The coding ECP 434(G>C) gene polymorphism determines the cytotoxicity of ECP but has minor effects on fibroblast-mediated gel contraction and no effect on RNase activity

Essential Role of Enzymatic Activity in the Leishmanicidal Mechanism of the Eosinophil Cationic Protein (RNase 3)

The recruitment of eosinophils into Leishmania lesions is frequently associated with a favorable evolution. A feasible effector for this process is eosinophil cationic protein (ECP, RNase 3), one of the main human eosinophil granule proteins, endowed with a broad spectrum of antimicrobial activity, including parasites. ECP was active on Leishmania promastigotes and axenic amastigotes (LC₅₀’s = 3 and 16 μM, respectively) but, in contrast to the irreversible membrane damage caused on bacteria and reproduced by its N-terminal peptides, it only induced a mild and transient plasma membrane destabilization on Leishmania donovani promastigotes. To assess the contribution of RNase activity to the overall leishmanicidal activity of ECP, parasites were challenged in parallel with a single-mutant version, ECP-H15A, devoid of RNase activity, that fully preserves the conformation and liposome permeabilization ability. ECP-H15A showed a similar uptake to ECP on promastigotes, but with higher LC₅₀’s (>25 μM) for both parasite stages. ECP-treated promastigotes showed a degraded RNA pattern, absent in ECP-H15A-treated samples. Moreover ECP, but not ECP-H15A, reduced more than 2-fold the parasite burden of infected macrophages. Altogether, our results suggest that ECP enters the Leishmania cytoplasm by an endocytic pathway, ultimately leading to RNA degradation as a key contribution to the leishmanicidal mechanism. Thus, ECP combines both membrane destabilization and enzymatic activities to effect parasite killing. Taken together, our data highlight the microbicidal versatility of ECP as an innate immunity component and support the development of cell-penetrating RNases as putative leishmanicidal agents.

Human RNase3 immune modulation by catalytic-dependent and independent modes in a macrophage-cell line infection model

The human RNase3 is a member of the RNaseA superfamily involved in host immunity. RNase3 is expressed by leukocytes and shows broad-spectrum antimicrobial activity. Together with a direct antimicrobial action, RNase3 exhibits immunomodulatory properties. Here, we have analysed the transcriptome of macrophages exposed to the wild-type protein and a catalytic-defective mutant (RNase3-H15A). The analysis of differently expressed genes (DEGs) in treated THP1-derived macrophages highlighted a common pro-inflammatory "core-response" independent of the protein ribonucleolytic activity. Network analysis identified the epidermal growth factor receptor (EGFR) as the main central regulatory protein. Expression of selected DEGs and MAPK phosphorylation were inhibited by an anti-EGFR antibody. Structural analysis suggested that RNase3 activates the EGFR pathway by direct interaction with the receptor. Besides, we identified a subset of DEGs related to the protein ribonucleolytic activity, characteristic of virus infection response. Transcriptome analysis revealed an early pro-inflammatory response, not associated to the protein catalytic activity, followed by a late activation in a ribonucleolytic-dependent manner. Next, we demonstrated that overexpression of macrophage endogenous RNase3 protects the cells against infection by Mycobacterium aurum and the human respiratory syncytial virus. Comparison of cell infection profiles in the presence of Erlotinib, an EGFR inhibitor, revealed that the receptor activation is required for the antibacterial but not for the antiviral protein action. Moreover, the DEGs related and unrelated to the protein catalytic activity are associated to the immune response to bacterial and viral infection, respectively. We conclude that RNase3 modulates the macrophage defence against infection in both catalytic-dependent and independent manners.

Host Regulators of Liver Fibrosis During Human Schistosomiasis

Liver fibrosis is a wound-healing process purposely aimed at restoring organ integrity after severe injury caused by autoimmune reactions, mechanical stress or infections. The uncontrolled solicitation of this process is pathogenic and a pathognomonic feature of diseases like hepatosplenic schistosomiasis where exacerbated liver fibrosis is centrally positioned among the drivers of the disease morbidity and mortality. Intriguingly, however, liver fibrosis occurs and progresses dissimilarly in schistosomiasis-diseased individuals with the same egg burden and biosocial features including age, duration of residence in the endemic site and gender. This suggests that parasite-independent and currently poorly defined host intrinsic factors might play a defining role in the regulation of liver fibrosis, the hallmark of morbidity, during schistosomiasis. In this review, we therefore provide a comprehensive overview of all known host candidate regulators of liver fibrosis reported in the context of human schistosomiasis.

