Functional chemotactic factor CP-10 and MRP-14 are abundant in murine abscesses

Murine Calprotectin Coordinates Mn(II) at a Hexahistidine Site with Ca(II)-Dependent Affinity

Manganese is an essential metal ion that bacterial pathogens need to acquire from the vertebrate host during infection. In the mammalian nutritional immunity strategy to combat bacterial infection, the host restricts bacterial access to Mn(II) by sequestering this metal nutrient using the protein calprotectin (CP). The role of murine calprotectin (mCP) in Mn(II) sequestration has been demonstrated in vivo, but the molecular basis of this function has not been evaluated. Herein, biochemical assays and electron paramagnetic resonance (EPR) spectroscopy are employed to characterize the Mn(II) binding properties of mCP. We report that mCP has one high-affinity Mn(II) binding site. This site is a His₆ site composed of His17 and His27 of mS100A8 and His92, His97, His105, and His107 of mS100A9. Similar to the human ortholog (hCP), Ca(II) binding to the EF-hand domains of mCP enhances the Mn(II) affinity of the protein; however, this effect requires ≈10-fold more Ca(II) than was previously observed for hCP. Mn(II) coordination to the His₆ site also promotes self-association of two mCP heterodimers to form a heterotetramer. Low-temperature X-band EPR spectroscopy revealed a nearly octahedral Mn(II) coordination sphere for the Mn(II)-His₆ site characterized by the zero-field splitting parameters D = 525 MHz and E/D = 0.3. Further electron-nuclear double resonance studies with globally ¹⁵N-labeled mCP provided hyperfine couplings from the coordinating ε-nitrogen atoms of the His ligands (a_iso = 4.3 MHz) as well as the distal δ-nitrogen atoms (a_iso = 0.25 MHz). Mn(II) competition assays between mCP and two bacterial Mn(II) solute-binding proteins, staphylococcal MntC and streptococcal PsaA, showed that mCP outcompetes both proteins for Mn(II) under conditions of excess Ca(II). In total, this work provides the first coordination chemistry study of mCP and reveals striking similarities in the Mn(II) coordination sphere as well as notable differences in the Ca(II) sensitivity and oligomerization behavior between hCP and mCP.

Initial Biochemical and Functional Evaluation of Murine Calprotectin Reveals Ca(II)-Dependence and Its Ability to Chelate Multiple Nutrient Transition Metal Ions

Calprotectin (CP) is an abundant host-defense protein that contributes to the metal-withholding innate immune response by sequestering nutrient metal ions from microbial pathogens in the extracellular space. Over the past decade, murine models of infectious disease have advanced understanding of the physiological functions of CP and its ability to compete with microbes for essential metal nutrients. Despite this extensive work, murine CP (mCP) has not been biochemically evaluated, and structural and biophysical understanding of CP is currently limited to the human orthologue. We present the reconstitution, purification, and characterization of mCP as well as the cysteine-null variant mCP-Ser. Apo mCP is a mS100A8/mS100A9 heterodimer, and Ca(II) binding causes two heterodimers to self-associate and form a heterotetramer. Initial metal-depletion studies demonstrate that mCP depletes multiple first-row transition metal ions, including Mn, Fe, Ni, Cu, and Zn, from complex microbial growth medium, indicating that mCP binds multiple nutrient metals with high affinity. Moreover, antibacterial activity assays show that mCP inhibits the growth of a variety of bacterial species. The metal-depletion and antibacterial activity studies also provide evidence that Ca(II) ions enhance these functional properties of mCP. This contribution provides the groundwork for understanding the similarities and differences between the human and murine orthologues of CP and for further elucidation of its biological coordination chemistry.

Vaginal epithelial cell-derived S100 alarmins induced by Candida albicans via pattern recognition receptor interactions are sufficient but not necessary for the acute neutrophil response during experimental vaginal candidiasis

Vulvovaginal candidiasis (VVC), caused by Candida albicans, affects women worldwide. Animal and clinical studies suggest that the immunopathogenic inflammatory condition of VVC is initiated by S100 alarmins in response to C. albicans, which stimulate polymorphonuclear neutrophil (PMN) migration to the vagina. The purpose of this study was to extend previous in vitro data and determine the requirement for the alarmin S100A8 in the PMN response and to evaluate pattern recognition receptors (PRRs) that initiate the response. For the former, PMN migration was evaluated in vitro or in vivo in the presence or absence of S100 alarmins initiated by several approaches. For the latter, vaginal epithelial cells were evaluated for PRR expression and C. albicans-induced S100A8 and S100A9 mRNAs, followed by evaluation of the PMN response in inoculated PRR-deficient mice. Results revealed that, consistent with previously reported in vitro data, eukaryote-derived S100A8, but not prokaryote-derived recombinant S100A8, induced significant PMN chemotaxis in vivo. Conversely, a lack of biologically active S100A8 alarmin, achieved by antibody neutralization or by using S100A9(-/-) mice, had no effect on the PMN response in vivo. In PRR analyses, whereas Toll-like receptor 4 (TLR4)- and SIGNR1-deficient vaginal epithelial cells showed a dramatic reduction in C. albicans-induced S100A8/S100A9 mRNAs in vitro, inoculated mice deficient in these PRRs showed PMN migration similar to that in wild-type controls. These results suggest that S100A8 alarmin is sufficient, but not necessary, to induce PMN migration during VVC and that the vaginal PMN response to C. albicans involves PRRs in addition to SIGNR1 and TLR4, or other induction pathways.

Engineering Candida albicans to secrete a host immunomodulatory factor

Gene knockout and transgenic mice are important tools that are widely used to dissect the mammalian hosts' responses to microbial invasion. A novel alternative is to engineer the pathogen itself to secrete host factors that stimulate or suppress specific immune defense mechanisms. Herein, we have described and validated an approach to facilitate the production and export of ectopic host proteins, from the most prevalent human fungal pathogen, Candida albicans. Our strategy utilized a prepropeptide from the C. albicans secreted aspartic proteinase, Sap2p. The prepeptide facilitates entry of Sap2p into the secretory pathway, while the propeptide maintains the protease as an inactive precursor, until proteolytic cleavage in the Golgi apparatus releases the mature protein. The Sap2p prepropeptide coding sequence was linked to that of two mammalian calcium-binding proteins, S100A8 and S100A9, which are associated with symptomatic vaginal candidiasis. The resulting expression constructs were then introduced into C. albicans. While the S100A8 protein is secreted into the growth medium intact, the S100A9 protein is apparently degraded during transit. Nonetheless, culture supernatants from both S100A8 and S100A9 expressing C. albicans strains acted as potent chemoattractants for a macrophage-like cell line and polymorphonuclear leukocytes. Thus, the pathogen-derived mammalian proteins possessed the expected biological activity.

