Mechanisms of G protein-coupled receptor-mediated degranulation

Environmental and Endogenous Acids Can Trigger Allergic-Type Airway Reactions

Inflammatory allergic and nonallergic respiratory disorders are spreading worldwide and often coexist. The root cause is not clear. This review demonstrates that, from a biochemical point of view, it is ascribable to protons (H+) released into cells by exogenous and endogenous acids. The hypothesis of acids as the common cause stems from two considerations: (a) it has long been known that exogenous acids present in air pollutants can induce the irritation of epithelial surfaces, particularly the airways, inflammation, and bronchospasm; (b) according to recent articles, endogenous acids, generated in cells by phospholipases, play a key role in the biochemical mechanisms of initiation and progression of allergic-type reactions. Therefore, the intracellular acidification and consequent Ca2+ increase, induced by protons generated by either acid pollutants or endogenous phospholipases, may constitute the basic mechanism of the multimorbidity of these disorders, and environmental acidity may contribute to their spread.

A novel antimicrobial peptide acting via formyl peptide receptor 2 shows therapeutic effects against rheumatoid arthritis

In oriental medicine, centipede Scolopendra subspinipes mutilans has long been used as a remedy for rheumatoid arthritis (RA), a well-known chronic autoimmune disorder. However, the molecular identities of its bioactive components have not yet been extensively investigated. We sought to identify bioactive molecules that control RA with a centipede. A novel antimicrobial peptide (AMP) (scolopendrasin IX) was identified from Scolopendra subspinipes mutilans. Scolopendrasin IX markedly activated mouse neutrophils, by enhancing cytosolic calcium increase, chemotactic cellular migration, and generation of superoxide anion in neutrophils. As a target receptor for scolopendrasin IX, formyl peptide receptor (FPR)2 mediates neutrophil activation induced by the AMP. Furthermore, scolopendrasin IX administration strongly blocked the clinical phenotype of RA in an autoantibody-injected model. Mechanistically, the novel AMP inhibited inflammatory cytokine synthesis from the joints and neutrophil recruitment into the joint area. Collectively, we suggest that scolopendrasin IX is a novel potential therapeutic agent for the control of RA via FPR2.

A putative G protein-coupled receptor involved in innate immune defense of Procambarus clarkii against bacterial infection

The immune functions of G protein-coupled receptor (GPCR) were widely investigated in mammals. However, limited researches on immune function of GPCRs were reported in invertebrates. In the present study, the immune functions of HP1R gene, a putative GPCR identified from red swamp crayfish Procambarus clarkii were reported. Expression of HP1R gene was significant up-regulated in response to heat-killed Aeromonas hydrophila challenge. HP1R gene silencing mediated by RNA interference significantly enhanced the susceptibility of red swamp crayfish to A. hydrophila and Vibrio alginolyticus, indicating that HP1R was required for red swamp crayfish to defend against bacterial challenge. In HP1R-silenced crayfish, increased bacterial burden and decreased THC in response to bacterial challenge were observed when compared with control crayfish. No significant difference of proPO gene expression was observed between HP1R-silenced and control crayfish after challenge with heat-killed A. hydrophila. However, PO activity in response to bacterial challenge was significantly reduced in HP1R-silenced crayfish. The results collectively indicated that HP1R was an important immune molecule which was required for red swamp crayfish to defend against bacterial infection.

The mast cell in innate and adaptive immunity

Mast cells (MCs) were once considered only as effector cells in pathogenic IgE- and IgG-mediated responses such as allergy. However, developments over the last 15 years have suggested that MCs have evolved in vertebrates as beneficial effector cells that are involved in the very first inflammatory responses generated during infection. This pro-inflammatory environment has been demonstrated to be important for initiating innate responses in many different models of infection and more recently, in the development of adaptive immunity as well. Interestingly this latter finding has led to the discovery that small MC-activating compounds can behave as adjuvants in vaccine formulations. Thus, our continued understanding of the MC in the context of infectious disease is likely to not only expand our scope of the MC in the normal processes of immunity, but provide new therapeutic targets to combat disease.

