CAP37, a neutrophil-derived multifunctional inflammatory mediator

Heparin-binding protein decreases apoptosis in human and murine neutrophils

BACKGROUND

Heparin-binding protein (HBP), a serine protease without any known proteolytic activity, is found in human polymorphonuclear leukocyte (PMN) granules, but not in mice. HBP potentiates the endotoxin-induced release of tumor necrosis factor (TNF) alpha, interleukin (IL)-1, and IL-6 from isolated monocytes. HBP has also been shown to increase the survival of cultured monocytes and protect them from oxidative stress. However, whether HBP affects PMNs themselves is not known.

MATERIALS AND METHODS

Based on our work with cultured monocytes and the survival benefit noted in experimental peritonitis, we hypothesized that HBP would have a beneficial effect on the survival of neutrophils. We evaluated the effect of HBP on apoptosis in murine peritoneal exudative cells elicited by intraperitoneal thioglycollate administration and in normal human neutrophils from volunteers. Leukocytes were isolated from the peritoneal cavity and blood of mice that underwent intraperitoneal thioglycollate instillation. The mouse peritoneal exudate cells and normal human neutrophils isolated from peripheral blood were used to study the effect of HBP on survival and apoptosis.

RESULTS

HBP decreased percentage apoptosis of mouse cells in both serum-enriched (from 24.8 to 4.5%) and serum-deprived (from 23.1 to 8.2%) cultures. In human PMNs, the protective effect of HBP was seen only in the serum-deprived group, with a decrease in percentage apoptosis from 69.1 to 43.3%.

CONCLUSIONS

For the first time, we have shown that HBP, in addition to its known augmentation of the proinflammatory response of monocytes, also acts as a prosurvival protein for neutrophils themselves, and thereby enhances local host defense.

Structure and function of the N-linked glycans of HBP/CAP37/azurocidin: crystal structure determination and biological characterization of nonglycosylated HBP

The three N-glycosylation sites of human heparin binding protein (HBP) have been mutated to produce a nonglycosylated HBP (ng-HBP) mutant. ng-HBP has been crystallized and tested for biological activity. Complete X-ray data have been collected to 2.1 A resolution, and the structure has been fully refined to an R-factor of 18.4% (R(free) 27.7%). The ng-HBP structure reveals that neither the secondary nor tertiary structure have changed due to the removal of the glycosylation, as compared to the previously determined glycosylated HBP structure. Although the primary events in N-linked glycosylation occurs concomitant with polypeptide synthesis and therefore possesses the ability to influence early events in protein folding, we see no evidence of glycosylation influencing the structure of the protein. The root-mean-square deviation between the superimposed structures was 0.24 A (on C alpha atoms), and only minor local structural differences are observed. Also, the overall stability of the protein seems to be unaffected by glycosylation, as judged by the B-factors derived from the two X-ray structures. The flexibility of a glycan site may be determined by the local polypeptide sequence and structure rather than the glycan itself. The biological in vitro activity assay data show that ng-HBP, contrary to glycosylated HBP, mediates only a very limited stimulation of the lipopolysaccharide induced cytokine release from human monocytes. In animal models of fecal peritonitis, glycosylated HBP treatment rescues mice from and an otherwise lethal injury. It appears that ng-HBP have significant effect on survival, and it can be concluded that ng-HBP can stimulate the host defence machinery albeit to a lesser extent than glycosylated HBP.

Heparin-binding protein targeted to mitochondrial compartments protects endothelial cells from apoptosis

Neutrophil-borne heparin-binding protein (HBP) is a multifunctional protein involved in the progression of inflammation. HBP is stored in neutrophil granules and released upon stimulation of the cells in proximity to endothelial cells. HBP affects endothelial cells in multiple ways; however, the molecular and cellular mechanisms underlying the interaction of HBP with these cells are unknown. Affinity isolation and enzymatic degradation demonstrated that HBP released from human neutrophils binds to endothelial cell-surface proteoglycans, such as syndecans and glypican. Flow cytometry indicated that a significant fraction of proteoglycan-bound HBP is taken up by the endothelial cells, and we used radiolabeled HBP to determine the internalization rate of surface-bound HBP. Confocal and electron microscopy revealed that internalized HBP is targeted to perinuclear compartments of endothelial cells, where it colocalizes with mitochondria. Western blotting of isolated mitochondria from HBP-treated endothelial cells showed that HBP is present in 2 forms - 28 and 22 kDa. Internalized HBP markedly reduced growth factor deprivation-induced caspase-3 activation and protected endothelial cells from apoptosis, suggesting that uptake and intracellular routing of exogenous HBP to mitochondria contributes to the sustained viability of endothelial cells in the context of locally activated neutrophils.