Immune Modulation by Human Secreted RNases at the Extracellular Space

The ribonuclease A superfamily is a vertebrate-specific family of proteins that encompasses eight functional members in humans. The proteins are secreted by diverse innate immune cells, from blood cells to epithelial cells and their levels in our body fluids correlate with infection and inflammation processes. Recent studies ascribe a prominent role to secretory RNases in the extracellular space. Extracellular RNases endowed with immuno-modulatory and antimicrobial properties can participate in a wide variety of host defense tasks, from performing cellular housekeeping to maintaining body fluid sterility. Their expression and secretion are induced in response to a variety of injury stimuli. The secreted proteins can target damaged cells and facilitate their removal from the focus of infection or inflammation. Following tissue damage, RNases can participate in clearing RNA from cellular debris or work as signaling molecules to regulate the host response and contribute to tissue remodeling and repair. We provide here an overall perspective on the current knowledge of human RNases’ biological properties and their role in health and disease. The review also includes a brief description of other vertebrate family members and unrelated extracellular RNases that share common mechanisms of action. A better knowledge of RNase mechanism of actions and an understanding of their physiological roles should facilitate the development of novel therapeutics.

Rapid Evolution of Primate Type 2 Immune Response Factors Linked to Asthma Susceptibility

Host immunity pathways evolve rapidly in response to antagonism by pathogens. Microbial infections can also trigger excessive inflammation that contributes to diverse autoimmune disorders including asthma, lupus, diabetes, and arthritis. Definitive links between immune system evolution and human autoimmune disease remain unclear. Here we provide evidence that several components of the type 2 immune response pathway have been subject to recurrent positive selection in the primate lineage. Notably, substitutions in the central immune regulator IL13 correspond to a polymorphism linked to asthma susceptibility in humans. We also find evidence of accelerated amino acid substitutions as well as gene gain and loss events among eosinophil granule proteins, which act as toxic antimicrobial effectors that promote asthma pathology by damaging airway tissues. These results support the hypothesis that evolutionary conflicts with pathogens promote tradeoffs for increasingly robust immune responses during animal evolution. Our findings are also consistent with the view that natural selection has contributed to the spread of autoimmune disease alleles in humans.

Protein post-translational modification in host defense: the antimicrobial mechanism of action of human eosinophil cationic protein native forms

Knowledge on the contribution of protein glycosylation in host defense antimicrobial peptides is still scarce. We have studied here how the post-translational modification pattern modulates the antimicrobial activity of one of the best characterized leukocyte granule proteins. The human eosinophil cationic protein (ECP), an eosinophil specific granule protein secreted during inflammation and infection, can target a wide variety of pathogens. Previous work in human eosinophil extracts identified several ECP native forms and glycosylation heterogeneity was found to contribute to the protein biological properties. In this study we analyze for the first time the antimicrobial activity of the distinct native proteins purified from healthy donor blood. Low and heavy molecular weight forms were tested on Escherichia coli cell cultures and compared with the recombinant non-glycosylated protein. Further analysis on model membranes provided an insight towards an understanding of the protein behavior at the cytoplasmic membrane level. The results highlight the significant reduction in protein toxicity and bacteria agglutination activity for heavy glycosylated fractions. Notwithstanding, the lower glycosylated fraction mostly retains the lipopolysaccharide binding affinity together with the cytoplasmic membrane depolarization and membrane leakage activities. From structural analysis we propose that heavy glycosylation interferes with the protein self-aggregation, hindering the cell agglutination and membrane disruption processes. The results suggest the contribution of post-translational modifications to the antimicrobial role of ECP in host defense.