UDP-glucose acting at P2Y14 receptors is a mediator of mast cell degranulation

UDP-glucose (UDPG), a glycosyl donor in the biosynthesis of carbohydrates, is an endogenous agonist of the G protein-coupled P2Y(14) receptor. RBL-2H3 mast cells endogenously express a P2Y(14) receptor at which UDPG mediates degranulation as indicated by beta-hexosaminidase (HEX) release. Both UDPG and a more potent, selective 2-thio-modified UDPG analog, MRS2690 (diphosphoric acid 1-alpha-d-glucopyranosyl ester 2-[(2-thio)uridin-5''-yl] ester), caused a substantial calcium transient in RBL-2H3 cells, which was blocked by pertussis toxin, indicating the presence of the G(i)-coupled P2Y(14) receptor, supported also by quantitative detection of abundant mRNA. Expression of the closely related P2Y(6) receptor was over 100 times lower than the P2Y(14) receptor, and the P2Y(6) agonist 3-phenacyl-UDP was inactive in RBL-2H3 cells. P2Y(14) receptor agonists also induced [(35)S]GTPgammaS binding to RBL-2H3 cell membranes, and phosphorylation of ERK1/2, P38 and JNK. UDPG and MRS2690 concentration-dependently enhanced HEX release with EC(50) values of 1150+/-320 and 103+/-18nM, respectively. The enhancement was completely blocked by pertussis toxin and significantly diminished by P2Y(14) receptor-specific siRNA. Thus, mast cells express an endogenous P2Y(14) receptor, which mediates G(i)-dependent degranulation and is therefore a potential novel therapeutic target for allergic conditions.

Heat shock protein 60 (HSP60) stimulates neutrophil effector functions

Neutrophil granulocytes belong to the first cells that enter sites of infection, where they eliminate infiltrating pathogens via phagocytosis and the release of antimicrobial mediators. Hence, recruitment of neutrophils and activation of neutrophil microbicidal functions are crucial steps in the early containment of infection. In this study, we show that hHSP60 binds to murine and human PMN strongly and specifically. We demonstrate that HSP60 serves as a chemoattractant and modulates neutrophil functions. Human PMN were incubated with HSP60 alone or prior to stimulation with fMLP or PMA acetate. We observed that HSP60, although not inducing neutrophil release of ROS and degranulation itself, strongly enhanced the production of reactive oxygen induced by PMA and the release of primary granule enzymes induced by both secondary stimuli. This sensitization of PMN was HSP60-specific. Moreover, PMN that had been preincubated with HSP60 exhibited a marked increase in the uptake of opsonized Escherichia coli in the absence of additional stimuli. Taken together, our results show for the first time that HSP60 modulates antimicrobial effector functions of neutrophil granulocytes. In this way and in agreement with its function as an endogenous danger signal, HSP60, which is released by damaged tissue, may promote early innate defense mechanisms against invading pathogens.

Arrestin 3 mediates endocytosis of CCR7 following ligation of CCL19 but not CCL21

Internalization of ligand bound G protein-coupled receptors, an important cellular function that mediates receptor desensitization, takes place via distinct pathways, which are often unique for each receptor. The C-C chemokine receptor (CCR7) G protein-coupled receptor is expressed on naive T cells, dendritic cells, and NK cells and has two endogenous ligands, CCL19 and CCL21. Following binding of CCL21, 21 +/- 4% of CCR7 is internalized in the HuT 78 human T cell lymphoma line, while 76 +/- 8% of CCR7 is internalized upon binding to CCL19. To determine whether arrestins mediated differential internalization of CCR7/CCL19 vs CCR7/CCL21, we used small interfering RNA (siRNA) to knock down expression of arrestin 2 or arrestin 3 in HuT 78 cells. Independent of arrestin 2 or arrestin 3 expression, CCR7/CCL21 internalized. In contrast, following depletion of arrestin 3, CCR7/CCL19 failed to internalize. To examine the consequence of complete loss of both arrestin 2 and arrestin 3 on CCL19/CCR7 internalization, we examined CCR7 internalization in arrestin 2(-/-)/arrestin 3(-/-) murine embryonic fibroblasts. Only reconstitution with arrestin 3-GFP but not arrestin 2-GFP rescued internalization of CCR7/CCL19. Loss of arrestin 2 or arrestin 3 blocked migration to CCL19 but had no effect on migration to CCL21. Using immunofluorescence microscopy, we found that arrestins do not cluster at the membrane with CCR7 following ligand binding but cap with CCR7 during receptor internalization. These are the first studies that define a role for arrestin 3 in the internalization of a chemokine receptor following binding of one but not both endogenous ligands.

