Mapping of genes for the human C5a receptor (C5AR), human FMLP receptor (FPR), and two FMLP receptor homologue orphan receptors (FPRH1, FPRH2) to chromosome 19

The formyl peptide receptors FPR1 and FPR2 as targets for inflammatory disorders: recent advances in the development of small-molecule agonists

Formyl peptide receptors (FPRs) comprise a class of chemoattractant pattern recognition receptors, for which several physiological functions like host-defences, as well as the regulation of inflammatory responses, have been ascribed. With accumulating evidence that agonism of FPR1/FPR2 can confer pro-resolution of inflammation, increased attention from academia and industry has led to the discovery of new and interesting small-molecule FPR1/FPR2 agonists. Focused attention on the development of appropriate physicochemical and pharmacokinetic profiles is yielding synthesis of new compounds with promising in vivo readouts. This review presents an overview of small-molecule FPR1/FPR2 agonist medicinal chemistry developed over the past 20 years, with a particular emphasis on interrogation in the increasingly sophisticated bioassays which have been developed.

Formyl peptide receptors in bone research

PURPOSE/AIM OF THE STUDY

The formyl peptide receptor (FPR) participates in the immune response, with roles in infection and inflammation. In this review article, we summarize the current literature on these roles before discussing the function of FPRs in the pathogenesis of musculoskeletal disorders including osteoarthritis (OA), degenerative disc disease (DDD), and rheumatoid arthritis (RA). Additionally, we discuss the potential diagnostic and therapeutic roles of FPRs in these domains.

METHODS

PubMed and Ovid MEDLINE searches were performed from 1965 through March 2022. Keywords included "FPR, tissue expression, inflammation, infection, musculoskeletal disorder, bone, rheumatoid arthritis, osteoarthritis, degenerative disc disease, mitochondria."

RESULTS

Sixty-nine studies were included in this review article. FPRs appear to be ubiquitous in the pathogenesis, diagnosis, and treatment of common musculoskeletal disorders. They can potentially be utilized for the earlier diagnosis of OA and DDD. They may be employed with mesenchymal stem cells (MSCs) to reverse OA and DDD pathologies. With anti-inflammatory, anti-osteolytic, and pro-angiogenic functions, they may broaden treatment options in RA.

CONCLUSIONS

FPRs appear to be heavily involved in the pathogenesis of common musculoskeletal conditions, including arthritis, degenerative disc disease, and rheumatoid arthritis. Furthermore, they demonstrate much promise in the diagnosis and treatment of these conditions. Their roles should continue to be explored.

Molecular Mechanisms of Desensitization Underlying the Differential Effects of Formyl Peptide Receptor 2 Agonists on Cardiac Structure-Function Post Myocardial Infarction

Formyl peptide receptor 2 (FPR2) plays an integral role in the transition of macrophages from a pro-inflammatory program to one that is pro-resolving. FPR2-mediated stimulation of resolution post myocardial infarction has demonstrated efficacy in rodent models and is hypothesized to reduce progression into heart failure. FPR2 agonists that promote long-lasting receptor internalization can lead to persistent desensitization and diminished therapeutic benefits. In vitro signaling profiles and propensities for receptor desensitization of two clinically studied FPR2 agonists, namely, BMS-986235 and ACT-389949, were evaluated. In contrast to BMS-986235, pre-stimulation with ACT-389949 led to a decrease in its potency to inhibit cAMP production. Moreover, ACT-389949 displayed greater efficacy for β-arrestin recruitment, while efficacy of Gi activation was similar for both agonists. Following agonist-promoted FPR2 internalization, effective recycling to the plasma membrane was observed only with BMS-986235. Use of G protein-coupled receptor kinase (GRK) knock-out cells revealed a differential impact of GRK2 versus GRK5/6 on β-arrestin recruitment and Gi activation promoted by the two FPR2 agonists. In vivo, decreases of granulocytes in circulation were greatly diminished in mice treated with ACT-389949 but not for BMS-986235. With short-term dosing, both compounds induced a pro-resolution polarization state in cardiac monocyte/macrophages post myocardial infarction. By contrast, with long-term dosing, only BMS-986235 preserved the infarct wall thickness and increased left ventricular ejection fraction in a rat model of myocardial infarction. Altogether, the study shows that differences in the desensitization profiles induced by ACT-389949 and BMS-986235 at the molecular level may explain their distinct inflammatory/pro-resolving activities in vivo.

Formylpeptide receptor 2: Nomenclature, structure, signalling and translational perspectives: IUPHAR review 35

We discuss the fascinating pharmacology of formylpeptide receptor 2 (FPR2; often referred to as FPR2/ALX since it binds lipoxin A₄ ). Initially identified as a low-affinity 'relative' of FPR1, FPR2 presents complex and diverse biology. For instance, it is activated by several classes of agonists (from peptides to proteins and lipid mediators) and displays diverse expression patterns on myeloid cells as well as epithelial cells and endothelial cells, to name a few. Over the last decade, the pharmacology of FPR2 has progressed from being considered a weak chemotactic receptor to a master-regulator of the resolution of inflammation, the second phase of the acute inflammatory response. We propose that exploitation of the biology of FPR2 offers innovative ways to rectify chronic inflammatory states and represents a viable avenue to develop novel therapies. Recent elucidation of FPR2 structure will facilitate development of the anti-inflammatory and pro-resolving drugs of next decade.

Exploiting formyl peptide receptor 2 to promote microglial resolution: a new approach to Alzheimer's disease treatment

Alzheimer's disease and dementia are among the most significant current healthcare challenges given the rapidly growing elderly population, and the almost total lack of effective therapeutic interventions. Alzheimer's disease pathology has long been considered in terms of accumulation of amyloid beta and hyperphosphorylated tau, but the importance of neuroinflammation in driving disease has taken greater precedence over the last 15-20 years. Inflammatory activation of the primary brain immune cells, the microglia, has been implicated in Alzheimer's pathogenesis through genetic, preclinical, imaging and postmortem human studies, and strategies to regulate microglial activity may hold great promise for disease modification. Neuroinflammation is necessary for defence of the brain against pathogen invasion or damage but is normally self-limiting due to the engagement of endogenous pro-resolving circuitry that terminates inflammatory activity, a process that appears to fail in Alzheimer's disease. Here, we discuss the potential for a major regulator and promoter of resolution, the receptor FPR2, to restrain pro-inflammatory microglial activity, and propose that it may serve as a valuable target for therapeutic investigation in Alzheimer's disease.

The Contribution of Formyl Peptide Receptor Dysfunction to the Course of Neuroinflammation: A Potential Role in the Brain Pathology

Chronic inflammatory processes within the central nervous system (CNS) are in part responsible for the development of neurodegenerative and psychiatric diseases. These processes are associated with, among other things, the increased and disturbed activation of microglia and the elevated production of proinflammatory factors. Recent studies indicated that the disruption of the process of resolution of inflammation (RoI) may be the cause of CNS disorders. It is shown that the RoI is regulated by endogenous molecules called specialized pro-resolving mediators (SPMs), which interact with specific membrane receptors. Some SPMs activate formyl peptide receptors (FPRs), which belong to the family of seven-transmembrane G protein-coupled receptors. These receptors take part not only in the proinflammatory response but also in the resolution of the inflammation process. Therefore, the activation of FPRs might have complex consequences.

This review discusses the potential role of FPRs, and in particular the role of FPR2 subtype, in the brain under physiological and pathological conditions and their involvement in processes underlying neurodegenerative and psychiatric disorders as well as ischemia, the pathogenesis of which involves the dysfunction of inflammatory processes.

