Identification of novel chemoattractant peptides for human leukocytes

A pathogen-derived metabolite induces microglial activation via odorant receptors

Microglia (MG), the principal neuroimmune sentinels in the brain, continuously sense changes in their environment and respond to invading pathogens, toxins, and cellular debris, thereby affecting neuroinflammation. Microbial pathogens produce small metabolites that influence neuroinflammation, but the molecular mechanisms that determine whether pathogen-derived small metabolites affect microglial activation of neuroinflammation remain to be elucidated. We hypothesized that odorant receptors (ORs), the largest subfamily of G protein-coupled receptors, are involved in microglial activation by pathogen-derived small metabolites. We found that MG express high levels of two mouse ORs, Olfr110 and Olfr111, which recognize a pathogenic metabolite, 2-pentylfuran, secreted by Streptococcus pneumoniae. These interactions activate MG to engage in chemotaxis, cytokine production, phagocytosis, and reactive oxygen species generation. These effects were mediated through the G_αs -cyclic adenosine monophosphate-protein kinase A-extracellular signal-regulated kinase and G_βγ -phospholipase C-Ca²⁺ pathways. Taken together, our results reveal a novel interplay between the pathogen-derived metabolite and ORs, which has major implications for our understanding of microglial activation by pathogen recognition. DATABASE: Model data are available in the PMDB database under the accession number PM0082389.

A membrane-tethering pepducin derived from formyl peptide receptor 3 shows strong therapeutic effects against sepsis

Formyl peptide receptors (FPRs) are G protein-coupled receptors mainly expressed in inflammatory myeloid cells. Previous reports demonstrated that human neutrophils express only FPR1 and FPR2 but not FPR3. Here, we found that FPR3 is expressed in sepsis patient derived neutrophils and Fpr3 is expressed in the mouse neutrophils. To test the role of Fpr3 in neutrophil activity, we synthesized Fpr3 pepducins and successfully developed an agonistic pepducin that stimulates Fpr3, eliciting calcium increase and chemotactic migration of neutrophils. We also found that administration of an Fpr3 pepducin in an experimental mouse sepsis model significantly increased the survival rate. The pepducin markedly inhibited lung injury, splenocyte apoptosis, and inflammatory cytokine production. Bacterial counts were significantly decreased by the pepducin in septic mice. Based on these results, we suggest that FPR3 can be regarded as a new target to control sepsis, and the newly generated Fpr3-based pepducin can be used for the development of anti-septic agents.

Novel CD11b+Gr-1+Sca-1+ myeloid cells drive mortality in bacterial infection

Extreme pathophysiological stressors induce expansion of otherwise infrequent leukocyte populations. Here, we found a previously unidentified CD11b⁺Gr-1⁺ myeloid cell population that expresses stem cell antigen-1 (Sca-1) induced upon experimental infection with Staphylococcus aureus. Although CD11b⁺Gr-1⁺Sca-1⁺ cells have impaired migratory capacity and superoxide anion-producing activity, they secrete increased levels of several cytokines and chemokines compared to Sca-1^- counterparts. The generation of CD11b⁺Gr-1⁺Sca-1⁺ cells is dependent on IFN-γ in vivo, and in vitro stimulation of bone marrow cells or granulocyte-macrophage progenitors with IFN-γ generated CD11b⁺Gr-1⁺Sca-1⁺ cells. Depletion of CD11b⁺Gr-1⁺Sca-1⁺ cells by administrating anti-Sca-1 antibody strongly increased survival rates in an S. aureus infection model by reducing organ damage and inflammatory cytokines. However, adoptive transfer of CD11b⁺Gr-1⁺Sca-1⁺ cells decreased survival rates by worsening the pathogenesis of S. aureus infection. Together, we found a previously unidentified pathogenic CD11b⁺Gr-1⁺Sca-1⁺ population that plays an essential role in mortality during bacterial infection.

FAM19A5, a brain-specific chemokine, inhibits RANKL-induced osteoclast formation through formyl peptide receptor 2

Osteoclasts can be differentiated from bone marrow-derived macrophages (BMDM). They play a key role in bone resorption. Identifying novel molecules that can regulate osteoclastogenesis has been an important issue. In this study, we found that FAM19A5, a neurokine or brain-specific chemokine, strongly stimulated mouse BMDM, resulting in chemotactic migration and inhibition of RANKL-induced osteoclastogenesis. Expression levels of osteoclast-related genes such as RANK, TRAF6, OSCAR, TRAP, Blimp1, c-fos, and NFATc1 were markedly decreased by FAM19A5. However, negative regulators of osteoclastogenesis such as MafB and IRF-8 were upregulated by FAM19A5. FAM19A5 also downregulated expression levels of RANKL-induced fusogenic genes such as OC-STAMP, DC-STAMP, and Atp6v0d2. FAM19A5-induced inhibitory effect on osteoclastogenesis was significantly reversed by a formyl peptide receptor (FPR) 2 antagonist WRW4 or by FPR2-deficiency, suggesting a crucial role of FPR2 in the regulation of osteoclastogenesis. Collectively, our results suggest that FAM19A5 and its target receptor FPR2 can act as novel endogenous ligand/receptor to negatively regulate osteoclastogenesis. They might be regarded as potential targets to control osteoclast formation and bone disorders.

A novel antimicrobial peptide isolated from centipede Scolopendra subspinipes mutilans stimulates neutrophil activity through formyl peptide receptor 2

In this study, we identified scolopendrasin X, a novel antimicrobial peptide (AMP), from centipede Scolopendra subspinipes mutilans. Scolopendrasin X strongly stimulated mouse neutrophils, resulting in intracellular calcium increase, chemotactic migration through pertussis toxin-sensitive G-protein and phospholipase C pathway, and increased superoxide anion production in neutrophils. Target receptor for scolopendrasin X, formyl peptide receptor (FPR)2 mediated scolopendrasin X-induced neutrophil activation. Moreover, scolopendrasin X significantly blocked inflammatory cytokine production induced by lipopolysaccharide in mouse neutrophils. Taken together, our results suggest that the novel AMP scolopendrasin X can be used as a material to regulate neutrophil activity through FPR2.

