express the CCR6 receptor and inflammatory cytokines, including IL-17, IL-21 and IL-22, which are involved in the spread of inflammatory response. The CCL20/CCR6 mechanism plays a crucial role in the recruitment of these pro-inflammatory cells to local tissues. To date, there are no drugs against CCR6 approved, and the development of small molecules against CCR6 is complicated due to the difficulty in screenings. This review highlights the potential as a therapeutic target of the CCR6 receptor in numerous diseases and the importance of the development of antibodies against CCR6 that could be a promising alternative to small molecules in the treatment of CCR6/CCL20 axis-related pathologies.

Engineered Human Antibody with Improved Endothelin Receptor Type A Binding Affinity, Developability, and Serum Persistence Exhibits Excellent Antitumor Potency

Endothelin receptor A (ET_A), a class A G protein-coupled receptor (GPCR), is a promising tumor-associated antigen due to its close association with the progression and metastasis of many types of cancer, such as colorectal, breast, lung, ovarian, and prostate cancer. However, only small-molecule drugs have been developed as ET_A antagonists with anticancer effects. In a previous study, we identified an antibody (AG8) with highly selective binding to human ET_A through screening of a human naïve immune antibody library. Although both in vitro and in vivo experiments indicated that the identified AG8 had anticancer effects, there is a need for improvement in biochemical and physicochemical properties such as the ET_A binding affinity, thermostability, and productivity. In this study, we engineered the framework regions of AG8 and isolated an anti-ET_A antibody (MJF1) exhibiting significantly improved thermostability and ET_A binding affinity. Subsequently, our previously isolated PFc29, an Fc variant with an enhanced pH-dependent human FcRn binding profile, was introduced to MJF1, and the resulting Fc-engineered anti-ET_A antibody (MJF1-PFc29) inhibited the proliferation of tumor cells comparably to MJF1 and showed a 4.2-fold increased serum half-life in human FcRn transgenic mice. Moreover, MJF1-PFc29 elicited higher tumor growth inhibition in colorectal cancer xenograft mice compared to MJF1. Our results demonstrate that the engineered human anti-ET_A antibody MJF1-PFc29 has great therapeutic potential and high antitumor potency against various types of cancers including colorectal cancer.

Gαq modulates the energy metabolism of osteoclasts

Introduction

The bacterial protein toxin Pasteurella multocida toxin (PMT) mediates RANKL-independent osteoclast differentiation. Although these osteoclasts are smaller, their resorptive activity is high which helps in efficient destruction of nasal turbinate bones of pigs.

Methods

The proteome of bone marrow-derived macrophages differentiated into osteoclasts with either RANKL or PMT was analysed. The results were verified by characterizing the metabolic activity using Seahorse analysis, a protein translation assay, immunoblots, real-time PCR as well as flow cytometry-based monitoring of mitochondrial activity and ROS production. A Gαq overexpression system using ER-Hoxb8 cells was used to identify Gαq-mediated metabolic effects on osteoclast differentiation and function.

Results

PMT induces the upregulation of metabolic pathways, which included strong glycolytic activity, increased expression of GLUT1 and upregulation of the mTOR pathway. As OxPhos components were expressed more efficiently, cells also displayed increased mitochondrial respiration. The heterotrimeric G protein Gαq plays a central role in this hypermetabolic cell activation as it triggers mitochondrial relocalisation of pSerSTAT3 and an increase in OPA1 expression. This seems to be caused by a direct interaction between STAT3 and OPA1 resulting in enhanced mitochondrial respiration. Overexpression of Gαq mimicked the hypermetabolic phenotype observed for PMT-induced osteoclasts and resulted in higher glycolytic and mitochondrial activity as well as increased bone resorptive activity. In addition, rheumatoid arthritis (RA) patients showed an increase in GNAQ expression, especially in the synovial fluid.

Discussion

Our study suggests that Gαq plays a key role in PMT-induced osteoclastogenesis. Enhanced expression of GNAQ at the site of inflammation in RA patients indicates its pathophysiological relevance in the context of inflammatory bone disorders.

A robust antibody discovery platform for difficult-to-express G protein-coupled receptors

G protein-coupled receptors (GPCRs) are in the spotlight as drug targets due to the fact that multiple research results have verified the correlation between the activation of GPCRs and disease indications. This is because the GPCRs are present across the cell membranes, which interact with either extracellular ligands or other types of compartments and simultaneously mediate intracellular signaling. Despite the importance of the GPCRs as drug targets, they are too difficult to express in soluble forms. Currently, the difficulty of preparing functional GPCRs and the lack of efficient antibody screening methods are the most challenging steps in the discovery of antibodies targeting GPCRs. In this study, we developed a powerful platform that facilitates isolating GPCR-specific antibodies by obviating difficulties in GPCR preparation. The strategies include (i) conjugation of the P9 peptide, an envelope protein of Pseudomonas phi6, to the N-terminus of GPCRs to improve the expression level of the GPCRs in Escherichia coli, (ii) stabilization of the GPCRs in their active forms with amphiphilic poly-γ-glutamate (APG) to shield the seven hydrophobic transmembrane domains, and (iii) further limiting the size of the APG complex to improve the chance to isolate antibodies targeting the proteins-of-interest. Capitalizing on the above strategies, we could prepare GPCR proteins in their active forms as facile as other general-soluble antigen proteins. Furthermore, this protocol was validated to be successful in discovering three individual GPCR-specific antibodies targeting glucagon-like peptide-1 receptor, C-X-C chemokine receptor type 4, and prostaglandin E2 receptor 4 in this study.

The diversity of neuroimmune circuits controlling lung inflammation

It is becoming increasingly appreciated that the nervous and immune systems communicate bidirectionally to regulate immunological outcomes in a variety of organs including the lung. Activation of neuronal signaling can be induced by inflammation, tissue damage, or pathogens to evoke or reduce immune cell activation in what has been termed a neuroimmune reflex. In the periphery, these reflexes include the cholinergic anti-inflammatory pathway, sympathetic reflex, and sensory nociceptor-immune cell pathways. Continual advances in neuroimmunology in peripheral organ systems have fueled small-scale clinical trials that have yielded encouraging results for a range of immunopathologies such as rheumatoid arthritis. Despite these successes, several limitations should give clinical investigators pause in the application of neural stimulation as a therapeutic for lung inflammation, especially if inflammation arises from a novel pathogen. In this review, the general mechanisms of each reflex, the evidence for these circuits in the control of lung inflammation, and the key knowledge gaps in our understanding of these neuroimmune circuits will be discussed. These limitations can be overcome not only through a better understanding of neuroanatomy but also through a systematic evaluation of stimulation parameters using immune activation in lung tissues as primary readouts. Our rapidly evolving understanding of the nervous and immune systems highlights the importance of communication between these cells in health and disease. This integrative approach has tremendous potential in the development of targeted therapeutics if specific challenges can be overcome.

