Effect of SPLUNC1 protein on the Pseudomonas aeruginosa and Epstein-Barr virus

Lung antimicrobial proteins and peptides: from host defense to therapeutic strategies

Representing severe morbidity and mortality globally, respiratory infections associated with chronic respiratory diseases, including complicated pneumonia, asthma, interstitial lung disease, and chronic obstructive pulmonary disease, are a major public health concern. Lung health and the prevention of pulmonary disease rely on the mechanisms of airway surface fluid secretion, mucociliary clearance, and adequate immune response to eradicate inhaled pathogens and particulate matter from the environment. The antimicrobial proteins and peptides contribute to maintaining an antimicrobial milieu in human lungs to eliminate pathogens and prevent them from causing pulmonary diseases. The predominant antimicrobial molecules of the lung environment include human α- and β-defensins and cathelicidins, among numerous other host defense molecules with antimicrobial and antibiofilm activity such as PLUNC (palate, lung, and nasal epithelium clone) family proteins, elafin, collectins, lactoferrin, lysozymes, mucins, secretory leukocyte proteinase inhibitor, surfactant proteins SP-A and SP-D, and RNases. It has been demonstrated that changes in antimicrobial molecule expression levels are associated with regulating inflammation, potentiating exacerbations, pathological changes, and modifications in chronic lung disease severity. Antimicrobial molecules also display roles in both anticancer and tumorigenic effects. Lung antimicrobial proteins and peptides are promising alternative therapeutics for treating and preventing multidrug-resistant bacterial infections and anticancer therapies.

STAT3 mutation-associated airway epithelial defects in Job syndrome

BACKGROUND

Job syndrome is a disease of autosomal dominant hyper-IgE syndrome (AD-HIES). Patients harboring STAT3 mutation are particularly prone to airway remodeling and airway infections.

OBJECTIVES

Airway epithelial cells play a central role as the first line of defense against pathogenic infection and express high levels of STAT3. This study thus interrogates how AD-HIES STAT3 mutations impact the physiological functions of airway epithelial cells.

METHODS

This study created human airway basal cells expressing 4 common AD-HIES STAT3 mutants (R382W, V463del, V637M, and Y657S). In addition, primary airway epithelial cells were isolated from a patient with Job syndrome who was harboring a STAT3-S560del mutation and from mice harboring a STAT3-V463del mutation. Cell proliferation, differentiation, barrier function, bacterial elimination, and innate immune responses to pathogenic infection were quantitatively analyzed.

RESULTS

STAT3 mutations reduce STAT3 protein phosphorylation, nuclear translocation, transcription activity, and protein stability in airway basal cells. As a consequence, STAT3-mutated airway basal cells give rise to airway epithelial cells with abnormal cellular composition and loss of coordinated mucociliary clearance. Notably, AD-HIES STAT3 airway epithelial cells are defective in bacterial killing and fail to initiate vigorous proinflammatory responses and neutrophil transepithelial migration in response to an experimental model of Pseudomonas aeruginosa infection.

CONCLUSIONS

AD-HIES STAT3 mutations confer numerous abnormalities to airway epithelial cells in cell differentiation and host innate immunity, emphasizing their involvement in the pathogenesis of lung complications in Job syndrome. Therefore, therapies must address the epithelial defects as well as the previously noted immune cell defects to alleviate chronic infections in patients with Job syndrome.

A novel antimicrobial peptide derived from human BPIFA1 protein protects against Candida albicans infection

Bactericidal/permeability-increasing fold containing family A, member 1 (BPIFA1) is an innate immunity defense protein. Our previous studies proved its antibacterial and antiviral effects, but its role in fungi remains unknown. The study aimed to identify antifungal peptides (AFP) derived from BPIFA1, and three antimicrobial peptides (AMP1-3) were designed. The antifungal effects were proved by growth inhibition assay. AMP3 activity was confirmed by germ tube growth experiment and XTT assay. Its effects on cell wall and membrane of Candida albicans were assessed by tannic acid and Annexin V-FITC/PI double staining, respectively. Additionally, scanning electron microscope (SEM) and transmission electron microscopy (TEM) were used for morphological and ultrastructural observation. The expression of ALS1, EAP1, and SUN41 was tested by qPCR. Ultimately, three AMPs could fight against C. albicans in vitro, and AMP3 was highly effective. It functioned by destroying the integrity of cell wall and normal structure of cell membrane. It also inhibited biofilm formation of C. albicans. In addition, AMP3 down-regulated the expression of ALS1, EAP1, and SUN41, those are known to be involved in virulence of C. albicans. Altogether, the study reported successful development of a novel AFP, which could be used as a new strategy for antifungal therapy.

Genome Scan for Variable Genes Involved in Environmental Adaptations of Nubian Ibex

The Nubian ibex (Capra nubiana) is a wild goat species that inhabits the Sahara and Arabian deserts and is adapted to extreme ambient temperatures, intense solar radiation, and scarcity of food and water resources. To investigate desert adaptation, we explored the possible role of copy number variations (CNVs) in the evolution of Capra species with a specific focus on the environment of Capra nubiana. CNVs are structural genomic variations that have been implicated in phenotypic differences between species and could play a role in species adaptation. CNVs were inferred from Capra nubiana sequence data relative to the domestic goat reference genome using read-depth approach. We identified 191 CNVs overlapping with protein-coding genes mainly involved in biological processes such as innate immune response, xenobiotic metabolisms, and energy metabolisms. We found copy number variable genes involved in defense response to viral infections (Cluster of Differentiation 48, UL16 binding protein 3, Natural Killer Group 2D ligand 1-like, and Interferon-induced transmembrane protein 3), possibly suggesting their roles in Nubian ibex adaptations to viral infections. Additionally, we found copy number variable xenobiotic metabolism genes (carboxylesterase 1, Cytochrome P450 2D6, Glutathione S-transferase Mu 4, and UDP Glucuronosyltransferase-2B7), which are probably an adaptation of Nubian ibex to desert diets that are rich in plant secondary metabolites. Collectively, this study's results advance our understanding of CNVs and their possible roles in the adaptation of Nubian ibex to its environment. The copy number variable genes identified in Nubian ibex could be considered as subjects for further functional characterizations.

The Multifunctional Roles of Short Palate, Lung, and Nasal Epithelium Clone 1 in Regulating Airway Surface Liquid and Participating in Airway Host Defense

Short palate, lung, and nasal epithelium clone 1 (SPLUNC1) is a kind of secretory protein, and gets expressed abundantly in normal respiratory epithelium of humans. As a natural immune molecule, SPLUNC1 is proved to be involved in inflammatory response and airway host defense. This review focuses on summarizing and discussing the role of SPLUNC1 in regulating airway surface liquid (ASL) and participating in airway host defense. PubMed and MEDLINE were used for searching and identifying the data in this review. The domain of bactericidal/permeability-increasing protein in SPLUNC1 and the α-helix, α4, are essential for SPLUNC1 to exert biological activities. As a natural innate immune molecule, SPLUNC1 plays a significant role in inflammatory response and airway host defense. Its special expression patterns are not only observed in physiological conditions, but also in some respiratory diseases. The mechanisms of SPLUNC1 in airway host defense include modulating ASL volume, acting as a surfactant protein, inhibiting biofilm formation, as well as regulating ASL compositions, such as LL-37, mucins, Neutrophil elastase, and inflammatory cytokines. Besides, potential correlations are found among these different mechanisms, especially among different ASL compositions, which should be further explored in more systematical frameworks. In this review, we summarize the structural characteristics and expression patterns of SPLUNC1 briefly, and mainly discuss the mechanisms of SPLUNC1 exerted in host defense, aiming to provide a theoretical basis and a novel target for future studies and clinical treatments.

A clinical study on the factors associated with nasopharyngeal carcinoma among the Chinese population

Nasopharyngeal carcinoma (NC) arises from the nasopharynx epithelium and the majority of NC cases globally are within China and Southeast Asia. Both short palate lung and nasal epithelium clone 1 (SPLUNC1) and myelodysplasia syndrome 1-ectopic viral integration site 1 (MDS1-EVI1) play an important role in carcinogenesis and have been found to be associated with nasopharyngeal carcinoma. In spite of their role in NC, the association between these genes and their polymorphisms in the development of NC has thus far not been studied. In the present study, the relationship between SPLUNC1 (rs2752903, T>C) and MDS1-EVI1 (rs6774494, G>A) polymorphisms and their role in the development of NC among the Chinese population were investigated. From a Chinese population of 1,059 patients with NC and 891 controls, genotype frequencies and the distribution of SPLUNC1 and MDS1-EVI1 polymorphisms were analyzed for possible susceptibility to NC. It was observed that those with MDS1-EVI1 CC (OR, 2.76; 95% CI, 1.96-3.81) and MDS1-EVI1 CT (OR, 1.51; 95% CI, 1.22-2.14) polymorphisms had an increased risk of developing NC. Those with SPLUNC1 AA genotypes also observed a higher risk for NC compared with SPLUNC1 GG genotypes (OR, 2.15; 95% CI, 1.62-3.15). When observing the gene-gene interaction between SPLUNC1 and MDS1-EVI1 polymorphisms, it was found that the presence of both SPLUNC1 CC and MDS1-EVI1 AA alleles was associated with a higher risk for NC compared with those who did not carry both alleles (OR, 6.75; 95% CI, 3.41-12.11). The present study suggested that the association between SPLUNC1 (rs2752903, T>C) and MDS1-EVI1 (rs6774494, G>A) polymorphisms may be a potent risk factor in the occurrence of NC.

