Degenerate 87-base-pair tandem repeats create hydrophilic/hydrophobic alternating domains in human mucin peptides mapped to 11p15

Mutational Impacts on the N and C Terminal Domains of the MUC5B Protein: A Transcriptomics and Structural Biology Study

Cholangiocarcinoma (CCA) involves various epithelial tumors historically linked with poor prognosis because of its aggressive sickness course, delayed diagnosis, and limited efficacy of typical chemotherapy in its advanced stages. In-depth molecular profiling has exposed a varied scenery of genomic alterations as CCA's oncogenic drivers. Previous studies have mainly focused on commonly occurring TP53 and KRAS alterations, but there is limited research conducted to explore other vital genes involved in CCA. We retrieved data from The Cancer Genome Atlas (TCGA) to hunt for additional CCA targets and plotted a mutational landscape, identifying key genes and their frequently expressed variants. Next, we performed a survival analysis for all of the top genes to shortlist the ones with better significance. Among those genes, we observed that MUC5B has the most significant p-value of 0.0061. Finally, we chose two missense mutations at different positions in the vicinity of MUC5B N and C terminal domains. These mutations were further subjected to molecular dynamics (MD) simulation, which revealed noticeable impacts on the protein structure. Our study not only reveals one of the highly mutated genes with enhanced significance in CCA but also gives insights into the influence of its variants. We believe these findings are a good asset for understanding CCA from genomics and structural biology perspectives.

Secreted Mucins on the Ocular Surface

Mucins, which play important roles on the ocular surface in wettability, lubrication, and barrier function, are classified into two categories: secreted mucins and membrane-associated mucins. The most important secreted mucin on the ocular surface is MUC5AC, which is secreted by the conjunctival goblet cells. In the human conjunctiva, goblet cells are present in higher concentrations in the fornix, inferior nasal bulbar, and the lid wiper on the lid margin. The number of conjunctival goblet cells and MUC5AC expression/secretion are decreased in a patient with dry eye. In Japan, drugs that stimulate mucin secretion or increase the number of conjunctival goblet cells are commercially available. A P2Y2 receptor, diquafosol, stimulates tear fluid secretion from conjunctival epithelial cells and promotes mucin secretion from conjunctival goblet cells. Rebamipide was marketed originally as an oral therapeutic drug to treat gastritis in Japan. Topical rebamipide increases numbers of goblet cells in the bulbar conjunctiva and the lid wiper area of palpebral conjunctiva. Many researchers have reported decreases in the ocular surface mucin expression including MUC5AC secreted by goblet cells in patients with dry eye. However, it is unknown whether changes in mucin expression on the ocular surface cause or result from dry eye. Further study is needed to determine the true mechanism of dry eye disease.

MUC Expression in Gallbladder Epithelial Tissues in Cholesterol-Associated Gallbladder Disease

Background/Aims

Gallstone pathogenesis is linked to mucin hypersecretion and bacterial infection. Several mucin genes have been identified in gallbladder epithelial cells (GBECs). We investigated MUC expression in cholesterol-associated gallbladder disease and evaluated the relationship between mucin and bacterial infection.

Methods

The present study involved 20 patients with cholesterol stones with cholecystitis, five with cholesterol stones with cholesterolosis, six with cholesterol polyps, two with gallbladder cancer, and six controls. Canine GBECs treated with lipopolysaccharide were also studied. MUC3, MUC5AC, MUC5B, and MUC6 antibodies were used for dot/slot immunoblotting and immunohistochemical studies of the gallbladder epithelial tissues, canine GBECs, and bile. Reverse-transcription polymerase chain reaction was performed to evaluate MUC3 and MUC5B expression.

Results

MUC3, MUC5AC, MUC5B, and MUC6 were expressed in the normal gallbladder epithelium, and of those, MUC3 and MUC5B exhibited the highest expression levels. Greatly increased levels of MUC3 and MUC5B expression were observed in the cholesterol stone group, and slightly increased levels were observed in the cholesterol polyp group; MUC3 and MUC5B mRNA was also upregulated in those groups. Canine GBECs treated with lipopolysaccharide also showed upregulation of MUC3 and MUC5B.

Conclusions

The mucin genes with the highest expression levels in gallbladder tissue in cholesterol-associated diseases were MUC3 and MUC5B. Cholesterol stones and gallbladder infections were associated with increased MUC3 and MUC5B expression.

