MUC5B is a major gel-forming, oligomeric mucin from human salivary gland, respiratory tract and endocervix: identification of glycoforms and C-terminal cleavage

The salivary mucin MUC5B and lactoperoxidase can be used for layer-by-layer film formation

In situ ellipsometry was used to study layer-by-layer film formation on hydrophilic and hydrophobized silica surfaces by alternating sequential adsorption of human mucin MUC5B and cationic proteins lysozyme, lactoferrin, lactoperoxidase or histatin 5, respectively. The stability of the multilayers was investigated by addition of sodium dodecyl sulfate solution (SDS). Atomic force microscopy was employed to investigate morphological structures on the surfaces during the layer-by-layer film build-up. It was clearly shown that, on both hydrophilic and hydrophobized silica, only MUC5B and lactoperoxidase showed the ability for multilayer formation, resulting in an approximately linear increase in adsorbed amount and film thickness with each deposition cycle. The net increase in amounts per cycle was larger on the hydrophilic silica. Further, MUC5B needs to be adsorbed first on the hydrophilic substrates to obtain this fast build-up behavior. Generally, addition of SDS solution showed that a large fraction of the adsorbed film could be desorbed. However, films on the hydrophobized silica were more resistant to surfactant elution. In conclusion, MUC5B-cationic protein multilayers can be formed on hydrophilic and hydrophobized silica, depending on the choice of the cationic protein as well as in which order the build-up is started on hydrophilic silica. Additionally, SDS disrupts the layer-by-layer film formed by MUC5B and lactoperoxidase.

Human airway surface epithelial regeneration is delayed and abnormal in cystic fibrosis

Cystic fibrosis (CF) at an advanced stage of the disease is characterized by airway epithelial injury and remodelling. Whether CF remodelling is related to infection and inflammation or due to an abnormal regenerative process is still undecided. We have recently established the expression and secretion profiles of interleukin (IL)-8, matrix metalloproteinase (MMP)-7, MMP-9, and tissue inhibitor of metalloproteinase (TIMP)-1 during non-CF airway epithelial regeneration in a humanized nude mouse xenograft model. To enhance our understanding of CF remodelling, we compared the regeneration process of non-infected human CF and non-CF nasal epithelia. In both CF and non-CF situations, epithelial regeneration was characterized by successive steps of cell adhesion and migration, proliferation, pseudostratification, and terminal differentiation. However, histological examination of the grafts showed a delay in differentiation of the CF airway epithelium. Cell proliferation was higher in the regenerating CF epithelium, and the differentiated CF epithelium exhibited a pronounced height increase and basal cell hyperplasia in comparison with non-CF epithelium. In addition, while the number of goblet cells expressing MUC5AC was similar in CF and non-CF regenerated epithelia, the number of MUC5B-immunopositive goblet cells was lower in CF grafts. The expression of human IL-8, MMP-7, MMP-9, and TIMP-1 was enhanced in CF epithelium, especially early in the regenerative process. Together, our data strongly suggest that the regeneration of human CF airway surface epithelium is characterized by remodelling, delayed differentiation, and altered pro-inflammatory and MMP responses.

Salivary Mucin MUC5B Could Be an Important Component of in Vitro Pellicles of Human Saliva: An in Situ Ellipsometry and Atomic Force Microscopy Study

This paper describes a combined investigation of the salivary and MUC5B films structure and topography in conditions similar to those found in the oral cavity in terms of ionic strength, pH, and protein concentration. AFM and ellipsometry were successfully used to give a detailed picture of the film structure and topography both on hydrophilic and on hydrophobic substrata. Regardless of the substrata, the salivary film can be described as having a two sublayer structure in which an inner dense layer is decorated by large aggregates. However, the shape and height of these larger aggregates largely depend on the type of substrata used. Additionally, we show that the adsorption of MUC5B is controlled by the type of substrata and the MUC5B film topography is similar to that of the larger aggregates present in the salivary films, especially on hydrophobic substrates. Therefore, we conclude that MUC5B is a major component in the salivary film when formed on hydrophobic substrates. Furthermore, we studied how resistant the salivary and MUC5B films are against elutability by buffer rinsing and addition of SDS solution. We conclude that the adsorbed proteins contain fractions with varying binding strengths to the two types of surfaces. Specifically, we have shown that the large MUC5B biomacromolecules on the hydrophobic substrates are especially resistant to both elution with buffer solution and SDS. Therefore, these large mucins can be responsible for the increased resistance of HWS films on hydrophobic substrates and can protect the intraoral surfaces against surface-active components present in oral health care products.

Distinctive epidermal growth factor receptor/extracellular regulated kinase-independent and -dependent signaling pathways in the induction of airway mucin 5B and mucin 5AC expression by phorbol 12-myristate 13-acetate

Elevated expression of gel-forming mucin (MUC) genes MUC5AC and MUC5B is a major pathological feature in various airway diseases. In this study, we show that phorbol 12-myristate 13-acetate (PMA) is a potent stimulator for MUC5B gene expression under air-liquid interface conditions in three airway epithelial cell systems: primary cultures of normal human bronchial epithelial cells, the immortalized normal bronchial epithelial cell line HBE1, and the human lung adenocarcinoma cell line A549. Stimulation was time- and dose-dependent, could be demonstrated by promoter-reporter gene transfection, and was sensitive to mithramycin A, suggesting the involvement of a specificity protein 1-based transcriptional mechanism in the stimulation. PMA-induced MUC5B message and promoter-reporter gene activity were specifically sensitive to inhibition of protein kinase C delta, which was further confirmed by the forced expression of dominant-negative mutant of protein kinase C delta. Regarding downstream transduction, PMA-induced MUC5B expression was sensitive to inhibitors and dominant-negative expression of signaling molecules involved in Ras/mitogen-activated protein kinase/extracellular signal-regulated kinase kinase kinase1-mediated c-Jun N-terminal kinase and p38 pathways. This contrasted with the inhibition of PMA-induced MUC5AC expression by inhibitors of the Ras/epidermal growth factor receptor/extracellular regulated kinase signaling pathway. These results demonstrate for the first time that PMA-stimulated MUC5AC and MUC5B expressions are regulated through distinctive epidermal growth factor receptor/extracellular regulated kinase-dependent and -independent signaling pathways.

Assay of mucins in human tear fluid

Mucin genes, both secreted (MUC2, MUC5AC, MUC5B, MUC7) and membrane associated (MUC1, MUC4, MUC16), have been reported to be expressed by ocular surface epithelia. The purpose of this study was to comprehensively assay the mucin content of human tear fluid using multiple antibodies for each mucin and to develop a sensitive, semi-quantitative method for the assay of mucins in tears. Tear washes were obtained by instillation of saline onto the ocular surface, followed by collection from the inferior fornix. Tear proteins were separated in 1% agarose gels, transferred to nitrocellulose membrane by vacuum blotting and probed with multiple antibodies recognizing MUC1, MUC2, MUC4, MUC5AC, MUC5B, MUC7 and MUC16. Binding was detected using chemiluminescence, and quantity was determined by densitometry. Serial dilutions of pooled tears from normal individuals were assayed to determine the linear range of detectability. MUC1, MUC4, MUC16, MUC5AC and low levels of MUC2 were consistently detected in human tear fluid, while MUC5B and MUC7 were not. Use of several antibodies recognizing different epitopes on the same mucin confirmed these findings. The antibodies to mucins bound to serial dilutions of tears in a linear fashion (r2 > 0.9), indicating the feasibility of semi-quantitation. MUC5AC in tear fluid had an increased electrophoretic mobility compared to MUC5AC isolated from conjunctival tissue. This study provides clear evidence that the mucin component of tears is a mixture of secreted and shed membrane-associated mucins, and for the first time demonstrates MUC16 in tear fluid. Immunoblots of tears using agarose gel electrophoresis and chemiluminescence detection provide a semi-quantitative assay for mucin protein that will be useful for comparisons with tears from diseased eyes or after pharmacological intervention.

Rapid transport of large polymeric nanoparticles in fresh undiluted human mucus

Nanoparticles larger than the reported mesh-pore size range (10-200 nm) in mucus have been thought to be much too large to undergo rapid diffusional transport through mucus barriers. However, large nanoparticles are preferred for higher drug encapsulation efficiency and the ability to provide sustained delivery of a wider array of drugs. We used high-speed multiple-particle tracking to quantify transport rates of individual polymeric particles of various sizes and surface chemistries in samples of fresh human cervicovaginal mucus. Both the mucin concentration and viscoelastic properties of these cervicovaginal samples are similar to those in many other human mucus secretions. Unexpectedly, we found that large nanoparticles, 500 and 200 nm in diameter, if coated with polyethylene glycol, diffused through mucus with an effective diffusion coefficient (D(eff)) only 4- and 6-fold lower than that for the same particles in water (at time scale tau = 1 s). In contrast, for smaller but otherwise identical 100-nm coated particles, D(eff) was 200-fold lower in mucus than in water. For uncoated particles 100-500 nm in diameter, D(eff) was 2,400- to 40,000-fold lower in mucus than in water. Much larger fractions of the 100-nm particles were immobilized or otherwise hindered by mucus than the large 200- to 500-nm particles. Thus, in contrast to the prevailing belief, these results demonstrate that large nanoparticles, if properly coated, can rapidly penetrate physiological human mucus, and they offer the prospect that large nanoparticles can be used for mucosal drug delivery.