Immunomodulatory function of the cystic fibrosis modifier gene BPIFA1

BACKGROUND

Cystic fibrosis (CF) is characterized by a progressive decline in lung function due to airway obstruction, infection, and inflammation. CF patients are particularly susceptible to respiratory infection by a variety of pathogens, and the inflammatory response in CF is dysregulated and prolonged. BPI fold containing family A, member 1 (BPIFA1) and BPIFB1 are proteins expressed in the upper airways that may have innate immune activity. We previously identified polymorphisms in the BPIFA1/BPIFB1 region associated with CF lung disease severity.

METHODS

We evaluated whether the BPIFA1/BPIFB1 associations with lung disease severity replicated in individuals with CF participating in the International CF Gene Modifier Consortium (n = 6,365). Furthermore, we investigated mechanisms by which the BPIFA1 and BPIFB1 proteins may modify lung disease in CF.

RESULTS

The association of the G allele of rs1078761 with reduced lung function was replicated in an independent cohort of CF patients (p = 0.001, n = 2,921) and in a meta-analysis of the full consortium (p = 2.39x10-5, n = 6,365). Furthermore, we found that rs1078761G which is associated with reduced lung function was also associated with reduced BPIFA1, but not BPIFB1, protein levels in saliva from CF patients. Functional assays indicated that BPIFA1 and BPIFB1 do not have an anti-bacterial role against P. aeruginosa but may have an immunomodulatory function in CF airway epithelial cells. Gene expression profiling using RNAseq identified Rho GTPase signaling pathways to be altered in CF airway epithelial cells in response to treatment with recombinant BPIFA1 and BPIFB1 proteins.

CONCLUSIONS

BPIFA1 and BPIFB1 have immunomodulatory activity and genetic variation associated with low levels of these proteins may increase CF lung disease severity.

Diverse phenotypes and endotypes of fungus balls caused by mixed bacterial colonization in chronic rhinosinusitis

BACKGROUND

The pathogenic roles of fungus and bacteria in chronic rhinosinusitis (CRS) remain unclear. Recently, we described the bacterial ball, which is distinct from the fungus ball, as an unusual phenotype of bacterial infection. In this study, we investigated the clinical, histopathologic, and immunologic characteristics of sinonasal microorganic materials, including fungus ball and bacterial ball.

METHODS

In this study, we enrolled 80 CRS patients with sinonasal microorganic materials and 10 control subjects who underwent skull base surgery or endoscopic dacryocystorhinostomy and had no signs or symptoms of nasal inflammation. All specimens were stained with hematoxylin-eosin, Gomori-methenamine-silver, and Gram stain to identify fungal organisms and Gram-positive/negative bacterial colonies. The expression of tumor necrosis factor (TNF)-α; interleukin (IL)-1β; S100A7; S100A8/A9; and short, palate, lung, and nasal epithelial clone 1 (SPLUNC1) were evaluated by enzyme-linked immunosorbent assay using sinus lavage fluid.

RESULTS

We histologically classified sinonasal microorganic materials into the following 4 groups: fungus ball (n = 45); bacterial ball (n = 6); mixed ball (formed by a mixture of fungus and bacteria, n = 27); and double ball (formed by separate fungal and bacterial balls, n = 2). Compared with the fungus ball, the mixed ball was more frequently detected in immunocompromised patients (p < 0.0001). In addition, TNF-α expression was significantly higher in fungus and mixed balls than in control, whereas the mixed ball showed higher expression of IL-1β compared with the fungus ball. Moreover, the expression of S100A7 and S100A8/A9 protein in the mixed ball was significantly decreased when compared with the fungus ball, whereas there was no significant difference in SPLUNC1 expression between fungus and mixed balls.

CONCLUSION

Our findings suggest that fungal and bacterial interactions are diverse in CRS. Specifically, the mixed ball is prevalent in CRS with an immunocompromised state and it may decrease epithelial barrier function.

BPIFA1 regulates lung neutrophil recruitment and interferon signaling during acute inflammation

Bpifa1 (BPI fold-containing group A member 1) is an airway host-protective protein with immunomodulatory properties that binds to LPS and is regulated by infectious and inflammatory signals. Differential expression of Bpifa1 has been widely reported in lung disease, yet the biological significance of this observation is unclear. We sought to understand the role of Bpifa1 fluctuations in modulating lung inflammation. We treated wild-type (WT) and Bpifa1^-/- mice with intranasal LPS and performed immunological and transcriptomic analyses of lung tissue to determine the immune effects of Bpifa1 deficiency. We show that neutrophil (polymorphonuclear cells, PMNs) lung recruitment and transmigration to the airways in response to LPS is impaired in Bpifa1^-/- mice. Transcriptomic analysis revealed a signature of 379 genes that differentiated Bpifa1^-/- from WT mice. During acute lung inflammation, the most downregulated genes in Bpifa1^-/- mice were Cxcl9 and Cxcl10. Bpifa1^-/- mice had lower bronchoalveolar lavage concentrations of C-X-C motif chemokine ligand 10 (Cxcl10) and Cxcl9, interferon-inducible PMN chemokines. This was consistent with lower expression of IFNγ, IFNλ, downstream IFN-stimulated genes, and IFN-regulatory factors, which are important for the innate immune response. Administration of Cxcl10 before LPS treatment restored the inflammatory response in Bpifa1^-/- mice. Our results identify a novel role for Bpifa1 in the regulation of Cxcl10-mediated PMN recruitment to the lungs via IFNγ and -λ signaling during acute inflammation.

An innate defense peptide BPIFA1/SPLUNC1 restricts influenza A virus infection

The airway epithelium secretes proteins that function in innate defense against infection. Bactericidal/permeability-increasing fold-containing family member A1 (BPIFA1) is secreted into airways and has a protective role during bacterial infections, but it is not known whether it also has an antiviral role. To determine a role in host defense against influenza A virus (IAV) infection and to find the underlying defense mechanism, we developed transgenic mouse models that are deficient in BPIFA1 and used these, in combination with in vitro three-dimensional mouse tracheal epithelial cell (mTEC) cultures, to investigate its antiviral properties. We show that BPIFA1 has a significant role in mucosal defense against IAV infection. BPIFA1 secretion was highly modulated after IAV infection. Mice deficient in BPIFA1 lost more weight after infection, supported a higher viral load and virus reached the peripheral lung earlier, indicative of a defect in the control of infection. Further analysis using mTEC cultures showed that BPIFA1-deficient cells bound more virus particles, displayed increased nuclear import of IAV ribonucleoprotein complexes, and supported higher levels of viral replication. Our results identify a critical role of BPIFA1 in the initial phase of infection by inhibiting the binding and entry of IAV into airway epithelial cells.

BPIFB1 (LPLUNC1) inhibits migration and invasion of nasopharyngeal carcinoma by interacting with VTN and VIM

Background:

Bactericidal/Permeability-increasing-fold-containing family B member 1 (BPIFB1, previously termed LPLUNC1) is highly expressed in the nasopharynx, significantly downregulated in nasopharyngeal carcinoma (NPC), and associated with prognosis in NPC patients. Because metastasis represents the primary cause of NPC-related death, we explored the role of BPIFB1 in NPC migration and invasion.

Methods:

The role of BPIFB1 in NPC metastasis was investigated in vitro and in vivo. A co-immunoprecipitation assay coupled with mass spectrometry was used to identify BPIFB1-binding proteins. Additionally, western blotting, immunofluorescence, and immunohistochemistry allowed assessment of the molecular mechanisms associated with BPIFB1-specific metastatic inhibition via vitronectin (VTN) and vimentin (VIM) interactions.

Results:

Our results showed that BPIFB1 expression markedly inhibited NPC cell migration, invasion, and lung-metastatic abilities. Additionally, identification of two BPIFB1-interacting proteins, VTN and VIM, showed that BPIFB1 reduced VTN expression and the formation of a VTN-integrin αV complex in NPC cells, leading to inhibition of the FAK/Src/ERK signalling pathway. Moreover, BPIFB1 attenuated NPC cell migration and invasion by inhibiting VTN- or VIM-induced epithelial–mesenchymal transition.

