Structural organization and classification of the human mucin genes

Bile-salt-stimulated lipase and mucins from milk of 'secretor' mothers inhibit the binding of Norwalk virus capsids to their carbohydrate ligands

Breast-feeding-associated protection against calicivirus diarrhoea is associated with the presence of high levels of 2-linked oligosaccharides in mother's milk, and human calicivirus strains including the NV (Norwalk virus) use gut 2-linked fucosylated glycans as receptors, suggesting the presence of decoy receptors in milk. Our aim was to analyse the ability of human milk to inhibit the attachment of rNV VLPs (recombinant NV-like particles) to their carbohydrate ligands and to characterize potential inhibitors found in milk. Milk from women with the secretor phenotype was strongly inhibitory, unlike milk from women that are non-secretors, which is devoid of 2-linked fucosylated structures. At least two fractions in human milk acted as inhibitors for the NV capsid attachment. The first fraction corresponded to BSSL (bile-salt-stimulated lipase) and the second to associated mucins MUC1 and MUC4. These proteins present tandem repeat O-glycosylated sequences that should act as decoy receptors for the NV, depending on the combined mother/child secretor status.

Laboratory findings in tear fluid analysis

The tear film, composed of the lipid, aqueous and mucin layers, has many functions including defending the ocular surface. The tear film covering the ocular surface presents a mechanical and antimicrobial barrier and ensures an optical refractive surface. The lipid component originates from the meibomian glands of the tarsus and forms the superficial layer of the tear film. The aqueous component contains electrolytes, water, and a large variety of proteins, peptides and glycoproteins, and is primarily secreted by the lacrimal gland. Mucins are glycoproteins expressed by epithelial tissues of mucous surfaces. They protect tissues by functioning as antioxidants, providing lubrication, and inhibiting bacterial adherence. Quantitatively and qualitatively, its composition must be maintained within the fairly narrow limits to maintain a healthy and functional visual system. Abnormalities of the tear film, affecting the constituents or the volume, can rapidly result in serious dysfunction of the eyelids and conjunctiva and ultimately affect the transparency of the cornea. Many ocular surface tests have been developed for the clinical diagnosis of dry eye syndromes. This paper provides an overview on laboratory methods for the analysis of the tear film. Understanding the components of the tear film will aid in the treatment of dry eye syndromes and the ocular surface diseases.

Differential Muc2 and Muc5ac secretion by stimulated guinea pig tracheal epithelial cells in vitro

BACKGROUND

Mucus overproduction is a characteristic of inflammatory pulmonary diseases including asthma, chronic bronchitis, and cystic fibrosis. Expression of two mucin genes, MUC2 and MUC5AC, and their protein products (mucins), is modulated in certain disease states. Understanding the signaling mechanisms that regulate the production and secretion of these major mucus components may contribute significantly to development of effective therapies to modify their expression in inflamed airways.

METHODS

To study the differential expression of Muc2 and Muc5ac, a novel monoclonal antibody recognizing guinea pig Muc2 and a commercially-available antibody against human MUC5AC were optimized for recognition of specific guinea pig mucins by enzyme-linked immunosorbent assay (ELISA), Western blot, and immunohistochemistry (IHC). These antibodies were then used to analyze expression of Muc2 and another mucin subtype (likely Muc5ac) in guinea pig tracheal epithelial (GPTE) cells stimulated with a mixture of pro-inflammatory cytokines [tumor necrosis factor-alpha (TNF-alpha), interleukin 1beta (IL-1beta), and interferon- gamma (IFN-gamma)].

RESULTS

The anti-Muc2 (C4) and anti-MUC5AC (45M1) monoclonal antibodies specifically recognized proteins located in Muc2-dominant small intestinal and Muc5ac-dominant stomach mucosae, respectively, in both Western and ELISA experimental protocols. IHC protocols confirmed that C4 recognizes murine small intestine mucosal proteins while 45M1 does not react. C4 and 45M1 also stained specific epithelial cells in guinea pig lung sections. In the resting state, Muc2 was recognized as a highly expressed intracellular mucin in GPTE cells in vitro. Following cytokine exposure, secretion of Muc2, but not the mucin recognized by the 45M1 antibody (likely Muc5ac), was increased from the GPTE cells, with a concomitant increase in intracellular expression of both mucins.

CONCLUSION

Given the tissue specificity in IHC and the differential hybridization to high molecular weight proteins by Western blot, we conclude that the antibodies used in this study can recognize specific mucin subtypes in guinea pig airway epithelium and in proteins from GPTE cells. In addition, Muc2 is highly expressed constitutively, modulated by inflammation, and secreted differentially (as compared to Muc5ac) in GPTE cells. This finding contrasts with expression patterns in the airway epithelium of a variety of mammalian species in which only Muc5ac predominates.

MUC1, MUC2, MUC4, MUC5AC and MUC6 expression in the progression of prostate cancer

Molecular changes are vital for the development of prognostic markers and therapeutic modalities of prostate cancer (CaP). There is growing interest in mucins as treatment targets in human malignancies, including CaP. The role of their expression in the progression of CaP is however unclear. We examined the expressions MUC1, MUC2, MUC4, MUC5AC and MUC6 in CaP tissues using tissue microarrays (TMAs) to look for tumor-associated antigens (TAAs) for targeted therapy. In this study, 120 paraffin-embedded specimens were selected from patients who underwent radical retro-pubic prostatectomy (RRP) or trans-urethral-resection of the prostate (TURP) for primary, untreated CaP and 10 matched lymph node metastases. A series of MUC monoclonal antibodies (mAbs) was used on TMAs by standard immunohistochemistry. Our results indicate that the over-expression of MUC1 was detected in 58% of primary CaP tissues and 90% of lymph node metastases but not in normal prostate or benign tissues, while the expression of MUC2, MUC4, MUC5AC and MUC6 was found to be negative in both normal and cancer tissues. Of the MUC1 positive tumors 86% were Gleason grade 7 or higher. Over-expression of MUC1 was found in late stage CaP while MUC2, 4, 5AC and 6 were negative in CaP. MUC1 is a TAA that is highly related to tumor progression in CaP patients. This antigen is ideal for targeted therapy to control micrometastases and hormone refractory disease but additional studies are necessary to assess its usefulness in patient biopsies and CaP bone metastases before clinical trial.

Retinoic acid can induce markers of endocrine transdifferentiation in pancreatic ductal adenocarcinoma: preliminary observations from an in vitro cell line model

BACKGROUND AND HYPOTHESIS

The pancreatic ductal adenocarcinoma (HPAF) cells have a multipotent stem cell potential. It was hypothesised that all-trans-retinoic acid (atRA) can induce transdifferentiation of these cells into cells with an endocrine phenotype.

MATERIAL AND METHODS

To explore this hypothesis, an in vitro system of cells was established. Some cells were treated with atRA at concentrations of 100 nmol/l (non-apoptosis-inducing) and 5 micromol/l (apoptosis-inducing) and harvested. Cells were examined for cell cycle kinetics, apoptosis (terminal deoxynucleotidyl transferase assay and p53 protein expression) and immunomorphological features of redifferentiation (MUC1 and DUPAN-2) and endocrine transdifferentiation (insulin, somatostatin, glucagon, neurone-specific enolase) by using immunoperoxidase staining methods. Levels of insulin, transforming growth factor (TGF) beta2, TGFalpha and epidermal growth factor receptor (EGFR) were measured by enzyme-linked immunosorbent assay (ELISA). The vehicle-treated cells served as a control group.

