Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Defensins”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 181 records · Page 10Linked to original sources
PubMed1992

Cationic defensins arise from charge-neutralized propeptides: a mechanism for avoiding leukocyte autocytotoxicity?

Defensins, small cationic polypeptides with antimicrobial and cytotoxic properties, are among the principal constituents of cytoplasmic granules of mammalian neutrophils and certain macrophages. To identify conserved structural features of defensin precursors that may be important for their targeting to cytoplasmic granules or for prevention of autocytotoxicity, we isolated and sequenced three neutrophil-specific rabbit defensin cDNAs that code for preproprotein precursors to the mature defensins NP-3a, NP-4, and NP-5. The preprodefensins NP-3a, NP-4, and NP-5, like the previously characterized preprodefensins, lack consensus sequences for N-linked glycosylation, suggesting that defensins are targeted to lysosome-like granules by a mechanism not dependent on the mannose-6-phosphate receptor. Analysis of all seven known myeloid prodefensins revealed a structure wherein an anionic propiece neutralizes the cationicity of the mature peptide. Because defensins apparently require cationic epitopes for cell membrane permeabilization and cytotoxicity, charge neutralization of mature peptides by their anionic propieces may prevent autocytotoxicity during defensin synthesis and processing.

Amino Acid Sequence↗
PubMed2005

Recent advances in the research and development of human defensins.

Human defensins are a family of cationic antimicrobial peptides with molecular weights of 4-5 kDa, containing a conserved six disulphide-linked cysteine motif. During the last two decades a series of endogenous alpha- and beta-human defensins were discovered. They exhibit a broad range of antimicrobial properties and are thought to be ideal therapeutic agents because of their potential ability to circumvent the problems of acquired resistance often observed with other antimicrobial therapies. Because of their appealing medical and pharmaceutical potential there has been an emphasis on human defensins in medical and molecular biology research in recent years. This paper aims to present a comprehensive review of recent advances in the study of human defensins including their discovery, classification, molecular properties, expression, mechanisms of action and potential medical applications. In addition, the advances in producing human defensins via genetic engineered cells are summarized from research works in our group (besides host cells including E. coli, B. subtilis and yeast systems, the cell-free protein synthesis system was also employed to express human beta-defensin-2) along with other related published works. The present challenges and prospects for the potential application of human defensins are also discussed.

Gene Expression Regulation↗
PubMed2000

Determination of defensin HNP-1, HNP-2, and HNP-3 in human saliva by using LC/MS.

The mass spectral profiling of saliva by liquid chromatography mass spectrometry in relation to particular types of pain is being examined. The aim is to develop a profile that could be useful for the assessment of patients and their treatment programs, as well as identifying unknown compounds observed in saliva. Defensin human neutrophil peptide-1 (HNP-1) and defensin HNP-2 were identified and confirmed, whereas defensin HNP-3 was tentatively identified. Linear calibration range of defensin HNP-1 and HNP-2 was 0.25 to 3 microg/ml with R(2) values of > 0.99 for both. The detection limit for defensin HNP-1 and HNP-2 was estimated at 0.1 microg/ml. The healthy subjects surveyed in this study had readily measurable salivary concentrations of defensin HNP-1 (8.6 +/- SD 8.0 microg/ml) and defensin HNP-2 (5.6 +/- SD 5.2 microg/ml).

Adult↗
PubMed1997

Critical role of lipid composition in membrane permeabilization by rabbit neutrophil defensins.