Conclusions:

This study represents the first demonstration of BPIFB1 function in NPC migration, invasion, and lung metastasis. Our findings indicate that re-expression of BPIFB1 might represent a useful strategy for preventing and treating NPC.

MicroRNA profiling study reveals miR-150 in association with metastasis in nasopharyngeal carcinoma

MicroRNAs (miRNAs) are small non-coding RNAs that play a crucial role in pathogenesis of human cancers. Several miRNAs have been shown to involve in nasopharyngeal carcinoma (NPC) pathogenesis through alteration of gene networks. A global view of the miRNA expression profile of clinical specimens would be the best way to screen out the possible miRNA candidates that may be involved in disease pathogenesis. In this study, we investigated the expression profiles of miRNA in formalin-fixed paraffin-embedded tissues from patients with undifferentiated NPC versus non-NPC controls using a miRNA real-time PCR platform, which covered a total of 95 cancer-related miRNAs. Hierarchical cluster analysis revealed that NPC and non-NPC controls were clearly segregated. Promisingly, 10 miRNA candidates were differentially expressed. Among them, 9 miRNAs were significantly up-regulated of which miR-205 and miR-196a showed the most up-regulated in NPC with the highest incidence percentage of 94.1% and 88.2%, respectively, while the unique down-regulated miR-150 was further validated in patient sera. Finally, the in vitro gain-of-function and loss-of-function assays revealed that miR-150 can modulate the epithelial-mesenchymal-transition property in NPC/HK-1 cells and led to the cell motility and invasion. miR-150 may be a potential biomarker for NPC and plays a critical role in NPC tumourigenesis.

Associations of Salivary BPIFA1 Protein in Chronic Periodontitis Patients with Type 2 Diabetes Mellitus

AIMS

To explore the differences in salivary BPI fold containing family A, member 1 (BPIFA1) concentration among type 2 diabetes mellitus (T2DM) subjects with various severities of chronic periodontitis and to determine whether BPIFA1 in saliva can be used as a potential biomarker of T2DM.

METHODS

Unstimulated saliva samples were collected from 44 subjects with T2DM and 44 without T2DM (NDM). Additionally, demographic data and general health parameters, including fasting blood glucose (FBG) and body mass index (BMI), were collected. We also detected full-mouth clinical periodontal parameters including probing pocket depth (PPD), clinical attachment level (CAL), bleeding index (BI), and plaque index (PLI). Salivary BPIFA1, tumor necrosis factor-α (TNF-α), and interleukin-6 (IL-6) concentrations were also detected.

RESULTS

BPIFA1 in saliva was detected at relatively high levels. T2DM subjects had decreased salivary BPIFA1 concentrations (P = 0.031). In T2DM subjects with nonperiodontitis or severe periodontitis, the level of BPIFA1 was significantly lower compared with that of NDM. Salivary TNF-α concentration displayed a similar trend to BPIFA1 in the NDM group.

CONCLUSIONS

BPIFA1 protein is rich in saliva and might be used as a potential predictive biomarker of T2DM, especially in patients with severe periodontitis and nonperiodontitis. This trial is registered with ChiCTR-ROC-17010310.

Short Palate, Lung, and Nasal Epithelial Clone 1 Has Antimicrobial and Antibiofilm Activities against the Burkholderia cepacia Complex

The opportunistic bacteria of the Burkholderia cepacia complex (Bcc) are extremely pathogenic to cystic fibrosis (CF) patients, and acquisition of Bcc bacteria is associated with a significant increase in mortality. Treatment of Bcc infections is difficult because the bacteria are multidrug resistant and able to survive in biofilms. Short palate, lung, and nasal epithelial clone 1 (SPLUNC1) is an innate defense protein that is secreted by the upper airways and pharynx. While SPLUNC1 is known to have antimicrobial functions, its effects on Bcc strains are unclear. We therefore tested the hypothesis that SPLUNC1 is able to impair Bcc growth and biofilm formation. We found that SPLUNC1 exerted bacteriostatic effects against several Bcc clinical isolates, including B. cenocepacia strain J2315 (50% inhibitory concentration [IC50] = 0.28 μM), and reduced biofilm formation and attachment (IC50 = 0.11 μM). We then determined which domains of SPLUNC1 are responsible for its antimicrobial activity. Deletions of SPLUNC1's N terminus and α6 helix did not affect its function. However, deletion of the α4 helix attenuated antimicrobial activity, while the corresponding α4 peptide displayed antimicrobial activity. Chronic neutrophilia is a hallmark of CF lung disease, and neutrophil elastase (NE) cleaves SPLUNC1. However, we found that the ability of SPLUNC1 to disrupt biofilm formation was significantly potentiated by NE pretreatment. While the impact of CF on SPLUNC1-Bcc interactions is not currently known, our data suggest that understanding this interaction may have important implications for CF lung disease.

Differential short palate, lung, and nasal epithelial clone 1 suppression in eosinophilic and noneosinophilic chronic rhinosinusitis with nasal polyps: implications for pathogenesis and treatment

PURPOSE OF REVIEW

Short palate, lung, and nasal epithelial clone 1 (SPLUNC1) is an epithelium-secreted protein that is involved in innate immunity. A protective role for SPLUNC1 in lower respiratory inflammation and chronic rhinosinusitis (CRS) has recently been recognized.

RECENT FINDINGS

An impaired epithelial immune barrier has been proposed to play a critical role in the pathogenesis of CRS. Recent research has demonstrated that SPLUNC1 is profoundly reduced in polyp tissues of CRS with nasal polyps (CRSwNP) compared with control tissues. Studies investigating the differential expression of SPLUNC1 in eosinophilic and noneosinophilic CRSwNP have been published. Nasal SPLUNC1 expression was inhibited by Th2 cytokines (IL-4 and IL-13) but was stimulated by toll-like receptor (TLR) agonists and glucocorticoids. Decreased SPLUNC1 expression in the sinus mucosa is associated with positive Pseudomonas aeruginosa bacterial colonization and poor surgical outcomes in CRS patients.

SUMMARY

These studies identify the role of SPLUNC1 in sinonasal innate immunity and the pathogenesis of CRS. Defective expression of SPLUNC1 in CRSwNP patients may lead to insufficient maintenance of the epithelial barrier function and enhanced bacterial colonization. The use of SPLUNC1 as a therapeutic target for CRSwNP remains to be determined.

New insights on the palate, lung, and nasal epithelium clone (PLUNC) proteins: Based on molecular and functional analysis of its homolog of YH1/SPLUNC1

The palate, lung, and nasal epithelium clone (PLUNC) proteins are intricate immune molecules and arisen questions from them are still unresolved. In order to identify the role of PLUNC family proteins, we had analyzed its homolog protein YH1/SPLUNC1, which highly expresses in nontumor nasopharyngeal epithelium while expresses weakly in nasopharyngeal carcinoma (NPC) tissues. It is found that YH1/SPLUNC1 protein expression level was higher in chronic normal nasopharynx inflammatory cells compared to NPC tissue cells. An approach to produce active YH1/SPLUNC1 protein had been established and recombinant YH1/SPLUNC1 protein could bind to all four Gram-positive and four Gram-negative bacteria we tested, and triggered the aggregation of those bacteria. Interestingly, YH1/SPLUNC1 protein has antimicrobial activity, and it can directly kill Escherichia coli and Acinetobacter haemolyticus. The microorganism cell showed morphological changes in cell wall such as cell damage and cytoplasmic leakage after exposure to YH1/SPLUNC1 protein, indicating that YH1/SPLUNC1 directly killed the microorganisms by cell wall permeabilization. All these results indicated that YH1/SPLUNC1 might be an important antimicrobial protein involved in innate immunity defense.

Structural Features Essential to the Antimicrobial Functions of Human SPLUNC1

SPLUNC1 is an abundantly secreted innate immune protein in the mammalian respiratory tract that exerts bacteriostatic and antibiofilm effects, binds to lipopolysaccharide (LPS), and acts as a fluid-spreading surfactant. Here, we unravel the structural elements essential for the surfactant and antimicrobial functions of human SPLUNC1 (short palate lung nasal epithelial clone 1). A unique α-helix (α4) that extends from the body of SPLUNC1 is required for the bacteriostatic, surfactant, and LPS binding activities of this protein. Indeed, we find that mutation of just four leucine residues within this helical motif to alanine is sufficient to significantly inhibit the fluid spreading abilities of SPLUNC1, as well as its bacteriostatic actions against Gram-negative pathogens Burkholderia cenocepacia and Pseudomonas aeruginosa. Conformational flexibility in the body of SPLUNC1 is also involved in the bacteriostatic, surfactant, and LPS binding functions of the protein as revealed by disulfide mutants introduced into SPLUNC1. In addition, SPLUNC1 exerts antibiofilm effects against Gram-negative bacteria, although α4 is not involved in this activity. Interestingly, though, the introduction of surface electrostatic mutations away from α4 based on the unique dolphin SPLUNC1 sequence, and confirmed by crystal structure, is shown to impart antibiofilm activity against Staphylococcus aureus, the first SPLUNC1-dependent effect against a Gram-positive bacterium reported to date. Together, these data pinpoint SPLUNC1 structural motifs required for the antimicrobial and surfactant actions of this protective human protein.