Use of poxvirus display to select antibodies specific for complex membrane antigens

Antibody discovery against complex antigens is limited by the availability of a reproducible pure source of concentrated properly folded antigen. We have developed a technology to enable direct incorporation of membrane proteins such as GPCRs and into the membrane of poxvirus. The protein of interest is correctly folded and expressed in the cell-derived viral membrane and does not require any detergents or refolding before downstream use. The poxvirus is selective in which proteins are incorporated into the viral membrane, making the antigen poxvirus an antigenically cleaner target for in vitro panning. Antigen-expressing virus can be readily purified at scale and used for antibody selection using any in vitro display platform.

Anti-GRP-R monoclonal antibody antitumor therapy against neuroblastoma

Standard treatment for patients with high-risk neuroblastoma remains multimodal therapy including chemoradiation, surgical resection, and autologous stem cell rescue. Immunotherapy has demonstrated success in treating many types of cancers; however, its use in pediatric solid tumors has been limited by low tumor mutation burdens. Gastrin-releasing peptide receptor (GRP-R) is overexpressed in numerous malignancies, including poorly-differentiated neuroblastoma. Monoclonal antibodies (mAbs) to GRP-R have yet to be developed but could serve as a potential novel immunotherapy. This preclinical study aims to evaluate the efficacy of a novel GRP-R mAb immunotherapy against neuroblastoma. We established four candidate anti-GRP-R mAbs by screening a single-chain variable fragment (scFv) library. GRP-R mAb-1 demonstrated the highest efficacy with the lowest EC50 at 4.607 ng/ml against GRP-R expressing neuroblastoma cells, blocked the GRP-ligand activation of GRP-R and its downstream PI3K/AKT signaling. This resulted in functional inhibition of cell proliferation and anchorage-independent growth, indicating that mAb-1 has an antagonist inhibitory role on GRP-R. To examine the antibody-dependent cellular cytotoxicity (ADCC) of GRP-R mAb-1 on neuroblastoma, we co-cultured neuroblastoma cells with natural killer (NK) cells versus GRP-R mAb-1 treatment alone. GRP-R mAb-1 mediated ADCC effects on neuroblastoma cells and induced release of IFNγ by NK cells under co-culture conditions in vitro. The cytotoxic effects of mAb-1 were confirmed with the secretion of cytotoxic granzyme B from NK cells and the reduction of mitotic tumor cells in vivo using a murine tumor xenograft model. In summary, GRP-R mAb-1 demonstrated efficacious anti-tumor effects on neuroblastoma cells in preclinical models. Importantly, GRP-R mAb-1 may be an efficacious, novel immunotherapy in the treatment of high-risk neuroblastoma patients.

Development of a Sensitive Anti-Human CCR9 Monoclonal Antibody (C9Mab-11) by N-Terminal Peptide Immunization

The C-C chemokine receptor 9 (CCR9) belongs to the G-protein-coupled receptor superfamily, and is highly expressed on the T cells and intestinal cells. CCR9 regulates various immune responses by binding to the C-C chemokine ligand, CCL25, and is involved in inflammatory diseases and tumors. Therefore, the development of sensitive monoclonal antibodies (mAbs) for CCR9 is necessary for treatment and diagnosis. In this study, we established a specific anti-human CCR9 (hCCR9) mAb; C₉Mab-11 (mouse IgG_2a, kappa), using the synthetic peptide immunization method. C₉Mab-11 reacted with hCCR9-overexpressed Chinese hamster ovary-K1 (CHO/hCCR9) and hCCR9-endogenously expressed MOLT-4 (human T-lymphoblastic leukemia) cells in flow cytometry. The dissociation constant (K_D) of C₉Mab-11 for CHO/hCCR9 and MOLT-4 cells were determined to be 1.2 × 10^-9 M and 4.9 × 10^-10 M, respectively, indicating that C₉Mab-11 possesses a high affinity for both exogenously and endogenously hCCR9-expressing cells. Furthermore, C₉Mab-11 clearly detected hCCR9 protein in CHO/hCCR9 cells using western blot analysis. In summary, C₉Mab-11 can be a useful tool for analyzing hCCR9-related biological responses.

Development of an Anti-Mouse CCR8 Monoclonal Antibody (C8Mab-1) for Flow Cytometry and Immunocytochemistry

It has been widely accepted that monoclonal antibody (mAb) is an effective tool for cancer immunotherapy. The C-C motif chemokine receptor 8 (CCR8) is highly expressed in regulatory T cells and many cancers and is associated with the progression of the cancers. However, its role in cancer progression remains unclear. Thus, the development of mAbs for CCR8 leads to cancer immunotherapy and elucidation of unknown mechanisms of CCR8-dependent cancer progression. In this study, we have developed an anti-mouse CCR8 (mCCR8) mAb (clone C₈Mab-1, rat IgG_2a, kappa) using the Cell-Based Immunization and Screening (CBIS) method. We showed that C₈Mab-1 and its recombinant antibody (recC₈Mab-1) bind to mCCR8-overexpressed Chinese hamster ovary (CHO)-K1 cells (CHO/mCCR8), but not to the parental CHO-K1 cells, in flow cytometry and immunofluorescence. Moreover, C₈Mab-1 and recC₈Mab-1 specifically reacted to P388 (a mouse lymphocyte-like cells) and J774-1 (a mouse macrophage-like cells), which express endogenous mCCR8, in both applications. These results suggest that C₈Mab-1, developed using the CBIS method, is useful for flow cytometry and immunocytochemistry against exogenous and endogenous mCCR8.

PAC1, VPAC1, and VPAC2 Receptor Expression in Rat and Human Trigeminal Ganglia: Characterization of PACAP-Responsive Receptor Antibodies

Pituitary adenylate cyclase-activating peptide (PACAP) is a neuropeptide expressed in the trigeminal ganglia (TG). The TG conducts nociceptive signals in the head and may play roles in migraine. PACAP infusion provokes headaches in healthy individuals and migraine-like attacks in patients; however, it is not clear whether targeting this system could be therapeutically efficacious. To effectively target the PACAP system, an understanding of PACAP receptor distribution is required. Therefore, this study aimed to characterize commercially available antibodies and use these to detect PACAP-responsive receptors in the TG. Antibodies were initially validated in receptor transfected cell models and then used to explore receptor expression in rat and human TG. Antibodies were identified that could detect PACAP-responsive receptors, including the first antibody to differentiate between the PAC_1n and PAC_1s receptor splice variants. PAC₁, VPAC₁, and VPAC₂ receptor-like immunoreactivity were observed in subpopulations of both neuronal and glial-like cells in the TG. In this study, PAC₁, VPAC₁, and VPAC₂ receptors were detected in the TG, suggesting they are all potential targets to treat migraine. These antibodies may be useful tools to help elucidate PACAP-responsive receptor expression in tissues. However, most antibodies exhibited limitations, requiring the use of multiple methodologies and the careful inclusion of controls.