We have examined the interactions of the six known rabbit neutrophil defensin antimicrobial peptides with large unilamellar vesicles (LUV) made from various lipid mixtures based on the lipid composition of Escherichia coli membranes. We find that the permeabilization of LUV made from E. coli whole lipid extracts differs dramatically from that of single-component LUV made from palmitoyl-oleoyl-phosphatidylglycerol (POPG). Specifically, defensins NP-1, NP-2, NP-3A, NP-3B, and a natural mixture of the six defensins cause fast nonpreferential leakage of high molecular weight dextrans as well as the low molecular weight fluorophore/quencher pair 8-aminonapthalene-1,3,6 trisulfonic acid (ANTS)/p-xylene-bis-pyridinium bromide (DPX) from E. coli whole lipid LUV through large, transient membrane lesions. In contrast, release of ANTS/DPX from POPG LUV induced by the defensins is slow and graded with preference for DPX (Hristova, K., Selsted, M. E., and White, S. H. (1996) Biochemistry 35, 11888-11894). Interestingly, defensins NP-4 and NP-5 alone do not induce leakage from E. coli whole lipid LUV, whereas only NP-4 is ineffective with POPG LUV. Examination of the sequences of the six defensins suggests that the inactivity of NP-4 and NP-5 may be due to their lower net positive charge and/or the substitution of a Thr for the Arg or Lys that follows the fourth Cys residue. We found the presence of three major lipid components of E. coli whole lipid to be essential for creation of the large lesions observed in LUV: phosphatidylethanolamine, phosphatidylglycerol, and cardiolipin. Cardiolipin appears to play a key role because no leakage can be induced when only phosphatidylglycerol and phosphatidylethanolamine are present. These results indicate the importance of membrane lipid composition in the permeabilization of cell membranes by rabbit defensins.

Amino Acid Sequence↗
PubMed1999

Production of beta-defensin antimicrobial peptides by the oral mucosa and salivary glands.

beta-Defensins are cationic peptides with broad-spectrum antimicrobial activity that are produced by epithelia at mucosal surfaces. Two human beta-defensins, HBD-1 and HBD-2, were discovered in 1995 and 1997, respectively. However, little is known about the expression of HBD-1 or HBD-2 in tissues of the oral cavity and whether these proteins are secreted. In this study, we characterized the expression of HBD-1 and HBD-2 mRNAs within the major salivary glands, tongue, gingiva, and buccal mucosa and detected beta-defensin peptides in salivary secretions. Defensin mRNA expression was quantitated by RNase protection assays. HBD-1 mRNA expression was detected in the gingiva, parotid gland, buccal mucosa, and tongue. Expression of HBD-2 mRNA was detected only in the gingival mucosa and was most abundant in tissues with associated inflammation. To test whether beta-defensin expression was inducible, gingival keratinocyte cell cultures were treated with interleukin-1beta (IL-1beta) or bacterial lipopolysaccharide (LPS) for 24 h. HBD-2 expression increased approximately 16-fold with IL-1beta treatment and approximately 5-fold in the presence of LPS. Western immunoblotting, liquid chromatography, and mass spectrometry were used to identify the HBD-1 and HBD-2 peptides in human saliva. Human beta-defensins are expressed in oral tissues, and the proteins are secreted in saliva; HBD-1 expression was constitutive, while HBD-2 expression was induced by IL-1beta and LPS. Human beta-defensins may play an important role in the innate defenses against oral microorganisms.

3T3 Cells↗
PubMed2004

Differential effects of alpha- and beta-defensin on cytokine production by cultured human bronchial epithelial cells.

Defensins are cysteine-rich cationic antimicrobial peptides that play an important role in innate immunity and are known to contribute to the regulation of host adaptive immunity. In addition to direct antimicrobial activities, it has been recently reported that alpha-defensins, mainly present in neutrophils in the lung, have a cytotoxic effect and induce IL-8 production from airway epithelial cells. Although beta-defensins are expressed in epithelial cells in various tissues, including lung, there are no reports of their effects on cytokine synthesis in airway epithelial cells. The aim of the present study was to determine the effects of both alpha- and beta-defensins on the cytokine production, transcription factor binding activity, and cytotoxicity in primary cultured human bronchial epithelial cells (HBECs). We used human neutrophil peptide-1 (HNP-1; alpha-defensin) and human beta-defensin-2 (HBD-2) to stimulate HBECs. The results showed that treatment of HBECs with HNP-1, but not HBD-2, increased IL-8 and IL-1beta mRNA expression in a dose-dependent manner and also enhanced IL-8 protein secretion and NF-kappaB DNA binding activity. The 24-h treatments with >20 microg/ml of HNP-1 or >50 microg/ml of HBD-2 were cytotoxic to HBECs. These results suggest that alpha- and beta-defensins have different effects on cytokine synthesis by airway epithelial cells, and we speculate that they play different roles in inflammatory lung diseases.

