Journal of Leukocyte Biology eBioscience full spectrum cell analysis
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

Originally published online as doi:10.1189/jlb.0905498 on December 19, 2005

Published online before print December 19, 2005
This Article
Right arrow Full Text (PDF)
Right arrow All Versions of this Article:
jlb.0905498v1
79/2/247    most recent
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Fu, H.
Right arrow Articles by Dahlgren, C.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Fu, H.
Right arrow Articles by Dahlgren, C.
(Journal of Leukocyte Biology. 2006;79:247-256.)
© 2006 by Society for Leukocyte Biology

Ligand recognition and activation of formyl peptide receptors in neutrophils

Huamei Fu, Jennie Karlsson, Johan Bylund, Charlotta Movitz, Anna Karlsson and Claes Dahlgren1

Department of Rheumatology and Inflammation Research, University of Göteborg, Sweden

1Correspondence: Department of Rheumatology and Inflammation Research, University of Göteborg, Sweden. E-mail: Claes.Dahlgren{at}microbio.gu.se

Key Words: chemoattractant receptors • phagocytes • receptor structure • receptor function


   INTRODUCTION
TOP
 INTRODUCTION
NEUTROPHIL FPR
 RECEPTOR DESENSITIZATION
 NEUTROPHIL SIGNALING BY FPR...
 FUTURE PERSPECTIVES
 REFERENCES
 
Neutrophil granulocytes, professional phagocytes of the innate immune system, can migrate in response to gradients of chemoattractants, soluble molecules serving as "danger signals." The chemotactic behavior of these cells is of great importance for the outcome of the continuously ongoing combat with invading microorganisms. In a number of inflammatory disorders, the chemoattractant-guided accumulation of neutrophils and their subsequent release of reactive oxygen species (ROS) and proteolytic enzymes are responsible for the tissue damage associated with such disease conditions. Research about the structure and function of neutrophil chemoattractants and their receptors is therefore of direct clinical importance and relevance. Although chemotaxis was defined as an important part of active immune reactivity already by Elie Metchnikoff in the late 19th century [1 ], the modern chemotaxis research era started first by the introduction of a filter technique in 1962 [2 ], which allowed quantitative determinations of neutrophil migration and a rational search for specific attractants derived from intruding microbes or activated/damaged host cells [3 ]. Following the discovery of bacteria-derived, formylated peptides as potent neutrophil chemoattractants in the mid-1970s [4 ], the list of structurally well-characterized leukocyte chemoattractants has steadily grown. Other microbial components, cleavage products from the complement system (e.g., C5a), lipid metabolites such as platelet-activating factor (PAF) and leukotriene B4 (LTB4), as well as a large group of chemokines are examples of such molecules [5 ] (Table 1 ). During the last two decades, a broad application of molecular biology techniques has also led to identification of the chemoattractant receptors. Despite the fact that these receptors recognize different chemoattractants specifically, they exhibit some sequence homologies and share structural features, all belonging to a pertussis toxin (PTX)-sensitive subfamily within the G protein-coupled receptor (GPCR) superfamily. The reader is referred to several excellent review articles, which in more detail discuss general aspects of the chemoattractant receptor family and neutrophil activation in inflammation [5 6 7 , 16 ].


View this table:
[in this window]
[in a new window]
  		Table 1. Human Neutrophil Chemoattractant Receptorsa

 
We intend to summarize the current knowledge about structure and function of two closely related neutrophil G protein-coupled chemoattractant receptors: the FPR, which was the first characterized member in the FPR family, and the closely related FPRL1, also called LXA4receptor, as this eicosanoid was the first specific agonist described for the receptor. A large number of agonists for these receptors have now been identified, and the same basic neutrophil functional responses are triggered by ligation of these receptors [16 ]—chemotaxis, receptor mobilization, secretion of proteolytic enzymes and inflammatory mediators, and production of ROS. Ligand recognition by the two neutrophil FPRs, linked to activation and signaling, is the subject of this review.


   NEUTROPHIL FPR
TOP
 INTRODUCTION
 NEUTROPHIL FPR
RECEPTOR DESENSITIZATION
 NEUTROPHIL SIGNALING BY FPR...
 FUTURE PERSPECTIVES
 REFERENCES
 
The two neutrophil FPR family receptors exhibit large similarities
During the 1970s and 1980s, several of the now-classical chemoattractants were discovered, and when their respective receptors were characterized, these were all recognized as members of the large family of GPCRs (Table 1) . In general, the chemoattractant receptors comprise a single 350–370 amino acid (aa) polypeptide chain, which spans the cell membrane seven times (Fig. 1 ). The N terminus and three loops, believed to be essential for interaction with the ligand, are exposed extracellularly, and the carboxyl terminus and three additional loops of importance for intracellular signaling, are facing the cytosolic side of the membrane [8 , 17 ]. The neutrophil chemoattractant GPCRs all share sequence similarities in some of the transmembrane domains as well as in the cytosolic signaling domains. In contrast, the surface-exposed regions (conferring the ligand specificity) of the GPCRs show a lower degree of sequence similarity [6 ].


Figure 1
View larger version (36K):
[in this window]
[in a new window]
  		Figure 1. Structure (a) and aa sequences of the human seven-transmembrane FPR and the closely related FPRL1. The positions that differ between the two receptors are marked in yellow. The mutations in FPR, associated with juvenile periodontitis (LJP), are marked in red, whereas the positions in FPR, known to vary between normal, healthy subjects, are marked in green. FPRL1 contains 350 aa, which is one less than in FPR. The blank position at position 274 (b) in FPRL1 was included to obtain a good alignment.

 
The FPR was the first neutrophil GPCR to be cloned and sequenced [18 ]. Soon after the FPR sequence was published, two orphan FPRLs, FPRL1 and FPRL2, were cloned from a promyelocyte cDNA library using low-stringency hybridization with the FPR cDNA as a probe [19 , 20 ]. It was previously thought that the cellular distribution of the FPR receptors was restricted to phagocytes, a view that has been reconsidered lately as these receptors have been found in a variety of cell types (Table 1) . The FPR variants are expressed differently in professional phagocytes, and neutrophils express FPR and FPRL1, whereas monocytes/macrophages express all three family members. The monocyte-specific family member was long considered an orphan receptor; however, recently Migeotte et al. [21 ] presented a specific FPRL2 agonist. The FPR gene family members differ with respect to their evolutionary history, illustrated, for example, by the fact that the human FPR is characterized by a high degree of single nucleotide polymorphism, whereas no FPRL1 polymorphisms have been described [22 ]. Moreover, the murine genome comprises six FPR family members (rather than three) with unique functional characteristics.

The human genes, designated fpr and fprl1, were mapped to chromosome 19 and encode proteins that are highly homologous. They exhibit an aa sequence similarity of 69% (Fig. 1) , but the degree of identity differs in different regions of the receptors. A high degree of identity is found in the three cytosolic loops of the receptors, whereas the carboxyl tail (also facing the cytosol) and the extracellular domains have lower degrees of identity. Taken together, this suggests that the ligand-binding epitopes (located in the extracellular domains) as well as the signaling properties (relying on the cytoplasmic tails) differ between the two receptors.