Druggable Lipid GPCRs: Past, Present, and Prospects

G protein-coupled receptors (GPCRs) have seven transmembrane spanning domains and comprise the largest superfamily with ~800 receptors in humans. GPCRs are attractive targets for drug discovery because they transduce intracellular signaling in response to endogenous ligands via heterotrimeric G proteins or arrestins, resulting in a wide variety of physiological and pathophysiological responses. The endogenous ligands for GPCRs are highly chemically diverse and include ions, biogenic amines, nucleotides, peptides, and lipids. In this review, we follow the KonMari method to better understand druggable lipid GPCRs. First, we have a comprehensive tidying up of lipid GPCRs including receptors for prostanoids, leukotrienes, specialized pro-resolving mediators (SPMs), lysophospholipids, sphingosine 1-phosphate (S1P), cannabinoids, platelet-activating factor (PAF), free fatty acids (FFAs), and sterols. This tidying up consolidates 46 lipid GPCRs and declutters several perplexing lipid GPCRs. Then, we further tidy up the lipid GPCR-directed drugs from the literature and databases, which identified 24 clinical drugs targeting 16 unique lipid GPCRs available in the market and 44 drugs under evaluation in more than 100 clinical trials as of 2019. Finally, we introduce drug designs for GPCRs that spark joy, such as positive or negative allosteric modulators (PAM or NAM), biased agonism, functional antagonism like fingolimod, and monoclonal antibodies (MAbs). These strategic drug designs may increase the efficacy and specificity of drugs and reduce side effects. Technological advances will help to discover more endogenous lipid ligands from the vast number of remaining orphan GPCRs and will also lead to the development novel lipid GPCR drugs to treat various diseases.

Discovery of BMS-986235/LAR-1219: A Potent Formyl Peptide Receptor 2 (FPR2) Selective Agonist for the Prevention of Heart Failure

Formyl peptide receptor 2 (FPR2) agonists can stimulate resolution of inflammation and may have utility for treatment of diseases caused by chronic inflammation, including heart failure. We report the discovery of a potent and selective FPR2 agonist and its evaluation in a mouse heart failure model. A simple linear urea with moderate agonist activity served as the starting point for optimization. Introduction of a pyrrolidinone core accessed a rigid conformation that produced potent FPR2 and FPR1 agonists. Optimization of lactam substituents led to the discovery of the FPR2 selective agonist 13c, BMS-986235/LAR-1219. In cellular assays 13c inhibited neutrophil chemotaxis and stimulated macrophage phagocytosis, key end points to promote resolution of inflammation. Cardiac structure and functional improvements were observed in a mouse heart failure model following treatment with BMS-986235/LAR-1219.

Is lipoxin A4 an effective treatment on fat embolism syndrome by attenuating pro-inflammatory response?

Fat embolism syndrome (FES) is characterized by high mortality and lack of effective treatment, the symptomatic therapy is most used to relieve clinical symptoms. Some studies have shown that inflammation is one of the main pathogeneses of FES. Lipoxin A4 is an endogenous-derived anti-inflammatory substance which was discovered recently. It can alleviate inflammatory response and promote inflammation resolution, and is referred as brake signal of inflammation. Therefore we hypothesize that lipoxin A4 may have a remission and therapeutic effect on FES by attenuating FES-induced inflammatory responses.

Mitochondria in innate immune signaling

Mitochondria are functionally versatile organelles. In addition to their conventional role of meeting the cell's energy requirements, mitochondria also actively regulate innate immune responses against infectious and sterile insults. Components of mitochondria, when released or exposed in response to dysfunction or damage, can be directly recognized by receptors of the innate immune system and trigger an immune response. In addition, despite initiation that may be independent from mitochondria, numerous innate immune responses are still subject to mitochondrial regulation as discrete steps of their signaling cascades occur on mitochondria or require mitochondrial components. Finally, mitochondrial metabolites and the metabolic state of the mitochondria within an innate immune cell modulate the precise immune response and shape the direction and character of that cell's response to stimuli. Together, these pathways result in a nuanced and very specific regulation of innate immune responses by mitochondria.

Synopsis of arachidonic acid metabolism: A review

Arachidonic acid (AA), a 20 carbon chain polyunsaturated fatty acid with 4 double bonds, is an integral constituent of biological cell membrane, conferring it with fluidity and flexibility. The four double bonds of AA predispose it to oxygenation that leads to a plethora of metabolites of considerable importance for the proper function of the immune system, promotion of allergies and inflammation, resolving of inflammation, mood, and appetite. The present review presents an illustrated synopsis of AA metabolism, corroborating the instrumental importance of AA derivatives for health and well-being. It provides a comprehensive outline on AA metabolic pathways, enzymes and signaling cascades, in order to develop new perspectives in disease treatment and diagnosis.

The common promoter polymorphism rs11666254 downregulates FPR2/ALX expression and increases risk of sepsis in patients with severe trauma

Background

Formyl peptide receptor 2-lipoxin receptor (FPR2/ALX) modulates the anti-inflammatory response and therefore may be a target for treating sepsis. The purpose of this study was to investigate the association between genetic variants of the FPR2/ALX gene and sepsis after severe trauma as well as to further analyze the functions of sepsis-related genetic polymorphisms.

Methods

Three tag single-nucleotide polymorphisms (tag SNPs) that captured all common alleles across the FPR2/ALX genomic region were genotyped using pyrosequencing in an initial sample consisting of 275 patients with severe trauma. The rs11666254 polymorphism, which had statistical significance, was genotyped in an additional 371 patients, and logistic regression analysis was performed to determine associations between the FPR2/ALX gene polymorphism and sepsis susceptibility after severe trauma. The messenger RNA (mRNA) and protein levels of FPR2/ALX in the lipopolysaccharide-stimulated white blood cells of trauma patients were determined by performing quantitative polymerase chain reactions and Western blot analysis. Tumor necrosis factor (TNF)-α production was measured by enzyme-linked immunosorbent assay. The effects of the promoter polymorphism rs11666254 on the transcription activity of FPR2/ALX were analyzed using a luciferase reporter assay.

Results

Among the three tag SNPs, only the rs11666254 polymorphism was found to be significantly associated with sepsis in trauma patients, and this association persisted after a pooled analysis of all 646 trauma patients, which showed that patients who carried the A allele of rs11666254 had a significantly higher risk of developing sepsis than individuals who carried the G allele. This SNP was also significantly associated with lower FPR2/ALX mRNA and protein expression as well as higher TNF-α production from the peripheral blood leukocyte response to bacterial lipoprotein stimulation. In addition, the rs11666254 polymorphism could significantly decrease the promoter activity of the FPR2/ALX gene.

Conclusions

The rs11666254 polymorphism in the FPR2/ALX gene is a functional SNP that increases sepsis susceptibility in patients after traumatic injury.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-017-1757-3) contains supplementary material, which is available to authorized users.

Annexin A1 and resolution of inflammation: tissue repairing properties and signalling signature

Inflammation is essential to protect the host from exogenous and endogenous dangers that ultimately lead to tissue injury. The consequent tissue repair is intimately associated with the fate of the inflammatory response. Restoration of tissue homeostasis is achieved through a balance between pro-inflammatory and anti-inflammatory/pro-resolving mediators. In chronic inflammatory diseases such balance is compromised, resulting in persistent inflammation and impaired healing. During the last two decades the glucocorticoid-regulated protein Annexin A1 (AnxA1) has emerged as a potent pro-resolving mediator acting on several facets of the innate immune system. Here, we review the therapeutic effects of AnxA1 on tissue healing and repairing together with the molecular targets responsible for these complex biological properties.