Cellular and molecular biology of airway mucins

Airway mucus constitutes a thin layer of airway surface liquid with component macromolecules that covers the luminal surface of the respiratory tract. The major function of mucus is to protect the lungs through mucociliary clearance of inhaled foreign particles and noxious chemicals. Mucus is comprised of water, ions, mucin glycoproteins, and a variety of other macromolecules, some of which possess anti-microbial, anti-protease, and anti-oxidant activities. Mucins comprise the major protein component of mucus and exist as secreted and cell-associated glycoproteins. Secreted, gel-forming mucins are mainly responsible for the viscoelastic property of mucus, which is crucial for effective mucociliary clearance. Cell-associated mucins shield the epithelial surface from pathogens through their extracellular domains and regulate intracellular signaling through their cytoplasmic regions. However, neither the exact structures of mucin glycoproteins, nor the manner through which their expression is regulated, are completely understood. This chapter reviews what is currently known about the cellular and molecular properties of airway mucins.

Mucin methods: genes encoding mucins and their genetic variation with a focus on gel-forming mucins

Mucin genes encode the polypeptide backbone of the mucin glycoproteins which are expressed on all epithelial surfaces and are major constituents of the mucus layer. Mucins are, thus, expressed at the interface between the external and the internal environment of the organism, and represent the first line of defence of our body. These genes often have an extensive region of repetitive exonic sequence which codes for the heavily glycosylated domain, whose roles include bacterial interactions and gel hydration. This region shows, in several of the genes, considerable inter-individual variation in repeat number and sequence. Because of their site of expression and their high variability in this important domain, mucin genes are good candidates for conferring differences in genetic susceptibility to multifactorial epithelial and inflammatory disease. However, progress in characterizing the genes has been considerably slower than the rest of the genome because of their size and the GC-rich content of the large, repetitive variable region. Some of the issues relating to the study of these genes are discussed in this chapter. In addition, methods and approaches that have been used successfully are described.

Mucin-bacterial interactions in the human oral cavity and digestive tract

Mucins are a family of heavily glycosylated proteins that are the major organic components of the mucus layer, the protective layer covering the epithelial cells in many human and animal organs, including the entire gastro-intestinal tract. Microbes that can associate with mucins benefit from this interaction since they can get available nutrients, experience physico-chemical protection and adhere, resulting in increased residence time. Mucin-degrading microorganisms, which often are found in consortia, have not been extensively characterized as mucins are high molecular weight glycoproteins that are hard to study because of their size, complexity and heterogeneity. The purpose of this review is to discuss how advances in mucus and mucin research, and insight in the microbial ecology promoted our understanding of mucin degradation. Recent insight is presented in mucin structure and organization, the microorganisms known to use mucin as growth substrate, with a specific attention on Akkermansia muciniphila, and the molecular basis of microbial mucin degradation owing to availability of genome sequences.

Current status of mucins in the diagnosis and therapy of cancer

Mucins are the most abundant high molecular weight glycoproteins in mucus. Their nature and glycosylation content dictates the biochemical and biophysical properties of viscoelastic secretions, pointing out an important role in diverse biological functions, such as differentiation, cell adhesions, immune responses, and cell signaling. Mucins are expressed in tubular organs by specialized epithelial cells in the body. Their aberrant expression is well documented in a variety of inflammatory or malignant diseases. From a prognosis point of view, their expression and alterations in glycosylation are associated with the development and progression of malignant diseases. Therefore, mucins can be used as valuable markers to distinguish between normal and disease conditions. Indeed, this alteration in glycosylation patterns generates several epitopes in the oligosaccharide side chains that can be used as diagnostic and/or prognostic markers. Furthermore, these characteristic tumor-associated epitopes are extensively used as appropriate immunotargets of malignant epithelial cells. Therefore, in an effort to detect and treat cancer at the earliest stage possible, mucins are analyzed as potential markers of disease for diagnosis, progression, and for therapeutic purposes. In this review, we focused on the current status of the distribution of mucins in normal and pathologic conditions and their clinical use both in cancer diagnosis and therapeutics treatments.

MUC2 mucin is a major carrier of the cancer-associated sialyl-Tn antigen in intestinal metaplasia and gastric carcinomas

Changes in mucin protein expression and in glycosylation are common features in pre-neoplastic lesions and cancer and are therefore used as cancer-associated markers. De novo expression of intestinal mucin MUC2 and cancer-associated sialyl-Tn antigen are frequently observed in intestinal metaplasia (IM) and gastric cancer. However, despite that these antigens often co-localize, MUC2 has not been demonstrated to be a carrier of sialyl-Tn. By using the in situ proximity ligation assay (in situ PLA), we herein could show that MUC2 is a major carrier of the sialyl-Tn antigen in all IM cases and in most gastric carcinoma cases. The requirement by in situ PLA for the presence of both antigens in close proximity increases the selectivity compared to measurement of co-localization, as determined by immunohistochemistry. Identification of the mucin which is the carrier of a carbohydrate structure offers unique advantages for future development of more accurate diagnostic and prognostic markers.