Neutrophils and renal failure

In many diseases and acute inflammatory disorders, important components of pathological processes are linked to the neutrophils' ability to release a complex assortment of agents that can destroy normal cells and dissolve connective tissue. This review summarizes the mechanisms of tissue destruction by neutrophils and the role of kidney-specific factors that promote this effect. Nicotinamide adenine dinucleotide phosphate H (NADPH) oxidase is a membrane-associated enzyme that generates a family of reactive oxygen intermediates (ROI). There is increasing evidence that ROIs are implicated in glomerular pathophysiology: ROIs contribute to the development of proteinuria, alter glomerular filtration rate, and induce morphological changes in glomerular cells. Specific neutrophil granules contain microbicidal peptides, proteins, and proteolytic enzymes, which mediate the dissolution of extracellular matrix, harm cell structures or cell function, and induce acute and potentially irreparable damage. Although both ROI and neutrophil-derived proteases alone have the potential for tissue destruction, it is their synergism that circumvents the intrinsic barriers designed to protect the host. Even small amounts of ROI can generate hypochlorus acid (HOCl) in the presence of neutrophil-derived myeloperoxidase (MPO) and initiate the deactivation of antiproteases and activation of latent proteases, which lead to tissue damage if not properly controlled. In addition, neutrophil-derived phospholipase products such as leukotrienes and platelet-activating factor contribute to vascular changes in acute inflammation and amplify tissue damage. Increasing evidence suggests that mesangial cells and neutrophils release chemotactic substances (eg, interleukin 8), which further promote neutrophil migration to the kidney, activate neutrophils, and increase glomerular injury. Also, the expression of adhesion molecules (eg, intercellular adhesion molecule 1 on kidney-specific cells and beta-2-integrins on leukocytes) has been correlated with the degree of injury in various forms of glomerulonephritis or after ischemia and reperfusion. Together, these results suggest that neutrophils and adhesion molecules play an important role in mediating tissue injury with subsequent renal failure. Conversely, chronic renal failure reduces neutrophil function and thereby can increase susceptibility to infection and sepsis.

Endocytosis of Heparin-Binding Protein (CAP37) Is Essential for the Enhancement of Lipopolysaccharide-Induced TNF-α Production in Human Monocytes

Heparin-binding protein (HBP), also known as CAP37, is a proteolytically inactive serine protease homologue that is released from activated granulocytes. However, HBP is not a biologically inactive molecule but rather a multifunctional protein with properties that include the enhancement of LPS-induced TNF-α production from monocytes. We have previously demonstrated that HBP is internalized in monocytes. In the current study, we hypothesize that HBP is internalized in monocytes via endocytosis, and this internalization is an important mechanism by which HBP enhances LPS-induced TNF-α release. Using whole blood from healthy donors and flow cytometry, we found that colchicine (0.1–10 mM), cytochalasin D (1000 μM), NH4Cl (10–50 mM), and bafilomycin A1 (0.1–3 μM) significantly reduced the affinity of FITC-HBP for CD14-positive monocytes. Using isolated human monocytes and ELISA, we found that colchicine (0.1 mM), cytochalasin D (30 and 300 μM), NH4Cl (30 mM), and bafilomycin A1 (1 μM) significantly reduced the effect of HBP (10 μg/ml) to enhance LPS (10 ng/ml)-induced TNF-α release after 24 h. These findings demonstrate that internalization of HBP in monocytes is essential for the enhancement of LPS-induced TNF-α release. Transport of HBP to an activating compartment depends on intact F-actin polymerization and endosomal acidification, an important mechanism for endosomal protein sorting and trafficking.