Promotion of formyl peptide receptor 1-mediated neutrophil chemotactic migration by antimicrobial peptides isolated from the centipede Scolopendra subspinipes mutilans

We investigated the effects of two antimicrobial peptides (AMPs) isolated from Scolopendra subspinipes mutilans on neutrophil activity. Stimulation of mouse neutrophils with the two AMPs elicited chemotactic migration of the cells in a pertussis toxin-sensitive manner. The two AMPs also stimulated activation of ERK and Akt, which contribute to chemotactic migration of neutrophils. We found that AMP-stimulated neutrophil chemotaxis was blocked by a formyl peptide receptor (FPR) 1 antagonist (cyclosporin H); moreover the two AMPs stimulated the chemotactic migration of FPR1-expressing RBL-2H3 cells but not of vector-expressing RBL-2H3 cells. We also found that the two AMPs stimulate neutrophil migration in vivo, and that this effect is blocked in FPR1-deficient mice. Taken together, our results suggest that the two AMPs stimulate neutrophils, leading to chemotactic migration through FPR1, and the two AMPs will be useful for the study of FPR1 signaling and neutrophil activation. [BMB Reports 2016; 49(9): 520-525]

Antimicrobial peptide scolopendrasin VII, derived from the centipede Scolopendra subspinipes mutilans, stimulates macrophage chemotaxis via formyl peptide receptor 1

In this study, we report that one of the antimicrobial peptides scolopendrasin VII, derived from Scolopendra subspinipes mutilans, stimulates actin polymerization and the subsequent chemotactic migration of macrophages through the activation of ERK and protein kinase B (Akt) activity. The scolopendrasin VII-induced chemotactic migration of macrophages is inhibited by the formyl peptide receptor 1 (FPR1) antagonist cyclosporine H. We also found that scolopendrasin VII stimulate the chemotactic migration of FPR1-transfected RBL-2H3 cells, but not that of vector-transfected cells; moreover, scolopendrasin VII directly binds to FPR1. Our findings therefore suggest that the antimicrobial peptide scolopendrasin VII, derived from Scolopendra subspinipes mutilans, stimulates macrophages, resulting in chemotactic migration via FPR1 signaling, and the peptide can be useful in the study of FPR1-related biological responses. [BMB Reports 2015; 48(8): 479-484]

Serum amyloid A inhibits RANKL-induced osteoclast formation

When mouse bone marrow-derived macrophages were stimulated with serum amyloid A (SAA), which is a major acute-phase protein, there was strong inhibition of osteoclast formation induced by the receptor activator of nuclear factor kappaB ligand. SAA not only markedly blocked the expression of several osteoclast-associated genes (TNF receptor-associated factor 6 and osteoclast-associated receptor) but also strongly induced the expression of negative regulators (MafB and interferon regulatory factor 8). Moreover, SAA decreased c-fms expression on the cell surface via shedding of the c-fms extracellular domain. SAA also restrained the fusion of osteoclast precursors by blocking intracellular ATP release. This inhibitory response of SAA is not mediated by the well-known SAA receptors (formyl peptide receptor 2, Toll-like receptor 2 (TLR2) or TLR4). These findings provide insight into a novel inhibitory role of SAA in osteoclastogenesis and suggest that SAA is an important endogenous modulator that regulates bone homeostasis.

Wnt5a stimulates chemotactic migration and chemokine production in human neutrophils

Wnt5a is a ligand that activates the noncanonical Wnt signaling pathways (β-catenin-independent pathways). Human neutrophils expressed several Wnt5a receptors, such as Frizzled 2, 5 and 8. Stimulation of human neutrophils with Wnt5a caused chemotactic migration and the production of two important chemokines, CXCL8 and CCL2. CCL2 production by Wnt5a was mediated by a pertussis toxin-sensitive G-protein-dependent pathway. Wnt5a also stimulated the phosphorylation of three mitogen-activated protein kinases (MAPKs: ERK, p38 MAPK and JNK) and Akt. Inhibition of ERK, p38 MAPK or JNK by specific inhibitors induced a dramatic reduction in Wnt5a-induced CCL2 production. Supernatant collected from lipopolysaccharide-stimulated macrophages induced neutrophil chemotaxis, which was significantly inhibited by anti-Wnt5a antibody. Our results suggested that Wnt5a may contribute to neutrophil recruitment, mediating the inflammation response.

Pertussis toxin enhances colony organization of enzymatic-dissociated single human embryonic stem cells

Human embryonic stem cells (hESCs) self-renew indefinitely as highly organized pluripotent colonies. Unlike mouse pluripotent stem cell colonies, human colonies form a uniform, flat, epithelium-like monolayer. Interestingly, it has been reported that colony morphology is closely correlated with the maintenance of pluripotency. However, the molecular mechanisms that underlie human pluripotent colony formation and organization are poorly understood. In this study, we used real-time imaging tools to examine the in vitro colony formation of enzymatically dissociated single hESCs under feeder-free conditions. We demonstrate that colony formation consists of 4 stages: attachment, migration, aggregation, and colony formation, which are facilitated in an intracellular, calcium-dependent manner. Moreover, we found that blocking G(i)-coupled G protein-coupled receptor (GPCR) signaling results in enhanced cell-cell interactions and plays an integral role in promoting the survival of hESCs in culture. From the imaging results, we identified the conditions required for colony formation, and we identified the importance of blocking G(i)-coupled GPCR by pertussis toxin in modulating hESC colony formation and organization. These results will likely be useful for engineering hESCs to further study the mechanisms involved in their function.

Identification of novel peptides that stimulate human neutrophils

Neutrophils play a key role in innate immunity, and the identification of new stimuli that stimulate neutrophil activity is a very important issue. In this study, we identified three novel peptides by screening a synthetic hexapeptide combinatorial library. The identified peptides GMMWAI, MMHWAM, and MMHWFM caused an increase in intracellular Ca2+ in a concentration-dependent manner via phospholipase C activity in human neutrophils. The three peptides acted specifically on neutrophils and monocytes and not on other non-leukocytic cells. As a physiological characteristic of the peptides, we observed that the three peptides induced chemotactic migration of neutrophils as well as stimulated superoxide anion production. Studying receptor specificity, we observed that two of the peptides (GMMWAI and MMHWFM) acted on formyl peptide receptor (FPR)1 while the other peptide (MMHWAM) acted on FPR2. Since the three novel peptides were specific agonists for FPR1 or FPR2, they might be useful tools to study FPR1- or FPR2-mediated immune response and signaling.