Damage-associated molecular pattern S100A9 increases bactericidal activity of human neutrophils by enhancing phagocytosis

The damage-associated molecular-pattern S100A9 is found at inflammatory sites in infections and various autoimmune diseases. It is released at very high concentrations in the extracellular milieu by activated neutrophils and monocytes in response to various agents. This proinflammatory protein is found in infected mucosae and tissue abscesses where it acts notably as a potent neutrophil activator. In this study, we examined the role of S100A9 in the control of infections. S100A9 was found to increase human neutrophil bactericidal activity toward Escherichia coli. Although S100A9 induced the accumulation of reactive oxygen species over time through the activation of NADPH oxidase, its antimicrobial activity was mediated mainly by enhancing the efficiency of neutrophil phagocytosis. Interestingly, S100A9 did not act by increasing cell surface expression of CD16, CD32, or CD64 in neutrophils, indicating that its biological effect in FcR-mediated phagocytosis is independent of upregulation of FcγR levels. However, S100A9-induced phagocytic activity required the phosphorylation of Erk1/2, Akt, and Syk. Taken together, our results demonstrate that S100A9 stimulates neutrophil microbicidal activity by promoting phagocytosis.

Epithelial cell-derived S100 calcium-binding proteins as key mediators in the hallmark acute neutrophil response during Candida vaginitis

Vulvovaginal candidiasis (VVC), caused by Candida species, is a significant problem in women of childbearing age. Similar to clinical observations, a robust vaginal polymorphonuclear neutrophil (PMN) migration occurs in a subset of mice without affecting vaginal fungal burden. We hypothesize that the vaginal PMN infiltrate and accompanying inflammation are not protective but instead are responsible for the symptoms of infection. The purpose of this study was to identify the signal(s) associated with the PMN response in the established mouse model. Vaginal lavage fluid from inoculated mice were categorized base on PMN counts, evaluated for PMN chemotactic activity and analyzed by SDS-PAGE and mass spectrometry (MS) for unique protein identification. The lavage fluid from inoculated mice with high, but not low, PMN levels showed increased chemotactic activity. Likewise, SDS-PAGE of lavage fluid with high PMN levels showed distinct protein patterns. MS revealed that bands at 6 and 14 kDa matched the PMN chemotactic calcium-binding proteins (CBPs), S100A8 and S100A9, respectively. The presence of the CBPs in lavage fluid was confirmed by Western blots and enzyme-linked immunosorbent assay. Vaginal tissues and epithelial cells from inoculated mice with high PMN levels stained more intensely and exhibited increased mRNA transcripts for both proteins compared to those in mice with low PMN levels. Subsequent antibody neutralization showed significant abrogation of the chemotactic activity when the lavage fluid was treated with anti-S100A8, but not anti-S100A9, antibodies. These results reveal that the PMN chemotactic CBP S100A8 and S100A9 are produced by vaginal epithelial cells following interaction with Candida and that S100A8 is a strong candidate responsible for the robust PMN migration during experimental VVC.

S-glutathionylation regulates inflammatory activities of S100A9

Reactive oxygen species generated by activated neutrophils can cause oxidative stress and tissue damage. S100A8 (A8) and S100A9 (A9), abundant in neutrophil cytoplasm, are exquisitely sensitive to oxidation, which may alter their functions. Murine A8 is a neutrophil chemoattractant, but it suppresses leukocyte transmigration in the microcirculation when S-nitrosylated. Glutathione (GSH) modulates intracellular redox, and S-glutathionylation can protect susceptible proteins from oxidative damage and regulate function. We characterized S-glutathionylation of A9; GSSG and GSNO generated S-glutathionylated A8 (A8-SSG) and A9 (A9-SSG) in vitro, whereas only A9-SSG was detected in cytosol of neutrophils activated with phorbol myristate acetate (PMA) but not with fMLP or opsonized zymosan. S-Glutathionylation exposed more hydrophobic regions in Zn(2+)-bound A9 but did not alter Zn(2+) binding affinity. A9-SSG had reduced capacity to form heterocomplexes with A8, but the arachidonic acid binding capacities of A8/A9 and A8/A9-SSG were similar. A9 and A8/A9 bind endothelial cells; S-glutathionylation reduced binding. We found little effect of A9 or A9-SSG on neutrophil CD11b/CD18 expression or neutrophil adhesion to endothelial cells. However, A9, A9-SSG and A8/A9 promoted neutrophil adhesion to fibronectin but, in the presence of A8, A9-mediated adhesion was abrogated by glutathionylation. S-Glutathionylation of A9 may protect its oxidation to higher oligomers and reduce neutrophil binding to the extracellular matrix. This may regulate the magnitude of neutrophil migration in the extravasculature, and together with the functional changes we reported for S-nitrosylated A8, particular oxidative modifications of these proteins may limit tissue damage in acute inflammation.

ANTI-INFECTIVE PROTECTIVE PROPERTIES OF S100 CALGRANULINS

The calgranulins are a subgroup of proteins in the S100 family (calgranulin A, S100A8; calgranulin B, S100A9 and calgranulin C, S100A12) that provide protective anti-infective and anti-inflammatory functions for the mammalian host. In this review, we discuss the structure-function relationships whereby S100A8 and S100A9, and for comparison, S100A12, provide intra- and extracellular protection during the complex interplay between infection and inflammation and how the calgranulins are regulated to optimally protect the host. Ideally located to support epithelial barrier function, calprotectin, a complex of S100A8/S100A9, is expressed in squamous mucosal keratinocytes and innate immune cells present at mucosal surfaces. The calgranulins are also abundantly produced in neutrophils and monocytes, whereas expression is induced in epidermal keratinocytes, gastrointestinal epithelial cells and fibroblasts during inflammation. The calgranulins show species-specific expression and function. For example, S100A8 is chemotactic in rodents but not in humans. In humans, S100A12 appears to serve as a functional chemotactic homolog to murine S100A8. Transition metal-binding and oxidation sites within calgranulins are able to create structural changes that may orchestrate new protective functions or binding targets. The calgranulins thus appear to adopt a variety of roles to protect the host. In addition to serving as a leukocyte chemoattractant, protective functions include oxidant scavenging, antimicrobial activity, and chemokine-like activities. Each function may reflect the concentration of the calgranulin, post-transcriptional modifications, oligomeric forms, and the proximal intracellular or extracellular environments. Calprotectin and the calgranulins are remarkable as multifunctional proteins dedicated to protecting the intra- and extracellular environments during infection and inflammation.