The FPR and its agonists
The FPR is a high-affinity pattern recognition receptor with the ability to track bacteria that release formylated peptides [4 ]. Accordingly, a number of N-formylated peptides, formed as part of prokaryotic protein synthesis [9 , 23 ], are potent neutrophil chemoattractants, supporting the idea that FPR may have a direct function in innate defense against bacterial infection. The receptor also binds formylated peptides of mitochondrial origin [9 ], and based on studies with free amino, desamino, and acetylated derivatives of the potent model peptide fMLF, it was believed that the formyl group was of utmost importance for the binding affinity and function of the chemoattractant. The formyl group may, however, be less essential than these studies gave reason to believe. Recent work reveals that FPR also recognizes nonformylated peptides as well as peptides with several other modifications, which all bind with high affinity and activate the receptor (Table 1) [16 , 24 , 25 ]. In addition, FPR recognizes and is activated by peptides that lack all sequence similarities with the peptides originally isolated from bacteria. Prominent examples of such proteins/peptides are, e.g., the GP-41 envelope protein of the human immunodeficiency virus type 1 [26 ], a peptide from glycoprotein G of herpes simplex virus type 2 [27 ], one member of the annexin family of calcium-regulated proteins [28 29 30 31 ], and the synthetic peptide WKYMVm [32 ]. Although no defined structure has been identified to be the determinant for FPR binding and activation, the close relationship between structural variation and function is illustrated by the fact that substitution of the carboxyterminal D-methionine in WKYMVm for the L-isomer generates a peptide that loses most of the FPR-binding affinity [33 ], and replacement of the formyl group in fMLF by a tert-Boc (tBoc) group generates a receptor-specific antagonist with low receptor affinity [34 ]. The antagonistic power of such peptides has also been shown to be influenced by other modifications at the N- or C-terminus of the peptide [10 , 11 ].

The structural domain of FPR that is involved in ligand binding has been suggested to include the second as well as the fifth transmembrane regions, and based on the fact that binding, not only of fMLF but also of other FPR agonists, is inhibited by the two known FPR antagonists, it seems reasonable to assume that they all use the same (or closely associated) binding structures/sites of the receptor. Subsequently, agonists that bind to another receptor site may be incorrectly considered as non-FPR binders if the antagonists are without effect. Moreover, the antagonistic properties of some of the Boc peptides are not totally specific, as illustrated by the fact that receptors other than FPR may also be blocked [30 ]. No such overlap has been shown to occur when using the cyclic peptide cyclosporin H (CsH) as antagonist, suggesting that the results obtained on receptor-specific events using this peptide should be more reliable than results obtained with Boc peptides. CsH has no direct resemblance with known peptide agonists, but despite this, it is a more potent and specific FPR antagonist than the Boc peptides [35 , 36 ].

The effects of antagonists in animal studies, together with the fact that mice lacking the murine FPR counterpart display increased susceptibility to infection, clearly illustrate the importance of FPR in host defense and/or inflammation [28 , 37 38 39 ]. It should be noticed, however, that the murine model is not totally translational to the human counterpart. The mouse has six genes with homologies to the human FPRs [40 ]; Fpr1 is a functional receptor for formylated peptides and has thus been classified as the ortholog of the human FPR [37 ]. However, the prototypic FPR agonist fMLF is a much less potent stimulus of murine than of human neutrophils [41 42 43 ]. The murine receptors Fpr-rs1 and Fpr-rs2 are more similar to FPRL1, sharing 74% and 76% aa identity, respectively, with this receptor [40 ]. In agreement with this, the weak FPRL1 agonist fMLF also binds Fpr-rs2, although with even lower affinity [44 ]. Although the FPRL1/FPRL2 agonist WKYMVM is a potent activator of murine neutrophils [41 , 42 ], our knowledge about the murine receptor preference for this agonist or agonists in general is insufficient. It is, however, evident that activation through these receptors induces similar functional responses as for those in humans [28 , 37 , 41 , 42 , 45 ], and at least in part, the same regulatory events are governed by human and murine receptors [42 ].

Structural and functional characteristics of FPR/FPRL1
In addition to the FPR, neutrophils express one of the FPRLs, FPRL1. For some years after its initial identification, FPRL1 was considered an orphan receptor, but following the discovery of FPRL1-specific ligands, it has become obvious that this receptor possesses large, functional similarities with the FPR [46 , 47 ]. The LXA4 was the first specific agonist shown to bind to FPRL1 with high affinity, and in contrast to the large number of other FPRL1 agonists identified in recent years, this agonist was described to be an inhibitor of neutrophil functions [48 ]. No pattern has yet been defined for the FPRL1-activating agonists (Table 1) , and the structural domain in FPRL1, which is responsible for ligand binding, has been suggested to involve different parts of the receptor, depending on the particular ligand [49 ]. The triggering of FPRL1 by stimuli, which have the ability to also activate FPR, is not affected by the two FPR antagonists Boc-MLF and CsH described earlier (although FPR binding is inhibited). This suggests that although certain agonists are recognized by both FPR and FPRL1, binding of these agonists to the two receptors does not involve identical binding structures/sites.

A number of different endogenous as well as microbial-derived agonists have been described for FPR and FPRL1 (Table 1) , but nothing is known at present about the precise role of any of these molecules in innate immune responses or in inflammatory reactions associated with different disease conditions. Besides the identification of various FPR and FPRL1 agonists, a number of specific antagonists have also been described. Replacement of the formyl group in the prototype agonist fMLF with a tBoc or isopropylureido group yields FPR antagonists, and the potency of such antagonists can be changed through a replacement and/or conformational change of the aa comprised in a peptide. A recent search for new FPR antagonists, using a ligand-based virtual screening technique, identified 30 different FPR antagonistic compounds belonging to nine distinct chemical families [50 ], suggesting that there will be an increasing number of antagonists also identified for FPRL1. The only FPRL1-specific antagonist described so far is the recently identified hexapeptide, WRWWWW [12 ]. This peptide has no effect on FPR signaling but blocks activation by most (but not all) FPRL1 agonists (our own unpublished observation and ref. [12 ]). The WRWWWW peptide also affects cellular activities mediated by FPRL2 (our unpublished observations), the FPR family member expressed selectively in cells of the monocytic linage.

Mature but resting neutrophils have little de novo protein synthesis, and their ability to mount a rapid response relies on preformed receptor molecules sorted into intracellular granules and/or the plasma membrane [51 ]. The two neutrophil FPRs are not present in promyelocytes, suggesting that both are expressed fairly late during neutrophil differentiation [32 ]. The two receptors also have the same subcellular distribution, revealed by fractionation studies, showing that the major portions are localized in the gelatinase and specific granules, mobilizable organelles that are translocated to the cell surface by priming agents such as bacterial lipopolysaccharides (LPS) and tumor necrosis factor {alpha} (TNF-{alpha}), as well as during extravasation from the bloodstream [32 , 52 , 53 ].

Binding of FPR and FPRL1 ligands to their respective receptor induces a variety of leukocyte activities, including the motor-driven events associated with the chemotactic locomotory response, believed to correlate with the transendothelial migration of neutrophils responding to a danger signal during inflammation. The fact that neutrophils, having exudated during an aseptic inflammation, are primed in their response to FPR and FPRL1 agonists [32 ] rather than being desensitized (ref. [54 ] and see below) suggests that neither of these receptors is involved in the cellular recruitment. Other functional responses include chemoattractant-induced mobilization of granules and generation of superoxide anions as a result of an activation of the neutrophil reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase.

Anti-inflammatory activities through FPR and FPRL1
Lipoxin formation and action have been shown to be of physiological relevance for the resolution of inflammation, and this inhibitory approach is currently developed as anti-inflammatory therapies. Neutrophils have been suggested to be important for the generation of potent lipid mediators and in the protective signaling [55 , 56 ]. Accordingly, LXA4 was the first high-affinity ligand described for FPRL1. The lipid was shown to activate monocytes through FPRL1, but its most prominent activity was the inhibition of neutrophil functions using the same receptor [56 , 57 ]. It is puzzling how LXA4 is capable of inducing pro- and anti-inflammatory activities through the same receptor, but it should be noticed that the binding data on which the identity of the receptor for LXA4 relies [48 ] lack some of the basic information required to interpret the results properly. Regarding the anti-inflammatory activities, these have been suggested to be mediated by two different mechanisms: LXA4 competes with activating agonists for binding to FPRL1, and binding of LXA4 switches the function of FPRL1 toward the generation of a not-yet-identified, inhibitory signal [58 , 59 ], suggested to involve a novel polyisoprenyl phosphate signaling pathway [60 ]. It is obvious that FPR and FPRL1 have the ability to transduce inhibitory signals (see Receptor Desensitization), and FPR has been suggested to possess the same type of signaling switch mechanism when triggered by peptides corresponding to N-terminal cleavage products of the calcium-regulated phospholipid-binding protein annexin I [13 , 28 , 61 ]. This event is even more puzzling, as both signals are suggested to be generated, not only by the same receptor but also in the same cell type. The fact that Boc derivatives block cellular activities induced by annexin I peptides supports the involvement of FPR [62 ], but based on studies of competitive binding with LXA4, it has been suggested that the full-length annexin I molecule as well as peptides derived from its N-terminal part inhibit neutrophil function through interaction with FPRL1 rather than with FPR [30 ]. However, these receptor-binding data also lack some basic background information required to evaluate the results properly, and the fact that Boc derivatives may also inhibit signaling through receptors other than FPR [30 ] raises a question about the receptor(s) responsible for the different responses triggered by annexin I peptides.