Polymorphisms associated with expression of BPIFA1/BPIFB1 and lung disease severity in cystic fibrosis

BPI fold containing family A, member 1 (BPIFA1) and BPIFB1 are putative innate immune molecules expressed in the upper airways. Because of their hypothesized roles in airway defense, these molecules may contribute to lung disease severity in cystic fibrosis (CF). We interrogated BPIFA1/BPIFB1 single-nucleotide polymorphisms in data from an association study of CF modifier genes and found an association of the G allele of rs1078761 with increased lung disease severity (P = 2.71 × 10(-4)). We hypothesized that the G allele of rs1078761 is associated with decreased expression of BPIFA1 and/or BPIFB1. Genome-wide lung gene expression and genotyping data from 1,111 individuals with lung disease, including 51 patients with CF, were tested for associations between genotype and BPIFA1 and BPIFB1 gene expression levels. Findings were validated by quantitative PCR in a subset of 77 individuals. Western blotting was used to measure BPIFA1 and BPIFB1 protein levels in 93 lung and 101 saliva samples. The G allele of rs1078761 was significantly associated with decreased mRNA levels of BPIFA1 (P = 4.08 × 10(-15)) and BPIFB1 (P = 0.0314). These findings were confirmed with quantitative PCR and Western blotting. We conclude that the G allele of rs1078761 may be detrimental to lung function in CF owing to decreased levels of BPIFA1 and BPIFB1.

Bactericidal/Permeability-increasing protein fold-containing family member A1 in airway host protection and respiratory disease

Bactericidal/permeability-increasing protein fold-containing family member A1 (BPIFA1), formerly known as SPLUNC1, is one of the most abundant proteins in respiratory secretions and has been identified with increasing frequency in studies of pulmonary disease. Its expression is largely restricted to the respiratory tract, being highly concentrated in the upper airways and proximal trachea. BPIFA1 is highly responsive to airborne pathogens, allergens, and irritants. BPIFA1 actively participates in host protection through antimicrobial, surfactant, airway surface liquid regulation, and immunomodulatory properties. Its expression is modulated in multiple lung diseases, including cystic fibrosis, chronic obstructive pulmonary disease, respiratory malignancies, and idiopathic pulmonary fibrosis. However, the role of BPIFA1 in pulmonary pathogenesis remains to be elucidated. This review highlights the versatile properties of BPIFA1 in antimicrobial protection and its roles as a sensor of environmental exposure and regulator of immune cell function. A greater understanding of the contribution of BPIFA1 to disease pathogenesis and activity may clarify if BPIFA1 is a biomarker and potential drug target in pulmonary disease.

SPLUNC1 Is a Significant Marker in Pleural Effusion from Lung Cancer Compared to Tuberculosis

SPLUNC1 (Short palate, lung and nasal epithelium clone1) protein is an abundant secretory product of epithelia present throughout the conducting airways. Although its function is still not fully known, most studies have focused on its defensive effect in the infection of human airways and its potential to serve as a molecular marker for lung cancer. In this study, we further evaluated the SPLUNC1 expression in patients with lung disease to explore its role in cancer or tuberculosis at the protein level. We generated a panel of antibodies by using protein from a eukaryotic expression system as the immunogen to mice. It was the panel of SPLUNC1 monoclonal antibodies that allowed us to comparatively determine SPLUNC1 protein in lung cancer and tuberculosis infection by detecting sera and pleural effusion other than airway surface. The results showed that the SPLUNC1 level was not significantly changed either from sera of lung cancer or control. There was a significant increase in pleural effusion from lung cancer when compared to tuberculosis. These results indicate that SPLUNC1 may be a useful marker for tracing lung cancer cells, based on its epithelial origin property in pleural effusion.

SPLUNC1 reduces the inflammatory response of nasopharyngeal carcinoma cells infected with the EB virus by inhibiting the TLR9/NF-κB pathway

Studies indicate that the natural immune-related protein short palate, lung, and nasal epithelium clone 1 (SPLUNC1) plays an antitumor role in nasopharyngeal epithelial tissue. However, the detailed mechanism of the tumor-suppressor effect of SPLUNC1 in the inflammatory microenvironment of Epstein-Barr virus (EBV)-associated nasopharyngeal carcinoma (NPC) remains elusive. The aim of the present study was to explore how SPLUNC1 reduces the inflammatory response of NPC cells infected with EBV by regulating the Toll-like receptor (TLR)9/NF-κB signaling pathway. As detected by immunohistochemistry and western blotting, SPLUNC1 protein expression exhibited low or negative expression in the NPC epithelial samples/cells, while it demonstrated positive expression in normal nasopharyngeal epithelial tissues/cells; this pattern of expression was the contrary to that of TLR9. The poorly differentiated HNE2 cell line had the highest efficiency of transfer of infection with EBV by 'cell-to-cell' contact method. The group of EBV-infected HNE2 cells showed significantly higher activation of the expression of TLR9/NF-κB signaling pathway-associated factors (TLR9, CD14, MyD88, IKK, P-IKβα, P-NF-κB and NF-κB). The levels of inflammatory cytokines IL-6, IL-8, IL-1β and TNF-α in the HNE2 cell group after EBV infection were higher than these levels in the uninfected cell group (P<0.05); Meanwhile, after EBV infection, the expression levels of TLR9/NF-κB pathway associated-protein and inflammatory cytokines IL-6, IL-8, IL-1β and TNF-α in the HNE2/SPLUNC1 cell group were lower than these levels in the HNE2/Vector cell group (P<0.05). After EBV-DNA direct transfection, cytokine mRNA expression levels of TLR9, IL-6, IL-8, IL-1β and TNF-α in the HNE2 cell group were significantly higher than these levels in the NP69 cell group (P<0.05). The expression levels of these cytokines in the HNE2/SPLUNC1 cell group were obviously lower than these levels in the HNE2/Vector cell group (P<0.05). These results suggest that EBV infection of NPC cells can activate the TLR9/NF-κB signaling pathway, promote the release of inflammatory cytokines and consequently enhance the inflammatory response, while SPLUNC1 can weaken the inflammatory response induced by EBV infection in NPC cells through the regulation of the TLR9/NF-κB signaling pathway and control of the tumor inflammatory microenvironment.

Increased susceptibility to otitis media in a Splunc1-deficient mouse model

Otitis media (inflammation of the middle ear) is one of the most common diseases of early childhood. Susceptibility to otitis is influenced by a number of factors, including the actions of innate immune molecules secreted by the epithelia lining the nasopharynx, middle ear and Eustachian tube. The SPLUNC1 (short palate, lung, nasal epithelial clone 1) protein is a highly abundant secretory product of the mammalian nasal, oral and respiratory mucosa that is thought to play a multifunctional role in host defense. In this study we investigated Splunc1 expression in the ear of the mouse, and examined whether this protein contributes to overall host defense in the middle ear and/or Eustachian tube. We found that Splunc1 is highly expressed in both the surface epithelium and in submucosal glands in these regions in wild-type mice. In mice lacking Splunc1, we noted histologically an increased frequency of otitis media, characterized by the accumulation of leukocytes (neutrophils with scattered macrophages), proteinaceous fluid and mucus in the middle ear lumens. Furthermore, many of these mice had extensive remodeling of the middle ear wall, suggesting a chronic course of disease. From these observations, we conclude that loss of Splunc1 predisposes mice to the development of otitis media. The Splunc1^−/− mouse model should help investigators to better understand both the biological role of Splunc1 as well as host defense mechanisms in the middle ear.

Summary: We document expression of the innate immune factor Splunc1 in the murine middle ear and Eustachian tube, and describe spontaneous development of otitis media in mice lacking functional Splunc1.