IL-10-dependent S100A8 gene induction in monocytes/macrophages by double-stranded RNA

The S100 calcium-binding proteins S100A8 and S100A9 are elevated systemically in patients with viral infections. The S100A8-S100A9 complex facilitated viral replication in human CD4(+) T lymphocytes latently infected with HIV-1- and S100A8-induced HIV-1 transcriptional activity. Mechanisms inducing the S100 genes and the potential source of these proteins following viral activation are unknown. In this study, we show that S100A8 was induced in murine macrophages, and S100A8 and S100A9 in human monocytes and macrophages, by polyinosinic:polycytidylic acid, a dsRNA mimetic. Induction was at the transcriptional level and was IL-10 dependent. Similar to LPS-induced S100A8, induction by dsRNA was dependent on p38 and ERK MAPK. Protein kinase R (PKR) mediates antiviral defense and participates in MyD88-dependent/independent signaling triggered by TLR4 or TLR3. Like IL-10, S100 induction by polyinosinic:polycytidylic acid and by LPS was inhibited by the specific PKR inhibitor 2-aminopurine, indicating a novel IL-10, PKR-dependent pathway. Other mediators such as IFN-beta, which synergized with dsRNA, may also be involved. C/EBPbeta bound the defined promoter region in response to dsRNA. S100A8 was expressed in lungs of mice infected with influenza virus and was maximal at day 8 with strong immunoreactivity in epithelial cells lining the airways and in mononuclear cells and declined early in the recovery phase, implying down-regulation by mediator(s) up-regulated during resolution of the infection. IL-10 is implicated in viral persistence. Since S100A8/S100A9 levels are likely to be maintained in conditions where IL-10 is raised, these proteins may contribute to viral persistence in patients infected by some RNA viruses.

Circulating calprotectin in ovarian carcinomas and borderline tumors of the ovary

OBJECTIVE

Recent studies indicate that circulating calprotectin may serve as a biomarker in some cancers. We investigated whether this is the case for ovarian neoplasms.

STUDY DESIGN

Calprotectin was analyzed with an enzyme-linked immunosorbent assay in EDTA-plasma collected prior to surgery from women with ovarian carcinomas (n = 89), borderline ovarian tumors (BOT, n = 39), and benign ovarian tumors (n = 71). Serum CA 125 was analyzed in the same study population.

RESULTS

Median plasma calprotectin concentration was elevated in ovarian carcinoma, compared with controls, as well as compared with BOT (both P < .001). A positive correlation was found between CA 125 and calprotectin concentrations in ovarian carcinoma. Receiver operating characteristic curves demonstrated a larger area under the curve for CA 125 (0.85) as compared with calprotectin (0.70).

CONCLUSION

Plasma calprotectin is elevated in invasive ovarian cancer, but when used as a tumor marker, it is inferior to CA 125.

Serum and mucosal S100 proteins, calprotectin (S100A8/S100A9) and S100A12, are elevated at diagnosis in children with inflammatory bowel disease

OBJECTIVE

Various markers characterize the complex inflammatory processes seen in chronic inflammatory bowel disease (IBD) including calprotectin, a complex of two S100 proteins, which has been evaluated and validated as a faecal marker of inflammation. However, the systemic and mucosal expression patterns of calprotectin and related S100 proteins are not well characterized in this disease. The objective of this study was to assess serum and mucosal levels of calprotectin, S100A12 and soluble receptor for advanced glycation end products (sRAGE), a putative S100 ligand, in a paediatric population with IBD.

MATERIAL AND METHODS

Children were enrolled at diagnosis of IBD, along with groups of children without IBD. Standard inflammatory markers and disease activity scores were collated. Calprotectin, S100A12 and sRAGE levels in serum and biopsy culture supernatants were measured by ELISA and tissue distribution of S100 proteins was investigated by immunohistochemistry.

RESULTS

Serum and mucosal calprotectin and S100A12 levels were increased in children with IBD as compared with non-IBD controls. Serum calprotectin levels correlated with S100A12 levels and with disease activity scores in children with IBD. sRAGE levels were not increased in IBD. S100A8, S100A9 and S100A12 were abundantly expressed throughout the lamina propria and epithelium in inflamed mucosa. In contrast, these proteins were present in the lamina propria, but not the epithelium, in non-inflamed mucosa.

CONCLUSIONS

Serum calprotectin and S100A12 are increased in children with IBD and indicate disease activity. Elevated levels of these proteins are present in the colonic mucosa and may contribute to the pathogenesis of IBD. Furthermore, an imbalance between sRAGE and S100A12 may contribute to inflammatory changes present in IBD.

Up-regulation of S100A8 and S100A9 protein in bronchial epithelial cells by lipopolysaccharide

Increased serum levels of the S100A8 (MRP-8) protein have been reported in inflammatory conditions including bacterial infection, arthritis, and cystic fibrosis (CF). This protein is expressed constitutively with S100A9 (MRP-14) in neutrophils and is regulated by inflammatory stimulants. It has been hypothesized that increased inflammatory response to persistent bacterial infection is a major feature of CF lung disease. Therefore, the authors wished to determine the involvement of these two proteins in the innate defense response of the bronchial epithelium to lipopolysaccharide (LPS). Human bronchial epithelial cells (16HBE14o-) and primary bronchial epithelial cells (NHBE) were grown at air-liquid interface (ALI) and stimulated for up to 96 hours with LPS from Pseudomonas aeruginosa. The 16HBE14o- cells responded to LPS with a 2.9-fold increase in S100A8 mRNA production after 12 hours. S100A9 mRNA production was increased by 1.8-fold after 12 hours and 2.9-fold after 24 hours. It was also found that the S100A8 and S100A9 proteins were increased in the secretions of the 16HBE14o- and NHBE cells after LPS stimulation. This finding suggests that S100A8 and S100A9 are involved in the innate defense of the bronchial epithelium.