MUC5AC and MUC5B mucins increase in cystic fibrosis airway secretions during pulmonary exacerbation

RATIONALE

Cystic fibrosis (CF) is believed to be associated with mucus hypersecretion; thus, the principal airway gel-forming mucins, MUC5AC and MUC5B, are also expected to be increased relative to non-CF secretions. However, we have shown that these mucins are decreased during stable CF disease.

OBJECTIVES

In this study, we determine if these mucins increase during a pulmonary exacerbation of CF.

METHODS

Expectorated sputum was collected from 11 adults with CF during stable disease and then during a pulmonary exacerbation and from 12 healthy control subjects. MUC5AC and MUC5B proteins were measured by Western blot. DNA content was measured using microfluorimetry.

RESULTS

MUC5AC protein increased by 908% and MUC5B by 59% (p < 0.05 for both) during an exacerbation compared with periods of stable disease. During stable disease, the vol/vol quantity of MUC5AC protein was 89% less than normal mucus, and the mucin-associated sugars, measured using a lectin binding assay, were 46% less compared with normal mucus. The concentration of DNA in CF sputum did not increase during an exacerbation.

CONCLUSIONS

During a CF exacerbation, concentration of secreted mucin increased to the amount found in mucus from normal subjects, suggesting that the capacity to secrete mucin in response to an infection or inflammatory stimulus is preserved in CF airways. This might help to protect the airway from injury.

Large scale identification of proteins, mucins, and their O-glycosylation in the endocervical mucus during the menstrual cycle

The mucus filling the human cervical opening blocks the entry to the uterus, but this has to be relative and allow for the sperm to penetrate at ovulation. We studied this mucus, its content of proteins and mucins, and the mucin O-glycosylation in cervical secretions before, during, and after ovulation. Cervical mucosal secretions from 12 subjects were collected, reduced-alkylated, separated with polyacrylamide or agarose/polyacrylamide gel electrophoresis, and stained with silver, Alcian blue, or Coomassie Blue stain. Protein and mucin bands from before and during ovulation were digested and subsequently analyzed by nano-LC-FT-ICR MS and MS/MS. We identified 194 proteins after searches against the NCBI non-redundant protein database and an in-house mucin database. Three gel-forming (MUC5B, MUC5AC, and MUC6) and two transmembrane mucins (MUC16 and MUC1) were identified. For the analysis of mucin O-glycosylation, separated mucins from six individuals were blotted to PVDF membranes, and the O-glycans were released by reductive beta-elimination and analyzed with capillary HPLC-MS and -MS/MS. At least 50 neutral, sialic acid-, and sulfate-containing oligosaccharides were found. An increase of GlcNAc-6GalNAcol Core 2 structures and a relative decrease of NeuAc residues are typical for ovulation, and NeuAc-6GalNAcol and NeuAc-3Gal- epitopes are typical for the non-ovulatory phases. The cervical mucus at ovulation is thus characterized by a relative increase in neutral fucosylated oligosaccharides. This comprehensive characterization of the mucus during the menstrual cycle suggests mucin glycosylation as the major alteration at ovulation, but the relation to the altered physicochemical properties and sperm penetrability is still not understood.

MUC5B secretion is up-regulated in sinusitis compared with controls

BACKGROUND

The mucus that lines the airway epithelium provides a barrier against pathogenic and noxious agents and participates in the innate mucosal response to inflammation and infection. Mucins are the major components of mucus and the macromolecules that impart rheologic properties to airway mucus. Airway mucus is overproduced in chronic rhinosinusitis (CRS). Biochemical and biophysical characterization of mucus in CRS and in normal airways will elucidate important aspects of CRS pathophysiology and allow the design of targeted medical treatments. The aim of this study was to estimate secretion of sinus mucus mucins in healthy individuals and CRS and correlate them with mucus biophysical properties.

METHODS

Twenty-seven sinus mucus samples from 21 patients were collected (14 subjects with CRS undergoing sinus surgery as part of their treatment and 7 control subjects undergoing hypophysectomy without sinonasal disease). Biophysical properties of the mucus were measured by rheometry. ELISA was done to estimate MUC5AC and MUC5B mucin content in comparison with standards, i.e., porcine gastric mucin (MUC5AC) and human salivary mucin (MUC5B).

RESULTS

MUC5B secretion +/- SEM was 0.49 +/- 0.16 microg/mL (n = 14) and 0.17 +/- 0.05 microg/mL (n = 7) and MUC5AC secretion +/- SEM was 1.26 +/- 0.26 microg/mL (n = 14) and 1.46 +/- 0.61 microg/mL (n = 7) in chronic sinusitis and control subjects, respectively. There was linear correlation between viscosity and mucin content in the control group but not in the CRS group.

CONCLUSION

MUC5B secretion is significantly up-regulated in CRS compared with control subjects (p = 0.04). Correlation between viscosity and mucin content was lost in CRS. This is likely to have important implications for future therapies in CRS.

The role of airway secretions in COPD: pathophysiology, epidemiology and pharmacotherapeutic options

Often considered an aggravating but otherwise benign component of chronic obstructive pulmonary disease (COPD), airway mucus hypersecretion is now recognised as a potential risk factor for an accelerated loss of lung function in COPD and is a key pathophysiological feature in many patients, particularly those prone to respiratory tract infection. Consequently, it is important to develop drugs that inhibit mucus hypersecretion in these susceptible patients. Conventional therapy including anticholinergics, beta2-adrenoceoptor agonists, alone or in combination with corticosteroids, mucolytics and macrolide antibiotics are not entirely or consistently effective in inhibiting airway mucus hypersecretion in COPD. Novel pharmacotherapeutic targets are being investigated, including inhibitors of nerve activity (e.g., BK(Ca) channel activators), tachykinin receptor antagonists, epoxygenase inducers (e.g., benzafibrate), inhibitors of mucin exocytosis (e.g., anti-MARCKS peptide and Munc-18B blockers), inhibitors of mucin synthesis and goblet cell hyperplasia (e.g., EGF receptor tyrosine kinase inhibitors, p38 MAP kinase inhibitors, MEK/ERK inhibitors, hCACL2 blockers and retinoic acid receptor-alpha antagonists), inducers of goblet cell apoptosis (e.g., Bax inducers or Bcl-2 inhibitors), and purinoceptor P(2Y2) antagonists to inhibit mucin secretion or P(2Y2) agonists to hydrate secretions. However, real and theoretical differences delineate the mucus hypersecretory phenotype in COPD from that in other hypersecretory diseases of the airways. More information is required on these differences to identify therapeutic targets pertinent to COPD which, in turn, should lead to rational design of anti-hypersecretory drugs for specific treatment of airway mucus hypersecretion in COPD.

The role of airway secretions in COPD--clinical applications

It has been established that mucus hypersecretion and decreased mucus clearance contribute to the morbidity of chronic obstructive pulmonary disease (COPD). Indeed, the classic definition of chronic bronchitis relies on determining the frequency and duration of sputum expectoration. Despite the well recognized importance of this symptom, there are few therapies routinely used to decrease the sputum production or to improve clearance. There are fewer well conducted clinical trials of existing medications and this has led many regulatory agencies, notably the Food and Drug Administration (FDA), to refuse to register these medications or approve their sale. Similarly, airway clearance devices and chest physical therapy have not been well studied in COPD. Carefully conducted studies of interventions to improve airway clearance, similar to those done in cystic fibrosis (CF), may help us to identify effective therapies and possibly novel diagnostic tests for the management of COPD.

The underlying cause of cervical cancer in oral contraceptive users may be related to cervical mucus changes

Oral contraceptives (OCs) remain among the most effective reversible methods of birth control available today, providing almost 100% effectiveness with an impressively high margin of safety and other important health benefits. However, concerns have been raised about the role that the hormones in OCs might play in the pathogenesis of cervical cancer. Evidence shows that long-term use of OCs (five or more years) may be associated with an increased risk of cancer of the cervix. The mechanism of increased risk of cervical cancer in OCs users has long been debated, and remains uncertain. Our hypothesis is that scanty, thick, and highly viscous cervical mucus obtained in OCs users intimately involved in the pathogenesis of cervical cancer. Possibly, this architecture of cervical mucus may modulate and prolong the effect of carcinogenic agents, which have been carried by coitus and stored in posterior vaginal fornix, on squamocolumnar junction of cervix by not permitting them to be removed because of its highly viscous pattern. The role of cervical mucus changes by means of specific mucin protein changes on the pathophysiology of cervical cancer in OCs users should be investigated.