Eosinophil granule proteins: form and function

Experimental and clinical data strongly support a role for the eosinophil in the pathogenesis of asthma, allergic and parasitic diseases, and hypereosinophilic syndromes, in addition to more recently identified immunomodulatory roles in shaping innate host defense, adaptive immunity, tissue repair/remodeling, and maintenance of normal tissue homeostasis. A seminal finding was the dependence of allergic airway inflammation on eosinophil-induced recruitment of Th2-polarized effector T-cells to the lung, providing a missing link between these innate immune effectors (eosinophils) and adaptive T-cell responses. Eosinophils come equipped with preformed enzymatic and nonenzymatic cationic proteins, stored in and selectively secreted from their large secondary (specific) granules. These proteins contribute to the functions of the eosinophil in airway inflammation, tissue damage, and remodeling in the asthmatic diathesis. Studies using eosinophil-deficient mouse models, including eosinophil-derived granule protein double knock-out mice (major basic protein-1/eosinophil peroxidase dual gene deletion) show that eosinophils are required for all major hallmarks of asthma pathophysiology: airway epithelial damage and hyperreactivity, and airway remodeling including smooth muscle hyperplasia and subepithelial fibrosis. Here we review key molecular aspects of these eosinophil-derived granule proteins in terms of structure-function relationships to advance understanding of their roles in eosinophil cell biology, molecular biology, and immunobiology in health and disease.

Asparagine-linked glycans determine the cytotoxic capacity of eosinophil cationic protein (ECP)

Eosinophil cationic protein (ECP) is a toxic, granule-stored protein of the eosinophil granulocyte. It is a heterogeneous protein; molecular weights can differ from 15 to 22 kDa, due to glycosylations. We purified high molecular weight ECP from blood donors with the ECP434GG (rs2073342) genotype, with the aim of examining whether removal of carbohydrates could enhance the cytotoxic capacity. The cytotoxic activity of the ECP pools was tested against the NCI-H69 cell line, before and after enzymatic deglycosylation. ECP was also analysed by SELDI-TOF MS to monitor the changes in molecular mass after deglycosylation. Five high molecular weight pools of ECP (HMW-ECP I-V) with decreasing degrees of glycosylation were tested at concentrations ranging from 0.02 to 0.6 μM. The activity ranged from EC50 of >0.6 μM to 0.04 μM; HMW-ECP II had the lowest activity and HMW-ECP V the highest. After deglycosylation with N-glycosidase F, pools HMW-ECP I-III were reduced to the same molecular weight of 15.78 kDa and acquired potent cytotoxic activities. HMW-ECP IV and V with molecular species at 16.3 and 16.1 kDa were highly cytotoxic as such and were only partially deglycosylated, with slight enhancement of the toxic properties. The results suggest the presence of several HMW-ECP molecular species with differences in their post-translational modifications and cytotoxic properties. We conclude that a fraction of native ECP is stored in a non-cytotoxic form, which can be converted into a cytotoxic form by N-deglycosylation, whereas another fraction is stored as a highly cytotoxic form carrying different post-translational modifications.

Eosinophil associated genes in the inflammatory bowel disease 4 region: Correlation to inflammatory bowel disease revealed

AIM: To study the association between inflammatory bowel disease (IBD) and genetic variations in eosinophil protein X (EPX) and eosinophil cationic protein (ECP).

METHODS: DNA was extracted from ethylene diamine tetraacetic acid blood of 587 patients with Crohn’s disease (CD), 592 with ulcerative colitis (UC) and 300 healthy subjects. The EPX405 (G > C, rs2013109), ECP434 (G > C, rs2073342) and ECP562 (G > C, rs2233860) gene polymorphisms were analysed, by the 5’-nuclease allelic discrimination assay. For determination of intracellular content of EPX and ECP in granulocytes, 39 blood samples was collected and extracted with a buffer containing cetyltrimethylammonium bromide. The intracellular content of EPX was analysed using an enzyme-linked immunosorbent assay. The intracellular content of ECP was analysed with the UniCAP^® system as described by the manufacturer. Statistical tests for calculations of results were χ² test, Fisher’s exact test, ANOVA, Student-Newman-Keuls test, and Kaplan-Meier survival curve with Log-rank test for trend, the probability values of P < 0.05 were considered statistically significant.

