G-protein-coupled receptors in HL-60 human leukemia cells

A2B adenosine receptor-triggered intracellular calcium mobilization: Cell type-dependent involvement of Gi, Gq, Gs proteins and protein kinase C

Activation of PLCβ enzymes by Giβγ and Gαq/11 proteins is a common mechanism to trigger cytosolic Ca2+ increase. We and others reported that Gαq/11 inhibitor FR900359 (FR) can inhibit both Gαq- and, surprisingly, Giβγ-mediated intracellular Ca2+ mobilization. Thus, the Gαi-Gβγ-PLCβ-Ca2+ signaling axis depends entirely on the presence of active Gαq, which reasonably explained FR-inhibited Giβγ-induced Ca2+ release. However, the conclusion that Giβγ signaling is controlled by Gαq derives mostly from HEK293 cells. Here we show that indeed in HEK293 cells both Gαq/11 siRNA and Gαq/11 inhibitors diminished Ca2+ increase triggered by native Gq-coupled P2Y1 receptors, or by transfected Gi-coupled A1- or Gs-coupled A2B adenosine receptors (ARs). However, in T24 bladder cancer cells, Gi inhibitor PTX, but not Gαq/11 inhibitors, FR, YM254890 (YM) or Gq/11 siRNA, inhibited Ca2+ increase triggered by native A2BAR activation. Simultaneous inactivation of Gi and Gs further suppressed A2BAR-triggered Ca2+ increase in T24 cells. The Gαq/11 inhibitor YM fully and partially inhibited endogenous P2Y1- and β2-adrenergic receptor-induced Ca2+ increase in T24 cells, respectively. PKC activator PMA partially diminished A2BAR-triggered but completely diminished β2-adrenergic receptor-triggered Ca2+ increase in T24 cells. Neither β-arrestin1 nor β-arrestin2 siRNA affected A2BAR-mediated Ca2+ increase. Unlike in T24 cells, YM inhibited native A2BAR-triggered calcium mobilization in MDA-MB-231 breast cancer cells. Thus, Gαq/11 is vital for Ca2+ increase in some cell types, but Giβγ-mediated Ca2+ signaling can be Gαq/11-dependent or independent based on cell type and receptor activated. Besides G proteins, PKC also modulates cytosolic Ca2+ increase depending on cell type and receptor.

A2B adenosine receptor-triggered intracellular calcium mobilization: Cell type-dependent involvement of Gi, Gq, Gs proteins and protein kinase C

Activation of PLCβ enzymes by Giβγ and Gαq/11 proteins is a common mechanism to trigger cytosolic Ca2+ increase. We and others reported that Gαq/11 inhibitor FR900358 (FR) can inhibit both and Gαq- and, surprisingly, Giβγ-mediated intracellular Ca2+ mobilization. Thus, the Gαi-Gβγ-PLCβ-Ca2+ signaling axis depends entirely on the presence of active Gαq, which reasonably explained FR-inhibited Giβγ-induced Ca2+ release. However, the conclusion that Giβγ signaling is controlled by Gαq derives mostly from HEK293 cells. Here we show that indeed in HEK293 cells both Gαq/11 siRNA and Gαq/11 inhibitors diminished Ca2+ increase triggered by native Gq-coupled P2Y1 receptors, or by transfected Gi-coupled A1-or Gs-coupled A2B adenosine receptors (ARs). However, in T24 bladder cancer cells, Gi inhibitor PTX, but not Gαq/11 inhibitors, FR, YM254890 (YM) or Gq/11 siRNA, inhibited Ca2+ increase triggered by native A2BAR activation. Simultaneous inactivation of Gi and Gs further suppressed A2BAR-triggered Ca2+ increase in T24 cells. The Gαq/11 inhibitor YM fully and partially inhibited endogenous P2Y1- and β2-adrenergic receptor-induced Ca2+ increase in T24 cells, respectively. PKC activator PMA partially diminished A2BAR-triggered but completely diminished β2-adrenergic receptor-triggered Ca2+ increase in T24 cells. Neither β-arrestin1 nor β-arrestin2 siRNA affected A2BAR-mediated Ca2+ increase. Unlike in T24 cells, YM inhibited native A2BAR-triggered calcium mobilization in MDA-MB-231 breast cancer cells. Thus, Gαq/11 is vital for Ca2+ increase in some cell types, but Giβγ-mediated Ca2+ signaling can be Gαq/11-dependent or independent based on cell type and receptor activated. Besides G proteins, PKC also modulates cytosolic Ca2+ increase depending on cell type and receptor.

GNA12 regulates C5a-induced migration by downregulating C5aR1-PLCβ2-PI3K-AKT-ERK1/2 signaling

Gna12 has been identified as one of the reported inflammatory bowel disease (IBD) susceptibility genes in genome-wide association studies (GWAS). However, the function of GNA12 in intestinal homeostasis remains unknown. Here we report that GNA12, a G-protein α subunit, regulates C5a-induced migration in macrophages. Deficiency of GNA12 results in enhanced migration induced by C5a in macrophages. Mechanistically, GNA12 suppresses C5a-induced migration by downregulating the C5aR1-PLCβ2-PI3K-AKT-ERK1/2 signaling. Therefore, our study reveals that GNA12 is an anti-inflammatory factor, which might alleviate the development of inflammation by inhibiting the excessive chemotactic migration of macrophages.

KRIT1-mediated regulation of neutrophil adhesion and motility

Loss of Krev interaction-trapped-1 (KRIT1) expression leads to the development of cerebral cavernous malformations (CCM), a disease in which abnormal blood vessel formation compromises the structure and function of the blood-brain barrier. The role of KRIT1 in regulating endothelial function is well-established. However, several studies have suggested that KRIT1 could also play a role in regulating nonendothelial cell types and, in particular, immune cells. In this study, we generated a mouse model with neutrophil-specific deletion of KRIT1 in order to investigate the effect of KRIT1 deficiency on neutrophil function. Neutrophils isolated from adult Ly6Gtm2621(cre)Arte Krit1flox/flox mice had a reduced ability to attach and spread on the extracellular matrix protein fibronectin and exhibited a subsequent increase in migration. However, adhesion to and migration on ICAM-1 was unchanged. In addition, we used a monomeric, fluorescently-labelled fragment of fibronectin to show that integrin activation is reduced in the absence of KRIT1 expression, though β1 integrin expression appears unchanged. Finally, neutrophil migration in response to lipopolysaccharide-induced inflammation in the lung was decreased, as shown by reduced cell number and myeloperoxidase activity in lavage samples from Krit1PMNKO mice. Altogether, we show that KRIT1 regulates neutrophil adhesion and migration, likely through regulation of integrin activation, which can lead to altered inflammatory responses in vivo.

Studying Neutrophil Function in vitro: Cell Models and Environmental Factors

Neutrophils are the most abundant immune cell type in the blood and constitute the first line of defense against invading pathogens. Despite their important role in many diseases, they are challenging to study due to their short life span and the inability to cryopreserve or expand them in vitro. Thus, research into neutrophils has to rely on cells freshly isolated from peripheral blood of human donors, introducing donor-dependent variation in the experimental data. To counteract these problems, researchers tried to develop adequate cell models, such as cell lines. For those functional studies that cannot rely on cell models, a standardization of protocols regarding neutrophil purification and culturing could be a solution. In this review, we provide an overview of the most commonly used models for neutrophil function (HL-60, PLB-985, NB4, Kasumi-1 and induced pluripotent stem cells). In addition, we describe the effects of glucose concentration, pH, oxygen tension and temperature on neutrophil function.

Cudrania tricuspidata Extract Protects against Reflux Esophagitis by Blocking H2 Histamine Receptors

Cudrania tricuspidata has been used in East Asia as a folk medicine for symptoms such as inflammation, allergy, and gastritis. Administration of C. tricuspidata extract to pylori-ligated rat stomachs reduces gastric acid secretion and alleviates esophagus damage caused by gastric reflux. Therefore, in this study we aimed to investigate whether C. tricuspidata extracts inhibit reflux esophagitis by blocking H₂ histamine receptor (H₂R). Dimaprit, a H₂R specific agonist, induced intracellular cyclic adenosine monophosphate (cAMP) production in U937 cells. Pretreatment with C. tricuspidata extracts significantly blocked dimaprit-induced cAMP production in a concentration-dependent manner. To extracted C. tricuspidata with different ethanol concentrations to determine the optimum method. We found that the 70% ethanol extract showed the most potent H₂R antagonistic effect against dimaprit-induced cAMP production. However, water extract did not show any H₂R blocking effect. These findings suggest that C. tricuspidata extracted using ethanol specifically inhibits gastric acid secretion and reduces esophageal injury by blocking H₂R in a competitive manner. Therefore, C. tricuspidata extracts may be used in food or medicine to prevent H₂R-related diseases, such as gastric hyperacidity and reflux esophagitis.