Mucin gene expression in rhinitis syndromes

Rhinitis and rhinosinusitis are often associated with airway diseases such as asthma, cystic fibrosis, and nasal polyposis. In these diseases, the alteration of both the quantity and quality of mucus results in an impaired mucociliary clearance, and this produces, in extreme cases, the airway obstruction. Mucins are the major component in mucus and are responsible for its viscoelastic properties. Mucin expression patterns have been shown to be altered in rhinitis-associated diseases. It has been proposed that this is one of the causes of hyperviscid mucus plugs in these pathologies. For this reason, the study of mucin expression and regulation in upper- and lower-airway diseases, such as asthma, cystic fibrosis, and nasal polyposis, may be crucial for the development of new therapies against mucus hypersecretion. In this review, we report major findings regarding mucin expression and regulation in rhinitis syndromes.

Mucin genes have different expression patterns in healthy and diseased upper airway mucosa

BACKGROUND

Mucus hyper-secretion is a feature of several airways diseases such as chronic rhinosinusitis, asthma, and cystic fibrosis (CF). Since mucins are major components of mucus, the knowledge of their distribution and regulation in nasal tissues is likely to improve mucus hyper-secretion therapy.

OBJECTIVE

The aim of this study was to evaluate and compare mucin gene expression at epithelial and glandular levels, and to identify potential mucin expression patterns for specific upper airways pathologies.

METHODS

Immunohistochemistry for MUC1, MUC2, and MUC4-MUC8 mucins was performed on healthy nasal mucosa (NM; n=12), bilateral nasal polyps (NP; n=38), NP from CF patients (n=10), and antrochoanal (AC) polyps (n=11). MUC2, MUC4, MUC5AC, and MUC6 mRNA expression were also analysed by in situ hybridization.

RESULTS

MUC1, MUC4, and MUC5AC mucins were highly expressed in the epithelium and their expression pattern was similar in all NP types, MUC1 and MUC4 being increased and MUC5AC decreased compared with NM. MUC8 was highly detected at both epithelial and glandular levels with marked variability between groups. MUC5B was mainly detected in glands and the expression in all polyp types was higher than in NM. Moreover, MUC5B expression was higher in NP epithelia from CF patients than in bilateral NP and healthy NM. Although MUC2 expression was low, especially in AC polyps, it was detected in most samples. In NM, MUC6 and MUC7 were scarcely detected and MUC7 expression was restricted to glands.

CONCLUSIONS

These results suggest that NP have a different pattern of mucin expression than healthy NM and that CF polyps (increased MUC5B) and AC polyps (decreased MUC2) have a different mucin expression pattern than bilateral NP.

A morphometric study of mucins and small airway plugging in cystic fibrosis

RATIONALE

Little knowledge exists on structural changes and plugging in small airways in cystic fibrosis.

OBJECTIVE

To characterise the extent of plugging and contribution of secreted mucins to the plugs.

METHODS

Small airways in patients with cystic fibrosis at transplantation (n = 18) were compared with control non-smokers (n = 10). Tissue sections were stained with Alcian blue (AB)/periodic acid-Schiff (PAS), for mucins MUC5B and MUC5AC, and for neutrophils and its chemoattractant interleukin (IL) 8. Epidermal growth factor receptor (EGFR) and its ligand pro-transforming growth factor alpha were also identified using immunohistochemical staining. Epithelial and luminal contents were assessed morphometrically.

RESULTS

Plugs occupying >50% of total luminal volume were found in 147 of 231 (63.6%) airways in patients with cystic fibrosis, but only in 1 of 39 (2.6%) airways in controls. In the epithelium of patients with cystic fibrosis, AB/PAS, MUC5B, and MUC5AC-stained volume densities were increased 10-fold (p < 0.01), indicating increased mucin production. In airway lumens, staining for mucins was also increased in cystic fibrosis, indicating increased mucin secretion. In the epithelium of patients with cystic fibrosis, neutrophil numbers were markedly increased and were inversely correlated with volume densities of mucous glycoconjugates (r = -0.66, p < 0.005). IL8 staining was increased in the epithelium of patients with cystic fibrosis and colocalised with mucins. Staining for EGFR and for pro-transforming growth factor alpha were increased in the epithelium of patients with cystic fibrosis; positive correlations were found between EGFR-stained volume density and both AB/PAS and IL8-stained volume densities.

CONCLUSIONS

Most of the small airways are plugged in cystic fibrosis at the time of transplantation. Mucins contribute to airway plugging. Recruited neutrophils may be involved in mucin secretion in the plugs. Increased expression of EGFR and its ligand suggests roles in mucin synthesis and neutrophil recruitment.

Identification of N-linked glycoproteins in human saliva by glycoprotein capture and mass spectrometry

Glycoproteins make up a major and important part of the salivary proteome and play a vital role in maintaining the health of the oral cavity. Because changes in the physiological state of a person are reflected as changes in the glycoproteome composition, mapping the salivary glycoproteome will provide insights into various processes in the body. Salivary glycoproteins were identified by the hydrazide coupling and release method. In this approach, glycoproteins were coupled onto a hydrazide resin, the proteins were then digested and formerly N-glycosylated peptides were selectively released with the enzyme PNGase F and analyzed by LC-MS/MS. Employing this method, coupled with in-solution isoelectric focusing separation as an additional means for pre-fractionation, we identified 84 formerly N-glycosylated peptides from 45 unique N-glycoproteins. Of these, 16 glycoproteins have not been reported previously in saliva. In addition, we identified 44 new sites of N-linked glycosylation on the proteins.

Relationships between mucinous gastric carcinoma, MUC2 expression and survival

AIM: To investigate the expression of the four secreted gel-forming mucins (MUC2, MUC5AC, MUC5B and MUC6) in a series of gastric carcinomas, classified according Laurén’s, Mulligan’s, WHO and Goseki’s classifications, with special attention to all the different components (major and minor) present in tumors and to follow up clinical data.

METHODS: Expression of MUC2, MUC5AC, MUC5B and MUC6 was investigated using immunohistochemistry and in situ hybridization.

RESULTS: Expression of secreted gel-forming mucins in gastric carcinoma was particularly complex, each mucin being not restricted to any histopathological type even considering all components (major and minor) present in a given tumor. There was a worst survival in patients with a higher content of mucus (Goseki II or IV) and high positive MUC2 expression.

CONCLUSION: Complexity of mucin gene expression patterns in gastric cancer may reflect a precise state of differentiation at the cell level not recognized in used morphologic classification systems. High expression of MUC2 was nevertheless associated with mucinous subtype of the WHO classification and with group II of Goseki’s classification identified by the major component of a particular tumor. The quantity and quality of mucus were related to survival.

Layer-by-layer assembly of mucin and chitosan--Influence of surface properties, concentration and type of mucin

Bovine submaxillary mucin (BSM) and chitosan were used to build layer-by-layer structures on solid substrates. The build-up was monitored using in situ ellipsometry to obtain time resolved values of the thickness and adsorbed amount. Additionally surface morphology during build-up was studied by atomic force microscopy (AFM). It was found that the adsorbed amount of the film increases approximately linearly with each deposition cycle on hydrophobized silica whereas construction on silica was found not to be possible at the experimental conditions used. We conclude that sufficient amount of the first mucin layer is crucial for the subsequent multilayer formation. The complex build-up kinetics on hydrophobized silica is characterized by adsorption and redissolution processes and the overall growth is the sum of both processes. AFM imaging on hydrophobized silica also confirmed the presence of redissolution processes and chitosan addition led to a reduction both in the number of surface aggregates and in the roughness of the surface. The present work also shows that by adjusting the relative concentrations of the polyelectrolytes it is possible to change the growth rate considerably. The final structures after deposition of 8 bilayers were found to have a high content of water and film stability test revealed that a substantial amount dissolves when increasing electrolyte concentration or pH of the ambient solution. Human mucin from saliva (MUC5B) was also used to create multilayers with chitosan on hydrophobized silica and it was revealed that no redissolution appears to be present in this system.

Nanomedicine for respiratory diseases

Nanotechnology provides new materials in the nanometer range with many potential applications in clinical medicine and research. Due to their unique size-dependent properties nanomaterial such as nanoparticles offer the possibility to develop both new therapeutic and diagnostic tools. Thus, applied nanotechnology to medical problems--nanomedicine--can offer new concepts that are reviewed. The ability to incorporate drugs into nanosystems displays a new paradigm in pharmacotherapy that could be used for cell-targeted drug delivery. Nontargeted nanosystems such as nanocarriers that are coated with polymers or albumin and solid lipid particles have been used as transporter in vivo. However, nowadays drugs can be coupled to nanocarriers that are specific for cells and/or organs. Thus, drugs that are either trapped within the carriers or deposited in subsurface oil layers could be specifically delivered to organs, tumors and cells. These strategies can be used to concentrate drugs in selected target tissues thus minimizing systemic side effects and toxicity. In addition to these therapeutic options, nanoparticle-based "molecular" imaging displays a field in which this new technology has set the stage for an evolutionary leap in diagnostic imaging. Based on the recent progress in nanobiotechnology there is potential for nanoparticles and -systems to become useful tools as therapeutic and diagnostic tools in the near future.