Bronchi↗
PubMed1991

Activated alpha 2-macroglobulin is a principal defensin-binding protein.

Defensins are highly abundant and variably cationic peptides that possess antimicrobial, cytotoxic, and chemoattractant properties and equip mammalian phagocytes for participation in host defense and inflammatory processes. We studied the binding of the human defensin HNP-1 by proteins in plasma and serum and identified activated (F-form) alpha 2-macroglobulin (alpha 2M) as a principal binding protein for HNP-1. In contrast, native (S-form) alpha 2M bound little HNP-1. The binding of HNP-1 by F-form alpha 2M was resistant to salt and boiling in 2% sodium dodecyl sulfate but was ablated by dithiothreitol. Pretreatment of methylamine-activated serum or plasma by iodoacetamide substantially decreased the binding of HNP-1 to alpha 2M, suggesting that thiol groups in activated alpha 2M play a role in defensin binding, possibly by covalently trapping defensins via thiol-disulfide exchange. Western blots of conventionally collected sera showed endogenous defensins complexed with the F-form of alpha 2M, indicating that the generation of defensin-alpha 2M complexes was not limited to the in vitro model of methylamine-activated serum or plasma and radiolabeled HNP-1. Previous studies indicated that native alpha 2M can be converted to its F-form by many proteases, including those released by neutrophils and platelets, and that the F-form is recognized and internalized by specific receptors on macrophages and hepatocytes. Our findings suggest that the alpha 2M system may function as a scavenger of defensins and other peptide mediators in inflamed tissues and may constitute an important mechanism for the regulation and containment of inflammation.

Blood Bactericidal Activity↗
PubMed1999

Neutrophil defensins induce histamine secretion from mast cells: mechanisms of action.

Defensins are endogenous antimicrobial peptides stored in neutrophil granules. Here we report that a panel of defensins from human, rat, guinea pig, and rabbit neutrophils all have histamine-releasing activity, degranulating rat peritoneal mast cells with EC50 ranging from 70 to 2500 nM, and between 45 and 60% of the total histamine released. The EC50 for defensin-induced histamine secretion correlates with their net basic charge at neutral pH. There is no correlation between histamine release and antimicrobial potency. Degranulation induced by defensins has characteristics similar to those of activation by substance P. The maximum percent histamine release is achieved in <10 s, and it can be markedly inhibited by pertussis toxin (100 ng/ml) and by pretreatment of mast cells with neuraminidase. These properties differ from those for degranulation induced by IgE-dependent Ag stimulation and by the calcium ionophore A23187. GTPase activity, a measure of G protein activation, was induced in a membrane fraction from mast cells following treatment with defensin. Thus, neutrophil defensins are potent mast cell secretagogues that act in a manner similar to substance P and 48/80, through a rapid G protein-dependent response that is mechanistically distinct from Ag/IgE-dependent mast cell activation. Defensins may provide important pathways for communication between neutrophils and mast cells in defenses against microbial agents and in acute inflammatory responses.

Amino Acid Sequence↗
PubMed1994

A marked decrease in defensin mRNA in the only case of congenital neutrophil-specific granule deficiency reported in Japan.

A deficiency of defensins (human neutrophil peptides, HNP) has been previously demonstrated in two individuals with congenital neutrophil-specific granule deficiency (SGD), but its genetic basis is not well understood. We have studied another case of SGD, the only case reported in Japan, to elucidate the molecular basis of defensin deficiency. Using Western blot analysis, we showed for the first time that HNP-4, a novel human defensin, was also deficient in the patient's neutrophils. Northern blot analysis demonstrated that the defensin mRNA was absent in the bone marrow cells of the patient. Limited Southern blot analysis, using a defensin cDNA probe, did not reveal any differences in fragment patterns of the genomic DNA between the patient and the control. We propose that the defensin deficiency in our patient is a consequence of a marked decrease in defensin mRNA in neutrophil precursors. Our findings were consistent with a previous speculation suggesting that the SGD defect occurs at the level of transcription.

