Purification and identification of formyl-methionyl-leucyl-phenylalanine as the major peptide neutrophil chemotactic factor produced by Escherichia coli

Influences of ozone exposure upon macrophage responsivity to N-formyl-methionyl-leucyl-phenylalanine: mobility and metabolic changes

Alveolar macrophages represent one of the first lines of cell defence in the lungs. They employ several mechanisms, including phagocytosis and secretion of reactive oxygen and nitrogen species. fMLP, a formylated peptide of bacterial origin, is a potent inducer of phagocyte chemotaxis and is also involved in generating antimicrobial agents such as nitric oxide (NO) and hydrogen peroxide (H2O2). In this study we analysed the in vitro effects of fMLP on the mobility of the THP-1 cell line, which served as a model for alveolar macrophages. Cell mobility and cytotoxicity were also analysed after pre-exposures to an atmosphere polluted with ozone (0.03-0.5 ppm) followed by a fMLP treatment. Finally, the secreted molecules (H2O2 and NO) were measured after ozone exposures ranging from 5 to 30 min and fMLP action. Activation by fMLP alone induced cell movement, whereas pre-exposure to the ozone concentrations decreased it. Addition of fMLP had different effects on cytotoxicity, mobility and metabolite secretion by the cells: (1) cytotoxicity increased depending on ozone concentrations and exposure times; (2) during the first 5 min and for all ozone concentrations, an average decrease of 50% of activated cell mobility was observed; (3) H2O2 was increased, even in combination with ozone; (4) NO was detected at 731 nM, a result that was not affected by ozone pre-exposure.

Peptide deformylase: a target for novel antibiotics?

Peptide deformylase (PDF) catalyses the hydrolytic removal of the N-terminal formyl group from nascent ribosome-synthesised polypeptides. Its activity is essential and it is present in all eubacteria. It is also present in the organelles of some eukaryotes. PDF represents a novel class of mononuclear iron protein, utilising an Fe(2+) ion to catalyse the hydrolysis of an amide bond. Due to its extreme lability, isolation and characterisation of PDF was not possible until very recently. This review will discuss the recent progress in the elucidation of the the structure and function of PDF, evaluating its suitability as a target for antibiotic design and summarising the current approaches to designing drugs that target PDF.

N-terminal residues of the chemotaxis inhibitory protein of Staphylococcus aureus are essential for blocking formylated peptide receptor but not C5a receptor

Staphylococcus aureus excretes a factor that specifically and simultaneously acts on the C5aR and the formylated peptide receptor (FPR). This chemotaxis inhibitory protein of S. aureus (CHIPS) blocks C5a- and fMLP-induced phagocyte activation and chemotaxis. Monoclonal anti-CHIPS Abs inhibit CHIPS activity against one receptor completely without affecting the other receptor, indicating that two distinct sites are responsible for both actions. A CHIPS-derived N-terminal 6 aa peptide is capable of mimicking the anti-FPR properties of CHIPS but has no effect on the C5aR. Synthetic peptides in which the first 6 aa are substituted individually for all other naturally occurring amino acids show that the first and third residue play an important role in blocking the FPR. Using an Escherichia coli expression system, we created mutant CHIPS proteins in which these amino acids are substituted. These mutant proteins have impaired or absent FPR- but still an intact C5aR-blocking activity, indicating that the loss of the FPR-blocking activity is not caused by any structural impairment. This identifies the first and third amino acid, both a phenylalanine, to be essential for CHIPS blocking the fMLP-induced activation of phagocytes. The unique properties of CHIPS to specifically inhibit the FPR with high affinity (kd=35.4 +/- 7.7 nM) could be an important new tool to further stimulate the fundamental research on the mechanisms underlying the FPR and its role in disease processes.

Retinol binding protein isolated from acute renal failure patients inhibits polymorphonuclear leucocyte functions

BACKGROUND

Protein factors accumulating in sera of patients with end-stage renal disease (ESRD) that interfere with the nonspecific immune response by inhibiting essential functions of polymorphonuclear leucocytes (PMNLs) have previously been described. No such factor has been isolated from acute renal failure (ARF) patients to date.

MATERIALS AND METHODS

Using a three-step chromatographic procedure involving ion exchange, size exclusion and hydrophobic interaction chromatography we purified the apo- and holo-form of retinol binding protein (RBP) from high-flux dialyser (polyacrylonitrile; AN69) ultrafiltrates of patients with ARF. Their effect on the chemotaxis of PMNLs isolated from healthy donors was determined by the under-agarose method. Whole-blood assays applying flow cytometry were used to assess phagocytosis and the oxidative metabolism of PMNLs. Apoptosis was assessed by determining the DNA content using propidium iodide.

RESULTS

Isolated apo- and holo-forms of RBP were truncated on their C-terminus as determined by mass spectrometry. All isolates significantly inhibited the chemotactic movement of PMNLs obtained from healthy donors and the PMNL oxidative metabolism stimulated by E. coli. These effects were concentration dependent. Retinol binding protein had no influence on the PMNL oxidative metabolism stimulated by PMA and on PMNL phagocytosis. Commercially available RBP isolated from urine influenced PMNL functions in the same way. Inhibition of p38 mitogen-activated protein kinase (MAPK) by SB203580 significantly attenuated the phagocytosis-induced respiratory burst and RBP did not lead to a further decrease. Polymorphonuclear leucocyte apoptosis was significantly inhibited by RBP.

CONCLUSIONS

The apo- and holo-forms of RBP isolated from the ultrafiltrate of ARF patients inhibit PMNL chemotaxis, oxidative metabolism and apoptosis. Therefore, RBP may be considered a uraemic toxin contributing to a disturbed immune defence.

Mild hyperthermia down-regulates receptor-dependent neutrophil function

Mild hypothermia impairs resistance to infection and, reportedly, impairs phagocytosis and oxidative killing of unopsonized bacteria. We evaluated various functions at 33 degrees-41 degrees C in neutrophils taken from volunteers. Adhesion on endothelial cells was determined using light microscopy. Adhesion molecule expression and receptors, phagocytosis, and release of reactive oxidants were assessed using flow cytometric assays. Adhesion protein CD11b expression on resting neutrophils was temperature-independent. However, up-regulation of CD11b with tumor necrosis factor (TNF)-alpha was increased by hypothermia and decreased with hyperthermia. Neutrophil adhesion to either resting or activated endothelial cells was not temperature-dependent. Bacterial uptake was inversely related to temperature, more so with Escherichia coli than Staphylococcus aureus. Temperature dependence of phagocytosis occurred only wi thopsonized bacteria. Hypothermia slightly increased N-formyl-L-methionyl-L-leucyl-phenylalanine receptors on neutrophils: hyperthermia decreased expression, especially with TNF-alpha. N-formyl-L-methionyl-L-leucyl-phenylalanine-induced H2O2 production was inversely related to temperature, especially in the presence of TNF-alpha. Conversely, phorbol-13-myristate-12-acetate, an activator of protein kinase C, induced an extreme and homogenous release of reactive oxidants that increased with temperature. In contrast to nonreceptor-dependent phagocytosis and oxidative killing, several crucial receptor-dependent neutrophil activities show temperature-dependent regulation, with hypothermia increasing function. The temperature dependence of neutrophil function is thus more complicated than previously appreciated.