Modulation of lipopolysaccharide-induced monocyte activation by heparin-binding protein and fucoidan

Activated polymorphonuclear leukocytes release heparin-binding protein (HBP; also known as CAP37 or azurocidin) from azurophilic granules. HBP is a strong chemoattractant for monocytes that also prolongs monocyte survival and potentiates endotoxin (lipopolysaccharide [LPS])-induced production of tumor necrosis factor alpha (TNF-alpha). We investigated the binding of fluorescein isothiocyanate-conjugated HBP to human monocytes in the presence of EDTA and the polysaccharide fucoidan. EDTA, which chelates divalent cations, has been widely used to study the role of divalent cations in receptor-ligand interactions or enzyme activity. Fucoidan has been used to inhibit the binding of various ligands to scavenger receptors or selectins. Scavenger receptors are multiligand receptors that mediate endocytosis of proteases, protease-inhibitor complexes, lipoproteins, and LPS-lipid A. Fucoidan also interferes with leukocyte rolling by binding to L-selectins (expressed on leukocytes) and P-selectins (expressed on platelets and endothelium). We demonstrate that the binding of the neutrophil-derived protein HBP to monocytes is inhibited in the presence of EDTA and fucoidan. In addition, fucoidan and EDTA abrogate the enhancing effect of HBP on LPS-induced TNF-alpha production. These data provide supporting evidence that HBP binds to a receptor expressed on monocytes. This receptor is dependent on divalent cations and is possibly related to the scavenger receptor. Furthermore, we demonstrate that fucoidan, by itself, stimulates TNF-alpha release from isolated monocytes in a CD14-independent fashion. This is an important finding for the interpretation of results from studies that use fucoidan to "block" either scavenger receptors or L- or P-selectins.

Heparin binding protein (CAP37) is an opsonin for Staphylococcus aureus and increases phagocytosis in monocytes

Heparin binding protein (HBP), also known as cationic antibiotic protein (CAP37) or azurocidin, is stored in azurophilic granules of neutrophils and is released to the extracellular space when granulocytes phagocytose Staphylococcus aureus. We investigated whether extracellular HBP also has the potential to increase phagocytosis of S. aureus by other phagocytes. We used flow cytometry to characterize the binding of HBP to S. aureus and to simultaneously measure phagocytosis and superoxide production of opsonized S. aureus in monocytes and granulocytes. Our results demonstrate that HBP is a strong opsonin for S. aureus, and that monocytes, but not granulocytes, increase phagocytosis of HBP-treated S. aureus. However, HBP-treated S. aureus increases the production of superoxide in both monocytes and granulocytes as compared with untreated S. aureus. These findings support the role of granulocytes in the afferent limb of inflammation and demonstrate that HBP, when released from activated granulocytes, potentiates bacterial uptake in monocytes and enhances the potential of microbial killing in monocytes and granulocytes.

Release of monocyte chemoattractants by polymorphonuclear leukocytes stimulated by their adhesion to stratum corneum opsonized via complement activation, measured with a human acute monocytic leukemic cell line, THP-1

Stratum corneum (SC) exposed to living tissues, induces inflammation characterized by the formation of mixed cell granulomas consisting of infiltrative polymorphonuclear leukocytes (PMNs) and monocytes/macrophages. In this study, to clarify the mechanism for the later monocyte accumulation in SC-induced granulomas, we evaluated monocyte chemotactic activity induced by PMNs treated with serum-opsonized SC by using a human acute monocytic leukemic cell line, THP-1. When the supernatant was obtained from a PMN suspension cultured with opsonized plantar SC, higher THP-1 chemotactic activity was detected as compared with that cultured with non-opsonized SC. Although some concentrations of the chemokines, MIP-1alpha and MIP-1beta, were detected in supernatants obtained from the PMN suspensions cultured with plantar SC than in the control suspensions of PMN alone, their production by PMN was not influenced by the opsonization procedure. In contrast, MCP-1 was found to be secreted from PMN suspensions constitutively, showing no correlation to this THP-1 chemotactic activity. Moreover, HPLC analysis of PMN suspensions indicated that factors with far higher molecular weight values than these chemokines are involved in the chemotaxis of THP-1 cells.