SPLUNC1 is associated with nasopharyngeal carcinoma prognosis and plays an important role in all-trans-retinoic acid-induced growth inhibition and differentiation in nasopharyngeal cancer cells

Human SPLUNC1 can suppress nasopharyngeal carcinoma (NPC) tumor formation; however, the correlation between SPLUNC1expression and NPC patient prognosis has not been reported. In the present study, we used a large-scale sample of 1015 tissue cores to detect SPLUNC1 expression and its association with patient prognosis. SPLUNC1 expression was reduced in NPC samples compared to nontumor nasopharyngeal epithelium tissues. Positive expression of SPLUNC1 in NPC predicted a better prognosis (disease-free survival, P = 0.034; overall survival, P = 0.048). Cox's proportional hazards model revealed that SPLUNC1 could be a significant prognostic factor affecting disease-free survival (P = 0.027). A cDNA micro-array analyzed by significant analysis of micro-array (SAM) and ingenuity pathway analysis (IPA) revealed that an indirect interaction existed between SPLUNC1 and retinoic acid (RA) in the cancer regulatory network. To further investigate the molecular mechanisms involved, we utilized several bioinformatics tools and identified 12 retinoid X receptors heterodimer binding sites in the promoter region of the SPLUNC1 gene. The transcriptional activity of the SPLUNC1 promoter was up-regulated significantly by all-trans-retinoic acid (ATRA). SPLUNC1 and retinoic acid receptor expression were induced significantly by ATRA, and removal of ATRA led to a progressive loss of SPLUNC1 and retinoic acid receptor expression. ATRA inhibited proliferation and induced the differentiation of NPC cells. Interestingly, over-expression of SPLUNC1 sensitized NPC cells to ATRA, whereas knockdown of SPLUNC1 in HNE1 cells increased cell viability. Under SPLUNC1 knockdown conditions, differentiation was reversed by ATRA treatment. We concluded that SPLUNC1 could potentially predict prognosis for NPC patients and play an important role in ATRA-induced growth inhibition and differentiation in NPC cells.

Structural characterization of the pulmonary innate immune protein SPLUNC1 and identification of lipid ligands

The short palate, lung and nasal epithelial clone 1 (SPLUNC1) protein is a member of the palate, lung, and nasal epithelium clone (PLUNC) family, also known as bactericidal/permeability-increasing (BPI) fold-containing protein, family A, member 1 (BPIFA1). SPLUNC1 is an abundant protein in human airways, but its function remains poorly understood. The lipid ligands of SPLUNC1 as well as other PLUNC family members are largely unknown, although some reports provide evidence that lipopolysaccharide (LPS) could be a lipid ligand. Unlike previous hypotheses, we found significant structural differences between SPLUNC1 and BPI. Recombinant SPLUNC1 produced in HEK 293 cells harbored several molecular species of sphingomyelin and phosphatidylcholine as its ligands. Significantly, in vitro lipid-binding studies failed to demonstrate interactions between SPLUNC1 and LPS, lipoteichoic acid, or polymyxin B. Instead, one of the major and most important pulmonary surfactant phospholipids, dipalmitoylphosphatidylcholine (DPPC), bound to SPLUNC1 with high affinity and specificity. We found that SPLUNC1 could be the first protein receptor for DPPC. These discoveries provide insight into the specific determinants governing the interaction between SPLUNC1 and lipids and also shed light on novel functions that SPLUNC1 and other PLUNC family members perform in host defense.

Mammalian short palate lung and nasal epithelial clone 1 (SPLUNC1) in pH-dependent airway hydration

The epithelia that line the conducting airways are the lung's first point of contact with inhaled pathogens and toxicants. As such, they are known to play an important role in the lung's innate defense system, which includes (i) the production of airway surface liquid (ASL) that helps cleanse the airways through the physical removal of pathogens and toxicants on the mucociliary escalator and (ii) the secretion of anti-microbial proteins into the ASL to kill inhaled pathogens. Interestingly, the recently crystallized short palate lung and nasal epithelial clone 1 (SPLUNC1) protein appears to be a multi-functional protein. That is, it not only acts as an anti-microbial agent, but also modulates ASL homeostasis by acting as an endogenous inhibitor of the epithelial Na(+) channel (ENaC). This review will focus on the latter function of SPLUNC1, and will discuss new structural and physiological data regarding SPLUNC1's failure to function as a regulator of ASL hydration in CF airways.

The effects of physical exercise and smoking habits on the expression of SPLUNC1 in nasal lavage fluids from allergic rhinitis subjects

OBJECTIVE

Palate lung nasal epithelial clone (PLUNC) is a family of proteins, which are proposed to participate in the innate immune defense against infections in the upper aero-digestive tract. The aim of this study was to investigate the expression of SPLUNC1 in allergic rhinitis subjects with considerations taken to the mucosal function and smoking habits.

METHODS

The participants, recruited from a cohort followed from infancy, were re-examined at the age of 18 years regarding allergy development. Based on medical histories and skin prick tests the participants were classified into groups with persistent allergic rhinitis (n=18), intermittent allergic rhinitis (n = 8) and healthy controls (n = 13). Seven subjects (3, 2 and 2 in each group, respectively) reported smoking habits. The SPLUNC1 levels in nasal lavage fluids were analyzed by Western blot. Changes in the volume of the proper nasal cavity before and after physical exercise (Vol2(increase)) were analyzed by acoustic rhinometry.

RESULTS

Compared to the control group the SPLUNC1 level was significantly lower in the persistent allergy group (3.8 ± 3.4 OD vs. 1.3 ± 1.5 OD; p = 0.02), but not in the intermittent allergy group without current exposure to allergens (3.6 ± 4.7 OD). No differences were found in Vol2(increase) between any of the allergy groups and controls. In smokers Vol2(increase) was significantly reduced (p < 0.01) and the SPLUNC1 levels were lower compared to non-smokers. A significant correlation was found between SPLUNC1 and Vol2(increase) (p < 0.01; r = 0.53) in non-smokers.

CONCLUSIONS

Current allergen exposure has an impact on SPLUNC1 expression in nasal lavage fluid, why allergy ought to be considered in study populations where analyses of SPLUNC1 levels are included in the reports. The normal nasal decongestion after exercise was not affected by allergy in contrast to smoking habits. The correlation between SPLUNC1 levels and Vol2(increase) in non-smokers may indicate involvement of SPLUNC1in the regulation of the normal function of the nasal mucosa. Complementary studies are needed to confirm the smoke-related reduction of SPLUNC1 expression and to analyze the possible participation of SPLUNC1 in the nasal mucosa regulation.

Ovocalyxin-36 is a pattern recognition protein in chicken eggshell membranes

The avian eggshell membranes are essential elements in the fabrication of the calcified shell as a defense against bacterial penetration. Ovocalyxin-36 (OCX-36) is an abundant avian eggshell membrane protein, which shares protein sequence homology to bactericidal permeability-increasing protein (BPI), lipopolysaccharide-binding protein (LBP) and palate, lung and nasal epithelium clone (PLUNC) proteins. We have developed an efficient method to extract OCX-36 from chicken eggshell membranes for purification with cation and anion exchange chromatographies. Purified OCX-36 protein exhibited lipopolysaccharide (LPS) binding activity and bound lipopolysaccharide (LPS) from Escherichia coli O111:B4 in a dose-dependent manner. OCX-36 showed inhibitory activity against growth of Staphylococcus aureus ATCC 6538. OCX-36 single nucleotide polymorphisms (SNPs) were verified at cDNA 211 position and the corresponding proteins proline-71 (Pro-71) or serine-71 (Ser-71) were purified from eggs collected from genotyped hens. A significant difference between Pro-71 and Ser-71 OCX-36 for S. aureus lipoteichoic acid (LTA) binding activity was detected. The current study is a starting point to understand the innate immune role that OCX-36 may play in protection against bacterial invasion of both embryonated eggs (relevant to avian reproductive success) and unfertilized table eggs (relevant to food safety).

Anti-BPIFA1/SPLUNC1: a new autoantibody prevalent in patients with endstage cystic fibrosis

BACKGROUND

Bactericidal/permeability increasing protein fold containing family A (BPIFA) 1, is a secreted protein of the upper airways that shares structural homology with BPI and exhibits comparable antimicrobial capacities. We hypothesized that CF patients have circulating IgG or IgA anti-BPIFA1 autoantibodies, similarly as reported for BPI autoantibodies.

METHODS

We analyzed pre- and post-transplantation sera from 67 endstage lung disease patients who underwent lung transplantation (LTx) because of COPD (n=27), CF (n=25), and ILD (n=15).

RESULTS

Anti-BPIFA1 (48%) and anti-BPI (92%) were elevated in CF patients compared to healthy controls, with anti-BPIFA1 IgG isotype being most prevalent, whereas anti-BPI is of the IgA isotype. Levels of anti-BPI autoantibodies significantly declined post-LTx, whereas anti-BPIFA1 did not. No relation was found between autoantibodies against BPIFA1 and BPI.

CONCLUSION

Our results indicate that BPIFA1 is a novel target for autoantibodies in CF. The function of these autoantibodies needed to be investigated in future studies.