Character of ocular surface mucins and their alteration in dry eye disease

At the ocular surface, three types of mucins are present. The large gel-forming mucin MUC5AC is expressed by conjunctival goblet cells. Some cells of the lacrimal gland acini express the small soluble mucin MUC7. The corneal and conjunctival epithelia express the membrane-associated mucins MUCs 1, 4, and 16. With the characterization of the mucin gene repertoire of the ocular surface epithelia, studies of the function of specific mucins, their gene regulation, and their alteration in ocular surface disease have begun. Current information suggests that all the mucins are hydrophilic and play a role in maintenance of water on the surface of the eye. The large secreted mucins represent the "janitorial service" that moves over the surface of the eye to wrap up and remove debris. The membrane-associated mucins form the glycocalyx, which provides a continuous barrier across the surface of the eye that prevents pathogen penetrance and has signaling capabilities that influence epithelial activity. Factors regulating mucin gene expression include retinoic acid, serum, and dexamethasone. Alteration in both secreted and membrane-associated mucins occur in drying ocular surface diseases. In Sjogren syndrome, MUC5AC expression is reduced, and in non-Sjogren dry eye, glycosylation of MUC16 appears to be altered. The pattern of expression of enzymes that glycosylate mucins is altered in ocular cicatricial pemphigoid. Therapies being evaluated for dry eye, including cyclosporine A, P2Y2 agonists, gefarnate, 15-(S)-HETE, and corticosteroids, may be efficacious due to their effect on mucin gene expression and secretion.

Mucin gene expression in human male urogenital tract epithelia

BACKGROUND

Mucins are large, hydrophilic glycoproteins that protect wet-surfaced epithelia from pathogen invasion as well as provide lubrication. At least 17 mucin genes have been cloned to date. This study sought to determine the mucin gene expression profile of the human male urogenital tract epithelia, to determine if mucins are present in seminal fluid and to assess the effect of androgens on mucin expression.

METHODS AND RESULTS

Testis, epididymis, vas deferens, seminal vesicle, prostate, bladder, urethra and foreskin were assessed for mucin expression by RT-PCR (for 14 mucin genes) and immunohistochemistry (nine antibodies for five mucins). Epithelia of the vas deferens, prostate and urethra expressed the greatest number of mucins, each with mRNA for between 5 and 8 mucins. Except for MUC20 in epididymis, mRNA for MUC1 and MUC20, both membrane-associated mucins, was detected in all tissues analysed. By comparison, MUC6 was more restricted in expression, being primarily detected in seminal vesicle. MUC1, MUC5B and MUC6 were detected in seminal fluid samples by immunoblot analysis. Androgens had no effect on mucin expression in cultured human prostatic epithelial cells.

CONCLUSIONS

Each region of urogenital tract epithelium expressed a unique mucin gene repertoire. Secretory mucins are present in seminal fluid, and androgens do not appear to regulate mucin gene expression in prostatic epithelial cells in culture.

Expression profile of mucins (MUC2, MUC5AC and MUC6) in Helicobacter pylori infected pre-neoplastic and neoplastic human gastric epithelium

BACKGROUND

Helicobacter pylori (H. pylori) causes gastritis and intestinal metaplasia (IM) that may evolve to gastric carcinoma. The objective of this study was to compare the profile of mucins in the progressive stages of H. pylori infected pre-neoplastic and neoplastic human gastric epithelium. We used a panel of monoclonal antibodies with well-defined specificities of MUC2, MUC5AC and MUC6 to characterize the expression pattern of mucins by immunohistochemistry.

METHODS

RUT and ELISA were down for H. pylori confirmation. Human gastric biopsy sections were stained using immunohistochemistry with MUC2, MUC5AC and MUC6 antibodies.

RESULTS

MUC5AC was expressed in the superficial epithelium and the upper part of the gastric pits. MUC6 expression was detected in the lower part of the gastric glands. MUC2 was expressed in intestinal metaplasia, mostly in goblet cells. The mucin expression profile in the progressive stages of H. pylori infected human gastric epithelium allows the identification of intestinal metaplasia, which is characterized by a decreased expression of the gastric mucins (MUC5AC and MUC6) and de novo expression of MUC2.