RESULTS

When compared with untreated cells, cells treated with 100 nmol/l and 5 micromol/l atRA were observed to show (1) decreased proliferative activity (cpm) as indicated by decreased incorporation of thymidine labelled with hydrogen-3; (2) cell cycle arrest; (3) increased apoptotic activity associated with p53 protein overexpression; (4) upregulated expression of the transdifferentiation and redifferentiation markers; (5) morphological changes indicative of transdifferentiation (increased cell size and appearance of dendrites); (6) decreased production of EGFR; (7) upregulation of TGFalpha and TGFbeta2; and (8) increase in basal and glucose-induced insulin secretion.

CONCLUSIONS

Functional endocrine transdifferentiation can be induced in HPAF lines by atRA. Further investigations are mandated to explore the underlying mechanisms of this transdifferentiation and to explore its in vivo extrapolation.

Mucin characteristics of human corneal-limbal epithelial cells that exclude the rose bengal anionic dye

PURPOSE

Rose bengal is an organic anionic dye used to assess damage of the ocular surface epithelium in ocular surface disease. It has been proposed that mucins have a protective role, preventing rose bengal staining of normal ocular surface epithelial cells. The current study was undertaken to evaluate rose bengal staining in a human corneal-limbal epithelial (HCLE) cell line known to produce and glycosylate membrane-associated mucins.

METHODS

HCLE cells were grown to confluence in serum-free medium and switched to DMEM/F12 with 10% serum to promote differentiation. Immunolocalization of the membrane-associated mucins MUC1 and MUC16 and the T-antigen carbohydrate epitope was performed with the monoclonal antibodies HMFG-2 and OC125 and jacalin lectin, respectively. To assess dye uptake, cultures were incubated for 5 minutes with 0.1% rose bengal and photographed. To determine whether exclusion of negatively charged rose bengal requires a negative charge at the cell surface, cells were incubated with fluoresceinated cationized ferritin. The effect of hyperosmotic stress on rose bengal staining in vitro was evaluated by increasing the ion concentration (Ca+2 and Mg+2) in the rose bengal uptake assay.

RESULTS

The cytoplasm and nucleus of confluent HCLE cells cultured in media without serum, lacking the expression of MUC16 but not MUC1, as well as human corneal fibroblasts, which do not express mucins, stained with rose bengal. Culture of HCLE cells in medium containing serum resulted in the formation of islands of stratified cells that excluded rose bengal. Apical cells of the stratified islands produced MUC16 and the T-antigen carbohydrate epitope on their apical surfaces. Colocalization experiments demonstrated that fluoresceinated cationized ferritin did not bind to these stratified cells, indicating that rose bengal is excluded from cells that lack negative charges. Increasing the amounts of divalent cations in the media reduced the cellular area protected against rose bengal uptake.

CONCLUSIONS

These results indicate that stratification and differentiation of corneal epithelial cells, as measured by the capacity to produce the membrane-associated mucin MUC16 and the mucin-associated T-antigen carbohydrate on their apical surfaces provide protection against rose bengal penetrance in vitro and suggest a role for membrane-associated mucins and their oligosaccharides in the protection of ocular surface epithelia.

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.

Quantitative analysis of MUC1 and MUC5AC mRNA in pancreatic juice for preoperative diagnosis of pancreatic cancer

Pancreatic juice is a promising type of diagnostic sample for pancreatic cancer, and members of the mucin (MUC) family are diagnostic candidates. To evaluate the utility of MUC family members as diagnostic markers, we measured MUC mRNA expression in pancreatic tissues and pancreatic juice obtained from patients with different pancreatic diseases as well as in pancreatic cancer cell lines by real-time PCR. Furthermore, to support the possibility of early diagnosis by quantification of MUC1 and MUC5AC, immunohistochemistry and microdissection-based quantitative analysis of mRNA were carried out. There was no significant correlation between MUC1 and MUC5AC expression in cell lines. When beta-actin was used as a reference gene, median MUC1 and MUC5AC mRNA expression levels were remarkably greater in tumoral tissues than in non-tumoral tissues, but median MUC4 and MUC6 mRNA expression levels were not. Receiver operating characteristic curve analysis showed that quantitative analysis of MUC1 and MUC5AC mRNA in pancreatic juice is better diagnostic modality than that of MUC4 and MUC6 mRNA. Immunohistochemistry showed that MUC1 and MUC5AC were highly expressed in invasive ductal carcinomas (IDC) and moderately expressed in high-grade pancreatic intraepithelial neoplasia (PanIN); no staining was observed in normal ducts. Analysis of cells isolated by microdissection showed stepwise upregulation of MUC1 and MUC5AC in the development of high-grade PanIN to IDC. Our results suggest that MUC1 and MUC5AC are upregulated stepwise in pancreatic carcinogenesis and that quantitative assessment of MUC1 and MUC5AC mRNA in pancreatic juice has high potential for preoperative diagnosis of pancreatic cancer.

Cell and molecular biology of human lacrimal gland and nasolacrimal duct mucins

The old concept that the lacrimal gland is only a serous gland has been superseded by the finding that lacrimal acinar cells are able to produce mucins--high-molecular-weight proteins--the major mass being carbohydrates with the common feature of tandem repeats of amino acids rich in serine, threonine, and proline in the central domain of the mucin core peptide. At the ocular surface, maintenance of the tear film, lubrication, and provision of a pathogen barrier on the epithelia, conjunctiva, and cornea have been shown to be facilitated by mucins that are present in membrane-anchored (lining epithelial cells) or secreted (goblet cells) form. Also in the lacrimal gland, both membrane-anchored (MUCs 1, 4, and 16) and secreted (MUCs 5B and 7) mucins have been identified. The lacrimal gland is the main contributor to the aqueous portion of the tear film. It is part of the lacrimal apparatus that comprises, together with the lacrimal gland, the paired lacrimal canaliculi, the lacrimal sac, and the nasolacrimal duct, which collects the tear fluid and conveys it into the nasal cavity. In this review, the latest information regarding mucin function in the human lacrimal gland and the human efferent tear ducts is summarized with regard to mucous epithelia integrity, rheological and antimicrobial properties of the tear film and tear outflow, age-related changes, and certain disease states such as the pathogenesis of dry eye, dacryostenosis, and dacryolith formation.

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.

Expression and genomic organization of zonadhesin-like genes in three species of fish give insight into the evolutionary history of a mosaic protein

Background

The mosaic sperm protein zonadhesin (ZAN) has been characterized in mammals and is implicated in species-specific egg-sperm binding interactions. The genomic structure and testes-specific expression of zonadhesin is known for many mammalian species. All zonadhesin genes characterized to date consist of meprin A5 antigen receptor tyrosine phosphatase mu (MAM) domains, mucin tandem repeats, and von Willebrand (VWD) adhesion domains. Here we investigate the genomic structure and expression of zonadhesin-like genes in three species of fish.

Results

The cDNA and corresponding genomic locus of a zonadhesin-like gene (zlg) in Atlantic salmon (Salmo salar) were sequenced. Zlg is similar in adhesion domain content to mammalian zonadhesin; however, the domain order is altered. Analysis of puffer fish (Takifugu rubripes) and zebrafish (Danio rerio) sequence data identified zonadhesin (zan) genes that share the same domain order, content, and a conserved syntenic relationship with mammalian zonadhesin. A zonadhesin-like gene in D. rerio was also identified. Unlike mammalian zonadhesin, D. rerio zan and S. salar zlg were expressed in the gut and not in the testes.

Conclusion

We characterized likely orthologs of zonadhesin in both T. rubripes and D. rerio and uncovered zonadhesin-like genes in S. salar and D. rerio. Each of these genes contains MAM, mucin, and VWD domains. While these domains are associated with several proteins that show prominent gut expression, their combination is unique to zonadhesin and zonadhesin-like genes in vertebrates. The expression patterns of fish zonadhesin and zonadhesin-like genes suggest that the reproductive role of zonadhesin evolved later in the mammalian lineage.