Heparin-Binding Protein (CAP37) Is Internalized in Monocytes and Increases LPS-Induced Monocyte Activation

Previous studies have shown that the neutrophil-derived heparin-binding protein (HBP), also known as CAP37 or azurocidin, potentiates the LPS-induced release of proinflammatory cytokines (TNF-α, IL-1, and IL-6) from isolated human monocytes. To date, the mechanisms by which HBP enhances LPS-induced monocyte activation have not been elucidated, and it is not known whether HBP also increases the LPS-induced production of other bioactive substances. We studied human monocytes activated by recombinant human HBP and LPS and their interaction with the LPS receptor CD14. We hypothesized that the stimulatory effect of HBP on the LPS-induced release of proinflammatory mediators from monocytes was mediated by specific binding of HBP to monocytes, which resulted in an up-regulation of CD14. Our results demonstrated that HBP alone (10 μg/ml) stimulated the production of TNF-α from isolated monocytes. In addition, HBP had an additive effect on LPS-induced production of TNF-α and PGE2, suggesting a generalized monocyte activation. We used flow cytometry to demonstrate that HBP had a high affinity to monocytes but not to the LPS receptor CD14, and experiments performed at 4°C indicated an energy-dependent step in this process. Confocal microscopy showed that monocytes internalize HBP within 30 min. These data suggest that mechanisms other than increased CD14 expression are responsible for the enhanced release of TNF-α or PGE2 in response to HBP and LPS.

Interaction of a synthetic peptide based on the neutrophil-derived antimicrobial protein CAP37 with dipalmitoyl-phosphatidylcholine membranes

CAP37, a cationic antimicrobial protein of Mr 37 kDa is constitutively expressed in human neutrophils. A synthetic peptide, CAP37 P20-44, corresponding to amino acid residues 20 through 44 of the native CAP37 molecule has been shown to mimic the antimicrobial activity of the native protein. An analog of peptide CAP37 P20-44 was synthesized in which the cysteine residues at positions 26 and 42 were replaced with serine residues (CAP37 P20-44Ser). This resulted in a peptide that no longer exhibited bactericidal activity. The effect of different concentrations of the active CAP37 peptide, CAP37 P20-44, and its inactive analog, CAP37 P20-44Ser, on artificial lipid membranes composed of dipalmitoyl phosphatidylcholine (DPPC) was studied using small-angle X-ray scattering and differential scanning calorimetry. The results indicated that CAP37 P20-44 perturbs the periodicity of the lamellar structure as shown by small angle X-ray diffraction, while the effect of the inactive peptide is not as strong. Differential scanning calorimetry further confirms that CAP37 P20-44 interacts with lipid membranes as indicated by increased width of the transition and decreased peak height. Moreover, it completely abolishes the pretransition temperature of the DPPC membranes. The effect of the inactive peptide, CAP37 P20-44Ser on the thermotropic properties of DPPC was small. These studies suggest that CAP37 perturbs the lamellar structure of lipid bilayers and further suggests that the antibiotic action of the molecule may be through its interactions with the lipid components of the Gram negative bacterial membrane.

Systemic inflammatory response syndrome

BACKGROUND

Localized inflammation is a physiological protective response which is generally tightly controlled by the body at the site of injury. Loss of this local control or an overly activated response results in an exaggerated systemic response which is clinically identified as systemic inflammatory response syndrome (SIRS). Compensatory mechanisms are initiated in concert with SIRS and outcome (resolution, multiple organ dysfunction syndrome or death) is dependent on the balance of SIRS and such compensatory mechanisms. No directed therapies have been successful to date in influencing outcome.

METHOD

This review examines the current spectrum and pathophysiology of SIRS.

RESULTS AND CONCLUSION

Further clinical and basic scientific research is required to develop the global picture of SIRS, its associated family of syndromes and their natural histories.

Structure of HBP, a multifunctional protein with a serine proteinase fold

The structure of human heparin binding protein reveals that the serine proteinase fold has been used as a scaffold for a multifunctional protein with antibacterial activity, monocyte and t-cell activating properties and endotoxin and heparin binding capacity.