Silencing the formylpeptide receptor FPR by short-interfering RNA

A double-stranded short-interfering RNA (siRNA) was designed to attenuate the expression and function of the formylpeptide receptor FPR, a G protein-coupled receptor mediating migration and activation of phagocytic leukocytes in response to bacterial chemotactic formylpeptides. Retrovirus-based constructs were generated to introduce FPR-siRNA into a rat leukemia cell line transfected to overexpress FPR. Cells infected with FPR-siRNAT28, which targets the nucleotides 926 to 944 of FPR mRNA corresponding to the third extracellular loop of the putative receptor protein, showed significantly reduced expression of FPR mRNA and protein, in association with impaired calcium mobilization and chemotactic responses to peptide agonists. Direct transduction of synthetic FPR-siRNAT28 into human macrophages also inhibited the expression of FPR and abrogated cell chemotaxis and the release of superoxide anions induced by the bacterial formylpeptide. FPR-siRNA additionally abrogated the expression and function of FPR in a human malignant glioma cell line. Our study demonstrates successful application of siRNA to silence a G protein-coupled chemoattractant receptor involved in inflammation and suggests the potential to use this approach in studies of receptor regulation and prevention of undesirable side effects associated with FPR activation.

Differential effects of clindamycin on neutrophils of healthy donors and septic patients

Antibiotics are frequently administered to ICU patients in case of bacterial infections. Little is known, however, about the interference of antibiotics with neutrophil host defence mechanisms in patients with sepsis and multiple organ dysfunction syndrome (MODS). With our study, evidence for differential clindamycin effects on neutrophils in healthy donors and septic patients without or with MODS was sought. Functional parameters (oxidative response and phagocytosis) and fMLP receptor expression were analysed. The study was approved by the local ethical board. Venous blood was drawn from healthy donors and septic patients. Neutrophils in PBS were incubated with 0, 5, 25 or 125 microg/ml clindamycin and analysed flow cytometrically. Neutrophils of patients with sepsis and MODS showed a significantly higher basal activation compared to healthy donors. Clindamycin application led to a dose-dependent significant suppression of the fMLP-induced oxidative response in patients with sepsis and MODS, but not in healthy donors or septic patients in the absence of MODS. In patients with sepsis and MODS, phagocytosis of Escherichia coli and Staphylococcus aureus was significantly suppressed by clindamycin 125 microg/ml. In both other treatment groups, clindamycin did not affect phagocytosis. fMLP receptor expression was not altered by clindamycin. High-dose clindamycin selectively suppresses functional responses of neutrophils in septic patients with MODS. Simultaneously applied drugs, such as general anaesthetics, may potentiate this modulation of antibacterial defence and inflammation.

Chemotaxis and calcium responses of phagocytes to formyl peptide receptor ligands is differentially regulated by cyclic ADP ribose

Cyclic ADP ribose (cADPR) is a calcium-mobilizing metabolite that regulates intracellular calcium release and extracellular calcium influx. Although the role of cADPR in modulating calcium mobilization has been extensively examined, its potential role in regulating immunologic responses is less well understood. We previously reported that cADPR, produced by the ADP-ribosyl cyclase, CD38, controls calcium influx and chemotaxis of murine neutrophils responding to fMLF, a peptide agonist for two chemoattractant receptor subtypes, formyl peptide receptor and formyl peptide receptor-like 1. In this study, we examine whether cADPR is required for chemotaxis of human monocytes and neutrophils to a diverse array of chemoattractants. We found that a cADPR antagonist and a CD38 substrate analogue inhibited the chemotaxis of human phagocytic cells to a number of formyl peptide receptor-like 1-specific ligands but had no effect on the chemotactic response of these cells to ligands selective for formyl peptide receptor. In addition, we show that the cADPR antagonist blocks the chemotaxis of human monocytes to CXCR4, CCR1, and CCR5 ligands. In all cases, we found that cADPR modulates intracellular free calcium levels in cells activated by chemokines that induce extracellular calcium influx in the apparent absence of significant intracellular calcium release. Thus, cADPR regulates calcium signaling of a discrete subset of chemoattractant receptors expressed by human leukocytes. Since many of the chemoattractant receptors regulated by cADPR bind to ligands that are associated with clinical pathology, cADPR and CD38 represent novel drug targets with potential application in chronic inflammatory and neurodegenerative disease.

Bacterial formyl peptides affect the innate cellular antimicrobial responses of larvalGalleria mellonella(Insecta: Lepidoptera)

The non-self cellular (hemocytic) responses of Galleria mellonella larvae, including the attachment to slides and the removal of the bacteria Xenorhabdus nematophila and Bacillus subtilis from the hemolymph, were affected by N-formyl peptides. Both N-formyl methionyl-leucyl-phenylalanine (fMLF) and the ester derivative decreased hemocyte adhesion in vitro, and both elevated hemocyte counts and suppressed the removal of both X. nematophila and B. subtilis from the hemolymph in vivo. The amide derivative and the antagonist tertiary-butoxy-carbonyl-methionyl-leucyl-phenylalanine (tBOC) increased hemocyte attachment to glass. The fMLF suppressed protein discharge from monolayers of granular cells with and without bacterial stimulation, while tBOC stimulated protein discharge. The peptide tBOC offset the effects of fMLF in vitro and in vivo. This is the first report implying the existence of formyl peptide receptors on insect hemocytes in which the compounds fMLF and tBOC inhibited and activated hemocyte activity, respectively.Key words: formyl peptides, hemocytes, Xenorhabdus, Bacillus.

Antimicrobial peptides from scorpion venom induce Ca(2+) signaling in HL-60 cells

Parabutoporin (PP) and opistoporin 1 (OP1) are amphipathic alpha-helical antimicrobial peptides that were recently isolated from scorpion venom. In assays in which single granulocyte-like HL-60 cells as well as cells in suspension were used, both peptides were able to induce a reversible Ca(2+) release from intracellular stores and to increase Ca(2+) influx. Both effects could be clearly differentiated for OP1, inducing Ca(2+) release at lower concentrations. The Ca(2+) release was pertussis toxin-sensitive indicating the involvement of G-proteins. Ca(2+) release depended on the stage of differentiation of the cells with undifferentiated cells being the most sensitive. Desensitization occurred with OP1. No cross-desensitization occurred between OP1 and the bacterial chemoattractant fMLP indicating the involvement of different types of receptors. Ca(2+) release by OP1 was found not to be mediated via interaction with the formyl peptide receptor-like 1. Although some of the results might favor a receptor-like interaction, the receptor involved could not be identified.