Human neutrophil calprotectin reduces the susceptibility of Borrelia burgdorferi to penicillin

Borrelia burgdorferi, the spirochetal agent of Lyme disease, is susceptible to killing by a variety of polymorphonuclear leukocyte (PMN) components. Some are most effective against metabolically active B. burgdorferi. The abundant PMN cytoplasmic protein calprotectin, elevated 10- to 100-fold in inflammation, inhibits the growth of spirochetes through chelation of the essential cation, Zn. Since the action of some therapeutic antibiotics depends on bacterial division, we investigated the antibiotic sensitivities of spirochetes in calprotectin. In physiologic calprotectin, B. burgdorferi is not eliminated by therapeutic doses of penicillin G; in contrast, doxycycline is effective. Calprotectin may modify the clearance of spirochetes at sites of inflammation.

S100A8 and S100A9 in Human Arterial Wall

Atherogenesis is a complex process involving inflammation. S100A8 and S100A9, the Ca2+-binding neutrophil cytosolic proteins, are associated with innate immunity and regulate processes leading to leukocyte adhesion and transmigration. In neutrophils and monocytes the S100A8-S100A9 complex regulates phosphorylation, NADPH-oxidase activity, and fatty acid transport. The proteins have anti-microbial properties, and S100A8 may play a role in oxidant defense in inflammation. Murine S100A8 is regulated by inflammatory mediators and recruits macrophages with a proatherogenic phenotype. S100A9 but not S100A8 was found in macrophages in ApoE-/- murine atherosclerotic lesions, whereas both proteins are expressed in human giant cell arteritis. Here we demonstrate S100A8 and S100A9 protein and mRNA in macrophages, foam cells, and neovessels in human atheroma. Monomeric and complexed forms were detected in plaque extracts. S100A9 was strongly expressed in calcifying areas and the surrounding extracellular matrix. Vascular matrix vesicles contain high levels of Ca2+-binding proteins and phospholipids that regulate calcification. Matrix vesicles characterized by electron microscopy, x-ray microanalysis, nucleoside triphosphate pyrophosphohydrolase assay and cholesterol/phospholipid analysis contained predominantly S100A9. We propose that S100A9 associated with lipid structures in matrix vesicles may influence phospholipid-Ca2+ binding properties to promote dystrophic calcification. S100A8 and S100A9 were more sensitive to hypochlorite oxidation than albumin or low density lipoprotein and immunoaffinity confirmed S100A8-S100A9 complexes; some were resistant to reduction, suggesting that hypochlorite may contribute to protein cross-linking. S100A8 and S100A9 in atherosclerotic plaque and calcifying matrix vesicles may significantly influence redox- and Ca2+-dependent processes during atherogenesis and its chronic complications, particularly dystrophic calcification.

S100A8 chemotactic protein is abundantly increased, but only a minor contributor to LPS-induced, steroid resistant neutrophilic lung inflammation in vivo

Neutrophilic lung inflammation is an essential component of host defense against diverse eukaryotic and prokaryotic pathogens, but in chronic inflammatory lung diseases, such as chronic obstructive lung disease (COPD), severe asthma, cystic fibrosis, and bronchiolitis, it may damage the host. Glucocorticosteroids are widely used in these conditions and in their infectious exacerbations; however, the clinical efficacy of steroids is disputed. In this study, we used a proteomic approach to identify molecules contributing to neutrophilic inflammation induced by transnasal administration of lipopolysaccharide (LPS) that were also resistant to the potent glucocorticosteroid dexamethasone (Dex). We confirmed that Dex was biologically active at both the transcript (suppression of GM-CSF and TNFalphatranscripts) and protein levels (induction of lipocortin) and used 2D-PAGE/MALDI-TOF to generate global expression profiles, identifying six LPS-induced proteins that were Dex resistant. Of these, S100A8, a candidate neutrophil chemotactic factor, was profiled in detail. Steroid refractory S100A8 expression was highly abundant, transcriptionally regulated, secreted into lung lavage fluid and immunohistochemically localized to tissue infiltrating neutrophils. However, in marked contrast to other vascular beds, neutralizing antibodies to S100A8 had only a weak anti-neutrophil recruitment effect and antibodies against the related S100A9 were ineffective. These data highlight the need for extensive in vivo profiling of proteomically identified candidate molecules and demonstrates that S100A8, despite its abundance, resistance to steroids and known chemotactic activity, is unlikely to be an important determinant of LPS-induced neutrophilic lung inflammation in vivo.

FGF-2, IL-1β and TGF-β regulate fibroblast expression of S100A8

Growth factors, including fibroblast growth factor-2 (FGF-2) and transforming growth factor-beta (TGF-beta) regulate fibroblast function, differentiation and proliferation. S100A8 and S100A9 are members of the S100 family of Ca2+-binding proteins and are now accepted as markers of inflammation. They are expressed by keratinocytes and inflammatory cells in human/murine wounds and by appropriately activated macrophages, endothelial cells, epithelial cells and keratinocytes in vitro. In this study, regulation and expression of S100A8 and S100A9 were examined in fibroblasts. Endotoxin (LPS), interferon gamma (IFNgamma), tumour-necrosis factor (TNF) and TGF-beta did not induce the S100A8 gene in murine fibroblasts whereas FGF-2 induced mRNA maximally after 12 h. The FGF-2 response was strongly enhanced and prolonged by heparin. Interleukin-1beta (IL-1beta) alone, or in synergy with FGF-2/heparin strongly induced the gene in 3T3 fibroblasts. S100A9 mRNA was not induced under any condition. Induction of S100A8 in the absence of S100A9 was confirmed in primary fibroblasts. S100A8 mRNA induction by FGF-2 and IL-1beta was partially dependent on the mitogen-activated-protein-kinase pathway and dependent on new protein synthesis. FGF-2-responsive elements were distinct from the IL-1beta-responsive elements in the S100A8 gene promoter. FGF-2-/heparin-induced, but not IL-1beta-induced responses were significantly suppressed by TGF-beta, possibly mediated by decreased mRNA stability. S100A8 in activated fibroblasts was mainly intracytoplasmic. Rat dermal wounds contained numerous S100A8-positive fibroblast-like cells 2 and 4 days post injury; numbers declined by 7 days. Up-regulation of S100A8 by FGF-2/IL-1beta, down-regulation by TGF-beta, and its time-dependent expression in wound fibroblasts suggest a role in fibroblast differentiation at sites of inflammation and repair.