CONCLUSION

In conclusion, our results suggest that there is altered expression of MUC5AC and MUC6 together with the aberrant expression of MUC2 in intestinal metaplasia, during the process of gastric carcinogenesis. The present study indicates that the MUC2 mucin expression pattern is a reliable marker of intestinal metaplasia, which appears in the context of H. pylori infected individuals.

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.

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.

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.

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.

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.

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.

MUC5B expression in gastric carcinoma: relationship with clinico-pathological parameters and with expression of mucins MUC1, MUC2, MUC5AC and MUC6

Previous studies have shown that mucin expression can be used to evaluate differentiation patterns of gastric carcinoma: MUC5AC expression is associated with diffuse type and early gastric carcinomas, and MUC2 expression is associated with mucinous gastric carcinomas. The role played by MUC5B in the evaluation of differentiation and biological behaviour of gastric carcinoma is largely unknown. Our aim was to characterise the pattern of expression of mucins MUC1, MUC2, MUC5AC, MUC5B and MUC6 in a series of 50 gastric carcinomas to evaluate whether MUC5B expression was associated with the clinico-pathological characteristics of the cases and/or with the co-expression of other mucins. A panel of six monoclonal antibodies (HMFG1, SM3, PMH1, CLH2, EU-MUC5Ba and CLH5) was used to determine the expression of mucins (MUC1, MUC1 underglycosylated form, MUC2, MUC5B, MUC5AC and MUC6, respectively) using immunohistochemistry. Cases were considered positive if more than 5% of the cells expressed immunoreactivity for the several mucins evaluated. Our results showed that: (a) expression of MUC5B was observed in 11 cases (22.0%) and was associated with the "unclassified" histological type of gastric carcinoma according to Laurén ( P = 0.03) and with the absence of venous invasion ( P = 0.02); (b) in this series, MUC5B expression had no impact on survival of patients with gastric carcinoma; (c) the expression of MUC5B was associated with the co-expression of MUC5AC ( P = 0.02) and (d) none of the cases with the so-called complete intestinal phenotype of mucin expression expressed MUC5B.

Expression of mucins in mucoid otitis media

A hallmark of mucoid otitis media (MOM, i.e., chronic otitis media with mucoid effusion) is mucus accumulation in the middle ear cavity, a condition that impairs transduction of sounds in the ear and causes hearing loss. The mucin identities of mucus and the underlying mechanism for the production of mucins in MOM are poorly understood. In this study, we demonstrated that the MUC5B and MUC4 were major mucins in MOM that formed distinct treelike polymers (mucus strands). The MUC5B and MUC4 mRNAs in the middle ear mucosa with MOM were up regulated 5-fold and 6-fold, compared with the controls. This upregulation was accompanied by the extensive proliferation of the MUC5B- and MUC4-producing cells in the middle ear epithelium. Further study indicated that the mucin hyperproduction was significantly linked to CD4+ and CD8+ T cells and/or CD68+ monocyte macrophages. It suggests that MUC5B and MUC4 expression may be regulated by the products of these cells.

Expression of MUC1 and MUC2 mucins in gastric carcinomas: their relationship with clinicopathologic parameters and prognosis

The aim of this study was to investigate the relationship between MUC1 and MUC2 mucin expressions and clinicopathologic variables in gastric carcinomas with regard to survival times. MUC1 and MUC2 expressions were revealed immunohistochemically in 143 gastric carcinomas. Of these 143 patients, follow-up data were available for 45 (median survival time of 30 months, ranging from 2 to 80 months). MUC1 was detected in 82 (58%), and MUC2 in 60 (42%) out of 143 cases. Papillary adenocarcinomas showed significantly higher MUC1 and MUC2 immunoreactivity than did signet-ring cell and mucinous tumors (p = 0.045 and p = 0.01, respectively). MUC1 was highly positive in intestinal-type carcinomas (p = 0.006), whereas intestinal and diffuse carcinomas did not differ in MUC2 expression. There was a positive correlation between tumor differentiation and MUC1 expression. However, no correlation was found between MUC1 and MUC2 expressions and angiolymphatic invasion. According to the TNM classification, stage 1A tumors have significantly lower rates of MUC1 reactivity compared to higher stages (p = 0.04). The patients with gastric carcinomas expressing MUC1 showed significantly poorer survival than those without MUC1 expression (p = 0.04). The present study suggests that MUC1 expression be a useful prognostic factor for predicting the outcome of gastric carcinoma patients, whereas the role of MUC2 expression is still unclear.