The Safety Evaluation of a Potent Angiogenic Activator, Synthetic Peptide (SFKLRY-NH2) for the Skin Application

A novel synthetic hexapeptide (SFKLRY-NH₂) that displays angiogenic activity has been identified by positional scanning of a synthetic peptide combinatorial library (PS-SPCL). This study was carried out to investigate the irritation of the SFKLRY-NH₂ on the skin. The tests were performed on the basis of Korea Food and Drug Administration (KFDA) guidelines. In results, cell toxicity is not appeared for SFKLRY-NH₂ in HaCaT cells and B16F10 cells. SFKLRY-NH₂ induced no skin irritation at low concentration (10 μM), mild irritation at high concentration (10mM). We consider that this result is helpful for saying about the safety of SFKLRY-NH₂ in clinical use.

Activation of CXCR2 by extracellular matrix degradation product acetylated Pro-Gly-Pro has therapeutic effects against sepsis

RATIONALE

Acetylated Pro-Gly-Pro (Ac-PGP) is an endogenous degradation product of extracellular collagen that binds to leukocyte-expressed chemoattractant receptor CXCR2. Although certain agents that block CXCR2-mediated signaling protect against experimental sepsis, the roles of Ac-PGP and CXCR2 in sepsis are unclear.

OBJECTIVES

To investigate the role of Ac-PGP and its receptor, CXCR2, in murine models of cecal ligation and puncture (CLP)-induced polymicrobial sepsis and organ injury.

METHODS

The impact of in vivo Ac-PGP treatment on animal survival after induction of experimental sepsis was assessed. Vital organ inflammation and immune cell apoptosis were evaluated by histology, and the modulation of proinflammatory cytokine production and bactericidal activity by Ac-PGP in mouse and human blood leukocytes was measured.

MEASUREMENTS AND MAIN RESULTS

The activation of CXCR2 by tripeptide agonist Ac-PGP dramatically improved survival in three experimental sepsis models. Ac-PGP elicited bactericidal activity via the generation of hydrogen peroxide, inhibited lung inflammation, and reduced immune cell apoptosis. Fluorescein isothiocyanate-labeled PGP bound directly to CXCR2, and the protective effect of Ac-PGP in sepsis was abolished in CXCR2-deficient mice. Ac-PGP treatment enhanced the production of type 1 cytokines (IFN-γ and IL-12) but inhibited the production of proinflammatory cytokines (tumor necrosis factor [TNF]-α, IL-1β, and IL-6) in vivo. In vitro, Ac-PGP directly increased IFN-γ production and decreased the LPS-stimulated production of TNF-α by mouse splenocytes and human leukocytes. Furthermore, direct treatment of LPS-stimulated splenocytes with IFN-γ resulted in diminished secretion of TNF-α and IL-6.

CONCLUSIONS

CXCR2 and Ac-PGP are thus novel target and starting molecules, respectively, for the development of therapeutic agents against sepsis.

Synthesis and biological activity of peptides equivalent to the IP22 repeat motif found in proteins from Dictyostelium and Mimivirus

A novel IP22 repeat motif of unknown function was discovered previously that comprises almost the entire structure of cmbB, a calmodulin-binding protein from Dictyostelium discoideum. An analysis of over 2000 IP22 repeats across 130 different proteins from different species allowed us to define a prototypical IP22 repeat: I/LPxxhxxhxhxxxhxxxhxxxx (where L=leucine, I=isoleucine, h=any hydrophobic amino acid, x=any amino acid). Here we describe the synthesis of three peptide variants of the IP22 motif: IP22-1 (IPNSVTSLKFGDGFNQPLTPGT; 22aa); IP22-2 (LPSTLKTISLSNSTDKKIFKNS; 22aa); and, IP22-3 (IPKSLRSLFLGKGYNQPLEF; 20aa) plus a control peptide from the N-term of cmbB (HNMNPFSPQLDEKKNSHIVEY; 21aa). The structure and purity of synthesized peptides were verified by HPLC and mass spectrometry. The peptides all dose-dependently enhanced random cell motility and cAMP-mediated chemotaxis in Dictyostelium but IP22-3 was most effective peaking in activity around 50 μM. Fluorescein isothiocyanate (FITC)-conjugated IP22 peptides did not penetrate cells suggesting these peptides affect cell motility via cell surface interactions. Treatment of cells with FITC-IP22 peptides also led to enhanced cell motility equivalent to the non-conjugated peptides. Treatment of IP22-3-stimulated cells with 50 μM LY294002, 20 μM quinacrine or both suggests that IP22-3 requires both phosphoinositol 3-kinase and phospholipase A2 signaling to elicit its effects, a mechanism unique from EGFL motility enhancing peptides. The mechanism of action and potential uses of IP22 repeat peptides are discussed.

Lysophosphatidylglycerol inhibits formyl peptide receptorlike-1-stimulated chemotactic migration and IL-1beta production from human phagocytes

In this study, we observed that lysophosphatidylglycerol (LPG) completely inhibited a formyl peptide receptor like-1 (FPRL1) agonist (MMK-1)-stimulated chemotactic migration in human phagocytes, such as neutrophils and monocytes. LPG also dramatically inhibited IL-1beta production by another FPRL1 agonist serum amyloid A (SAA) in human phagocytes. However, LPG itself induced intracellular calcium increase and superoxide anion production in human phagocytes. Keeping in mind that phagocytes migration and IL-1beta production by FPRL1 are important for the induction of inflammatory response, our data suggest that LPG can be regarded as a useful material for the modulation of inflammatory response induced by FPRL1 activation.

Functional expression of formyl peptide receptor family in human NK cells

We determined the expression of the formyl peptide receptor (FPR) family and the functional roles of the FPR family in NK cells. All tested human NK cells express two members of the FPR family (FPR1 and FPR2). The expression of FPR3 was noted to occur in a donor-specific manner. The stimulation of NK cells with FPR family-selective agonists (fMLF (N-formyl-Met-Leu-Phe), MMK-1, F2L, and WKYMVm (Trp-Lys-Tyr-Met-Val-d-Met)) elicited cytolytic activity in resting NK cells, but not in IL-2-activated NK cells; the cytolytic activity was not inhibited by pertussis toxin. The FPR family agonists also stimulated chemotactic migration of IL-2-activated NK cells, but not resting NK cells; the chemotactic migration was completely inhibited by pertussis toxin. WKYMVm stimulates ERK, p38 MAPK, and JNK activities in both resting and IL-2-activated NK cells. WKYMVm-induced chemotactic migration was partially inhibited by PD98059 (2'-amino-3'-methoxyflavone); however, the inhibition of JNK by its selective inhibitor (SP600125, anthra[1,9-cd]pyrazol-6(2H)-one) dramatically inhibited the WKYMVm-induced cytolytic activity. Furthermore, WKYMVm-induced chemotactic migration and cytolytic activity were partly inhibited by FPR family-selective antagonists (cyclosporin H and WRWWWW). Taken together, our findings indicate that human NK cells express functional members of the FPR family, and in turn the activation of the three members of the FPR receptor family elicit cytolytic activity in NK cells, thus suggesting that the receptors are potentially important therapeutic targets for the modulation of NK cell-mediated immune responses.