Based on neutrophil experiments confirming that LXA4 lacks the ability to generate cell-activating signals through FPRL1 but also showing that LXA4 is unable to desensitize FPRL1 or compete with a specific peptide agonist for receptor binding [63 ], we have suggested that LXA4 has a receptor distinct from FPRL1. These results imply that the inhibitory signals generated in neutrophils by LXA4 are not transduced through FPRL1. This would be in agreement with results obtained with human renal mesangial cells, showing that LXA4 stimulation involves a receptor distinct from FPRL1 [64 ].

It is also of interest that annexin I has been shown to have binding sites distinct from the FPR family members [65 ]. With respect to the dual signaling induced by annexin I-related peptides, we have shown recently, using a somewhat shorter peptide than those discussed above, that the proinflammatory (neutrophil-activating) signals are generated by FPR, whereas the anti-inflammatory (neutrophil-inhibiting) signals are generated by a receptor distinct from FPR and FPRL1 [31 ]. The identity of the receptor inducing an inhibitory signal remains to be elucidated.


   RECEPTOR DESENSITIZATION
TOP
 INTRODUCTION
 NEUTROPHIL FPR
 RECEPTOR DESENSITIZATION
NEUTROPHIL SIGNALING BY FPR...
 FUTURE PERSPECTIVES
 REFERENCES
 
Receptor cross-talk and hierarchy
When neutrophils encounter increasing concentration of a chemoattractant, they gradually become nonresponsive to further stimulation by the same agonist. This process, known as homologous desensitization [66 ], is also important to limit or terminate the response to higher concentrations of an attractant, avoiding prolonged activation and thereby a continuation of an inflammatory event. Cells desensitized to FPR or FPRL1 agonists are also desensitized to a second stimulation with the GPCR agonists IL-8 or PAF, suggesting the existence of a hierarchical receptor cross-talk within the GPCR receptor family [47 , 67 ]. This type of hierarchy may be of importance in guiding the neutrophils to the site of bacterial infections when facing multiple gradients of different chemoattractants. Cross-desensitization experiments with specific FPR and FPRL1 agonists have suggested that these receptors are hierarchically, equally strong. It is important to point out that receptor desensitization is a highly regulated process, and the mechanism differs depending on the receptor studied and the type of desensitization involved. The phosphorylation of occupied GPCRs by specific GPCR kinases, ß-arrestin binding, phosphorylation of nonoccupied GPCR by second messengers, and physical GPCR coupling to the cytoskeleton are proposed mechanisms by which these receptors are desensitized [6 , 68 ]. With respect to FPR and FPRL1, receptor binding to the cytoskeleton is most probably an important mechanism in desensitization, but it is definitely not the only mechanism operating [69 ]. It is also important to point out that although agonist binding to FPR and FPRL1 triggers inhibitory signals that also desensitize unrelated receptors, desensitization experiments alone cannot be used to determine the identity of the receptor involved when cells are triggered by a new agonist.

Receptor coupling to the cytoskeleton and the basis for reactivation
The importance of the actin cytoskeleton beneath the neutrophil cell membrane (also known as the cortical cytoskeleton) for regulation of cellular processes is supported clearly by the fact that disruption of this actin network inhibits cell locomotion and phagocytosis and at the same time, facilitates secretion [70 ]. Remodeling of the cytoskeleton is regulated tightly by multiple mechanisms involving a large number of actin-binding proteins, actin regulatory proteins, and second messengers (such as Ca2+), small guanosine 5'-triphosphate-binding proteins, and formation/degradation of membrane lipid phosphatidylinositols [71 ]. Cytochalasins are a group of fungal products, which bind to the so-called plus end of actin filaments and thereby prevent actin polymerization [72 ]. Treatment of neutrophils with cytochalasins enhances the rate and duration of fMLF- as well as of WKYMVM-induced superoxide production. As opposed to this, the oxidative response induced by phorbol myristate acetate (a protein kinase C activator, which bypasses the receptor activation level) is unaffected by the presence of cytochalasin [47 , 73 ]. This indicates an involvement of the cytoskeleton in FPR/FPRL1 desensitization and NADPH-oxidase termination (Fig. 2 ). The basis for such cytoskeleton-dependent GPCR desensitization is a direct cessation of the intracellular signaling when the receptor-ligand complex is coupled to the cytoskeleton. The association of the receptor-ligand complex to the cytoskeleton physically segregates the receptor from the signaling G protein into different plasma membrane domains [68 ]. The precise mechanism for how activated receptors become associated with the actin cytoskeleton and how this association separates the receptor from the G protein is not yet understood. Sequence comparison of actin-binding proteins with the cytoplasmic domains of FPR reveals a 15 aa-long sequence, which displays 40–50% identity with the actin-binding proteins coronin [74 ] and vinculin [75 ]. It is interesting that this actin-binding sequence is located in a signaling region that contains several potential phosphorylation sites [76 ]. This raises the question of whether binding to the cytoskeleton interferes with receptor phosphorylation and/or with G protein interaction. Future studies focusing on the structure-function relationship between the involved molecules are required to shed more light on and increase our understanding of the role of the cytoskeleton in GPCR desensitization.


Figure 2
View larger version (23K):
[in this window]
[in a new window]
  		Figure 2. Schematic drawing of the FPR and FPRL1 in different stages of activation, deactivation, and reactivation. (a) The deactivation state can be reached directly, if the interaction occurs at 15°C, or following an activation process, if the interaction occurs at 37°C, but to reduce the complexity of the figure, we have only included one deactivated state, common for neutrophil-agonist interaction at 15°C as well as 37°C. It should be pointed out, however, that the deactivated state might differ in some respects depending on the temperature during which the induction occurs. PMNL, Polymorphonuclear leukocytes. (b) Deactivation induced by ligand binding to FPR, FPRL1, or C5aR also results in a deactivation of the response to PAF, IL-8, and LTB4 (heterologous deactivation/desensitization).

 
Desensitized/deactivated FPR/FPRL1 can be reactivated to produce superoxide by the secondary addition of a cytoskeleton-disrupting agent such as cytochalasin B [47 , 69 ], further supporting the notion that desensitization relies on an intact actin cytoskeleton (Fig. 2) . However, the phenomenon of the cytochalasin B-induced GPCR reactivation is by no means a rule; i.e., cells desensitized to IL-8 or PAF cannot be reactivated [77 ]. It is important to remember that neutrophils are also equipped with other deactivation systems, in addition to the cytoskeletal network, which can turn the superoxide-generating NADPH oxidase off. Direct phosphorylation of the signaling receptor has been demonstrated previously to be such a mechanism in the visual system [78 ] and in the ß-adrenergic receptor system [79 ]. The existence of other desensitization systems besides the cytoskeleton is made obvious by experiments showing that the IL-8- or PAF-triggered superoxide production is unaffected by the presence of cytochalasin B and is somehow terminated much more rapidly than the fMLF- or WKYMVM-triggered response [47 ].