Respiratory tract mucin genes and mucin glycoproteins in health and disease

This review focuses on the role and regulation of mucin glycoproteins (mucins) in airway health and disease. Mucins are highly glycosylated macromolecules (> or =50% carbohydrate, wt/wt). MUC protein backbones are characterized by numerous tandem repeats that contain proline and are high in serine and/or threonine residues, the sites of O-glycosylation. Secretory and membrane-tethered mucins contribute to mucociliary defense, an innate immune defense system that protects the airways against pathogens and environmental toxins. Inflammatory/immune response mediators and the overproduction of mucus characterize chronic airway diseases: asthma, chronic obstructive pulmonary diseases (COPD), or cystic fibrosis (CF). Specific inflammatory/immune response mediators can activate mucin gene regulation and airway remodeling, including goblet cell hyperplasia (GCH). These processes sustain airway mucin overproduction and contribute to airway obstruction by mucus and therefore to the high morbidity and mortality associated with these diseases. Importantly, mucin overproduction and GCH, although linked, are not synonymous and may follow from different signaling and gene regulatory pathways. In section i, structure, expression, and localization of the 18 human MUC genes and MUC gene products having tandem repeat domains and the specificity and application of MUC-specific antibodies that identify mucin gene products in airway tissues, cells, and secretions are overviewed. Mucin overproduction in chronic airway diseases and secretory cell metaplasia in animal model systems are reviewed in section ii and addressed in disease-specific subsections on asthma, COPD, and CF. Information on regulation of mucin genes by inflammatory/immune response mediators is summarized in section iii. In section iv, deficiencies in understanding the functional roles of mucins at the molecular level are identified as areas for further investigations that will impact on airway health and disease. The underlying premise is that understanding the pathways and processes that lead to mucus overproduction in specific airway diseases will allow circumvention or amelioration of these processes.

TFF peptides and mucins are major components of dacryoliths

PURPOSE

The study was performed to determine whether trefoil factor peptides (TFF) and/or mucins are components of dacryoliths and to gain further insight into dacryolith composition and formation.

METHODS

Twenty dacryoliths found in lacrimal surgery in patients suffering from primary acquired nasolacrimal duct obstruction were analyzed for the presence of TFF peptides (TFF1, 2, 3), mucins (MUC1, 2, 3, 4, 5AC, 5B, 6, 7, 8), defense cells (T- and B lymphocytes, macrophages, neutrophils), and antimicrobial substances (alpha defensins 1-3, secretory phospholipase A(2)) by means of light microscopy, histochemistry, immunohistochemistry, reverse transcription-polymerase chain reaction (RT-PCR) and real-time PCR.

RESULTS

All dacryoliths except one revealed clear immunoreactivity for all three TFF peptides. The immunohistochemical distribution of mucins was inhomogeneous throughout the different dacryoliths. However, in some dacryoliths all mucins investigated were detected. MUC8 showed reactivity in 14 out of 15 dacryoliths analyzed by immunohistochemistry. Most dacryoliths contained alpha defensins 1-3 as the secretory product of neutrophils. T and B lymphocytes, macrophages and secretory phospholipase A(2) were only present in single dacryoliths. Quantification of TFF peptide expression supported the immunohistochemical finding that all three TFF peptides are augmented in dacryoliths.

CONCLUSIONS

Dacryoliths consist partly of secreted mucins comparable with the mucin spectrum of the epithelium of healthy nasolacrimal ducts. Beside TFF1 and TFF3, both of which are produced under healthy circumstances, TFF2 is additionally induced and secreted in cases of dacryolithiasis. All three TFF peptides appear to be augmented in dacryoliths. With regard to their rheologic properties, TFF peptides may play a functional role in dacryolith formation. However, our results raise the question of whether TFF peptides per se influence dacryolith formation or whether their secretion, as in secretion of mucins and alpha defensins 1-3, is merely a secondary phenomenon.

Prognostic value of mucins in the classification of ampullary carcinomas

The ampulla of Vater is of high clinical relevance with regard to influx of chyme, ascending inflammation, intubation during diagnostic and therapeutic endoscopic investigation, therapeutic papillotomy, and especially to malignant transformation. Little is known about the distribution of mucins in the ampulla. In this study, we have investigated the mucin distribution in the normal ampulla of Vater and compared it to duodenal mucosa and Brunner glands. Expression of mucins in the ampulla of Vater and duodenum was monitored by reverse transcription-polymerase chain reaction and localization of the products by immunohistochemistry. The samples investigated originated from 30 autopsy cases. Mucins MUC1, MUC3, MUC4, MUC5AC, MUC5B, MUC6, MUC7, and MUC8 were expressed in the ampulla of Vater. Immunohistochemistry revealed production of MUC4, MUC5AC, MUC5B, and MUC6. The mucin composition varied in comparison with the duodenum referring to MUC2, MUC7, and MUC8. Detected mucins contribute to innate immunity, epithelial restitution, and protection against the aggressive secretions of the liver, gall bladder, and pancreas. By cross-linking, they influence the rheological properties of the secretions in the ampulla and facilitate unidirectional flow into the duodenum. Knowledge of their pattern of expression has prognostic value with regard to the detection of malignancy. The observed differences in the mucin distribution between the duodenum and the ampulla of Vater support the use of MUC2, MUC7, and MUC8 as useful tool in the classification of ampullary carcinomas.

Regulation of mucin expression: mechanistic aspects and implications for cancer and inflammatory diseases

Mucins are large multifunctional glycoproteins whose primary functions are to protect and lubricate the surfaces of epithelial tissues lining ducts and lumens within the human body. Several lines of evidence also support the involvement of mucins in more complex biological processes such as epithelial cell renewal and differentiation, cell signaling, and cell adhesion. Recent studies have uncovered the role of select mucins in the pathogenesis of cancer, underscoring the importance of a detailed knowledge about mucin biology. Under normal physiological conditions, the production of mucins is optimally maintained by a host of elaborate and coordinated regulatory mechanisms, thereby affording a well-defined pattern of tissue-, time-, and developmental state-specific distribution. However, mucin homeostasis may be disrupted by the action of environmental and/or intrinsic factors that affect cellular integrity. This results in an altered cell behavior that often culminates into a variety of pathological conditions. Deregulated mucin production has indeed been associated with numerous types of cancers and inflammatory disorders. It is, therefore, crucial to comprehend the underlying basis of molecular mechanisms controlling mucin production in order to design and implement adequate therapeutic strategies for combating these diseases. Herein, we discuss some physiologically relevant regulatory aspects of mucin production, with a particular emphasis on aberrations that pertain to pathological situations. Our views of the achievements, the conceptual and technical limitations, as well as the future challenges associated with studies of mucin regulation are exposed.

Treatment of airway mucus hypersecretion

Airway mucus hypersecretion is now recognized as a key pathophysiological feature in many patients with asthma, chronic obstructive pulmonary disease (COPD) and cystic fibrosis. Consequently, it is important to develop drugs that inhibit mucus hypersecretion in these susceptible patients. Conventional therapies, including anticholinergics, ss2-adrenoceptor agonists, corticosteroids, mucolytics and macrolide antibiotics, have variable efficacy in inhibiting airway mucus hypersecretion, and are less effective in COPD than in asthma. Novel pharmacotherapeutic targets are being investigated, including inhibitors of nerve activity (e.g. large conductance calcium-activated potassium, BKCa, channel activators), tachykinin receptor antagonists, epoxygenase inducers (e.g. benzafibrate), inhibitors of mucin exocytosis (e.g. anti-myristoylated alanine-rich C kinase substrate (MARCKS), peptide and Munc-18B blockers), inhibitors of mucin synthesis and goblet cell hyperplasia (e.g. epidermal growth factor (EGF), receptor tyrosine kinase inhibitors, p38 mitogen-activated protein (MAP), kinase inhibitors, MAP kinase kinase/extracellular signal-regulated kinase (MEK/ERK), inhibitors, human calcium-activated chloride (hCACL2), channel blockers and retinoic acid receptor-a antagonists), inducers of goblet cell apoptosis (e.g. Bax inducers or Bcl-2 inhibitors), and purinoceptor P(2Y2) antagonists to inhibit mucin secretion or P(2Y2) agonists to hydrate secretions. However, real and theoretical differences delineate the mucus hypersecretory phenotype in asthma from that in COPD. More information is required on these differences to identify specific therapeutic targets which, in turn, should lead to rational design of anti-hypersecretory drugs for treatment of airway mucus hypersecretion in asthma and COPD.