LL-37 inhibits serum amyloid A-induced IL-8 production in human neutrophils

Serum amyloid A (SAA) has been regarded as an important mediator of inflammatory responses. The effect of several formyl peptide receptor-like 1 (FPRL1) ligands on the production of IL-8 by SAA was investigated in human neutrophils. Among the ligands tested, LL-37 was found to specifically inhibit SAA-induced IL-8 production in transcriptional and post-transcriptional levels. Since SAA stimulated IL-8 production via ERK and p38 MAPK in human neutrophils, we tested the effect of LL-37 on SAA induction for these two MAPKs. LL-37 caused a dramatic inhibition of ERK and p38 MAPK activity, which is induced by SAA. LL-37 was also found to inhibit SAA-stimulated neutrophil chemotactic migration. Further, the LL-37-induced inhibitory effect was mediated by FPRL1. Our findings indicate that LL-37 is expected to be useful in the inhibition of SAA signaling and for the development of drugs against SAA-related inflammatory diseases.

Identification of novel synthetic peptide showing angiogenic activity in human endothelial cells

A novel synthetic hexapeptide (SFKLRY-NH(2)) that displays angiogenic activity has been identified by positional scanning of a synthetic peptide combinatorial library (PS-SPCL). The peptide induced proliferation, migration, and capillary-like tube formation in primary cultured HUVECs, and augmented vessel sprouting ex vivo while attenuated by the treatment with pertussis toxin (PTX) or U73122 (PLC-inhibitor) suggesting the influence of PTX-sensitive G-proteins and PLC. In addition, SFKLRY-NH(2) up-regulated the expression of VEGF-A in HUVECs and the neutralizing antibody against VEGF suppressed SFKLRY-NH(2)-induced tube formation activity. Taken together, these results suggest that SFKLRY-NH(2) may induce blood vessel formation by PTX-sensitive G protein-coupled receptor-PLC-Ca(2+) signaling cascade leading into VEGF-A expression in HUVECs.

Signal transduction of hyaluronic acid-peptide conjugate for formyl peptide receptor like 1 receptor

Agonistic and antagonistic peptides for formyl peptide receptor like 1 (FPRL1) receptor have been investigated as novel drug candidates for inflammatory diseases such as sepsis, asthma, and rheumatoid arthritis. In this work, a novel protocol for the synthesis of hyaluronic acid (HA)-peptide (CWRYMVm) conjugate for FPRL1 receptor was successfully developed for further clinical applications of peptide drugs. Aminoethyl methacrylated HA (HAAEMA) was synthesized by the coupling reaction of tetrabutyl ammonium salt of HA (HA-TBA) and AEMA using benzotriazol-1-yloxy-tris(dimethylamino) phosphonium hexafluorophosphate (BOP) in dimethyl sulfoxide (DMSO). Then, HA-AEMA was conjugated with CWRYMVm in water via Michael addition reaction between methacrylate group of HA-AEMA and thiol group in cysteine. The formation of HA-peptide conjugate was confirmed by 1H NMR and gel permeation chromatography (GPC). The average number of conjugated peptide molecules could be controlled from 5 to 23 per single HA chain. The HA-peptide conjugate showed serum stability longer than four days. In Vitro signal transduction activity of the HA-peptide conjugate for FPRL1 receptor was confirmed from the elevated levels of phospho-extracellular signal-regulated kinase (pERK) and calcium ion in FPRL1 overexpressing RBL-2H3 cells. The partially decreased biological activity of HA-peptide conjugates by the steric hindrance of HA was recovered after its degradation by hyaluronidase treatment.

Serum amyloid A induces CCL2 production via formyl peptide receptor-like 1-mediated signaling in human monocytes

Although the presence of an elevated level of serum amyloid A (SAA) has been regarded as a cardiovascular risk factor, the role of SAA on the progress of atherosclerosis has not been fully elucidated. In the present study, we investigated the effect of SAA on the production of CCL2, an important mediator of monocyte recruitment, and the mechanism underlying the action of SAA in human monocytes. The stimulation of human monocytes with SAA elicited CCL2 production in a concentration-dependent manner. The production of CCL2 by SAA was found to be mediated by the activation of NF-kappaB. Moreover, the signaling events induced by SAA included the activation of ERK and the induction of cyclooxygenase-2, which were required for the production of CCL2. Moreover, SAA-induced CCL2 induction was inhibited by a formyl peptide receptor-like 1 (FPRL1) antagonist. We also found that the stimulation of FPRL1-expressing RBL-2H3 cells induced CCL2 mRNA accumulation, but the vector-expressing RBL-2H3 cells combined with SAA did not. Taken together, our findings suggest that SAA stimulates CCL2 production and, thus, contributes to atherosclerosis. Moreover, FPRL1 was found to be engaged in SAA-induced CCL2 induction, and cyclooxygenase-2 induction was found to be essential for SAA-induced CCL2 expression. These results suggest that SAA and FPRL1 offer a developmental starting point for the treatment of atherosclerosis.

Collagen-binding motif peptide, a cleavage product of osteopontin, stimulates human neutrophil chemotaxis via pertussis toxin-sensitive G protein-mediated signaling

The collagen-binding motif (CBM) peptide, a cleavage product of osteopontin (OPN), stimulated intracellular calcium increase in human neutrophils. CBM peptide-stimulated calcium was inhibited by pertussis toxin (PTX), suggesting the influence of PTX-sensitive G-proteins. In addition CBM peptide stimulated the chemotactic migration of human neutrophils and human monocytes. CBM peptide-induced neutrophil chemotaxis was completely inhibited by PTX, once again indicating the influence of Gi proteins. CBM peptide was also found to induce mitogen activated protein kinase activation. CBM peptide-induced neutrophil chemotaxis was mediated by p38 kinase as well as an extracellular signal-regulated protein kinase. Taken together, the results suggest that a cleavage product of OPN, CBM peptide, initiates immune responses by inducing neutrophil trafficking via certain PTX-sensitive cell surface receptors.