   NEUTROPHIL SIGNALING BY FPR AND FPRL1
TOP
 INTRODUCTION
 NEUTROPHIL FPR
 RECEPTOR DESENSITIZATION
 NEUTROPHIL SIGNALING BY FPR...
FUTURE PERSPECTIVES
 REFERENCES
 
Activation similarities and the role of intracellular Ca2+
The biology of FPR and the downstream signaling pathways it activates have been studied extensively as a model system in GPCR research, and details about the signal transduction pathways for the onset of discrete neutrophil functions can be found in several recent reviews [6 , 16 , 76 , 80 ]. In contrast, little is known about signaling from FPRL1, but it is reasonable to assume that it uses similar signaling pathways as FPR, an assumption based on the facts that the two receptors are structurally similar, and the cellular responses they induce are almost identical. In brief, neutrophil signaling upon chemoattractant stimulation through FPR and FPRL1 starts with a rapid, conformational change of the occupied receptor followed by a dissociation of G proteins into two parts: the {alpha} and ß{gamma} subunits [81 ]. The dissociated protein subunits activate multiple downstream second messengers, including various phospholipases and protein kinases [6 , 82 ]. It is obvious that despite a profound, functional similarity regarding the cellular responses mediated through various GPCRs, they use distinct signaling pathways or different signaling molecules for specialized cellular responses [67 , 83 , 84 ].

An immediate consequence of the production of inositol 1,4,5-trisphosphate (IP3) upon cleavage of membrane phosphatidylinositol 4,5 bisphosphate (PIP2) by phospholipase C (PLC) is the transient elevation of intracellular Ca2+, characterized by a release of Ca2+ from intracellular Ca2+ storage organelles exposing IP3 receptors [85 ]. In resting neutrophils, the cytosolic Ca2+ concentration is kept at low levels (~100 nM) as compared with the level outside of the cells. However, the cytosolic concentration can rise up to µM levels upon chemoattractant stimulation and then return to basal levels quite rapidly. Such a transient rise in Ca2+ has long been considered essential for various neutrophil functions; however, recent evidence indicates that an elevation of Ca2+ alone is neither sufficient nor required for certain FPR/FPRL1-mediated neutrophil responses. It is clear that although the cytoskeleton-remodeling proteins require Ca2+ for proper function [86 ], cytoskeleton-dependent cellular processes such as neutrophil polarization, membrane ruffling, chemotaxis, and phagocytosis can also take place in Ca2+-depleted cells [87 ]. With respect to activation of the superoxide-generating system, an increase of intracellular Ca2+ alone is not sufficient [88 ], and it can occur without an elevation of cytosolic Ca2+ [47 , 69 , 77 ]. In line with the non-Ca2+ dependency, exocytosis of neutrophil secretory vesicles induced by fMLF or LTB4 is extensive, even in a Ca2+-free buffer [52 ]. Moreover, a transient elevation of Ca2+ alone is not sufficient for the low level of neutrophil azurophilic granule mobilization induced during fMLF stimulation; a second synergistic signal is required [89 , 90 ].

Despite the fact that the two highly related receptors, FPR and FPRL1, recognize ligands with large, structural diversities [91 ], the receptors induce almost indistinguishable cellular responses [33 , 46 , 47 , 69 ]. Both receptors can be primed by TNF-{alpha} and LPS to the same degree, and they can undergo desensitization/reactivation when coupled to/uncoupled from the cytoskeleton [47 ]. Results obtained from studies in leukocytes and in receptor-transfected cell lines show that FPR- and FPRL1-induced responses are sensitive to PTX, a toxin that inactivates G proteins through adenosine 5'-diphosphate ribosylation; i.e., both receptors transduce signals through G proteins [92 ], possibly through Gi1 and Gi2. Studies using synthetic peptides and fusion proteins derived from the intracellular regions of the FPR predict that the second intracellular loop and the carboxyl-terminal tail are important for effective FPR/G protein coupling, unlike the findings presented for other GPCR systems such as ß-adrenergic receptors and the muscarinic acetylcholine receptor, in which the third intracellular loop is of importance for G protein signaling [93 ].

Distinct differences between FPR and FPRL1 signaling
The plasma membranes of many cells, including neutrophils, contain a type of liquid-ordered microdomains or lipid rafts, enriched in cholesterol and suggested to be of prime importance in the outside-in signaling, leading to priming or a direct cellular activation [94 95 96 ]. The signaling machinery as well as the active signaling receptors have to be localized to these lipid microdomains for maximal signaling activity [95 ]. Treatment of cells with cholesterol-depleting reagents disrupt the integrity of the rafts, and such an approach has been used to determine the importance of the microdomains in signaling through FPR and FPRL1. Cholesterol depletion had little effect on the neutrophil response to high concentrations of a FPR agonist, whereas the response induced by a FPRL1 agonist was impaired greatly [97 ]. The exact mechanism involved is yet to be determined, but the proposed hypothesis suggests a difference between the two receptors in their ability to couple to the signaling G protein, a process affected by the disruption of the lipid rafts [97 ].

In attempts to investigate the role of the cytoskeletal protein gelsolin in neutrophil activation, a cell-permeable peptide, PBP10, was used. The sequence of PBP10 corresponds to the PIP2 binding region of gelsolin [98 ], and this peptide selectively blocks FPRL1-mediated activation [99 ]. The activity triggered by the FPRL1-specific agonist WKYMVM was blocked by PBP10 with a 50% inhibitory concentration of 0.05 µM, whereas PBP10 was without any inhibitory effect on the FPR-specific agonist fMLF, even at concentrations up to 10 µM. Treatment of neutrophils with PBP10 prior to WKYMVM stimulation did not alter the Ca2+ response, suggesting that the PBP10-mediated, inhibitory effect on the FPRL1 response is independent of PLC and affects a signal generated in a PLC-independent signaling pathway. Additional results further supporting the notion that PBP10 affects intracellular signaling induced preferentially by FPRL1 are that a cell-impermeable peptide containing the same aa sequence as PBP10 was without effect on a FPRL1-mediated cellular response; cell-permeable peptides with reduced affinity for PIP2 inhibited the WKYMVM-induced response to a lower degree; the activation with another FPRL1-specific agonist was also inhibited by PBP10; and PBP10 was without effect when fMLF was replaced by another FPR-specific agonist. Apparently, this PBP10-sensitive pathway is essential and selective for FPRL1-mediated responses in human neutrophils. It is intriguing that fMLF-induced responses could be inhibited by PBP10 but only if the cytoskeleton was disrupted previously by cytochalasin B. Thus, FPR has the ability to trigger the PBP10-sensitive signaling, but this pathway is normally blocked by the cytoskeletal network [99 ].

Taken together, these data clearly demonstrate many functional similarities between FPR and FPRL1 but at the same time, points to the existence of a fundamental difference in intracellular signaling between the two neutrophil receptors. The precise mechanism by which PBP10 selectively interferes with the signaling pathway used by FPRL1 and the manner in which the cytoskeleton blocks/competes with the PBP10-sensitive pathway when FPR is stimulated remain to be investigated. Future studies could potentially use PBP10 as a tool to probe the PIP2 signaling and also to study the importance of the PBP10-sensitive signaling pathway from FPR and/or FPRL1, expressed in other cell types such as astrocytes and microglia cells.


   FUTURE PERSPECTIVES
TOP
 INTRODUCTION
 NEUTROPHIL FPR
 RECEPTOR DESENSITIZATION
 NEUTROPHIL SIGNALING BY FPR...
 FUTURE PERSPECTIVES
REFERENCES
 
During the last decade, a broad application of cellular and molecular biology technologies has generated an impressive amount of knowledge about the FPR family in terms of structure, expression patterns, signaling processes, biological roles, and regulation of signaling. This increase in knowledge would not have been possible before the genes encoding the different receptors were cloned, and the possibilities for exogenous expression or selective knockout systems were at hand. The extensively used mouse model systems have, however, several limitations. Mice and men have encountered different evolutionary pressures and by that, developed distinct and sometimes unique ways/solutions to combat invading microbes and to regulate inflammation. Moreover, cells used for exogenous receptor expression often lack the functional repertoire and the complexity in signaling that characterize professional phagocytes.