Advancement of cell-penetrating peptides in combating triple-negative breast cancer

Extensive research efforts have been made and are still ongoing in the search for an ideal anti-cancer therapy. Almost all chemotherapeutics require a carrier or vehicle, a drug delivery system that can transport the drug specifically to the targeted cancer cells, sparing normal cells. Cell-penetrating peptides (CPPs) provide an effective and efficient pathway for the intra-cellular transportation of various bioactive molecules in several biomedical therapies. They are now well-recognized as facilitators of intracellular cargo delivery and have excellent potential for targeted anti-cancer therapy. In this review, we explain CPPs, recent progress in the development of new CPPs, and their utilization to transport cargoes such as imaging agents, chemotherapeutics, and short-interfering RNAs (siRNA) into tumor cells, contributing to the advancement of novel tumor-specific delivery systems.

A systematic review on the kappa opioid receptor and its ligands: New directions for the treatment of pain, anxiety, depression, and drug abuse

Kappa opioid receptor (KOR) is a member of the opioid receptor system, the G protein-coupled receptors that are expressed throughout the peripheral and central nervous systems and play crucial roles in the modulation of antinociception and a variety of behavioral states like anxiety, depression, and drug abuse. KOR agonists are known to produce potent analgesic effects and have been used clinically for the treatment of pain, while KOR antagonists have shown efficacy in the treatment of anxiety and depression. This review summarizes the history, design strategy, discovery, and development of KOR ligands. KOR agonists are classified as non-biased, G protein-biased, and β-arrestin recruitment-biased, according to their degrees of bias. The mechanisms and associated effects of the G protein signaling pathway and β-arrestin recruitment signaling pathway are also discussed. Meanwhile, KOR antagonists are classified as long-acting and short-acting, based on their half-lives. In addition, we have special sections for mixed KOR agonists and selective peripheral KOR agonists. The mechanisms of action and pharmacokinetic, pharmacodynamic, and behavioral studies for each of these categories are also discussed in this review.

Genetic tagging of the adenosine A2A receptor reveals its heterogeneous expression in brain regions

The adenosine A_2A receptor (A_2AR), a G protein-coupled receptor, is involved in numerous and varied physiological and pathological processes, including inflammation, immune responses, blood flow, and neurotransmission. Accordingly, it has become an important drug target for the treatment of neuropsychiatric disorders. However, the exact brain distribution of A_2AR in regions outside the striatum that display relatively low levels of endogenous A_2AR expression has hampered the exploration of A_2AR functions under both physiological and pathological conditions. To further study the detailed distribution of the A_2AR in low-expression regions, we have generated A_2AR knock-in mice in which the 3xHA-2xMyc epitope tag sequence was fused to the C-terminus of A_2AR (A_2AR-tag mice) via CRISPR/Cas9 technology. Here, using CRISPR/Cas9 technology, we have generated A_2AR knock-in mice in which the 3xHA-2xMyc epitope tag sequence was fused to the C-terminus of A_2AR (A_2AR-tag mice). The A_2AR-tag mice exhibited normal locomotor activity and emotional state. Consistent with previous studies, A_2AR fluorescence was widely detected in the striatum, nucleus accumbens, and olfactory tubercles, with numerous labeled cells being evident in these regions in the A_2AR-tag mouse. Importantly, we also identified the presence of a few but clearly labeled cells in heterogeneous brain regions where A_2AR expression has not previously been unambiguously detected, including the lateral septum, hippocampus, amygdala, cerebral cortex, and gigantocellular reticular nucleus. The A_2AR-tag mouse represents a novel useful genetic tool for monitoring the expression of A_2AR and dissecting its functions in brain regions other than the striatum.

Adhesion G protein-coupled receptor gluing action guides tissue development and disease

Phylogenetic analysis of human G protein-coupled receptors (GPCRs) divides these transmembrane signaling proteins into five groups: glutamate, rhodopsin, adhesion, frizzled, and secretin families, commonly abbreviated as the GRAFS classification system. The adhesion GPCR (aGPCR) sub-family comprises 33 different receptors in humans. Majority of the aGPCRs are orphan receptors with unknown ligands, structures, and tissue expression profiles. They have a long N-terminal extracellular domain (ECD) with several adhesion sites similar to integrin receptors. Many aGPCRs undergo autoproteolysis at the GPCR proteolysis site (GPS), enclosed within the larger GPCR autoproteolysis inducing (GAIN) domain. Recent breakthroughs in aGPCR research have created new paradigms for understanding their roles in organogenesis. They play crucial roles in multiple aspects of organ development through cell signaling, intercellular adhesion, and cell-matrix associations. They are involved in essential physiological processes like regulation of cell polarity, mitotic spindle orientation, cell adhesion, and migration. Multiple aGPCRs have been associated with the development of the brain, musculoskeletal system, kidneys, cardiovascular system, hormone secretion, and regulation of immune functions. Since aGPCRs have crucial roles in tissue patterning and organogenesis, mutations in these receptors are often associated with diseases with loss of tissue integrity. Thus, aGPCRs include a group of enigmatic receptors with untapped potential for elucidating novel signaling pathways leading to drug discovery. We summarized the current knowledge on how aGPCRs play critical roles in organ development and discussed how aGPCR mutations/genetic variants cause diseases.

Development of an Anti-human CCR2 Monoclonal Antibody (C2Mab-9) by N-Terminal Peptide Immunization

The CC chemokine receptor type-2 (CCR2) is one of the members of the G protein-coupled receptor superfamily, which are expressed on the cell surface of immune and tumor cells. CCR2 binds to the C-C motif chemokine ligand 2 (CCL2)/monocyte chemoattractant protein-1 (MCP-1), which is produced by various cells, including tumor and immune-related cells. Therefore, the development of sensitive monoclonal antibodies (mAbs) for CCR2 has been desired for treatment and diagnosis. In this study, we established a specific antihuman CCR2 (hCCR2) mAb, C₂Mab-9 (mouse IgG₁, kappa), using the synthetic peptide immunization method. Flow cytometric and immunocytochemical results showed that C₂Mab-9 reacted with hCCR2-expressing U937 (human histiocytic lymphoma) and natural killer cells. Furthermore, C₂Mab-9 showed the moderate binding affinity for both cells. Conclusively, C₂Mab-9 can be a useful tool for analyzing hCCR2-related biological responses.

What Makes GPCRs from Different Families Bind to the Same Ligand?

G protein-coupled receptors (GPCRs) are the largest class of cell-surface receptor proteins with important functions in signal transduction and often serve as therapeutic drug targets. With the rapidly growing public data on three dimensional (3D) structures of GPCRs and GPCR-ligand interactions, computational prediction of GPCR ligand binding becomes a convincing option to high throughput screening and other experimental approaches during the beginning phases of ligand discovery. In this work, we set out to computationally uncover and understand the binding of a single ligand to GPCRs from several different families. Three-dimensional structural comparisons of the GPCRs that bind to the same ligand revealed local 3D structural similarities and often these regions overlap with locations of binding pockets. These pockets were found to be similar (based on backbone geometry and side-chain orientation using APoc), and they correlate positively with electrostatic properties of the pockets. Moreover, the more similar the pockets, the more likely a ligand binding to the pockets will interact with similar residues, have similar conformations, and produce similar binding affinities across the pockets. These findings can be exploited to improve protein function inference, drug repurposing and drug toxicity prediction, and accelerate the development of new drugs.