F2L, a peptide derived from heme-binding protein, inhibits LL-37-induced cell proliferation and tube formation in human umbilical vein endothelial cells

F2L, a peptide derived from heme-binding protein, was originally identified as an endogenous ligand for formyl peptide receptor-like (FPRL)2. Previously, we reported that F2L inhibits FPR and FPRL1-mediated signaling in neutrophils. Since endothelial cells express functional FPRL1, we examined the effect of F2L on LL-37 (an FPRL1 agonist)-induced signaling in human umbilical vein endothelial cells (HUVECs). F2L stimulated the chemotactic migration in HUVECs. However, F2L inhibited FPRL1 activity, resulting in the inhibition of cell proliferation and tube formation induced by LL-37 in HUVECs. We suggest that F2L will potentially be useful in the study of FPRL1 signaling and the development of drugs to treat diseases involving the FPRL1 in the vascular system.

Cryptides: buried secrets in proteins

The proteome originally described the entire set of proteins expressed by a genome, tissue or organism. Subsequently this term was limited to all the expressed proteins at a given time under defined conditions. Hence, specializations such as functional proteome, cancer proteome, liver proteome and so forth have arisen. One particular proteome that has been recently described is the cryptome, a unique subset of already known proteins that has the ability of generating bioactive peptides and proteins when submitted to proteolytic cleavage, rather than the classical processing pathways. This is an idea in agreement with the concept that evolution is not related to the amount of genes or putative proteins that could be secreted by an organism, but to the way these proteins are processed. These 'new' molecules may have related or increased properties when compared to the 'original' molecule or possess completely unrelated biological effects, thus increasing the array of biological roles that can be associated to one given protein (or gene). In this work, we review this recent concept and put it into the toxinology field as well, an area in which the diversity of functional molecules (and roles) is essential for the survival of a given organism.

Lysophosphatidylglycerol stimulates chemotactic migration and tube formation in human umbilical vein endothelial cells

In this study, we observed that lysophosphatidylglycerol (LPG) stimulates extracellular signal-regulated kinase (ERK) in human umbilical vein endothelial cells (HUVECs). LPG-stimulated ERK activity was not inhibited by pertussis toxin (PTX), indicating PTX-sensitive G-proteins-independent manner. In terms of functional aspect, LPG induced chemotactic migration of HUVECs in a PTX-insensitive manner. Preincubation of HUVECs with an ERK inhibitor (PD98059) completely inhibited LPG-induced chemotactic migration, suggesting the crucial role of ERK in the process. LPG-induced ERK activation and chemotactic migration in HUVECs were not affected by an lysophosphatidic acid receptor-selective antagonist (Ki16425), indicating lysophosphatidic acid receptors-independency. We also found that LPG stimulated tube formation in HUVECs. Taken together we suggest that LPG stimulates HUVECs and result in chemotactic migration and tube formation, suggesting a new aspect of LPG as a modulator of endothelial cell functioning.

Lysophosphatidylethanolamine stimulates chemotactic migration and cellular invasion in SK-OV3 human ovarian cancer cells: involvement of pertussis toxin-sensitive G-protein coupled receptor

We investigated whether lysophosphatidylethanolamine (LPE) modulates cellular signaling in different cell types. SK-OV3 ovarian cancer cells and OVCAR-3 ovarian cancer cells were responsive to LPE. LPE-stimulated intracellular calcium concentration ([Ca(2+)](i)) increase was inhibited by U-73122, suggesting that LPE stimulates calcium signaling via phospholipase C activation. Moreover, pertussis toxin (PTX) almost completely inhibited [Ca(2+)](i) increase by LPE, indicating the involvement of PTX-sensitive G-proteins. Furthermore, we found that LPE stimulated chemotactic migration and cellular invasion in SK-OV3 ovarian cancer cells. We examined the role of lysophosphatidic acid receptors on LPE-stimulated cellular responses using HepG2 cells transfected with different LPA receptors, and found that LPE failed to stimulate nuclear factor kappa B-driven luciferase. We suggest that LPE stimulates a membrane bound receptor, different from well known LPA receptors, resulting in chemotactic migration and cellular invasion in SK-OV3 ovarian cancer cells.

F2L, a peptide derived from heme-binding protein, inhibits formyl peptide receptor-mediated signaling

F2L is an acetylated amino-terminal peptide derived from the cleavage of the human heme-binding protein. Very recently, F2L was identified as an endogenous chemoattractant peptide acting specifically through formyl peptide receptor-like (FPRL)2. In the present study, we report that F2L stimulates chemotactic migration in human neutrophils. However, F2L inhibits formyl peptide receptor (FPR) and FPRL1 activities, resulting in the complete inhibition of intracellular calcium increases, and superoxide generation induced by N-formyl-Met-Leu-Phe, MMK-1, or Trp-Lys-Tyr-Met-Val-d-Met (WKYMVm) in human neutrophils. In terms of the inhibitory role of F2L on FPR- and FPRL-mediated signaling, we found that F2L competitively inhibits the binding of (125)I-WKYMVm to its specific receptors, FPR and FPRL1. F2L is the first endogenous molecule that inhibits FPR- and FPRL1-mediated signaling, and is expected to be useful in the study of FPR and FPRL1 signaling and in the development of drugs to treat diseases involving the FPR family of receptors.

Alkylating agent methyl methanesulfonate (MMS) induces a wave of global protein hyperacetylation: implications in cancer cell death

Protein acetylation modification has been implicated in many cellular processes but the direct evidence for the involvement of protein acetylation in signal transduction is very limited. In the present study, we found that an alkylating agent methyl methanesulfonate (MMS) induces a robust and reversible hyperacetylation of both cytoplasmic and nuclear proteins during the early phase of the cellular response to MMS. Notably, the acetylation level upon MMS treatment was strongly correlated with the susceptibility of cancer cells, and the enhancement of MMS-induced acetylation by histone deacetylase (HDAC) inhibitors was shown to increase the cellular susceptibility. These results suggest protein acetylation is important for the cell death signal transduction pathway and indicate that the use of HDAC inhibitors for the treatment of cancer is relevant.