Although research about FPR continues and our understanding of its role increases, regarding the aspects of structure/function, intracellular signaling, and importance in innate immunity, it is interesting to note that FPRL1 has switched from being an orphan FPR homologue to being considered a promiscuous receptor, important in its own right. Future research will undoubtedly generate large amounts of interesting data and possibly uncover unique features of this receptor. The research will hopefully also reveal whether the receptors in the FPR family should be considered promiscuous with affinity for a number of different agonists or if the apparently unrelated agonists turn out to share a common pattern on a higher level than the sequence of aa. This common pattern may well be on a physico-chemical level or could be of a more subtle nature, where the receptors could be considered pattern recognition entities or sensors of danger signals. There may also be pathophysiological roles of FPRL1, as indicated by the association with multiple inflammatory neurodegenerative disease and amyloidosis [100 101 102 ]. This again highlights the notion of the inflammatory process being a double-edged sword that needs to be controlled carefully. Considering the implication of GPCRs in the pathogenesis of multiple inflammatory diseases, it is tempting to speculate that FPR/FPRL1 may potentially be used as targets for a novel, anti-inflammatory drug design in the future. However, to develop better and more selective prophylactic or treatment strategies against inflammatory diseases, it is of importance to understand the molecular mechanisms as well as the precise signaling pathways underlying FPR/FPRL1 activation in phagocytes as well as other cells. As for FPR and FPRL1, an expansion in basic knowledge and pathophysiological roles for the third human member of the formyl peptide family, FPRL2, may be expected in the coming years.

Received September 5, 2005; revised October 6, 2005; accepted October 28, 2005.


   REFERENCES
TOP
 INTRODUCTION
 NEUTROPHIL FPR
 RECEPTOR DESENSITIZATION
 NEUTROPHIL SIGNALING BY FPR...
 FUTURE PERSPECTIVES
 REFERENCES
 