Cognitive Impairment, Sleep Disturbance, and Depression in Women with Silicone Breast Implants: Association with Autoantibodies against Autonomic Nervous System Receptors

Background: Silicone breast implants (SBIs) has been shown to be associated with an increased risk of autoimmune diseases. In the current study, we aimed to explore the potential association between circulating autoantibodies against the autonomic nervous system and cognitive impairment, memory deficit, and depressive symptoms reported by women with SBIs. Methods: ELISA assays were used to quantify anti-adrenergic receptors (α1, α2, β1, β2), anti-muscarinic receptors (M1-M5), anti-endothelin receptor type A, and anti-angiotensin II type 1 receptor titers in the sera of 93 symptomatic female subjects with SBIs and 36 age-matched healthy female controls. Results: A significant difference was detected in the level of autoantibodies against the autonomic nervous system receptors in women with SBIs who reported memory impairment, cognitive impairment, and sleep disturbance as compared with both women with SBIs who did not complain of these symptoms or with healthy individuals without SBIs. Conclusions: Clinical symptoms such as depression, cognitive impairment, and sleep disturbances were found to be associated with dysregulation of the levels of circulating autoantibodies targeting the autonomous nervous system receptors in women with SBIs. These autoantibodies may have diagnostic significance in diseases associated with breast implants.

Establishment of Novel Anti-Mouse CCR3 Monoclonal Antibodies (C3Mab-6 and C3Mab-7) by N-terminal Peptide Immunization

The CC chemokine receptor 3 (CCR3) is a member of the G protein-coupled receptor family that is highly expressed in eosinophils and basophils. CCR3 has been proposed as a therapeutic target for human immunodeficiency virus and allergy diagnosis. Therefore, in this study, we developed specific and sensitive monoclonal antibodies (mAbs) for mouse CCR3 (mCCR3), which are useful for flow cytometry by peptide immunization. The established anti-mCCR3 mAbs, C₃Mab-6 (rat IgG₁, kappa) and C₃Mab-7 (rat IgG₁, kappa), reacted with mCCR3-overexpressed Chinese hamster ovary-K1 (CHO/mCCR3), in addition to mCCR3-endogenously expressed cell lines, such as P388 (mouse lymphoid neoplasma) and J774-1 (mouse macrophage-like) through flow cytometry. Kinetic analyses using flow cytometry indicated that the dissociation constants (K_Ds) of C₃Mab-6 for CHO/mCCR3, P388, and J774-1 cells were 8.7 × 10^-9 M, 1.4 × 10^-7 M, and 1.7 × 10^-7 M, respectively, whereas the K_Ds of C₃Mab-7 for these cell lines were 3.7 × 10^-9 M, 5.1 × 10^-7 M, and 3.1 × 10^-7 M, respectively. Results also indicated that C₃Mab-6 and C₃Mab-7 are useful for detecting cells expressing CCR3 through flow cytometry, thereby making them potentially beneficial for treating CCR3-expressing cells.

C9Mab-1: An Anti-Mouse CCR9 Monoclonal Antibody for Immunocytochemistry

C-C motif chemokine receptor 9 (CCR9) is a G protein-coupled receptor, which is highly expressed in T-lymphocytes and different cancer cells. CCR9 aggravates immune diseases and cancer progression and is considered a biomarker and a therapeutic target of diseases. The development of specific monoclonal antibody (mAbs) for human CCR9 (hCCR9) is required to diagnose and treat immune diseases and cancers. Previously, we established the cell-based immunization and screening (CBIS) method, which does not need purified target proteins. Anti-hCCR9 mAb (clone C₉Mab-1; mouse IgG₁, kappa) was also developed using the CBIS method. C₉Mab-1 is usable for flow cytometry against exogenously and endogenously expressing hCCR9. This study showed that C₉Mab-1 and its recombinant antibody (recC₉Mab-1) specifically detected exogenous hCCR9 stably overexpressed in Chinese hamster ovary (CHO)-K1 cells and endogenous hCCR9 expressed in a human T-lymphoblastic leukemia cell line MOLT-4 cells through immunocytochemistry. This study provides a new application of C₉Mab-1 and recC₉Mab-1 in immunocytochemistry.

C3Mab-3: A Monoclonal Antibody for Mouse CC Chemokine Receptor 3 for Flow Cytometry

CC chemokine receptor 3 (CCR3) belongs to the G protein-coupled receptor family and is highly expressed in eosinophils and basophils. CCR3 is essential for recruiting eosinophils into the lung. Moreover, CCR3 was found in the serum of colorectal cancer patients higher than in the control group. Therefore, CCR3 will be a useful target for asthma and colorectal cancer diagnosis. This study developed a specific and sensitive monoclonal antibody (mAb) for mouse CCR3 (mCCR3), which is useful for flow cytometry using the Cell-Based Immunization and Screening method. The established anti-mCCR3 mAb, C₃Mab-3 (rat IgG_2a, kappa), reacted with mCCR3-overexpressed Chinese hamster ovary-K1 (CHO/mCCR3) cells through flow cytometry. C₃Mab-3 also reacted with P388 (mouse lymphoid neoplasma) and J774-1 (mouse macrophage-like) cells, which express mCCR3 endogenously. Kinetic analyses using flow cytometry indicated that K_Ds of C₃Mab-3 for CHO/mCCR3, P388, and J774-1 cells were 4.3 × 10^-8 M, 2.6 × 10^-7 M, and 2.4 × 10^-7 M, respectively. C₃Mab-3 could be a valuable tool for elucidating mCCR3-related biological response using flow cytometry.

C8Mab-2: An Anti-Mouse C-C Motif Chemokine Receptor 8 Monoclonal Antibody for Immunocytochemistry

C-C motif chemokine receptor 8 (CCR8) is a G protein-coupled receptor predominantly expressed in regulatory T (Treg) and T helper 2 cells. The evidence that CCR8 expression in Treg is increased in cancers, CCR8 increases migration activity of Treg, and CCR8 induces the anti-apoptotic activity in T cell leukemia and lymphoma suggests that CCR8 is associated with cancer development. Thus, developing a specific monoclonal antibody (mAb) for CCR8 is useful for diagnostic and therapeutic purposes and the anti-CCR8 mAb becomes a remarkable experimental tool for basic research. We previously developed an anti-mouse CCR8 (mCCR8) mAb called C₈Mab-2 (rat IgG_2b, kappa) that was applicable to flow cytometric analysis for both endogenous and exogenous mCCR8. This study showed that C₈Mab-2 and recombinant C₈Mab-2 (recC₈Mab-2) were specifically bound to exogenously expressed mCCR8 in mCCR8-overexpressed Chinese hamster ovary-K1 cells. In addition, we found that C₈Mab-2 and recC₈Mab-2 recognized endogenous mCCR8 in P388 (a mouse lymphocyte-like cell line) and J774-1 cells (a mouse macrophage-like cell line). These data demonstrate that C₈Mab-2 and recC₈Mab-2 are useful for immunocytochemical analysis.