Cryptides: functional cryptic peptides hidden in protein structures

Peptidergic hormones, neurotransmitters, and neuromodulators are extracellular signaling molecules that play central roles in physiological signal transmissions between various cells, tissues, and organs. These factors are primarily translated as inactive precursor proteins according to the genetic information. These precursor proteins are then cleaved by various proteases including signal peptidases and processing enzymes to produce matured bioactive factors. During these processes, various fragmented peptides are also produced from the same precursor proteins. Such fragmented peptides may have various unexpected biological activities that have not been identified yet because these peptides are considered to be produced and released along with mature factors at the same secretary pathways. Recently, we found that various fragmented peptides of mitochondrial proteins that are produced during the maturation processes, such as fragments of cytochrome c oxidase, activate neutrophils whose functions are distinct from their parent proteins. These findings suggest the existence of many different functional peptides whose functions have not been identified yet. These unidentified peptides may play a variety of roles in various regulatory mechanisms, and therefore, they are expected to provide novel regulatory and signaling mechanisms, "Peptide World".

Expression and functional role of formyl peptide receptor in human bone marrow-derived mesenchymal stem cells

We investigated the expression of formyl peptide receptor (FPR) and its functional role in human bone marrow-derived mesenchymal stem cells (MSCs). We analyzed the expression of FPR by using ligand-binding assay with radio-labeled N-formyl-met-leu-phe (fMLF), and found that MSCs express FPR. FMLF stimulated intracellular calcium increase, mitogen-activated protein kinases activation, and Akt activation, which were mediated by G(i) proteins. MSCs were chemotactically migrated to fMLF. FMLF-induced MSC chemotaxis was also completely inhibited by pertussis toxin, LY294002, and PD98059, indicating the role of G(i) proteins, phosphoinositide 3-kinase, and extracellular signal regulated protein kinase. N-terminal fragment of annexin-1, Anx-1(2-26), an endogenous agonist for FPR, also induced chemotactic migration of MSCs. Thus MSCs express functional FPR, suggesting a new (patho)physiological role of FPR and its ligands in regulating MSC trafficking during induction of injured tissue repair.

S1P stimulates chemotactic migration and invasion in OVCAR3 ovarian cancer cells

OVCAR3 ovarian cancer cells express three sphingosine 1-phosphate (S1P) receptors, S1P(1), S1P(2), and S1P(3), but not S1P(4). Stimulation of OVCAR3 cells with S1P induced intracellular calcium increases, which were partly inhibited by VPC 23019 (an S1P(1/3) antagonist). S1P-induced calcium increases were mediated by phospholipase C and pertussis toxin (PTX)-sensitive G-proteins in OVCAR3 cells. S1P stimulated extracellular signal-regulated kinase, p38 kinase, and Akt which were inhibited by PTX. S1P-stimulated chemotactic migration of OVCAR3 cells in a PTX-sensitive manner, indicating crucial role of G(i) protein(s) in the process. S1P-induced chemotactic migration of OVCAR3 cells was completely inhibited by LY294002 and SB203580. Pretreatment of VPC 23019 (an S1P(1/3) antagonist) completely inhibited S1P-induced chemotaxis. S1P also induced invasion of OVCAR3 cells, which was also inhibited by VPC 23019. Taken together, this study suggests that S1P stimulate chemotactic migration and cellular invasion, and VPC 23019-sensitive S1P receptor(s) might be involved in the processes.

Effect of lysophosphatidylglycerol on several signaling molecules in OVCAR-3 human ovarian cancer cells: involvement of pertussis toxin-sensitive G-protein coupled receptor

In this study, we observed that lysophosphatidylglycerol (LPG) stimulated intracellular calcium ([Ca(2+)](i)) increase in OVCAR-3 human ovarian cancer cells. LPG-stimulated [Ca(2+)](i) increase was inhibited by U-73122 but not by U-73343, suggesting that LPG stimulates calcium signaling via phospholipase C activation. Moreover, pertussis toxin (PTX) almost completely inhibited [Ca(2+)](i) increase by LPG, indicating the activation of PTX-sensitive G-proteins. LPG-induced [Ca(2+)](i) increase was only observed in OVCAR-3 ovarian cancer cells and SK-OV3 ovarian cancer cells among tested several cell types. LPG also induced extracellular signal-regulated kinase (ERK) and Akt phosphorylation in OVCAR-3 ovarian cancer cells. Pertussis toxin did not affect the LPG-induced activation of ERK and Akt phosphorylation. We also found that LPG failed to stimulate NF-kappaB-driven luciferase activity in exogenously LPA(1), LPA(2), or LPA(3)-transfected HepG2 cells. Taken together we suggest that LPG stimulates a membrane bound receptor which is different from well-known LPA receptors (LPA(1), LPA(2), and LPA(3)), resulting in at least two different signaling cascades; one involves a pertussis toxin-sensitive and phospholipase C-dependent [Ca(2+)](i) increase, and the other involves a pertussis toxin-insensitive activation of ERK and Akt in ovarian cancer cells.

Sphingosylphosphorylcholine stimulates human monocyte-derived dendritic cell chemotaxis

AIM

To investigate the effects of sphingosylphosphorylcholine (SPC) on human monocyte-derived dendritic cell (DC) chemotaxis.

METHODS

Human DC were generated from peripheral blood monocytes by culturing them with granulocyte macrophage-colony stimulating factor and interleukin-4. The effect of SPC on the DC chemotactic migration was measured by chemotaxis assay. Intracellular signaling event involved in the SPC-induced DC chemotaxis was investigated with several inhibitors for specific kinase. The expression of the SPC receptors was examined by reverse transcription polymerase chain reaction.

RESULTS

We found that SPC induced chemotactic migration in immature DC (iDC) and mature DC (mDC). In terms of SPC-induced signaling events, mitogen activated protein kinase activation and Akt activation in iDC and mDC were stimulated. SPC-induced chemotaxis was mediated by extracellular signal-regulated protein kinase and phosphoino-sitide-3-kinase, but not by calcium in both iDC and mDC. Although mDC express ovarian cancer G protein-coupled receptor 1, but not G protein-coupled receptor 4, iDC do not express any of these receptors. To examine the involvement of sphingosine-1-phosphate (S1P) receptors, we checked the effect of an S1P receptor antagonist (VPC23019) on SPC-induced DC chemotaxis. VPC23019 did not affect SPC-induced DC chemotaxis.