Chemotaxis Receptors and Signaling

Chemotaxis is an important cellular response common in biology. In many chemotaxing cells the signal that regulates movement is initiated by G protein-coupled receptors on the cell surface that bind specific chemoattractants. These receptors share important structural similarities with other G protein-coupled receptors, including rhodopsin, which currently serves as the best starting point for modeling their structures. However, the chemotaxis receptors also share a number of relatively unique structural features that are less common in other GPCRs. The chemoattractant ligands of chemotaxis receptors exhibit a broad variety of sizes and chemical properties, ranging from small molecules and peptides to protein ligands. As a result, different chemotaxis receptors have evolved specialized mechanisms for the early steps of ligand binding and receptor activation. The mechanism of transmembrane signaling is currently under intensive study and several alternate mechanisms proposing different conformational rearrangements of the transmembrane helices have been proposed. Some chemotaxis receptors are proposed to form dimers, and in certain cases dimer formation is proposed to play a role in transmembrane signaling. In principle the structural and dynamical changes that occur during transmembrane signaling could be specialized for different receptors, or could be broadly conserved. Extensive mutagenesis studies have been carried out, and have begun to identify critical residues involved in ligand binding, receptor activation, and transmembrane signaling.

Interferon-gamma increases hPepT1-mediated uptake of di-tripeptides including the bacterial tripeptide fMLP in polarized intestinal epithelia

Interferon-gamma causes a global phenotypic switch in intestinal epithelial function, in which enterocytes become immune accessory cells. The phenotypic switch is characterized by a down-regulation of membrane transporters and up-regulation of immune accessory molecules in intestinal epithelial cells. However, the effect of interferon-gamma on the intestinal epithelia di-tripeptide hPepT1 transporter has not been investigated. In this study we demonstrate that 1) interferon-gamma increases di-tripeptide uptake in dose- and time-dependent manner in model intestinal epithelia (Caco-2 BBE cell monolayers), 2) the increase in di-tripeptides induced by interferon-gamma is hPepT1 mediated, 3) interferon-gamma does not affect the hPept1 expression at the mRNA and protein levels 4) interferon-gamma increases the intracellular pH and consequently enhances the H+-electrochemical gradient across apical plasma membrane in model intestinal epithelia (Caco2-BBE monolayers). We suggest that interferon-gamma could increase the hPepT1 mediated di-tripeptides uptake in inflamed epithelial cells. Under these conditions, interferon-gamma will increase the intracellular amount of such diverse prokaryotic and eucaryotic small di-tripeptides in inflamed epithelial cells. The intracellular accumulation of such di-tripeptides may be important in enterocytes becoming immune accessory cells.

The human formyl peptide receptor as model system for constitutively active G-protein-coupled receptors

According to the two-state model of G-protein-coupled receptor (GPCR) activation, GPCRs isomerize from an inactive (R) state to an active (R*) state. In the R* state, GPCRs activate G-proteins. Agonist-independent R/R* isomerization is referred to as constitutive activity and results in an increase in basal G-protein activity, i.e. GDP/GTP exchange. Agonists stabilize the R* state and further increase, whereas inverse agonists stabilize the R state and decrease, basal G-protein activity. Constitutive activity is observed in numerous wild-type GPCRs and disease-causing GPCR mutants with increased constitutive activity. The human formyl peptide receptor (FPR) exists in several isoforms (FPR-26, FPR-98 and FPR-G6) and activates chemotaxis and cytotoxic cell functions of phagocytes through G(i)-proteins. Studies in HL-60 leukemia cell membranes demonstrated inhibitory effects of Na(+) and pertussis toxin on basal G(i)-protein activity, suggesting that the FPR is constitutively active. However, since HL-60 cells express several constitutively active chemoattractant receptors, analysis of constitutive FPR activity was difficult. Sf9 insect cells do not express chemoattractant receptors and G(i)-proteins and provide a sensitive reconstitution system for FPR/G(i)-protein coupling. Such expression studies showed that FPR-26 is much more constitutively active than FPR-98 and FPR-G6 as assessed by the relative inhibitory effects of Na(+) and of the inverse agonist cyclosporin H on basal G(i)-protein activity. Site-directed mutagenesis studies suggest that the E346A exchange in the C-terminus critically determines dimerization and constitutive activity of FPR. Moreover, N-glycosylation of the N-terminus seems to be important for constitutive FPR activity. Finally, we discuss some future directions of research.

Characterization of a human peptide deformylase: implications for antibacterial drug design

Ribosomal protein synthesis in eubacteria and eukaryotic organelles initiates with an N-formylmethionyl-tRNA(i), resulting in N-terminal formylation of all nascent polypeptides. Peptide deformylase (PDF) catalyzes the subsequent removal of the N-terminal formyl group from the majority of bacterial proteins. Deformylation was for a long time thought to be a feature unique to the prokaryotes, making PDF an attractive target for designing novel antibiotics. However, recent genomic sequencing has revealed PDF-like sequences in many eukaryotes, including man. In this work, the cDNA encoding Homo sapiens PDF (HsPDF) has been cloned and a truncated form that lacks the N-terminal 58-amino-acid targeting sequence was overexpressed in Escherichia coli. The recombinant, Co(2+)-substituted protein is catalytically active in deformylating N-formylated peptides, shares many of the properties of bacterial PDF, and is strongly inhibited by specific PDF inhibitors. Expression of HsPDF fused to the enhanced green fluorescence protein in human embryonic kidney cells revealed its location in the mitochondrion. However, HsPDF is much less active than its bacterial counterpart, providing a possible explanation for the apparent lack of deformylation in the mammalian mitochondria. The lower catalytic activity is at least partially due to mutation of a highly conserved residue (Leu-91 in E. coli PDF) in mammalian PDF. PDF inhibitors had no detectable effect on two different human cell lines. These results suggest that HsPDF is likely an evolutional remnant without any functional role in protein formylation/deformylation and validates PDF as an excellent target for antibacterial drug design.

Subinhibitory concentrations of the deformylase inhibitor actinonin increase bacterial release of neutrophil-activating peptides: a new approach to antimicrobial chemotherapy

Bacterial protein synthesis starts with a formylated methionine residue, and this residue is sequentially cleaved away by a unique peptide deformylase (PDF) and a methionine aminopeptidase to generate mature proteins. The formylation-deformylation of proteins is a unique hallmark of bacterial metabolism and has recently become an attractive target for the development of antimicrobial agents. The innate immune system uses the formylation of bacterial proteins as a target, and professional phagocytes, e.g., neutrophils, express specific receptors for bacterium-derived formylated peptides. Activation of formyl peptide receptors (FPR) mediates neutrophil migration and the release of oxygen radicals and other antimicrobial substances from these cells. We hypothesize that the use of a PDF inhibitor would increase the production of proinflammatory peptides from the bacteria and thus trigger a more pronounced innate immune response. We tested this hypothesis by exposing Escherichia coli to subinhibitory doses of the PDF inhibitor actinonin and show that actinonin indeed increases the production and secretion of neutrophil-activating peptides that activate human neutrophils through FPR. These findings could be potentially used as a new approach to antibacterial chemotherapy.