Monosodium urate monohydrate crystals induce the release of the proinflammatory protein S100A8/A9 from neutrophils

The neutrophil cytoplasmic protein S100A8/A9 (along with S100A8 and S100A9) is chemotactic and stimulates neutrophil adhesion by activating the beta2-integrin CD11b/CD18. It is also essential to neutrophil migration in vivo in response to monosodium urate monohydrate (MSUM) crystals, the principal etiologic agent of gout. S100A8/A9 is present in the synovial fluid of patients with gout and arthritis and is secreted by activated monocytes; however, its mechanism of release by neutrophils remains unknown. The aim of this study was to identify the mechanism of stimulation of the release of S100A8/A9 by MSUM-activated neutrophils. Here, we show that S100A8/A9 is released by neutrophils stimulated with MSUM crystals and that this release could be enhanced by preincubating neutrophils with granulocyte macrophage-colony stimulating factor. Antibodies directed against CD11b and CD16 blocked the release induced by MSUM crystals, suggesting that Fc receptor for immunoglobulin G (FcgammaR)IIIB (CD16) and CD11b/CD18 were involved in the stimulation by MSUM crystals. Neutrophil preincubation with the Src kinase inhibitor 4-amino-5-(4-chlorophenyl)-7-(t-butyl) pyrazolo[3,4-d]pyrimidine and the Syk tyrosine kinase inhibitor trans-3,3',4,5'-tetrahydrozystilbene significantly reduced the release of S100A8/A9, suggesting that the Src tyrosine kinase family and Syk were involved. In addition, wortmannin reduced neutrophil release of S100A8/A9, indicating a potential involvement of phosphatidylinolitol-3 kinase in this release. Preincubation of neutrophils with the tubulin depolymerization promoters nocodazole and vincristine reduced MSUM-induced release, suggesting a tubulin-associated pathway of release. These results indicate that S100A8/A9 is released by MSUM crystal-stimulated neutrophils following activation of CD11b, CD16, Src kinases, Syk, and tubulin polymerization.

Blockade of S100A8 and S100A9 suppresses neutrophil migration in response to lipopolysaccharide

Recently, proinflammatory activities had been described for S100A8 and S100A9, two proteins found at inflammatory sites and within the neutrophil cytoplasm. In this study, we investigated the role of these proteins in neutrophil migration in vivo in response to LPS. LPS was injected into the murine air pouch, which led to the release of S100A8, S100A9, and S100A8/A9 in the pouch exudates that preceded accumulation of neutrophils. Passive immunization against S100A8 and S100A9 led to a 52% inhibition of neutrophil migration in response to LPS at 3 h postinjection. Injection of LPS was also associated with an increase in peripheral blood neutrophils and the presence in serum of S100A9 and S100A8/A9. Intravenous injection of S100A8, S100A9, or S100A8/A9 augmented the number of circulating neutrophils and diminished the number of neutrophils in the bone marrow, demonstrating that S100A8 and S100A9 induced the mobilization of neutrophils from the bone marrow to the blood. Finally, passive immunization with anti-S100A9 inhibited the neutrophilia associated with LPS injection in the air pouch. These results suggest that S100A8 and S100A9 play a role in the inflammatory response to LPS by inducing the release of neutrophils from the bone marrow and directing their migration to the inflammatory site.

Role of S100A8 and S100A9 in neutrophil recruitment in response to monosodium urate monohydrate crystals in the air-pouch model of acute gouty arthritis

OBJECTIVE

To examine the role of chemokines, S100A8, and S100A9 in neutrophil accumulation induced by the causative agent of gout, monosodium urate monohydrate (MSU) crystals.

METHODS

MSU crystal-induced neutrophil migration was studied in the murine air-pouch model. Release of chemokines, S100A8, S100A9, and S100A8/A9 in response to MSU crystals was quantified by enzyme-linked immunosorbent assays. Recruited cells were counted following acetic blue staining, and the subpopulations were characterized by Wright-Giemsa staining of cytospins.

RESULTS

MSU crystals induced the accumulation of neutrophils following injection in the air pouch, which correlated with the release of the chemokines CXCL1, CXCL2, CCL2, and CCL3. However, none of these was found to play an important role in neutrophil migration induced by MSU crystals by passive immunization with antibodies directed against each chemokine. S100A8, S100A9, and S100A8/A9 were also found at high levels in the pouch exudates following injection of MSU crystals. In addition, injection of S100A8, S100A9, or S100A8/A9 led to the accumulation of neutrophils in the murine air pouch, demonstrating their proinflammatory activities in vivo. Passive immunization with anti-S100A8 and anti-S100A9 led to a total inhibition of the accumulation of neutrophils. Finally, S100A8/A9 was found at high concentrations in the synovial fluid of patients with gout.

CONCLUSION

S100A8 and S100A8/A9 are essential to neutrophil migration induced by MSU crystals. These results suggest that they might be involved in the pathogenesis of gout.