CONCLUSION

The results suggest that SPC may play a role in regulating DC trafficking during phagocytosis and the T cell-stimulating phase, and the unique SPC receptor, which is different from S1P receptors, is involved in SPC-induced chemotaxis.

N-terminal proteolytic processing by cathepsin G converts RANTES/CCL5 and related analogs into a truncated 4-68 variant

N-terminal proteolytic processing modulates the biological activity and receptor specificity of RANTES/CCL5. Previously, we showed that an unidentified protease associated with monocytes and neutrophils digests RANTES into a variant lacking three N-terminal residues (4-68 RANTES). This variant binds CCR5 but exhibits lower chemotactic and antiviral activities than unprocessed RANTES. In this study, we characterize cathepsin G as the enzyme responsible for this processing. Cell-mediated production of the 4-68 variant was abrogated by Eglin C, a leukocyte elastase and cathepsin G inhibitor, but not by the elastase inhibitor elastatinal. Further, anti-cathepsin G antibodies abrogated RANTES digestion in neutrophil cultures. In accordance, reagent cathepsin G specifically digested recombinant RANTES into the 4-68 variant. AOP-RANTES and Met-RANTES were also converted into the 4-68 variant upon exposure to cathepsin G or neutrophils, while PSC-RANTES was resistant to such cleavage. Similarly, macaque cervicovaginal lavage samples digested Met-RANTES and AOP-RANTES, but not PSC-RANTES, into the 4-68 variant and this processing was also inhibited by anti-cathepsin G antibodies. These findings suggest that cathepsin G mediates a novel pathway for regulating RANTES activity and may be relevant to the role of RANTES and its analogs in preventing HIV infection.

Leukotriene B4 stimulates human monocyte-derived dendritic cell chemotaxis

Although leukotriene B4 (LTB4) has been reported to stimulate monocytes and neutrophils, its role on dendritic cell (DC) activity has not been examined. Here, we investigated the expression of LTB4 receptor and the effect of LTB4 on human DC chemotaxis. We analyzed LTB4 receptors, BLT1 and BLT2, by using RT-PCR. DCs express BLT2 but not BLT1 mRNA. DCs were chemotactically migrated to LTB4. LTB4-induced DC chemotaxis was completely inhibited by pertussis toxin, indicating the role of Gi proteins. LTB4 induced mitogen activated protein kinase activation and Akt activation. LTB4-induced DC chemotaxis was mediated by extracellular signal-regulated protein kinase and phosphoinositide 3-kinase but not by p38 kinase. BLT2-selevite antagonist, LY255283, almost completely inhibited DC chemotaxis induced by LTB4 but not by Trp-Lys-Tyr-Met-Val-D-Met. Thus human myeloid DCs express functional BLT2 but not BLT1, suggesting a physiological role of LTB4 and BLT2 in regulating DC trafficking during induction of immune responses.

A small compound that inhibits lipopolysaccharide-induced tumor necrosis factor-alpha production

Lipopolysaccharide (LPS) is critically involved in the inflammatory responses via generation of several pro-inflammatory cytokines. Since tumor necrosis factor-alpha (TNF-alpha) is one of the major pro-inflammatory cytokines which is induced by LPS treatment, the development of molecules capable of modulating LPS-induced TNF-alpha production is an issue of concern. We identified a novel synthetic compound that inhibits LPS-induced TNF-alpha production in human peripheral blood mononuclear cells (PBMCs). The active compound SM-7409 inhibited LPS-induced TNF-alpha production in a concentration-dependent manner, showing maximal activity at 5 microM. SM-7409 inhibited LPS-induced TNF-alpha mRNA transcript accumulation and protein expression. We also found that SM-7409 strongly inhibits LPS-induced extracellular signal-regulated protein kinase activity in PBMCs. Moreover, we found that SM-7409 strongly inhibits the LPS-induced other pro-inflammatory cytokines, such as interleukin (IL)-1beta and IL-8 in PBMCs. SM-7409 also dramatically inhibits the LPS-induced TNF-alpha production in neutrophils. Taken together, our results demonstrate that SM-7409 is a synthetic compound that inhibits LPS-induced TNF-alpha production, and thus SM-7409 should be useful for the development of chemotherapies targeting LPS-mediated inflammatory responses.

Sphingosine-1-phosphate stimulates rat primary chondrocyte proliferation

Rat primary chondrocytes express the sphingosine-1-phosphate (S1P) receptor, S1P(2), S1P(3), S1P(4), but not S1P(1). When chondrocytes were stimulated with S1P or phytosphingosine-1-phosphate (PhS1P, an S1P(1)- and S1P(4)-selective agonist), phospholipase C-mediated cytosolic calcium increase was dramatically induced. S1P and PhS1P also stimulated two kinds of mitogen-activated protein kinases, extracellular signal-regulated kinase (ERK) and p38 kinase in chondrocytes. In terms of the two phospholipids-mediated functional modulation of chondrocytes, S1P and PhS1P stimulated cellular proliferation. The two phospholipids-induced chondrocyte proliferations were almost completely blocked by PD98059 but not by SB203580, suggesting that ERK but not p38 kinase is essentially required for the proliferation. Pertussis toxin almost completely inhibited the two phospholipids-induced cellular proliferation and ERK activation, indicating the crucial role of G(i) protein. This study demonstrates the physiological role of two important phospholipids (S1P and PhS1P) on the modulation of rat primary chondrocyte proliferation, and the crucial role played by ERK in the process.

Trp-Arg-Trp-Trp-Trp-Trp antagonizes formyl peptide receptor like 2-mediated signaling

Although formyl peptide receptor like 2 (FPRL2) has been regarded as an important classical chemoattractant receptor, its functional role and signaling pathway have not been fully investigated, because of the lack of its specific ligand. Recently F2L, a heme-binding protein fragment peptide, has been reported as an FPRL2-selective endogenous agonist. In the present study, we examined the effect of Trp-Arg-Trp-Trp-Trp-Trp-CONH2 (WRWWWW, WRW4), on F2L-induced cell signaling. WRW4 inhibited the activation of FPRL2 by F2L, resulting in the complete inhibition of intracellular calcium increase and chemotactic migration induced by F2L. WRW4 also completely inhibited F2L-induced NF-kappaB activation in FPRL2-transfected HEK293 cells. WRW4 specifically inhibited F2L-induced intracellular calcium increase and chemotactic migration in mature monocyte-derived dendritic cells, which express FPRL2 but not the other FPR family. Taken together, WRW4 is the first FPRL2 antagonist and is expected to be useful in the study of FPRL2 signaling and in development of drugs against FPRL2-related cellular responses.