The increase in mucin exocytosis and the upregulation of MUC genes encoding for membrane-bound mucins induced by the thiol-activated exotoxin listeriolysin O is a host cell defence response that inhibits the cell-entry of Listeria monocytogenes

In vivo Listeria monocytogenes infection results in the massive release of mucus by goblet cells into the lumen of the intestine. We have previously reported that apical infection by L. monocytogenes is followed by listeriolysin O (LLO)-dependent stimulation of mucus exocytosis, and the upregulation of the MUC genes. Here, we report that L. monocytogenes EGD wild-type bacteria enter cultured human polarized, mucin-secreting, HT29-MTX cells apically by an InlA-dependent mechanism. The LLO-induced increase in mucin secretion together with an increase in transcription of the MCU4 and MUC12 genes encoding for membrane-bound mucins, results in the inhibition of the cell-entry of L. monocytogenes into mucin-secreting, HT29-MTX cells. Moreover, we report that sialic acid residues in mucins are crucial for the inhibition of L. monocytogenes internalization. Based on these findings, we suggest that the LLO-induced mucin exocytosis and upregulation of the MUC genes encoding for membrane-bound mucins constitute a host cell defence response that inhibits the cell-entry of L. monocytogenes.

MUC4 expression is a novel prognostic factor in patients with invasive ductal carcinoma of the pancreas

BACKGROUND

Many patients with invasive ductal carcinoma of the pancreas (IDC) have a poor outcome. MUC4 expression has been implicated as a marker for diagnosis and progression of IDC, but there are no studies of the relation between MUC4 expression and patient prognosis in IDC.

AIMS

To investigate the prognostic significance of MUC4 expression in IDC.

METHODS

The expression profiles of MUC4, ErbB2, p27, and MUC1 were investigated in IDC tissues from 135 patients by means of immunohistochemistry.

RESULTS

MUC4 was expressed in 43 of the 135 patients with IDC (31.9%). The survival of 21 patients with high MUC4 expression (>20% of neoplastic cells stained) was significantly worse than that of the 114 patients with low MUC4 expression (<20% of neoplastic cells stained) (p = 0.0043). Univariate analysis showed that high MUC4 expression (p = 0.0061), large primary tumour status (>T2) (p = 0.0436), distant metastasis (p = 0.0383), lymphatic invasion (p = 0.0243), and surgical margins (p = 0.0333) were significant risk factors affecting the outcome of patients with IDC. Backward stepwise multivariate analysis showed that MUC4 expression (p = 0.0121), lymph node metastasis (p = 0.0245), and lymphatic invasion (p = 0.0239) were significant independent risk factors. ErbB2, p27, and MUC1 were not independent risk factors.

CONCLUSIONS

This study shows that MUC4 expression in IDC is a new independent factor for poor prognosis and predicts the outcome of patients with IDC.

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.

Decreased mucin concentrations in tear fluids of contact lens wearers

Characteristics of tear-film may be influenced by contact lens wear, because contact lenses present the habitual, direct rubbing action of the lids upon the covered ocular surface and may cause changes of tear-film. In the present paper, influence of contact lens on proteins in tear samples was studied using carbohydrates attached to the protein as a marker. We found that N-acetylneuraminic acid (Neu5Ac) was significantly decreased in tear samples of volunteers wearing contact lens (wearing, 86.1 +/- 57.7 nmol/ml; normal, 190.2 +/- 121.9 nmol/ml). Analysis by polyacrylamide gel electrophoresis demonstrated that the amounts of major proteins in tear fluids, such as lactoferrin and secretory immunoglobulin A were not changed upon wearing contact lenses. In contrast, cellulose acetate membrane electrophoresis revealed that mucin band in tear samples from contact lens wearers showed significant decrease as examined by lectin staining.

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.

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.

The StcE protease contributes to intimate adherence of enterohemorrhagic Escherichia coli O157:H7 to host cells

Enterohemorrhagic Escherichia coli (EHEC) O157:H7 is a diarrheal pathogen that causes attaching and effacing (A/E) lesions on intestinal epithelial cells. Strains of the O157 serogroup carry the large virulence plasmid pO157, which encodes the etp type II secretion system that secretes the genetically linked zinc metalloprotease StcE. The Ler regulator controls expression of many genes involved in A/E lesion formation, as well as StcE, suggesting StcE may be important at a similar time during colonization. Our laboratory has previously demonstrated that StcE cleaves C1-esterase inhibitor, a regulator of multiple inflammation pathways. Here we report two new substrates for StcE, mucin 7 and glycoprotein 340, and that purified StcE reduces the viscosity of human saliva. We tested the hypothesis that StcE contributes to intimate adherence of EHEC to host cells by cleavage of glycoproteins from the cell surface. The fluorescent actin stain (FAS) test was used to observe the intimate adherence represented by fluorescently stained bacteria colocalized with regions of bundled actin formed on HEp-2 cells. An E. coli O157:H7 strain with a stcE gene deletion was not affected in its ability to generally adhere to HEp-2 cells, but it did score threefold lower on the FAS test than wild-type or complemented strains. Addition of exogenous recombinant StcE increased intimate adherence of the mutant to wild-type levels. Thus, StcE may help block host clearance of E. coli O157:H7 by destruction of some classes of glycoproteins, and it contributes to intimate adherence of E. coli O157:H7 to the HEp-2 cell surface.

Phenotypic alterations of mucins and cytokeratins during gallbladder carcinogenesis

In order to evaluate the significance of altered expression of mucin and cytokeratin during gallbladder carcinogenesis, we characterized the expressional profiles of MUC1, MUC2, MUC5AC, MUC6, CK7 and CK20 in 33 normal mucosa, 31 adenomas, 55 dysplasias and 131 carcinomas of the gallbladder. In normal gallbladder mucosa, the expressions of MUC5AC and MUC6 were diffuse and MUC1 expression was absent. However, in adenomas, dysplasias and carcinomas, the expressions of MUC5AC and MUC6 tended to decrease, whereas MUC1 expression was elevated. MUC2 and CK20 were infrequently expressed in all of the gallbladder epithelia, but adenomas expressing MUC2 and/or CK20 were more frequently associated with carcinomas and showed a higher grade of atypia than those without these antigens. In carcinomas, MUC1 expression was related to invasive growth, lymph node metastasis and a non-papillotubular type, whereas MUC6 expression was related to non-invasive growth. CK7 was diffusely expressed in almost all lesions, but carcinomas with a loss of CK7 expression showed poor survival. In conclusion, normal gallbladder mucosa has a gastric phenotype, but during carcinogenesis and tumor progression, the gastric phenotype is gradually lost and the aberrant expression of MUC1 occurs. The intestinal phenotype is not common in the gallbladder.

The DHE cell line as a model for studying rat gastro-intestinal mucin expression: effects of dexamethasone

The expression of mucin genes was evaluated in rat intestinal cell lines in order to establish an in vitro model for investigating the regulation of intestinal mucin expression in this species. Two rat intestinal cancer cell lines (DHE, LGA) and three nontumoral rat intestinal cell lines (IEC6, IEC17, IEC18) were screened. The mRNA expression of rMuc1, rMuc2, rMuc3, rMuc4, and rMuc5AC mucin genes was studied by semiquantitative RT-PCR, real-time RT-PCR and Northern-blot analysis. Results were correlated with immunohistochemical expression of rat gastric and intestinal mucin proteins, and secretion of glycoconjugates was examined by enzyme-linked lectin assay. We showed that mRNA of rMucl and rMuc2 were constitutively expressed in all IEC cell populations but periodic acid Schiff staining of these cells did not reveal the presence of glycoproteins. DHE cells expressed rMuc1-5AC mRNA and LGA expressed the same mucins but the level of rMuc4 was much lower. Mucin mRNA expression also differed in relation with the length of cultivation. Immunocytochemical studies revealed the presence of gastric and intestinal mucins in the two tumoral cell lines. Functional experiments showed that bethanechol, A23187 and PMA stimulated release of glycoconjugates in DHE but not in LGA cells. Treatment of DHE cells with dexamethasone (10(-7) mol/l) enhanced rMuc2 mRNA but decreased rMuc1 and rMuc5AC mRNA. Real-time RT-PCR showed that the expression of rMuc1 and rMuc5AC genes was reduced by more than tenfold after 24 h. The increased expression of rMuc2 gene was confirmed by Northern blot analysis. In conclusion, DHE cells provide a valuable cellular model for research on rat mucin secretion and expression.

