Human beta defensin 1 gene: six new variants

Human β-defensins and psoriasin/S100A7 expression in salivary glands: anti-oncogenic molecules for potential therapeutic approaches

BACKGROUND

Host defence peptides (HDPs), including human β-defensins (hBDs) and psoriasin/S100A7, exert antimicrobial and immunoregulatory functions of the innate defense system. In addition to these functions, the search for cancer biomarkers has identified HDPs as playing a potential role in both tumor suppression and oncogenesis. Although HDPs are highly expressed in salivary glands, their role as molecules for potential diagnostic and therapeutic approaches has not yet been analyzed.

OBJECTIVE

The aim of the present study was to investigate whether expression levels of putative pro- or anti-oncogenic hBDs, including hBD-1, -2, -3, and psoriasin/S100A7, are altered in salivary gland tumor tissue as potential targets for molecular-based therapeutic approaches.

METHODS

We analyzed the expression levels of hBD-1, -2, -3, and psoriasin/S100A7 by quantitative real-time polymerase chain reaction (qrt-PCR) and immunohistochemistry in a case control study by comparing salivary gland tumor samples relative to healthy control specimens from 58 patients. Expression level analysis of hBD-1, -2, -3, and psoriasin/S100A7 by qrt-PCR was normalized to the endogenous 18S rRNA expression levels.

RESULTS

The results demonstrate the significant downregulation of hBD-1 (p < 0.001), hBD-2 (p = 0.003), hBD-3 (p = 0.002), and psoriasin/S100A7 (p = 0.003) mRNA in human salivary gland tumors compared with healthy control specimens. Protein expression levels of hBD-1, -2, -3, and psoriasin/S100A7 in salivary gland tumor tissue were strongly reduced compared with healthy control specimens.

CONCLUSION

The data indicates a putative role of the innate defense system in salivary gland tumor formation. The identification of immunoregulatory molecules as diagnostic biomarkers or therapeutic targets could provide new approaches for molecular-based diagnostic and therapeutic support to treat salivary gland tumors as well as other malignancies. We suggest that HDPs should be taken into consideration for use in molecular-based therapeutic approaches.

Association of a genetic polymorphism (-44 C/G SNP) in the human DEFB1 gene with expression and inducibility of multiple beta-defensins in gingival keratinocytes

Background

Human β-defensins (hBDs) are antimicrobial peptides with a role in innate immune defense. Our laboratory previously showed that a single nucleotide polymorphism (SNP) in the 5' untranslated region of the hBD1 gene (DEFB1), denoted -44 (rs1800972), is correlated with protection from oral Candida. Because this SNP alters the putative mRNA structure, we hypothesized that it alters hBD1 expression.

Methods

Transfection of reporter constructs and evaluation of antimicrobial activity and mRNA expression levels in keratinocytes from multiple donors were used to evaluate the effect of this SNP on constitutive and induced levels of expression.

Results

Transfection of CAT reporter constructs containing the 5' untranslated region showed that the -44 G allele yielded a 2-fold increase in CAT protein compared to other common haplotypes suggesting a cis effect on transcription or translation. The constitutive hBD1 mRNA level in human oral keratinocytes was significantly greater in cells from donors with the -44 GG genotype compared to those with the common CC genotype. Surprisingly, the hBD3 mRNA level as well as antimicrobial activity of keratinocyte extracts also correlated with the -44 G allele. Induced levels of hBD1, hBD2, and hBD3 mRNA were evaluated in keratinocytes challenged with Toll-like receptor 2 and 4 ligands, interleukin-1β, TNFα, and interferon-γ (IFNγ). In contrast to constitutive expression levels, IFNγ-induced keratinocyte hBD1 and hBD3 mRNA expression was significantly greater in cells with the common CC genotype, but there was no clear correlation of genotype with hBD2 expression.

Conclusion

The DEFB1 -44 G allele is associated with an increase in overall constitutive antimicrobial activity and expression of hBD1 and hBD3 in a manner that is consistent with protection from candidiasis, while the more common C allele is associated with IFNγ inducibility of these β-defensins and is likely to be more protective in conditions that enhance IFNγ expression such as chronic periodontitis. These results suggest a complex relationship between genetics and defensin expression that may influence periodontal health and innate immune responses.