Regulation of leukocyte degranulation by cGMP-dependent protein kinase and phosphoinositide 3-kinase: potential roles in phosphorylation of target membrane SNARE complex proteins in rat mast cells

We examined the roles of cGMP-dependent protein kinase (PKG) and PI3K in degranulation induced by fMLF and by FcepsilonRI cross-linking. In rat basophilic leukemia-2H3 cells expressing formyl peptide receptor, the PKG inhibitors KT5823 and Rp-8-Br-PET-cGMP, as well as the PI3K inhibitor LY294002, reduced agonist-stimulated beta-hexosaminidase release in a dose-dependent manner. These inhibitors also abolished vesicular fusion with the plasma membrane, as evidenced by diminished annexin V staining. Agonist-induced degranulation was completely blocked when LY294002 was applied together with one of the PKG inhibitors, suggesting an additive and possibly synergistic effect. In contrast, the PKG inhibitors did not affect fMLF-induced intracellular calcium mobilization and Akt phosphorylation. Likewise, LY294002 did not alter fMLF-induced elevation of intracellular cGMP concentration, and the inhibitory effect of LY294002 was not reversed by a cell-permeable analog of cGMP. Treatment with fMLF induced phosphorylation of soluble N-ethylmaleimide-sensitive factor-attachment protein (SNAP)-23, syntaxins 2, 4, and 6, and Monc18-3. The induced phosphorylation of SNAP-23 and syntaxins 2 and 4 was blocked by Rp-8-Br-PET-cGMP and LY294002. However, LY294002 was less effective in inhibiting Munc18-3 phosphorylation. The induced phosphorylation of syntaxin 6 was not effectively blocked by either Rp-8-Br-PET-cGMP or LY294002. Treatment of human neutrophils with the PKG inhibitors and LY294002 reduced enzyme release from primary, secondary, and tertiary granules. These results suggest that PKG and PI3K are involved in degranulation, possibly through phosphorylation of target membrane SNAP receptor proteins and their binding proteins.

Human Fallopian Tube Neutrophils – A Distinct Phenotype from Blood Neutrophils

PROBLEM

The role of neutrophils in the human Fallopian tube (FT) is unknown. In order to provide insights into their functions in the FT, we systematically compared neutrophils from normal FT and peripheral blood (PB).

METHOD OF STUDY

Flow cytometric analysis of surface receptors, granule proteins, and intracellular cytokines expressed by neutrophils from enzymatically dispersed FT and PB was performed.

RESULTS

Fallopian tube neutrophils expressed significantly higher levels of CD64, human class II histocompatibility antigen DR (HLA-DR), gamma-interferon, and vascular endothelial growth factor than those from PB. Fewer FT neutrophils expressed IL-8 receptors compared to PB, while more expressed the receptor for the bacterial-derived chemoattractant formyl-Met-Leu-Phe (fMLP). The number of FT neutrophils containing the granule proteins matrix metalloproteinase-9, lactoferrin, and myeloperoxidase was decreased versus PB.

CONCLUSION

Fallopian tube neutrophils exhibit a phenotype distinct from PB neutrophils, suggesting functional activation of innate immune defense in the female reproductive tract as well as a potential role in maintaining normal FT physiology.

Functional expression of the P2Y14 receptor in human neutrophils

Previous studies using quantitative reverse transcriptase polymerase chain reaction (RT-PCR) analysis have shown that the P2Y(14) receptor is expressed at high levels in human neutrophils. Therefore the primary aim of this study was to determine whether the P2Y(14) receptor is functionally expressed in human neutrophils. In agreement with previous studies RT-PCR analysis detected the expression of P2Y(14) receptor mRNA in human neutrophils. UDP-glucose (IC(50)=1 microM) induced a small but significant inhibition (circa 30%) of forskolin-stimulated cAMP accumulation suggesting functional coupling of endogenously expressed P2Y(14) receptors to the inhibition of adenylyl cyclase activity in human neutrophils. In contrast, the other putative P2Y(14) receptor agonists UDP-galactose and UDP-glucuronic acid (at concentrations up to 100 microM) had no significant effect, whereas 100 microM UDP-N-acetylglucosamine-induced a small but significant inhibition of forskolin-stimulated cAMP accumulation (20% inhibition). UDP-galactose, UDP-glucuronic acid and UDP-N-acetylglucosamine behaved as partial agonists by blocking UDP-glucose mediated inhibition of forskolin-induced cAMP accumulation. Treatment of neutrophils with pertussis toxin (G(i/o) blocker) abolished the inhibitory effects of UDP-glucose on forskolin-stimulated cAMP accumulation. UDP-glucose (100 microM) also induced a modest increase in extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation, whereas the other sugar nucleotides had no effect on ERK1/2 activation. Finally, UDP-glucose and related sugar nucleotides had no significant effect on N-formyl-methionyl-leucyl-phenylalanine-induced elastase release from neutrophils. In summary, although we have shown that the P2Y(14) receptor is functionally expressed in human neutrophils (coupling to inhibition of forskolin-induced cAMP and ERK1/2 activation) it does not modulate neutrophil degranulation (assessed by monitoring elastase release). Clearly further studies are required in order to establish the functional role of the P2Y(14) receptor expressed in human neutrophils.