Development of a Novel Anti-Mouse CCR4 Monoclonal Antibody (C4Mab-1) by N-Terminal Peptide Immunization

The CC chemokine receptor type-4 (CCR4) belongs to the G-protein-coupled receptor superfamily, expressed on the cell surface of T cells and its malignancy. Two CCR4 ligands (CCL17 and CCL22) bind to CCR4 that mediate physiological and pathological functions of T cell immune responses. Anti-CCR4 monoclonal antibody (mAb) mogamulizumab is approved for adult T cell leukemia/lymphoma and cutaneous T cell lymphomas. In addition, mogamulizumab can deplete regulatory T cells, implying the application to solid tumors as an immunomodulator. Therefore, the development of sensitive mAbs for CCR4 has been desired for basic research, diagnosis, and therapy. In this study, a specific, and sensitive anti-mouse CCR4 (mCCR4) mAb, C₄Mab-1 (rat IgG₁, kappa), was established using N-terminal peptide immunization. C₄Mab-1 reacted with mCCR4-overexpressed Chinese hamster ovary (CHO)-K1 cells, P388 (mouse lymphoid neoplasm), and J774-1 (mouse macrophage-like) cells in flow cytometry. Kinetic analyses using flow cytometry showed that K_Ds of C₄Mab-1 for CHO/mCCR4, P388, and J774-1 cells were 4.2 × 10^-9 M, 5.4 × 10^-7 M, and 1.1 × 10^-6 M, respectively. C₄Mab-1 could be a valuable tool for elucidating mCCR4-related biological responses.

Development of a Novel Anti-Mouse CCR2 Monoclonal Antibody (C2Mab-6) by N-Terminal Peptide Immunization

The CC chemokine receptor type-2 (CCR2) belongs to the G-protein-coupled receptor superfamily, expressed on the cell surface of immune cells and tumors. CCR2 binds to the CC motif chemokine 2/monocyte chemoattractant protein-1, a CC chemokine, which is produced by various cells, including immune-related cells and tumors. Therefore, the development of sensitive monoclonal antibodies (mAbs) for CCR2 has been desired for treatment and diagnosis. This study established a novel, specific, and sensitive anti-mouse CCR2 (mCCR2) mAb; C₂Mab-6 (rat IgG₁, kappa), using the mCCR2 synthetic peptide immunization method. C₂Mab-6 reacted with mCCR2-overexpressed Chinese hamster ovary-K1 cells and L1210 (murine leukemia) cells, which express endogenous mCCR2 in flow cytometry. Furthermore, C₂Mab-6 showed a high binding affinity for both cells. Hence, C₂Mab-6 can be a useful tool for analyzing mCCR2-related biological responses, using flow cytometry.

Knock-In Mouse Models to Investigate the Functions of Opioid Receptors in vivo

Due to their low expression levels, complex multi-pass transmembrane structure, and the current lack of highly specific antibodies, the assessment of endogenous G protein-coupled receptors (GPCRs) remains challenging. While most of the research regarding their functions was performed in heterologous systems overexpressing the receptor, recent advances in genetic engineering methods have allowed the generation of several unique mouse models. These animals proved to be useful to investigate numerous aspects underlying the physiological functions of GPCRs, including their endogenous expression, distribution, interactome, and trafficking processes. Given their significant pharmacological importance and central roles in the nervous system, opioid peptide receptors (OPr) are often referred to as prototypical receptors for the study of GPCR regulatory mechanisms. Although only a few GPCR knock-in mouse lines have thus far been generated, OPr are strikingly well represented with over 20 different knock-in models, more than half of which were developed within the last 5 years. In this review, we describe the arsenal of OPr (mu-, delta-, and kappa-opioid), as well as the opioid-related nociceptin/orphanin FQ (NOP) receptor knock-in mouse models that have been generated over the past years. We further highlight the invaluable contribution of such models to our understanding of the in vivo mechanisms underlying the regulation of OPr, which could be conceivably transposed to any other GPCR, as well as the limitations, future perspectives, and possibilities enabled by such tools.

Targeting GPCRs and Their Signaling as a Therapeutic Option in Melanoma

Simple Summary

Sixteen G-protein-coupled receptors (GPCRs) have been involved in melanogenesis or melanomagenesis. Here, we review these GPCRs, their associated signaling, and therapies.

Abstract

G-protein-coupled receptors (GPCRs) serve prominent roles in melanocyte lineage physiology, with an impact at all stages of development, as well as on mature melanocyte functions. GPCR ligands are present in the skin and regulate melanocyte homeostasis, including pigmentation. The role of GPCRs in the regulation of pigmentation and, consequently, protection against external aggression, such as ultraviolet radiation, has long been established. However, evidence of new functions of GPCRs directly in melanomagenesis has been highlighted in recent years. GPCRs are coupled, through their intracellular domains, to heterotrimeric G-proteins, which induce cellular signaling through various pathways. Such signaling modulates numerous essential cellular processes that occur during melanomagenesis, including proliferation and migration. GPCR-associated signaling in melanoma can be activated by the binding of paracrine factors to their receptors or directly by activating mutations. In this review, we present melanoma-associated alterations of GPCRs and their downstream signaling and discuss the various preclinical models used to evaluate new therapeutic approaches against GPCR activity in melanoma. Recent striking advances in our understanding of the structure, function, and regulation of GPCRs will undoubtedly broaden melanoma treatment options in the future.

Antibody Library Screening Using Yeast Biopanning and Fluorescence-Activated Cell Sorting

Yeast surface display (YSD) emerged as a prominent screening methodology for the isolation of monoclonal antibodies (mAbs) against various antigens. However, phage display remains the gold standard in cell panning-based screenings to isolate mAbs against difficult-to-screen targets, such as G-protein coupled receptors (GPCR) and ion channels. Herein we describe a step-by-step protocol to establish and perform the isolation of mAbs using YSD in a fluorescence-activated cell sorting (FACS)-assisted biopanning manner, yielding a variety of antibodies binding their antigen with high affinity in the natural environment of the cell. Upon mixing antibody-displaying yeast cells with antigen-displaying mammalian cells, complexes are specifically formed and isolated for enrichment of yeast cells encoding binders against the antigen. The utilization of mammalian cells expressing the respective target accounts for accessibility of the epitope and the correct conformation of the antigen. Furthermore, critical characterization methods mandatory for this kind of antibodies are illuminated.