Potential role of human beta-defensin 1 in Helicobacter pylori-induced gastritis

OBJECTIVE

Helicobacter pylori-induced gastric inflammation is dependent on the persistence of the microorganism in the gastric epithelium. Modulation of the host epithelial antimicrobial responses may be a critical determinant in H. pylori-induced gastritis. Human beta-defensins (hBDs) are important components of the host defence at mucosal surfaces. The aim of the present study was to investigate the relevance of three single nucleotide polymorphisms (SNPs) of the human beta defensin-1 (hBD-1) gene in H. pylori-induced gastritis and to assess the mRNA expression of hBD-1 in H. pylori-infected AGS cells.

MATERIAL AND METHODS

Three SNPs of the beta defensin DEFB1 gene, DEFB1 G-20A (rs11362), DEFB1 C-44G (rs1800972) and DEFB1 G-52A (rs1799946), were genotyped either by Custom TaqMan SNP genotyping assays or by restriction fragment length polymorphism (RFLP) in 150 patients with chronic active gastritis; 100 serologically H. pylori-positive subjects without gastric or duodenal symptoms served as controls. hBD-1 mRNA expression in AGS cells was measured by quantitative reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

Significant differences in frequencies of the GA and AA genotypes of G-52A SNPs were observed between patients with chronic active gastritis and healthy controls. The maximum level of hBD-1 mRNA expression in AGS cells was observed at 24 h after infection with H. pylori, this not being dependent on the presence of the cag pathogenicity island (PAI).

CONCLUSIONS

The results of these genetic and in vitro experiments suggest that not only the inducible, but also the constitutive form of hBD may be important in the pathogenesis of H. pylori-induced gastritis.

Association of beta-defensin 1 single nucleotide polymorphisms with Crohn's disease

OBJECTIVE

It has been suggested that deficient defensin expression is associated with the chronic inflammation of Crohn's disease. The regional localization of Crohn's disease, ileal or colonic disease can be linked to different defensin profiles. As constitutive beta-defensin 1 has a colonic expression, we considered it of interest to investigate single nucleotide polymorphisms (SNPs) of the beta-defensin 1 gene (DEFB1) in Crohn's disease.

MATERIAL AND METHODS

Three SNPs of the DEFB1 gene, DEFB1 G-20A (rs11362), DEFB1 C-44G (rs1800972) and DEFB1 G-52A (rs1799946), were genotyped either by Custom TaqMan SNP genotyping assays or by restriction fragment length polymorphisms (RFLP) in 190 patients with Crohn's disease and 95 Hungarian controls.

RESULTS

It was found that the G-20A and C-44G SNPs had a strong association with the colonic and ileocolonic localizations of the disease, respectively, but no association was detected for the ileal localization. A significantly higher frequency of the GA genotype of G-20A was observed among patients with colonic localization (60%) as compared with healthy controls (39%), with an odds ratio (OR) of 2.39. The GG genotype of C-44G SNP, which is regarded as a protective genotype, was much less frequent (4%) among patients than among controls (12%), OR 3.367.

CONCLUSIONS

These results indicate that genetic variations in the DEFB1 gene encoding constitutive human beta-defensin 1 may be associated with the risk for Crohn's disease and may determine disease phenotype, e.g. colonic localization.

