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

The anti-inflammatory effect of 2-(4-hydroxy-3-prop-2-enyl-phenyl)-4-prop-2-enyl-phenol by targeting Lyn kinase in human neutrophils

The undesirable respiratory burst in neutrophils can lead to inflammation and tissue damage. This study investigates the effect and the underlying mechanism of 2-(4-hydroxy-3-prop-2-enyl-phenyl)-4-prop-2-enyl-phenol (honokiol), a lignan extracted from the stem bark of Magnolia officinalis Rehd. et Wils (Magnoliaceae), on N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP)-induced respiratory burst in human neutrophils. Signaling pathways regulated by honokiol which modulate fMLP-induced respiratory burst and cathepsin G release were evaluated by phosphorylation of Src family kinase induced by fMLP, Src family kinases activities and by immunoblotting analysis of the downstream targets of Src kinase. Briefly, honokiol inhibited fMLP-induced superoxide anion production (IC50 = 9.80 ± 0.21 μM, n = 4), cathepsin G release (IC50 = 14.23 ± 1.43 μM, n = 4) and migration (IC50 = 5.69 ± 1.51 μM, n = 4) in a concentration dependent manner. Further, honokiol specifically suppresses fMLP-induced Lyn (a member of the Src kinase family) phosphorylation, by inhibiting Lyn kinase activity. Consequently, honokiol attenuated the downstream targets of Lyn kinase, such as Tec translocation from the cytosol to the inner leaflet of the plasma membrane, phosphorylation of AKT, P38, PLCγ2, protein kinase C and membrane localization of p47(phox). On the other hand, fMLP-induced phosphorylation of Hck, Fgr kinase activity (other members of Src kinase), downstream phosphorylation of Vav1 and extracellular signal-regulated kinase remained unaffected. In addition, honokiol neither inhibited NADPH oxidase activity nor increased cyclic AMP levels. Honokiol is not a competitive or allosteric antagonist of fMLP. In conclusion, honokiol specifically modulates fMLP-mediated neutrophil activation by inhibiting Lyn activation which subsequently interferes with the activation of PLCγ2, AKT, p38, protein kinase C, and p47(phox).

Measurement of phospholipid metabolism in intact neutrophils

Phospholipid-metabolizing enzymes are important participants in neutrophil signal transduction pathways. The methods discussed herein describe assays for assessing the activities of phospholipase A2 (PLA2), phospholipase C (PLC), phospholipase D (PLD), and phosphoinositide 3-OH-kinase in intact neutrophils. PLA2 activity is measured as the release of radiolabeled arachidonic acid. PLC activity is measured as the accumulation of inositol 1,4,5-trisphosphate (IP3), a water-soluble product, using a commercially available radioreceptor assay kit. PLD activity is measured as the appearance of its radiolabeled products, phosphatidic acid and phosphatidylethanol. PI3-K activity is measured as the appearance of its radiolabeled product, phosphatidylinositol-3,4,5-trisphosphate.

Toxoplasma gondii inhibits mast cell degranulation by suppressing phospholipase Cγ-mediated Ca(2+) mobilization

Toxoplasma gondii is well-known to subvert normal immune responses, however, mechanisms are incompletely understood. In particular, its capacity to alter receptor-activated Ca²⁺-mediated signaling processes has not been well-characterized. In initial experiments, we found evidence that T. gondii infection inhibits Ca²⁺ responses to fMetLeuPhe in murine macrophages. To further characterize the mechanism of inhibition of Ca²⁺ mobilization by T. gondii, we used the well-studied RBL mast cell model to probe the capacity of T. gondii to modulate IgE receptor-activated signaling within the first hour of infection. Ca²⁺ mobilization that occurs via IgE/FcεRI signaling leads to granule exocytosis in mast cells. We found that T. gondii inhibits antigen-stimulated degranulation in infected cells in a strain-independent manner. Under these conditions, we found that cytoplasmic Ca²⁺ mobilization, particularly antigen-mediated Ca²⁺ release from intracellular stores, is significantly reduced. Furthermore, stimulation-dependent activation of Syk kinase leading to tyrosine phosphorylation and activation of phospholipase Cγ is inhibited by infection. Therefore, we conclude that inhibitory effects of infection are likely due to parasite-mediated inhibition of the tyrosine kinase signaling cascade that results in reduced hydrolysis of phosphatidylinositol 4,5-bisphosphate. Interestingly, inhibition of IgE/FcεRI signaling persists when tachyzoite invasion is arrested via cytochalasin D treatment, suggesting inhibition is mediated by a parasite-derived factor secreted into the cells during the invasion process. Our study provides direct evidence that immune subversion by T. gondii is initiated concurrently with invasion.