Role of Mucins in the Function of the Corneal and Conjunctival Epithelia

The surface of the eye is covered by a tear film, which is held in place by a wet-surfaced, stratified, corneal and conjunctival epithelia. Both are vital for light refraction and protection of vision. Maintenance of tear film on the ocular surface, lubrication, and provision of a pathogen barrier on this wet surface is facilitated by a class of large, highly glycosylated, hydrophilic glycoproteins--the mucins. In the past 15 years, a number of mucin genes have been cloned, and based on protein sequence, categorized as either secreted or membrane associated. Both types of mucins are expressed by ocular surface epithelia. Goblet cells intercalated within the stratified epithelium of the conjunctiva secrete the large gel-forming mucin MUC5AC, and lacrimal gland epithelia secrete the small soluble mucin MUC7. Apical cells of the stratified epithelium of both corneal and conjunctival epithelium express at least three membrane-associated mucins (MUCs 1, 4, and 16), which extend from their apical surface to form the thick glycocalyx at the epithelium-tear film interface. The current hypothesis regarding mucin function and tear film structure is that the secreted mucins form a hydrophilic blanket that moves over the glycocalyx of the ocular surface to clear debris and pathogens. Mucins of the glycocalyx prevent cell-cell and cell-pathogen adherence. The expression and glycosylation of mucins are altered in drying, keratinizing ocular surface diseases.

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.

Expression of mucin core proteins in extramammary Paget's disease

Extramammary Paget's disease (EPD) is a relatively common skin cancer wherein tumor cells have mucin in their cytoplasm. However, little is known about mucin expression in EPD. We examined immunohistochemically the expression of mucin core proteins (MUC1, MUC2, MUC5AC and MUC6) in 36 cases of EPD and found different patterns of expression in intraepithelial (n = 36), microinvasive (n = 13) and invasive lesions (n = 6). In normal skin, MUC1 was expressed in the sebaceous, eccrine and apocrine glands. MUC2, MUC5AC and MUC6 were not expressed in any of these. In the 36 intraepithelial lesions, MUC1 and MUC5AC were expressed in 35 and 36 lesions, respectively. MUC1 expression was also observed in all 13 microinvasive lesions and in all six invasive lesions. In contrast to the intraepithelial lesions, a decrease or loss of MUC5AC expression was observed in five out of 13 microinvasive lesions and in all six invasive lesions. MUC2 and MUC6 were not expressed in any of the EPD lesions examined. The combination of immunohistochemical staining for MUC1 and MUC5AC was useful for identifying invasive Paget cells. The decrease or loss of MUC5AC expression may have an important role in the invasive growth of Paget cells.

The mucin profile of noninvasive and invasive mucinous cystic neoplasms of the pancreas

Recently, it was shown that ductal adenocarcinomas and intraductal papillary-mucinous neoplasms of the pancreas differ in their expression of the mucin markers MUC1 and MUC2 while both tumors express MUC5AC. It is not known whether mucinous cystic neoplasms of the pancreas have their own mucin profile. To clarify this issue, 22 mucinous cystic neoplasms were examined immunohistologically for their expression of MUC1, MUC2, MUC5AC, and MUC6 and also for the protein products of the tumor suppressor genes p53 and DPC4 and the mismatch repair genes. Noninvasive mucinous cystic neoplasms, regardless of the degree of cellular atypia, were all positive for MUC5AC and negative for MUC1, with the exception of the cyst-lining epithelium of a single case with eosinophilic cytology (case no. 16). Only in cases with an invasive component was MUC1 expression observed. MUC2 expression was restricted to goblet cells scattered within the epithelium of the mucinous cystic neoplasms and was often accompanied by endocrine cells, a further indication of intestinal differentiation. DPC4 expression was maintained in all tumors, except for three invasive carcinomas. p53 nuclear reactivity was found in one borderline tumor and four invasive mucinous cystic carcinomas. The results suggest that the epithelium of noninvasive mucinous cystic neoplasms does not differ in its expression of MUC5AC from ductal adenocarcinomas, intraductal papillary-mucinous neoplasms, and metaplastic pancreatic duct epithelium. The fact that noninvasive mucinous cystic neoplasms lack MUC1 expression (except for an eosinophilic variant) but express it when they become invasive might be used as a marker indicating the step of progression from noninvasiveness to invasiveness.

Significance of mucin on the ocular surface

PURPOSE

To review the significance of mucin in the tear film and the ocular surface epithelium.