  1. Tauber, A.I., Chernyak, L. (1991) Metchnikoff and the Origins of Immunology Oxford University Press New York, NY.
  2. Boyden, S. (1962) The chemotactic effect of mixtures of antibody and antigen on polymorphonuclear leucocytes J. Exp. Med. 115,453-466[Abstract]
  3. Brown Cramer, E. (1992) Cell biology of phagocyte migration Gallin, J. I. Goldstein, I. M. Snyderman, R. eds. Inflammation: Basic Principles and Clinical Correlates ,341-351 Raven New York, NY.
  4. Schiffmann, E., Corcoran, B. A., Wahl, S. M. (1975) N-formylmethionyl peptides as chemoattractants for leucocytes Proc. Natl. Acad. Sci. USA 72,1059-1062[Abstract/Free Full Text]
  5. Uhing, R.J., Snyderman, R. (1999) Chemoattractant stimulus-response coupling Gallin, J.I. Snyderman, R. eds. Inflammation: Basic Principles and Clinical Correlates ,607-626 Lippincott Williams & Wilkins Philadelphia, PA.
  6. Miller, A. F., Falke, J. J. (2004) Chemotaxis receptors and signaling Adv. Protein Chem. 68,393-444[Medline]
  7. Ye, R. D., Boulay, F. (1997) Structure and function of leukocyte chemoattractant receptors Adv. Pharmacol. 39,221-289[Medline]
  8. Murphy, P. M. (1994) The molecular biology of leukocyte chemoattractant receptors Annu. Rev. Immunol. 12,593-633[CrossRef][Medline]
  9. Rabiet, M. J., Huet, E., Boulay, F. (2005) Human mitochondria-derived N-formylated peptides are novel agonists equally active on FPR and FPRL1, while Listeria monocytogenes-derived peptides preferentially activate FPR Eur. J. Immunol. 35,2486-2495[CrossRef][Medline]
  10. Dalpiaz, A., Ferretti, M. E., Vertuani, G., Traniello, S., Scatturin, A., Spisani, S. (2002) C- and N-terminal residue effect on peptide derivatives’ antagonism toward the formyl-peptide receptor Eur. J. Pharmacol. 436,187-196[CrossRef][Medline]
  11. Dalpiaz, A., Ferretti, M. E., Pecoraro, R., Fabbri, E., Traniello, S., Scatturin, A., Spisani, S. (1999) Phe-D-Leu-Phe-D-Leu-Phe derivatives as formylpeptide receptor antagonists in human neutrophils: cellular and conformational aspects Biochim. Biophys. Acta 1432,27-39[CrossRef][Medline]
  12. Bae, Y. S., Lee, H. Y., Jo, E. J., Kim, J. I., Kang, H. K., Ye, R. D., Kwak, J. Y., Ryu, S. H. (2004) Identification of peptides that antagonize formyl peptide receptor-like 1-mediated signaling J. Immunol. 173,607-614[Abstract/Free Full Text]
  13. Perretti, M., Flower, R. J. (2004) Annexin 1 and the biology of the neutrophil J. Leukoc. Biol. 76,25-29[Abstract/Free Full Text]
  14. Alten, R., Gromnica-Ihle, E., Pohl, C., Emmerich, J., Steffgen, J., Roscher, R., Sigmund, R., Schmolke, B., Steinmann, G. (2004) Inhibition of leukotriene B4-induced CD11B/CD18 (Mac-1) expression by BIIL 284, a new long-acting LTB4 receptor antagonist, in patients with rheumatoid arthritis Ann. Rheum. Dis. 63,170-176[Abstract/Free Full Text]
  15. Princen, K., Hatse, S., Vermeire, K., Aquaro, S., De Clercq, E., Gerlach, L. O., Rosenkilde, M., Schwartz, T. W., Skerlj, R., Bridger, G., Schols, D. (2004) Inhibition of human immunodeficiency virus replication by a dual CCR5/CXCR4 antagonist J. Virol. 78,12996-13006[Abstract/Free Full Text]
  16. Le, Y., Murphy, P. M., Wang, J. M. (2002) Formyl-peptide receptors revisited Trends Immunol. 23,541-548[CrossRef][Medline]
  17. Murphy, P. M. (1997) Neutrophil receptors for interleukin-8 and related CXC chemokines Semin. Hematol. 34,311-318[Medline]
  18. Boulay, F., Tardif, M., Brouchon, L., Vignais, P. (1990) Synthesis and use of a novel N-formyl peptide derivative to isolate a human N-formyl peptide receptor cDNA Biochem. Biophys. Res. Commun. 168,1103-1109[CrossRef][Medline]
  19. Boulay, F., Tardif, M., Brouchon, L., Vignais, P. (1990) The human N-formylpeptide receptor. Characterization of two cDNA isolates and evidence for a new subfamily of G-protein-coupled receptors Biochemistry 29,11123-11133[CrossRef][Medline]
  20. Ye, R. D., Cavanagh, S. L., Quehenberger, O., Prossnitz, E. R., Cochrane, C. G. (1992) Isolation of a cDNA that encodes a novel granulocyte N-formyl peptide receptor Biochem. Biophys. Res. Commun. 184,582-589[CrossRef][Medline]
  21. Migeotte, I., Riboldi, E., Franssen, J. D., Gregoire, F., Loison, C., Wittamer, V., Detheux, M., Robberecht, P., Costagliola, S., Vassart, G., Sozzani, S., Parmentier, M., Communi, D. (2005) Identification and characterization of an endogenous chemotactic ligand specific for FPRL2 J. Exp. Med. 201,83-93[Abstract/Free Full Text]
  22. Sahagun-Ruiz, A., Colla, J. S., Juhn, J., Gao, J. L., Murphy, P. M., McDermott, D. H. (2001) Contrasting evolution of the human leukocyte N-formylpeptide receptor subtypes FPR and FPRL1R Genes Immun. 2,335-342[CrossRef][Medline]
  23. Fu, H., Dahlgren, C., Bylund, J. (2003) Subinhibitory concentrations of the deformylase inhibitor actinonin increase bacterial release of neutrophil-activating peptides: a new approach to antimicrobial chemotherapy Antimicrob. Agents Chemother. 47,2545-2550[Abstract/Free Full Text]
  24. Gao, J. L., Becker, E. L., Freer, R. J., Muthukumaraswamy, N., Murphy, P. M. (1994) A high potency nonformylated peptide agonist for the phagocyte N-formylpeptide chemotactic receptor J. Exp. Med. 180,2191-2197[Abstract/Free Full Text]
  25. Chen, J., Bernstein, H. S., Chen, M., Wang, L., Ishii, M., Turck, C. W., Coughlin, S. R. (1995) Tethered ligand library for discovery of peptide agonists J. Biol. Chem. 270,23398-23401[Abstract/Free Full Text]
  26. Su, S. B., Gao, J., Gong, W., Dunlop, N. M., Murphy, P. M., Oppenheim, J. J., Wang, J. M. (1999) T21/DP107, a synthetic leucine zipper-like domain of the HIV-1 envelope gp41, attracts and activates human phagocytes by using G-protein-coupled formyl peptide receptors J. Immunol. 162,5924-5930[Abstract/Free Full Text]
  27. Bellner, L., Thoren, F., Nygren, E., Liljeqvist, J. A., Karlsson, A., Eriksson, K. (2005) A proinflammatory peptide from herpes simplex virus type 2 glycoprotein G affects neutrophil, monocyte, and NK cell functions J. Immunol. 174,2235-2241[Abstract/Free Full Text]
  28. Gavins, F. N., Yona, S., Kamal, A. M., Flower, R. J., Perretti, M. (2003) Leukocyte antiadhesive actions of annexin 1: ALXR- and FPR-related anti-inflammatory mechanisms Blood 101,4140-4147[Abstract/Free Full Text]
  29. Walther, A., Riehemann, K., Gerke, V. (2000) A novel ligand of the formyl peptide receptor: annexin I regulates neutrophil extravasation by interacting with the FPR Mol. Cell 5,831-840[CrossRef][Medline]
  30. Perretti, M., Chiang, N., La, M., Fierro, I. M., Marullo, S., Getting, S. J., Solito, E., Serhan, C. N. (2002) Endogenous lipid- and peptide-derived anti-inflammatory pathways generated with glucocorticoid and aspirin treatment activate the lipoxin A4 receptor Nat. Med. 8,1296-1302[CrossRef][Medline]
  31. Karlsson, J., Fu, H., Boulay, F., Dahlgren, C., Hellstrand, K., Movitz, C. (2005) Neutrophil NADPH-oxidase activation by an annexin AI peptide is transduced by the formyl peptide receptor (FPR), whereas an inhibitory signal is generated independently of the FPR family receptors J. Leukoc. Biol. 78,762-771[Abstract/Free Full Text]
  32. Dahlgren, C., Christophe, T., Boulay, F., Madianos, P. N., Rabiet, M. J., Karlsson, A. (2000) The synthetic chemoattractant Trp-Lys-Tyr-Met-Val-D-Met activates neutrophils preferentially through the lipoxin A(4) receptor Blood 95,1810-1818[Abstract/Free Full Text]
  33. Christophe, T., Karlsson, A., Dugave, C., Rabiet, M. J., Boulay, F., Dahlgren, C. (2001) The synthetic peptide Trp-Lys-Tyr-Met-Val-Met-NH2 specifically activates neutrophils through FPRL1/lipoxin A4 receptors and is an agonist for the orphan monocyte-expressed chemoattractant receptor FPRL2 J. Biol. Chem. 276,21585-21593[Abstract/Free Full Text]
  34. Freer, R. J., Day, A. R., Radding, J. A., Schiffmann, E., Aswanikumar, S., Showell, H. J., Becker, E. L. (1980) Further studies on the structural requirements for synthetic peptide chemoattractants Biochemistry 19,2404-2410[CrossRef][Medline]
  35. Dalpiaz, A., Pecoraro, R., Vertuani, G., Spisani, S., Rizzuti, O., Fabbri, E., Scatturin, A. (1999) Formylpeptide receptor antagonists: structure and activity Boll. Chim. Farm. 138,44-48[Medline]