Splitomicin inhibits fMLP-induced superoxide anion production in human neutrophils by activate cAMP/PKA signaling inhibition of ERK pathway

Splitomicin, is a cell-permeable lactone derived from naphthol and known to be a potent selective inhibitor of Sir2 (silent information regulator 2). Previous studies have demonstrated that naphtholic compounds possess an inhibitory effect on neutrophils. Here, we present our investigation on the inhibitory effects of splitomicin in human neutrophils. The primary goal of our study was to locate a possible candidate on inflammatory reactions and to hopefully develop a novel anti-inflammatory therapy. Neutrophils were prepared following standard procedures. Neutrophils induced by either fMLP (1 μM) or PMA (100 nM) were observed using a flow cytometer and the intracellular production of superoxide anions was investigated at different splitomicin concentrations. The cytosolic Ca(++) influx concentration was measured using a fluorescence spectrophotometer, and Mac-1 expression was detected with a flow cytometer. The MAP kinases were measured using western blotting. Our results showed that splitomicin inhibited superoxide anion production by fMLP (1 μM) and NaF (20mM) in a concentration-dependent manner (37.5-450 μM). Splitomicin (300 and 450 μM) also suppressed fMLP-induced intracellular calcium ion mobilization and extracellular-signal regulated kinase (ERK) phosphorylation. Moreover, splitomicin could inhibit fMLP-induced Mac-1 expression and increase cAMP levels in human neutrophils. Our data demonstrated that splitomicin exhibits a noticeable inhibitory effect on superoxide anion production in human neutrophils. This negative effect was well-correlated with increased cAMP levels via PKA activity and the subsequent inhibition of ERK (p42/p44) phosphorylation to decrease superoxide anion production.

5-Hydroxy-7-methoxyflavone inhibits N-formyl-L-methionyl-L-leucyl-L-phenylalanine-induced superoxide anion production by specific modulate membrane localization of Tec with a PI3K independent mechanism in human neutrophils

Respiratory burst mediates crucial bactericidal mechanism in neutrophils. However, undesirable respiratory burst leads to pathological inflammation and tissue damage. This study investigates the effect and the underlying mechanism of 5-hydroxy-7-methoxyflavone (MCL-1), a lignan extracted from the leaves of Muntingia calabura L. (Tiliaceae), on N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP)-induced respiratory burst and cathepsin G release in human neutrophils. Signaling pathways regulated by MCL-1 to oppose fMLP-induced respiratory burst were evaluated by membrane localization of Tec induced by fMLP and by immunoblotting analysis of downstream phosphorylation targets of Tec. Briefly, MCL-1 specific inhibited fMLP-induced superoxide anion production in a concentration-dependent (IC(50)=0.16±0.01 μM) and Tec kinase-dependent manner, however, MCL-1 did not affect fMLP-induced cathepsin G release. Further, MCL-1 suppressed fMLP-induced Tec translocation from the cytosol to the inner leaflet of the plasma membrane, and subsequently activation of phospholipase Cγ2 (PLCγ2). Moreover, MCL-1 attenuated PLCγ2 activity and intracellular calcium concentration notably through extracellular calcium influx. Consequently, fMLP-induced phosphorylation of protein kinase C (PKC) and membrane localization of p47(phox) were decreased by MCL-1 in a Tec-dependent manner, while the phosphorylation of extracellular signal-regulated kinase (ERK), p38, AKT and Src tyrosine kinase family remained unaffected. In addition, MCL-1 neither inhibited NADPH oxidase activity nor increased cyclicAMP levels. MCL-1 specific opposes fMLP-mediated respiratory burst by inhibition of membrane localization of Tec and subsequently interfered with the activation of PLCγ2, protein kinase C, and p47(phox).