Identification of the SPLUNC1 ENaC-inhibitory domain yields novel strategies to treat sodium hyperabsorption in cystic fibrosis airway epithelial cultures

The epithelial sodium channel (ENaC) is responsible for Na(+) and fluid absorption across colon, kidney, and airway epithelia. Short palate lung and nasal epithelial clone 1 (SPLUNC1) is a secreted, innate defense protein and an autocrine inhibitor of ENaC that is highly expressed in airway epithelia. While SPLUNC1 has a bactericidal permeability-increasing protein (BPI)-type structure, its NH2-terminal region lacks structure. Here we found that an 18 amino acid peptide, S18, which corresponded to residues G22-A39 of the SPLUNC1 NH2 terminus inhibited ENaC activity to a similar degree as full-length SPLUNC1 (∼2.5 fold), while SPLUNC1 protein lacking this region was without effect. S18 did not inhibit the structurally related acid-sensing ion channels, indicating specificity for ENaC. However, S18 preferentially bound to the βENaC subunit in a glycosylation-dependent manner. ENaC hyperactivity is contributory to cystic fibrosis (CF) lung disease. Unlike control, CF human bronchial epithelial cultures (HBECs) where airway surface liquid (ASL) height was abnormally low (4.2 ± 0.6 μm), addition of S18 prevented ENaC-led ASL hyperabsorption and maintained CF ASL height at 7.9 ± 0.6 μm, even in the presence of neutrophil elastase, which is comparable to heights seen in normal HBECs. Our data also indicate that the ENaC inhibitory domain of SPLUNC1 may be cleaved away from the main molecule by neutrophil elastase, suggesting that it may still be active during inflammation or neutrophilia. Furthermore, the robust inhibition of ENaC by the S18 peptide suggests that this peptide may be suitable for treating CF lung disease.

Short palate, lung, and nasal epithelial clone-1 is a tightly regulated airway sensor in innate and adaptive immunity

Short palate, lung, and nasal epithelial clone-1 (SPLUNC1) is a protein abundantly expressed by the respiratory epithelium of the proximal lower respiratory tract, a site of great environmental exposure. Previous studies showed that SPLUNC1 exerts antimicrobial effects, regulates airway surface liquid and mucociliary clearance, and suppresses allergic airway inflammation. We studied SPLUNC1 to gain insights into its role in host defense. In the lower respiratory tract, concentrations of SPLUNC1 are high under basal conditions. In models of pneumonia caused by common respiratory pathogens, and in Th1-induced and Th2-induced airway inflammation, SPLUNC1 secretion is markedly reduced. Pathogen-associated molecular patterns and IFN-γ act directly on airway epithelial cells to inhibit SPLUNC1 mRNA expression. Thus, SPLUNC1 is quickly suppressed during infection, in response to an insult on the epithelial surface. These experiments highlight the finely tuned fluctuations of SPLUNC1 in response to exposures in the respiratory tract, and suggest that the loss of SPLUNC1 is a crucial feature of host defense across air-breathing animal species.

LPLUNC1 inhibits nasopharyngeal carcinoma cell growth via down-regulation of the MAP kinase and cyclin D1/E2F pathways

Long-palate, lung and nasal epithelium clone 1 (LPLUNC1) gene expression is relatively tissue specific. It is highly expressed in nontumor nasopharyngeal epithelial tissues, but its expression is reduced in nasopharyngeal carcinoma (NPC), indicating that LPLUNC1 may be associated with the tumorigenesis of NPC. To study the effects of LPLUNC1 on NPC tumorigenesis, a full-length LPLUNC1 expression plasmid was stably transfected into the NPC cell line, 5-8F. Our data indicated that LPLUNC1 inhibited NPC cell proliferation in vitro and tumor formation in vivo. LPLUNC1 also delayed cell cycle progression from G1 to S phase and inhibited the expression of cyclin D1, cyclin-dependent kinase 4 (CDK4) and phosphorylated Rb. To further investigate the molecular mechanisms underlying the suppressive effects of LPLUNC1 on NPC tumorigenesis, cDNA microarray was performed. These studies revealed that LPLUNC1 inhibited the expression of certain mitogen-activated protein (MAP) kinases (MAPK) kinases and cell cycle-related molecules. Western blotting confirmed that the expression of MEK1, phosphorylated ERK1/2, phosphorylated JNK1/2, c-Myc and c-Jun were inhibited by LPLUNC1. Furthermore, the transcriptional activity of AP-1 was down-regulated by LPLUNC1, suggesting that the MAPK signaling pathway is regulated by LPLUNC1. Taken together, the present study indicates that LPLUNC1 delays NPC cell growth by inhibiting the MAPK and cyclin D1/E2F pathways and suggests that LPLUNC1 may represent a promising candidate tumor suppressor gene associated with NPC.

SPLUNC1/BPIFA1 contributes to pulmonary host defense against Klebsiella pneumoniae respiratory infection

Epithelial host defense proteins comprise a critical component of the pulmonary innate immune response to infection. The short palate, lung, nasal epithelium clone (PLUNC) 1 (SPLUNC1) protein is a member of the bactericidal/permeability-increasing (BPI) fold-containing (BPIF) protein family, sharing structural similarities with BPI-like proteins. SPLUNC1 is a 25 kDa secretory protein that is expressed in nasal, oropharyngeal, and lung epithelia, and has been implicated in airway host defense against Pseudomonas aeruginosa and other organisms. SPLUNC1 is reported to have surfactant properties, which may contribute to anti-biofilm defenses. The objective of this study was to assess the importance of SPLUNC1 surfactant activity in airway epithelial secretions and to explore its biological relevance in the context of a bacterial infection model. Using cultured airway epithelia, we confirmed that SPLUNC1 is critically important for maintenance of low surface tension in airway fluids. Furthermore, we demonstrated that recombinant SPLUNC1 (rSPLUNC1) significantly inhibited Klebsiella pneumoniae biofilm formation on airway epithelia. We subsequently found that Splunc1(-/-) mice were significantly more susceptible to infection with K. pneumoniae, confirming the likely in vivo relevance of this anti-biofilm effect. Our data indicate that SPLUNC1 is a crucial component of mucosal innate immune defense against pulmonary infection by a relevant airway pathogen, and provide further support for the novel hypothesis that SPLUNC1 protein prevents bacterial biofilm formation through its ability to modulate surface tension of airway fluids.

SPLUNC1 regulates cell progression and apoptosis through the miR-141-PTEN/p27 pathway, but is hindered by LMP1

Little is known about the role of the host defensive protein short palate, lung and nasal epithelium clone 1 (SPLUNC1) in the carcinogenesis of nasopharyngeal carcinoma (NPC). Here we report that SPLUNC1 plays a role at a very early stage of NPC carcinogenesis. SPLUNC1 regulates NPC cell proliferation, differentiation and apoptosis through miR-141, which in turn regulates PTEN and p27 expression. This signaling axis is negatively regulated by the EBV-coded gene LMP1. Therefore we propose that SPLUNC1 suppresses NPC tumor formation and its inhibition by LMP1 provides a route for NPC tumorigenesis.

Decreased SPLUNC1 expression is associated with Pseudomonas infection in surgically treated chronic rhinosinusitis patients who may require repeated sinus surgery

OBJECTIVES/HYPOTHESIS

Chronic rhinosinusitis colonized with Pseudomonas aruginosa is difficult to treat and is related to biofilm formation. Repeated sinus surgery is often required for these patients. Short palate, lung, and nasal epithelial clone 1 (SPLUNC1) is an epithelium-secreted protein that is involved in innate immunity and has anti-Pseudomonas and antibiofilm functions. This study examined if SPLUNC1 expression was related to sinusitis with bacterial culture positive for Pseudomonas and the possibility of using SPLUNC1 to predict treatment outcomes for sinusitis.

STUDY DESIGN

Nonrandomized retrospective study.

METHODS

This was a retrospective study of patients at a tertiary referral center. Pseudomonas aruginosa infection was compared to clinical variables such as SPLUNC1 mRNA expression levels, immunohistochemical (IHC) stain intensity, Lund-Mackay sinus computed tomography scores, rapid recurrent sinusitis, requirement for repeat sinus surgery, Phadiatop test results, age, gender, nasal polyp(s), and patients' presence/absence of diabetes mellitus. Comparisons between groups were performed using the χ(2) test or Fisher exact test when one confronter was <5. The statistical analyses were carried out with SPSS version 13.

RESULTS

P. aeruginosa sinus infections were associated with lower sinus mucosa SPLUNC1 expression (P = .0018), weaker SPLUNC1 IHC staining intensity (P = .011), and poor postoperative outcome (i.e., need repeated sinus surgery) (P < .001). Other factors were not associated with Pseudomonas sinus infection.

CONCLUSIONS

Sinusitis with positive P. aeruginosa bacterial culture is associated with decreased SPLUNC1 sinus mucosa expression. Repeated sinus surgeries are more frequently needed for these patients.