Adult↗
PubMed1992

Defensins: endogenous antibiotic peptides from human leukocytes.

A variety of endogenous antimicrobial peptides equip mammals, amphibians, insects and plants to defend themselves against microbial pathogens. Defensins are small peptides of mammalian cells that contain 29-35 amino acid residues, including six invariant cysteines that form three intramolecular disulphide bonds. They are produced by the sequential proteolysis of precursors that contain approximately 95 amino acids and are synthesized by several types of cells, especially the bone marrow precursors of blood neutrophils. Defensins constitute 5-7% of the total protein in human neutrophils and are present in high concentration in the azurophil granules and phagocytic vacuoles. The production of defensins by human neutrophils amounts to approximately 10 mg/kg body weight per day. In certain mammalian species lung macrophages and specialized epithelial (Paneth) cells in the small intestine also produce defensins. Defensins are complexly folded, amphipathic, rich in antiparallel beta-sheet but devoid of alpha-helical domains. Their unusually broad antimicrobial spectrum encompasses Gram-positive and Gram-negative bacteria, many fungi, mycobacteria, spirochetes and several enveloped viruses. The antimicrobial properties of defensins result from their insertion into target cell membranes and the formation of voltage-sensitive channels. Given their abundance and broad spectrum of antimicrobial activity, defensins may contribute substantially to innate resistance to infection.

Amino Acid Sequence↗
PubMed1996

Human enteric defensin genes: chromosomal map position and a model for possible evolutionary relationships.

Defensins, a family of antimicrobial peptides isolated from several mammalian species, have a proposed functional role in innate host defense. In humans, certain defensin genes are expressed in phagocytic cells of hematopoietic origin, while others are expressed in Paneth cells, epithelial cells of the small intestine. In this study, we determined the chromosomal localization of the human defensin (HD) genes expressed in Paneth cells, HD-5 and HD-6. Analysis of a panel of human/hamster hybrids localized both HD-5 and HD-6 to chromosome 8. Southern blot analysis of DNA from cell lines that contain either chromosome 8 deletions or duplications further localized these two genes to 8p21-pter. Fluorescence in situ hybridization analysis of metaphase chromosomes using an HD-5 probe further supported the regional map assignment. Previous studies had localized the hematopoietic genes to chromosome 8p23, and the current work is consistent with both the enteric and the myeloid defensin genes being located at the same cytogenetic region of chromosome 8. In addition, the evolutionary relationships of this gene family were addressed using dot matrix sequence analysis. From this analysis, a model for the possible evolutionary history of the human defensin genes is proposed. According to this model, an early duplication of a primordial defensin gene yielded the ancestral genes of present day HD-5 and HD-6. The model further suggests that a subsequent unequal meiotic crossover event had generated an additional gene, comprised of a hybrid of sequences from the two parental genes, and that this hybrid gene then served as the ancestor to present day hematopoietic defensin genes.

Amino Acid Sequence↗
PubMed2002

Identification and characterization of a novel murine beta-defensin-related gene.

Beta-defensins comprise a family of cationic peptides, which are predominately expressed at epithelial surfaces and have a broad-range antimicrobial activity. We have assembled two BAC-based contigs from the chromosomal region 8A4 that contain the murine defensins, and we have mapped six reported beta-defensin genes. In addition, we have isolated and functionally characterized a novel beta-defensin gene that deviates from the canonical six cysteine motif present in the mature functional peptide of all other beta-defensins. This defensin-related gene (Defr1) is most highly expressed in testis and heart. The genomic organization is highly similar to Defb3, 4, 5, and 6, and the exon 1 sequence is very highly conserved. A synthetic Defr1 peptide displayed antimicrobial activity against Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, and Burkholderia cepacia. The antimicrobial activity of Defr1 against S. aureus, E.coli, and B. cepacia was found to be reduced in raised concentration of NaCl, but its action against P. aeruginosa was independent of NaCl concentration. This is the first report of a functional beta defensin that lacks one of the conserved cysteine residues in its predicted mature peptide. This study has major implications for the structure and functions of these important host defense molecules.