State-Targeting Stabilization of Adenosine A2A Receptor by Fusing a Custom-Made De Novo Designed α-Helical Protein

G-protein coupled receptors (GPCRs) are known for their low stability and large conformational changes upon transitions between multiple states. A widely used method for stabilizing these receptors is to make chimeric receptors by fusing soluble proteins (i.e., fusion partner proteins) into the intracellular loop 3 (ICL3) connecting the transmembrane helices 5 and 6 (TM5 and TM6). However, this fusion approach requires experimental trial and error to identify appropriate soluble proteins, residue positions, and linker lengths for making the fusion. Moreover, this approach has not provided state-targeting stabilization of GPCRs. Here, to rationally stabilize a class A GPCR, adenosine A2A receptor (A2AR) in a target state, we carried out the custom-made de novo design of α-helical fusion partner proteins, which can fix the conformation of TM5 and TM6 to that in an inactive state of A2AR through straight helical connections without any kinks or intervening loops. The chimeric A2AR fused with one of the designs (FiX1) exhibited increased thermal stability. Moreover, compared with the wild type, the binding affinity of the chimera against the agonist NECA was significantly decreased, whereas that against the inverse agonist ZM241385 was similar, indicating that the inactive state was selectively stabilized. Our strategy contributes to the rational state-targeting stabilization of GPCRs.

A human antibody against human endothelin receptor type A that exhibits antitumor potency

Endothelin receptor A (ET_A), a class A G-protein-coupled receptor (GPCR), is involved in the progression and metastasis of colorectal, breast, lung, ovarian, and prostate cancer. We overexpressed and purified human endothelin receptor type A in Escherichia coli and reconstituted it with lipid and membrane scaffold proteins to prepare an ET_A nanodisc as a functional antigen with a structure similar to that of native GPCR. By screening a human naive immune single-chain variable fragment phage library constructed in-house, we successfully isolated a human anti-ET_A antibody (AG8) exhibiting high specificity for ET_A in the β-arrestin Tango assay and effective inhibitory activity against the ET-1-induced signaling cascade via ET_A using either a CHO-K1 cell line stably expressing human ET_A or HT-29 colorectal cancer cells, in which AG8 exhibited IC₅₀ values of 56 and 51 nM, respectively. In addition, AG8 treatment repressed the transcription of inhibin βA and reduced the ET_A-induced phosphorylation of protein kinase B and extracellular regulated kinase. Furthermore, tumor growth was effectively inhibited by AG8 in a colorectal cancer mouse xenograft model. The human anti-ET_A antibody isolated in this study could be used as a potential therapeutic for cancers, including colorectal cancer.

A therapeutic antibody that targets a receptor involved in cancer progression shows significant anti-cancer effects in trials in mice. Endothelin receptor A (ET_A) promotes the progression and metastasis of several cancers, and patients with high ET_A expression often have poor survival rates. Several small molecule drugs that target ET_A are currently undergoing trials. Now, Sang Taek Jung at the Korea University in Seoul, together with scientists across South Korea, have identified and isolated a human antibody that specifically binds to ET_A. The team developed an antigen that mimics ET_A, and identified and isolated the antibody it bound to. The antibody exhibited potent anti-tumor effects in cell cultures and trials in mice. Such therapeutic antibodies show higher affinity for their targets than other drugs, resulting in fewer side effects and higher efficacy.

The Contribution of Phospholipase C in Vomiting in the Least Shrew (Cryptotis Parva) Model of Emesis

Gq and Gβγ protein-dependent phospholipase C (PLC) activation is extensively involved in G protein-coupled receptor (GPCR)-mediated signaling pathways which are implicated in a wide range of physiological and pathological events. Stimulation of several GPCRs, such as substance P neurokinin 1-, dopamine D2/3-, histamine H1- and mu-opioid receptors, can lead to vomiting. The aim of this study was to investigate the role of PLC in vomiting through assessment of the emetic potential of a PLC activator (m-3M3FBS), and the antiemetic efficacy of a PLC inhibitor (U73122), in the least shrew model of vomiting. We find that a 50 mg/kg (i.p.) dose of m-3M3FBS induces vomiting in ∼90% of tested least shrews, which was accompanied by significant increases in c-Fos expression and ERK1/2 phosphorylation in the shrew brainstem dorsal vagal complex, indicating activation of brainstem emetic nuclei in m-3M3FBS-evoked emesis. The m-3M3FBS-evoked vomiting was reduced by pretreatment with diverse antiemetics including the antagonists/inhibitors of: PLC (U73122), L-type Ca2+ channel (nifedipine), IP3R (2-APB), RyR receptor (dantrolene), ERK1/2 (U0126), PKC (GF109203X), the serotoninergic type 3 receptor (palonosetron), and neurokinin 1 receptor (netupitant). In addition, the PLC inhibitor U73122 displayed broad-spectrum antiemetic effects against diverse emetogens, including the selective agonists of serotonin type 3 (2-Methyl-5-HT)-, neurokinin 1 receptor (GR73632), dopamine D2/3 (quinpirole)-, and muscarinic M1 (McN-A-343) receptors, the L-type Ca2+ channel (FPL64176), and the sarco/endoplasmic reticulum Ca2+-ATPase inhibitor thapsigargin. In sum, PLC activation contributes to emesis, whereas PLC inhibition suppresses vomiting evoked by diverse emetogens.

Identification of the interactome of the DP1 receptor for Prostaglandin D2: Regulation of DP1 receptor signaling and trafficking by IQGAP1

BACKGROUND

Mechanisms governing localization, trafficking and signaling of G protein-coupled receptors (GPCRs) are critical in cell function. Protein-protein interactions are determinant in these processes. However, there are very little interacting proteins known to date for the DP1 receptor for prostaglandin D₂.

METHODS

We performed LC-MS/MS analyses of the DP1 receptor interactome in HEK293 cells. To functionally validate our LC-MS/MS data, we studied the implications of the interaction with the IQGAP1 scaffold protein in the trafficking and signaling of DP1.

RESULTS

In addition to expected interacting proteins such as heterotrimeric G protein subunits, we identified proteins involved in signaling, trafficking, and folding localized in various cell compartments. Endogenous DP1-IQGAP1 co-immunoprecipitation was observed in colon cancer HT-29 cells. The interaction was augmented by DP1 agonist activation in HEK293 cells and GST-pulldown assays showed that IQGAP1 binds to intracellular loops 2 and 3 of DP1. Co-localization of the two proteins was observed by confocal microscopy at the cell periphery and in intracellular vesicles in the basal state. PGD₂ treatment resulted in the redistribution of the DP1-IQGAP1 co-localization in the perinuclear vicinity. DP1 receptor internalization was promoted by overexpression of IQGAP1, while it was diminished by IQGAP1 knockdown with DsiRNAs. DP1-mediated ERK1/2 activation was augmented and sustained overtime by overexpression of IQGAP1 when compared to DP1 expressed alone. IQGAP1 knockdown decreased ERK1/2 activation by DP1 stimulation. Interestingly, ERK1/2 signaling by DP1 was increased when IQGAP2 was silenced, while it was impaired by IQGAP3 knockdown.