Human beta-defensin-1, a potential chromosome 8p tumor suppressor: control of transcription and induction of apoptosis in renal cell carcinoma

Human beta-defensin-1 (hBD-1) is a candidate tumor suppressor gene located on chromosome 8p23. Previously, we showed that cancer-specific loss of hBD-1 was found in 90% of renal clear cell carcinomas and in 82% of prostate cancers. To investigate the possible mechanisms of decreased gene expression and determine the function of hBD-1 protein in urological cancers, we sequenced hBD-1 gene coding regions in prostatic and renal cancer samples. We then analyzed the frequency distribution of promoter polymorphisms and determined the effect of these base changes on transcriptional activity of the hBD-1 promoter. A polymorphism at -688 bases upstream of the ATG start codon affects hBD-1 promoter activity, leading to a rate of reporter gene transcription that is 40% to 50% lower than the wild-type sequence when tested in either DU145 or TSU-Pr1 cell lines. In addition, a polymorphism at -44 bases was shown to enhance transcription up to 2.3 times more than the wild-type sequence in the same cell lines. In addition, three novel hBD-1 promoter mutations were found in renal and prostate cancer clinical samples. An iso-5-aza-2'-deoxycytidine treatment was effective in transcription up-regulation in DU145, suggesting a possible upstream methylation-dependent effect. Synthetic hBD-1 peptide inhibited bladder cancer cell TSU-Pr1 proliferation. Overexpression of the hBD-1 gene in renal cancer cells SW156 resulted in caspase-3-mediated apoptosis. These data support the hypothesis that hBD-1 is a potential tumor suppressor gene for urological cancers. Promoter point mutations may be responsible for cancer-specific loss of hDB-1 expression.

The role of cathelicidin and defensins in pulmonary inflammatory diseases

Antimicrobial peptides (AMPs) protect the epithelia of mucosal organs like the respiratory or the gastrointestinal tract from invading microorganisms. As an integral part of the innate immune system they display antimicrobial activity against gram- and gram-negative bacteria as well as against fungi and enveloped and non-enveloped viruses. Besides their microbicidal effects they have important functions in the regulation of repair and inflammation. AMPs are sometimes referred to as 'alarmins' due to their ability to recruit, modulate and activate components of the immune system. In contrast, some AMPs suppress activation of the immune system. AMPs are also involved in tissue repair, cancer biology and angiogenesis. Based on their antimicrobial and immunomodulatoy functions, AMPs are probably involved in the pathogenesis of infectious and inflammatory diseases of the lung. Inborn or acquired deficiencies contribute to susceptibility to infection and colonisation. The potential pro-inflammatory role of AMPs contributes to the disease processes in inflammatory disorders such as asthma, chronic obstructive pulmonary disease, sepsis or pulmonary fibrosis. This review summarises the knowledge about the functions of AMPs in the pulmonary innate host defence system and their role in respiratory disease.

SNPs in human beta-defensin 1 gene (DEFB1): frequencies in a Mexican population and new PCR-RFLPs assays

Polymerase chain reaction-restriction fragment length polymorphism assays for two single nucleotide polymorphisms in the human beta-defensin 1 gene have been validated with real-time PCR in 101 healthy individuals from western Mexico. Allele frequencies were 52.5% (692-A) and 98.5% (1836-A). These assays can be confidently used as a cheaper alternative genotyping method for these sites.

Association of beta-defensin 1 single nucleotide polymorphisms with atopic dermatitis

BACKGROUND

Atopic dermatitis (AD) is a chronic multifactorial allergic disease with unclear etiology. The antimicrobial human beta-defensin 1 is chemotactic for dendritic cells, which are important regulators of allergic immune responses. In an attempt to identify useful markers that could predict susceptibility to AD, we investigated single nucleotide polymorphisms (SNPs) of the beta-defensin 1 gene (DEFB1) with potential functional consequences.

METHODS

Four SNPs of the DEFB1 gene were genotyped either by real-time polymerase chain reaction or polymerase chain reaction-restriction fragment length polymorphisms in 59 patients with AD and 151 controls from the Mexican population. Correlation analyses were carried out between genetic, environmental and clinical variables in AD patients.

RESULTS

The genotypes associated with susceptibility to AD and no other allergy were 692 GG (OR = 3.21, 95% CI 1.37-7.34) and 1654 AA (OR = 17.37, 95% CI 1.62-860.83). The allele 668 C is a risk factor for AD (OR = 2.23, 95% CI 1.22-4.01) and the allele A in site 1836 correlates with earlier age at onset (Spearman's rho = 0.232; p = 0.03). The prolonged duration of breastfeeding correlates with earlier age at onset as well as with the severity of AD.