Multiple roles of mucins in pancreatic cancer, a lethal and challenging malignancy

Mucins are members of an expanding family of large multifunctional glycoproteins. Pancreatic mucins have important biological functions, including the protection, lubrication, and moisturisation of the surfaces of epithelial tissues lining ductal structures within the pancreas. Several lines of evidence support the notion that deregulated mucin production is a hallmark of inflammatory and neoplastic disorders of the pancreas. Herein, we discuss the factors that contribute to the lethality of pancreatic cancer as well as the key role played by mucins, particularly MUC1 and MUC4, in the development and progression of the disease. Aspects pertaining to the aberrant expression and glycosylation of mucins are discussed, with special emphasis on their potential impact on the design and implementation of adequate diagnostic and therapeutic strategies for combating this lethal malignancy.

MUC1, MUC2 and MUC5AC expressions in cardiac myxoma

BACKGROUND

Cardiac myxoma, the most common primary tumor of the heart, has a variable clinical presentation and immunohistochemical profile. An abundant mucopolysaccharidic matrix exists, including mucin, within cardiac myxoma. This investigation first reports the expressions of mucin genes in cardiac myxoma.

METHODS

A retrospective study was conducted between December 1976 and February 2003, comprising 101 consecutive patients with cardiac myxoma who were treated with surgical excision. Detailed clinical parameters also were reviewed. Mucin genes, namely MUC1, MUC2 and MUC5AC, were studied immunohistochemically in 47 randomly selected patients.

RESULTS

The study group contained 57 (57%) women and 44 (43%) men, with a mean age of 38+/-21 years. Their presentations included: asymptomatic (41%), dyspnea (35%), stroke (23%), chest pain (7%), fever (6%), syncope (5%) and tricuspid regurgitation (70%). The sample included 90 myxoma located in the left atrium, 3 (3%) recurrent myxoma and 8 (8%) myxoma not located in the left atrium. The myxoma did not differ with location or clinical event in terms of pathological scores, such as vascular proliferation, inflammation, cellularity, hyaline, calcification and thrombosis. Cardiac myxoma is characterized by excessive mucus secretion. Expression of membrane-associated MUC1 was considerably higher than that of the secreted mucins, MUC2 and MUC5AC (P<0.05). Furthermore, expression of MUC5AC is related to lesser embolism (P<0.05).

CONCLUSIONS

This work first examined the immunohistochemical expression of mucin (MUC1, MUC2 and MUC5AC) in cardiac myxoma. This investigation then showed that the expression of representative membrane-associated mucin, MUC1, and/or secretory mucins, MUC2 and MUC5AC, in cardiac myxoma was associated with important tumor clinicopathological characteristics. Moreover, MUC5AC appears related to lesser embolism. This approach can help distinguish the potential roles of secretory mucins versus membrane-associated mucins in the development of cardiac myxoma.

Expression of mucins and E-cadherin in gastric carcinoma and their clinical significance

AIM: To investigate the expression of three types of mucin (MUC1, MUC2, MUC5AC) and E-cadherin in human gastric carcinomas and their clinical significance.

METHODS: Ninety-four gastric cancer specimens were classified according to WHO criteria and detected by immun-ohistochemical assay of expression of mucins and E-cadherin.

RESULTS: The positive expression rates of MUC1, MUC2, MUC5AC and E-cadherin were 82% (77/94), 84% (79/94), 40% (38/94) and 56% (53/94) respectively. MUC1 expression was significantly correlated with the types of cancer (the positive rates of MUC1 in well and moderately differentiated tubular adenocarcinoma, poorly differentiated adenocarcinoma, signet-ring cell carcinoma and mucinous carcinoma were 91%, 87%, 71%, 71%, respectively, P < 0.05), age of patients (the positive rates of it among the people who are younger than 40 years, between 40-60 years and over 60 year were 74%, 81%, 89%, P < 0.05), lymph nodes involvement (the positive rates in the non-interfered group and the interfered group were 78%, 85%, P < 0.05) and tumor size (the positive rates in the tumors with the size less than 3 cm, 3-6 cm and larger than 6 cm were 69%, 92%, 69%, P < 0.05); MUC2 expression was significantly associated with types of cancers and had the strongest expression in mucinous carcinomas (the positive rates of MUC2 in well and moderately differentiated tubular adenocarcinoma, poorly differentiated adenocarcinoma, signet-ring cell carcinoma and mucinous carcinoma were 94%, 70%, 81%, 100%, P < 0.05), but it had no obvious relation to age, gender, tumor location, lymph nodes involvement, depth of invasion and metastasis to extra-gastric organs (P > 0.05); MUC5AC expression was not related to any of the characteristics investigated except that it had relation to gender, whereas MUC5AC showed the tendency to higher expression in less invasive lesions and lower expression in advanced stage cancers (P > 0.05); No significant difference was found for E-cadherin expression. There were strong positive relationships between the expression of MUC1 and E-cadherin, MUC2 and E-cadherin, MUC1 and MUC2 (R = 0.33, R = 0.22, R = 0.32, respectively, P < 0.05). According to the COX proportional hazards model, older patients, involvement of lymph nodes, different types of gastric cancer and MUC2 expression were significantly associated with poorer outcome of gastric carcinoma patients (β = 0.08, β = 3.94, β = 1.33, β = 0.75, respectively, P < 0.05).

CONCLUSION: MUC1 and MUC2 are good markers of different types of gastric cancer. MUC2 is especially a good marker of mucinous carcinoma. MUC1, MUC2 may interfere with the function of E-cadherin in gastric carcinomas, and have synergic effect on progression of gastric cancers.

A role for human MUC4 mucin gene, the ErbB2 ligand, as a target of TGF-beta in pancreatic carcinogenesis

MUC4: encodes a large transmembrane mucin that is overexpressed in pancreatic adenocarcinomas. The molecular mechanisms responsible for that altered pattern of expression are unknown. TGF-beta, a pleiotropic cytokine, regulates numerous genes involved in pancreatic carcinogenesis via activation of the Smads proteins and MUC4 promoter is rich in Smad-binding elements. Our aim was to study whether the regulation of MUC4 expression by TGF-beta in pancreatic cancer cells was strictly dependent on Smad4 activity. Three pancreatic cancer cell lines, CAPAN-1 (MUC4+/Smad4-), CAPAN-2 (MUC4+/Smad4+) and PANC-1 (MUC4-/Smad4+), were used. By RT-PCR, transfection assays and immunohistochemistry, we show that (i) both MUC4 mRNA and apomucin expression are upregulated by TGF-beta, (ii) Smad2 positively cooperates with Smad4 to activate the promoter, (iii) activation of Smad4 by exogenous TGF-beta induces Smad4 binding to the promoter, (iv) Smad7 and c-ski both inhibit activation by Smad4. When Smad4 is mutated and inactive, TGF-beta activates MUC4 expression via MAPK, PI3K and PKA signaling pathways. Absence of expression in PANC-1 cells is due to histone deacetylation. Altogether, these results indicate that upregulation of MUC4 by TGF-beta is restricted to well-differentiated pancreatic cancer cells, and point out a novel mechanism for TGF-beta as a key molecule in targeting MUC4 overexpression in pancreatic adenocarcinomas.