Multifunctional role of human SPLUNC1 in Pseudomonas aeruginosa infection

The human short PLUNC1 (SPLUNC1) protein has been identified as a component of the pulmonary antimicrobial response based on its structural similarity to the bactericidal/permeability-increasing (BPI) protein. Using a genetically modified mouse model, we recently verified the antimicrobial activity of SPLUNC1 against Pseudomonas aeruginosa in vivo. To further define the mechanism of epithelial SPLUNC1-mediated antibacterial action, we carried out studies to determine how SPLUNC1 protects the host from acute respiratory infections. P. aeruginosa treated with recombinant human SPLUNC1 protein showed decreased growth in vitro. This antibacterial activity was due to growth inhibition, as a consequence of a SPLUNC1-induced increase in bacterial cell permeability. Removal of SPLUNC1 allowed the recovery of P. aeruginosa and suggested no permanent cell injury or direct killing of bacteria. Further investigation showed coating of bacterial cells by SPLUNC1. We suggest that this "bacterial cell coating" is necessary for the bacteriostatic function of SPLUNC1. Additionally, we demonstrated a novel role for SPLUNC1 as a chemoattractant that facilitated migration of macrophages and neutrophils. Taking the findings together, we propose synergistic roles for human SPLUNC1 as an antibacterial agent with bacteriostatic and chemotactic activities.

Bactericidal/permeability increasing protein: a multifaceted protein with functions beyond LPS neutralization

Bactericidal permeability increasing protein (BPI), a 55-60 kDa protein, first reported in 1975, has gone a long way as a protein with multifunctional roles. Its classical role in neutralizing endotoxin (LPS) raised high hopes among septic shock patients. Today, BPI is not just a LPS-neutralizing protein, but a protein with diverse functions. These functions can be as varied as inhibition of endothelial cell growth and inhibition of dendritic cell maturation, or as an anti-angiogenic, chemoattractant or opsonization agent. Though the literature available is extremely limited, it is fascinating to look into how BPI is gaining major importance as a signalling molecule. In this review, we briefly summarize the recent research focused on the multiple roles of BPI and its use as a therapeutic.

Interleukin 13 exposure enhances vitamin D-mediated expression of the human cathelicidin antimicrobial peptide 18/LL-37 in bronchial epithelial cells

Vitamin D is an important regulator of the expression of antimicrobial peptides, and vitamin D deficiency is associated with respiratory infections. Regulating expression of antimicrobial peptides, such as the human cathelicidin antimicrobial peptide 18 (hCAP18)/LL-37, by vitamin D in bronchial epithelial cells requires local conversion of 25(OH)-vitamin D(3) (25D(3)) into its bioactive metabolite, 1,25(OH)(2)-vitamin D(3) (1,25D(3)), by CYP27B1. Low circulating vitamin D levels in childhood asthma are associated with more-severe exacerbations, which are often associated with infections. Atopic asthma is accompanied by Th2-driven inflammation mediated by cytokines such as interleukin 4 (IL-4) and IL-13, and the effect of these cytokines on vitamin D metabolism and hCAP18/LL-37 expression is unknown. Therefore, we investigated this with well-differentiated bronchial epithelial cells. To this end, cells were treated with IL-13 with and without 25D(3), and expression of hCAP18/LL-37, CYP27B1, the 1,25D(3)-inactivating enzyme CYP24A1, and vitamin D receptor was assessed by quantitative PCR. We show that IL-13 enhances the ability of 25D(3) to increase expression of hCAP18/LL-37 and CYP24A1. In addition, exposure to IL-13 resulted in increased CYP27B1 expression, whereas vitamin D receptor (VDR) expression was not significantly affected. The enhancing effect of IL-13 on 25D(3)-mediated expression of hCAP18/LL-37 was further confirmed using SDS-PAGE Western blotting and immunofluorescence staining. In conclusion, we demonstrate that IL-13 induces vitamin D-dependent hCAP18/LL-37 expression, most likely by increasing CYP27B1. These data suggest that Th2 cytokines regulate the vitamin D metabolic pathway in bronchial epithelial cells.

Identification of SPLUNC1's ENaC-inhibitory domain yields novel strategies to treat sodium hyperabsorption in cystic fibrosis airways

The epithelial sodium channel (ENaC) is responsible for Na+ and fluid absorption across colon, kidney, and airway epithelia. We have previously identified SPLUNC1 as an autocrine inhibitor of ENaC. We have now located the ENaC inhibitory domain of SPLUNC1 to SPLUNC1's N terminus, and a peptide corresponding to this domain, G22-A39, inhibited ENaC activity to a similar degree as full-length SPLUNC1 (∼2.5 fold). However, G22-A39 had no effect on the structurally related acid-sensing ion channels, indicating specificity for ENaC. G22-A39 preferentially bound to the β-ENaC subunit in a glycosylation-dependent manner. ENaC hyperactivity is contributory to cystic fibrosis (CF) lung disease. Addition of G22-A39 to CF human bronchial epithelial cultures (HBECs) resulted in an increase in airway surface liquid height from 4.2±0.6 to 7.9±0.6 μm, comparable to heights seen in normal HBECs, even in the presence of neutrophil elastase. Our data also indicate that the ENaC inhibitory domain of SPLUNC1 may be cleaved away from the main molecule by neutrophil elastase, which suggests that it may still be active during inflammation or neutrophilia. Furthermore, the robust inhibition of ENaC by the G22-A39 peptide suggests that this peptide may be suitable for treating CF lung disease.

Chu H, Peters AT, Tan BK, Conley DB, Grammer LC, Kern RC, Schleimer RP. Reduced expression of antimicrobial PLUNC proteins in nasal polyp tissues of patients with chronic rhinosinusitis

BACKGROUND

Chronic rhinosinusitis (CRS) is a disease characterized by inflammation of the nasal mucosa and paranasal sinuses. This inflammation may result in part from decreased epithelial barrier and innate immune responses, leading to frequent bacterial and fungal colonization. The objectives of this study were to investigate the expression of innate immune proteins of the palate lung and nasal epithelium clone (PLUNC) family in patients with CRS.

METHODS

Nasal tissue samples were collected from control subjects and CRS patients with and without nasal polyps. Expression of the members of the PLUNC family was analyzed by real-time PCR. Expression of SPLUNC1 and LPLUNC2 proteins was analyzed by ELISA, immunoblot, and immunohistochemical analysis.

RESULTS

Levels of mRNA for most of the members of the PLUNC family were profoundly reduced in nasal polyps (NPs) compared to uncinate tissue from control subjects or patients with CRS. LPLUNC2 and SPLUNC1 proteins were decreased in NPs of patients with CRS compared to uncinate tissue from control subjects. Immunohistochemical data revealed that within submucosal glands of sinonasal tissues, SPLUNC1 and LPLUNC2 were differentially expressed, in serous and mucous cells, respectively. The decrease in the expression of these molecules is probably explained by a decrease in the number of glands in NPs as revealed by correlations with levels of the glandular marker lactoferrin.

CONCLUSIONS

Decreased SPLUNC1 and LPLUNC2 in NPs reflect a profound decrease in the number of submucosal glands. Decreased glands may lead to a localized defect in the production and release of glandular innate defense molecules.

Inhibition of Epstein-Barr virus infection by lactoferrin

Lactoferrin (LF) is a multifunctional glycoprotein that plays an important role in native immune defense against infections, including human herpetic viruses, such as cytomegalovirus and herpes simplex virus types 1 and 2. However, its anti-Epstein-Barr virus (EBV, a γ-herpesvirus) function has not been reported in the literature. EBV is widespread in all human populations and is believed to be linked to tumorigenesis, such as lymphomas and nasopharyngeal carcinoma (NPC). We previously reported that LF expressed a significantly lower level in NPC tissues and was a likely tumor suppressor. Since EBV infection is a major carcinogen of NPC development, we investigated the effect of LF on EBV infection and found that LF could protect human primary B lymphocytes and nasopharyngeal epithelial cells from EBV infection, but had no effect on EBV genome DNA replication. LF prevented EBV infection of primary B cells mediated by its direct binding to the EBV receptor (CD21) on the B-cell surface. Tissue array immunohistochemistry revealed that LF expression was significantly downregulated in NPC specimens, in which high EBV viral capsid antigen-IgA levels were observed. These data suggest that LF may inhibit EBV infection and that its downregulation could contribute to NPC development.