Hydrophilic residues at position 3 highlight unforeseen features of the fMLP receptor pocket

The peptides for-Met-Leu-Tyr-OMe, for-Met-Leu-Glu-OMe, for-Met-Leu-Asp-OMe and for-Met-Leu-Ser-OMe were synthesized to investigate the importance of a hydrophilic side chain of the residue at position 3 on biological activities of human neutrophils. A number of in vitro essays were carried out, including: chemotaxis, superoxide anion production, lysozyme release and receptor binding. Our results highlight that for-Met-Leu-Asp-OMe acts as a full agonist with a higher efficacy than formyl-Met-Leu-Phe-OMe, the tripeptide normally used as a model chemoattractant for the study of cell functions. The other analogs show efficacies that are in the same range or a little less than the prototype. The main point emerging from this study is that the role of Phe substitution needs to be re-hypothesised.

A novel function for chemokines: downregulation of neutrophil migration

Migration is a key function of stem cells during ontogenesis, of fibroblasts in wound healing and of immune cells in host defence. The signals that initiate migration are as important as signals that terminate migration, once the destination has been reached. We now show that formyl-methionyl-leucyl-phenylalanine (fMLP)-induced migration of neutrophils was inhibited by increasing concentrations of interleukin-8 (IL-8). IL-8 dose dependently increased the frequency and the duration of stop-periods, whereas the percentage of cells of a population that was locomotory active remained constant. The stop-signal delivered by IL-8 was intracellularly transduced by a dichotomic pathway: (i) the activation of the adenylyl cyclase leads to an increase of cytosolic cyclic adenosine monophosphate, which results in an activation of the sarcoplasmatic/endoplasmatic reticulum calcium ATPase pump and a calcium sequestration; (ii) the activation of the phospholipase Cbeta (PLCbeta) generates inositol-1,4,5-phosphate (IP3) and diacylglycerol (DAG), which results in IP3-mediated release of intracellularly stored calcium in the endoplasmatic reticulum and DAG-mediated activation of protein kinase C. Thus, we show for the first time that a chemokine, IL-8, in concert with fMLP, downregulates the neutrophil migration through the regulation of the intracellular calcium concentration via the adenylyl cyclase and the PLCbeta2.

Formylpeptides trigger selective molecular pathways that are required in the physiological functions of human neutrophils

For-Met-Delta(z)Leu-Phe-OMe ([Delta(z)Leu(2)]) is a conformationally restricted for-Met-Leu-Phe-OMe (fMLP-OMe) analogue able to discriminate between different responses of human neutrophils. In contrast, [Delta(z)Leu(2)] significantly activates the transduction pathways-involving Ca(2+), inositol phosphate, and cyclic AMP (cAMP) enhancement, as is the case with the full agonist fMLP-OMe. Here, we have studied the specific involvement of protein kinase C (PKC) isoforms and mitogen activated protein kinases (MAPKs) in the presence or absence of extracellular Ca(2+), being the cation clearly involved in the activation of neutrophils by fMLP. A strong correlation has been found between PKC isoforms, MAPKs and the selective physiological functions by [Delta(z)Leu(2)]-activated neutrophils. In a calcium-free condition, our data suggest that the failure of PKC beta1 translocation and of p38 MAPK phosphorylation by the analogue refers to its inability to induce chemotaxis, and that the failure by both fMLP-OMe and [Delta(z)Leu(2)] to evoke extracellular response kinase 1 and 2 (ERK1/2) phosphorylation would suggest a reduction in superoxide anion production.

The formyl peptide N-formyl-methionyl-leucyl-phenylalanine downregulates the expression of FcgammaRs in interferon-gamma-activated monocytes/macrophages in vitro and in vivo

N-Formyl peptides are cleavage products of bacterial and mitochondrial proteins that have pro-inflammatory activities and play an important role in antibacterial host defence. FcgammaRI is a receptor for the Fc portion of immunoglobulin G expressed in monocytes that mediates cytotoxicity and is upregulated by interferon-gamma (IFN-gamma) and interleukin-10 (IL-10). In this report, we demonstrate that N-formyl-methionyl-leucyl-phenylalanine (FMLP) downregulates the expression of FcgammaRI in IFN-gamma-treated monocytes, but not in IL-10-treated monocytes. We determine that supernatants obtained from monocytes treated with IFN-gamma and then exposed to FMLP induce the downregulation of FcgammaRI in naïve monocytes. This effect is abrogated by the protease inhibitors phenylmethylsulphonyl fluoride and phosphoramidon, which inhibit serine and metalloproteases, respectively. Supernatants from FMLP-treated neutrophils also induce the downregulation of FcgammaRI, when added to naïve monocytes. Similar observations were obtained in vivo in a mouse model of chronic inflammation. In vivo, FMLP also downregulates the expression of FcgammaRs in IFN-gamma-activated macrophages. Our results support the existence of a new mechanism through which FMLP could modulate the activity of monocytes/macrophages during bacterial infections.

Ca2+ response in neutrophils after exposure to bacterial N-formyl-methionyl-leucyl-phenylalanine: delayed response in ulcerative colitis

OBJECTIVE

In acute stages of ulcerative colitis (UC), neutrophils migrate from the circulation into inflamed colonic tissue, initiated by yet unknown stimuli. The bacterial peptide N-formyl-methionyl-leucyl-phenylalanine (FMLP) is a component of the surface membrane of colonic bacteria such as Escherichia coli and stimulates Ca2+ influx into neutrophils, reflecting the fact that ionized calcium is an important secondary messenger for several neutrophil functions, including locomotion, phagocytosis and free oxygen radical production. Recent studies have revealed that Ca2+ dependent ICAM-1/beta 2-integrin mediated neutrophil migration is impaired in UC patients. The aim of the present work was to study the influx of Ca2+ into peripheral blood neutrophils of UC patients after exposure to FMLP and after binding of either beta 2-integrins or intercellular adhesion molecule-1 (ICAM-1).

METHODS

The relative intracellular Ca2+ levels ([Ca2+]i ) were measured spectrofluorometrically in neutrophils isolated from eight UC patients and eight controls. The cells were exposed to 1 nm FMLP, 5 pm free ICAM-1, or antibodies binding ICAM-1 or the beta 2-integrins CD11a, CD11b, CD11c and CD18.

RESULTS

A pronounced increase in [Ca2+]i was observed by exposure of cells to FMLP, and neutrophils from UC patients showed a consistent and significant delayed response as compared to cells from control subjects (P < 0.01). Antibody mediated cross-linking of CD18 triggered a small but detectable increase in [Ca2+]i, which did not differ between patients and controls.

CONCLUSION

A delayed response to bacterial peptides appears to be a phenotypic trait for neutrophils of UC patients. A connection between FMLP stimulated Ca2+ influx and CD11/CD18 upregulation is discussed.