Differential regulation of MUC5AC/Muc5ac and hCLCA-1/mGob-5 expression in airway epithelium

This study demonstrates that the two biomarkers, MUC5AC/ Muc5ac and hCLCA1/Gob5, which are frequently associated with surface mucous/goblet cells in asthmatic airways, are differentially regulated. Intratracheal instillation of IL-13 (0.5 mug/mouse lung) elicited 8- and 110-fold induction of Muc5ac and Gob5 messages, respectively, within 24 h in wild-type mouse lung, whereas these inductions were abrogated in Stat6 knockout mice. The induction of MUC5AC/Muc5ac message could not be duplicated in vitro with primary tracheobronchial epithelial (TBE) cells derived from wild-type mice or humans, despite significant inductions still seen for hCLCA1/Gob5. Further studies with JAK inhibitors and STAT6 signaling showed active signaling of the JAK/STAT6 pathway in these primary TBE cultures by IL-13 in the regulation of hCLCA1 expression. Dual immunofluorescent staining with antibodies specific to MUC5AC and hCLCA1 revealed a differential nature of the expression of these two biomarkers by distinct cell types of primary TBE cultures. Finally, MUC5AC expression could be elevated by a bacterial product, peptidoglycan, without any induction of hCLCA1. Thus, these results suggest that the two biomakers of the metaplastic airway mucous cell type are differentially regulated by JAK/STAT6-dependent and -independent pathways.

Immunohistochemical analysis of MUC5B apomucin expression in breast cancer and non-malignant breast tissues

A deregulation of several MUC genes (MUC1, MUC2, MUC3, MUC5AC, and MUC6) was previously demonstrated in breast carcinomas. Considering that recently we found the "non-mammary" MUC5B mRNA in primary breast tumors (Berois et al. 2003), we undertook the present study to evaluate the expression profile of MUC5B protein product in breast tissues, using LUM5B-2 antisera raised against sequences within the non-glycosylated regions of this apomucin. Expression of MUC5B by breast cancer cells was confirmed by immunocytochemistry, in situ hybridization, and Western blot on MCF-7 cancer cells. Using an immunohistochemical procedure, MUC5B apomucin was detected in 34/42 (81%) primary breast tumors, in 13/14 (92.8%) samples of non-malignant breast diseases, in 8/19 (42.1%) samples of normal-appearing breast epithelia adjacent to cancer, and in 0/5 normal control breast samples. The staining pattern of MUC5B was very different when comparing breast cancer cells (cytoplasmic) and non-malignant breast cells (predominantly apical and in the secretory material). We analyzed MUC5B mRNA expression using RT-PCR in bone marrow aspirates from 22/42 patients with breast cancer to compare with MUC5B protein expression in the primary tumors. Good correlation was observed because the six MUC5B-positive bone marrow samples also displayed MUC5B expression in the tumor. Our results show, for the first time at the protein level, that MUC5B apomucin is upregulated in breast cancer. Its characterization could provide new insights about the glycobiology of breast cancer cells.

Expression of Membrane-Bound Mucins (MUC1 and MUC4) and Secreted Mucins (MUC2, MUC5AC, MUC5B, MUC6 and MUC7) in Mucoepidermoid Carcinomas of Salivary Glands

Mucins are glycoproteins normally synthesized by a variety of secretory epithelial cells. The aim of this study was to investigate the expression of mucins (MUC1, MUC2, MUC4, MUC5AC, MUCB, MUC6, MUC7) in mucoepidermoid carcinomas, the most frequent malignant tumor of salivary glands. Forty mucoepidermoid carcinomas and twenty-two normal salivary glands were studied for these mucins by immunohistochemistry from formalin-fixed and paraffin-embedded material. Normal salivary glands frequently expressed MUC1 and MUC4, mainly in ductal cells; MUC5B and MUC7 stained mucous and serous acini respectively of submandibular and minor salivary glands; and MUC5AC and MUC2 were poorly detected in excretory ducts. All mucoepidermoid carcinomas expressed MUC1, and 38/40 tumors expressed MUC4. Both membrane-bound mucins stained membranes and cytoplasm of all cell types (epidermoid, intermediate, mucous, clear and columnar). MUC5AC and MUC5B stained glandular differentiated cells in most tumors (29/40 and 33/40 cases, respectively). MUC6 was positive in 13/40 tumors, and both MUC2 and MUC7 in only 2/40 tumors. The high expression of MUC1 was related to high histologic grades, high recurrence and metastasis rates and a shorter disease-free interval (P < 0.05). Conversely, MUC4 high expression was mainly related to low-grade tumors, lower recurrence rates and a longer disease-free interval (P < 0.05). In conclusion, mucoepidermoid carcinomas of salivary glands usually express MUC1, MUC4, MUC5AC and MUC5B; less frequently MUC6; and rarely MUC2 and MUC7. This mucin expression pattern can be useful for diagnostic purposes. Therefore, MUC1 expression is related to tumor progression and worse prognosis, whereas MUC4 expression is related to a better prognosis.

Mucin gene expression in nasal polyps

CONCLUSIONS

A large set of mucin genes is expressed in nasal polyps. The expression pattern is complex and may reflect the wide spectrum of variables involved in polyp formation and progression. Prospective studies including subgroups of nasal polyps and involving substantial numbers of cases in each subgroup will be required to elucidate these variables and to understand how they affect mucus secretion.

OBJECTIVE

At present, 15 of the 19 known mucin genes are expressed in the human airways. Nasal polyps might be expected to have a mucin expression pattern comparable to that of the airways. The aim of this study was to investigate mucin expression in nasal polyps.

MATERIAL AND METHODS

Nasal polyp samples were obtained from 20 patients during functional endoscopic sinus surgery. Normal (control) sphenoid sinus mucosa was obtained from patients undergoing trans-sphenoid hypophysectomy. The expression of eight mucin genes (MUC1-4, -5AC, -5B, -6 and -7) was studied by in situ hybridization utilizing digoxigenin-labelled oligonucleotide probes.

RESULTS

MUC6 and -7 were not expressed in sphenoid sinus mucosa, while all the studied mucin genes were expressed in nasal polyps. Expression patterns varied widely between individual polyps. The predominant epithelial mucin genes were MUC4, -5AC and -3, while MUC5B and -7 were mainly of glandular origin. MUC1, -2 and -6 were weakly expressed. The major alteration in gene expression in nasal polyps was found in the submucosal glands. MUC4 and -5AC represent a major component of both submucosal glands and epithelial cells in nasal polyps.

Promoter Analysis and Aberrant Expression of theMUC5BGene in Diffuse Panbronchiolitis

Diffuse panbronchiolitis (DPB) is a chronic inflammatory airway disease predominantly affecting Asian populations. DPB is considered to be a complex genetic disease. Considering the mucous hypersecretion of the disease, we hypothesized that the transcriptional activity of mucin genes may be altered in DPB. We analyzed nucleotide sequences of regulatory region of six mucin genes--MUC1, MUC2, MUC4, MUC5AC, MUC5B, and MUC7--and detected their promoter polymorphisms. Among them, the insertion/deletion polymorphism identified in the MUC5B gene was significantly associated with the disease (p = 0.0001). Transcriptional activity observed in the three major promoter haplotypes corresponded to the strength of the disease association in which these haplotypes are involved. Immunohistochemistry of the lung tissues of DPB revealed that MUC5B was abundantly expressed not only in bronchial glands but also in increased numbers of goblet cells on the bronchial surface, where MUC5AC is predominant and MUC5B expression is generally scarce in the normal lung. Marked mucous hypersecretion observed in DPB may be partly explained by increased and aberrant expression of MUC5B. The possible involvement of MUC5B gene in DPB was demonstrated. A further role of the MUC5B polymorphism in its pathogenesis should be studied in the future.

The role of mRNA stability in airway remodelling

As a consequence of long-term exposure to inflammatory mediators, the airways of asthmatics become remodelled. Airway fibrosis becomes apparent, with thickening of the lamina recticularis and increased interstitial matrix deposition being typical features of an asthmatic airway. Mucus hypersecretion occurs, airway smooth muscle mass is increased and neovascularization is evident in the subepithelial mucosa. As development of a remodelled airway is correlated with deterioration of lung function in asthmatics, there is an urgent need for therapies that reduce airway inflammation and reverse structural changes in a remodelled airway. However, in order to design efficacious anti-remodelling agents we first need a greater understanding of the molecular mechanism/s underlying the development of airway remodelling. To date, however, most studies have primarily focused on the transcriptional regulation of genes that promote airway remodelling. Post-transcriptional mechanisms, such as control of mRNA stability, remain largely unexplored. Levels of cellular mRNA transcripts are regulated by controlling the rate at which the mRNA decays, thus investigation into the mechanisms underlying mRNA stability in asthma are of critical importance. Therefore, this review will present an overview of the control of mRNA stability and examine how mRNA stability may play a role in the development of airway remodelling in asthma.

An enzyme-linked immunosorbent assay (ELISA) for the determination of mucin levels in bronchoalveolar lavage fluid

INTRODUCTION

A method to measure the mucin concentration in bronchoalveolar lavage (BAL) fluid was developed to aid efforts to identify pharmacologically the mechanisms that modulate pathophysiological mucin secretion. Mucins are the major macromolecular components of mucus. In the airways, mucus is the first line of defense against inhaled microorganisms (infection) and particulates (irritation).