CONCLUSIONS

Our findings define the putative DP1 interactome, a patho-physiologically important receptor, and validated the interaction with IQGAP1 in DP1 function. Our data also reveal that IQGAP proteins may differentially regulate GPCR signaling.

GENERAL SIGNIFICANCE

The identified putative DP1-interacting proteins open multiple lines of research in DP1 and GPCR biology in various cell compartments.

Directed Evolution: Methodologies and Applications

Directed evolution aims to expedite the natural evolution process of biological molecules and systems in a test tube through iterative rounds of gene diversifications and library screening/selection. It has become one of the most powerful and widespread tools for engineering improved or novel functions in proteins, metabolic pathways, and even whole genomes. This review describes the commonly used gene diversification strategies, screening/selection methods, and recently developed continuous evolution strategies for directed evolution. Moreover, we highlight some representative applications of directed evolution in engineering nucleic acids, proteins, pathways, genetic circuits, viruses, and whole cells. Finally, we discuss the challenges and future perspectives in directed evolution.

Amino terminal recognition by a CCR6 chemokine receptor antibody blocks CCL20 signaling and IL-17 expression via β-arrestin

Background

CCR6 chemokine receptor is an important target in inflammatory diseases. Th17 cells express CCR6 and a number of inflammatory cytokines, including IL-17 and IL-22, which are involved in the propagation of inflammatory immune responses. CCR6 antagonist would be a potential treatment for inflammatory diseases such as psoriasis or rheumatoid arthritis. The aim of this study is to develop an antagonistic monoclonal antibody (mAb) against human CCR6 receptor (hCCR6).

Results

We generate monoclonal antibodies against hCCR6 immunizing Balb/c mice with hCCR6 overexpressing cells. The antibodies were tested by flow cytometry for specific binding to hCCR6, cloned by limiting dilution and resulted in the isolation and purification monoclonal antibody 1C6. By ELISA and flow cytometry, was determined that the antibody obtained binds to hCCR6 N-terminal domain. The ability of 1C6 to neutralize hCCR6 signaling was tested and we determined that 1C6 antibody were able to block response in β-arrestin recruitment assay with IC₅₀ 10.23 nM, but did not inhibit calcium mobilization. In addition, we found in a chemotaxis assay that 1C6 reduces the migration of hCCR6 cells to their ligand CCL20. Finally, we determined by RT-qPCR that the expression of IL-17A in Th17 cells treated with 1C6 was inhibited.

Conclusions

In the present study, we applied whole cell immunization for successfully obtain an antibody that is capable to neutralize hCCR6 signaling and to reduce hCCR6 cells migration and IL-17 expression. These results provide an efficient approach to obtain therapeutic potential antibodies in the treatment of CCR6-mediated inflammatory diseases.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12896-021-00699-2.

Soluble ligands as drug targets for treatment of inflammatory bowel disease

Inflammatory bowel disease (IBD), which includes Crohn's disease and ulcerative colitis, is characterized by persistent inflammation in a hereditarily susceptible host. In addition to gastrointestinal symptoms, patients with IBD frequently suffer from extra-intestinal complications such as fibrosis, stenosis or cancer. Mounting evidence supports the targeting of cytokines for effective treatment of IBD. Cytokines can be included in a newly proposed classification "soluble ligands" that has become the third major target of human protein therapeutic drugs after enzymes and receptors. Soluble ligands have potential significance for research and development of anti-IBD drugs. Compared with traditional drug targets for IBD treatment, such as receptors, at least three factors contribute to the increasing importance of soluble ligands as drug targets. Firstly, cytokines are the main soluble ligands and targeting of them has demonstrated efficacy in patients with IBD. Secondly, soluble ligands are more accessible than receptors, which are embedded in the cell membrane and have complex tertiary membrane structures. Lastly, certain potential target proteins that are present in membrane-bound forms can become soluble following cleavage, providing further opportunities for intervention in the treatment of IBD. In this review, 49 drugs targeting 25 distinct ligands have been evaluated, including consideration of the characteristics of the ligands and drugs in respect of IBD treatment. In addition to approved drugs targeting soluble ligands, we have also assessed drugs that are in preclinical research and drugs inhibiting ligand-receptor binding. Some new types of targetable soluble ligands/proteins, such as epoxide hydrolase and p-selectin glycoprotein ligand-1, are also introduced. Targeting soluble ligands not only opens a new field of anti-IBD drug development, but the circulating soluble ligands also provide diagnostic insights for early prediction of treatment response. In conclusion, soluble ligands serve as the third-largest protein target class in medicine, with much potential for the drugs targeting them.

Development of Anti-Mouse CC Chemokine Receptor 8 Monoclonal Antibodies for Flow Cytometry

CC chemokine receptor 8 (CCR8) belongs to the class A of G protein-coupled receptor. It is highly expressed on Treg and T helper 2 (T_H2) cells recruited to the inflammation site and is implicated in allergy and asthma. Recently, CCR8+Treg cells have been suggested to be a master regulator in the immunosuppressive tumor microenvironment; therefore, developing sensitive monoclonal antibodies (mAbs) for CCR8 has been desired. This study established a specific and sensitive mAb for mouse CCR8 (mCCR8), which is useful for flow cytometry by using the Cell-Based Immunization and Screening (CBIS) method. The established anti-mCCR8 mAb, C₈Mab-2 (rat IgG_2b, kappa), reacted with mCCR8-overexpressed Chinese hamster ovary-K1 (CHO/mCCR8) cells and P388 (mouse lymphoid neoplasma) or J774-1 (mouse macrophage-like) cells, which express endogenous mCCR8 by flow cytometry. C₈Mab-2, which was established by the CBIS method, could be useful for elucidating the mCCR8-related biological response by flow cytometry.

Ectopically expressed olfactory receptors OR51E1 and OR51E2 suppress proliferation and promote cell death in a prostate cancer cell line

Olfactory receptors (ORs), the largest family of G protein–coupled receptors, are expressed in the nasal epithelium where they mediate the sense of smell. However, ORs are also found in other non-nasal tissues, but the role of these ectopic ORs in cell signaling, proliferation, and survival is not well understood. Here, using an inducible expression system in the lymph node carcinoma of the prostate (LNCaP) cell line, we investigated two ectopic ORs, OR51E1 and OR51E2, which have been shown to be upregulated in prostate cancer. We found that, consistent with previous studies, OR51E1 stimulated adenylyl cyclase in response to treatment by short-chain to medium-chain organic acids (C3–C9) but not by acetate. OR51E2 responded to acetate and propionate but not to the longer chain organic acids. Stimulation of LNCaP cells with butyrate inhibited their growth, and the knockdown of the endogenous OR51E1 negated this cytostatic effect. Most significantly, overexpression of OR51E1 or OR51E2 suppressed LNCaP cell proliferation. Overexpression of another ectopic OR OR2AT4, β2-adrenergic receptor, or treatment of cells with forskolin did not suppress cell proliferation, indicating that a rise in cAMP is not sufficient to induce cytostasis. Overexpression of OR51E1 caused an upregulation of cytostatic and cell death markers including p27, p21, and p53, strongly increased annexin V staining, and stimulated extracellular signal–regulated protein kinases 1 and 2. Overexpression and/or activation of OR51E1 did not affect human embryonic kidney 293 cell proliferation, indicating that cytotoxicity of OR51E1/OR51E2 is specific for LNCaP cells. Together, our results further our understanding of prostate cancer etiology and suggest that ectopic ORs may be useful therapeutic targets.