Novel intra- and inter-molecular sulfinamide bonds in S100A8 produced by hypochlorite oxidation

Hypochlorite is a major oxidant generated when neutrophils and macrophages are activated at inflammatory sites, such as in atherosclerotic lesions. Murine S100A8 (A8) is a major cytoplasmic protein in neutrophils and is secreted by macrophages in response to inflammatory stimuli. After incubation with reagent HOCl for 10 min, approximately 85% of A8 was converted to 4 oxidation products, with electrospay ionization mass spectrometry masses of m/z 10354, 10388, 10354 +/- 1, and 20707 +/- 3. All were resistant to reduction by dithiothreitol. Initial formation of a reactive Cys sulfenic acid intermediate was demonstrated by the rapid conjugation of 5,5-dimethyl-1,3-cyclohexanedione (dimedone) to HOCl-treated A8 to form stable adducts. Matrix-assisted laser desorption-reflectron time of flight peptide mass fingerprinting of isolated oxidation products confirmed the mass additions observed in the full-length proteins. Both Met(36/73) were converted to Met(36/73) sulfoxides. An additional product with an unusual mass addition of m/z 14 (+/-0.2) was identified and corresponded to the addition of oxygen to Cys(41), conjugation to various epsilon-amines of Lys(6), Lys(34/35), or Lys(87) with loss of dihydrogen and formation of stable intra- or inter-molecular sulfinamide cross-links. Specific fragmentations identified in matrix-assisted laser desorption-post source decay spectra and low energy collisional-induced dissociation tandem mass spectroscopy spectra of sulfinamide-containing digest peptides confirmed Lys(34/35) to Cys(41) sulfinamide bonds. HOCl oxidation of mutants lacking Cys(41) (Ala(41)S100A8) or specific Lys residues (e.g. Lys(34/35), Ala(34/35)S100A8) did not form sulfinamide cross-links. HOCl generated by myeloperoxidase and H(2)O(2) and by phorbol 12-myristate 13-acetate-activated neutrophils also formed these products(.) In contrast to the disulfide-linked dimer, oxidized monomer retained normal chemotactic activity for neutrophils. Sulfinamide bond formation represents a novel oxidative cross-linking process between thiols and amines and may be a general consequence of HOCl protein oxidation in inflammation not identified previously. Similar modifications in other proteins could potentially regulate normal and pathological processes during aging, atherogenesis, fibrosis, and neurogenerative diseases.

Il-10 up-regulates macrophage expression of the S100 protein S100A8

The murine calcium binding protein S100A8 (A8) is a leukocyte chemoattractant, but high levels may be protective and scavenge hypochlorite. A8 is induced by LPS, IFN-gamma, and TNF in elicited macrophages. Th2 cytokines generally suppress proinflammatory gene expression, and IL-4 and IL-13 partially decreased A8 induction in macrophages and endothelial cells stimulated by LPS or IFN. In contrast, IL-10 synergized with LPS and IFN to increase mRNA levels > or =9-fold and secreted A8 levels approximately 4-fold. IL-10 decreased the optimal time of mRNA expression induced by LPS from 24 to 8 h. Blocking experiments indicated that endogenous IL-10 contributes to gene induction by LPS. Cooperation between IL-10 and LPS was not due to altered mRNA stability but was dependent on de novo protein synthesis. Transfection analysis with A8 luciferase constructs confirmed that synergy was due to increased transcription. The region of the promoter involved was localized to a 178-bp fragment flanking the transcription start site of the gene. This region was also responsible for the suppressive effects of IL-4 and IL-13. Forskolin, CTP-cAMP, and PGE(2) also enhanced LPS- and IFN-induced A8 mRNA, whereas indomethacin significantly reduced synergy between IL-10 and LPS. Mitogen-activated protein kinase/cyclooxygenase 2/cAMP pathways involving CCAAT-enhancing binding protein, located within the active promoter, may mediate A8 gene up-regulation in a manner mechanistically distinct to genes regulated by IL-10 via the STAT pathway. A8 exhibits pleiotropic effects, and the high levels secreted as a result of IL-10 synergy may regulate untoward inflammatory damage by virtue of its an antioxidant capacity.

IFN-gamma and TNF regulate macrophage expression of the chemotactic S100 protein S100A8

The murine calcium-binding protein S100A8 is a potent chemoattractant for neutrophils and monocytes in vivo and in vitro but may also play a protective role. We show that the kinetics of induction of S100A8 mRNA in elicited murine macrophages (Mac) by LPS, IFN-gamma, and TNF were distinct from the C-C chemokines monocyte chemoattractant protein-1 (MCP-1), macrophage-inflammatory protein-1alpha (MIP-1alpha), and RANTES. Monomeric S100A8 was predominantly secreted. IFN substantially increased S100A8 mRNA levels after 1 h with optimal induction after 12 h; induction by TNF was slower and more sustained. TNF did not up-regulate MCP-1 and MIP-1alpha mRNA in these cells. Luciferase reporter assays confirmed that LPS and IFN induce S100A8 gene transcription and mRNA in LPS-treated Mac showed little decay over 16 h, whereas transcripts induced by IFN and TNF were markedly less stable. Newly synthesized proteins may be required for mRNA transcription and stabilization in response to LPS. S100A9 associates with A8 in neutrophils, but was not coinduced with S100A8. S100A8 gene induction in Mac stimulated with LPS and IFN may be modulated by mobilization of intracellular Ca2+ concentration from distinct intracellular stores and/or the extracellular compartment and by distinct pathways involving protein kinase C and leading to activation of mitogen-activated protein kinase.

Reactions of hypochlorous acid with tyrosine and peptidyl-tyrosyl residues give dichlorinated and aldehydic products in addition to 3-chlorotyrosine

The toxicity of hypochlorous acid (HOCl) generated from activated neutrophils has been associated with several pathological processes such as atherosclerosis. Formation of 3-chlorotyrosine (Cl-Tyr) has been used as a marker for assessing the involvement of HOCl in such processes. In this study, we aimed to investigate the formation of Cl-Tyr from reaction of HOCl with tyrosine (both free and peptide-bound) and the fate of Cl-Tyr under such conditions. Tyrosine, N-acetyltyrosine, bovine serum albumin, and human low density lipoproteins were incubated with a range of reagent hypochlorite concentrations for varying periods in 10 mM phosphate buffer (pH 7.4) at 22 degrees C. The reaction products, and several biological samples, were hydrolyzed (in the case of proteins), isolated, and purified by high pressure liquid chromatography and characterized or quantitated by mass spectrometry and NMR. A significant amount of 3,5-dichlorotyrosine (diCl-Tyr) was obtained from the bovine serum albumin, low density lipoprotein, and some biological samples, in addition to Cl-Tyr, indicating that Cl-Tyr competes effectively for HOCl even when tyrosine is present in great excess. Cl-Tyr and diCl-Tyr were also formed from free tyrosine but then reacted further with HOCl. This finding differs from a claim in the literature that Cl-Tyr was not formed in such a system. The further reaction products of Cl-Tyr and diCl-Tyr with HOCl were elucidated as their corresponding mono- and dichlorinated 4-hydroxyphenylacetaldehydes. These results indicate the importance of assessing other products of HOCl action in addition to Cl-Tyr.