METHODS

An enzyme-linked immunosorbent assay (ELISA) was developed, comparing two monoclonal anti-mucin antibodies (A10G5 and 45M1) raised to human mucin, to quantify the mucin in BAL fluid from animal models of pulmonary inflammation. To validate the ELISA method, rats were exposed to ovalbumin (OVA, in sensitized rats), lipopolysaccharide (LPS), vanadium pentoxide (V(2)O(5)), or saline. One hundred microliters of BAL fluid was analyzed for mucin concentration. Pooled BAL fluid from untreated rats was used as an internal "plate standard", as a standard mucin that cross-reacts with A10G5 was unavailable.

RESULTS

We found both antibodies reacted with rat, human, and guinea-pig mucin; where the 45M1 antibody also reacted with the mucin in porcine BAL, while A10G5 did not. We determined the mucin concentration in each BAL fluid sample relative to the standard, defined as a mucin concentration of 100 plate units. BAL fluid from LPS (218+/-25 plate units, n=5), OVA (386+/-31, n=3), V(2)O(5) (1208+/-450, n=6) challenged rats displayed significantly elevated mucin concentration over their saline controls (126+/-22, n=12). Subsequently, the 45M1 antibody displayed immunoreactivity with a commercially available crude preparation of porcine stomach mucin, allowing us to calculate the concentration of mucin directly compared to the known concentration of the porcine stomach mucin standard. Both the 45M1 and A10G5 based ELISA assays detected higher mucin content in the saline challenged rat than the saline challenged guinea pig BAL.

DISCUSSION

The recent availability of the 45M1 antibody and the use of the crude purification of porcine stomach mucin as a reference standard should allow for direct comparison of mucin concentration in BAL (and other fluids).

Altered O-glycosylation and sulfation of airway mucins associated with cystic fibrosis

Cystic fibrosis (CF) is the most lethal genetic disorder in Caucasians and is characterized by the production of excessive amounts of viscous mucus secretions in the airways of patients, leading to airway obstruction, chronic bacterial infections, and respiratory failure. Previous studies indicate that CF-derived airway mucins are glycosylated and sulfated differently compared with mucins from nondiseased (ND) individuals. To address unresolved questions about mucin glycosylation and sulfation, we examined O-glycan structures in mucins purified from mucus secretions of two CF donors versus two ND donors. All mucins contained galactose (Gal), N-acetylglucosamine (GlcNAc), N-acetylgalactosamine (GalNAc), fucose (Fuc), and sialic acid (Neu5Ac). However, CF mucins had higher sugar content and more O-glycans compared with ND mucins. Both ND and CF mucins contained GlcNAc-6-sulfate (GlcNAc-6-Sul), Gal-6-Sul, and Gal-3-Sul, but CF mucins had higher amounts of the 6-sulfated species. O-glycans were released from CF and ND mucins and derivatized with 2-aminobenzamide (2-AB), separated by ion exchange chromatography, and quantified by fluorescence. There was nearly a two-fold increase in sulfation and sialylation in CF compared with ND mucin. High performance liquid chromatography (HPLC) profiles of glycans showed differences between the two CF samples compared with the two ND samples. Glycan compositions were defined by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). Unexpectedly, 260 compositional types of O-glycans were identified, and CF mucins contained a higher proportion of sialylated and sulfated O-glycans compared with ND mucins. These profound structural differences in mucin glycosylation in CF patients may contribute to inflammatory responses and increased pathogenesis by Pseudomonas aeruginosa.

MUC5B glycosylation in human saliva reflects blood group and secretor status

This study aimed to characterize human salivary glycoforms and the natural glycosylation variation of the major ABO blood group bearing high molecular weight glycoprotein fraction MG1, which mainly consists of MUC5B mucin. Reduced and alkylated mucins from individuals of blood group A, B, and O were purified by sodium dodecyl sulfate-agarose/polyacrylamide composite gel electrophoresis (SDS-AgPAGE), blotted to polyvinylidene fluoride (PVDF) membranes, and visualized with alcian blue. O-linked oligosaccharides were released from MUC5B glycoform bands by reductive beta-elimination and analyzed by liquid chromatography (LC) electrospray ion trap mass spectrometry (MS). Slow electrophoretically migrating MUC5B components (sm) were found to be dominated by neutral oligosaccharides, and fast-migrating (fm) components were dominated by sulfated oligosaccharides. ABO blood group-specific sequences were found on all glycoforms, and novel oligosaccharides containing blood group A and B type sequences were sequenced. This is the first molecular description of the influence of the blood group ABO system on salivary MUC5B oligosaccharides. Expanding these results from the three A, B, and O individuals into larger population (29 individuals), we found oligosaccharide sequences corresponding to the blood group of the donor on MUC5B from 23 individuals. The remaining six individuals were characterized by a high degree of sialylation. These individuals were assigned as nonsecretors, whereas blood group-expressing individuals were assigned as secretors. Western blot assays with antibodies confirmed increased expression of Sialyl Lewis a (Si-Le(a)) in the nonsecretors. Our results highlight that salivary MUC5B consists of glycoforms with distinct glycosylation that vary extensively between individuals and that some of this variation is owing to blood group and secretor status.

Rhesus monkey gastric mucins: oligomeric structure, glycoforms and Helicobacter pylori binding

Mucins isolated from the stomach of Rhesus monkey are oligomeric glycoproteins with a similar mass, density, glycoform profile and tissue localization as human MUC5AC and MUC6. Antibodies raised against the human mucins recognize those from monkey, which thus appear to be orthologous to those from human beings. Rhesus monkey muc5ac and muc6 are produced by the gastric-surface epithelium and glands respectively, and occur as three distinct glycoforms. The mucins are substituted with the histo blood-group antigens B, Le(a) (Lewis a), Le(b), Le(x), Le(y), H-type-2, the Tn-antigen, the T-antigen, the sialyl-Le(x) and sialyl-Le(a) structures, and the expression of these determinants varies between individuals. At neutral pH, Helicobacter pylori strains expressing BabA (blood-group antigen-binding adhesin) bind Rhesus monkey gastric mucins via the Le(b) or H-type-1 structures, apparently on muc5ac, as well as on a smaller putative mucin, and binding is inhibited by Le(b) or H-type-1 conjugates. A SabA (sialic acid-binding adhesin)-positive H. pylori mutant binds to sialyl-Le(x)-positive mucins to a smaller extent compared with the BabA-positive strains. At acidic pH, the microbe binds to mucins substituted by sialylated structures such as sialyl-Le(x) and sialylated type-2 core, and this binding is inhibited by DNA and dextran sulphate. Thus mucin- H. pylori binding occurs via at least three different mechanisms: (1) BabA-dependent binding to Le(b) and related structures, (2) SabA-dependent binding to sialyl-Le(x) and (3) binding through a charge-mediated mechanism to sialylated structures at low pH values.

MUC5AC and MUC5B Mucins Are Decreased in Cystic Fibrosis Airway Secretions

Cystic fibrosis (CF) is characterized by progressive airway obstruction. Although it has been postulated that this is due in part to mucus hypersecretion, there are no published data showing an increase in the gel-forming mucins MUC5AC or MUC5B in CF secretions. We used confocal microscopy to assess the amount of mucin-like glycoprotein and DNA in CF sputum and found more mucin in bronchitis sputum and a much greater amount of DNA in CF sputum. We then used antibodies to MUC5AC and MUC5B with Western gels and dot-blot to quantify mucin in sputum from 12 patients with CF and 11 subjects without lung disease. There was a 70% decrease in MUC5B and a 93% decrease in MUC5AC in CF sputum (P < 0.005 for both). We conclude that the vol/vol concentration of MUC5AC and MUC5B are decreased in the CF airways relative to normal mucus. This may be due to a relative increase in other components of sputum in the CF airway or to a primary defect in mucin secretion in CF.

Regulation of MUC5AC mucin secretion and airway surface liquid metabolism by IL-1beta in human bronchial epithelia

Mucociliary transport in the airways significantly depends on the liquid and mucin components of the airway surface liquid (ASL). The regulation of ASL water and mucin content during pathological conditions is not well understood. We hypothesized that airway epithelial mucin production and liquid transport are regulated in response to inflammatory stimuli and tested this hypothesis by investigating the effects of the pleiotropic, early-response cytokine, IL-1beta, on cultured primary human bronchial epithelial and second-passage, normal human tracheo-bronchial epithelial (NHTBE) cell cultures. Fully differentiated NHTBE cultures secreted two major airway mucins, MUC5AC and MUC5B. IL-1beta, in a dose- and time-dependent manner, increased the secretion of MUC5AC, but not MUC5B. MUC5AC mRNA levels were only transiently increased at 1 and 4 h after the start of IL-1beta treatment and returned to control levels thereafter, even though MUC5AC mucin production remained elevated for at least 72 h. Synchronous with elevated MUC5AC secretion, ASL volume increased, its percentage of solid was reduced, and the pH/[HCO(3)(-)] of the ASL was elevated. ASL volume changes reflected altered ion transport, including an upregulation of Cl(-) secretory currents (via CFTR and Ca(2+)-activated Cl(-) conductance) and an inhibition of epithelial sodium channel (ENaC)-mediated absorptive Na(+) currents. IL-1beta increased CFTR mRNA levels without affecting those for ENaC subunits. The synchronous regulation of ASL mucin and liquid metabolism triggered by IL-1beta may be an important defense mechanism of the airway epithelium to enhance mucociliary clearance during airway inflammation.