RESULTS: The genotype frequency for males with UC and with an age of disease onset of ≥ 45 years (n = 57) was for ECP434 and ECP562, GG = 37%, GC = 60%, CC = 4% and GG = 51%, GC = 49%, CC = 0% respectively. This was significantly different from the healthy subject’s genotype frequencies of ECP434 (GG = 57%, GC = 38%, CC = 5%; P = 0.010) and ECP562 (GG = 68%, GC = 29%,CC = 3%; P = 0.009). The genotype frequencies for females, with an age of disease onset of ≥ 45 years with CD (n = 62), was for the ECP434 and ECP562 genotypes GG = 37%, GC = 52%, CC = 11% and GG = 48%, GC = 47% and CC = 5% respectively. This was also statistically different from healthy controls for both ECP434 (P = 0.010) and ECP562 (P = 0.013). The intracellular protein concentration of EPX and ECP was calculated in μg/10⁶ eosinophils and then correlated to the EPX 405 genotypes. The protein content of EPX was highest in the patients with the CC genotype of EPX405 (GG = 4.65, GC = 5.93, and CC = 6.57) and for ECP in the patients with the GG genotype of EPX405 (GG = 2.70, GC = 2.47 and CC = 1.90). ANOVA test demonstrated a difference in intracellular protein content for EPX (P = 0.009) and ECP (P = 0.022). The age of disease onset was linked to haplotypes of the EPX405, ECP434 and ECP562 genotypes. Kaplan Maier curve showed a difference between haplotype distributions for the females with CD (P = 0.003). The highest age of disease onset was seen in females with the EPX405CC, ECP434GC, ECP562CC haplotype (34 years) and the lowest in females with the EPX405GC, ECP434GC, ECP562GG haplotype (21 years). For males with UC there was also a difference between the highest and lowest age of the disease onset (EPX405CC, ECP434CC, ECP562CC, mean 24 years vs EPX405GC, ECP434GC, ECP562GG, mean 34 years, P = 0.0009). The relative risk for UC patients with ECP434 or ECP562-GC/CC genotypes to develop dysplasia/cancer was 2.5 (95%CI: 1.2-5.4, P = 0.01) and 2.5 (95%CI: 1.1-5.4, P = 0.02) respectively, compared to patients carrying the GG-genotypes.

CONCLUSION: Polymorphisms of EPX and ECP are associated to IBD in an age and gender dependent manner, suggesting an essential role of eosinophils in the pathophysiology of IBD.

Eosinophil cationic protein: overview of biological and genetic features

The eosinophil cationic protein (ECP) is a small polypeptide that originates from activated eosinophil granulocytes. A wide range of stimuli has been shown to induce the secretion of ECP. The gene that encodes the human ECP is located on chromosome 14, and the protein shares the overall three-dimensional structure and the RNase active-site residues with other proteins in the RNase A superfamily. Several single-nucleotide polymorphisms in the human ECP gene have been currently described. ECP has many biological functions, including an immunoregulatory function, the regulation of fibroblast activity, and the induction of mucus secretion in the airway. Additionally, the protein is a potent cytotoxic molecule and has the capacity to kill mammalian and nonmammalian cells. The purpose of this article was to review the known biological and genetic characteristics of ECP that contribute to the understanding of this protein's role in the development and progression of a wide variety of diseases.

Polymorphisms in the RNASE3 gene are associated with susceptibility to cerebral malaria in Ghanaian children

Background

Cerebral malaria (CM) is the most severe outcome of Plasmodium falciparum infection and a major cause of death in children from 2 to 4 years of age. A hospital based study in Ghana showed that P. falciparum induces eosinophilia and found a significantly higher serum level of eosinophil cationic protein (ECP) in CM patients than in uncomplicated malaria (UM) and severe malaria anemia (SA) patients. Single nucleotide polymorphisms (SNPs) have been described in the ECP encoding-gene (RNASE3) of which the c.371G>C polymorphism (rs2073342) results in an arginine to threonine amino acid substitution p.R124T in the polypeptide and abolishes the cytotoxicity of ECP. The present study aimed to investigate the potential association between polymorphisms in RNASE3 and CM.

Methodology/Principal Findings

The RNASE3 gene and flanking regions were sequenced in 206 Ghanaian children enrolled in a hospital based malaria study. An association study was carried out to assess the significance of five SNPs in CM (n = 45) and SA (n = 56) cases, respectively. The two severe case groups (CM and SA) were compared with the non-severe control group comprising children suffering from UM (n = 105). The 371G allele was significantly associated with CM (p = 0.00945, OR = 2.29, 95% CI = 1.22–4.32) but not with SA. Linkage disequilibrium analysis demonstrated significant linkage between three SNPs and the haplotype combination 371G/*16G/*94A was strongly associated with susceptibility to CM (p  = 0.000913, OR = 4.14, 95% CI = 1.79–9.56), thus, defining a risk haplotype. The RNASE3 371GG genotype was found to be under frequency-dependent selection.