CONCLUSIONS

The DEFB1 gene is probably involved in the incidence and development of AD, but additional functional studies will be necessary to understand the biological role of these SNPs.

Molecular evolution of animal antimicrobial peptides: widespread moderate positive selection

An increasing number of studies in both vertebrates and invertebrates show that the evolution of antimicrobial peptides is driven by positive selection. Because these diverse molecules show potential for therapeutic applications, they are currently the targets of much structural and functional research, providing extensive background data for evolutionary studies. In this paper, patterns of molecular evolution in antimicrobial peptide genes are reviewed. Evidence for positive selection on antimicrobial peptides includes an excess of nonsynonymous nucleotide substitutions, an excess of charge-changing amino acid substitutions, nonneutral patterns of allelic variation, and functional assays in vivo and in vitro that show improved antimicrobial effects for derived sequence variants. Positive selection on antimicrobial peptides may be as common as, but perhaps weaker than, selection on the best-known example of adaptively evolving immunity genes, the major histocompatibility complex. Thus, antimicrobial peptides present a useful and underutilized model for the study of adaptive molecular evolution.

Contribution of alpha- and beta-defensins to lung function decline and infection in smokers: an association study

Background

Alpha-defensins, which are major constituents of neutrophil azurophilic granules, and beta-defensins, which are expressed in airway epithelial cells, could contribute to the pathogenesis of chronic obstructive pulmonary disease by amplifying cigarette smoke-induced and infection-induced inflammatory reactions leading to lung injury. In Japanese and Chinese populations, two different beta-defensin-1 polymorphisms have been associated with chronic obstructive pulmonary disease phenotypes. We conducted population-based association studies to test whether alpha-defensin and beta-defensin polymorphisms influenced smokers' susceptibility to lung function decline and susceptibility to lower respiratory infection in two groups of white participants in the Lung Health Study (275 = fast decline in lung function and 304 = no decline in lung function).

Methods

Subjects were genotyped for the alpha-defensin-1/alpha-defensin-3 copy number polymorphism and four beta-defensin-1 polymorphisms (G-20A, C-44G, G-52A and Val38Ile).

Results

There were no associations between individual polymorphisms or imputed haplotypes and rate of decline in lung function or susceptibility to infection.

Conclusion

These findings suggest that, in a white population, the defensin polymorphisms tested may not be of importance in determining who develops abnormally rapid lung function decline or is susceptible to developing lower respiratory infections.

Antimicrobial peptides in the oral environment: expression and function in health and disease

The oral cavity is a unique environment in which antimicrobial peptides play a key role in maintaining health and may have future therapeutic applications. Present evidence suggests that alpha-defensins, beta-defensins, LL-37, histatin, and other antimicrobial peptides and proteins have distinct but overlapping roles in maintaining oral health and preventing bacterial, fungal, and viral adherence and infection. The expression of the inducible hBD-2 in normal oral epithelium, in contrast to other epithelia, and the apparent differential signaling in response to commensal and pathogenic organisms, provides new insights into innate immunity in this body site. Commensal bacteria are excellent inducers of hBD-2 in oral epithelial cells, suggesting that the commensal bacterial community acts in a manner to benefit the overall innate immune readiness of oral epithelia. This may have major significance for understanding host defense in the complex oral environment.

Correlated expression of human beta defensin-1, -2 and -3 mRNAs in gingival tissues of young children

OBJECTIVE

Human beta-defensins (hBDs) are a group of antimicrobial peptides, expressed by the epithelial cells of many organs including gingival epithelium. The present study examined correlation between the gene expressions of hBD-1, -2, -3 mRNAs and the inflammatory cytokines in human gingival tissues.

STUDY DESIGN

The gingival tissues were obtained from surgical discards from 20 different patients (age range, 5-13 years). The expression levels of mRNAs were evaluated by quantitative RT-PCR with LightCycler. The mRNA expression levels were normalized with those of keratin 10 mRNA. The data were statistically analysed using Person's correlation coefficient.