Amino Acid Sequence↗
PubMed2003

Defensins in saliva and the salivary glands.

Saliva contains several types of antimicrobial peptides that play a role in innate immunity. Peptides that were recently added to this list are the defensins. The purpose of this review is to summarize what is known about the production and role of defensins in the salivary glands and to discuss their therapeutic potential. The Alpha-defensins, human neutrophil defensins (HNP)-1, -2, and -3, have been detected in saliva and may be derived from neutrophils. The Beta-defensins, human Beta-defensins (HBD)-1 and -2, have also been detected in saliva. Although it has been speculated that salivary HBDs are derived from keratinocytes that line the oral mucosa rather than from the salivary glands, the HBD-1 peptide was recently found to be specifically expressed in salivary ductal cells, although not in acini. Defensins may be useful for the treatment of periodontal disease and for the prevention of caries and periodontitis.

Animals↗
PubMed1996

Cloning and characterization of cDNAs encoding the antibacterial peptide, defensin A, from the mosquito, Aedes aegypti.

Insect defensins are cationic, inducible antibacterial peptides. Four full-length cDNAs encoding defensin A from the mosquito Aedes aegypti were cloned using polymerase chain reaction (PCR) and sequenced. All four cDNAs are 473 base pairs long, bearing an open reading frame of 98 amino acids with a few substitutions in the signal peptide domain. The deduced amino acid sequence of Aedes aegypti defensin (AaDef) contains a signal peptide sequence of 18 amino acids followed by a 40-amino acid putative propeptide domain and a 40-amino acid mature peptide domain. The mature peptide, with a predicted M(r) of 4148, shows 80% identity and 93% similarity to Phormia defensin A, and is identical to the peptide sequencing data for mosquito defensin A of Lowenberger et al. (1995) and B of Chalk et al. (1995). There are three potential phosphorylation sites but no glycosylation sites detected in AaDef. Three putative disulfide linkages between cysteines, characteristic of insect defensins, are conserved in AaDef. Aedes aegypti defensin mRNA is produced in response to a bacterial challenge; it is dramatically enhanced 6 h after bacterial injection, continues to increase through 24 h, and is maintained at high levels until at least 30 h post-bacterial injection.

Aedes↗
PubMed2005

Screening of copy number polymorphisms in human beta-defensin genes using modified real-time quantitative PCR.

Defensins are cationic antimicrobial peptides, which play an important role in host immune defense to some infectious diseases as well as immune disease and skin disease. Recent studies identified that the genes coding for human beta-defensin 2 (DEFB4), human beta-defensin 3 (DEFB103) and human beta-defensin 4 (DEFB104) showed variation in copy numbers. This variation may have an impact on gene expression levels. Here, we have demonstrated a real-time PCR-based method to measure beta-defensin gene copy number. Using this relative real-time quantitative PCR, we developed a new rapid and reliable approach, which involves amplification of the target locus (DEFB4 or DEFB103 or DEFB104) and the single-copy reference locus (human serum albumin, ALB) in a single PCR reaction. A calibrator was prepared by recombining one copy of the target gene and one copy of the reference gene into a plasmid. After correcting the PCR amplification efficiency, which differed between the defensin gene and ALB gene, and normalization by the calibrator, the ratio of the copy number of the target gene to that of the reference gene in an unknown sample was determined. This normalized ratio directly related to the gene copy number. The assay was validated using previously genotyped samples, which demonstrated high accuracy and reliability of the method. Furthermore, this method was used to screen the copy number variations of these three beta-defensin genes in healthy blood donors. This method proved to be a reliable and fast tool to genotype gene copy number variations in projects associating genomic variations with gene expression or with population phenotypes in epidemiologic studies.

Base Sequence↗
PubMed2006

The concentration-dependent chemokine release and pro-apoptotic effects of neutrophil-derived alpha-defensin-1 on human bronchial and alveolar epithelial cells.