Formyl peptide receptors promotes neural differentiation in mouse neural stem cells by ROS generation and regulation of PI3K-AKT signaling

This study aimed to determine whether formyl peptide receptors (FPRs) regulated the differentiation of neural stem cells (NSCs). FPRs promote the migration of NSCs both in vitro and in vivo. However, the role of FPRs during differentiation of NSCs is unknown. Analysis by Western blot showed significantly increased expression of FPR1 and FPR2 during differentiation of NSCs. The activation of FPRs promotes NSCs to differentiate into neurons with more primary neurites and branch points and longer neurites per cell. Meanwhile, this activation also inhibits the differentiation of NSC into astrocytes. This bidirectional effect can be inhibited by the FPRs-specific inhibitor. Moreover, it was found that the activation of FPRs increased the generation of reactive oxygen species (ROS) and phosphorylation of AKT in the NSCs, while N-acetylcysteine and LY294002 inhibited the FPRs-stimulated increase in ROS generation and AKT phosphorylation, and blocked the FPRs-stimulated neural differentiation into neurons. Therefore, FPRs-stimulated neural differentiation was mediated via ROS and PI3K-AKT signaling pathways. Collectively, the present findings provided a novel insight into the functional role of FPRs in neurogenesis, with important implications for its potential use as a candidate for treating brain or spinal cord injury.

The Formyl Peptide Receptors: Diversity of Ligands and Mechanism for Recognition

The formyl peptide receptors (FPRs) are G protein-coupled receptors that transduce chemotactic signals in phagocytes and mediate host-defense as well as inflammatory responses including cell adhesion, directed migration, granule release and superoxide production. In recent years, the cellular distribution and biological functions of FPRs have expanded to include additional roles in homeostasis of organ functions and modulation of inflammation. In a prototype, FPRs recognize peptides containing N-formylated methionine such as those produced in bacteria and mitochondria, thereby serving as pattern recognition receptors. The repertoire of FPR ligands, however, has expanded rapidly to include not only N-formyl peptides from microbes but also non-formyl peptides of microbial and host origins, synthetic small molecules and an eicosanoid. How these chemically diverse ligands are recognized by the three human FPRs (FPR1, FPR2 and FPR3) and their murine equivalents is largely unclear. In the absence of crystal structures for the FPRs, site-directed mutagenesis, computer-aided ligand docking and structural simulation have led to the identification of amino acids within FPR1 and FPR2 that interact with several formyl peptides. This review article summarizes the progress made in the understanding of FPR ligand diversity as well as ligand recognition mechanisms used by these receptors.

Rubimetide, humanin, and MMK1 exert anxiolytic-like activities via the formyl peptide receptor 2 in mice followed by the successive activation of DP1, A2A, and GABAA receptors

Rubimetide (Met-Arg-Trp), which had been isolated as an antihypertensive peptide from an enzymatic digest of spinach ribulose-bisphosphate carboxylase/oxygenase (Rubisco), showed anxiolytic-like activity prostaglandin (PG) D2-dependent manner in the elevated plus-maze test after administration at a dose of 0.1mg/kg (ip.) or 1mg/kg (p.o.) in male mice of ddY strain. In this study, we found that rubimetide has weak affinities for the FPR1 and FPR2, subtypes of formyl peptide receptor (FPR). The anxiolytic-like activity of rubimetide (0.1mg/kg, ip.) was blocked by WRW4, an antagonist of FPR2, but not by Boc-FLFLF, an antagonist of FPR1, suggesting that the anxiolytic-like activity was mediated by the FPR2. Humanin, an endogenous agonist peptide of the FPR2, exerted an anxiolytic-like activity after intracerebroventricular (icv) administration, which was also blocked by WRW4. MMK1, a synthetic agonist peptide of the FPR2, also exerted anxiolytic-like activity. Thus, FPR2 proved to mediate anxiolytic-like effect as the first example of central effect exerted by FPR agonists. As well as the anxiolytic-like activity of rubimetide, that of MMK1 was blocked by BW A868C, an antagonist of the DP1-receptor. Furthermore, anxiolytic-like activity of rubimetide was blocked by SCH58251 and bicuculline, antagonists for adenosine A2A and GABAA receptors, respectively. From these results, it is concluded that the anxiolytic-like activities of rubimetide and typical agonist peptides of the FPR2 were mediated successively by the PGD2-DP1 receptor, adenosine-A2A receptor, and GABA-GABAA receptor systems downstream of the FPR2.

Formyl peptide receptor modulators: a patent review and potential applications for inflammatory diseases (2012-2015)

INTRODUCTION

The activation of leukocytes and the subsequent immune cascade play an essential role in sterile and infectious inflammation. Dysregulation of these immune responses or excess leukocyte activation can induce tissue damage, organ dysfunction and mortality. Formyl peptide receptors (FPRs) are functionally diverse pattern recognition receptors responsible for recognizing different endogenous damage-associated molecular patterns or exogenous pathogen-associated molecular patterns. FPRs mediate leukocyte activation during inflammation. FPR1 antagonists and FPR2 agonists have demonstrated significant anti-inflammatory effects based on in vitro and in vivo studies. An increasing number of synthesized compounds targeting FPRs, especially potential FPR1 antagonists and FPR2 agonists, have been disclosed in patents. Areas covered: This article summarizes the current pharmacology patents related to FPR family modulators and their therapeutic indications based on a review of patent applications disclosed between 2012 and 2015. Expert opinion: In this review, FPR1 modulators comprise β-1,3-glucan synthase inhibitors containing an FPR ligand moiety, template-fixed peptidomimetics, cyclosporin H, and dipeptide derivatives. FPR2 modulators include phenylurea, bridged spiro[2.4]heptane ester, naphthalene, aminotriazole, polycyclic pyrrolidine-2,5-dione, imidazolidine-2,4-dione, (2-ureidoacetamido)alkyl, amide, oxazolyl-methylether, oxazole, thiazole, and crystalline potassium salt derivatives. These compounds have potential applications for human conditions such as inflammatory lung diseases, ischemia-reperfusion injury, sepsis, inflammatory bowel disease, and wound healing. FPRs are emerging as important targets for treating leukocyte-dominant inflammation.

Formylpeptide Receptors Promote the Migration and Differentiation of Rat Neural Stem Cells

Neural stem cells (NSCs) bear characteristics for proliferation, migration and differentiation into three main neural cell type(s): neurons, astrocytes and/or oligodendrocytes. Formylpeptide receptors (Fprs), belonging to the family of G protein-coupled chemoattractant receptors, have been detected on neurons in the central nervous system (CNS). Here, we report that Fpr1 and Fpr2 are expressed on NSCs as detected with immunohistochemistry, RT-PCR and WB assays. In addition, Fpr1 and Fpr2 promoted NSC migration through F-actin polymerization and skewed NSC differentiation to neurons. Our study demonstrates a unique role of Fpr1 and Fpr2 in NSCs and opens a novel window for cell replacement therapies for brain and spinal cord injury.

New development in studies of formyl-peptide receptors: critical roles in host defense

Formyl-peptide receptors are a family of 7 transmembrane domain, Gi-protein-coupled receptors that possess multiple functions in many pathophysiologic processes because of their expression in a variety of cell types and their capacity to interact with a variety of structurally diverse, chemotactic ligands. Accumulating evidence demonstrates that formyl-peptide receptors are critical mediators of myeloid cell trafficking in the sequential chemotaxis signal relays in microbial infection, inflammation, and immune responses. Formyl-peptide receptors are also involved in the development and progression of cancer. In addition, one of the formyl-peptide receptor family members, Fpr2, is expressed by normal mouse-colon epithelial cells, mediates cell responses to microbial chemotactic agonists, participates in mucosal development and repair, and protects against inflammation-associated tumorigenesis. These novel discoveries greatly expanded the current understanding of the role of formyl-peptide receptors in host defense and as potential molecular targets for the development of therapeutics.