What Makes Antibodies Against G Protein-Coupled Receptors so Special? A Novel Concept to Understand Chronic Diseases

Expressions of G protein-coupled receptors (GPCR) on immune and tissue resident cells are the consequence of the cellular environment, which is highly variable. As discussed here, antibodies directed to GPCR (GPCR abs), their levels and correlations to other abs, serve as biomarkers for various diseases. They also could reflect the individual interplay between the environment and the immune system. Thus, GPCR abs could display pathogenic chronic conditions and could help to identify disease-related pathways. Moreover, by acting as ligands to their corresponding receptors, GPCR abs modulate autoimmune as well as non-autoimmune diseases. This article introduces GPCR abs as drivers for diseases by their capability to induce a specific signaling and by determining immune cell homeostasis. The identification of the individual GPCR ab function is challenging but might be pivotal in the comprehension of the aetiology of diseases. This, hopefully, will lead to the identification of novel therapeutic strategies. This article provides an overview about concepts and recent developments in research. Accordingly, GPCR abs could represent ideal candidates for precision medicine. Here, we introduce the term antibodiom to cover the network of abs with GPCR abs as prominent players.

Discovery and characterization of a neutralizing pan-ELR+CXC chemokine monoclonal antibody

CXCR1 and CXCR2 signaling play a critical role in neutrophil migration, angiogenesis, and tumorigenesis and are therefore an attractive signaling axis to target in a variety of indications. In human, a total of seven chemokines signal through these receptors and comprise the ELR⁺CXC chemokine family, so named because of the conserved ELRCXC N-terminal motif. To fully antagonize CXCR1 and CXCR2 signaling, an effective therapeutic should block either both receptors or all seven ligands, yet neither approach has been fully realized clinically. In this work, we describe the generation and characterization of LY3041658, a humanized monoclonal antibody that binds and neutralizes all seven human and cynomolgus monkey ELR⁺CXC chemokines and three of five mouse and rat ELR⁺CXC chemokines with high affinity. LY3041658 is able to block ELR⁺CXC chemokine-induced Ca²⁺ mobilization, CXCR2 internalization, and chemotaxis in vitro as well as neutrophil mobilization in vivo without affecting other neutrophil functions. In addition to the in vitro and in vivo activity, we characterized the epitope and structural basis for binding in detail through alanine scanning, crystallography, and mutagenesis. Together, these data provide a robust preclinical characterization of LY3041658 for which the efficacy and safety is being evaluated in human clinical trials for neutrophilic skin diseases.

A peptide immunoaffinity LC-MS/MS strategy for quantifying the GPCR protein, S1PR1 in human colon biopsies

Background: S1PR1, a G protein-coupled receptor (GPCR) protein, is a therapeutic target for treatment of autoimmune diseases. As a potential biomarker for drug effect and patient stratification, it is of great significance to measure it in biological samples. However, due to the hydrophobic nature of S1PR1 and the difficulties in extraction and solubilization, as well as low expression levels, quantitative determination of S1PR1 remains challenging. Results: In this work, a peptide immunoaffinity LC-MS/MS method was developed to quantify S1PR1 in biopsy-sized colon samples with an LLOQ of 7.81 pM. Conclusion: Peptide immunoaffinity LC-MS/MS based strategy has achieved the desired sensitivity for low abundance S1PR1, and the same strategy could be applied to quantify S1PR1 in multiple species and other GPCR proteins.

Synthetic nanobodies as angiotensin receptor blockers

There is considerable interest in developing antibodies as functional modulators of G protein-coupled receptor (GPCR) signaling for both therapeutic and research applications. However, there are few antibody ligands targeting GPCRs outside of the chemokine receptor group. GPCRs are challenging targets for conventional antibody discovery methods, as many are highly conserved across species, are biochemically unstable upon purification, and possess deeply buried ligand-binding sites. Here, we describe a selection methodology to enrich for functionally modulatory antibodies using a yeast-displayed library of synthetic camelid antibody fragments called "nanobodies." Using this platform, we discovered multiple nanobodies that act as antagonists of the angiotensin II type 1 receptor (AT1R). Following angiotensin II infusion in mice, we found that an affinity matured nanobody antagonist has comparable antihypertensive activity to the angiotensin receptor blocker (ARB) losartan. The unique pharmacology and restricted biodistribution of nanobody antagonists may provide a path for treating hypertensive disorders when small-molecule drugs targeting the AT1R are contraindicated, for example, in pregnancy.

Cellular Heterogeneity of the Luteinizing Hormone Receptor and Its Significance for Cyclic GMP Signaling in Mouse Preovulatory Follicles

Meiotic arrest and resumption in mammalian oocytes are regulated by 2 opposing signaling proteins in the cells of the surrounding follicle: the guanylyl cyclase natriuretic peptide receptor 2 (NPR2), and the luteinizing hormone receptor (LHR). NPR2 maintains a meiosis-inhibitory level of cyclic guanosine 5'-monophosphate (cGMP) until LHR signaling causes dephosphorylation of NPR2, reducing NPR2 activity, lowering cGMP to a level that releases meiotic arrest. However, the signaling pathway between LHR activation and NPR2 dephosphorylation remains incompletely understood, due in part to imprecise information about the cellular localization of these 2 proteins. To investigate their localization, we generated mouse lines in which hemagglutinin epitope tags were added to the endogenous LHR and NPR2 proteins, and used immunofluorescence and immunogold microscopy to localize these proteins with high resolution. The results showed that the LHR protein is absent from the cumulus cells and inner mural granulosa cells, and is present in only 13% to 48% of the outer mural granulosa cells. In contrast, NPR2 is present throughout the follicle, and is more concentrated in the cumulus cells. Less than 20% of the NPR2 is in the same cells that express the LHR. These results suggest that to account for the LH-induced inactivation of NPR2, LHR-expressing cells send a signal that inactivates NPR2 in neighboring cells that do not express the LHR. An inhibitor of gap junction permeability attenuates the LH-induced cGMP decrease in the outer mural granulosa cells, consistent with this mechanism contributing to how NPR2 is inactivated in cells that do not express the LHR.