Defensins play a pivotal role in antimicrobial reactions, inflammatory responses, wound repair, and specific immunity. In inflammatory and infectious lung diseases, alpha-defensins are released from recruited neutrophils, and modulate a variety of lung cell functions. We found that human bronchial and alveolar epithelial cells treated with low and moderate concentrations (5 and 10 micro g/ml) of purified neutrophil-derived alpha-defensin-1 secreted more interleukin (IL)-8 and monocyte chemoattractant protein (MCP)-1 in a dose- and time-dependent manner. Under moderate and high concentrations (10 and 20 micro g/ml) of alpha-defensin-1, we observed typical apoptotic changes in the lung epithelial cells after stimulation for 24 h. Furthermore, alpha-defensin-1 triggered lung cell detachment in a time- and dose-dependent manner at moderate and high concentrations. Prior to the detachment, caspase-3 activity significantly increased. On confocal laser microscopy, rapid translocation of alpha-defensin-1 to the endoplasmic reticulum (ER) was noted. These findings suggest that neutrophil-derived alpha-defensin-1 has pro-inflammatory and apoptotic effects in human bronchial and alveolar epithelial cells, which are concentration-dependent and may be associated with ER activity.

Amino Acid Chloromethyl Ketones↗
PubMed2005

Detection of individual human neutrophil alpha-defensins (human neutrophil peptides 1, 2 and 3) in unfractionated gingival crevicular fluid--a MALDI-MS approach.

The role of antimicrobial peptides is particularly important in the oral cavity where there is constant challenge by microorganisms. The alpha-defensins are a group of cationic peptides that comprise 30-50% of the total protein in azurophilic granules of human neutrophils. They include the human neutrophil peptides (HNP) 1, 2 and 3 which have almost identical amino acid sequences but differ in their biological activities. The amino acid sequence similarities of the defensins have made it difficult to unequivocally determine the presence of individual defensins using antibody-based techniques. However, by virtue of their cationic nature we postulated that the defensins would fly particularly well in mass spectrometry and that this characteristic would allow facile identification of individual HNPs in unfractionated gingival crevicular fluid (GCF) from periodontitis patients and healthy controls. Although there was variability in levels of defensins detected in periodontal health and disease, HNP-1 was always identified as the major peak in the triad and HNP-3 as the minor peak, lending support to the hypothesis that HNP-2 may arise by post-translational proteoyltic cleavage of HNP-3 rather than HNP-1. The finding that the defensins were more abundant in a higher proportion of the healthy sites studied could be linked to a more intact defensin barrier in periodontal health.

Adult↗
PubMed2003

Evolution of primate theta-defensins: a serpentine path to a sweet tooth.

Retrocyclins (ancestral human theta-defensins) are cyclic antimicrobial octadecapeptides that interfere with viral uptake and protect human cells from infection by T- and M-tropic strains of HIV-1 in vitro. As are other theta-defensins, retrocyclins are lectins that bind gp120, CD4, and galactosylceramide-all of which are implicated in HIV-1 uptake. Although theta-defensin mRNA transcripts are present in human bone marrow, spleen, thymus, testis, and skeletal muscle, a premature stop codon aborts their translation. We found six theta-defensin (DEFT) genes in the human genome; five on chromosome 8p23 and one on chromosome 1. All six of these pseudogenes, as well as their homologues in chimpanzees and gorillas, contained the same premature stop codon mutation. Whereas we found intact DEFT genes in DNA from several Old World Monkeys, Hylobates syndactylus (a lesser ape) and orangutans, no homologues were present in DNA from six New World Monkeys and five prosimians. We conclude that DEFT genes and theta-defensins arose in Old World Monkeys by mutation of a pre-existing alpha-defensin gene. Although intact DEFT genes survive in some nonhuman primates, our hominid ancestors lost their ability to produce theta-defensins after the orangutan and hominid lineages diverged. It is possible (but may be difficult to prove) that this mutation rendered our species more susceptible to infection by HIV-1.

Amino Acid Sequence↗