Surface modification of PGP for a neutrophil-nanoparticle co-vehicle to enhance the anti-depressant effect of baicalein

Exploiting cells as vehicles combined with nanoparticles combined with therapy has attracted increasing attention in the world recently. Red blood cells, leukocytes and stem cells have been used for tumor immunotherapy, tissue regeneration and inflammatory disorders, and it is known that neutrophils can accumulate in brain lesions in many brain diseases including depression. N-Acetyl Pro-Gly-Pro (PGP) peptide shows high specific binding affinity to neutrophils through the CXCR2 receptor. In this study, PGP was used to modify baicalein-loaded solid lipid nanoparticles (PGP-SLNs) to facilitate binding to neutrophils in vivo. Brain-targeted delivery to the basolateral amygdala (BLA) was demonstrated by enhanced concentration of baicalein in the BLA. An enhanced anti-depressant effect was observed in vitro and in vivo. The mechanism involved inhibition of apoptosis and a decrease in lactate dehydrogenase release. Behavioral evaluation carried out with rats demonstrated that anti-depression outcomes were achieved. The results indicate that PGP-SLNs decrease immobility time, increase swimming time and climbing time and attenuate locomotion in olfactory-bulbectomized (OB) rats. In conclusion, PGP modification is a strategy for targeting the brain with a cell-nanoparticle delivery system for depression therapy.

Direct Macromolecular Drug Delivery to Cerebral Ischemia Area using Neutrophil-Mediated Nanoparticles

Delivery of macromolecular drugs to the brain is impeded by the blood brain barrier. The recruitment of leukocytes to lesions in the brain, a typical feature of neuroinflammation response which occurs in cerebral ischemia, offers a unique opportunity to deliver drugs to inflammation sites in the brain. In the present study, cross-linked dendrigraft poly-L-lysine (DGL) nanoparticles containing cis-aconitic anhydride-modified catalase and modified with PGP, an endogenous tripeptide that acts as a ligand with high affinity to neutrophils, were developed to form the cl PGP-PEG-DGL/CAT-Aco system. Significant binding efficiency to neutrophils, efficient protection of catalase enzymatic activity from degradation and effective transport to receiver cells were revealed in the delivery system. Delivery of catalase to ischemic subregions and cerebral neurocytes in MCAO mice was significantly enhanced, which obviously reducing infarct volume in MCAO mice. Thus, the therapeutic outcome of cerebral ischemia was greatly improved. The underlying mechanism was found to be related to the inhibition of ROS-mediated apoptosis. Considering that neuroinflammation occurs in many neurological disorders, the strategy developed here is not only promising for treatment of cerebral ischemia but also an effective approach for various CNS diseases related to inflammation.

Pharmacological Characterization of Human Histamine Receptors and Histamine Receptor Mutants in the Sf9 Cell Expression System

A large problem of histamine receptor research is data heterogeneity. Various experimental approaches, the complex signaling pathways of mammalian cells, and the use of different species orthologues render it difficult to compare and interpret the published results. Thus, the four human histamine receptor subtypes were analyzed side-by-side in the Sf9 insect cell expression system, using radioligand binding assays as well as functional readouts proximal to the receptor activation event (steady-state GTPase assays and [35S]GTPγS assays). The human H1R was co-expressed with the regulators of G protein signaling RGS4 or GAIP, which unmasked a productive interaction between hH1R and insect cell Gαq. By contrast, functional expression of the hH2R required the generation of an hH2R-Gsα fusion protein to ensure close proximity of G protein and receptor. Fusion of hH2R to the long (GsαL) or short (GsαS) splice variant of Gαs resulted in comparable constitutive hH2R activity, although both G protein variants show different GDP affinities. Medicinal chemistry studies revealed profound species differences between hH1R/hH2R and their guinea pig orthologues gpH1R/gpH2R. The causes for these differences were analyzed by molecular modeling in combination with mutational studies. Co-expression of the hH3R with Gαi1, Gαi2, Gαi3, and Gαi/o in Sf9 cells revealed high constitutive activity and comparable interaction efficiency with all G protein isoforms. A comparison of various cations (Li+, Na+, K+) and anions (Cl-, Br-, I-) revealed that anions with large radii most efficiently stabilize the inactive hH3R state. Potential sodium binding sites in the hH3R protein were analyzed by expressing specific hH3R mutants in Sf9 cells. In contrast to the hH3R, the hH4R preferentially couples to co-expressed Gαi2 in Sf9 cells. Its high constitutive activity is resistant to NaCl or GTPγS. The hH4R shows structural instability and adopts a G protein-independent high-affinity state. A detailed characterization of affinity and activity of a series of hH4R antagonists/inverse agonists allowed first conclusions about structure/activity relationships for inverse agonists at hH4R. In summary, the Sf9 cell system permitted a successful side-by-side comparison of all four human histamine receptor subtypes. This chapter summarizes the results of pharmacological as well as medicinal chemistry/molecular modeling approaches and demonstrates that these data are not only important for a deeper understanding of HxR pharmacology, but also have significant implications for the molecular pharmacology of GPCRs in general.

Modulation of Human Neutrophil Responses by the Essential Oils from Ferula akitschkensis and Their Constituents

Essential oils were obtained by hydrodistillation of the umbels+seeds and stems of Ferula akitschkensis (FAEOu/s and FAEOstm, respectively) and analyzed by gas chromatography and gas chromatography-mass spectrometry. Fifty-two compounds were identified in FAEOu/s; the primary components were sabinene, α-pinene, β-pinene, terpinen-4-ol, eremophilene, and 2-himachalen-7-ol, whereas the primary components of FAEOstm were myristicin and geranylacetone. FAEOu/s, β-pinene, sabinene, γ-terpinene, geranylacetone, isobornyl acetate, and (E)-2-nonenal stimulated [Ca(2+)]i mobilization in human neutrophils, with the most potent being geranylacetone (EC50 = 7.6 ± 1.9 μM) and isobornyl acetate 6.4 ± 1.7 (EC50 = 7.6 ± 1.9 μM). In addition, treatment of neutrophils with β-pinene, sabinene, γ-terpinene, geranylacetone, and isobornyl acetate desensitized the cells to N-formyl-Met-Leu-Phe (fMLF)- and interleukin-8 (IL-8)-induced [Ca(2+)]i flux and inhibited fMLF-induced chemotaxis. The effects of β-pinene, sabinene, γ-terpinene, geranylacetone, and isobornyl acetate on neutrophil [Ca(2+)]i flux were inhibited by transient receptor potential (TRP) channel blockers. Furthermore, the most potent compound, geranylacetone, activated Ca(2+) influx in TRPV1-transfected HEK293 cells. In contrast, myristicin inhibited neutrophil [Ca(2+)]i flux stimulated by fMLF and IL-8 and inhibited capsaicin-induced Ca(2+) influx in TRPV1-transfected HEK293 cells. These findings, as well as pharmacophore modeling of TRP agonists, suggest that geranylacetone is a TRPV1 agonist, whereas myristicin is a TRPV1 antagonist. Thus, at least part of the medicinal properties of Ferula essential oils may be due to modulatory effects on TRP channels.

The histamine H4-receptor and the central and peripheral nervous system: A critical analysis of the literature

Expression and function of histamine H4R in central and peripheral nervous system have been a matter of controversy for more than a decade. The scientific discussion is often limited to a few publications postulating the presence of functional H4R on neurons of the central and peripheral nervous system, but the even larger number of reports showing negative data is often neglected. In this article, we critically review the existing literature on H4R in central and peripheral nervous system and discuss the weak points often overlooked by the community. We identified as most important problems (i) insufficient validation or quality of antibodies, (ii) missing knockout controls, (iii) uncritical interpretation of RT-PCR results instead of qPCR experiments, (iv) insufficient controls to confirm specificity of pharmacological tools, (v) uncritical reliance on results produced by a single method and (vi) uncritical reliance on results not reproduced by independent research groups. Additionally, there may be a publication as well as a citation bias favoring the awareness of positive results, but neglecting negative data. We conclude that H4R expression on neurons of the brain is not convincingly supported by the current literature, at least as long as the positive data are not reproduced by independent research groups. Expression and function of H4R on peripheral neurons or non-neuronal cells of the nervous system, specifically on microglia is an interesting alternative hypothesis that, however, requires further verification. This article is part of a Special Issue entitled 'Histamine Receptors'.