5-hydroxy-2-(4-hydroxy-3-methoxyphenyl)-3,7-dimethoxy-4H-chromen-4-one (MSF-2) suppresses fMLP-mediated respiratory burst in human neutrophils by inhibiting phosphatidylinositol 3-kinase activity

Respiratory burst mediates crucial bactericidal mechanism in neutrophils. However, undesirable respiratory burst leads to pathological inflammation and tissue damage. This study investigates the effect and the underlying mechanism of 5-hydroxy-2-(4-hydroxy-3-methoxyphenyl)-3,7-dimethoxy-4H-chromen-4-one (MSF-2), a lignan extracted from the fruit of Melicope Semecarprifolia, on fMLP-induced respiratory burst in human neutrophils and suggests a possible therapeutic approach to ameliorate disease associated with neutrophil hyperactivation. MSF-2 inhibited fMLP-induced neutrophil superoxide anion production, cathepsin G release and migration in human neutrophils isolated from healthy volunteers, reflecting inhibition of phosphatidylinositol 3-kinase (PI3K) activation. Specifically, PI3K/AKT activation results in migration, degranulation and superoxide anion production in neutrophils. MSF-2 suppresses PI3K activation and phosphatidylinositol (3,4,5)-trisphosphate (PIP3) production, and consequently inhibits downstream activation of PDK1 and AKT. Further, PI3K also stimulates respiratory burst via PLC-dependent elevation of intracellular calcium. MSF-2 reduces fMLP-mediated PLCγ2 activation and intracellular calcium accumulation notably through extracellular calcium influx in a PI3K and PLC-dependent manner. However, MSF-2 is not a competitive or allosteric antagonist of fMLP. Additionally, in an in vivo study, MSF-2 prevents fMLP-induced neutrophil infiltration and inflammation in mice. In conclusion, MSF-2 opposes fMLP-mediated neutrophil activation and inflammation by inhibiting PI3K activation and subsequent activation of AKT and PLCγ2.

Secondary metabolites from the leaves of Neolitsea hiiranensis and the anti-inflammatory activity of some of them

Seven sesquiterpenoids, hiiranlactones A-D (1-4), (-)-ent-6α-methoxyeudesm-4(15)-en-1β-ol (5), (+)-villosine (6), hiiranepoxide (7), and one triterpenoid, hiiranterpenone (8), together with 22 known compounds, were isolated from the leaves of Neolitsea hiiranensis (Lauraceae). Their structures were elucidated by spectroscopic analysis and single crystal X-ray diffraction. Among the isolates, hiiranlactone B (2) and hiiranlactone D (4) exhibited inhibitory activity against fMLP-induced superoxide production by human neutrophils with IC(50) values of 21.86±3.97 and 25.78±4.77μM, respectively.

A benzodiazepines derived compound, 4-(3-chlorophenyl)-1,3-dihydronaphtho [2,3-b][1,4]diazepin-2-one (ND700C), inhibits fMLP-induced superoxide anion release by activating protein phosphatase 2A in human neutrophils

We studied the mechanism underlying the inhibitory effect of a benzodiazepines derivative, 4-(3-chlorophenyl)-1,3-dihydronaphtho [2,3-b][1,4]diazepin-2-one (ND700C), on superoxide anion production induced by formly-methionyl-leucyl-phenylalanine (fMLP) in human neutrophils. ND700C inhibited the fMLP-induced superoxide anion production and cathepsin G release in a concentration-dependent manner with respective IC50 values of 5.0+/-0.5 and 8.7+/-0.8muM. In addition, ND700C was found to suppress fMLP-induced intracellular calcium mobilization and the phosphorylation of ERK and Akt. In another study, ND700C was observed to cause a rapid increase in intracellular cAMP level by up to threefold. Furthermore, when H89 was used to inhibit cAMP-dependent protein kinase A (PKA), we discovered that ND700C's suppressive effects on calcium mobilization, phosphorylation, and superoxide anion production were abrogated. ND700C demonstrated additive effect on the PGE1-induced increase in cAMP. However, this additive effect was not demonstrated with the IBMX-induced rise in cAMP. Our results indicated that ND700C did not directly inhibit the activity of phosphodiesterase 4. In another set of experiments, calyculin A and okadaic acid (both protein phosphatase 2A inhibitors) were found to reverse ND700C's positive effect on cAMP level. This observation suggested the involvement of protein phosphatase 2A in ND700C's cAMP-elevating mechanism. We found that the activity of protein phosphatase 2A was activated by ND700C. Furthermore, protein phosphatase 2A was co-immunoprecipitated with phosphodiesterase 4 after ND700C treatment in human neutrophils.