PepT1-mediated fMLP transport induces intestinal inflammation in vivo

In the present study, the effect of H(+)/peptide transporter (PepT1)-mediated N-formylmethionyl-leucyl-phenylalanine (fMLP) transport on inflammation in vivo in the rat small intestine, which expresses high PepT1 levels, and in the rat colon, which does not express PepT1, were investigated using myeloperoxidase (MPO) activity and histological analysis. We found that 10 microM fMLP perfusion in the jejunum for 4 h significantly increased MPO activity and altered the architecture of jejunal villi. In contrast, 10 microM fMLP perfusion in the colon for 4 h did not induce any inflammation. In addition, we have shown that 50 mM Gly-Gly alone did not affect basal MPO activity but completely inhibited the MPO activity induced by 10 microM fMLP in the jejunum. Together, these experiments demonstrate that 1) the differential expression of PepT1 between the small intestine and the colon plays an important role in epithelial-neutrophil interactions and 2) the inhibition of fMLP uptake by jejunal epithelial cells (expressing PepT1) reduces the neutrophil ability to move across the epithelium, in agreement with our previously published in vitro study. This report constitutes the first in vivo study showing the implication of a membrane transporter (PepT1) in intestinal inflammation.

Identification, cloning, and functional characterization of a murine lipoxin A4 receptor homologue gene

To identify additional members of the murine N-formyl-Met-Leu-Phe peptide receptor family (fMLF-R), a mouse macrophage cDNA library was screened using the open reading frame of murine N-formyl peptide receptor. Four individual hybridizing cDNA clones were maintained through tertiary screening. One cDNA clone was a truncated, polyadenylated version of the previously described murine-fMLF-R. The other three cDNA clones varied in length, but contained identical open reading frame sequences. One clone, 8C10, was selected for further study and shared 70% sequence identity with murine-fMLF-R and 89% sequence identity with murine lipoxin A4 receptor cDNA. When placed into the pcDNA-3 expression vector and cotransfected with Galpha16 cDNA into COS-1 cells, 8C10 cDNA induced the production of inositol-1,4,5-triphosphate when concentrations of 1-1600 nM lipoxin A4 (LXA4) were tested as ligands. Northern blot analysis of murine organs indicated that the 8C10 message is present in lung, spleen, and adipose tissue. Moreover, mice treated with LPS demonstrated increased expression of 8C10 message in spleen and adipose tissue, while showing a slight reduction in lung. We have also characterized the 8C10 structural gene from a 129Sv/J genomic library and have determined its size to be >6.1 kb in length and comprised of two exons separated by a 4.8-kb intron. Collectively, these data indicate that this homologue receptor is closely related to the murine LXA4 receptor and functionally responds to LXA4 as a ligand.

Identification of diacylated ureas as a novel family of fungus-specific leukocyte-activating pathogen-associated molecules

Polymorphonuclear leukocytes represent primary components of the host's innate immune defenses against fungal infection, suggesting involvement of fungal leukocyte attractants. We have found in various fungi, but not in bacteria or host cells, unstable lipid-like leukocyte chemoattractants, which also induced adherence and degranulation in human neutrophils. Purification from bakers' yeast and structural analyses by electrospray mass spectrometry, (1)H NMR spectroscopy, and chemical synthesis revealed these inflammatory mediators as diacylated ureas, a novel class of unstable lipoids. The N,N'-dipalmitoleyl urea appeared to be the most potent innate immune responses inducing compound eliciting half-maximum neutrophil chemotactic activity at 140 nm. The all-trans isomer, N,N'-dipalmitelaidyl urea, was found to be inactive with respect to stimulation of degranulation in neutrophils, which indicates a Delta(9) cis-double bond to be essential for bioactivity of these diacyl ureas. N,N'-Dipalmitoleyl urea elicited Ca(2+) mobilization in neutrophils, which was found to be pertussis toxin-sensitive and sensitive toward a carboxylmethyltransferase inhibitor, indicating that these diacyl ureas activate leukocytes via a putative Galpha(i)-protein-coupled receptor. Their isolation exclusively from fungi suggests that these lipoids are fungus-specific pathogen-associated molecules that may alert the human innate immunity system to the presence of a fungal infection.

The immunology of mucosal models of inflammation

In recent years the status of the inflammatory bowel diseases (IBDs) as canonical autoimmune diseases has risen steadily with the recognition that these diseases are, at their crux, abnormalities in mucosal responses to normally harmless antigens in the mucosal microflora and therefore responses to antigens that by their proximity and persistence are equivalent to self-antigens. This new paradigm is in no small measure traceable to the advent of multiple models of mucosal inflammation whose very existence is indicative of the fact that many types of immune imbalance can lead to loss of tolerance for mucosal antigens and thus inflammation centered in the gastrointestinal tract. We analyze the immunology of the IBDs through the lens of the murine models, first by drawing attention to their common features and then by considering individual models at a level of detail necessary to reveal their individual capacities to provide insight into IBD pathogenesis. What emerges is that murine models of mucosal inflammation have given us a road map that allows us to begin to define the immunology of the IBDs in all its complexity and to find unexpected ways to treat these diseases.

Cholesterol-modulating agents selectively inhibit calcium influx induced by chemoattractants in human neutrophils

The effects of cholesterol-perturbing agents on the mobilization of calcium induced upon the stimulation of human neutrophils by chemotactic factors were tested. Methyl-beta-cyclodextrin and filipin did not alter the initial peak of calcium mobilization but shortened the duration of the calcium spike that followed the addition of fMet-Leu-Phe. These agents also inhibited the influx of Mn(2+) induced by fMet-Leu-Phe or thapsigargin. Methyl-beta-cyclodextrin and filipin completely abrogated the mobilization of calcium induced by 10(-10) m platelet-activating factor, which at this concentration depends to a major extent on an influx of calcium as well as the influx of calcium induced by 10(-7) m platelet-activating factor. On the other hand, methyl-beta-cyclodextrin and filipin enhanced the mobilization of calcium induced by ligation of FcgammaRIIA, an agonist that did not induce a detectable influx of calcium. Finally, methyl-beta-cyclodextrin and filipin enhanced the stimulation of the profile of tyrosine phosphorylation, the activity of phospholipase D (PLD), and the production of superoxide anions induced by fMet-Leu-Phe. These results suggest that the calcium channels utilized by chemotactic factors in human neutrophils are either located in cholesterol-rich regions of the plasma membrane, or that the mechanisms that lead to their opening depend on the integrity of these microdomains.

Characterization of the human fMLP receptor in neutrophils and in Xenopus oocytes

1. N-formyl peptides (e.g. fMLP; N-formyl-L-methionyl-L-leucyl-phenylalanine) are potent mediators for inflammatory reactions. We report functional expression in Xenopus oocytes of human fMLP-R98 cDNA, without co-expression of the promiscuous G-protein subunit, Galpha-16. 2. Stimulation of voltage-clamped oocytes (-70 mV) with fMLP produced a dose-dependent biphasic inward current with fast and slow components. Analysis using GTP-gamma-S and cholera and pertussis toxins suggested these currents are mediated by an endogenous G-protein of the Gq family. 3. The fast current reversed at -25 mV and was blocked by SITS (4-acetamido-4'-isothiocyanatostilbene-2,2'-disulphonic acid), suggesting the current is carried by Cl(-). The slow current showed weak inward rectification, was Ca(2+)-dependent and blocked by Cd(2+), 4-AP (4-aminopyridine) and haloperidol, suggesting activation of a mixed population of cation channels. 4. Comparative experiments with human neutrophils using flow cytometric analysis showed that the proportion of neutrophils activated by fMLP was reduced in the presence of SITS, in the absence of external calcium and in the presence of Cd(2+), TEA (tetraethylammonium) and haloperidol but not 4-AP. In addition, the oxidative burst from activated neutrophils was reduced by SITS and by the absence of external calcium but not by Cd(2+), TEA, 4-AP or haloperidol. 5. We suggest that in human neutrophils activation by fMLP is dependent on store-operated calcium influx that appears to be regulated by Cl(-) channels and linked, in part, to non-selective cation channels.