No evidence for histamine H4 receptor in human monocytes

The histamine H4 receptor (H4R) is a classic pertussis toxin-sensitive Gi protein-coupled receptor that mediates increases in intracellular calcium concentration ([Ca(2+)]i). The presence of H4R in human eosinophils has been rigorously documented by several independent groups. It has also been suggested that H4R is expressed in human monocytes, but this suggestion hinges in part on H4R antibodies with questionable specificity. This situation prompted us to reinvestigate H4R expression in human monocytes. As positive control, we studied human embryonic kidney 293T cells stably expressing the human H4R (hH4R). In these cells, histamine (HA) and the H4R agonist UR-PI376 (2-cyano-1-[4-(1H-imidazol-4-yl)butyl]-3-[(2-phenylthio)ethyl]guanidine) induced pertussis toxin-sensitive [Ca(2+)]i increases. However, in quantitative real-time polymerase chain reaction studies we failed to detect hH4R mRNA in human monocytes and U937 promonocytes. In human monocytes, ATP and N-formyl-l-methionyl-l-leucyl-l-phenylalanine increased [Ca(2+)]i, but HA, UR-PI376, and 5-methylhistamine (a dual H4R/H2 receptor agonist) did not. In U937 promonocytes and differentiated U937 cells, HA increased [Ca(2+)]i, but this increase was mediated via HA H1 receptor. In conclusion, there is no evidence for the presence of H4R in human monocytes.

Functional selectivity of G-protein-coupled receptors: from recombinant systems to native human cells

In the mid 1990s, it was assumed that a two-state model, postulating an inactive (R) state and an active (R*) state provides the molecular basis for GPCR activation. However, it became clear that this model could not accommodate many experimental observations. Accordingly, the two-state model was superseded by a multi-state model according to which any given ligand stabilizes a unique receptor conformation with distinct capabilities of activating down-stream G-proteins and β-arrestin. Much of this research was conducted with the β2-adrenoceptor in recombinant systems. At the molecular level, there is now no doubt anymore that ligand-specific receptor conformations, also referred to as functional selectivity, exist. This concept holds great potential for drug discovery in terms of developing drugs with higher selectivity for specific cells and/or cell functions and fewer side effects. A major challenge is the analysis for functional selectivity in native cells. Here, I discuss our current knowledge on functional selectivity of three representative GPCRs, the β2-adrenoceptor and the histamine H2- and H4-receptors, in recombinant systems and native human cells. Studies with human neutrophils and eosinophils support the concept of functional selectivity. A major strategy for the analysis of functional selectivity in native cells is to generate complete concentration/response curves with a large set of structurally diverse ligands for multiple parameters. Next, correlations of potencies and efficacies are analyzed, and deviations of the correlations from linearity are indicative for functional selectivity. Additionally, pharmacological inhibitors are used to dissect cell functions from each other.

Lung inflammation caused by adenosine-5'-triphosphate is mediated via Ca2+/PKCs-dependent COX-2/PGE2 induction

Up-regulation of cyclooxygenase (COX)-2 and prostaglandin E2 (PGE2) are implicated in lung inflammation. Adenosine 5'-triphosphate (ATP) has been shown to act via activation of P2 purinoceptors, leading to COX-2 expression in various inflammatory diseases. The mechanisms of ATP-induced COX-2 expression and PGE2 release remain unclear. We showed that pretreatment with the inhibitors of P2 receptors (PPADS and Suramin), Gq protein (GPA2A), phosphatidylcholine-phospholipase C (PC-PLC; D609), phosphoinositide-phospholipase C (PI-PLC; ET-18-OCH3), Ca(2+)/calmodulin-dependent protein kinase II (CaMKII; KN62), protein kinase C (PKC; Gö6976, Ro-318220, GF109203X, and rottlerin), MEK1/2 (PD98059), p38 MAPK (SB202190), and nuclear factor-kappaB (NF-κB; Bay11-7082) and the intracellular calcium chelator (BAPTA/AM) or transfection with siRNAs of these molecules and cPLA2 reduced ATPγS-induced COX-2 expression or PGE2 production in A549 cells. In addition, ATPγS-induced elevation of intracellular Ca(2+) concentration was attenuated by PPADS, Suramin, D609, or ET-18-OCH3. ATPγS-induced p38 MAPK, p42/p44 MAPK, and NF-κB p65 activation were inhibited by Gö6976, Ro-318220, GF109203X, or rottlerin. ATPγS also induced cPLA2 phosphorylation and activity, which were reduced via inhibition of P2 receptors, PKCs, p38 MAPK, and p42/p44 MAPK. ATPγS-induced cPLA2 expression was inhibited by SB202190, PD98059, or Bay11-7082. In the in vitro study, we established that ATPγS induced PGE2 generation via a cPLA2/COX-2-dependent pathway. In the in vivo study, we found that ATPγS induced COX-2 mRNA expression in the lungs and leukocyte (mainly eosinophils and neutrophils) count in bronchoalveolar lavage (BAL) fluid in mice via a P2 receptors-dependent signaling pathway. We concluded that ATPγS may induce lung inflammation via a cPLA2/COX-2/PGE2-dependent pathway.

Evidence for ligand-specific conformations of the histamine H(2)-receptor in human eosinophils and neutrophils

The histamine H(2)-receptor (H(2)R) couples to G(S)-proteins and induces adenylyl cyclase-mediated cAMP accumulation. In human neutrophils and eosinophils, the H(2)R reduces chemotactic peptide-stimulated superoxide anion (O(2)(-)) formation. However, pharmacological characterization of the H(2)R in these cells is far from being complete. The aim of this study was to provide a comprehensive profiling of the H(2)R in neutrophils and eosinophils. Histamine inhibited O(2)(-) formation in human neutrophils more effectively than in eosinophils. H(2)R agonists mimicked the effects of histamine and H(2)R antagonists blocked the effects of histamine. We noticed multiple discrepancies in the potencies and efficacies of H(2)R agonists with respect to cAMP accumulation and inhibition of O(2)(-) formation in both cell types. There were also differences in the antagonist profiles between cAMP accumulation and inhibition of O(2)(-) formation in neutrophils. Moreover, the pharmacological profile of the recombinant H(2)R did not match the H(2)R profile in native cells. The H(2)R sequence identified in human neutrophils corresponds to the published H(2)R sequence, excluding the exclusive expression of a new H(2)R isoform as explanation for the differences. Very likely, the differences between ligands are explained by the existence of ligand-specific receptor conformations with unique affinities, potencies and efficacies. Thus, our data provide evidence for the notion that the concept of ligand-specific receptor conformations can be extended from recombinant systems to native cells.

The signaling mechanisms mediating the inhibitory effect of TCH-1116 on formyl peptide-stimulated superoxide anion generation in neutrophils

In fMLP (formyl-Met-Leu-Phe)-stimulated rat neutrophils, a mixture of regioisomers benzo[a]furo[2,3-c]phenazine-10-carboxylic acid and benzo[a]furo[2,3-c]phenazine-11-carboxylic acid (TCH-1116) inhibited O(2)(-) (superoxide anion) generation, which was not mediated by scavenging the generated O(2)(-) or by a cytotoxic effect on neutrophils. TCH-1116 had no effect on the arachidonic acid-induced NADPH oxidase activation in a cell-free system, whereas it effectively attenuated the phosphorylation of Ser residues in p47(phox) and the association between p47(phox) and p22(phox) in fMLP-stimulated neutrophils. The interaction of p47(phox) with PKC (protein kinase C) isoforms (α, βI, βII, δ and ζ) was attenuated by TCH-1116, whereas TCH-1116 did not affect the PKC isoforms membrane translocation, phosphorylation (Ser660) and kinase activity. TCH-1116 effectively attenuated the association between PKB/Akt (protein kinase B) and p47(phox), Akt phosphorylation (Thr308/Ser473) and kinase activities of Akt and human recombinant PDK (3-phosphoinositide-dependent kinase) 1, whereas it had no effect on recruitment of Akt, phospho-PDK1 (Ser241) and p110γ to membrane. Moreover, the interaction of p21-activated kinase (PAK) 1 with p47(phox) and the phosphorylation of PAK1 (Thr423 but not Ser144) were inhibited by TCH-1116, but without affecting the membrane recruitment of PAK1. The cellular cyclic AMP level was not changed by TCH-1116. Taken together, these results suggest that TCH-1116 inhibits fMLP-stimulated O(2)(-) generation in rat neutrophils through the blockade of PKC, Akt and PAK signaling pathways.