CONCLUSION

ND700C inhibited fMLP-induced superoxide anion production through a PKA-dependent pathway. ND700C increased cAMP by activating protein phosphatase 2A, which subsequently inhibited phosphodiesterase 4.

(2R,3R)-2-(3',4'-dihydroxybenzyl)-3-(3'',4''-dimethoxybenzyl)butyrolactone suppresses fMLP-induced superoxide production by inhibiting fMLP-receptor binding in human neutrophils

This study investigated the mechanism underlying the inhibiting effect of (2R,3R)-2-(3',4'-dihydroxybenzyl)-3-(3'',4''-dimethoxybenzyl) butyrolactone (PP-6), a lignan from Piper philippinum, on superoxide anion production induced by the chemotactic peptide formyl-methionyl-leucyl-phenylalanine (fMLP) in human neutrophils. Human neutrophils were stimulated with fMLP (1 microM), PMA (100 nM) or leukotriene B(4) (LTB(4); 1 microM) and induced superoxide anion release. PP-6 specifically inhibited fMLP-induced superoxide anion production in a concentration-dependent manner with an IC(50) value of 0.3+/-0.1 microM. Intracellular signaling caused by fMLP, PMA or LTB(4) were evaluated. PP-6 specifically inhibited fMLP-induced intracellular calcium mobilization and ERK (p42/p44), Akt and p38 phosphorylation. Moreover, PP-6 specifically inhibited fMLP-induced Mac-1 expression without affecting this caused by LTB(4) or PMA. PP-6 did not increase cAMP level in human neutrophils. PP-6 did not inhibit superoxide anion production by NaF (20 mM), a direct activator of G-protein, the target of the inhibitory action of PP-6 appears to be a component of the signal transduction pathway upstream of G-protein. PP-6 inhibited FITC-fMLP binding to neutrophils in a concentration-dependent manner with an IC(50) of 1.5+/-0.2 microM. PP-6 did not bring a parallel shift in the concentration response of fMLP-induced superoxide anion. Additionally, the inhibiting effect of PP-6 on fMLP-induced superoxide anion was reversed when PP-6 was washed out. These experimental results suggest that PP-6 exerts non-competitive and reversible antagonistic effect on fMLP receptor.

The synthetic melanocortin (CKPV)2 exerts broad anti-inflammatory effects in human neutrophils

Natural melanocortin peptides exert broad effects on the host and they have remarkable therapeutic potential. However, successful use of melanocortins as therapeutic agents depends on the design of molecules that have more stable pharmacological profiles. The synthetic peptide (CKPV)(2), based on the C-terminal sequence of alpha-melanocyte stimulating hormone (alpha-MSH), has anti-tumor necrosis factor-alpha (TNF-alpha) effects in vitro and in vivo and is a promising candidate to treat inflammation. Because neutrophil activity is a major target for anti-inflammatory therapies, we determined whether (CKPV)(2) modulates human neutrophil functions in vitro. Incubation of freshly-separated human neutrophils with 10(-12)-10(-6)M (CKPV)(2) significantly inhibited activities relevant to the inflammatory reaction. Neutrophil migration toward the two chemoattractants interleukin 8 (IL-8) and N-formyl-methionyl-leucyl-phenylalanine (fMLP) was significantly inhibited by (CKPV)(2). (CKPV)(2) also inhibited reactive oxygen intermediate (ROI) production induced by phorbol 12-myristate 13-acetate (PMA), but not that induced by fMLP. Because these effects of (CKPV)(2) were abolished by the adenylyl cyclase inhibitor 2',5'-dideoxyadenosine (ddAdo), they appear to be cAMP-dependent. Finally, the peptide reduced lipopolysaccharide (LPS)-stimulated expression of TNF-alpha, interleukin-1beta (IL-1beta), interleukin-8 (IL-8), and intercellular adhesion molecule 1 (ICAM-1), as well as TNF-alpha protein release in cell supernatants. The data indicate that (CKPV)(2) modulates broad cAMP-dependent, anti-inflammatory pathways in human neutrophils.