Staphylococcal alpha-toxin provokes neutrophil-dependent cardiac dysfunction: role of ICAM-1 and cys-leukotrienes

The role of polymorphonuclear neutrophils (PMN) in septic myocardial dysfunction is presently unknown. Staphylococcus aureus infections are frequently associated with septic sequelae. Therefore, we perfused isolated rat hearts with low doses of alpha-toxin, the major staphylococcal exotoxin, followed by application of human PMN, N-formyl-methionyl-leucyl-phenylalanine, and arachidonic acid. In contrast to sham-perfused hearts (no alpha-toxin), a rise in coronary perfusion pressure (CPP) and a reduction of contractile function were noted, and cardiac expression of intercellular adhesion molecule (ICAM)-1 was detected by immunohistochemical methods and real-time PCR. Histological analysis and myeloperoxidase activity indicated cardiac PMN accumulation in alpha-toxin-challenged hearts. Major quantities of cysteinyl (cys)-leukotrienes (LT), LTB4, and 5-hydroxyeicosatetraenoic acid (5-HETE) were found in the perfusate of alpha-toxin-exposed hearts. With an anti-ICAM-1 antibody, neutrophil accumulation, leukotriene (LT) synthesis, coronary vasoconstriction, and the accompanying cardiodepression were suppressed. Similarly, the lipoxygenase inhibitor MK-886 blocked LT synthesis and maintained cardiac function. We conclude that low-dose alpha-toxin provokes coronary endothelial ICAM-1 expression and neutrophil accumulation, with subsequent synthesis of cys-LTs, LTB4, and 5-HETE under conditions of appropriate stimulation. This response is linked with coronary vasoconstriction and contractile dysfunction, with cys-LT synthesis and maldistribution of perfusion offered as likely underlying mechanisms.

C- and N-terminal residue effect on peptide derivatives' antagonism toward the formyl-peptide receptor

The biological action of several X-Phe-D-Leu-Phe-D-Leu-Z (X=3',5'-dimethylphenyl-ureido; Z=Phe, Lys, Glu, Tyr) analogues was analysed on human neutrophils to evaluate their ability to antagonize formyl-peptide receptors. X-Phe-D-Leu-Phe-D-Leu-Phe analogues obtained as C-terminal olo or amido derivatives and T-Phe-D-Leu-Phe-D-Leu-Phe analogues (T=thiazolyl-ureido) were also analysed. The activities of pentapeptide derivatives were compared with those of X-Phe-D-Leu-Phe-D-Leu-Phe chosen as reference antagonist. Our results demonstrate that X-Phe-D-Leu-Phe-D-Leu-Phe-olo, X-Phe-D-Leu-Phe-D-Leu-Glu and X-Phe-D-Leu-Phe-D-Leu-Tyr are more active antagonists than X-Phe-D-Leu-Phe-D-Leu-Phe. The presence of Lys (X-Phe-D-Leu-Phe-D-Leu-Lys) seems, instead, to inhibit the formyl-peptide receptor antagonist properties. The presence of the N-terminal thiazolyl-ureido group seems to considerably contribute to the receptor antagonist properties of T-Phe-D-Leu-Phe-D-Leu-Phe-OH. The introduction of the C-terminal methyl ester (T-Phe-D-Leu-Phe-D-Leu-Phe-OMe) or amido group (X-Phe-D-Leu-Phe-D-Leu-Phe-NH2) appears detrimental for the affinity and formyl-peptide receptor antagonist properties of the Phe-D-Leu-Phe-D-Leu-Phe derivatives. The examined peptides inhibit superoxide anion production and lysozyme release more efficaciously than neutrophil chemotaxis.

Power spectral analysis of the shape of fMLP-stimulated granulocytes. A tool for the study of cytoskeletal organization under normal and pathological conditions

fMLP (N-formyl-methionyl-leucyl-phenylalanine) is a powerful activator of granulocytes, eliciting different metabolic responses, such as generation of reactive oxygen species, production of arachidonic acid metabolites, and release of lysosomal enzymes. fMLP determines also a dramatic rearrangement of the actin cytoskeleton; under non-gradient conditions this entails characteristic alterations in cell shape (chemokinesis), while under gradient conditions it is instrumental in promoting cell migration up the gradient (chemotaxis). Here we analyze mathematically the cell contour of fMLP-stimulated human granulocytes stimulated with fMLP under non-gradient conditions, using the methods for study of stochastic series. The cell contours were drawn and divided into 200 segments of equal linear length and the angles between consecutive segments were computed. The derived series of angles were examined for autocorrelations and from the autocorrelation function the power spectrum was calculated. Our results show that the pattern of lamellipodial extensions of the cell membrane is not entirely randomly-designed, but it is partly regulated by deterministic components, as revealed by the presence of statistically significant periodicities. Soon after fMLP stimulation, the power spectrum of the cell contours exhibits a single distinct peak at frequency 0.07, indicating a prevalence of prominent lamellipodia, each one covering in the average 1/15 of the linearized cell contour. Some 30 min after fMLP stimulation the power spectrum becomes flatter (indicating a general decrement of the deterministic component), but still presents one single peak; the latter is shifted to the right (frequency 0.13), indicating the prevalence of less prominent and regular, but more numerous, protrusions, each one covering 1/20 to 1/30 of the cell contour.

Receptors for chemotactic formyl peptides as pharmacological targets

Leukocytes accumulate at sites of inflammation and immunological reaction in response to locally existing chemotactic mediators. N-formyl peptides, such as fMet-Leu-Phe (fMLF), are some of the first identified and most potent chemoattractants for phagocytic leukocytes. In addition to the bacterial peptide fMLF and the putative endogenously produced formylated peptides, a number of novel peptide agonists have recently been identified that selectively activate the high-affinity fMLF receptor FPR and/or its low-affinity variant FPRL1, both of which belong to the seven-transmembrane (STM), G protein-coupled receptor (GPCR) superfamily. These agonists include peptide domains derived from the envelope proteins of human immunodeficiency virus type 1 (HIV-1) and at least three amyloidogenic polypeptides, the human acute phase protein serum amyloid A, the 42 amino acid form of beta amyloid peptide and a 21 amino acid fragment of human prion. Furthermore, a cleavage fragment of neutrophil granule-derived bactericidal cathelicidin, LL-37, is also a chemotactic agonist for FPRL1. Activation of formyl peptide receptors results in increased cell migration, phagocytosis, release of proinflammatory mediators, and the signaling cascade culminates in heterologous desensitization of other STM receptors including chemokine receptors CCR5 and CXCR4, two coreceptors for HIV-1. Thus, by interacting with a variety of exogenous and host-derived agonists, formyl peptide receptors may play important roles in proinflammatory and immunological diseases and constitute a novel group of pharmacological targets.