G551D cystic fibrosis mice exhibit abnormal regulation of inflammation in lungs and macrophages

The major cause of death in cystic fibrosis (CF) is chronic lung disease associated with persistent infection by the bacterium, Pseudomonas aeruginosa. S100A8, an S-100 calcium-binding protein with chemotactic activity, is constitutively expressed in the lungs and serum of CF patients. Levels of S100A8 mRNA were found to be three to four times higher in the lungs of mice carrying the G551D mutation in CF transmembrane conductance regulator compared with littermate controls. Intravenous injection of bacterial LPS induced S100A8 mRNA in the lung to a greater extent in G551D mice than in wild-type littermates. Localization of S100A8 mRNA and protein in the lung indicate that it is a marker for neutrophil accumulation. Bone marrow-derived macrophages from G551D mice were shown to also exhibit hypersensitivity to LPS, measured by induction of TNF-alpha. These results provide evidence that the pathology of CF relates to abnormal regulation of the immune system.

Characterization of a B cell surface antigen with homology to the S100 protein MRP8

The S100 proteins comprise a large sub-family of the EF-hand calcium-binding proteins. Here we describe a novel monoclonal antibody recognizing a B cell surface antigen. This monoclonal antibody immunoprecipitates three proteins in the 12-18 kDa range and the smallest of these proteins has a striking homology at its amino-terminus to human MRP8, a myeloid specific member of the S100 family. Similarly to MRP8 in myeloid cells, this antigen is expressed in the cytoplasm of B cells and is secreted by LPS-induced activated B cells. This surface antigen is not B cell specific. Since MRP8 is not expressed by lymphoid cells, however, this antibody appears to recognize a new member of the S100 family.

Oxidation regulates the inflammatory properties of the murine S100 protein S100A8

The myeloid cell-derived calcium-binding murine protein, S100A8, is secreted to act as a chemotactic factor at picomolar concentrations, stimulating recruitment of myeloid cells to inflammatory sites. S100A8 may be exposed to oxygen metabolites, particularly hypochlorite, the major oxidant generated by activated neutrophils at inflammatory sites. Here we show that hypochlorite oxidizes the single Cys residue (Cys41) of S100A8. Electrospray mass spectrometry and SDS-polyacrylamide gel electrophoresis analysis indicated that low concentrations of hypochlorite (40 microM) converted 70-80% of S100A8 to the disulfide-linked homodimer. The mass was 20,707 Da, 92 Da more than expected, indicating additional oxidation of susceptible amino acids (possibly methionine). Phorbol 12-myristate 13-acetate activation of differentiated HL-60 granulocytic cells generated an oxidative burst that was sufficient to efficiently oxidize exogenous S100A8 within 10 min, and results implicate involvement of the myeloperoxidase system. Moreover, disulfide-linked dimer was identified in lung lavage fluid of mice with endotoxin-induced pulmonary injury. S100A8 dimer was inactive in chemotaxis and failed to recruit leukocytes in vivo. Positive chemotactic activity of recombinant Ala41S100A8 indicated that Cys41 was not essential for function and suggested that covalent dimerization may structurally modify accessibility of the chemotactic hinge domain. Disulfide-dependent dimerization may be a physiologically significant regulatory mechanism controlling S100A8-provoked leukocyte recruitment.

Overexpression, oxidative refolding, and zinc binding of recombinant forms of the murine S100 protein MRP14 (S100A9)

Recombinant murine MRP14 (mMRP14) was produced in Escherichia coli using the pGEX expression system. The mass of fusion protein, by electrospray ionization-mass spectrometry (ESI/MS), was 39,213 Da which compares well with the theoretical mass (39,210.4 Da). Thrombin digestion of fusion protein was expected at a cloned thrombin consensus sequence (. LVPRGS. ) located between glutathione S-transferase and mMRP14. Analysis of products of digestion by C4 reverse-phase HPLC and SDS-PAGE/Western blotting revealed two immunoreactive cleavage products with molecular weights around 13, 000. Masses of the two proteins determined by ESI/MS were 13,062 and 11,919 Da. The larger product corresponded to the expected mass of recombinant mMRP14 (13,061.9 Da). Analysis of the protein sequence of recombinant mMRP14 revealed a thrombin-like consensus sequence (. NNPRGH. ) located close to the C-terminus. The smaller protein corresponded to a truncated form of rec mMRP14 (rec MRP141-102) with a calculated mass of 11,918.6 Da. Optimization of the cleavage conditions resulted in >95% full-length rec mMRP14. Native mMRP14 contains one intramolecular disulfide bond between Cys79 and Cys90. The full-length recombinant protein was renatured and oxidized in ammonium acetate (pH approximately 7) for 96 h and formed >95% of the native intramolecular disulfide-bonded form. MRP141-102 bound substantially less 65Zn2+ compared to native mMRP14 or rec mMRP14 after transfer to polyvinylidene difluoride and incubation with 65ZnCl2, implicating the His residues located within the C-terminal domain in Zn2+ binding.

Identification of posttranslational modifications and cDNA sequencing errors in the rat S100 proteins MRP8 and 14 using electrospray ionization mass spectrometry

MRP8 and 14 are S100 proteins expressed by myeloid cells and are predicted to have important functions in inflammation. The proteins were isolated from spleens from three rat strains. Electrospray ionization mass spectrometry indicated masses of 10,149 +/- 2 Da for MRP8 and 13,069 +/- 2 Da for MRP14 compared to masses calculated from proteins derived from their cDNA sequences of 10,211 and 13,214 Da, respectively, indicating posttranslational modifications and/or errors in the derived protein sequences. Several endoprotease digest peptides did not correspond to any theoretical digest products after comparison of ESI masses with those derived from the theoretical digest. Both proteins were N-terminally acetylated after deletion of the initiator Met, reducing the theoretical masses by 89 Da. A peptide with mass 28 Da greater than the theoretical was isolated from the Asp N digestion of MRP8. N-terminal sequencing indicated translated Val instead of the predicted Ala at position 72 of MRP8. A peptide 56 Da less than the theoretical was isolated from the chymotryptic digestion of MRP14, and the carboxyamidomethylated form was N-terminally sequenced and found to have translated Ser instead of the predicted Arg at position 105. In addition, His106 was methylated. The corrected theoretical masses, incorporating the posttranslational modifications and sequencing errors, are 10,149.4 and 13,069.9 Da for MRP8 and 14, respectively, in good agreement with the experimental masses.