Human leukocyte elastase is an endogenous ligand for the integrin CR3 (CD11b/CD18, Mac-1, alpha M beta 2) and modulates polymorphonuclear leukocyte adhesion

Integrin CR3 (CD11b/CD18, Mac-1, alpha M beta 2) mediates the transient adhesion of polymorphonuclear leukocytes (PMN) to surfaces coated with fibrinogen, C3bi, ICAM-1, and other ligands. Recent studies (Cai, T.-Q., and S.D. Wright 1995. J. Biol. Chem. 270:14358) suggest that adhesion may be favored by stimulus-dependent changes in the kinetics of ligand binding by CR3. Cell detachment, on the other hand, must occur by a different mechanism because binding kinetics cannot affect cell adhesion after binding of ligand has occurred. We have sought a mechanism that would reverse binding of ligand to CR3 and report here that lysates of PMN contain an endogenous ligand that binds CR3 and competes the binding of C3bi. Purification and sequence analysis identified the structurally homologous azurophilic granule proteins, elastase, protease 3, and azurocidin as candidates. Studies with purified elastase and azurocidin showed that each bound specifically to purified, immobilized CR3. Elastase may play a role in modulating integrin-mediated cell adhesion because it is expressed at the cell surface, and the expression level is inversely proportional to cell adhesivity. Furthermore, a monoclonal antibody against elastase prevented detachment of PMN from fibrinogen-coated surfaces and blocked chemotaxis, confirming a role for this protein in regulating integrin-mediated adhesion. These studies suggest a model for release of integrin-mediated cell adhesion in which endogenous ligands such as elastase may release adhesion by "'eluting" substrate-bound ligand. A role for the proteolytic activity of elastase appears likely but is not demonstrated in this study.

Secretion of type-1-fimbriae binding proteins from human neutrophil granulocytes

Granule matrix proteins secreted from human neutrophils after ionomycin stimulation were separated by SDS-PAGE, blotted onto a polyvinylidene diflouride (PVDF) membrane and overlaid with the mannose-binding lectin concanavalin A (Con A) or Escherichia coli bacteria exposing type-I-fimbriae. Four proteins of approximately 30, 40, 70 and 80 kD, respectively, derived from both the azurophil and the specific granules were shown to expose mannose-containing structures by binding of Con A. Such reactivity was also shown for a 90-kD protein from the light membrane fraction enriched in plasma membrane and secretory vesicles. When blots of granule matrix proteins were exposed to type-I-fimbriated bacteria, a total of seven proteins was recognized; four of the five Con A-binding proteins (40, 70, 80 and 90 kD) was detected also by the bacteria in addition to three proteins not detected by Con A (50, 60 and 100 kD). The role of the secreted type-1-fimbriae binding proteins as anti-adhesin candidates is discussed.

Characterization of recombinant human HBP/CAP37/azurocidin, a pleiotropic mediator of inflammation-enhancing LPS-induced cytokine release from monocytes

Neutrophil-derived heparin-binding protein (HBP) is a strong chemoattractant for monocytes. We report here for the first time the expression of recombinant HBP. A baculovirus containing the human HBP cDNA mediated in insect cells the secretion of a 7-residue N-terminally extended HBP form (pro-HBP). Deletion of the pro-peptide-encoding cDNA sequence resulted in correctly processed HBP at the N-terminus. Electrospray mass spectrum analysis of recombinant HBP yielded a molecular weight of 27.237 +/- 3 amu. Consistent with this mass is a HBP form of 225 amino acids (mature part +3 amino acid C-terminal extension). The biological activity of recombinant HBP was confirmed by its chemotactic action towards monocytes. Furthermore, we have shown that recombinant HBP stimulates in a dose-dependent manner the lipopolysaccharide (LPS)-induced cytokine release from human monocytes.

Antibiotic proteins of polymorphonuclear leukocytes

The polymorphonuclear leukocyte (PMN) plays an essential role in the innate defense of the mammalian host against bacterial invaders. Responding chemotactically, the PMN delivers a complex antibiotic arsenal to sites of infection. Among these cytotoxic systems is an array of antimicrobial proteins and peptides that the PMN directs at microorganisms both before (i.e. extracellularly) and after sequestration into a phagocytic vacuole. In addition to their microbicidal capacity, several of these proteins bind to and neutralize the endotoxic activity of Gram-negative bacterial lipopolysaccharides (LPS). In this review the principle features of these antibiotic proteins are briefly summarized with emphasis on their possible actions in biological settings. In many instances, additional functions independent of cytotoxicity have been described raising the possibility that some of these proteins subserve multiple roles in inflammation.