  36. Wenzel-Seifert, K., Seifert, R. (1993) Cyclosporin H is a potent and selective formyl peptide receptor antagonist. Comparison with N-t-butoxycarbonyl-L-phenylalanyl-L-leucyl-L-phenylalanyl-L- leucyl-L-phenylalanine and cyclosporins A, B, C, D, and E J. Immunol. 150,4591-4599[Abstract]
  37. Gao, J. L., Lee, E. J., Murphy, P. M. (1999) Impaired antibacterial host defense in mice lacking the N-formylpeptide receptor J. Exp. Med. 189,657-662[Abstract/Free Full Text]
  38. Fillion, I., Ouellet, N., Simard, M., Bergeron, Y., Sato, S., Bergeron, M. G. (2001) Role of chemokines and formyl peptides in pneumococcal pneumonia-induced monocyte/macrophage recruitment J. Immunol. 166,7353-7361[Abstract/Free Full Text]
  39. Gavins, F. N., Kamal, A. M., D’Amico, M., Oliani, S. M., Perretti, M. (2005) Formyl-peptide receptor is not involved in the protection afforded by annexin 1 in murine acute myocardial infarct FASEB J. 19,100-102[Abstract/Free Full Text]
  40. Gao, J. L., Chen, H., Filie, J. D., Kozak, C. A., Murphy, P. M. (1998) Differential expansion of the N-formylpeptide receptor gene cluster in human and mouse Genomics 51,270-276[CrossRef][Medline]
  41. He, R., Tan, L., Browning, D. D., Wang, J. M., Ye, R. D. (2000) The synthetic peptide Trp-Lys-Tyr-Met-Val-D-Met is a potent chemotactic agonist for mouse formyl peptide receptor J. Immunol. 165,4598-4605[Abstract/Free Full Text]
  42. Bylund, J., Samuelsson, M., Collins, L. V., Karlsson, A. (2003) NADPH-oxidase activation in murine neutrophils via formyl peptide receptors Exp. Cell Res. 282,70-77[CrossRef][Medline]
  43. Sugawara, T., Miyamoto, M., Takayama, S., Kato, M. (1995) Separation of neutrophils from blood in human and laboratory animals and comparison of the chemotaxis J. Pharmacol. Toxicol. Methods 33,91-100[CrossRef][Medline]
  44. Hartt, J. K., Barish, G., Murphy, P. M., Gao, J. L. (1999) N-formylpeptides induce two distinct concentration optima for mouse neutrophil chemotaxis by differential interaction with two N-formylpeptide receptor (FPR) subtypes. Molecular characterization of FPR2, a second mouse neutrophil FPR J. Exp. Med. 190,741-747[Abstract/Free Full Text]
  45. Kenny, M. T., Torney, H. L., Balistreri, F. J. (1989) Comparative effect of the naphthalenic ansamycins rifamycin SV, rifampin and cyclopentylrifampicin on murine neutrophil function Int. J. Immunopharmacol. 11,915-920[CrossRef][Medline]
  46. Betten, A., Dahlgren, C., Hermodsson, S., Hellstrand, K. (2003) Histamine inhibits neutrophil NADPH oxidase activity triggered by the lipoxin A4 receptor-specific peptide agonist Trp-Lys-Tyr-Met-Val-Met Scand. J. Immunol. 58,321-326[CrossRef][Medline]
  47. Fu, H., Bylund, J., Karlsson, A., Pellme, S., Dahlgren, C. (2004) The mechanism for activation of the neutrophil NADPH-oxidase by the peptides formyl-Met-Leu-Phe and Trp-Lys-Tyr-Met-Val-Met differs from that for interleukin-8 Immunology 112,201-210[CrossRef][Medline]
  48. Fiore, S., Maddox, J. F., Perez, H. D., Serhan, C. N. (1994) Identification of a human cDNA encoding a functional high-affinity lipoxin A4 receptor J. Exp. Med. 180,253-260[Abstract/Free Full Text]
  49. Le, Y., Ye, R. D., Gong, W., Li, J., Iribarren, P., Wang, J. M. (2005) Identification of functional domains in the formyl peptide receptor-like 1 for agonist-induced cell chemotaxis FEBS J. 272,769-778[CrossRef][Medline]
  50. Edwards, B. S., Bologa, C., Young, S. M., Balakin, K. V., Prossnitz, E. R., Savchuck, N. P., Sklar, L. A., Oprea, T. I. (2005) Integration of virtual screening with high throughput flow cytometry to identify novel small molecule formylpeptide receptor antagonists Mol. Pharmacol. 68,1301-1310[Abstract/Free Full Text]
  51. Faurschou, M., Borregaard, N. (2003) Neutrophil granules and secretory vesicles in inflammation Microbes Infect. 5,1317-1327[CrossRef][Medline]
  52. Sengelov, H., Kjeldsen, L., Borregaard, N. (1993) Control of exocytosis in early neutrophil activation J. Immunol. 150,1535-1543[Abstract]
  53. Bylund, J., Karlsson, A., Boulay, F., Dahlgren, C. (2002) Lipopolysaccharide-induced granule mobilization and priming of the neutrophil response to Helicobacter pylori peptide Hp(2-20), which activates formyl peptide receptor-like 1 Infect. Immun. 70,2908-2914[Abstract/Free Full Text]
  54. Follin, P., Wymann, M. P., Dewald, B., Ceska, M., Dahlgren, C. (1991) Human neutrophil migration into skin chambers is associated with production of NAP-1/IL8 and C5a Eur. J. Haematol. 47,71-76[Medline]
  55. Serhan, C. N., Chiang, N. (2004) Novel endogenous small molecules as the checkpoint controllers in inflammation and resolution: entree for resoleomics Rheum. Dis. Clin. North Am. 30,69-95[CrossRef][Medline]
  56. Levy, B. D., Serhan, C. N. (2003) Exploring new approaches to the treatment of asthma: potential roles for lipoxins and aspirin-triggered lipid mediators Drugs Today (Barc.) 39,373-384[Medline]
  57. Serhan, C. N. (2002) Lipoxins and aspirin-triggered 15-epi-lipoxin biosynthesis: an update and role in anti-inflammation and pro-resolution Prostaglandins Other Lipid Mediat. 68-69,433-455
  58. Chiang, N., Fierro, I. M., Gronert, K., Serhan, C. N. (2000) Activation of lipoxin A(4) receptors by aspirin-triggered lipoxins and select peptides evokes ligand-specific responses in inflammation J. Exp. Med. 191,1197-1208[Abstract/Free Full Text]
  59. Fierro, I. M., Colgan, S. P., Bernasconi, G., Petasis, N. A., Clish, C. B., Arita, M., Serhan, C. N. (2003) Lipoxin A4 and aspirin-triggered 15-epi-lipoxin A4 inhibit human neutrophil migration: comparisons between synthetic 15 epimers in chemotaxis and transmigration with microvessel endothelial cells and epithelial cells J. Immunol. 170,2688-2694[Abstract/Free Full Text]
  60. Levy, B. D., Fokin, V. V., Clark, J. M., Wakelam, M. J., Petasis, N. A., Serhan, C. N. (1999) Polyisoprenyl phosphate (PIPP) signaling regulates phospholipase D activity: a "stop" signaling switch for aspirin-triggered lipoxin A4 FASEB J. 13,903-911[Abstract/Free Full Text]
  61. Ernst, S., Lange, C., Wilbers, A., Goebeler, V., Gerke, V., Rescher, U. (2004) An annexin 1 N-terminal peptide activates leukocytes by triggering different members of the formyl peptide receptor family J. Immunol. 172,7669-7676[Abstract/Free Full Text]
  62. Solito, E., Kamal, A., Russo-Marie, F., Buckingham, J. C., Marullo, S., Perretti, M. (2003) A novel calcium-dependent proapoptotic effect of annexin 1 on human neutrophils FASEB J. 17,1544-1546[Abstract/Free Full Text]
  63. Christophe, T., Karlsson, A., Rabiet, M. J., Boulay, F., Dahlgren, C. (2002) Phagocyte activation by Trp-Lys-Tyr-Met-Val-Met, acting through FPRL1/LXA4R, is not affected by lipoxin A4 Scand. J. Immunol. 56,470-476[CrossRef][Medline]
  64. McMahon, B., Stenson, C., McPhillips, F., Fanning, A., Brady, H. R., Godson, C. (2000) Lipoxin A4 antagonizes the mitogenic effects of leukotriene D4 in human renal mesangial cells. Differential activation of MAP kinases through distinct receptors J. Biol. Chem. 275,27566-27575[Abstract/Free Full Text]
  65. Srikrishna, G., Panneerselvam, K., Westphal, V., Abraham, V., Varki, A., Freeze, H. H. (2001) Two proteins modulating transendothelial migration of leukocytes recognize novel carboxylated glycans on endothelial cells J. Immunol. 166,4678-4688[Abstract/Free Full Text]
  66. Ali, H., Richardson, R. M., Haribabu, B., Snyderman, R. (1999) Chemoattractant receptor cross-desensitization J. Biol. Chem. 274,6027-6030[Free Full Text]
  67. Heit, B., Tavener, S., Raharjo, E., Kubes, P. (2002) An intracellular signaling hierarchy determines direction of migration in opposing chemotactic gradients J. Cell Biol. 159,91-102[Abstract/Free Full Text]
  68. Klotz, K. N., Jesaitis, A. J. (1994) Neutrophil chemoattractant receptors and the membrane skeleton Bioessays 16,193-198[CrossRef][Medline]
  69. Bylund, J., Bjorstad, A., Granfeldt, D., Karlsson, A., Woschnagg, C., Dahlgren, C. (2003) Reactivation of formyl peptide receptors triggers the neutrophil NADPH-oxidase but not a transient rise in intracellular calcium J. Biol. Chem. 278,30578-30586[Abstract/Free Full Text]