Identification of noncovalent dimeric complexes of the recombinant murine S100 protein CP10 by electrospray ionization mass spectrometry and chemical cross-linking

CP10 is a chemotactic S100 protein expressed by murine myeloid cells. A specific noncovalently linked dimeric complex of recombinant Ala43 CP10 was identified after electrospray ionization mass spectrometry using a nondenaturing solvent of 5-mM ammonium acetate (pH 6.5) and source temperature of 50 degrees C. With a low cone voltage (75 V), major ions were observed at approximately 2075, 2305, and 2613 Da, which were attributed to partially desolvated multiply charged noncovalently linked dimeric species (+10, +9, and +8 charge states, respectively). Deconvolution produced a broad peak centered around 20750 Da corresponding to the approximate mass of dimeric recombinant Ala43 CP10. Increasing the cone voltage, the collisionally activating the complex, gradually reduced the intensity of these dimeric ions, with a concomitant increase in higher and lower charge state monomeric ions. The intensities of these dimeric ions were greatly reduced in spectra recorded with a source temperature of 140 degrees C and cone voltage of 75 V, indicating a thermally unstable noncovalent complex. Similar spectra were obtained using recombinant CP10. Specific noncovalent S100 dimeric complexes were confirmed by chemically cross-linking recombinant Ala43 CP10 or CP10 with bis (sulfosuccinimidyl) suberate, followed by SDS/PAGE. The dominant silver-stained and CP10-immunoreactive component migrated at 20,000 suggested that the complex represents the major isoform in solution.

Immunodetection of the murine chemotactic protein CP-10 in bleomycin-induced pulmonary injury

The murine S-100 protein designated CP-10 is a potent chemotactic factor for phagocytic cells, exhibiting optimal activity in the picomolar range. We assessed the role of this cytokine in the inflammatory response to pulmonary injury following intratracheal administration of bleomycin to mice. In the lungs of normal animals, strong cytoplasmic immunostaining for CP-10 was demonstrable in all recognisable neutrophil leucocytes sequestered within alveolar capillaries. Following induction of pulmonary inflammation in susceptible C57BL/6 mice, numerous CP-10-positive neutrophils were observed, but many of the recruited neutrophils did not exhibit staining for CP-10. No other cells were immunoreactive. The concentration of CP-10 in bronchoalveolar lavage (BAL) fluids from normal mice and mice administered intratracheal saline was below the level of detection by enzyme immunoassay. In contrast, nanomolar levels of CP-10 were detected in unconcentrated BAL fluids from C57BL/6 mice after bleomycin-induced injury, and the presence of monomeric CP-10 was demonstrable by Western blotting. Elevation of CP-10 levels correlated with the influx of inflammatory cells in C57BL/6 mice, but was not demonstrable in BAL fluids from BALB/c mice, which are resistant to pulmonary injury by bleomycin. We conclude that CP-10 may contribute to the recruitment of inflammatory cells in bleomycin-induced lung damage.

Induction of the S100 Chemotactic Protein, CP-10, in Murine Microvascular Endothelial Cells by Proinflammatory Stimuli

Microvascular endothelial cells (EC) have multiple functions in inflammatory responses, including the production of chemoattractants that enhance leukocyte transmigration into tissues. Chemotactic protein, 10 kD (CP-10), is an S100 protein with potent chemotactic activity for myeloid cells in vitro and in vivo and is expressed in neutrophils and lipopolysaccharide (LPS)-activated macrophages. We show here that CP-10 is induced in murine endothelioma cell lines (bEnd-3, sEnd-1, and tEnd-1) after activation with LPS and interleukin-1 (IL-1) but not tumor necrosis factor α (TNFα) or interferon γ (IFNγ). Induction was not mediated by endogenous release of IL-1 or TNFα and was not directly upregulated by phorbol myristate acetate, calcium ionophore, or vitamin D3. EC were exquisitely sensitive to IL-1 activation (3.4 U/mL) and CP-10 mRNA induction with IL-1 occurred earlier (8 hours) than with LPS (12 hours). Furthermore, some microvessels and capillaries in delayed-type hypersensitivity lesions expressed cytoplasmic CP-10. Responses to LPS and not IL-1 in vitro were regulated by the degree of cell confluence and by TNFα costimulation. The related MRP-14 mRNA had a different induction pattern. Monomeric and homodimeric CP-10 upregulated by activation was predominantly cell-associated. EC-derived CP-10 may contribute to amplification of inflammatory processes by enhancing leukocyte shape changes and transmigration in the microcirculation.

Induction of the S100 Chemotactic Protein, CP-10, in Murine Microvascular Endothelial Cells by Proinflammatory Stimuli

Microvascular endothelial cells (EC) have multiple functions in inflammatory responses, including the production of chemoattractants that enhance leukocyte transmigration into tissues. Chemotactic protein, 10 kD (CP-10), is an S100 protein with potent chemotactic activity for myeloid cells in vitro and in vivo and is expressed in neutrophils and lipopolysaccharide (LPS)-activated macrophages. We show here that CP-10 is induced in murine endothelioma cell lines (bEnd-3, sEnd-1, and tEnd-1) after activation with LPS and interleukin-1 (IL-1) but not tumor necrosis factor α (TNFα) or interferon γ (IFNγ). Induction was not mediated by endogenous release of IL-1 or TNFα and was not directly upregulated by phorbol myristate acetate, calcium ionophore, or vitamin D3. EC were exquisitely sensitive to IL-1 activation (3.4 U/mL) and CP-10 mRNA induction with IL-1 occurred earlier (8 hours) than with LPS (12 hours). Furthermore, some microvessels and capillaries in delayed-type hypersensitivity lesions expressed cytoplasmic CP-10. Responses to LPS and not IL-1 in vitro were regulated by the degree of cell confluence and by TNFα costimulation. The related MRP-14 mRNA had a different induction pattern. Monomeric and homodimeric CP-10 upregulated by activation was predominantly cell-associated. EC-derived CP-10 may contribute to amplification of inflammatory processes by enhancing leukocyte shape changes and transmigration in the microcirculation.