Signalling and pharmacological properties of the P2Y receptor

The P2Y(14) receptor is a relatively broadly expressed G protein-coupled receptor that is prominently associated with immune and inflammatory cells as well as with many epithelia. This receptor historically was thought to be activated selectively by UDP-glucose and other UDP-sugars. However, UDP is also a very potent agonist of this receptor, and may prove to be one of its most important cognate activators.

Gi-dependent cell signaling responses of the human P2Y14 receptor in model cell systems

Eight G protein-coupled receptors comprise the P2Y receptor family of cell signaling proteins. The goal of the current study was to define native cell signaling pathways regulated by the uridine nucleotide sugar-activated P2Y(14) receptor (P2Y(14)-R). The P2Y(14)-R was stably expressed in human embryonic kidney (HEK) 293 and C6 rat glioma cells by retroviral infection. Nucleotide sugar-dependent P2Y(14)-R activation was examined by measuring inhibition of forskolin-stimulated cAMP accumulation. The effect of P2Y(14)-R activation on mitogen-activated protein kinase signaling also was studied in P2Y(14)-HEK293 cells and in differentiated HL-60 human myeloid leukemia cells. UDP-Glc, UDP-galactose, UDP-glucuronic acid, and UDP-N-acetylglucosamine promoted inhibition of forskolin-stimulated cAMP accumulation in P2Y(14)-HEK293 and P2Y(14)-C6 cells, and this signaling effect was abolished by pretreatment of cells with pertussis toxin. Inhibition of cAMP formation by nucleotide sugars also was observed in direct assays of adenylyl cyclase activity in membranes prepared from P2Y(14)-C6 cells. UDP-Glc promoted concentration-dependent and pertussis toxin-sensitive extracellular signal-regulated kinase (ERK) 1/2 phosphorylation in P2Y(14)-HEK293 cells. P2Y(14)-R mRNA was not observed in wild-type HL-60 cells but was readily detected in dimethyl sulfoxide-differentiated cells. Consistent with this observation, no effect of UDP-Glc was observed in wild-type HL-60 cells, but UDP-Glc-promoted pertussis toxin-sensitive activation of ERK1/2 occurred after differentiation. These results illustrate that the human P2Y(14)-R signals through G(i) to inhibit adenylyl cyclase, and P2Y(14)-R activation also leads to ERK1/2 activation. This work also identifies two stable P2Y(14)-R-expressing cell lines and differentiated HL-60 cells as model systems for the study of P2Y(14)-R-dependent signal transduction.

Inhibition of superoxide anion generation by CHS-111 via blockade of the p21-activated kinase, protein kinase B/Akt and protein kinase C signaling pathways in rat neutrophils

In formyl-Met-Leu-Phe (fMLP)-stimulated rat neutrophils, 2-benzyl-3-(4-hydroxymethylphenyl)indazole (CHS-111) inhibited superoxide anion (O(2)(-)) generation, which was not mediated by scavenging the generated O(2)(-) or by a cytotoxic effect, and attenuated migration. CHS-111 had no effect on the arachidonic acid-induced NADPH oxidase activation or the GTPgammaS-stimulated Rac2 membrane translocation in cell-free systems, whereas it effectively attenuated the membrane recruitment of p40(phox), p47(phox) and p67(phox), phosphorylation of Ser residues in p47(phox), association between p47(phox) and p22(phox), and Rac activation in fMLP-stimulated neutrophils. Moreover, the phosphorylation and membrane recruitment of p21-activated kinase (PAK), PAK kinase activity and the interaction of PAK with p47(phox) were inhibited by CHS-111. CHS-111 effectively reduced Akt kinase activity and the association between Akt and p47(phox), moderately inhibited the membrane recruitment of Akt and phospho-PDK1, and slightly attenuated Akt (Thr308) phosphorylation, whereas it had no effect on Akt (Ser473) phosphorylation or p110gamma membrane translocation. The membrane recruitment of protein kinase C (PKC)-alpha, -betaI, -betaII, -delta and -zeta, PKC phosphorylation and PKC kinase activity was attenuated by CHS-111, whereas CHS-111 did not affect the phosphorylation of p38 mitogen-activated protein kinase (MAPK) or downstream MAPK-activated protein kinase-2. Higher concentrations of CHS-111 were required to decrease fMLP-stimulated intracellular free Ca(2+) concentration ([Ca(2+)](i)) elevation in the presence but not in the absence of extracellular Ca(2+), and to reduce cellular cyclic AMP but slightly increase cyclic GMP levels. Taken together, these results suggest that CHS-111 inhibits fMLP-stimulated O(2)(-) generation in rat neutrophils through the blockade of PAK, Akt and PKC signaling pathways.

Mitocryptide-2: purification, identification, and characterization of a novel cryptide that activates neutrophils

Neutrophils are a class of leukocytes involved in innate immunity by monitoring and scavenging invading microorganisms and toxic substances. The actions of neutrophils in damaged tissues are still not well understood, particularly in the early stage of inflammation, and as-yet-unknown neutrophil-activating substances are proposed to induce their acute transmigration and activation. Here, we isolated and identified from porcine hearts a neutrophil-activating peptide. Structural analyses indicated that the primary structure of this peptide is formyl-Met-Thr-Asn-Ile-Arg-Lys-Ser-His-Pro-Leu-Met-Lys-Ile-Ile-Asn, which is identical to that of the N-terminal pentadecapeptide of porcine mitochondrial cytochrome b; we therefore named the newly isolated peptide "mitocryptide-2" (MCT-2), since we have recently purified and identified mitocryptide-1, a different class of a neutrophil-activating peptide. Synthetic MCT-2 and its human homolog hMCT-2 induced beta-hexosaminidase release in and chemotaxis of HL-60 cells differentiated into neutrophilic/granulocytic cells. The induction of beta-hexosaminidase release, chemotaxis, and the increase in the intracellular free Ca(2+) concentration by hMCT-2 were completely suppressed by pertussis toxin, indicating the involvement of G(i)- or G(o)-type G proteins in the signaling pathways. Moreover, MCT-2 and hMCT-2 also stimulated beta-hexosaminidase secretion in human neutrophils isolated from peripheral blood in a concentration-dependent manner. Additionally, these peptides partially competed with [(3)H]formyl-Met-Leu-Phe binding to HL-60 cells differentiated into neutrophilic/granulocytic cells, presenting the possibility that the receptor for MCT-2 and hMCT-2 is one of the formyl peptide receptors. These results demonstrate that MCT-2 and its human homolog hMCT-2 are cryptides that activate neutrophils, thus suggesting the presence of regulatory mechanisms involving such mitocryptides in innate immunity.

Discovery of mitocryptide-1, a neutrophil-activating cryptide from healthy porcine heart

Although neutrophils are known to migrate in response to various chemokines and complement factors, the substances involved in the early stages of their transmigration and activation have been poorly characterized to date. Here we report the discovery of a peptide isolated from healthy porcine hearts that activated neutrophils. Its primary structure is H-Leu-Ser-Phe-Leu-Ile-Pro-Ala-Gly-Trp-Val-Leu-Ser-His-Leu-Asp-His-Tyr-Lys-Arg-Ser-Ser-Ala-Ala-OH, and it was indicated to originate from mitochondrial cytochrome c oxidase subunit VIII. This peptide caused chemotaxis at concentrations lower than that inducing beta-hexosaminidase release. Such responses were observed in neutrophilic/granulocytic differentiated HL-60 cells but not in undifferentiated cells, and G(i2)-type G proteins were suggested to be involved in the peptide signaling. Moreover the peptide activated human neutrophils to induce beta-hexosaminidase secretion. A number of other amphipathic neutrophil-activating peptides presumably originating from mitochondrial proteins were also found. The present results suggest that neutrophils monitor such amphipathic peptides including the identified peptide as an initiation signal for inflammation at injury sites.