[MUC genes: mucin or not mucin? That is the question]

Mucins are macromolecules lying the cells in contact with external environment and protect the epithelium against constant attacks such as digestive fluids, microorganisms, pollutants, and toxins. Mucins are the main components of mucus and are synthesized and secreted by specialized cells of the epithelium (goblet cells, cells of mucous glands) or non mucin-secreting cells. Human mucin genes show common features: large size of their mRNAs, large nucleotide tandem repeat domains, complex expression both at tissular and cellular level. Since 1987, 21 MUC symbols have been used to designate genes encoding O-glycoproteins containing tandem repeat domains rich in serine, threonine and proline. Some of these genes encode true mucins while others encode non mucin adhesion O-glycoproteins. In this paper, we propose a classification based on sequence similarities and expression areas. Two main families can be distinguished: secreted mucins or gel-forming mucins (MUC2, MUC5AC, MUC5B, MUC6), and membrane-bound mucins (MUC1, MUC3, MUC4, MUC12, MUC17). Muc-deficient mice will provide important models in the study of functional relationships between these two mucin families.

Identification of disulfide bonds among the nine core 2 N-acetylglucosaminyltransferase-M cysteines conserved in the mucin beta6-N-acetylglucosaminyltransferase family

Bovine core 2 beta1,6-N-acetylglucosaminyltransferase-M (bC2GnT-M) catalyzes the formation of all mucin beta1,6-N-acetylglucosaminides, including core 2, core 4, and blood group I structures. These structures expand the complexity of mucin carbohydrate structure and thus the functional potential of mucins. The four known mucin beta1,6-N-acetylglucosaminyltransferases contain nine conserved cysteines. We determined the disulfide bond assignments of these cysteines in [(35)S]cysteine-labeled bC2GnT-M isolated from the serum-free conditioned medium of Chinese hamster ovary cells stably transfected with a pSecTag plasmid. This plasmid contains bC2GnT-M cDNA devoid of the 5'-sequence coding the cytoplasmic tail and transmembrane domain. The C18 reversed phase high performance liquid chromatographic profile of the tryptic peptides of reduced-alkylated (35)S-labeled C2GnT-M was established using microsequencing. Each cystine pair was identified by rechromatography of the C8 high performance liquid chromatographic radiolabeled tryptic peptides of alkylated bC2GnT-M on C18 column. Among the conserved cysteines in bC2GnT-M, the second (Cys(113)) was a free thiol, whereas the other eight cysteines formed four disulfide bridges, which included the first (Cys(73)) and sixth (Cys(230)), third (Cys(164)) and seventh (Cys(384)), fourth (Cys(185)) and fifth (Cys(212)), and eighth (Cys(393)) and ninth (Cys(425)) cysteine residues. This pattern of disulfide bond formation differs from that of mouse C2GnT-L, which may contribute to the difference in substrate specificity between these two enzymes. Molecular modeling using disulfide bond assignments and the fold recognition/threading method to search the Protein Data Bank found a match with aspartate aminotransferase structure. This structure is different from the two major protein folds proposed for glycosyltransferases.

Mucin dynamics in the chick small intestine are altered by starvation

The absorptive surface of the small intestine is covered by a layer of mucus secreted by goblet cells. The secreted mucins and thickness of the adherent layer influence nutrient digestion and absorption processes as well as the functionality of the mucosa. In this study, methods for the analysis of mucin synthesis and dynamics in the chick small intestine are described. A fragment of chicken mucin cDNA was isolated and characterized; this fraction had 60% homology to human mucin MUC-5AC. The thickness of the mucus adherent layer and the relative amounts of mucin glycoprotein and mRNA were also examined in the small intestines of control and starved chicks. Relative amounts of intestinal mucin mRNA and protein increased in the duodenum and jejunum of starved chicks, and mucus adherent layer thickness decreased throughout the small intestine. In starved chicks, higher mRNA expression and protein concentrations with lower amounts of adherent mucus may be related to a higher rate of degradation of the mucus layer, a lower rate of mucus secretion, or an altered rate of mucin turnover. It thus appears that starvation alters mucus dynamics in the small intestine, and this may affect intestinal digestive function and defense.

Microbial-gut interactions in health and disease. Epithelial cell responses

Intestinal epithelial cells are unique in that they represent the only host cells that are constantly interacting with a very large bacterial population in the lumen. The single monolayer of epithelial cells consists of subpopulations with distinct functions that include protection against luminal microorganisms. Although the microbial flora remains to be fully characterized, its normal relationship with the host intestinal epithelial cells appears to be predominantly symbiotic or commensal. The molecular complexity of the epithelial-microbial relationship has been shown in studies that have examined the establishment of the resident bacteria in germ-free mice. Recent work has also demonstrated the ability of resident bacteria to enhance epithelial protective responses. The mechanisms by which epithelial cells may avoid pro-inflammatory responses to resident microorganisms, while retaining the capacity to respond to pathogens, are also being characterized.

MUC4 mucin expression in human pancreatic tumours is affected by organ environment: the possible role of TGFbeta2

MUC4 is highly expressed in human pancreatic tumours and pancreatic tumour cell lines, but is minimally or not expressed in normal pancreas or chronic pancreatitis. Here, we investigated the aberrant regulation of MUC4 expression in vivo using clonal human pancreatic tumour cells (CD18/HPAF) grown either orthotopically in the pancreas (OT) or ectopically in subcutaneous tissue (SC) in the nude mice. Histological examination of the OT and SC tumours showed moderately differentiated and anaplastic morphology, respectively. The OT tumour cells showed metastases to distant lymph nodes and faster tumour growth (P<0.01) compared to the SC tumours. The MUC4 transcripts in OT tumours were very high compared to the undetectable levels in SC tumours. The SC tumour cells regained their ability to express MUC4 transcripts after in vitro culture. Immunohistochemical analysis using MUC4-specific polyclonal antiserum confirmed the results obtained by Northern blot analysis. Interestingly, the OT tumours showed expression of TGFβ2 compared to no expression in SC, suggesting a possible link between MUC4 and TGFβ2. The MUC4 expression, morphology, and metastasis of human pancreatic tumour cells are regulated by a local host microenvironment. TGFβ2 may serve as an interim regulator of this function.

Generation and characterization of anti-MUC4 monoclonal antibodies reactive with normal and cancer cells in humans

We have previously cloned the full-length cDNA (approximately 28 Kb) and established the complete genomic organization (25 exons/introns over 100 kb) of the human MUC4 mucin. This large molecule is predicted to protrude over 2 microm above the cell surface, in which MUC4alpha is an extracellular mucin-type glycoprotein subunit and MUC4beta is the transmembrane subunit. Over two thirds of the encoded protein sequence consists of 16-amino-acid tandem repeats (TR), which are flanked by unique sequences. In this study we generated and characterized monoclonal antibodies (MAbs) directed against the TR region of MUC4. Mice were immunized with a KLH-conjugated MUC4 TR peptide, STGDTTPLPVTDTSSV. Several clones were purified by three rounds of limited dilutions and stable clones presenting a sustained antibody production were selected for subsequent characterization. Antibodies were tested for their reactivity and specificity to recognize the MUC4 peptide and further screened by enzyme-linked immunosorbent assay (ELISA) and Western blotting analyses. One of the MAbs (8G7) was strongly reactive against the MUC4 peptide and with native MUC4 from human tissues or pancreatic cancer cells in Western blotting, immunohistochemistry, and confocal analysis. Anti-MUC4 MAb may represent a powerful tool for the study of MUC4 function under normal and pathological conditions and for diagnosis of solid tumors including those in the breast, pancreas, lungs, and ovaries.