RESULTS

The expression levels of hBD-1,-2 and -3 were significantly correlated with each other and also correlated with that of TNF-alpha.

CONCLUSIONS

The results indicate that the expression levels of hBDs vary from one individual to another.

Single-nucleotide polymorphisms and haplotype analysis in beta-defensin genes in different ethnic populations

Beta-defensins are cationic antimicrobial peptides expressed by epithelial cells and exhibit antibacterial, antifungal, and antiviral properties. The defensins are part of the innate host defense network and may have a significant protective role in the oral cavity and other mucosa. Defects or alteration in expression of the beta-defensins may be associated with susceptibility to infection and mucosal disorders. We examined the occurrence of single-nucleotide polymorphisms (SNPs) in the human beta-defensin genes DEFB1 and DEFB2 encoding human beta-defensin-1 and -2 (hBD-1, hBD-2), respectively, in five ethnic populations and defined haplotypes in these populations. Fifteen SNPs were identified in both DEFB1 and DEFB2. Coding region SNPs were found in very low frequency in both genes. One nonsynonymous DEFB1 SNP, G1654A (Val --> Ile), and one nonsynonymous DEFB2 SNP, T2312A (Leu --> His), were identified. Seven sites in each gene exhibited statistically significant differences in frequency between ethnic groups, with the greatest variation in the promoter and in the 5'-untranslated region of DEFB1. DEFB1 displayed 10 common haplotypes, including one cosmopolitan haplotype. Eight common haplotypes were found in DEFB2, including one cosmopolitan haplotype shared among all five ethnic groups. Our results show that genotypic variability among ethnic groups will need to be addressed when performing associative genetic studies of innate defense mechanisms and susceptibility to disease.

Single-nucleotide polymorphisms (SNPs) in human beta-defensin 1: high-throughput SNP assays and association with Candida carriage in type I diabetics and nondiabetic controls

beta-Defensins are cationic antimicrobial peptides expressed in epithelia. They exhibit antibacterial, antifungal, and antiviral properties. Defensins are a component of the innate immune response, and it has been proposed that they have a protective role in the oral cavity. Previous studies have shown that human beta-defensin 1 (hBD-1) is constitutively expressed in oral epithelial cells but that expression varies between individuals. We tested the hypothesis that genetic variations in defensin peptide expression may be associated with opportunistic infections. This may be critical in the immunocompromised patient population, in which innate immune responses may have a relatively more important role. Oral Candida carriage status and the presence of six single-nucleotide polymorphisms (SNPs) in the DEFB1 gene encoding hBD-1 were evaluated in type I diabetic patients (n = 43) and nondiabetic controls (n = 50). Genomic DNA was obtained from buccal swabs. Portions of the DEFB1 gene were amplified, and each SNP was analyzed by a TaqMan assay, standardized with control DNA of known genotype. Candida carriage status was determined from unstimulated saliva on CHROMagar plating medium. A low level of Candida carriage was defined as < or = 350 CFU/ml. A high level of Candida carriage was seen in 44% of the diabetic subjects but only in 28% of the nondiabetic controls (P < 0.05). C. albicans predominated; however, diabetic subjects, especially those with high levels of carriage, showed an increased proportion of Candida glabrata and C. tropicalis. There was a strong association between an SNP in the 5' untranslated region (C-->G at position -44) and Candida carriage in both groups. Among individuals in the diabetic population who had the SNP allele 2 (G), 58% had low CFU, while 6% had high CFU. The C-->G SNP at position -44 is associated with low levels of Candida carriage. The resultant odd ratios are statistically significant for a protective effect (odd ratios, 25 for diabetic subjects and 8.5 for nondiabetic subjects). These results indicate that genetic variations in the DEFB1 gene encoding hBD-1 may have a major role in mediating and/or contributing to susceptibility to oral infection.