The role of formylated peptides and formyl peptide receptor 1 in governing neutrophil function during acute inflammation

Neutrophil migration to sites of inflammation and the subsequent execution of multiple functions are designed to contain and kill invading pathogens. These highly regulated and orchestrated processes are controlled by interactions between numerous receptors and their cognate ligands. Unraveling and identifying those that are central to inflammatory processes may represent novel therapeutic targets for the treatment of neutrophil-dominant inflammatory disorders in which dysregulated neutrophil recruitment, function, and elimination serve to potentiate rather than resolve an initial inflammatory insult. The first G protein-coupled receptor to be described on human neutrophils, formyl peptide receptor 1 (FPR1), is one such receptor that plays a significant role in the execution of these functions through multiple intracellular signaling pathways. Recent work has highlighted important observations with regard to both receptor function and the importance and functional relevance of FPR1 in the pathogenesis of a range of both sterile and infective inflammatory conditions. In this review, we explore the multiple components of neutrophil migration and function in both health and disease, with a focus on the role of FPR1 in these processes. The current understanding of FPR1 structure, function, and signaling is examined, alongside discussion of the potential importance of FPR1 in inflammatory diseases suggesting that FPR1 is a key regulator of the inflammatory environment.

Enemy attraction: bacterial agonists for leukocyte chemotaxis receptors

The innate immune system recognizes conserved microorganism-associated molecular patterns (MAMPs), some of which are sensed by G protein-coupled receptors (GPCRs), and this leads to chemotactic leukocyte influx. Recent studies have indicated that these processes are crucial for host defence and rely on a larger set of chemotactic MAMPs and corresponding GPCRs than was previously thought. Agonists, such as bacterial formyl peptides, enterococcal pheromone peptides, staphylococcal peptide toxins, bacterial fermentation products and the Helicobacter pylori peptide HP(2-20), stimulate specific GPCRs. The importance of leukocyte chemotaxis in host defence is highlighted by the fact that some bacterial pathogens produce chemotaxis inhibitors. How the various chemoattractants, receptors and antagonists shape antibacterial host defence represents an important topic for future research.

Identification of oligomer proanthocyanidins (F2) isolated from grape seeds as a formyl peptide receptor 1 partial agonist

Formyl peptide receptor 1 (FPR1) plays an important role in the rapid progression of glioblastoma and has been considered as a molecular target for the treatment. Previously, we have shown that oligomer proanthocyanidins (F2, degree of polymerization 2-15), isolated from grape seeds, inhibited FPR1-mediated chemotaxis of U-87 glioblastoma cells. In the present study, we investigated the capacity of F2 to interact with FPR1. The cross attenuation of chemotaxis revealed that F2 shared FPR1 with formyl-methionyl-leucyl-phenylalanine (fMLF), which is a prototype agonist of FPR1. F2 was chemotactic for U-87 cells, and the chemotactic response was abolished when FPR1 gene was silenced or FPR1 was competitively occupied. We further show that F2 specifically blocked the binding of fluorescent agonist to FPR1. Interestingly, F2 exhibited the characteristic of a partial agonist for FPR1, as shown by its capacity to activate FPR1-mediated PI3K-PKC-MAPK pathways. Meanwhile, F2 also attenuated fMLF-triggered MAPK activation, suggesting that F2 could antagonize the effect of an agonist. Furthermore, F2 abolished the invasion of U-87 cells induced by fMLF. Thus, we have identified F2 as a novel, partial agonist for FPR1, which may be useful for glioblastoma therapy.

Molecular biology for formyl peptide receptors in human diseases

Leukocytes accumulate at sites of inflammation and immunological reaction in response to locally existing chemotactic mediators. The first chemotactic factors structurally defined were N-formyl peptides. Subsequently, numerous ligands were identified to activate formyl peptide receptors (FPRs) that belong to the seven-transmembrane G protein-coupled receptor superfamily. FPRs interact with this menagerie of structurally diverse pro- and anti-inflammatory ligands to possess important regulatory effects in multiple diseases, including inflammation, amyloidosis, Alzheimer's disease, prion disease, acquired immunodeficiency syndrome, obesity, diabetes, and cancer. How these receptors recognize diverse ligands and how they contribute to disease pathogenesis and host defense are basic questions currently under investigation that would open up new avenues for the future management of inflammation-related diseases.

Molecular characterization of three novel chemokine receptors in rainbow trout (Oncorhynchus mykiss)

Chemokines signal through a family of seven-transmembrane domain G-coupled receptors in order to regulate both leukocyte mobilization and activate the recruited cells. Although many chemokines have been identified in rainbow trout (Oncorhynchus mykiss), only a few chemokine receptors have been reported to date. In this work, we have cloned three novel chemokine receptors in rainbow trout. One of these receptors seems to be a clear orthologue of CCR6, while the second one constitutes a novel CCR9 gene different from the previous CCR9 reported in this species. This gene, which we have designated as CCR9B, represents another lineage of fish CCR9 genes, not previously identified. Finally, a deeper phylogenetic analysis of the third novel chemokine receptor gene, which had been identified on the basis of sequence similarity to CCR3, constitutes a novel lineage of CCR receptors which has no equivalent in humans and that may be teleost-specific. We have designated this novel gene as CCR13, to avoid any possible ascription to mammalian genes. Further transcriptional studies revealed that CCR6 was constitutively transcribed in thymus, gills, hindgut and peripheral blood leukocytes (PBLs), while CCR9B was strongly transcribed in thymus and PBLs but also in spleen, gills, hindgut and brain at lower levels. CCR13, on the other hand, was strongly detected in spleen, head kidney and PBLs and faintly in thymus, gills, brain and gonad. The data provided constitutes a step forward the identification of novel chemokine receptors that may contribute to a future understanding of chemokine signalling in fish.

Association analysis of formyl peptide receptor 2 (FPR2) polymorphisms and aspirin exacerbated respiratory diseases

Aspirin-exacerbated respiratory diseases (AERD) are associated with the metabolism of arachidonic acid. FPR2 (formyl peptide receptor2) is a high-affinity ligand receptor for potent anti-inflammatory lipid metabolites: lipoxins. Thus, functional alterations of the FPR2 may contribute to AERD. We investigated the relationship between single-nucleotide polymorphisms (SNPs) in the FPR2 and AERD. Asthmatics were categorized into AERD <15% decreases in forced expiratory volume in one second (FEV(1)), and/or naso-ocular reactions after oral aspirin challenge (n=170) and aspirin-tolerant asthma (ATA, n=268). In all, 11 SNPs were genotyped. FPR2 protein expressions on CD14-positive monocytes in peripheral blood were measured using flow cytometric analysis. We performed RT-PCR of the FPR2 mRNA expressed by peripheral blood mononuclear cells. Logistic regression analysis showed that the minor allele frequency of FPR2 -4209T>G (rs1769490) in intron 2 was significantly lower in the AERD group (n=170) than in the ATA group (n=268) (P=0.006, P(corr)=0.04, recessive model). The decline of FEV(1) after aspirin challenge was significantly lower in the subjects with GG homozygotes of FPR2 -4209T>G than those with the other genotypes (P=0.0002). Asthmatic homozygotes for FPR2 -4209T>G minor allele exhibited significantly higher FPR2 protein expression in CD14-positive monocytes than did those with the common allele of FPR2 -4209T>G allele (P=0.01). There was no difference in the expression of the wild form and the exon 2 deleted variant form of FPR2 gene according to the genotypes of FPR2 -4209T>G. The minor allele at FPR2 -4209T>G may have a protective role against the development of AERD, via increase of FPR2 protein expression in inflammatory cells.