Distribution of mucins at the ocular surface

Mucins are vital for maintenance of a healthy, wet ocular surface. Once only thought to be secreted by goblet cells, mucins are now also known to be of the membrane-associated type. Stratified ocular surface epithelia express at their apical-tear fluid surface a repertoire of membrane-associated mucins including MUC1, MUC4, MUC16. These mucins are concentrated on the tips of the microplicae, forming a dense glycocalyx at the epithelial tear film interface. A major mucin of the secretory class is the goblet-cell-derived gel-forming mucin MUC5AC. A small soluble mucin, MUC7, is expressed by the lacrimal gland acini. Our hypothesis of the role/distribution of the secreted and membrane-associated mucins at the ocular surface is that the secreted mucins are soluble in the tear fluid, and are moved about and shunted to the nasolacrimal duct and by the eyelids during blinking. Thus, in the tears, the secreted mucins act as clean-up/debris removing multimeric networks that at the same time, through their hydrophilic nature, hold fluids in place and harbor defense molecules secreted by the lacrimal gland. Membrane-associated mucins, on the other hand, form a dense barrier in the glycocalyx at the epithelial tear film interface. This barrier prevents pathogen penetrance and is a lubricating surface that allows lid epithelia to glide over the corneal epithelia without adherence. The secreted mucins move easily over the glycocalyx mucins because both have anionic character that creates repulsive forces between them. Little is known regarding regulation of expression and glycosylation of mucins by ocular surface epithelia. Since ocular surface drying diseases alter both goblet cell and mucin production, and production and glycosylation of membrane-associated mucins, studies of mucin gene regulation and glycosylation may yield treatment modalities for these diseases.

Mucin gene expression in cardiac myxoma

Myxoma is the most common benign neoplasm of the heart. This work is the first to present an unusual left atrium and mitral valve cardiac myxoma which cannot be completely resected. This cardiac myxoma was also associated with abundant mucopolysaccharidic matrix, including mucin. Mucin gene expression is cell- and tissue-specific, with variations during cell differentiation and inflammation, and is altered during carcinogenesis. The expression of mucin genes in cardiac myxoma has never been elucidated previously. Detailed immunohistochemical analysis of MUC1, MUC2 and MUC5AC has been performed in this left atrium and mitral valve myxoma. Notably, the expressions of mucins in cardiac myxoma must be further evaluated.

Identification and genetic characterization of a novel proteinase, PrtR, from the human isolate Lactobacillus rhamnosus BGT10

A novel proteinase, PrtR, produced by the human vaginal isolate Lactobacillus rhamnosus strain BGT10 was identified and genetically characterized. The prtR gene and flanking regions were cloned and sequenced. The deduced amino acid sequence of PrtR shares characteristics that are common for other cell envelope proteinases (CEPs) characterized to date, but in contrast to the other cell surface subtilisin-like serine proteinases, it has a smaller and somewhat different B domain and lacks the helix domain, and the anchor domain has a rare sorting signal sequence. Furthermore, PrtR lacks the insert domain, which otherwise is situated inside the catalytic serine protease domain of all CEPs, and has a different cell wall spacer (W) domain similar to that of the cell surface antigen I and II polypeptides expressed by oral and vaginal streptococci. Moreover, the PrtR W domain exhibits significant sequence homology to the consensus sequence that has been shown to be the hallmark of human intestinal mucin protein. According to its alpha(S1)- and beta-casein cleavage efficacy, PrtR is an efficient proteinase at pH 6.5 and is distributed throughout all L. rhamnosus strains tested. Proteinase extracts of the BGT10 strain obtained with Ca(2+)-free buffer at pH 6.5 were proteolytically active. The prtR promoter-like sequence was determined, and the minimal promoter region was defined by use of prtR-gusA operon fusions. The prtR expression is Casitone dependent, emphasizing that nitrogen depletion elevates its transcription. This is in correlation with the catalytic activity of the PrtR proteinase.

Expression of MUC1 (EMA) and E-cadherin in renal cell carcinoma: a systematic immunohistochemical analysis of 188 cases

MUC1 (epithelial membrane antigen) is a membrane-associated mucin known to interfere with both cell-cell and cell-matrix adhesions. Overexpression has been associated with poor prognosis in a variety of cancers. We investigated the expression of MUC1 (using two different antibodies, MA695 and E29) and E-cadherin in renal cell carcinomas (137 conventional, 23 chromophobe, 20 papillary, and eight unclassified tumors) with respect to diagnostic and prognostic significance using a tissue microarray technique. Immunoreactivity was correlated with histological subtype, pT-stage, and grade using the chi2 test or the Fisher's exact test, respectively. Impact on disease-free survival was analyzed using the Kaplan-Meier method and the log-rank test. Immunoreactivity of more than 10% of cancer cells with MA695, E 29, and E-cadherin antibodies was found in 112/133 (84%), 86/133 (65%), and 7/131 (5%) conventional, 20/22 (91%), 19/22 (86%), and 21/22 (95%) chromophobe, 13/20 (65%), 8/20 (40%), and 3/20 (15%) papillary as well as 5/8 (63%), 5/8 (63%), and 4/8 (50%) unclassified carcinomas, respectively. The two different MUC1 antibodies yielded comparable staining results. A diffuse cytoplasmic staining pattern for MUC1 was found exclusively in chromophobe carcinomas, whereas conventional and papillary subtypes showed predominantly membranous staining (P<0.0001). Regarding papillary carcinomas, MUC1 was predominantly associated with type 1 (P=0.0001), and E-cadherin with type 2 (P=0.049) tumors. The cellular staining pattern of MUC1 in conventional tumors was related to pT-stage (P=0.002) and tumor grade (P=0.001): Low-stage (pT1/pT2) and grade (G1/G2) tumors showed a predominantly apical membranous staining, high-stage (pT3a/pT3b) and grade (G3/G4) tumors a predominantly circumferential membranous staining (with or without additional diffuse cytoplasmic immunoreactivity), which, in the conventional subtype, was associated with poor prognosis (P<0.0001). In conclusion, MUC1 and E-cadherin are diagnostically and prognostically useful markers in renal tumor pathology, especially when cellular staining patterns are considered.

Diagnostic value of MUC4 immunostaining in distinguishing epithelial mesothelioma and lung adenocarcinoma

The distinction between pleural malignant mesothelioma and pleural infiltration by adenocarcinomas has complex therapeutic and medicolegal implications. Although the panel of adenocarcinoma-associated antibodies and one or two mesothelioma markers is useful in this purpose, most of these antibodies are not totally specific. We determined the diagnostic value of MUC4 immunostaining in this issue. MUC4 gene expression was also studied by in situ hybridization and RT-PCR. MUC4 is a membrane-bound mucin that has been suggested to be implicated in malignant progression in humans and rats. The MUC4 gene is expressed in various normal epithelial tissues of endodermic origin and carcinomas. In the respiratory tract, MUC4 transcripts have been detected in normal respiratory epithelium and lung carcinomas. MUC4 protein was expressed in 32 of 35 (91.4%) lung adenocarcinomas on paraffin-embedded tissue. None of the 41 malignant mesotheliomas nor the 32 cases of benign mesothelial cells expressed MUC4 at the protein and mRNA levels. We conclude that MUC4 is a very specific (100%) and sensitive (91.4%) marker of lung adenocarcinomas on paraffin-embedded tissue that could be useful in diagnostic practice in the distinction between malignant mesothelioma and adenocarcinoma.