  70. Howard, T. H., Watts, R. G. (1994) Actin polymerization and leukocyte function Curr. Opin. Hematol. 1,61-68[Medline]
  71. Carlier, M. F. (1998) Control of actin dynamics Curr. Opin. Cell Biol. 10,45-51[CrossRef][Medline]
  72. Maruyama, K., Hartwig, J. H., Stossel, T. P. (1980) Cytochalasin B and the structure of actin gels. II. Further evidence for the splitting of F-actin by cytochalasin B Biochim. Biophys. Acta 626,494-500[Medline]
  73. Jesaitis, A. J., Tolley, J. O., Allen, R. A. (1986) Receptor-cytoskeleton interactions and membrane traffic may regulate chemoattractant-induced superoxide production in human granulocytes J. Biol. Chem. 261,13662-13669[Abstract/Free Full Text]
  74. de Hostos, E. L., Bradtke, B., Lottspeich, F., Guggenheim, R., Gerisch, G. (1991) Coronin, an actin-binding protein of Dictyostelium discoideum localized to cell surface projections, has sequence similarities to G protein ß subunits EMBO J. 10,4097-4104[Medline]
  75. Coutu, M. D., Craig, S. W. (1988) cDNA-derived sequence of chicken embryo vinculin Proc. Natl. Acad. Sci. USA 85,8535-8539[Abstract/Free Full Text]
  76. Prossnitz, E. R., Ye, R. D. (1997) The N-formyl peptide receptor: a model for the study of chemoattractant receptor structure and function Pharmacol. Ther. 74,73-102[CrossRef][Medline]
  77. Bylund, J., Pellme, S., Fu, H., Mellqvist, U. H., Hellstrand, K., Karlsson, A., Dahlgren, C. (2004) Cytochalasin B triggers a novel pertussis toxin-sensitive pathway in TNF-{alpha}-primed neutrophils BMC Cell Biol. 5,21[CrossRef][Medline]
  78. Wilden, U., Hall, S. W., Kuhn, H. (1986) Phosphodiesterase activation by photoexcited rhodopsin is quenched when rhodopsin is phosphorylated and binds the intrinsic 48-kDa protein of rod outer segments Proc. Natl. Acad. Sci. USA 83,1174-1178[Abstract/Free Full Text]
  79. Lefkowitz, R. J., Hausdorff, W. P., Caron, M. G. (1990) Role of phosphorylation in desensitization of the ß-adrenoceptor Trends Pharmacol. Sci. 11,190-194[CrossRef][Medline]
  80. Dalpiaz, A., Spisani, S., Biondi, C., Fabbri, E., Nalli, M., Ferretti, M. E. (2003) Studies on human neutrophil biological functions by means of formyl-peptide receptor agonists and antagonists Curr. Drug Targets Immune Endocr. Metabol. Disord. 3,33-42[CrossRef][Medline]
  81. Bokoch, G. M. (1995) Chemoattractant signaling and leukocyte activation Blood 86,1649-1660[Free Full Text]
  82. Thelen, M., Wirthmueller, U. (1994) Phospholipases and protein kinases during phagocyte activation Curr. Opin. Immunol. 6,106-112[CrossRef][Medline]
  83. Jones, S. A., Wolf, M., Qin, S., Mackay, C. R., Baggiolini, M. (1996) Different functions for the interleukin 8 receptors (IL-8R) of human neutrophil leukocytes: NADPH oxidase and phospholipase D are activated through IL-8R1 but not IL-8R2 Proc. Natl. Acad. Sci. USA 93,6682-6686[Abstract/Free Full Text]
  84. Nick, J. A., Avdi, N. J., Young, S. K., Knall, C., Gerwins, P., Johnson, G. L., Worthen, G. S. (1997) Common and distinct intracellular signaling pathways in human neutrophils utilized by platelet activating factor and fMLP J. Clin. Invest. 99,975-986[Medline]
  85. Berridge, M. J. (1993) Inositol trisphosphate and calcium signaling Nature 361,315-325[CrossRef][Medline]
  86. Janmey, P. A. (1994) Phosphoinositides and calcium as regulators of cellular actin assembly and disassembly Annu. Rev. Physiol. 56,169-191[Medline]
  87. Zaffran, Y., Lepidi, H., Bongrand, P., Mege, J. L., Capo, C. (1993) F-actin content and spatial distribution in resting and chemoattractant-stimulated human polymorphonuclear leucocytes. Which role for intracellular-free calcium? J. Cell Sci. 105,675-684[Abstract]
  88. Dahlgren, C. (1987) Difference in extracellular radical release after chemotactic factor and calcium ionophore activation of the oxygen radical-generating system in human neutrophils Biochim. Biophys. Acta 930,33-38[Medline]
  89. Niessen, H. W., Kuijpers, T. W., Roos, D., Verhoeven, A. J. (1991) Release of azurophilic granule contents in fMLP-stimulated neutrophils requires two activation signals, one of which is a rise in cytosolic-free Ca2+ Cell. Signal. 3,625-633[CrossRef][Medline]
  90. Nusse, O., Serrander, L., Foyouzi-Youssefi, R., Monod, A., Lew, D. P., Krause, K. H. (1997) Store-operated Ca2+ influx and stimulation of exocytosis in HL-60 granulocytes J. Biol. Chem. 272,28360-28367[Abstract/Free Full Text]
  91. Bylund, J. (2002) Recognition by leukocyte formyl peptide receptors: promiscuous binding or pattern recognition? Rheumatology & Inflammatory Research, Ph.D. thesis Göteborg University Gothenburg, Sweden.
  92. Bylund, J., Christophe, T., Boulay, F., Nystrom, T., Karlsson, A., Dahlgren, C. (2001) Proinflammatory activity of a cecropin-like antibacterial peptide from Helicobacter pylori Antimicrob. Agents Chemother. 45,1700-1704[Abstract/Free Full Text]
  93. Schreiber, R. E., Prossnitz, E. R., Ye, R. D., Cochrane, C. G., Bokoch, G. M. (1994) Domains of the human neutrophil N-formyl peptide receptor involved in G protein coupling. Mapping with receptor-derived peptides J. Biol. Chem. 269,326-331[Abstract/Free Full Text]
  94. Simons, K., Ikonen, E. (1997) Functional rafts in cell membranes Nature 387,569-572[CrossRef][Medline]
  95. Xue, M., Vines, C. M., Buranda, T., Cimino, D. F., Bennett, T. A., Prossnitz, E. R. (2004) N-formyl peptide receptors cluster in an active raft-associated state prior to phosphorylation J. Biol. Chem. 279,45175-45184[Abstract/Free Full Text]
  96. Guichard, C., Pedruzzi, E., Dewas, C., Fay, M., Pouzet, C., Bens, M., Vandewalle, A., Ogier-Denis, E., Gougerot-Pocidalo, M. A., Elbim, C. (2005) Interleukin-8-induced priming of the neutrophil oxidative burst requires sequential recruitment of NADPH oxidase components into lipid rafts J. Biol. Chem. 280,37021-37032[Abstract/Free Full Text]
  97. Tuluc, F., Meshki, J., Kunapuli, S. P. (2003) Membrane lipid microdomains differentially regulate intracellular signaling events in human neutrophils Int. Immunopharmacol. 3,1775-1790[CrossRef][Medline]
  98. Cunningham, C. C., Vegners, R., Bucki, R., Funaki, M., Korde, N., Hartwig, J. H., Stossel, T. P., Janmey, P. A. (2001) Cell permeant polyphosphoinositide-binding peptides that block cell motility and actin assembly J. Biol. Chem. 276,43390-43399[Abstract/Free Full Text]
  99. Fu, H., Bjorkman, L., Janmey, P., Karlsson, A., Karlsson, J., Movitz, C., Dahlgren, C. (2004) The two neutrophil members of the formylpeptide receptor family activate the NADPH-oxidase through signals that differ in sensitivity to a gelsolin-derived phosphoinositide-binding peptide BMC Cell Biol. 5,50[CrossRef][Medline]
  100. Stone, M. J. (1990) Amyloidosis: a final common pathway for protein deposition in tissues Blood 75,531-545[Free Full Text]
  101. Su, S. B., Gong, W., Gao, J. L., Shen, W., Murphy, P. M., Oppenheim, J. J., Wang, J. M. (1999) A seven-transmembrane, G protein-coupled receptor, FPRL1, mediates the chemotactic activity of serum amyloid A for human phagocytic cells J. Exp. Med. 189,395-402[Abstract/Free Full Text]
  102. Le, Y., Gong, W., Tiffany, H. L., Tumanov, A., Nedospasov, S., Shen, W., Dunlop, N. M., Gao, J. L., Murphy, P. M., Oppenheim, J. J., Wang, J. M. (2001) Amyloid (ß)42 activates a G-protein-coupled chemoattractant receptor, FPR-like-1 J. Neurosci. 21,RC123[Abstract/Free Full Text]



This article has been cited by other articles:


Home page
 GlycobiologyHome page
H. Forsman, E. Salomonsson, K. Onnheim, J. Karlsson, A. Bjorstad, H. Leffler, J. Bylund, A. Karlsson, and C. Dahlgren
The {beta}-galactoside binding immunomodulatory lectin galectin-3 reverses the desensitized state induced in neutrophils by the chemotactic peptide f-Met-Leu-Phe: role of reactive oxygen species generated by the NADPH-oxidase and inactivation of the agonist
Glycobiology, November 1, 2008; 18(11): 905 - 912.
[Abstract] [Full Text] [PDF]

Home page
 Infect. Immun.Home page
A. Martner, C. Dahlgren, J. C. Paton, and A. E. Wold
Pneumolysin Released during Streptococcus pneumoniae Autolysis Is a Potent Activator of Intracellular Oxygen Radical Production in Neutrophils
Infect. Immun., September 1, 2008; 76(9): 4079 - 4087.