Migration of dendritic cell subsets and their precursors

The ability of dendritic cells (DCs) to initiate and orchestrate immune responses is a consequence of their localization within tissues and their specialized capacity for mobilization. The migration of a given DC subset is typified by a restricted capacity for recirculation, contrasting markedly with T cells. Routes of DC migration into lymph nodes differ notably for distinct DC subsets. Here, we compare the distinct migratory patterns of plasmacytoid DCs (pDCs), CD8alpha(+) DCs, Langerhans cells, and conventional myeloid DCs and discuss how the highly regulated patterns of DC migration in vivo may affect their roles in immunity. Finally, to gain a more molecular appreciation of the specialized migratory properties of DCs, we review the signaling cascades that govern the process of DC migration.

Formyl peptide receptor-mediated ERK1/2 activation occurs through G(i) and is not dependent on beta-arrestin1/2

Formyl peptide receptor (FPR) and C5a receptor (C5aR) are chemoattractant G protein-coupled receptors (GPCRs) involved in the innate immune response against bacterial infections and tissue injury. Like other GPCRs, they recruit beta-arrestin1/2 to the plasma membrane and activate the extracellular signal-regulated kinases 1 and 2 (ERK1/2). Previous studies with several GPCRs have suggested that beta-arrestins play an important role as signal transducers by scaffolding signaling molecules such as ERK1/2. This function of the beta-arrestins was not discovered until several years after their role in desensitization and endocytosis had been reported. In this study, we investigated the role of the beta-arrestins in the activation of ERK1/2 and receptor endocytosis. We took advantage of previously described mutants of FPR that have defects in G(i) coupling or beta-arrestin recruitment. The results obtained with the mutant FPRs, as well as experiments using an inhibitor of G(i) and cells overexpressing beta-arrestin2, showed that activation of ERK1/2 takes place through G(i) and is not affected by beta-arrestins. However, overexpression of beta-arrestin2 does enhance FPR sequestration from the cell surface, suggesting a role in desensitization, as shown for many other GPCRs. Experiments with CHO C5aR cells showed similar sensitivity to the G(i) inhibitor as CHO FPR cells, suggesting that the predominant activation of ERK1/2 through G protein may be a common characteristic among chemoattractant receptors.

IL-8 release of HL-60 cells treated with electric currents of different wave forms

Human promyelocytic leukaemia HL-60 cells which have been differentiated by DMSO to granulocytes were used to investigate the effect of different waveforms on the release of interleukine-8 (IL-8). The cells were prestimulated with 100 pM fMLP and subsequently treated for 15 min with different electrical fields and currents. Three hours later the release of IL-8 into the medium was determined by ELISA. Varying the frequency of the sinusoidal electrical current between 0 and 20 Hz resulted in 2 maxima of IL-8 release at 5 and 13 Hz. Prestimulated cells were treated with sine-, triangular-, and rectangular-waveforms at 5 Hz in the current intensity range of 0-3 mA/cm(2). For the three waveforms tested, the IL-8 release was enhanced 1.5 fold. Treatment of the cells with capacitively coupled electric fields of 5 Hz using field strengths between 0 and 10 V(eff)/cm had no effect on the release of IL-8. In comparison to the positive results after sine wave exposure alone, an exposure with sine wave current to which noise had been superimposed had no effect on the HL-60 cells. From these investigations it can be concluded that for electrical current treatment of prestimulated HL-60 cells the release of IL-8 does not depend on the waveform if the waveform information is not destroyed by superimposed noise.

Isoliquiritigenin selectively inhibits H(2) histamine receptor signaling

Isoliquiritigenin, one of the major constituents of Glycyrrhiza uralensis (licorice), is a natural pigment with a simple chalcone structure 4,2',4'-trihydroxychalcone. In this study, isoliquiritigenin showed selective H(2) histamine receptor (H(2)R) antagonistic effect and remarkably reduced several H(2)R-mediated physiological responses. Preincubation of U937 and HL60 hematopoietic cells with isoliquiritigenin significantly inhibited H(2)R agonist-induced cAMP response in a concentration-dependent manner without affecting the viability of cells. Isoliquiritigenin also blocked the binding affinity of [(3)H]tiotidine to membrane receptors in HL-60 cells. Isoliquiritigenin did not affect the elevation of cAMP levels induced by cholera toxin, forskolin, or isoproterenol, indicating that the action site of isoliquiritigenin is not G(s) protein, effector enzyme, adenylyl cyclase, or beta(2)-adrenoceptor. Isoliquiritigenin affected neither H(1)R-nor H(3)R-mediated signaling. In molecular docking studies, isoliquiritigenin exhibited more favorable interactions with H(2)R than histamine. Isoliquiritigenin prominently inhibited H(2)R selective agonist dimaprit-induced cAMP generation in MKN-45 gastric cancer cell. Moreover, isoliquiritigenin reduced gastric acid secretion and protected gastric mucosal lesion formation in pylorus-ligated rat model. Taken together, the results demonstrate that isoliquiritigenin is an effective H(2)R antagonist and provides the basis for designing novel H(2)R antagonist.

N1-(3-cyclohexylbutanoyl)-N2-[3-(1H-imidazol-4-yl)propyl]guanidine (UR-AK57), a potent partial agonist for the human histamine H1- and H2-receptors

Both the histamine H1-receptor (H1R) and H2-receptor (H2R) exhibit pronounced species selectivity in their pharmacological properties; i.e., bulky agonists possess higher potencies and efficacies at guinea pig (gp) than at the corresponding human (h) receptor isoforms. In this study, we examined the effects of NG-acylated imidazolylpropylguanidines substituted with a single phenyl or cyclohexyl substituent on H1R and H2R species isoforms expressed in Sf9 insect cells. N1-(3-Cyclohexylbutanoyl)-N2-[3-(1H-imidazol-4-yl)propyl]guanidine (UR-AK57) turned out to be the most potent hH2R agonist identified so far (EC50 of 23 nM in the GTPase assay at the hH2R-Gsalpha fusion protein expressed in Sf9 insect cells). UR-AK57 was almost a full-hH2R agonist and only slightly less potent and efficacious than at gpH2R-Gsalpha. Several NG-acylated imidazolylpropylguanidines showed similar potency at hH2R and gpH2R. Most unexpectedly, UR-AK57 exhibited moderately strong partial hH1R agonism with a potency similar to that of histamine, whereas at gpH1R, UR-AK57 was only a very weak partial agonist. Structure/activity relationship studies revealed that both the alkanoyl chain connecting the aromatic or alicyclic substituent with the guanidine moiety and the nature of the carbocycle (cyclohexyl versus phenyl ring) critically determine the pharmacological properties of this class of compounds. Collectively, our data show that gpH1R and gpH R do not necessarily exhibit preference for bulky agonists (2) compared with hH1R and hH2R, respectively, and that UR-AK57 is a promising starting point for the development of both potent and efficacious hH1R and hH2R agonists.

Probing ligand-specific histamine H1- and H2-receptor conformations with NG-acylated Imidazolylpropylguanidines

Impromidine (IMP) and arpromidine (ARP)-derived guanidines are more potent and efficacious guinea pig (gp) histamine H(2)-receptor (gpH(2)R) than human (h) H(2)R agonists and histamine H(1)-receptor (H(1)R) antagonists with preference for hH(1)R relative to gpH(1)R. We examined N(G)-acylated imidazolylpropylguanidines (AIPGs), which are less basic than guanidines, at hH(2)R, gpH(2)R, rat H(2)R (rH(2)R), hH(1)R, and gpH(1)R expressed in Sf9 cells as probes for ligand-specific receptor conformations. AIPGs were similarly potent H(2)R agonists as the corresponding guanidines IMP and ARP, respectively. Exchange of pyridyl in ARP against phenyl increased AIPG potency 10-fold, yielding the most potent agonists at the hH(2)R-G(salpha) fusion protein and gpH(2)R-G(salpha) identified so far. Some AIPGs were similarly potent and efficacious at hH(2)R-G(salpha) and gpH(2)R-G(salpha). AIPGs stabilized the ternary complex in hH(2)R-G(salpha) and gpH(2)R-G(salpha) differently than the corresponding guanidines. Guanidines, AIPGs, and small H(2)R agonists exhibited distinct agonist properties at hH(2)R, gpH(2)R, and rH(2)R measuring adenylyl cyclase activity. In contrast to ARP and IMP, AIPGs were partial H(1)R agonists exhibiting higher efficacies at hH(1)R than at gpH(1)R. This is remarkable because, so far, all bulky H(1)R agonists exhibited higher efficacies at gpH(1)R than at hH(1)R. Collectively, our data suggest that AIPGs stabilize different active conformations in hH(2)R, gpH(2)R, and rH(2)R than guanidines and that, in contrast to guanidines, AIPGs are capable of stabilizing a partially active state of hH(1)R.