Expression of beta-defensin 1 and 2 mRNA by human monocytes, macrophages and dendritic cells

Human beta-defensins are broad-spectrum antimicrobial peptides known to be produced by epithelial cells. It was recently shown that beta-defensins also display chemotactic activity for dendritic cells (DC) and T cells, and thus may serve to link innate and adaptive immunity. The aim of the present study was to explore expression of mRNA for these peptides in mononuclear phagocytes and DC. The results revealed that monocytes, monocyte-derived-macrophages (MDM), and monocyte-derived-dendritic cells (DC) all express human-beta-defensin-1 (hBD-1) mRNA. hBD-1 mRNA expression by monocytes and MDM was increased after activation with interferon-gamma (IFN-gamma) and/or lipopolysaccharide (LPS) in a dose- and time-dependent fashion. Alveolar macrophages showed an intense hBD-1 expression, which could not be further increased. Expression of hBD-1 mRNA by immature DC was low, and increased considerably after maturation. Monocytes, MDM, alveolar macrophages and DC showed a limited expression of human beta-defensin-2 (hBD-2) mRNA, which could only be increased in monocytes and alveolar macrophages by IFN-gamma and/or LPS in a dose- and time-dependent fashion. Immunocytochemical stainings demonstrated the expression of hBD-2 peptide by freshly isolated blood monocytes and alveolar macrophages in cytospin preparations.

Structural and functional characterization of hBD-1(Ser35), a peptide deduced from a DEFB1 polymorphism

beta-Defensins are mammalian antimicrobial peptides that share a unique disulfide-bonding motif of six conserved cysteines. An intragenic polymorphism of the DEFB1 gene that changes a highly conserved Cys to Ser in the peptide coding region has recently been described. The deduced peptide cannot form three disulfide bonds, as one of the cysteines is unpaired. We have determined the cysteine connectivities of a corresponding synthetic hBD-1(Ser35) peptide, investigated the structure by circular dichroism spectroscopy, and assayed the in vitro antimicrobial activity. Despite a different arrangement of the disulfides, hBD-1(Ser35) proved as active as hBD-1 against the microorganisms tested. This activity likely depends on the ability of hBD-1(Ser35) to adopt an amphipathic conformation in hydrophobic environment, similar to the wild type peptide, as suggested by CD spectroscopy.

Genetic variants of human beta-defensin-1 and chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is due to interactions between cigarette smoke exposure and other risk factors. Genetic variations of human beta-defensin-1 (hBD-1), an endogenous antimicrobial peptide in the airway, were investigated in 60 patients and 213 healthy volunteers by single-strand conformation and restriction fragment length polymorphism analysis and DNA sequencing. Four nucleotide variations in the 5' and 3' untranslated regions and two nonsynonymous substitutions in the coding region were identified. Of these, a newly found Ile38 variant was observed in 15.0% of patients but only in 2.8% of healthy individuals and was significantly associated with the disease (OR = 6.1, 95% confidence intervals 2.0-8.3, P = 0.0012). More than 80% of those with Ile38 experienced sputum production for more than 3 months during the follow-up period. Genetic variations in hBD-1 may define a high-risk subgroup of COPD where the component of chronic bronchitis is predominant.

Defensins -- innate immunity at the epithelial frontier

Physical barrier function was formerly believed to play the major role in mucosal protection against luminal bacteria. This view has now been challenged by the discovery of specialized molecules that possess antimicrobial activity. More than 100 peptides have been identified so far, and the number is still growing. These peptides are distributed widely and conserved throughout phylogeny. The epithelial expression of antimicrobial peptides is of particular interest as many pathogens adhere to epithelial surfaces and may eventually invade the host. This rapidly acting defence system of innate immunity is already engaged before adoptive immune interactions take place. These antimicrobial peptides consist of constitutive and inducible forms, potentiating this barrier function in terms of an inflammatory response. One important subgroup of antimicrobial peptides is the family of defensins, which are classified as alpha (alpha-) and beta (beta-) defensins. Eight different peptides with varying antimicrobial properties have been identified. They are distributed widely in humans, and organ-specific expression patterns have been observed. Homologous peptides have been found in other mammals, vertebrates, invertebrates, insects and plants. The identification of alpha-defensins and their murine counterparts, cryptdins, in the small intestine prompted intensive research into epithelial antimicrobial defence.