Conclusions/Significance

The 371G allele of RNASE3 is associated with susceptibility to CM and forms part of a risk associated haplotype GGA defined by the markers: rs2073342 (G-allele), rs2233860 (G-allele) and rs8019343 (A-allele) respectively. Collectively, these results suggest a hitherto unrecognized role for eosinophils in CM pathogenesis.

Whole-exome sequencing uncovers frequent GNAS mutations in intraductal papillary mucinous neoplasms of the pancreas

Intraductal papillary mucinous neoplasm (IPMN) is a common pancreatic cystic neoplasm that is often invasive and metastatic, resulting in a poor prognosis. Few molecular alterations unique to IPMN are known. We performed whole-exome sequencing for a primary IPMN tissue, which uncovered somatic mutations in KCNF1, DYNC1H1, PGCP, STAB1, PTPRM, PRPF8, RNASE3, SPHKAP, MLXIPL, VPS13C, PRCC, GNAS, KRAS, RBM10, RNF43, DOCK2, and CENPF. We further analyzed GNAS mutations in archival cases of 118 IPMNs and 32 pancreatic ductal adenocarcinomas (PDAs), which revealed that 48 (40.7%) of the 118 IPMNs but none of the 32 PDAs harbored GNAS mutations. G-protein alpha-subunit encoded by GNAS and its downstream targets, phosphorylated substrates of protein kinase A, were evidently expressed in IPMN; the latter was associated with neoplastic grade. These results indicate that GNAS mutations are common and specific for IPMN, and activation of G-protein signaling appears to play a pivotal role in IPMN.

Predictors of histology, tissue eosinophilia and mast cell infiltration in Hodgkin's lymphoma--a population-based study

OBJECTIVE

Classical Hodgkin's lymphoma (HL) lesions comprise few tumour cells, surrounded by numerous inflammatory cells. Like in other malignancies, the microenvironment is presumed to be clinically important in HL; however, microenvironment predictors remain poorly characterised. The aim of this study was to investigate how selected patient characteristics and genetic factors affect HL phenotype, in particular tissue eosinophilia, mast cell counts and HL histological subtype.

METHODS

In a population-based study, patients with HL were interviewed about potential HL risk factors. Available tumours, n=448, were classified histologically; the number of eosinophils and mast cells were estimated, and eosinophil cationic protein (ECP) and eosinophil protein-x (EPX) gene polymorphisms were determined. Associations were assessed in regression models.

RESULTS

Self-reported history of asthma was predictive of having tumour eosinophilia [≥200 eosinophils/10 high power fields, univariate odds ratio (OR)=2.22, 95% CI 1.06-4.64, P=0.03]. High numbers of eosinophils were predominantly seen in patients carrying the genotype ECP434GG [multivariate relative levels (RLs)=1.84, 95% CI 1.02-3.30, P=0.04]. Lower number of eosinophils was seen in Epstein-Barr virus (EBV)-positive tumours (univariate RL=0.52, 95% CI 0.3-0.9, P=0.02) and in older patients (univariate RL=0.85, 95% CI 0.73-0.99, P=0.03). Well-known factors such as young age, female sex and EBV-negative status predicted nodular sclerosis histology.

CONCLUSION

The number of eosinophils in HL tumours is influenced by patient traits such as asthma, ECP genotype and EBV status. EBV status was predictive of histology.

Refining the eosinophil cationic protein antibacterial pharmacophore by rational structure minimization

Sequence analysis of eosinophil cationic protein (ECP), a ribonuclease of broad antimicrobial activity, allowed identification of residues 1-45 as the antimicrobial domain. We have further dissected ECP(1-45) with a view to defining the minimal requirements for antimicrobial activity. Structure-based downsizing has focused on both α-helices of ECP(1-45) and yielded analogues with substantial potency against Gram-negative and -positive strains. Analogues ECP(8-36) and ECP(6-17)-Ahx-(23-36) (Ahx, 6-aminohexanoic acid) involve 36% and 40% size reduction relative to (1-45), respectively, and display a remarkably ECP-like antimicrobial profile. Both retain segments required for self-aggregation and lipolysaccharide binding, as well as the bacterial agglutination ability of parent ECP. Analogue (6-17)-Ahx-(23-36), in particular, is shown by NMR to preserve the helical traits of the native 8-16 (α1) and 33-36 (α2) regions and can be proposed as the minimal structure capable of reproducing the activity of the entire protein.