Serum Amyloid A Induces Contrary Immune Responses via Formyl Peptide Receptor-Like 1 in Human Monocytes

Although the level of serum amyloid A has been reported to be up-regulated during inflammatory response, the role of serum amyloid A on the regulation of inflammation and immune response has not been elucidated. We found that serum amyloid A stimulated the production of tumor necrosis factor (TNF)-alpha and interleukin (IL)-10, which are proinflammatory and anti-inflammatory cytokines, respectively, in human monocytes. Low concentrations of serum amyloid A stimulated TNF-alpha production with maximal activity at 6 h after stimulation, whereas high concentrations of serum amyloid A stimulated IL-10 production with maximal activity at 12 h. The activations of the two cytokines by serum amyloid A occurred at both the transcription and translational levels. Signaling events induced by serum amyloid A included the activation of two mitogen-activated protein kinases (extracellular signal-regulated kinase and p38 kinase), which were found to be required for TNF-alpha and IL-10 production, respectively. The stimulation of formyl peptide receptor-like-1-expressing RBL-2H3 cells, but not of vector-expressing RBL-2H3 cells with serum amyloid A, induced mitogen-activated protein kinases activation and the accumulation of the RNAs of these two cytokines. Together, our findings suggest that serum amyloid A modulates contrary immune responses via formyl peptide receptor-like 1, by inducing TNF-alpha or IL-10, and demonstrate that extracellular signal-regulated kinase and p38 kinase play counteracting roles in this process.

Pituitary Adenylate Cyclase-Activating Polypeptide 27 Is a Functional Ligand for Formyl Peptide Receptor-Like 1

Although the neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) has been implicated in the regulation of several immune responses, its target receptors and signaling mechanisms have yet to be fully elucidated in immune cells. In this study, we found that PACAP27, but not PACAP38, specifically stimulated intracellular calcium mobilization and ERK phosphorylation in human neutrophils. Moreover, formyl peptide receptor-like 1 (FPRL1) was identified as a PACAP27 receptor, and PACAP27 was found to selectively stimulate intracellular calcium increase in FPRL1-transfected rat basophil leukocytes-2H3 cell lines. In addition, PACAP27-induced calcium increase and ERK phosphorylation were specifically inhibited by an FPRL1 antagonist, Trp-Arg-Trp-Trp-Trp-Trp (WRW4), thus supporting the notion that PACAP27 acts on FPRL1. In terms of the functional role of PACAP27, we found that the peptide stimulated CD11b surface up-regulation and neutrophil chemotactic migration, and that these responses were completely inhibited by WRW4. The interaction between PACAP27 and FPRL1 was analyzed further using truncated PACAPs and chimeric PACAPs using vasoactive intestinal peptide, and the C-terminal region of PACAP27 was found to perform a vital function in the activation of FPRL1. Taken together, our study suggests that PACAP27 activates phagocytes via FPRL1 activation, and that this results in proinflammatory behavior, involving chemotaxis and the up-regulation of CD11b.

Lysophosphatidylserine Stimulates L2071 Mouse Fibroblast Chemotactic Migration via a Process Involving Pertussis Toxin-Sensitive Trimeric G-Proteins

Lysophosphatidylserine (LPS) may be generated after phosphatidylserine-specific phospholipase A2 activation. However, the effects of LPS on cellular activities and the identities of its target molecules have not been fully elucidated. In this study, we observed that LPS stimulates an intracellular calcium increase in L2071 mouse fibroblast cells, and that this increase was inhibited by 1-[6-((17beta-3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl]-1H-pyrrole-2,5-dione (U-73122) but not by pertussis toxin, suggesting that LPS stimulates calcium signaling via G-protein coupled receptor-mediated phospholipase C activation. Moreover, LPS-induced calcium mobilization was not inhibited by the lysophosphatidic acid receptor antagonist, (S)-phosphoric acid mono-{2-octadec-9-enoylamino-3-[4-(pyridine-2-ylmethoxy)-phenyl]-propyl} ester (VPC 32183), thus indicating that LPS binds to a receptor other than lysophosphatidic acid receptors. It was also found that LPS stimulates two types of mitogen-activated protein kinase [i.e., extracellular signal-regulated protein kinase (ERK) and p38 kinase] in L2071 cells. Furthermore, these LPS-induced ERK and p38 kinase activations were inhibited by pertussis toxin, which suggests the role of pertussis toxin-sensitive G-proteins in the process. In terms of functional issues, LPS stimulated L2071 cell chemotactic migration, which was completely inhibited by pertussis toxin, indicating the involvement of pertussis toxin-sensitive G(i) protein(s). This chemotaxis of L2071 cells induced by LPS was also dramatically inhibited by 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY294002) and by 2'-amino-3'-methoxyflavone (PD98059). This study demonstrates that LPS stimulates at least two different signaling cascades, one of which involves a pertussis toxin-insensitive but phospholipase C-dependent intracellular calcium increase, and the other involves a pertussis toxin-sensitive chemotactic migration mediated by phosphoinositide 3-kinase and ERK.

Lysophosphatidic acid stimulates cell proliferation in rat chondrocytes

Rat primary chondrocytes express the lysophosphatidic acid (LPA) receptor, LPA1, LPA3, but not LPA2. When chondrocytes were stimulated with LPA, phospholipase C-mediated cytosolic calcium increase was dramatically induced. LPA also stimulated two kinds of mitogen-activated protein kinase, extracellular signal-regulated kinase (ERK) and p38 kinase in chondrocytes. In terms of the LPA-mediated functional modulation of chondrocytes, LPA stimulated cellular proliferation. We examined the signaling pathways involved in LPA-mediated cellular proliferation. LPA-induced chondrocyte proliferation was almost completely blocked by 2'-amino-3'-methoxyflavone (PD98059) but not by 4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)1H-imidazole (SB203580), suggesting that ERK activity is essentially required for the process. Pertussis toxin almost completely inhibited the LPA-induced cellular proliferation and ERK activation, indicating the role of G(i/o) protein(s) in the processes. This study demonstrates the physiological role of LPA on the modulation of rat primary chondrocyte proliferation, and the crucial role played by ERK in the process.