New chemotactic dimeric peptides show high affinity and potency at the human formylpeptide receptor

A number of analogues of the prototypical peptide for-Met-Leu-Phe-OMe (fMLP-OMe) have been studied in order to evaluate their ability to interact with formylpeptide receptors and to induce specific biological responses in human neutrophils. In vitro assays were carried out and receptor binding, chemotaxis, superoxide anion release and secretagogue activity were evaluated. The fMLP-OMe analogues synthesized, with the general formula for-Met-Leu-Phe-Xaa-Lys(OMe)-Phe-Leu-Met-for (Xaa=Gly, beta-Ala, gamma-aminobutyric acid, 5-aminovaleric acid, and 6-aminocaproic acid), were constituted by two fMLP units linked by a Lys residue, with an amino acid spacer between them. Competition binding experiments revealed that the new compounds have much more affinity for formylpeptide receptors than the reference ligand, with good correlation between receptor affinity and length of spacer. The EC(50) values for the killing mechanisms of each analogue were similar to each other, the affinity and potency, once again, being strictly dependent on the chain length. Furthermore the analogues proved to be more potent full agonists than the prototype fMLP-OMe in these functions, while chemotaxis was poorly induced. The dimeric fMLP-OMe analogues are one of the few examples of formylpeptides which exhibit a receptor affinity greater than the parent fMLP-OMe thereby rendering them suitable to be used as carriers for various drugs.

Measurement of phospholipid metabolism in intact neutrophils

Phospholipid metabolizing enzymes are important participants in neutrophil signal transduction pathways. The methods discussed herein describe assays for assessing the activities of phospholipase (PL)A2, PLC, PLD, and phosphoinositide 3-OH-kinase (PI3-K) in intact neutrophils. PLA2 activity is measured as the release of radiolabed arachidonic acid. PLC activity is measured as the accumulation of inositol 1,4,5-trisphosphate (IP3), a water-soluble product, using a commercially available radioreceptor assay kit. PLD activity is measured as the appearance of its radiolabeled products, phosphatidic acid and phosphatidylethanol. PI3-K activity is measured as the appearance of its radiolabeled product, phosphatidylinositol-3,4,5-trisphosphate.

Involvement of phosphatidylinositol-phospholipase C in immune response to Salmonella lipopolysacharide in chicken macrophage cells (HD11)

The activation of phospholipases is one of the earliest key events in receptor-mediated cellular responses to a number of extracellular signaling molecules. Lipopolysaccharide (LPS) is a principle component of the outer membrane of Gram-negative bacteria and a prime target for recognition by the innate immune system. In the present study, we evaluated the role of specific phospholipase in the activation of a chicken macrophage cell line HD11 by LPS. Activation of HD11 cells by LPS results in induction of nitric oxide (NO). Using selective inhibitors, we have identified that phosphatidylinositol (PI)-phospholipase C (PI-PLC), but not phosphatidylcholine (PC)-phospholipase C (PC-PLC) nor PC-phospholipase D (PC-PLD), was required for LPS-induced NO production. Preincubation with PI-PLC selective inhibitors (U-73122 and ET-18-OCH3) abrogated LPS-induced NO production in HD11 cells, whereas PC-PLC inhibitor (D609), phosphatide phosphohydrolase inhibitor (propranolol), and PC-PLD inhibitor (n-butanol) had no inhibitory effects. We also showed that inhibition of protein kinase C (PKC) by selective inhibitors Ro 31-8220 and calphostin C and chelating intracellular Ca2+ by BAPTA-AM significantly reduced NO production in LPS-stimulated HD11 cells. Our results demonstrate that PI-PLC plays a critical role, most likely through activation of PKC pathway, in TLR4 mediated immune responses of avian macrophage cells to LPS.