Curcuma longa extract protects against gastric ulcers by blocking H2 histamine receptors

Curcuma longa has been commonly used as a traditional remedy for a variety of symptoms such as inflammation, gastritis and gastric ulcer. When C. longa extract was administered per os to pylori-ligated rat stomachs, it reduced gastric acid secretion and protected against the formation of gastric mucosal lesions. We therefore tested whether C. longa extract inhibits gastric ulcers by blocking the H(2) histamine receptor. Dimaprit, a H(2) histamine receptor agonist, induced intracellular cAMP production in U937 and HL-60 promyelocytes. Pretreatment with C. longa extract significantly blocked dimaprit-induced cAMP production in a concentration dependent manner, but had no effect on the elevation of cAMP levels triggered by isoproterenol-induced beta(2)-adrenoceptor activation in U937 cells. To identify the active component(s) of C. longa extract, we sequentially fractionated it by extraction with ethyl acetate, n-butanol and water. We found that the ethyl acetate extract showed the most potent H(2)R antagonistic effect against dimaprit-induced cAMP production. However, curcumin, a major component of C. longa extract, showed no H(2)R blocking effect. C. longa ethanol extract and ethylacetate extract also blocked the binding of [(3)H]-tiotidine to membrane receptors on HL-60 cells. These findings suggest that the extract from C. longa specifically inhibits gastric acid secretion by blocking H(2) histamine receptors in a competitive manner.

Response to genistein: Assaying the activation status and chemotaxis efficacy of isolated neutrophils

Neutrophil (PMN) activation and chemotaxis toward inflammatory stimuli play critical roles in host defense and tissue inflammation. To determine the molecular mechanisms that regulate PMN function, many studies currently employ in vitro PMN activation and transmigration assays using freshly isolated peripheral PMN or PMN isolated from bone marrow. However, due to the highly sensitive nature of PMN, cell activation or priming can occur during isolation, which demands assay(s) that ensure the consistency of isolated PMN prior to using them in subsequent experiments. Here, we introduce a simple screening assay based on the observation that in transmigration assays, isolated PMN differentially respond to the tyrosine kinase inhibitor genistein and this is related to their activation status. As shown, we observed that isolated PMN for which early migration is enhanced by genistein have an overall high transmigration efficacy and that over 80% of applied PMN migrate across collagen-coated filters in a 2 h time period. Conversely, the inhibitory/non-enhancement effect of genistein is accompanied by a poor PMN transmigration, with less than 25% of applied PMN transmigrating across. Further analysis of PMN spontaneous adhesion, degranulation and cell surface CD11b/CD18 expression suggests that reduced migration of PMN is associated with PMN activation/priming that happens, in most cases, during the in vitro cell isolation procedure regardless of the blood donor. Thus, based on these observations, we developed a "genistein assay" to directly predict PMN status after each isolation. From our experience, this assay has not only revealed new insights into the mechanisms of PMN activation and assisted in functional assays, but it has also provided a method that can be mastered by both inexperienced and experienced researchers to assay isolated PMN and thus avoid using inconsistent cells (e.g. pre-activated PMN) in their experiments.

Structural organization of the neutrophil NADPH oxidase: phosphorylation and translocation during priming and activation

The reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase is part of the microbicidal arsenal used by human polymorphonuclear neutrophils (PMNs) to eradicate invading pathogens. The production of a superoxide anion (O2-) into the phagolysosome is the precursor for the generation of more potent products, such as hydrogen peroxide and hypochlorite. However, this production of O2- is dependent on translocation of the oxidase subunits, including gp91phox, p22phox, p47phox, p67phox, p40phox, and Rac2 from the cytosol or specific granules to the plasma membrane. In response to an external stimuli, PMNs change from a resting, nonadhesive state to a primed, adherent phenotype, which allows for margination from the vasculature into the tissue and chemotaxis to the site of infection upon activation. Depending on the stimuli, primed PMNs display altered structural organization of the NADPH oxidase, in that there is phosphorylation of the oxidase subunits and/or translocation from the cytosol to the plasma or granular membrane, but there is not the complete assembly required for O2- generation. Activation of PMNs is the complete assembly of the membrane-linked and cytosolic NADPH oxidase components on a PMN membrane, the plasma or granular membrane. This review will discuss the individual components associated with the NADPH oxidase complex and the function of each of these units in each physiologic stage of the PMN: rested, primed, and activated.

The Role of Cyclooxygenase-2 in Mediating the Effects of Histamine on Cell Proliferation and Vascular Endothelial Growth Factor Production in Colorectal Cancer

PURPOSE

Activity of histidine decarboxylase, the key enzyme in the synthesis of histamine, has been shown to be increased in several types of human tumors. We attempted to establish whether the possible involvement of histidine decarboxylase and histamine in colorectal carcinogenesis might be mediated by the activation of the cyclooxygenase-2 (COX-2) pathway.

EXPERIMENTAL DESIGN

Expression/activity of histidine decarboxylase, histamine content, and prostaglandin E2 (PGE2) production were analyzed in 33 colorectal cancer samples and in the HT29, Caco-2, and HCT116 colon cancer cell lines. The effects of histamine, celecoxib, and H1, H2, and H4 receptor antagonists on COX-2 expression/activity, cell proliferation, and vascular endothelial growth factor (VEGF) production were assessed in the three colon cancer lines that showed different constitutive COX-2 expression.

RESULTS

We showed the up-regulation of histidine decarboxylase protein expression and activity in the tumor specimens when compared with normal colonic mucosa. Histidine decarboxylase activity and histamine content were also significantly higher in metastatic tumors than in nonmetastatic ones. These variables significantly correlated with tumor PGE(2) production. The administration of histamine increased COX-2 expression/activity, cell proliferation, and VEGF production in the COX-2-positive HT29 and Caco-2 cells. Treatment with either H2/H4 receptor antagonists or celecoxib prevented these effects. Histamine had no effect on both the COX-2 pathway and VEGF production in the COX-2-negative HCT116 cells.

CONCLUSIONS

Our data showed that histamine exerts both a proproliferative and a proangiogenic effect via H2/H4 receptor activation. These effects are likely to be mediated by increasing COX-2-related PGE2 production in COX-2-expressing colon cancer cells.

Neutrophil differentiated HL-60 cells model Mac-1 (CD11b/CD18)-independent neutrophil transepithelial migration

During active intestinal inflammation granulocytes accumulate in the lumen of the gut where they damage the epithelium through the release of various products such as reactive oxygen species and proteolytic enzymes. Previously, using function blocking monoclonal antibodies, we showed that neutrophil migration across intestinal epithelial monolayers in response to various chemoattractants was partially beta(2) integrin Mac-1 (CD11b/CD18)-independent. Here, we show that treating neutrophils with intact monoclonal antibody (mAb) to CD18 activates the cells to express more CD11b. Thus our goal now was to determine whether neutrophil Mac-1-independent transepithelial migration proceeds independently of prior cell activation through Mac-1. We took two approaches, one using blocking Fab' fragments of mAb to CD18 and the second was to develop a neutrophil differentiated HL-60 cell line which is Mac-1 deficient to further study neutrophil/epithelial cell interaction. Anti-CD18 Fab' minimally activated neutrophils but inhibited approximately 75% of transepithelial migration to fMLP while having a minimal effect (</=25% inhibition) on the migration to C5a. Upon incubation with dimethylsulphoxide, HL-60 cells differentiated and up-regulated CD11b expression and migrated to C5a and n-formyl methionyl leucyl phenylalanine in a similar manner to peripheral blood neutrophils. In contrast, CD11b expression was minimal on HL-60 cells differentiated with dibutytyl cAMP to a neutrophil-like phenotype. These cells, however, readily migrated across both intestinal and lung epithelial monolayers in response to C5a. We conclude that Mac-1-independent transepithelial migration does not require prior activation of cells via Mac-1 ligation because HL-60 cells lacking Mac-1 (CD11b/CD18) expression migrate effectively. HL-60 cells differentiated with dbcAMP should greatly assist in the search for the Mac-1-independent ligands for neutrophil migration across epithelium.