Dual host-defence functions of SPLUNC2/PSP and synthetic peptides derived from the protein

PSP (parotid secretory protein)/SPLUNC2 (short palate, lung and nasal epithelium clone 2) is expressed in human salivary glands and saliva. The protein exists as an N-glycosylated and non-glycosylated form and both appear to induce agglutination of bacteria, a major antibacterial function for salivary proteins. Both forms of PSP/SPLUNC2 bind LPS (lipopolysaccharide), suggesting that the protein may also play an anti-inflammatory role. Based on the predicted structure of PSP/SPLUNC2 and the location of known antibacterial and anti-inflammatory peptides in BPI (bactericidal/permeability-increasing protein) and LBP (LPS-binding protein), we designed GL13NH2 and GL13K, synthetic peptides that capture these proposed functions of PSP/SPLUNC2. GL13NH3 agglutinates bacteria, leading to increased clearance by macrophages and reduced spread of infection in a plant model. GL13K kills bacteria with a minimal inhibitory concentration of 5-10 μg/ml, kills bacteria in biofilm and retains activity in 150 mM NaCl and 50% saliva. Both peptides block endotoxin action, but only GL13K appears to bind endotoxin. The peptides do not cause haemolysis, haemagglutination in serum, inhibit mammalian cell proliferation or induce an inflammatory response in macrophages. These results suggest that the GL13NH2 and the modified peptide GL13K capture the biological activity of PSP/SPLUNC2 and can serve as lead compounds for the development of novel antimicrobial and anti-inflammatory peptides.

Functional roles of SPLUNC1 in the innate immune response against Gram-negative bacteria

PLUNC (palate, lung and nasal epithelium clone)-associated gene originally referred to one gene, but now has been extended to represent a gene family that consists of a number of genes with peptide sequence homologies and predicted structural similarities. PLUNC-like proteins display sequence homology with BPI (bactericidal/permeability-increasing protein), a 456-residue cationic protein produced by precursors of polymorphonuclear leucocytes that have been shown to possess both bactericidal and LPS (lipopolysaccharide)-binding activities. The human PLUNC is also known as LUNX (lung-specific X protein), NASG (nasopharyngeal carcinoma-related protein) and SPURT (secretory protein in upper respiratory tract). The gene originally named PLUNC is now recognized as SPLUNC1. Its gene product SPLUNC1 is a secretory protein that is abundantly expressed in cells of the surface epithelium in the upper respiratory tracts and secretory glands in lung, and in the head and the neck region. The functional role of SPLUNC1 in innate immunity has been suggested but not clearly defined. The present review describes recent findings that support antimicrobial and anti-inflammatory functions of SPLUNC1 in Gram-negative bacteria-induced respiratory infection.

MAPK/AP-1 activation mediates TLR2 agonist-induced SPLUNC1 expression in human lung epithelial cells

BACKGROUND

Short Palate Lung and Nasal epithelium Clone 1 (SPLUNC1) is a newly described host defense protein, primarily expressed in large airway epithelial cells. Reduced SPLUNC1 has been reported in allergic and cigarette smoke-exposed airways. We found that Mycoplasma pneumoniae increases SPLUNC1 in airway epithelium in part via activating TLR2-NF-κB pathway. However, the contribution of additional signaling pathways to TLR2-mediated SPLUNC1 expression remains unclear. In the present study, we investigated if TLR2-induced mitogen-activated protein kinase (MAPK)/activator protein-1 (AP-1) signaling regulates SPLUNC1 expression in human lung epithelial cells.

METHODS

Human lung epithelial NCI-H292 cells were stimulated with a TLR2 agonist Palmitoyl (3)-Cys-Ser-Lys (4)-OH (Pam(3)CSK(4)). MAPK/AP-1 activation and its role in SPLUNC1 regulation were investigated by Western blot, c-Jun activation assay, chromatin immunoprecipitation (ChIP) and real-time PCR. SPLUNC1 promoter activity was assessed by a luciferase reporter assay.

RESULTS

Pam(3)CSK(4) increased SPLUNC1 expression in NCI-H292 cells in a dose- and time-dependent manner, and enhanced SPLUNC1 promoter activity. Pam(3)CSK(4)-treated cells demonstrated activated MAPK and c-Jun compared to untreated cells. ChIP assay indicated increased c-Jun binding to the SPLUNC1 promoter following Pam(3)CSK(4) stimulation. Inhibition of ERK1/2 significantly reduced Pam(3)CSK(4)-mediated c-Jun activation and SPLUNC1 expression.

CONCLUSIONS

Our results for the first time demonstrate that TLR2-mediated MAPK/AP-1 activation up-regulates lung epithelial SPLUNC1 expression at the transcriptional level. Understanding SPLUNC1 gene regulation should provide more specific therapeutic targets to restore deficient SPLUNC1 production in diseased airways.

SPLUNC1 promotes lung innate defense against Mycoplasma pneumoniae infection in mice

Short palate, lung, and nasal epithelium clone 1 (SPLUNC1) protein is highly expressed in normal airways, but is dramatically decreased in allergic and cigarette smoke exposure settings. We have previously demonstrated SPLUNC1 in vitro antibacterial property against Mycoplasma pneumoniae (Mp). However, its in vivo biological functions remain unclear. The objectives of this study were to determine the in vivo functions of SPLUNC1 following bacterial (eg, Mp) infection, and to examine the underlying mechanisms. We generated SPLUNC1-deficient mice and utilized transgenic mice overexpressing human SPLUNC1 exclusively within the airway epithelium. These mice were infected with Mp and, twenty-four hours post infection, their host defense responses were compared to littermate controls. Mp levels and inflammatory cells increased in the lungs of SPLUNC1(-/-) mice as compared to wild type controls. SPLUNC1 deficiency was shown to contribute to impaired neutrophil activation. In contrast, mice overexpressing hSPLUNC1 exclusively in airway epithelial cells demonstrated lower Mp levels. Furthermore, neutrophil elastase activity was significantly increased in mice overexpressing hSPLUNC1. Lastly, we demonstrated that SPLUNC1 enhanced Mp-induced human neutrophil elastase (HNE) activity, and HNE directly inhibited the growth of Mp. Our findings demonstrate a critical in vivo role of SPLUNC1 in host defense against bacterial infection, and likely provide a novel therapeutic approach to restore impaired lung innate immune responses to bacteria in patients with chronic lung diseases.

Distribution of human PLUNC/BPI fold-containing (BPIF) proteins

Although gene expression studies have shown that human PLUNC (palate, lung and nasal epithelium clone) proteins are predominantly expressed in the upper airways, nose and mouth, and proteomic studies have indicated they are secreted into airway and nasal lining fluids and saliva, there is currently little information concerning the localization of human PLUNC proteins. Our studies have focused on the localization of three members of this protein family, namely SPLUNC1 (short PLUNC1), SPLUNC2 and LPLUNC1 (long PLUNC1). Western blotting has indicated that PLUNC proteins are highly glycosylated, whereas immunohistochemical analysis demonstrated distinct patterns of expression. For example, SPLUNC2 is expressed in serous cells of the major salivary glands and in minor mucosal glands, whereas SPLUNC1 is expressed in the mucous cells of these glands. LPLUNC1 is a product of a population of goblet cells in the airway epithelium and nasal passages and expressed in airway submucosal glands and minor glands of the oral and nasal cavities. SPLUNC1 is also found in the epithelium of the upper airways and nasal passages and in airway submucosal glands, but is not co-expressed with LPLUNC1. We suggest that this differential expression may be reflected in the function of individual PLUNC proteins.

Human parotid secretory protein is a lipopolysaccharide-binding protein: identification of an anti-inflammatory peptide domain

Parotid secretory protein (PSP) (C20orf70) is a salivary protein of unknown function. The protein belongs to the palate, lung, and nasal epithelium clone (PLUNC) family of mucosal secretory proteins that are predicted to be structurally similar to lipid-binding and host-defense proteins including bactericidal/permeability-increasing protein and lipopolysaccharide-binding protein. However, the PLUNC proteins exhibit significant sequence variation and different biological functions have been proposed for different family members. This study tested the functional implications of the proposed similarity of PSP to the acute phase protein lipopolysaccharide-binding protein (LBP). PSP was identified in human saliva and was soluble in 70% ethanol, as shown for other PLUNC proteins. PSP binds lipopolysaccharide and can be eluted by non-ionic detergent, but not by urea or high salt. A synthetic PSP peptide, GL13NH2, which corresponds to a lipopolysaccharide-inhibiting peptide from LBP, inhibited the binding of lipopolysaccharide to both PSP and lipopolysaccharide-binding protein. Peptides from other regions of PSP and the control peptide polymyxin B showed no effect on the binding of PSP to lipopolysaccharide. GL13NH2 also inhibited lipopolysaccharide-stimulated secretion of tumor necrosis factor from macrophages. The other PSP peptides had no effect in this assay. PSP peptides had no or only minor effect on macrophage cell viability. These results indicate that PSP is a lipopolysaccharide-binding protein that is functionally related to LBP, as suggested by their predicted structural similarities.