Effective attenuation of acute lung injury in vivo and the formyl peptide-induced neutrophil activation in vitro by CYL-26z through the phosphoinositide 3-kinase γ pathway

5-[4-Acridin-9-ylamino]phenyl]-5-methyl-3-methylenedihydrofuran-2-one (CYL-26z) inhibited the polymorphonuclear leukocyte (PMNL) infiltration and protein leakage into the lungs in lipopolysaccharide (LPS)-induced acute lung injury (ALI) in mice as determined on the basis of PMNL and protein contents in bronchoalveolar lavage (BAL) fluid and myeloperoxidase (MPO) content in whole lung extracts. CYL-26z also attenuated the formyl-Met-Leu-Phe (fMLP)-induced neutrophil chemotaxis and respiratory burst in vitro (IC(50) 8.4+/-0.9microM and 2.0+/-0.6microM, respectively). CYL-26z had no effect on superoxide anion (O(2)(-)) generation during dihydroxyfumaric acid autoxidation or on the NADPH oxidase activity in two cell-free systems (the arachidonic acid-induced assembly of NADPH oxidase and the preassembled oxidase caused by phorbol ester treatment), whereas it inhibited NaF-induced respiratory burst. Inhibition of respiratory burst by CYL-26z was readily reversible by washing. Only slight, but significant, inhibition of extracellular signal regulated kinase (ERK) phosphorylation and p38 mitogen-activated protein kinase (MAPK) activation in response to fMLP by CYL-26z up to 30microM was obtained. CYL-26z effectively blocked the formation of phosphatidylinositol-3,4,5-trisphosphate (PtdIns(3,4,5)P(3)) as determined by immunofluorescence microscopy and flow cytometry assays and the dual phosphorylation of protein kinase B (PKB/Akt) on S473 and T308 residues in fMLP-stimulated neutrophils. The membrane recruitment of p110gamma and Ras, the Ras activation, and the association between p110gamma and Ras were also attenuated by CYL-26z. These results indicate that the blockade of Ras activation by CYL-26z attenuated the downstream phosphoinositide 3-kinase (PI3K) gamma signaling, which is involved in chemoattractant-induced neutrophil chemotaxis and respiratory burst, and may have a beneficial anti-inflammatory effect on ALI.

Signal transduction pathways triggered by selective formylpeptide analogues in human neutrophils

Human neutrophils are highly specialised for their primary function, i.e. phagocytosis and destruction of microorganisms. Leukocyte recruitment to sites of inflammation and infection is dependent upon the presence of a gradient of locally produced chemotactic factors. The bacterial peptide N-formyl-methionyl-leucyl-phenylalanine (fMLP) was one of the first of these to be identified and is a highly potent leukocyte chemoattractant. It interacts with its receptor on the neutrophil membrane, activating these cells through a G-protein-coupled pathway. Two functional fMLP receptors have thus far been cloned and characterized, namely FPR (formyl peptide receptor) and FPRL1 (FPR like-1), with high and low affinities for fMLP, respectively. FMLP is known to activate phospholipase C (PLC), PLD, PLA2 and phosphatidylinositol-3-kinase (PI3K), and it also activates tyrosine phosphorylation. The second messengers resulting from the fMLP receptor interaction act on various intracellular kinases, including protein kinase C (PKC) and mitogen-activated protein kinases (MAPKs). The activation of these signal transduction pathways is known to be responsible for various biochemical responses which contribute to physiological defence against bacterial infection and cell disruption. This review will consider the ability of selective analogues (ligands able to discriminate between different biological responses) to activate a single spectrum of signal transduction pathways capable of producing a unique set of cellular responses, hypothesising that a distinctive imprint of signal protein activation may exist. Through more complete understanding of intracellular signaling, new drugs could be developed for the selective inflammatory blockade.