METHODS

Summary of the information on how mucin derived from the corneal and conjunctival epithelia and from goblet cells plays a role in the stability of the tear film over the ocular surface. The change in mucin expression derived from the ocular surface epithelium is also discussed with reference to ocular surface disease.

RESULTS

The corneal and conjunctival epithelia produce transmembrane mucins such as MUC1, MUC2, and MUC4. In contrast, goblet cells produce the gel-forming secretory mucin, MUC5AC. The lacrimal gland produces MUC7. On the ocular surface, cooperation between transmembrane mucin and secretory mucin is necessary for the stability of the tear film. The expression of mucin from the ocular surface epithelium is coordinated from the time of eyelid opening and is altered in conditions such as squamous metaplasia and dry eye. This alteration may result in instability of the tear film. CONCLU SION: The induction of mucin from the ocular surface may facilitate the stability of the tear film, and increased knowledge may lead to the development of a new modality for the treatment of dry eye.

Pattern changes of mucin gene expression with pneumococcal otitis media

OBJECTIVE

mucins, known to be important components of the mucociliary transport system in the middle ear and Eustachian tube, are subject to changes under inflammatory conditions. Which mucin genes are up-regulated or activated during an inflammatory reaction of the middle ear and Eustachian tube, however, is poorly understood. The purpose of this study was to characterize mucin gene expression in middle ears and Eustachian tubes with pneumococcal ear infection.

METHODS

sixteen rats received intrabullar inoculation of Streptococcus pneumoniae type 6A at 2.5x10(6) colony forming units (CFU). Four animals were sacrificed on days 1, 3, 7, and 14, respectively. The profile of mucin gene expression in the middle ear and Eustachian tube was examined by reverse transcription polymerase chain reaction (RT-PCR) at the above time points. Sixteen rats that received intrabullar inoculation of phosphate-buffered saline (PBS) served as controls.

RESULTS

the Muc2 mucin gene was expressed in middle ear mucosa of the control rats. Following pneumococcal inoculation, Muc1-Muc5 mucin genes were expressed in the middle ear mucosa in a time-dependent manner. In the Eustachian tube, the Muc2, Muc4 and Muc5 mucin genes were expressed in both control and pneumococcal inoculation groups.

CONCLUSION

Muc1, Muc3, Muc4, and Muc5 mucin genes were activated in the middle ear mucosa by pneumococci, which may contribute to hyper-production of mucin in acute pneumococcal otitis media.

Altered mucin gene expression in stone-containing intrahepatic bile ducts and cholangiocarcinomas

Neoplastic transformation of epithelial cells is commonly associated with alterations in the synthesis and structures of mucin. Mucin protein epitopes and mRNA levels were frequently altered in adenocarcinomas compared to corresponding normal tissues. Clinically, hepatolithiasis has been regarded as a risk factor for cholangiocarcinoma. The aims of this study were to determine the possible alteration of mucin gene expression in stone-containing intrahepatic bile ducts and cholangiocarcinomas and to try to predict whether or not hepatolithiasis has a predisposition to development of cholangiocarcinoma. In situ hybridization with DIG-tailed oligonucleotides was performed on sections of paraffin-embedded tissues of stone-containing intrahepatic bile ducts, cholangiocarcinomas, and normal controls to identify the expression of MUC2, MUC3, MUC4, MUC5B, and MUC5AC in nonneoplastic and neoplastic biliary epithelium. The findings showed that (1) while multiple diverse mucin genes were expressed in the biliary epithelium, MUC3 and MUC5B mRNA were the main mucin genes expressed in the biliary epithelium of stone-containing intrahepatic bile ducts and normal controls; (2) absent or decreased expression of MUC2, MUC3, and MUC5B of mRNA was found in cholangiocarcinomas in contrast to nonneoplastic biliary epithelium; and (3) increased expression of MUC4 and MU5AC of mRNA was found in cholangiocarcinomas and the biliary epithelium, especially for dysplastic cells of stone-containing intrahepatic bile ducts compared with normal controls. In this study, using in situ hybridization we demonstrated that neoplastic transformation of the biliary epithelium is accompained by alterations in mucin gene expression, the altered mucin gene expression in dysplastic cells of stone-containing intrahepatic bile ducts may reflect a higher potential for malignant transformation in these cells, and it could be a precursor of cholangiocarcinoma in the presence of hepatolithiasis.