Transcriptional regulation of the human FPR2/ALX gene: evidence of a heritable genetic variant that impairs promoter activity

Lipoxin (LX) A(4,) a main endogenous stop-signal of inflammation, activates the G-protein-coupled receptor FPR2/ALX, which triggers potent anti-inflammatory signaling in vivo. Thus, the regulation of FPR2/ALX expression may have pathophysiological and therapeutic relevance. Here, we mapped a nucleotide sequence with strong FPR2/ALX promoter activity. Chromatin immunoprecipitation revealed specificity protein 1 (Sp1) binding to the core promoter. Site-directed mutagenesis of the Sp1 cis-acting element and Sp1 overexpression established that this transcription factor is key for maximal promoter activity, which is instead suppressed by DNA methylation. LXA(4) enhanced FPR2/ALX promoter activity (+74%) and mRNA expression (+87.5%) in MDA-MB231 cells. A single nucleotide mutation (A/G) was detected in the core promoter of one subject with history of cardiovascular disease and of his two daughters. This mutation reduced by ∼35-90% the promoter activity in vitro. Moreover, neutrophils from individuals carrying the A/G variant displayed ∼10- and 3-fold reduction in FPR2/ALX mRNA and protein, respectively, compared with cells from their relatives or healthy volunteers expressing the wild-type allele. These results uncover FPR2/ALX transcriptional regulation and provide the first evidence of mutations that affect FPR2/ALX transcription, thus opening new opportunities for the understanding of the LXA(4)-FPR2/ALX axis in human disease.

Production of a bioengineered G-protein coupled receptor of human formyl peptide receptor 3

G-protein coupled receptors (GPCRs) participate in a wide range of vital regulations of our physiological actions. They are also of pharmaceutical importance and have become many therapeutic targets for a number of disorders and diseases. Purified GPCR-based approaches including structural study and novel biophysical and biochemical function analyses are increasingly being used in GPCR-directed drug discovery. Before these approaches become routine, however, several hurdles need to be overcome; they include overexpression, solubilization, and purification of large quantities of functional and stable receptors on a regular basis. Here we report milligram production of a human formyl peptide receptor 3 (FPR3). FPR3 comprises a functionally distinct GPCR subfamily that is involved in leukocyte chemotaxis and activation. The bioengineered FPR3 was overexpressed in stable tetracycline-inducible mammalian cell lines (HEK293S). After a systematic detergent screening, fos-choline-14 (FC-14) was selected for subsequent solubilization and purification processes. A two-step purification method, immunoaffinity using anti-rho-tag monoclonal antibody 1D4 and gel filtration, was used to purify the receptors to near homogeneity. Immunofluorescence analysis showed that expressed FPR3 was predominantly displayed on cellular membrane. Secondary structural analysis using circular dichroism showed that the purified FPR3 receptor was correctly folded with >50% α-helix, which is similar to other known GPCR secondary structures. Our method can readily produce milligram quantities of human FPR3, which would facilitate in developing human FPR as therapeutic drug targets.

Transcriptional variations mediated by an alternative promoter of the FPR3 gene

Formyl peptide receptor 3 (FPR3) is a potential player in innate immunity and appears with FPR2 as a FPR cluster during primate evolution. Comparative genome analyses indicate that a segmental duplication (SD) event upstream of the FPR3 gene after the divergence of New and Old World monkeys led to the emergence of an alternative promoter. In this study we combined computational and experimental approaches to identify a FPR3 gene that is controlled by an alternative promoter derived during a SD event. Its transcriptional activity was detected by quantitative reverse transcription polymerase chain reaction. Human alternative transcripts (FPR3-1 and FPR3-2) showed tissue-specific patterns with strong expressions in lung or uterus, while the FPR3-1 transcript of rhesus macaque is broadly expressed in various tissues. Overall, transcriptional variations of FPR3 occur by an alternative promoter during primate evolution.

Processing of HEBP1 by cathepsin D gives rise to F2L, the agonist of formyl peptide receptor 3

The peptide F2L was previously characterized as a high-affinity natural agonist for the human formyl peptide receptor (FPR) 3. F2L is an acetylated 21-aa peptide corresponding with the N terminus of the intracellular heme-binding protein 1 (HEBP1). In the current work, we have investigated which proteases were able to generate the F2L peptide from its precursor HEBP1. Structure-function analysis of F2L identified three amino acids, G(3), N(7), and S(8), as the most important for interaction of the peptide with FPR3. We expressed a C-terminally His-tagged form of human HEBP1 in yeast and purified it to homogeneity. The purified protein was used as substrate to identify proteases generating bioactive peptides for FPR3-expressing cells. A conditioned medium from human monocyte-derived macrophages was able to generate bioactivity from HEBP1, and this activity was inhibited by pepstatin A. Cathepsin D was characterized as the protease responsible for HEBP1 processing, and the bioactive product was identified as F2L. We have therefore determined how F2L, the specific agonist of FPR3, is generated from the intracellular protein HEBP1, although it is unknown in which compartment the processing by cathepsin D occurs in vivo.

Peptide surfactants for cell-free production of functional G protein-coupled receptors

Two major bottlenecks in elucidating the structure and function of membrane proteins are the difficulty of producing large quantities of functional receptors, and stabilizing them for a sufficient period of time. Selecting the right surfactant is thus crucial. Here we report using peptide surfactants in commercial Escherichia coli cell-free systems to rapidly produce milligram quantities of soluble G protein-coupled receptors (GPCRs). These include the human formyl peptide receptor, human trace amine-associated receptor, and two olfactory receptors. The GPCRs expressed in the presence of the peptide surfactants were soluble and had α-helical secondary structures, suggesting that they were properly folded. Microscale thermophoresis measurements showed that one olfactory receptor expressed using peptide surfactants bound its known ligand heptanal (molecular weight 114.18). These short and simple peptide surfactants may be able to facilitate the rapid production of GPCRs, or even other membrane proteins, for structure and function studies.

Novel anti-inflammatory--pro-resolving mediators and their receptors

Resolution of inflammation, an actively coordinated program, is essential to maintain host health. It involves effective removal of inflammatory stimuli and the spatio-temporal control of leukocyte trafficking as well as chemical mediator generation. During the active resolution process, new classes of small, local acting endogenous autacoids, namely the lipoxins, D and E series resolvins, (neuro)protectins, and maresins have been identified. These specialized pro-resolving lipid mediators (SPM) prevent excessive inflammation and promote removal of microbes and apoptotic cells, thereby expediting resolution and return to tissue homeostasis. As part of their molecular mechanism, SPM exert their potent actions via activating specific pro-resolving G-protein coupled receptors. Together these SPM and their receptors provide new concepts and opportunities for therapeutics, namely promoting active resolution as opposed to the conventionally used enzyme inhibitors and receptor antagonists. This approach may offer new targets suitable for drug design for treating inflammation related diseases, for the new terrain of resolution pharmacology.