The mouse secreted gel-forming mucin gene cluster

Using genomic cosmid and BAC clones and genome shotgun supercontigs available in GenBank, we determined the complete gene structure of the four mouse secreted gel-forming mucin genes Muc2, Muc5ac, Muc5b and Muc6 and the organization of the genomic locus harboring these genes. The mouse secreted gel-forming mucin gene is 215 kb on distal chromosome 7 to 69.0 cM from the centromere and organized as: Muc6-Muc2-Muc5ac-Muc5b with Muc2, Muc5ac and Muc5b arranged in the same orientation and Muc6 in opposite. Mouse mucin genes have highly similar genomic organization to each other and to their respective human homologues indicating that they have been well conserved through evolution. Deduced peptides showed striking sequence similarities in their N- and C-terminal regions whereas the threonine/serine/proline-rich central region is specific for each other and for species. Expression studies also showed that they have expression patterns similar to human mucin genes with Muc2 expressed in small and large intestines, Muc5ac and Muc6 in stomach, and Muc5b in laryngo-tracheal tract. These data constitute an important initial step for investigation of mucin gene regulation and mucin function through the use of animal models.

Genome-wide search and identification of a novel gel-forming mucin MUC19/Muc19 in glandular tissues

Gel-forming mucins are major contributors to the viscoelastic properties of mucus secretion. Currently, four gel-forming mucin genes have been identified: MUC2, MUC5AC, MUC5B, and MUC6. All these genes have five major cysteine-rich domains (four von Willebrand factor [vWF] C or D domains and one Cystine-knot [CT] domain) as their distinctive features, in contrast to other non-gel-forming type of mucins. The CT domain is believed to be involved in the initial mucin dimer formation and have very succinct relationship between different gel-forming mucins across different species. Because of gene duplication and evolutional modification, it is very likely that other gel-forming mucin genes exist. To search for new gel-forming mucin candidate genes, a "Hidden Markov Model"(HMM) was built from the common features of the CT domains of those gel-forming mucins. By using this model to screen all protein databases as well as the six-frame translated expression sequence tag and translated human genomic databases, we identified a locus located at the peri-centromere region of human chromosome 12 and the corresponding homologous region of mouse chromosome 15. We cloned the 3' end of this gene and its mouse homolog. We found one vWF C domain, one CT domain, and various mucin-like threonine/serine-rich repeats. Phylogenetic analysis indicated the close relationship between this gene and the submaxillary mucin from porcine and bovine. A polydispersed signal was observed on the Northern blot, which indicates very large mRNA size. Further analysis of the upstream genomic sequences generated from human and mouse genome projects revealed three additional vWF D domains and many mucin-like threonine/serine-rich repeats. The expression of this gene is restricted to the mucous cells of various glandular tissues, including sublingual gland, submandibular gland, and submucosal gland of the trachea. Based on the chronological convention, we have given the name MUC19 to the human ortholog and Muc19 to the mouse.

MUC1 and MUC2 expression in salivary gland tumors and in non-neoplastic salivary gland tissue

The expression of MUC1 and MUC2 was studied in salivary gland tumors and non-neoplastic salivary gland tissue. Formalin-fixed paraffin-embedded specimens from 101 patients (21 pleomorphic adenomas (PA), 22 Warthin's tumors (WT), 26 adenoid cystic carcinomas (ACC), 13 acinic cell adenocarcinomas (ACA), 9 mucoepidermoid carcinomas (MC), and 10 specimens of non-neoplastic parotid and submandibular gland tissue) were immunostained. All salivary gland tumors expressed MUC1. A strong immunoreactivity was noted in WT and MC, a moderate in ACC and ACA, and a weak in PA. Strong expression of MUC2 was noted in all WT, moderate expression in MC, and weak expression in PA and ACA. All cases of ACC except for two were negative for MUC2. In general, MUC1 expression was stronger than that of MUC2. Non-neoplastic salivary gland tissue revealed a moderate MUC1 and MUC2 expression in excretory ducts and a strong expression in striated ducts. The apical plasma membrane of some serous acini expressed MUC1. Mucous acini were negative for both antigens. No change in immunoreactivity was noted in cases of chronic sclerosing sialadenitis. In conclusion, the different expression pattern of MUC1 and MUC2 in salivary gland neoplasia may be of additional value for the classification of salivary gland tumors.

Human epithelium from conjunctival impression cytology expresses MUC7 mucin gene

PURPOSE

To prove that noninvasive methods of obtaining conjunctival tissue, such as conjunctival impression cytology (CIC), could be valid alternatives that are simpler, faster, and more convenient for patients than biopsy to analyze mRNA levels of mucin genes.

METHODS

Using the semiquantitative reverse-transcriptase polymerase chain reaction, we studied the presence of the mucin genes described on the ocular surface thus far and attempted to detect the presence of MUC7 in CIC samples from 10 healthy donors.

RESULTS

Conjunctival cells recovered by CIC expressed all the genes studied. There were no statistically significant differences between male and female subjects, and there was a significant correlation between the two eyes of the same donor only in the expression of MUC7.

CONCLUSION

CIC is a valid, noninvasive technique to detect the mRNAs of ocular genes in healthy individuals. MUC1, MUC2, MUC4, MUC5AC, and MUC7 mucin genes could be all detected in each CIC sample. This technique may be a useful tool to study the expression of some genes in ocular diseases.

Quantitative RT-PCR assay for MUC3 and VEGF mRNA in renal clear cell carcinoma: relationship with nuclear grade and prognosis

OBJECTIVES

To investigate, by real-time quantitative reverse transcriptase-polymerase chain reaction, the expression of MUC3 and vascular endothelial growth factor (VEGF) to correlate them with histologic parameters and with prognosis. Human mucins are large O-glycoproteins expressed in epithelial tissues. Deregulation of mucin genes has been demonstrated in several epithelial neoplasms. In the kidney, MUC3 is expressed in normal convoluted tubules and in renal clear cell carcinoma.

METHODS

Twenty-six renal clear cell carcinoma specimens were studied. For all tumors, samples of normal and tumor kidney were frozen. After RNA extraction, using ultracentrifugation through a cesium chloride cushion, VEGF and MUC3 mRNA were analyzed by real-time quantitative reverse transcriptase-polymerase chain reaction. The pathologic parameters included Fuhrman nuclear grade and TNM stage. All follow-up data were available.

RESULTS

The median level of MUC3 and VEGF expression was greater in tumor areas compared with normal areas (P < 0.002 and P < 0.001, respectively). The MUC3 tumor/normal tissue expression ratio was greater in nuclear grade 3 tumor than in low grades (grade 1-2; P < 0.005). No statistically significant relationship was found with the prognosis for MUC3 and VEGF in our study.

CONCLUSIONS

The results of this study demonstrate that MUC3 and VEGF are overexpressed in renal clear cell carcinoma, and the MUC3 expression ratio is greater in nuclear grade 3 than in grades 1 and 2 (low grades) tumor. These findings suggest the implication of MUC3 in renal carcinogenesis.

Mucin biosynthesis: bovine C2GnT-M gene, tissue-specific expression, and herpes virus-4 homologue

Mucin glycans are the major determinant of mucin functions. Mucin glycan branch structures, which increase structural heterogeneity and thus functional potential, are extended from beta6 N-acetylglucosaminides formed by beta6 N-acetylglucosaminyltransferases (beta6GnT). Core 2 beta6GnT-M (C2GnT-M) is the only branching enzyme that can synthesize all known mucin beta6 N-acetylglucosaminides. We report the cloning of four different bovine (b) C2GnT-M transcripts that are different only at 5'-untranslated regions. Two bC2GnT-M transcripts are found exclusively in tracheal epithelium and testis, whereas the other two are found in all other mucus-secreting tissues. The bC2GnT-M gene contains four exons spanning 5.3 kb, and the entire open reading frame is in one exon. The bC2GnT-M ORF has 95, 83, and 75% sequence identity to those of bovine herpes virus type 4 (BHV-4), human, and rat C2GnT-Ms, respectively. The homology between bovine and BHV-4 C2GnT-M genes is in the region between 170 nucleotides upstream from ATG start codon and 114 nucleotides downstream from TGA stop codon of the viral gene. Localized at the nonconserved region of the viral genome, the BHV-4 C2GnT-M gene is the only known viral C2GnT-M gene. The results suggest that BHV-4 acquired its C2GnT-M gene from the bovine gene. The mechanism of the viral acquisition of bC2GnT-M gene and the roles of the C2GnT-M gene in the survival and pathogenesis of this virus remain to be elucidated.