New Monoclonal Antibodies to Non-Glycosylated Domains of the Secreted Mucins MUC5B and MUC7

The separation and characterization of salivary mucins is not straightforward because of their large size, heterogeneity, and molecular interactions. The MUC5B and MUC7 mucins are major glycoprotein components of saliva that are thought to play a vital role in maintaining oral health. MUC5B is also a major component of respiratory mucus and is produced by the tracheal and bronchial glands, while MUC7 has a more limited pattern of expression in the bronchial tree. MUC5B is a gel-forming mucin and thus confers viscosity, whereas MUC7 is much smaller. MUC7 has anti-fungal activity, and both mucins interact with bacteria. The aim of this work was to produce new monoclonal antibodies that can be used to quantify and characterize these mucins by standard laboratory procedures. Peptide sequences in non-conserved and non-glycosylated regions were selected and monoclonal antibodies produced by an efficient immunization and cloning strategy, and screening against purified mucins. Three new antibodies-EU-MUC5Ba and EU-MUC5Bb (against MUC5B) and EU-MUC7a (against MUC7)-were isolated that do not show cross-reactivity with other gel-forming mucins. All work on immunohistochemistry can be used for semi-quantitative immunoblotting after agarose gel electrophoresis. These reagents are valuable tools to study changes in these mucins in oral and respiratory disease, and unlike other monoclonal antibodies to these mucins they recognize epitopes that are not affected by glycosylation.

Calcium-dependent protein interactions in MUC5B provide reversible cross-links in salivary mucus

The macromolecular organization within saliva was investigated by tracer diffusion measurements of fluorescent polystyrene microspheres by fluorescence recovery after photobleaching using a confocal microscope (confocal-FRAP). There was a concentration-dependent reduction in microsphere diffusion; this was much greater in the presence of calcium (10 mm) and was reduced by the addition of EGTA (10 mm). These effects on tracer diffusion showed that native saliva contained a macromolecular organization that was sensitive to free calcium concentrations. This was supported by a major increase in the weight average molecular weight of the high molecular weight mucin fraction in saliva (10-62 x 106) and an increase in intrinsic viscosity of saliva (733 to 1203 ml/g) both caused by calcium. Analysis of the change in tracer diffusion in saliva showed a 20-fold increase in the apparent pore size (from 130 nm in 10 mm CaCl2 to 2600 nm in 10 mm EGTA at physiological concentration). The effect was specific for calcium and was unaffected by up to 2 m NaCl. The calcium binding activity was contained in a high buoyant density fraction of saliva excluded from Sepharose CL-2B. Calcium binding to this fraction gave an approximate Kd of 7 x 10-6 m, and the binding was irreversibly destroyed by treatment with 6 m guanidinium chloride and by mild reduction, suggesting it to be to a protein site. This fraction of saliva was shown to contain MUC5B as the single major protein species by positive ion electrospray ionization-tandem mass spectrometry analysis. The results suggested that oligomeric MUC5B in saliva is assembled into much larger linear or branched assemblies through calcium-mediated protein cross-links.

Mucin-rich variant of salivary duct carcinoma: a clinicopathologic and immunohistochemical study of four cases

Salivary duct carcinoma is a relatively uncommon aggressive neoplasm, typically found in the parotid glands of older men. The histologic appearance is that of an in situ and invasive high-grade adenocarcinoma, and it closely resembles ductal carcinoma of the breast. Several variants of the latter are very well known, but only papillary, sarcomatoid, and low-grade subtypes have so far been reported in salivary duct carcinoma. This study describes the clinicopathologic and immunohistochemical findings in four examples of an additional previously undescribed variant, rich in mucin. Each tumor showed areas of typical salivary duct carcinoma, but in addition there were lakes of epithelial mucin-containing malignant cells, i.e., mucinous (colloid) carcinoma. All four tumors expressed androgen receptors, cytokeratins, epithelial membrane antigen, gross cystic disease fluid protein-15, and carcinoembryonic antigen, but S-100 protein, other myoepithelial markers, and estrogen and progesterone receptors were negative. The mucin antigen profile showed positivity for MUC2, MUC5B, and MUC6 in all cases but only rare staining with MUC5AC and MUC7. Strong immunohistochemical overexpression of HER2/neu was demonstrated in one tumor, together with amplification by fluorescence in situ hybridization; another case was weakly positive with just one antiserum, but the remaining two tumors were completely negative. Small quantities of mucin have often been described in salivary duct carcinoma but not large extracellular mucinous lakes, which though prominent in the present series, were not as extensive as in mucinous adenocarcinoma. The relatively poor clinical outcome of the patients in our study mirrored that seen in usual-type salivary duct carcinoma and emphasizes the importance of differentiating mucin-rich salivary duct carcinoma from pure mucinous (colloid) adenocarcinoma, a tumor not fully defined, but possibly with a better prognosis.

Interleukin-1 beta and tumor necrosis factor-alpha induce MUC5AC overexpression through a mechanism involving ERK/p38 mitogen-activated protein kinases-MSK1-CREB activation in human airway epithelial cells

Mucin hypersecretion is commonly observed in many inflammatory diseases of the respiratory tract. MUC5AC is generally recognized to be a major airway mucin because MUC5AC is highly expressed in the goblet cells of human airway epithelium. Moreover, it is regulated by various inflammatory cytokines. However, the mechanisms by which the interleukin (IL)-1beta and tumor necrosis factor (TNF)-alpha induce MUC5AC gene expression in normal nasal epithelial cells, and the signal molecules involved, especially in the downstream signaling of mitogen-activated protein (MAP) kinases, remain unclear. Here we show that pharmacologic or genetic inhibition of either ERK or p38 MAP kinase pathway abolished IL-1beta- and TNF-alpha-induced MUC5AC gene expression in normal human nasal epithelial cells. Our results also indicate that the activation of mitogen- and stress-activated protein kinase 1 (MSK1) and cAMP-response element-binding protein and cAMP-response element signaling cascades via ERK and p38 MAP kinases are crucial aspects of the intracellular mechanisms that mediate MUC5AC gene expression. Taken together, these studies give additional insights into the molecular mechanism of IL-1beta- and TNF-alpha-induced MUC5AC gene expression and enhance our understanding on mucin hypersecretion during inflammation.

High levels of sulfated mucins in bronchoalveolar lavage fluid of ICU patients with ventilator-associated pneumonia

OBJECTIVE

To compare the levels of sulfated mucins in bronchoalveolar lavage fluid (BALF) in ICU patients with ventilator-associated pneumonia (VAP) with those in non-infectious controls, i.e., ventilated ICU patients without VAP, and nonventilated patients.

DESIGN AND SETTING

Prospective study in a mixed intensive care unit and outpatient clinic of a university hospital.

PATIENTS

The study included 56 ventilated ICU patients with VAP, 21 ventilated ICU patients without VAP, and 26 nonventilated outpatients with no pulmonary infection.

MEASUREMENTS AND RESULTS

Total cell count and differential cell count of BALF samples were determined, and sulfated mucin levels were measured. For this we used the monoclonal antibody F2 against the sulfated Lewis C structure (SO(3)-3Galbeta1-3GlcNAc). Sulfated mucin levels were significantly increased in ICU patients with VAP than in those without VAP and nonventilated patients. No statistical difference was found between the two groups of ICU patients regarding APACHE II score and the duration of mechanical ventilation prior to the bronchoalveolar lavage.

CONCLUSIONS

The increased levels of sulfated mucins in ICU patients with VAP are associated with infection and not with ventilation. The increase in sulfated mucins may favor the persistence of those micro-organisms that possess mucin sulfatase activity, which enable them to survive within the mucus, especially Pseudomonas aeruginosa.

Distribution of respiratory mucin proteins in human nasal mucosa

OBJECTIVES/HYPOTHESIS

The upper respiratory tract is involved in many acute and chronic respiratory tract diseases that present with the symptom of mucus hypersecretion. Mucin genes that encode for the backbone of glycoproteins contribute to the viscoelastic property of airway mucus. We examined the cellular expression and distribution of two major respiratory mucus-forming glycoproteins, MUC5AC and MUC5B, in normal human nasal tissues.

METHODS

Immunohistochemical analysis using polyclonal antibodies against the mucins MUC5AC and MUC5B was performed in normal human nasal tissues.