Expression of MUC1 and MUC2 and carbohydrate antigen Tn change during malignant transformation of biliary papillomatosis

AIM

Biliary papillomatosis is characterized by papillary proliferations of biliary lining cells without invasion or metastasis. The neoplastic character and biological behaviour of this disease remain still speculative. These issues were examined in this study.

METHODS AND RESULTS

Mucin core protein MUC1, MUC2, MUC3, MUC5AC and carbohydrate antigens (T, Tn and sialosyl Tn) were immunohistochemically examined, using 11 lesions of biliary papillomatosis from seven patients, and five lesions of biliary papillomatosis with foci of carcinoma from four patients. Five cases of papillary intrahepatic cholangiocarcinoma and 12 histologically normal livers were used as a control. Patients with biliary papillomatosis alone or with carcinoma were middle-aged or elderly (five men and six women). Microscopically, biliary papillomatosis showed a villous, papillo-tubular, papillary, or papillo-villous pattern with a thin fibrovascular core. Cytologically, they were classifiable into biliary epithelial or pyloric gland-like type. The former was frequent in the cases associated with carcinoma. Expression of MUC1, Tn antigen and sialosyl Tn antigen was frequent and marked in biliary papillomatosis alone and with carcinoma and also intrahepatic papillary carcinoma. In addition, marked expression of MUC1 and Tn antigen were rather frequent in biliary papillomatosis with carcinoma and intrahepatic biliary papillary carcinoma compared with biliary papillomatosis. MUC2 was rather frequent and marked in biliary papillomatosis alone compared to other two disease groups. Focal expression of MUC5AC and MUC2 was rather frequent and infrequent irrespective of disease group, respectively. Focal expression of T antigen was frequent in papillary ICC.

CONCLUSION

Biliary papillomatosis could undergo overt malignant transformation along with altered phenotypic expression of MUC proteins and mucin carbohydrate antigens.

Characterization of mucins in human middle ear and Eustachian tube

Mucins are important glycoproteins in the mucociliary transport system of the middle ear and Eustachian tube. Little is known about mucin expression within this system under physiological and pathological conditions. This study demonstrated the expression of MUC5B, MUC5AC, MUC4, and MUC1 in the human Eustachian tube, whereas only MUC5B mucin expression was demonstrated in noninflamed middle ears. MUC5B and MUC4 mucin genes were upregulated 4.2- and 6-fold, respectively, in middle ears with chronic otitis media (COM) or mucoid otitis media (MOM). This upregulation of mucin genes was accompanied by an increase of MUC5B- and MUC4-producing cells in the middle ear mucosa. Electron microscopy of the secretions from COM and MOM showed the presence of chainlike polymeric mucin. These data indicate that the epithelium of the middle ear and Eustachian tube expresses distinct mucin profiles and that MUC5B and MUC4 mucins are highly produced and secreted in the diseased middle ear. These mucins may form thick mucous effusion in the middle ear cavity and compromise the function of the middle ear.

Aberrant expression of human mucin gene MUC5B in gastric carcinoma and cancer cells. Identification and regulation of a distal promoter

In gastric cancer, altered expression of MUC1, MUC2, MUC5AC, and MUC6 mucin genes has already been described. We show in this report by the means of in situ hybridization, reverse transcriptase-polymerase chain reaction, and transfection assays that MUC5B is also abnormally expressed in gastric carcinomatous tissues and cell lines. We thus undertook to elucidate the molecular mechanisms that regulate the transcription of MUC5B in gastric cancer cells. To this end, high expressing (KATO-III) and low expressing (AGS) gastric cancer cell lines were chosen to study human mucin gene MUC5B expression and promoter activity. Sequencing of the promoter region revealed a distal TATA box located 1 kilobase upstream of the proximal TATA box. Functional activity of the promoter was addressed by using deletion mutants covering 2044 nucleotides upstream of the MUC5B transcription start site. We identified a distal promoter 10 times more active than the proximal promoter in KATO-III cells. In AGS cells, both promoters, much less active, showed the same range of activity. Binding assays allowed us to show that the transcription factor ATF-1 binds to a cis-element present in the distal promoter. Sp1, which binds to both promoters specifically transactivates the proximal promoter. Treatment of transfected cells with PMA, cholera toxin A subunit, and calcium ionophore showed that only PMA led to a substantial activation of the distal promoter. MUC5B 5'-flanking region having a high GC content, influence of methylation on the MUC5B expression was assessed. Our results indicate that repression of MUC5B expression visualized in AGS cells is due in part to the presence of numerous methylated cytosine residues throughout the 5'-flanking region. Altogether these results demonstrate that MUC5B expression in gastric cancer cells is governed by a highly active distal promoter that is up-regulated by protein kinase C and that repression is under the influence of methylation.