Organellar peptide deformylases: universality of the N-terminal methionine cleavage mechanism

Most mature proteins do not retain their initial N-terminal amino acid (methionine in the cytosol and N-formyl methionine in the organelles). Recent studies have shown that dedicated machinery is involved in this process in plants. In addition to cytosolic and organelle-targeted methionine aminopeptidases, organellar peptide deformylases have been identified. Here, we attempt to answer questions about the mechanism, specificity and significance of N-terminal methionine cleavage in plant organelles. It seems to be universal because orthologues of plant deformylases are found in most living organisms.

Staphylococcal resistance to antimicrobial peptides of mammalian and bacterial origin

Antimicrobial host defense peptides, such as defensins, protegrins, and platelet microbicidal proteins are deployed by mammalian skin, epithelia, phagocytes, and platelets in response to Staphylococcus aureus infection. In addition, staphylococcal products with similar structures and activities, called bacteriocins, inhibit competing microorganisms. Staphylococci have developed resistance mechanisms, which are either highly specific for certain host defense peptides or bacteriocins or which broadly protect against a range of cationic antimicrobial peptides. Experimental infection models can be used to study the molecular mechanisms of antimicrobial peptides, the peptide resistance strategies of S. aureus, and the therapeutic potential of peptides in staphylococcal diseases.

Fas/Fas ligand system mediates epithelial injury, but not pulmonary host defenses, in response to inhaled bacteria

The Fas/Fas ligand (FasL) system has been implicated in alveolar epithelial cell apoptosis during pulmonary fibrosis and acute respiratory distress syndrome. However, Fas ligation can also lead to cell activation and cytokine production. The goal of this study was to determine the role of the Fas/FasL system in host defenses against Escherichia coli, Staphylococcus aureus, and Streptococcus pneumoniae. We administered bacteria by aerosolization into the lungs of Fas-deficient (lpr) mice and wild-type (C57BL/6) mice and measured bacterial clearance at 6 and 12 h. One hour prior to euthanasia, the mice received an intraperitoneal injection of human serum albumin (HSA) for alveolar permeability determinations. At all times after bacterial challenges, the lungs of the lpr mice contained similar or lower numbers of bacteria than those of the C57BL/6 mice. Alveolar permeability changes, as determined by bronchoalveolar lavage fluid HSA concentrations, were less severe in the lpr mice 6 h after the challenges. In response to E. coli, the lpr mice had significantly more polymorphonuclear leukocytes (PMN) and macrophage inflammatory protein 2 in the lungs, whereas histopathologic changes were less severe. In contrast, in response to the gram-positive cocci, the lpr animals had similar or lower numbers of PMN. We conclude that the Fas/FasL system contributes to the development of permeability changes and tissue injury during-gram negative bacterial pneumonia. The Fas/FasL system did not have a major role in the clearance of aerosolized bacteria from the lungs at the bacterial doses tested.

Colonic epithelial hPepT1 expression occurs in inflammatory bowel disease: transport of bacterial peptides influences expression of MHC class 1 molecules

BACKGROUND & AIMS

hPepT1 is an intestinal epithelial apical membrane transporter responsible for uptake of di/tripeptides (including bacterial derived proinflammatory n-formyl peptides). hPepT1 expression normally has a strict axial gradient-highest in the proximal small intestine with no expression in the colon.

METHODS

Small intestinal-like cells (Caco2-BBE), and colonic-like cells (HT29-Cl.19A), and colonic mucosa from diseased and control patients were used in the present study.

RESULTS

hPepT1 expression occurs aberrantly in the colon with chronic ulcerative colitis (6 patients) and Crohn's disease (4 patients), but not in normal colon (4 patients) or colon with microscopic colitis (4 patients). To model expression of hPepT1 by colonic-like cells in inflamed states, we stably transfected HT29-Cl.19A cells with a modified hPepT1 tagged on the N-terminus with green fluorescence protein. Analysis of transfected cells revealed that: GFP-hPepT1 protein, like the natural protein, is targeted to the apical plasma membrane. In addition, the tagged protein retains the capability of di/tripeptide absorption, and the expression of the tagged protein by HT29-Cl.19A cells permits absorption of N-formyl-methionyl-leucyl-phenylalanine (fMLP), as occurs in hPepT1 expressing Caco2-BBE cells. fMLP uptake by colonic cells expressing GFP-hPepT1 specifically enhances major histocompatibility complex class I surface expression.

CONCLUSIONS

These data collectively indicate that, in some states of chronic inflammation, hPepT1 may be anomolously expressed in the colon. Further, transport of fMLP by hPepT1 potentially stimulates expression of key accessory immune molecule, MHC-1.

Bacterial formyl peptide mediated chemotaxis and extracellular acidification in shrimp haemocytes

The bacterial formyl peptide N-formylmethionine-leucine-phenylalanine (fMLP) is a potent chemoattractant for mammalian neutrophils. In this study, we demonstrated the binding of fluorescent dye-conjugated-fMLP to haemocytes of the penaeid shrimp Penaeus penicillatus (Alcock), through the use of flow cytometry. Fluorescence microscopy with rhodamine-fMLP suggested that fMLP receptors are present only in sub-populations of the haemocytes: granulocytes and the semi-granular cells. In addition, fMLP dose-dependently mediated chemotaxis in sub-populations of haemocytes. Microphysiometry experiments demonstrated rapid extracellular acidification upon addition of fMLP, which is in agreement with the observation in neutrophils. t-BOC, the specific fMLP receptor antagonist, was able to block the binding, chemotaxis and extracellular acidification induced by the peptide. The ability of shrimp haemocytes to migrate toward fMLP in vitro suggests that this mechanism may be important for the accumulation of these cells in infected tissues of the shrimps.

Fas-mediated apoptosis of neutrophils in sera of patients with infection

In the presence of infection, neutropenia is considered to be a marker of poor prognosis; conversely, neutrophilia may not be a determinant of a better prognosis. Since apoptotic neutrophils are compromised functionally, we evaluated the effect of infection on neutrophil apoptosis. The rate of apoptosis was greater for neutrophils isolated from patients with infection than for healthy controls. Escherichia coli did not directly modulate the rate of neutrophil apoptosis. However, sera from infected patients promoted (P < 0.001) neutrophil apoptosis. Interestingly, the sera of patients with different types of infection (gram negative, gram positive, or culture negative) exerted a more or less identical response on neutrophil apoptosis. Sera of infected patients showed a fivefold greater content of FasL compared to controls. Moreover, anti-FasL antibody partly attenuated the infected-serum-induced neutrophil apoptosis. In in vitro studies, E. coli enhanced monocyte FasL expression. Moreover, conditioned media prepared from activated macrophages from control mice showed enhanced apoptosis of human as well as mouse neutrophils. On the contrary, conditioned media prepared from activated macrophages isolated from FasL-deficient mice induced only a mild degree of neutrophil apoptosis. These results suggest that neutrophils in patients with infection undergo apoptosis at an accelerated rate. Infection not only promoted monocyte expression of FasL but also increased FasL content of the serum. Because the functional status of apoptotic cells is compromised, a significant number of neutrophils may not be participating in the body's defense. Since neutrophils play the most important role in innate immunity, their compromised status in the presence of infection may transfer the host defense burden from an innate response to acquired immunity. The present study provides some insight into the lack of correlation between neutrophilia and the outcome of infection.