C5a differentially stimulates the ERK1/2 and p38 MAPK phosphorylation through independent signaling pathways to induced chemotactic migration in RAW264.7 macrophages

We elucidate the roles of various protein kinases involved in complement 5a (C5a)-induced cell migration. Results showed that extracellular signal-regulated kinase1/2 (ERK1/2), p38 mitogen-activated protein kinase (p38 MAPK) and phosphatidylinositol 3-kinase (P13K) were necessary for C5a-induced migration, whereas protein kinase C and c-Jun N-terminal kinase (JNK) were nonessential. C5a-induced migration was also suppresses by phospholipase C (PLC) inhibitor U73122 and pertussis toxin (PTX). We found that C5a-induced, time-dependent (1) ERK1/2 phosphorylation was markedly diminished by PTX, U73122, P13K inhibitors wortmannin and LY294002 and ERK1/2 inhibitor PD98059; (2) Akt phosphorylation was also attenuated by the above inhibitors except PD98059; (3) p38 MAPK phosphorylation was only affected by PTX. Furthermore, C5a also stimulated PLCbeta(2) membrane translocation in a time-dependent manner that occurred early prior to Akt phosphorylation and could be abolished only by PTX and U73122. These results suggest that C5a, through the activation of PTX-sensitive G protein, to differentially stimulate ERK1/2 and p38 MAPK phosphorylation and evoke cell migration. That is, ERK1/2 but not p38 MAPK phosphorylation is down stream of P13K/Akt and modulated by PLC. Additionally, beta(2) isoform may be one of the participates in C5a signal and acts more upstream of P13K/Akt.

Nanosecond pulsed electric fields modulate cell function through intracellular signal transduction mechanisms

These studies describe the effects of nanosecond (10-300 ns) pulsed electric fields (nsPEF) on mammalian cell structure and function. As the pulse durations decrease, effects on the plasma membrane (PM) decrease and effects on intracellular signal transduction mechanisms increase. When nsPEF-induced PM electroporation effects occur, they are distinct from classical PM electroporation effects, suggesting unique, nsPEF-induced PM modulations. In HL-60 cells, nsPEF that are well below the threshold for PM electroporation and apoptosis induction induce effects that are similar to purinergic agonistmediated calcium release from intracellular stores, which secondarily initiate capacitive calcium influx through store-operated calcium channels in the PM. NsPEF with durations and electric field intensities that do or do not cause PM electroporation, induce apoptosis in mammalian cells with a well-characterized phenotype typified by externalization of phosphatidylserine on the outer PM and activation of caspase proteases. Treatment of mouse fibrosarcoma tumors with nsPEF also results in apoptosis induction. When Jurkat cells were transfected by electroporation and then treated with nsPEF, green fluorescent protein expression was enhanced compared to electroporation alone. The results indicate that nsPEF activate intracellular mechanisms that can determine cell function and fate, providing an important new tool for probing signal transduction mechanisms that modulate cell structure and function and for potential therapeutic applications for cancer and gene therapy.

Response of cyclic AMP by DMSO differentiated HL-60 cells exposed to electric interferential current after prestimulation

The action of interferential current (IFC) upon intracellular content of cyclic adenosine monophosphate (cAMP) after prestimulation with the chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine (fMLP) has been investigated. Human promyelocytes (HL-60) differentiated to granulocytes by dimethylsulphoxide (DMSO) have been treated with different concentrations of fMLP. This enhances their cAMP content. The half maximal effective concentration (EC50) was about 4 nM. Exposure to IFC with modulation frequencies of 35 and 125 Hz (5 min, 250 microA/cm2) after prestimulation with various concentrations of fMLP had no enhancing effect at low or high concentrations of fMLP. In contrast, at medium concentrations in the range of about 100 pM fMLP, a significant enhancement of cAMP could be observed. This synergistic effect of fMLP and IFC has been examined in detail by varying the modulation frequency, current density, and exposure time. Enhancement of cAMP content could be observed at certain modulation frequencies and exposure times suggesting a window effect, whereas for the current density in the range measured (8.5 microA/cm2-2.5 mA/cm2) a constant enhancement could be observed. The synergistic effect of fMLP and IFC could only be observed in the treatment sequence of fMLP followed by IFC; an inverse sequence had no effect on the cAMP content. .

Stimulation of Capacitative Calcium Entry in HL-60 Cells by Nanosecond Pulsed Electric Fields

Nanosecond pulsed electric fields (nsPEFs) are hypothesized to affect intracellular structures in living cells providing a new means to modulate cell signal transduction mechanisms. The effects of nsPEFs on the release of internal calcium and activation of calcium influx in HL-60 cells were investigated by using real time fluorescent microscopy with Fluo-3 and fluorometry with Fura-2. nsPEFs induced an increase in intracellular calcium levels that was seen in all cells. With pulses of 60 ns duration and electric fields between 4 and 15 kV/cm, intracellular calcium increased 200-700 nM, respectively, above basal levels (approximately 100 nM), while the uptake of propidium iodide was absent. This suggests that increases in intracellular calcium were not because of plasma membrane electroporation. nsPEF and the purinergic agonist UTP induced calcium mobilization in the presence and absence of extracellular calcium with similar kinetics and appeared to target the same inositol 1,4,5-trisphosphate- and thapsigargin-sensitive calcium pools in the endoplasmic reticulum. For cells exposed to either nsPEF or UTP in the absence of extracellular calcium, there was an electric field-dependent or UTP dose-dependent increase in capacitative calcium entry when calcium was added to the extracellular media. These findings suggest that nsPEFs, like ligand-mediated responses, release calcium from similar internal calcium pools and thus activate plasma membrane calcium influx channels or capacitative calcium entry.

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

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

Diverse effects of nanosecond pulsed electric fields on cells and tissues

The application of pulsed electric fields to cells is extended to include nonthermal pulses with shorter durations (10-300 ns), higher electric fields (< or =350 kV/cm), higher power (gigawatts), and distinct effects (nsPEF) compared to classical electroporation. Here we define effects and explore potential application for nsPEF in biology and medicine. As the pulse duration is decreased below the plasma membrane charging time constant, plasma membrane effects decrease and intracellular effects predominate. NsPEFs induced apoptosis and caspase activation that was calcium-dependent (Jurkat cells) and calcium-independent (HL-60 and Jurkat cells). In mouse B10-2 fibrosarcoma tumors, nsPEFs induced caspase activation and DNA fragmentation ex vivo, and reduced tumor size in vivo. With conditions below thresholds for classical electroporation and apoptosis, nsPEF induced calcium release from intracellular stores and subsequent calcium influx through store-operated channels in the plasma membrane that mimicked purinergic receptor-mediated calcium mobilization. When nsPEF were applied after classical electroporation pulses, GFP reporter gene expression was enhanced above that observed for classical electroporation. These findings indicate that nsPEF extend classical electroporation to include events that primarily affect intracellular structures and functions. Potential applications for nsPEF include inducing apoptosis in cells and tumors, probing signal transduction mechanisms that determine cell fate, and enhancing gene expression.

A stochastic view of lymphocyte motility and trafficking within the lymph node

Two-photon microscopy is providing literal insight into the cellular dynamics of lymphoid organs and, guided by analysis of three-dimensional images, into mechanisms that underlie cell migration and antigen recognition in vivo. This review describes lymphocyte motility and antigen recognition in the native tissue environment and compares these results with a much more extensive literature on lymphocyte motility, signaling, and chemotaxis in vitro. We discuss the in vitro literature on dynamic aspects of lymphocyte motility, chemotaxis, and the response to antigen and present the view that random migration of lymphocytes may drive a stochastic mechanism of antigen recognition in lymphoid organs, rather than being guided by chemotaxis.

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

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

Reactivation of formyl peptide receptors triggers the neutrophil NADPH-oxidase but not a transient rise in intracellular calcium

In neutrophils, coupling of chemoattractants to their cell surface receptor at low temperature (<or=15 degrees C) leads to receptor deactivation/desensitization without any triggering of the superoxide anion-generating NADPH-oxidase. We show that the deactivated formyl peptide receptors (FPRs) can be reactivated/resensitized by the cytoskeleton-disrupting drug cytochalasin B. Such cytoskeleton-dependent receptor reactivation occurs also with the closely related receptors FPR-like-1 and C5aR but not with the receptors for interleukin-8 and platelet-activating factor. The reactivation state was further characterized with FPR as a model. The signals generated by receptor reactivation induced superoxide production that was terminated in 5-8 min, after which the neutrophils entered a new state of homologous deactivation. FPR antagonists were potent inhibitors of the superoxide production induced by the reactivated receptors, suggesting that the occupied receptors turn into an actively signaling state when the cytoskeleton is disrupted. The signals generated by the reactivated receptor were pertussis toxin-sensitive, indicating involvement of a G-protein. However, no transient elevation of intracellular Ca2+ accompanies the NADPH-oxidase activation. This was not due to a general down-regulation of phospholipase C/Ca2+ signaling, and despite the fact that no intracellular Ca2+ transient was generated, protein kinase C still appeared to be involved in the response. Further, phosphatidylinositol 3-kinase, mitogen-activated protein kinase, and MEK all participated in the generation of second messengers from the reactivated receptors.