Expression and signaling of formyl-peptide receptors in the brain

The human formyl-peptide receptor (FPR) and its variants FPRL1 and FPRL2 belong to the G-protein coupled seven transmembrane receptor (GPCR) family sensitive to pertussis toxin. FPR and FPRL1 were first detected in phagocytic leukocytes, and FPRL2 was found in monocytes and in dendritic cells. The three receptors were subsequently identified in other cell types or tissues, including neuronal cells and brain, where FPR and FPRL1 play a key role in angiogenesis, cell proliferation, protection against and cell death, as well as in neuroendocrine functions. Binding of different agonists to FPRs triggers several signaling pathways, activates NFkB and STAT3 transcriptional factors and induces the accumulation of the CDK inhibitors p21(waf1/cip1), p16(INK4) and p27(kip1). Signaling molecules, such as ERKs, JNK, PKC, p38MAPK, PLC and PLD are involved in these intracellular cascades. In this article we briefly review FPRs expression and signaling in neuronal cells.

Computational structure-activity relationship analysis of small-molecule agonists for human formyl peptide receptors

N-formyl peptide receptors (FPRs) are important in host defense. Because of the potential for FPRs as therapeutic targets, recent efforts have focused on identification of non-peptide agonists for two FPR subtypes, FPR1 and FPR2. Given that a number of specific small-molecule agonists have recently been identified, we hypothesized that computational structure-activity relationship (SAR) analysis of these molecules could provide new information regarding molecular features required for activity. We used a training set of 71 compounds, including 10 FPR1-specific agonists, 36 FPR2-specific agonists, and 25 non-active analogs. A sequence of (1) one-way analysis of variance selection, (2) cluster analysis, (3) linear discriminant analysis, and (4) classification tree analysis led to the derivation of SAR rules with high (95.8%) accuracy for correct classification of compounds. These SAR rules revealed key features distinguishing FPR1 versus FPR2 agonists. To verify predictive ability, we evaluated a test set of 17 additional FPR agonists, and found that the majority of these agonists (>94%) were classified correctly as agonists. This study represents the first successful application of classification tree methodology based on atom pairs to SAR analysis of FPR agonists. Importantly, these SAR rules represent a relatively simple classification approach for virtual screening of FPR1/FPR2 agonists.

Complement and its role in innate and adaptive immune responses

The complement system plays a crucial role in the innate defense against common pathogens. Activation of complement leads to robust and efficient proteolytic cascades, which terminate in opsonization and lysis of the pathogen as well as in the generation of the classical inflammatory response through the production of potent proinflammatory molecules. More recently, however, the role of complement in the immune response has been expanded due to observations that link complement activation to adaptive immune responses. It is now appreciated that complement is a functional bridge between innate and adaptive immune responses that allows an integrated host defense to pathogenic challenges. As such, a study of its functions allows insight into the molecular underpinnings of host-pathogen interactions as well as the organization and orchestration of the host immune response. This review attempts to summarize the roles that complement plays in both innate and adaptive immune responses and the consequences of these interactions on host defense.

Identification of novel small-molecule agonists for human formyl peptide receptors and pharmacophore models of their recognition

N-formyl peptide receptor (FPR1) and N-formyl peptide receptor-like 1 (FPRL1, now known as FPR2) are G protein-coupled receptors involved in host defense and sensing cellular dysfunction. Because of the potential for FPR1/FPR2 as a therapeutic target, our recent high-throughput screening efforts have focused on the identification of unique nonpeptide agonists of FPR1/FPR2. In the present studies, we screened a chemolibrary of drug-like molecules for their ability to induce intracellular calcium mobilization in RBL-2H3 cells transfected with human FPR1 or FPR2. Screening of these compounds resulted in the identification of novel and potent agonists that activated both FPR1 and FPR2, as well as compounds that were specific for either FPR1 or FPR2 with EC(50) values in the low micromolar range. Specificity of the compounds was supported by analysis of calcium mobilization in HL-60 cells transfected with human FPR1 and FPR2. In addition, all but one agonist activated intracellular calcium flux and chemotaxis in human neutrophils, irrespective of agonist specificity for FPR1 or FPR2. Molecular modeling of the group of FPR1 and FPR2 agonists using field point methodology allowed us to create pharmacophore models for ligand binding sites and formulate requirements for these specific N-formyl peptide receptor agonists. These studies further demonstrate that agonists of FPR1/FPR2 include compounds with wide chemical diversity and that analysis of such compounds can enhance our understanding of their ligand/receptor interaction.

A novel fluorescent cross-reactive formylpeptide receptor/formylpeptide receptor-like 1 hexapeptide ligand

Formylpeptide receptors (FPRs) are implicated in a variety of immunological and inflammatory response cascades. Further understanding of FPR-family ligand interactions could play an integral role in biological and therapeutic discovery. Fluorescent reporter ligands for the family are desirable experimental tools for increased understanding of ligand/receptor interactions. The ligand binding affinity and fluorescent reporting activity of the peptide WK(FL)YMVm was explored though use of the high throughput HyperCyt flow cytometric platform. Relative binding affinities of several known FPR and FPRL1 peptide ligands were compared in a duplex assay format. The fluorescent W-peptide ligand, WK(FL)YMVm, proved to be a high-affinity, cross-reactive reporter ligand for the FPR/FPRL1 duplex assay. Ligand specificity was demonstrated for each receptor, with known, selective peptide ligands. The binding site specificity of the reporter ligand was further verified by a fluorescent confocal microscopy internalization experiment. The fluorescent peptide ligand WK(FL)YMVm binds with high affinity to both FPR and FPRL1. The differential affinities of known peptide ligands were observed with the use of this fluorescent probe in high throughput screening flow cytometry.

Duplex high-throughput flow cytometry screen identifies two novel formylpeptide receptor family probes

Of recent, clinical interest have been two related human G-protein coupled receptors: formylpeptide receptor (FPR), linked to antibacterial inflammation and malignant glioma cell metastasis; and FPR like-1 (FPRL1), linked to chronic inflammation in systemic amyloidosis, Alzheimer's disease, and prion diseases. In association with the National Institutes of Health (NIH) Molecular Library Screening Network, we implemented a flow-cytometry-based high-throughput screening (HTS) approach for identifying selective small molecule FPR and FPRL1 ligands. The screening assay measured the ability of test compounds to competitively displace a high-affinity, fluorescein- labeled peptide ligand from FPR, FPRL1, or both. U937 cells expressing FPR and rat basophil leukemia (RBL) cells expressing FPRL1 were tested together in a "duplex" format. The U937 cells were color coded with red-fluorescent dye allowing their distinction during analysis. Compounds, cells, and fluorescent ligand were sequentially combined (no wash) in 15 microl assay volumes in 384-well plates. Throughput averaged approximately 11 min per plate to analyze approximately 4,000 cells ( approximately 2,000/receptor) in a 2 microl aspirate from each well. In primary single concentration HTS of 24,304 NIH Small Molecule Repository compounds, 253 resulted in inhibition >30% (181 for FPR, 72 for FPRL1) of which 40 had selective binding inhibition constants (K(i)) < or = 4 microM (34 for FPR and 6 for FPRL1). An additional 1,446 candidate compounds were selected by structure-activity-relationship analysis of the hits and screened to identify novel ligands for FPR (3570-0208, K(i) = 95 +/- 10 nM) and FPRL1 (BB-V-115, K(i) = 270 +/- 51 nM). Each was a selective antagonist in calcium response assays and the most potent small molecule antagonist reported for its respective receptor to date. The duplex assay format reduced assay time, minimized reagent requirements, and provided selectivity information at every screening stage, thus proving to be an efficient means to screen for selective receptor ligand probes.