Modulation of neutrophil phospholipase C activity and cyclic AMP levels by fMLP-OMe analogues

The N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP)-OMe (1) analogues for-Thp-Leu-Ain-OMe (2), for-Thp-Leu-Phe-OMe (3), for-Met-Leu-Ain-OMe (4), for-Met-Delta(z)Leu-Phe-OMe (5), for-Met-Lys-Phe-For-Met-Lys-Phe (6), for-Met-Leu-Pheol-COMe (7), and for-Nle-Leu-Phe-OMe (8) have been studied. Some of these have been found selective towards the activation of different biological responses of human neutrophils. In particular, peptides 2 and 3, which evoke only chemotaxis, are ineffective in enhancing inositol phosphate, as well as cyclic AMP (cAMP) levels. On the contrary, analogues 5 and 7, which induce superoxide anion production and degranulation, but not chemotaxis, significantly increase the levels of the two intracellular messengers, as is the case of the full agonists 1 and 6. The Ca(2+) ionophore A23187 also activates phospholipase C (PLC) and increases the nucleotide levels; when tested in combination with peptide 1 or 5, a supra-additive enhancement of cAMP concentration is obtained. The PLC blocker, U-73122, inhibits the formylpeptide-induced inositol phosphate formation, as well as cAMP increase. Moreover, this drug drastically reduces superoxide anion release triggered by 1 or 5, whereas it inhibits to a much lesser extent neutrophil chemotaxis induced by 1 or 2. Our results suggest that: (i) PLC stimulation is involved in cAMP enhancement by formylpeptides; (ii) the activation of PLC by formylpeptides, in conditions of increased Ca(2+) influx, induces a supra-additive enhancement of the nucleotide; (iii) the inability of pure chemoattractants to significantly alter the PLC activity or cAMP level, differently from full agonists or peptides specific in inducing superoxide anion release, appears as a general property. Thus, the activation of neutrophil PLC seems essential for superoxide anion release, but less involved in the chemotactic response.

Formyl-methionyl-leucyl-phenylalanine induces prostaglandin E2 release from human amnion-derived WISH cells by phospholipase C-mediated [Ca+]i rise

The presence of binding sites for formyl-methionyl-leucyl-phenylalanine (fMLP), its effect on prostaglandin E (PGE) release, and the signal transduction pathway activated by the peptide were investigated in human amnion-derived WISH cells. Our results demonstrate that specific binding sites for fMLP are present on WISH cells and that the peptide induces a significant increase of prostaglandin (PG)E2 release. The kinetic properties of binding are similar to those previously found in amnion tissue prior to the onset of labor, i.e., only one population of binding sites with low affinity for the peptide is present. Binding of 3H-fMLP in WISH cells is inhibited by N-t-butoxycarbonyl-methionyl-leucyl-phenylalanine, an fMLP receptor antagonist, with an IC50 value very close to that shown by nonlaboring amnion. The fMLP-induced PGE2 output is inhibited by indomethacin, quinacrine, and U-73122, inhibitors of cyclooxygenase, phospholipase A2, and phospholipase C, respectively. As regards the transduction pathway activated by fMLP, we demonstrate that phospholipase C activation, followed by an increase of intracellular calcium concentration ([Ca2+]i), is involved in response to the peptide. Our results add further evidence to the role of proinflammatory agents in the determination of labor. Furthermore, because WISH cells appear to behave like nonlaboring amnion tissue, they represent the ideal candidate for in vitro investigation of the events triggering the mechanism of delivery.

Met-Ile-Phe-Leu derivatives: full and partial agonists of human neutrophil formylpeptide receptors

The biological action of a series of Met-Ile-Phe-Leu analogues was analyzed on human neutrophils, to evaluate their ability to interact with formylpeptide receptors and to induce the related neutrophil responses. Three in vitro assays were carried out: receptor binding, chemotaxis and superoxide anion release. Our results demonstrate that formyl-Met-Ile-Phe-Leu derivatives act as more potent full agonists than formyl-Met-Leu-Phe, the tripeptide normally used as a model chemoattractant for the study of cell functions. On the other hand, the presence of N-ureidoisopropyl substituent in tetrapeptides imparts weak partial agonist properties. It has furthermore been demonstrated that the C-terminal methyl esterification or amination weakly influences the properties of tetrapeptide homologues. Finally, t-Boc-Met-Ile-Phe-Leu derivatives do not appear able to interact with formylpeptide receptors.

Characterization of the binding site on the formyl peptide receptor using three receptor mutants and analogs of Met-Leu-Phe and Met-Met-Trp-Leu-Leu

The formyl peptide receptor (FPR) is a chemotactic G protein-coupled receptor found on the surface of phagocytes. We have previously shown that the formyl peptide binding site maps to the membrane-spanning region (Miettinen, H. M., Mills, J. S., Gripentrog, J. M., Dratz, E. A., Granger, B. L., and Jesaitis, A. J. (1997) J. Immunol. 159, 4045-4054). Recent reports have indicated that non-formylated peptides, such as MMWLL can also activate this receptor (Chen, J., Bernstein, H. S., Chen, M., Wang, L., Ishi, M., Turck, C. W., and Coughlin, S. R. (1995) J. Biol. Chem. 270, 23398-23401.) Here we show that the selectivity for the binding of different NH(2)-terminal analogs of MMWLL or MLF can be markedly altered by mutating Asp-106 to asparagine or Arg-201 to alanine. Both D106N and R201A produced a similar change in ligand specificity, including an enhanced ability to bind the HIV-1 peptide DP178. In contrast, the mutation R205A exhibited altered specificity at the COOH terminus of fMLF, with R205A binding fMLF-O-butyl > fMLF-O-methyl > fMLF, whereas wt FPR bound fMLF > fMLF-O-methyl approximately fMLF-O-butyl. These data, taken together with our previous finding that the leucine side chain of fMLF is probably bound to FPR near FPR (93)VRK(95) (Mills, J. S., Miettinen, H. M., Barnidge, D., Vlases, M. J., Wimer-Mackin, S., Dratz, E. A., and Jesaitis, A. J. (1998) J. Biol. Chem. 273, 10428-10435.), indicate that the most likely positioning of fMLF in the binding pocket of FPR is approximately parallel to the fifth transmembrane helix with the formamide group of fMLF hydrogen-bonded to both Asp-106 and Arg-201, the leucine side chain pointing toward the second transmembrane region, and the COOH-terminal carboxyl group of fMLF ion-paired with Arg-205.