Eukaryotic chemotaxis: distinctions between directional sensing and polarization

Directional sensing and polarization are fundamental cellular responses that play a central role in health and disease. In this review we define each process and evaluate a series of models previously proposed to explain these phenomena. New findings show that directional sensing by G protein-coupled receptors is localized at a discrete step in the signaling pathway downstream of G protein activation but upstream of the accumulation of PIP3. Local levels of PIP3, whether triggered by chemoattractants, particle binding, or spontaneous events, determine the sites of new actin-filled projections. Robust control of the temporal and spatial levels of PIP3 is achieved by reciprocal regulation of PI3K and PTEN. These observations suggest that a local excitation-global inhibition model can account for the localization of PI3K and PTEN and thereby explain directional sensing. However, elements of other models, including positive feedback and the reaction of the cytoskeleton, must be invoked to account for polarization.

Functional differences between human formyl peptide receptor isoforms 26, 98, and G6

The formyl peptide receptor (FPR) is expressed in neutrophils, couples to G(i)-proteins and activates phospholipase C, chemotaxis and cytotoxic cell functions. FPR isoforms 26, 98, and G6 differ from each other in amino acids 101, 192 and 346 (FPR-26: V101, N192, E346; FPR-98: L101, N192, A346; FPR-G6: V101, K192, A346), but the functional significance of those structural differences is unknown. In order to address this question, we analyzed FPR-26, FPR-98 and FPR-G6 by co-expressing recombinant FLAG epitope-tagged FPRs with the G-protein G(i)alpha(2)beta(1)gamma(2) in Sf9 insect cells and measured high-affinity agonist binding and guanosine 5'- O-(3-thiotriphosphate) (GTPgammaS) binding. The B(max) values of high-affinity agonist binding with FPR-98 and FPR-G6 were much lower than with FPR-26. FPR-98 and FPR-G6 activated considerably fewer G(i)-proteins, and were much less constitutively active, than FPR-26. Whereas FPR-26 migrated as a monomer in SDS polyacrylamide electrophoresis, FPR-98 and FPR-G6 migrated as dimers and tetramers. In terms of immunoreactivity, FRP-98 and FPR-G6 were expressed at higher levels than FPR-26. Single amino acid exchanges at positions 101 (V-->L), 192 (N-->K) and 346 (E-->A) in FPR-26 revealed that E346 accounts for FPR-26 migrating as a monomer and the high constitutive activity of FPR-26. The V101L, N192K and E346A exchanges all reduced high-affinity agonist binding and the number of G(i)-proteins activated by FPR-26. We conclude that (i) FPR isoforms 98 and G6 exhibit a partial G(i)-protein coupling defect relative to FPR-26 and that (ii) E346 critically determines constitutive activity, G(i)-protein coupling and physical state of FPR-26.

Beta-carotene regulates NF-kappaB DNA-binding activity by a redox mechanism in human leukemia and colon adenocarcinoma cells

We demonstrated previously that beta-carotene may affect cell growth by a redox mechanism. The purpose of this study was to determine whether the redox-sensitive transcription factor nuclear factor (NF)-kappaB may be involved in the growth-inhibitory and proapoptotic effects of the carotenoid. To test this hypothesis, human leukemic cells (HL-60) and colon adenocarcinoma cells (LS-174 and WiDr) were treated with beta-carotene, alone or in combination with alpha-tocopherol or N-acetylcysteine, and changes in 1) cell oxidative status, 2) cell growth and apoptosis, 3) DNA-binding activity of NF-kappaB and 4) expression of c-myc, a NF-kappaB target gene involved in apoptosis, were evaluated. In HL-60 cells, beta-carotene induced a significant increase in reactive oxygen species (ROS) production (P < 0.001) and in oxidized glutathione (GSSG) content (P < 0.005) at concentrations >/=10 micro mol/L. These effects were always accompanied by a sustained elevation of NF-kappaB and by a significant inhibition (P < 0.002) of cell growth. NF-kappaB DNA-binding activity increased at 3 h and persisted for at least 48 h. Colon adenocarcinoma cells displayed substantial differences in their sensitivity to beta-carotene, exhibiting increased ROS levels and activation of NF-kappaB at concentrations much lower in LS-174 cells (2.5-5.0 micro mol/L) than in WiDr cells (50-100 micro mol/L). In all cell lines studied, alpha-tocopherol and N-acetylcysteine inhibited the effects of beta-carotene on NF-kappaB, cell growth and apoptosis, and normalized the increased expression of c-myc induced by the carotenoid. These data suggest that the redox regulation of NF-kappaB induced by beta-carotene is involved in the growth-inhibitory and proapoptotic effects of the carotenoid in tumor cells.

Efficient adenylyl cyclase activation by a beta2-adrenoceptor-G(i)alpha2 fusion protein

The G-protein G(i)alpha can activate adenylyl cyclase (AC), but the relevance of this AC activation is unknown. We used receptor-G protein co-expression and receptor-G protein fusion proteins to investigate G(i)alpha(2) regulation of AC in Sf9 cells. G(i)alpha(2) was fused to the beta(2)-adrenoceptor (beta(2)AR), a preferentially G(s)-coupled receptor, or the formyl peptide receptor (FPR), a G(i)-coupled receptor. The FPR co-expressed with, or fused to, G(i)alpha(2), reduced AC activity. In contrast, the beta(2)AR fused to G(i)alpha(2) was a highly efficient AC activator, while the beta(2)AR co-expressed with G(i)alpha(2) was not. Agonist efficiently stimulated incorporation of [alpha-32P]GTP azidoanilide into beta(2)AR-G(i)alpha(2). We explain AC activation by beta(2)AR-G(i)alpha(2) by a model in which there is interaction of the beta(2)AR and AC, preventing tethered G(i)alpha(2) from interacting with the inhibitory G(i)alpha site of AC. The postulated beta(2)AR/AC interaction brings G(i)alpha(2) into close proximity of the G(s)alpha site of AC, enabling G(i)alpha(2) to activate AC.

Temporal and spatial regulation of chemotaxis

The ability to sense and respond to shallow gradients of extracellular signals is remarkably similar in Dictyostelium discoideum amoebae and mammalian leukocytes. Chemoattractant receptors and G proteins are fairly evenly distributed along the cell surface. Receptor occupancy generates local excitatory and global inhibitory processes that balance to control the chemotactic response. Uniform stimuli transiently recruit PI3Ks to, and release PTEN from, the plasma membrane, while gradients of chemoattractant cause the two enzymes to bind to the membrane at the front and back of the cell, respectively. Interference with PI3Ks alters chemotaxis, and disruption of PTEN broadens PI localization and actin polymerization in parallel. Thus, counteracting signals from the upstream elements of the pathway converge to regulate the key enzymes of PI metabolism, localize these lipids, and direct pseudopod formation.

Leukotriene B4 receptors

Leukotriene B4 (LTB4) is a potent chemotactic agent and activating factor for granulocytes. Two cell surface receptors for LTB4 (BLT1 and BLT2) have been isolated in the last few years. These receptors are G-protein-coupled receptors (GPCR), and they have 45% amino acid identity. BLT1 and BLT2 are high- and low- affinity receptors, respectively. Cells transfected with BLT1 and BLT2 show LTB4-dependent intracellular signal transduction and chemotaxis in vitro. The distribution and pharmacological characteristics of BLT1 and BLT2 are different, suggesting distinct roles for these receptors in vivo. The open reading frame (ORF) of BLT2 overlaps the promoter of BLT1, a so called 'promoter in ORF'. Based on recent publications on BLT1 transgenic and knock out mice phenotypes, it appears that LTB4 plays important roles in inflammation in addition to host defense in vivo.