Biological activity of for-Met-Leu-Phe-OMe analogs: Relevant substitutions specifically trigger killing mechanisms in human neutrophils

Two analogs of the prototypical peptide for-Met-Leu-Phe-OMe (fMLP-OMe), for-Gln-Tyr-Phe-OMe (1) and for-Gln-Tyr-Tyr-OMe (2), carrying unusual hydrophilic residues, were synthesized in order to investigate whether they provoked specific biological responses, as well as intracellular calcium mobilization, in human neutrophils. Whereas neither compound stimulates chemotaxis, both are able to elicit lysosomal enzyme production. However compound 1 is able to trigger copious superoxide anion production while compound 2 only elicits minor superoxide anion production. In binding experiments on formylpeptide receptors, the newly synthesized compounds for-Gln-Tyr-Phe-OMe (1) and for-Gln-Tyr-Tyr-OMe (2) showed affinity values in the micromolar range. These derivatives demonstrate inability to find a positive contribute from single substitutions. A very important result of this research is the evidence of the ability of the formyl group alone to trigger the primary target of the human neutrophil activity, i.e. killing mechanisms, by activating the specific receptor conformation.

A 'pure' chemoattractant formylpeptide analogue triggers a specific signalling pathway in human neutrophil chemotaxis

As it has not yet been established whether the second messengers involved in the neutrophil response have identical or specific signalling requirements for each physiological function, protein kinase C (PKC) isoforms and mitogen activated protein kinases (MAPKs) were studied in human chemotaxis triggered by the full agonist for-Met-Leu-Phe-OMe (fMLP-OMe) and the 'pure' chemoattractant for-Thp-Leu-Ain-OMe [Thp1,Ain3] analogue. Experiments were performed in the presence or absence of extracellular Ca2+, known to be an important modulator of second messengers. Our data demonstrate that specific PKC beta1 translocation and p38 MAPK phosphorylation are strongly associated with the chemotactic response of the neutrophils triggered by both peptides, while Ca2+ is not necessary for chemotaxis to occur. PKC and MAPK inhibitors were used in Western blotting assays and in cell locomotion experiments to investigate if the MAPK signalling pathway was controlled by PKC activation. The most important finding emerging from this study is that PKC and MAPK activate the chemotactic function of human neutrophils by two independent pathways.

Human beta-defensin-2 functions as a chemotactic agent for tumour necrosis factor-alpha-treated human neutrophils

Neutrophils are the effector cells in both innate and adaptive immunity, where they perform the functions of phagocytosis and killing of bacteria. They respond to a large number of chemoattractants, but their response to epithelial cell-derived human beta-defensins (hBD) has not been investigated. Here we report that hBD-2, but not hBD-1, is a specific chemoattractant for tumour necrosis factor (TNF)-alpha-treated human neutrophils. The optimal concentration required for maximal chemotactic activity was 5 micro g/ml. The effect of hBD-2 on neutrophils was dependent on the G-protein-phospholipase C pathway, as demonstrated by inhibition by pertussis toxin and U-73122. In addition, ligand-receptor analysis indicated that the binding of hBD-2 was markedly inhibited by macrophage inflammatory protein (MIP)-3alpha, a specific and unique ligand for CCR6. Furthermore, anti-CCR6 antibody could almost completely suppress the cell migration induced by hBD-2, suggesting that hBD-2 mainly utilizes CCR6 as a functional receptor. Thus, our finding that hBD-2 is a potent chemoattractant for human neutrophils through specific receptors provides a novel mechanism by which this peptide contributes to the host defence system by recruiting neutrophils to inflammation/infection sites. This also suggests an important link between epithelial cell-derived antibacterial peptides and neutrophils during infection or inflammation.