International Union of Basic and Clinical Pharmacology. LXXIII. Nomenclature for the formyl peptide receptor (FPR) family

Formyl peptide receptors (FPRs) are a small group of seven-transmembrane domain, G protein-coupled receptors that are expressed mainly by mammalian phagocytic leukocytes and are known to be important in host defense and inflammation. The three human FPRs (FPR1, FPR2/ALX, and FPR3) share significant sequence homology and are encoded by clustered genes. Collectively, these receptors bind an extraordinarily numerous and structurally diverse group of agonistic ligands, including N-formyl and nonformyl peptides of different composition, that chemoattract and activate phagocytes. N-formyl peptides, which are encoded in nature only by bacterial and mitochondrial genes and result from obligatory initiation of bacterial and mitochondrial protein synthesis with N-formylmethionine, is the only ligand class common to all three human receptors. Surprisingly, the endogenous anti-inflammatory peptide annexin 1 and its N-terminal fragments also bind human FPR1 and FPR2/ALX, and the anti-inflammatory eicosanoid lipoxin A4 is an agonist at FPR2/ALX. In comparison, fewer agonists have been identified for FPR3, the third member in this receptor family. Structural and functional studies of the FPRs have produced important information for understanding the general pharmacological principles governing all leukocyte chemoattractant receptors. This article aims to provide an overview of the discovery and pharmacological characterization of FPRs, to introduce an International Union of Basic and Clinical Pharmacology (IUPHAR)-recommended nomenclature, and to discuss unmet challenges, including the mechanisms used by these receptors to bind diverse ligands and mediate different biological functions.

Human formyl peptide receptor 1 (FPR1) c.32C>T SNP is associated with decreased soluble E-selectin levels

Aims: The human formyl peptide receptor (FPR) is a G protein-coupled chemoattractant receptor that is thought to mediate inflammatory responses. The FPR1 gene is highly polymorphic. In a recent study, the FPR1 c.32C>T SNP, resulting in the amino-acid substitution I11T, was reported to be significantly associated with C-reactive protein levels. Therefore, this study sought to determine if the impact of such a genetic variation extends to other clinical parameters associated with inflammation, including cytokines, adhesion molecules and inflammatory markers. Materials & methods: This study was carried out on a subsample of 325 adults selected from the STANISLAS cohort study. The FPR1 c.32C>T SNP was genotyped using PCR amplification followed by restriction enzyme digestion. Anthropometric measurements and biochemical profiles were assessed for each individual. Results: The allele frequencies of FPR1 c.32C>T were 0.74 for the 32C allele and 0.26 for the 32T allele. Genotype frequencies were 0.55 for C/C, 0.38 for C/T and 0.07 for T/T. After adjusting for age, sex, BMI, alcohol and cigarette consumption, oral contraceptive, antibiotics and anti-inflammatory drug use, statistical analysis (under a recessive model of inheritance) demonstrated that serum E-selectin levels were 68% lower in individuals homozygous for T/T than in those with C/T or C/C genotypes (p = 0.001). However, no significant correlations were found for C-reactive protein or the other 18 tested clinical parameters that were analyzed in this study. Conclusion: The FPR1 c.32C>T SNP may be associated with E-selectin levels in the French population. Although of importance, these findings need confirmation in larger studies.

Formyl peptide receptor-like 2 is expressed and functional in plasmacytoid dendritic cells, tissue-specific macrophage subpopulations, and eosinophils

The formyl peptide receptor (FPR) is a key player in innate immunity and host defense mechanisms. In humans and other primates, a cluster of genes encodes two related receptors, FPR-like 1 and FPR-like 2 (FPRL1 and FPRL2). Despite their high sequence similarity, the three receptors respond to different sets of ligands and display a different expression pattern in leukocyte populations. Unlike FPR and FPRL1, FPRL2 is absent from neutrophils, and two endogenous peptide agonists, F2L and humanin, were recently described. In the present work, we investigated the detailed functional distribution of FPRL2 in leukocytes by quantitative PCR, flow cytometry, immunohistochemistry, and chemotaxis assays, with the aim of raising hypotheses regarding its potential functions in the human body. We describe that FPRL2 is highly expressed and functional in plasmacytoid dendritic cells and up-regulated upon their maturation. FPRL2 is also expressed in eosinophils, which are recruited but do not degranulate in response to F2L. FPRL2 is expressed and functional in macrophages differentiated from monocytes in vitro in different conditions. However, in vivo, only specific subsets of macrophages express the receptor, particularly in the lung, colon, and skin, three organs chronically exposed to pathogens and exogenous aggressions. This distribution and the demonstration of the production of the F2L peptide in mice underline the potential role of FPRL2 in innate immunity and possibly in immune regulation and allergic diseases.

Identification of formyl peptides from Listeria monocytogenes and Staphylococcus aureus as potent chemoattractants for mouse neutrophils

The prototypic formyl peptide N-formyl-Met-Leu-Phe (fMLF) is a major chemoattractant found in Escherichia coli culture supernatants and a potent agonist at human formyl peptide receptor (FPR) 1. Consistent with this, fMLF induces bactericidal functions in human neutrophils at nanomolar concentrations. However, it is a much less potent agonist for mouse FPR (mFPR) 1 and mouse neutrophils, requiring micromolar concentrations for cell activation. To determine whether other bacteria produce more potent agonists for mFPR1, we examined formyl peptides from Listeria monocytogenes and Staphylococcus aureus for their abilities to activate mouse neutrophils. A pentapeptide (N-formyl-Met-Ile-Val-Ile-Leu (fMIVIL)) from L. monocytogenes and a tetrapeptide (N-formyl-Met-Ile-Phe-Leu (fMIFL)) from S. aureus were found to induce mouse neutrophil chemotaxis at 1-10 nM and superoxide production at 10-100 nM, similar to the potency of fMLF on human neutrophils. Using transfected cell lines expressing mFPR1 and mFPR2, which are major forms of FPRs in mouse neutrophils, we found that mFPR1 is responsible for the high potency of fMIVIL and fMIFL. In comparison, activation of mFPR2 requires micromolar concentrations of the two peptides. Genetic deletion of mfpr1 resulted in abrogation of neutrophil superoxide production and degranulation in response to fMIVIL and fMIFL, further demonstrating that mFPR1 is the primary receptor for detection of these formyl peptides. In conclusion, the formyl peptides from L. monocytogenes and S. aureus are approximately 100-fold more potent than fMLF in activating mouse neutrophils. The ability of mFPR1 to detect bacterially derived formyl peptides indicates that this important host defense mechanism is conserved in mice.

Receptor "hijacking" by malignant glioma cells: a tactic for tumor progression

Gliomas are the most common and deadly tumors in the central nervous system (CNS). In the course of studying the role of chemoattractant receptors in tumor growth and metastasis, we discovered that highly malignant human glioblastoma and anaplastic astrocytoma specimens were stained positively for the formylpeptide receptor (FPR), which is normally expressed in myeloid cells and accounts for their chemotaxis and activation induced by bacterial peptides. Screening of human glioma cell lines revealed that FPR was expressed selectively in glioma cell lines with a more highly malignant phenotype. FPR expressed in glioblastoma cell lines mediates cell chemotaxis, proliferation and production of an angiogenic factor, vascular endothelial growth factor (VEGF), in response to agonists released by necrotic tumor cells. Furthermore, FPR in glioblastoma cells activates the receptor for epidermal growth factor (EGFR) by increasing the phosphorylation of a selected tyrosine residue in the intracellular tail of EGFR. Thus, FPR hijacked by human glioblastoma cells exploits the function of EGFR to promote rapid tumor progression.