Analysing the eosinophil cationic protein--a clue to the function of the eosinophil granulocyte

Eosinophil granulocytes reside in respiratory mucosa including lungs, in the gastro-intestinal tract, and in lymphocyte associated organs, the thymus, lymph nodes and the spleen. In parasitic infections, atopic diseases such as atopic dermatitis and asthma, the numbers of the circulating eosinophils are frequently elevated. In conditions such as Hypereosinophilic Syndrome (HES) circulating eosinophil levels are even further raised. Although, eosinophils were identified more than hundred years ago, their roles in homeostasis and in disease still remain unclear. The most prominent feature of the eosinophils are their large secondary granules, each containing four basic proteins, the best known being the eosinophil cationic protein (ECP). This protein has been developed as a marker for eosinophilic disease and quantified in biological fluids including serum, bronchoalveolar lavage and nasal secretions. Elevated ECP levels are found in T helper lymphocyte type 2 (atopic) diseases such as allergic asthma and allergic rhinitis but also occasionally in other diseases such as bacterial sinusitis. ECP is a ribonuclease which has been attributed with cytotoxic, neurotoxic, fibrosis promoting and immune-regulatory functions. ECP regulates mucosal and immune cells and may directly act against helminth, bacterial and viral infections. The levels of ECP measured in disease in combination with the catalogue of known functions of the protein and its polymorphisms presented here will build a foundation for further speculations of the role of ECP, and ultimately the role of the eosinophil.

NMR structural determinants of eosinophil cationic protein binding to membrane and heparin mimetics

Eosinophil cationic protein (ECP) is a highly stable, cytotoxic ribonuclease with the ability to enter and disrupt membranes that participates in innate immune defense against parasites but also kills human cells. We have used NMR spectroscopy to characterize the binding of ECP to membrane and heparin mimetics at a residue level. We believe we have identified three Arg-rich surface loops and Trp(35) as crucial for membrane binding. Importantly, we have provided evidence that the interaction surface of ECP with heparin mimetics is extended with respect to that previously described (fragment 34-38). We believe we have identified new sites involved in the interaction for the first time, and shown that the N-terminal alpha-helix, the third loop, and the first and last beta-strands are key for heparin binding. We have also shown that a biologically active ECP N-terminal fragment comprising the first 45 residues (ECP1-45) retains the capacity to bind membrane and heparin mimetics, thus neither the ECP tertiary structure nor its high conformational stability are required for cytotoxicity.

Eosinophil cationic protein (ECP) is processed during secretion

The eosinophil granulocyte is an inflammatory cell involved in allergic diseases such as asthma and rhinitis. Eosinophil cationic protein (ECP) is a basic and potentially cytotoxic granule protein that is released from the eosinophil upon activation. The aim was to study secretion of molecular variants of ECP from blood eosinophils with the hypothesis that the stored noncytotoxic ECP is altered into cytotoxic species upon release from the cell. Eosinophil granulocytes were purified to >95% from venous blood from birch pollen allergic subjects, with symptoms of rhinitis, and from healthy control subjects during the birch pollen season. The cells were stimulated with IL-5, GM-CSF, or serum-opsonized Sephadex particles. Concentration of ECP in cells or supernatants was measured by means of a fluoroenzyme immunoassay, and ECP heterogeneity was studied using an affinity capture assay with the surface-enhanced laser desorption/ionization-time of flight mass spectrometry technique. Extracts of unstimulated eosinophils contained 10 major ECP variants, with molecular masses ranging from 16.1 to 17.7 kDa. Stimulation with particles mainly induced the secretion of two molecular variants at 16.1 and 16.3 kDa, while cytokine stimulation gave rise to a different secretion profile. ECP variants in the pellet extracts remained unaffected by cell activation. The modifications of secreted ECP were partly explained by differences in N-linked glycosylations. Secretion of ECP from eosinophils involves protein modification. The molecular masses of released ECP have acquired the masses of the cytotoxic species.