RESULTS

An abundant staining of submucosal mucus gland and epithelial goblet cells for MUC5B was found. Immunohistochemical analysis of MUC5AC showed staining of surface epithelium goblet cells, whereas there was no staining of glandular cells. Comparison of the expression to lower airways revealed a similar pattern of expression of both mucins.

CONCLUSIONS

The data in the present study demonstrated the localization of the two major respiratory mucin proteins in human nasal mucosa with a similar distribution of expression of MUC5AC and MUC5B in normal upper and lower airways. Mucin protein expression parallels that of mucin messenger RNA expression.

A high-density putative monomeric mucin is the major [35S]labelled macromolecular product of human colorectal mucins in organ culture

We have studied the biosynthesis of mucins in organ cultures of human colon using isopycnic density-gradient centrifugation following pulse labelling with [(35)S]sulphate and [(3)H]-D-glucosamine. A high-density [(35)S]sulphate labelled component, of larger size than MUC2 monomers, appeared in the tissue and also in the medium. It was not degraded by reduction, trypsin digestion, digestion with chondroitin ABC lyase or heparan sulphate III lyase, but was cleaved into smaller fragments following alkaline borohydride treatment and appears to be a monomeric, mucin-like molecule containing a protease-resistant domain with a larger hydrodynamic volume than MUC2 monomers. Although this macromolecule incorporated much more radiolabel than MUC2, it was not detected using chemical analysis and thus appears to be a component with a high metabolic turnover present in a very small amount. Most of the [(3)H]-D-glucosamine label was associated with low-density material that was well separated from MUC2, which was poorly labelled. Most of MUC2 was associated with the tissue as an 'insoluble' complex. The amount of MUC2 remained constant and its associated radiolabel increased only slightly with time. Analysis of the MUC2 subunits from the reduced 'insoluble' complex showed the typical reduction-insensitive oligomers and confirmed that the radiolabel was associated with this mucin. The large size of the [(35)S]-labelled putative monomeric mucin makes it difficult to separate it from reduced insoluble complex MUC2. As a result, many studies of intestinal mucin synthesis and secretion in the past have most likely been performed on 'mixtures' of this mucin and MUC2 and are thus not possible to interpret as the metabolic behaviour of oligomeric mucins.

Strain- and blood group-dependent binding of Helicobacter pylori to human gastric MUC5AC glycoforms

BACKGROUND & AIMS

In the stomach, Helicobacter pylori is found both in the mucus layer and adhering to the gastric epithelium. The aim of this study is to characterize the binding of H. pylori to human gastric mucins.

METHODS

H. pylori strains that bind the Lewis(b) (Le(b)) structure (via the BabA adhesin) and/or sialylated structures, along with isogenic adhesion deletion mutants, were used to identify microbe-binding mucins. Gastric mucins from 5 healthy individuals, isolated by density-gradient centrifugation, were investigated for H. pylori binding at neutral pH using a microtiter-based technique.

RESULTS

H. pylori strains that express the BabA adhesins were shown to bind to the MUC5AC mucin in individuals expressing the Le(b) antigen. Further fractionation with an ion-exchange chromatography revealed Le(b)-positive MUC5AC glycoforms that differed in their receptor properties for different H. pylori strains. None of the H. pylori strains studied bound to mucins from Le(b)-negative individuals. However, all strains bound to low-density, nonmucin, Le(b)-negative material on top of the gradients.

CONCLUSIONS

Binding of H. pylori to human gastric MUC5AC isolated from healthy individuals is BabA dependent and mediated by the Le(b) structure presented by the mucin. However, the BabA adhesins demonstrate strain-dependent preference in binding to MUC5AC glycoforms substituted with Le(b), allowing for great interindividual variability in host-microbe interactions.

Airway mucus: its components and function

The airway surface liquid (ASL), often referred to as mucus, is a thin layer of fluid covering the luminal surface of the airway. The major function of mucus is to protect the lung through mucociliary clearance against foreign particles and chemicals entering the lung. The mucus is comprised of water, ions, and various kinds of macromolecules some of which possess the protective functions such as anti-microbial, anti-protease, and anti-oxidant activity. Mucus glycoproteins or mucins are mainly responsible for the viscoelastic property of mucus, which is crucial for the effective mucociliary clearance. There are at least eight mucin genes identified in the human airways, which will potentially generate various kinds of mucin molecules. At present, neither the exact structures of mucin proteins nor their regulation are understood although it seems likely that different types of mucins are involved in different functions and might also be associated with certain airway diseases. The fact that mucins are tightly associated with various macromolecules present in ASL seems to suggest that the defensive role of ASL is determined not only by these individual components but rather by a combination of these components. Collectively, mucins in ASL may be compared to aircraft carriers carrying various types of weapons in defense of airbome enemies.

Heterogeneity and persistence length in human ocular mucins

Atomic force microscopy (AFM) has been used to investigate the heterogeneity and flexibility of human ocular mucins and their subunits. We have paid particular attention, in terms of theory and experiment, to the problem of inducing the polymers to assume equilibrium conformations at a surface. Mucins deposited from a buffer containing Ni(2+) ions adopt extended conformations on mica akin to those observed for DNA under similar conditions. The heterogeneity of the intracellular native mucins is evident from a histogram of contour lengths, reflecting, in part, the diversity of mucin gene products expressed. Reduction of the native mucin with dithiothreitol, thereby breaking the S==S bonds between cysteine residues, causes a marked reduction in polymer length. These results reflect the modes of transport and assembly of newly synthesized mucins in vivo. By modifying the worm-like chain model for applicability to two dimensions, we have confirmed that under the conditions employed mucin adsorbs to mica in an equilibrated conformation. The determined persistence length of the native mucin, 36 nm, is consistent with that of an extended, flexible polymer; such characteristics will influence the properties of the gels formed in vivo.

Induction of MUC2 and MUC5AC mucins by factors of the epidermal growth factor (EGF) family is mediated by EGF receptor/Ras/Raf/extracellular signal-regulated kinase cascade and Sp1

The 11p15 mucin genes (MUC2, MUC5AC, MUC5B and MUC6) possess a cell-specific pattern of expression in normal lung that is altered during carcinogenesis. Growth factors of the epidermal growth factor family are known to target key genes that in turn may affect the homeostasis of lung mucosae. Our aim was to study the regulation of the 11p15 mucin genes both at the promoter and protein levels to assess whether their altered expression may represent a key event during lung carcinogenesis. Studies were performed in the mucoepidermoid NCI-H292 lung cancer cell line. Cell treatment with epidermal growth factor (EGF), transforming growth factor alpha (TGF-alpha), or tumor necrosis factor alpha (TNF-alpha) resulted in a dramatic increase of MUC2 and MUC5AC mRNAs levels, promoter activity, and apomucin expression, whereas those of MUC5B and MUC6 were unchanged. pGL3 deletion mutants of MUC2, MUC5AC, and MUC5B promoters were constructed and used in transient transfection assays to characterize EGF- and TGF-alpha-responsive regulatory regions within the promoters. They were located in the -2627/-2097 and -202/-1 regions of MUC2 and MUC5AC promoters, respectively. Finally, we demonstrate that transcription factor Sp1 not only binds and activates MUC2 and MUC5AC promoters but also participates to their EGF- and TGF-alpha-mediated up-regulation. We also show that Sp3 is a strong inhibitor of 11p15 mucin gene transcription. In conclusion, MUC2 and MUC5AC are two target genes of EGFR ligands in lung cancer cells, and up-regulation of these two genes goes through concomitant activation of the EGFR/Ras/Raf/Extracellular Signal-regulated Kinase-signaling pathway and Sp1 binding to their promoters.

Cell type specific expression of secretory TFF peptides: colocalization with mucins and synthesis in the brain

The "TFF domain" is an ancient cysteine-rich shuffled module forming the basic unit for the family of secretory TFF peptides (formerly P-domain peptides and trefoil factors). It is also an integral component of mosaic proteins associated with mucous surfaces. Three mammalian TFF peptides are known (i.e., TFF1-TFF3); however, in Xenopus laevis the pattern is more complex (xP1, xP4.1, xP4.2, and xP2). TFF peptides are typical secretory products of a variety of mucin-producing epithelial cells (e.g., the conjunctiva, the salivary glands, the gastrointestinal tract, the respiratory tract, and the uterus). Each TFF peptide shows an unique expression pattern and different mucin-producing cells are characterized by their specific TFF peptide/secretory mucin combinations. TFF peptides have a pivotal role in maintaining the surface integrity of mucous epithelia in vivo. They are typical constituents of mucus gels, they modulate rapid mucosal repair ("restitution") by their motogenic and their cell scattering activity, they have antiapoptotic effects, and they probably modulate inflammatory processes. Pathological expression of TFF peptides occurs as a result of chronic inflammatory diseases or certain tumors. TFF peptides are also found in the central nervous system, at least in mammals. In particular, TFF3 is synthesized from oxytocinergic neurons of the hypothalamus and is released from the posterior pituitary into the bloodstream.