Expression of human mucin genes during normal and abnormal renal development

Human mucin genes encode large O-glycoproteins, which are expressed in various epithelial tissues. The proteins are the main components of mucus, but also might be involved in morphogenesis of or carcinogenesis in many organs. We studied the expression of human mucin genes during fetal kidney development and in malformed cystic renal diseases in 10 normal fetal kidneys and 12 malformed kidneys by in situ hybridization and immunohistochemical analysis. MUC1, MUC3, and MUC6 were expressed in normal fetal kidney. MUC1 was expressed from 7.5 weeks of gestation in the metanephric blastema and throughout fetal life in the ureteric buds, distal convoluted tubules, and collecting ducts. MUC3 was expressed weakly in immature tubules from 8 weeks of gestation, after which it was expressed weakly and focally in the proximal convoluted tubules. MUC6 was expressed at 9.5 weeks of gestation in the tips of the ureteric buds and later in the collecting ducts. In malformative cystic diseases, only MUC1 expression was retained; no expression of MUC6 and MUC3 was observed. These results implicate human mucin genes (MUC1, MUC3, and MUC6) in renal morphogenesis processes.

Mucin Expression in Nonneoplastic and Neoplastic Glandular Epithelia of the Uterine Cervix

Although it is well known that the uterine cervix contains mucin-producing glandular epithelium, only a few studies have described the changes in mucin that accompany malignant transformation. In this study the authors evaluated the characteristics of mucin expression in the normal endocervical epithelium and mucinous and endometrioid adenocarcinomas of the uterine cervix. The normal endocervical epithelium was characterized by predominant sulfomucin and MUC1 expression in all sites and MUC5AC expression in the surface epithelium, while MUC2 was not detected at all and pyloric gland type mucin (using antibody HIK1083) was detected in less than 1% of cases. Cervical adenocarcinomas, especially mucinous adenocarcinomas, showed marked variability in mucin expression that included mucins of pyloric gland and intestinal type.

Pharmacology of airway goblet cell mucin release

Airway mucus hypersecretion is one of the major clinical manifestations of patients suffering from various pulmonary diseases. However, no drugs are yet available to control airway mucus hypersecretion. For the past 15 years, a plethora of information has amassed with regard to the pharmacology of airway goblet cell mucin secretion using various primary cell culture systems. The recent discovery of various MUC genes has also greatly stimulated research in this field. Nevertheless, the heterogeneity of the oligosaccharide structure of mucin molecules makes it extremely difficult to assess the significance of the information derived from the pharmacological studies. Therefore, it seems crucially important to understand the roles of individual mucins in conjunction with normal airway physiology and pathology, which should be the future research directions necessary for studying airway goblet cell mucin pharmacology.

Characterization of the mouse Muc3 membrane bound intestinal mucin 5' coding and promoter regions: regulation by inflammatory cytokines

The mouse Muc3 mucin is a membrane-bound glycoprotein highly expressed in the intestinal tract. We have characterized the mouse Muc3 5' structure and regulation of its promoter by cytokines and growth factors. The first two exons of Muc3 are separated by an intron of over 8 kb. Exon 3 contains the tandem repeat domain. Ten exons reside 3' to the tandem repeat domain. The 5' nonrepetitive sequence contains 104 amino acids characterized by a putative signal sequence, a single cysteine and 28% serine/threonine. No TATA box is found near the transcription start site. The promoter has consensus binding sites for AP1, CREB, SP1, NF kappa B, GATA binding protein and Cdx. Muc3 promoter constructs demonstrate that IL4, IL6, EGF or PMA increased promoter activity to 35-58% of control. TNF alpha and IFN gamma showed lesser stimulation. These data indicate that cytokines and growth factors are capable of regulating Muc3 gene expression, suggesting that this protein may play an active role in intestinal mucosal defense.

Alterations of MUC1 and MUC3 expression in gastric carcinoma: relevance to patient clinicopathological features

AIMS

Several studies have reported conflicting and inconclusive results concerning the clinical relevance of mucin expression in gastric carcinoma. This study investigated the correlations between aberrant expression of mucins in gastric carcinoma and patient clinicopathological features.

METHODS

The expression of MUC1, MUC2, MUC3, MUC5AC, and MUC6 was investigated immunohistochemically in gastric carcinoma (n = 46) in relation to patient clinicopathological features.

RESULTS

All normal gastric mucosa samples expressed MUC1, MUC5AC, and MUC6. MUC1, MUC2, MUC3, MUC5AC, and MUC6 were expressed in 29, 31, 30, 18, and 21 of the 46 cases of gastric carcinoma, respectively. The number of cases expressing MUC1 was significantly higher (p < 0.01) in patients with a small tumour size (>/= 5 cm) and in patients in clinical stages I-II, compared with clinical stages III-IV (p < 0.05). Expression was significantly lower (p < 0.05) in patients exhibiting metastasis. The number of cases expressing MUC3 was significantly higher in patients in clinical stages III-IV (p < 0.05), and in those with serosal invasion (p < 0.05) or metastasis (p<0.01). No significant relations were found between MUC2, MUC5AC, MUC6, and clinical stage, metastasis, or tumour size.

CONCLUSIONS

Membrane bound mucins MUC1 and MUC3 appear to be associated with the development of gastric carcinoma. Patients who maintained high immunoreactivity for anti-MUC1 antibody had a better prognosis, whereas those with an increase in anti-MUC3 immunoreactivity had a poorer prognosis, as judged by tumour size, serosal invasion, and metastasis. However, no correlation was found between MUC2, MUC5AC, or MUC6 and clinical prognosis.

MUC6 is a marker of seminal vesicle-ejaculatory duct epithelium and is useful for the differential diagnosis with prostate adenocarcinoma

The diagnosis of prostate adenocarcinoma is usually made on needle biopsies. Numerous benign lesions may mimic malignancy, especially when the focus of carcinoma is limited. The presence of seminal vesicle-ejaculatory duct epithelium on prostate biopsy is not rare and could cause confusion with adenocarcinoma. Lipochrome pigments are frequently encountered in seminal vesicle-ejaculatory duct but may be also seen in prostate adenocarcinoma. Prostate specific antigen immunostaining in difficult cases is sometimes used, but high-grade adenocarcinomas may be negative. In one previous report, MUC6 was found to be expressed in seminal vesicle but not in normal prostate. MUC6 belongs to the family of human mucin genes. So we investigated herein the immunohistochemical expression of MUC6 in prostate adenocarcinomas and seminal vesicle-ejaculatory duct. We have tested 30 prostate adenocarcinomas of various grade, 10 normal seminal vesicles, and 10 prostate adenocarcinomas invading the seminal vesicles. The tissues were fixed in 10% buffered formalin and embedded in paraffin. Immunohistochemistry was performed using the avidin-biotin-peroxidase complex technique. All adenocarcinomas and normal prostate structures tested were negative. In contrast, all seminal vesicles were diffusely immunostained with MUC6 antibody. We concluded that MUC6 is a valuable marker of seminal vesicle-ejaculatory duct and is useful for the differential diagnosis with prostate adenocarcinoma.