N-Formyl peptide receptor subtypes in human neutrophils activate L-plastin phosphorylation through different signal transduction intermediates

We investigated the coupling of the fMLP (N -formyl-L-methionyl-L-leucyl-L-phenylalanine; 'chemotactic peptide') receptor with phosphorylation of the actin-binding protein L-plastin in neutrophils. Using two-dimensional IEF (isoelectric focusing)/PAGE and MALDI-TOF (matrix-assisted laser desorption ionization-time-of-flight)-MS, L-plastin was identified as a major phosphoprotein in fMLP-stimulated neutrophils whose phosphorylation was dependent on phosphoinositide 3-kinase, PLD (phospholipase D) and PKC (protein kinase C) activity. Two fMLP receptor subtypes were identified in neutrophils, characterized by a distinct sensitivity to fMLP and antagonistic peptides. Both receptor subtypes induced the phosphorylation of L-plastin. L-plastin phosphorylation induced by low-affinity fMLP receptors involves an action of phosphoinositide 3-kinase, PLD and PKC isotypes. In contrast, none of these intermediates are utilized by high-affinity fMLP receptors in the phosphorylation of L-plastin. However, the PKC inhibitor Ro-31-8220 inhibits L-plastin phosphorylation induced by the high-affinity fMLP receptor. Thus, an as yet unknown Ro-31-8220-sensitive kinase regulates L-plastin phosphorylation in response to the high-affinity fMLP receptor. The results suggest a model in which receptor subtypes induce a similar endpoint event through different signal-transduction intermediates. This may be relevant in the context of cell migration in which one receptor subpopulation may become desensitized in a concentration gradient of chemoattractant.

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.

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.

Chemoattractant receptor-stimulated F-actin polymerization in the human neutrophil is signaled by 2 distinct pathways

We characterized the overall rate of F-actin polymerization in the pseudopod region by measuring the rate of extension of single pseudopods stimulated by f-Met-Leu-Phe. The rate of pseudopod extension was measured in the presence of inhibitors for signaling molecules that are known to be involved in motility. Our data show the existence of 2 distinct signaling pathways of actin polymerization in the pseudopod region: a phosphoinositide 3-kinase gamma (PI3Kgamma)-dependent and -independent pathway. The PI3Kgamma dependent signaling of F-actin polymerization also depends on protein kinase C zeta and protein kinase B (Akt/PKB). The PI3Kgamma-independent pathway depends on GTPase RhoA, the RhoA ROCK kinase, Src family tyrosine kinases, and NADPH, and is modulated by cAMP.

Magnesium sulfate inhibits the oxytocin-induced production of inositol 1,4,5-trisphosphate in cultured human myometrial cells

OBJECTIVE

The purpose of this study was to determine the effects of magnesium sulfate on inositol trisphosphate production and the mechanism of these effects.

STUDY DESIGN

Myometrium was obtained at the time of cesarean delivery from women before labor at term. Inositol trisphosphate was measured in the primary myometrial cell cultures after stimulation with oxytocin, sodium fluoride, or Bay K 8644 with or without preincubation with magnesium sulfate or nifedipine. Experiments were performed in either calcium-containing or calcium-free medium that contained egtazic acid and after preincubation with the intracellular calcium chelator BAPTA-acetoxymethylester. Inositol trisphosphate production was measured by radioreceptor assay. In separate experiments, changes in intracellular calcium concentrations ([Ca(2+)](i)) were measured with the use of Fura-2 and spectrophotofluorometry.

RESULTS

Oxytocin, sodium fluoride, and Bay K 8644 increased inositol trisphosphate production 2- to 4-fold. Preincubation with magnesium sulfate (3 x 10(-3) mol/L) for > or = 5 minutes decreased oxytocin-, sodium fluoride-, and Bay K 8644-induced inositol trisphosphate production in either calcium-containing or calcium-free media. Preincubation with BAPTA-acetoxymethylester decreased oxytocin-stimulated inositol trisphosphate production by 78% in calcium-containing media and completely prevented the oxytocin response in calcium-free media. Magnesium sulfate decreased inositol trisphosphate production in calcium-containing media but had no additional effect in calcium-free media. Oxytocin and Bay K 8644 increased [Ca(2+)](i) in either calcium-containing or calcium-free media, and magnesium sulfate reduced this in both cases.

CONCLUSION

Magnesium sulfate appears to inhibit phosphatidylinositol-4, 5-bisphosphate-specific phospholipase C activity and subsequent calcium release in cultured myometrial cells by a direct effect on phospholipase C.