Receptors for complement C5a. The importance of C5aR and the enigmatic role of C5L2

Complement component C5a is one of the most potent inflammatory chemoattractants and has been implicated in the pathogenesis of numerous inflammatory diseases. C5a binds two receptors, C5aR and C5L2. Most of the C5a functional effects occur through C5aR, and the pharmaceutical industry has focused on this receptor for the development of new anti-inflammatory therapies. We used a novel approach to generate and test therapeutics that target C5aR. We created human C5aR knock-in mice, and used neutrophils from these to immunize wild-type mice. This yielded high-affinity blocking mAbs to human C5aR. We tested these anti-human C5aR mAbs in mouse models of inflammation, using the human C5aR knock-in mice. These antibodies completely prevented disease onset and were also able to reverse established disease in the K/B x N arthritis model. The physiological role of the other C5a receptor, C5L2 is still unclear, and our studies with blocking mAbs to human C5L2 have failed to demonstrate a clear functional role in signaling to C5a. The development of effective mAbs to human C5aR is an alternative approach to drug development, for this highly attractive target.

Study of synthetic peptides derived from the PKI55 protein, a protein kinase C modulator, in human neutrophils stimulated by the methyl ester derivative of the hydrophobic N-formyl tripeptide for-Met-Leu-Phe-OH

Elucidation of the involvement of protein kinase C subtypes in several diseases is an important challenge for the future development of new drug targets. We previously identified the PKI55 protein, which acts as a protein kinase C modulator, establishing a feedback loop of inhibition. The PKI55 protein is able to penetrate the cell membrane of activated human T-lymphocytes and to inhibit the activity of alpha, beta(1) and beta(2) protein kinase C isoforms. The present study aimed to identify the minimal amino acid sequence of PKI55 that is able to inhibit the enzyme activity of protein kinase C. Peptides derived from both C- and N-terminal sequences were synthesized and initially assayed in rat brain protein kinase C to identify which part of the entire protein maintained the in vitro effects described for PKI55, and then the active peptides were tested on the isoforms alpha, beta(1), beta(2), gamma, delta, epsilon and zeta to identify their specific inhibition properties. Specific protein kinase C isoforms have been associated with the activation of specific signal transduction pathways involved in inflammatory responses. Thus, the potential therapeutic role of the selected peptides has been studied in polymorphonuclear leukocytes activated by the methyl ester derivative of the hydrophobic N-formyl tripeptide for-Met-Leu-Phe-OH to evaluate their ability to modulate chemotaxis, superoxide anion production and lysozyme release. These studies have shown that only chemotactic function is significantly inhibited by these peptides, whereas superoxide anion production and lysozyme release remain unaffected. Western blotting experiments also demonstrated a selective reduction in the levels of the protein kinase C beta(1) isoform, which was previously demonstrated to be associated with the polymorphonuclear leukocyte chemotactic response.

Disruption of the C5a receptor gene increases resistance to acute Gram-negative bacteremia and endotoxic shock: opposing roles of C3a and C5a

The host response to intravascular, Gram-negative bacteria includes profound immunologic, hematologic and physiologic changes. Numerous host defense mechanisms are activated by Gram-negative bacteria, including the complement system. Activation of the complement system leads to cleavage of C5 with subsequent generation of the C5a anaphylatoxin peptide. C5a mediates potent, proinflammatory activities by binding to the C5a receptor (C5aR, CD88). In this study, we report the targeted disruption of the murine C5aR gene (C5aR-/- mice) and define the role of the C5aR in a model of Gram-negative bacteremia. Following an intravenous infusion of heat-killed Escherichia coli, the C5aR-/- mice were completely protected from the mortality suffered by their wild-type littermates (P<0.001). The C5aR-/- mice were also significantly (P=0.008) more resistant to mortality following an intravenous infusion of purified E. coli endotoxin compared to the wild-type littermates. In addition, the C5aR-/- mice were resistant to the thrombocytopenia and hemoconcentration observed in wild-type animals. Lethality in the wild-type mice was reversed by pre-treatment with either the histamine antagonist diphenhydramine or triprolidine. The wild-type littermates were also rescued following pre-treatment with the basophil and mast cell-stabilizing agent - cromolyn sodium. Collectively, these data demonstrate that not only is the absence of the C5aR protective in E. coli bacteremia, but that C5aR-dependent histamine release plays a major role in shock induced by Gram-negative septicemia. Moreover, they provide additional in vivo evidence that C3a and C5a have divergent biological functions in Gram-negative bacteremia and shock.

Serum amyloid A mediates human neutrophil production of reactive oxygen species through a receptor independent of formyl peptide receptor like-1

Serum amyloid A (SAA) is one of the acute-phase reactants, a group of plasma proteins that increases immensely in concentration during microbial infections and inflammatory conditions, and a close relationship between SAA levels and disease activity in rheumatoid arthritis (RA) has been observed. RA is an inflammatory disease, where neutrophils play important roles, and SAA is thought to participate in the inflammatory reaction by being a neutrophil chemoattractant and inducer of proinflammatory cytokines. The biological effects of SAA are reportedly mediated mainly through formyl peptide receptor like-1 (FPRL1), a G protein-coupled receptor (GPCR) belonging to the formyl peptide receptor family. Here, we confirmed the affinity of SAA for FPRL1 by showing that stably transfected HL-60 cells expressing FPRL1 were activated by SAA and that the response was inhibited by the use of the FPRL1-specific antagonist WRWWWW (WRW4). We also show that SAA activates the neutrophil NADPH-oxidase and that a reserve pool of receptors is present in storage organelles mobilized by priming agents such as TNF-alpha and LPS from Gram-negative bacteria. The induced activity was inhibited by pertussis toxin, indicating the involvement of a GPCR. However, based on FPRL1-specific desensitization and use of FPRL1 antagonist WRW4, we found the SAA-mediated effects in neutrophils to be independent of FPRL1. Based on these findings, we conclude that SAA signaling in neutrophils is mediated through a GPCR, distinct from FPRL1. Future identification and characterization of the SAA receptor could lead to development of novel, therapeutic targets for treatment of RA.

Pharmacological Characterization of a Novel Nonpeptide Antagonist for Formyl Peptide Receptor-Like 1

A series of quinazolinone derivatives were synthesized based on a hit compound identified from a high-throughput screening campaign targeting the human formyl peptide receptor-like 1 (FPRL1). Based on structure-activity relationship analysis, we found that substitution on the para position of the 2-phenyl group of the quinazolinone backbone could alter the pharmacological properties of the compound. The methoxyl substitution produced an agonist 4-butoxy-N-[2-(4-methoxy-phenyl)-4-oxo-1,4-dihydro-2H-quinazolin-3-yl]-benzamide (Quin-C1; C1), whereas a hydroxyl substitution resulted in a pure antagonist, Quin-C7 (C7). Several partial agonists were derived from other substitutions on the para position. C7 partially displaced [(125)I]Trp-Lys-Tyr-Met-Val-d-Met-NH(2) (WKYMVm) binding to FPRL1 but not [(3)H]N-formyl-Met-Leu-Phe to formyl peptide receptor. In functional assays using FPRL1-expressing RBL-2H3 cells, C7 inhibited calcium mobilization and chemotaxis induced by WKYMVm and C1 and degranulation elicited by C1. C7 also suppressed C1-induced extracellular signal-regulated kinase phosphorylation and reduced arachidonic acid-induced ear edema in mice. This study represents the first characterization of a nonpeptidic antagonist for FPRL1 and suggests the prospect of using low molecular weight compounds as modulators of chemoattractant receptors in vitro and in vivo.