Alternate splicing at the 3'-end of the human pancreatic tumor-associated mucin MUC4 cDNA

MUC4 is a membrane-bound mucin and is considered as the human homologue of the rat sialomucin complex (SMC). The deduced structural organization of the wild type-MUC4 cDNA (WT-MUC4) sequence revealed two subunits: a large amino mucin type subunit (MUC4alpha) and a transmembrane subunit (MUC4beta). MUC4beta is a membrane-bound growth factor like subunit and contains three EGF-like domains. The MUC4 gene is expressed in several normal tissues like trachea, lung, and testis. It is not expressed in a normal human pancreas; however, its dysregulation results in high levels of expression in pancreatic tumors and tumor cell lines. Recently, we have demonstrated the presence of alternative splice events in the 3'-end of the MUC4 cDNA that generated new putative variants (sv1-sv10) in normal human testis and in a pancreatic tumor cell line (HPAF). In search of MUC4 variant(s) that are specific to pancreatic adenocarcinoma, we investigated the splicing phenomena in the MUC4 cDNA sequence by using a large panel of pancreatic tumor cell lines. We have identified ten alternative splice events located downstream to the central large tandem repeat domain. These splice events generated 12 variant species (sv4, sv9, sv10-18, and sv21) of MUC4 cDNAs. The deduced amino acid sequence of these variant MUC4 cDNAs revealed two distinct types: a family of secreted and a membrane-associated variant form. Among the members of MUC4 secreted variant family, three (sv4, sv12, and sv13) of ten showed a short 144 residue COOH-terminus compared to 1154 residues in WT-MUC4. The variants with this short COOH-terminus (144 residues) was found in 37% (4/11) of the tumor lines. The putative membrane-bound variant sv10 was detected in 37% (4/11) pancreatic tumor cell lines but not in any normal human tissues. In conclusion, we have identified novel splice variant(s) of MUC4 in pancreatic adenocarcinoma.

Heterogeneity of high-molecular-weight human salivary mucins

The existence of high-molecular-weight glycoproteins in saliva and salivary secretions has been recognized for nearly 30 years. These proteins, called mucins, are essential for oral health and perform many diverse functions in the oral cavity. Mucins have been intensively studied, and much has been learned about their biochemical properties and their interactions with oral micro-organisms and other salivary proteins. In the past several years, the major high-molecular-weight mucin in salivary secretions has been identified as MUC5B, one of a family of 11 human mucin gene products expressed in tissue-specific patterns in the gastrointestinal, respiratory, and reproductive tracts. MUC5B is one of four gel-forming mucins which exist as multimeric proteins with molecular weights greater than 20-40 million daltons. The heavily glycosylated mucin multimers form viscous layers which protect underlying epithelial surfaces from microbial, mechanical, and chemical assault. Another class of mucin molecules, the membrane-bound mucins, is structurally and functionally distinct from the gel-forming mucins. These proteins do not form multimers and can exist as both secreted and membrane-bound forms, with the latter anchored to epithelial cell membranes through a short membrane-spanning domain. In the present work, we show that two of the membrane-bound mucins, MUC1 and MUC4, are expressed in all major human salivary glands as well as in buccal epithelial cells. While the functions of these mucins in the oral environment are not understood, it is possible that they form a structural framework on the cell surface which not only is cytoprotective, but also may serve as a scaffold upon which MUC5B, and possibly other salivary proteins, assemble.

Coordinated localisation of mucins and trefoil peptides in the ulcer associated cell lineage and the gastrointestinal mucosa

BACKGROUND AND AIMS

Trefoil factor family (TFF) peptides and the chromosome 11p15.5 mucin glycoproteins are expressed and secreted in a site specific fashion along the length of the gastrointestinal tract. Evidence for coexpression of mucins and trefoil peptides has been suggested in numerous gastrointestinal mucosal pathologies. The ulcer associated cell lineage (UACL) occurs at sites of chronic ulceration in Crohn's disease, expresses all three trefoil peptides, and is implicated in mucosal restitution. We tested the hypothesis that individual trefoil peptides are uniquely localised with specific mucins in the UACL and normal gastrointestinal epithelia.

METHODS

Expression of mucin genes in the UACL from small bowel tissue of patients with Crohn's disease was detected by in situ hybridisation, and localisation of the products by immunohistochemistry. Colocalisation of mucins and trefoil peptides was demonstrated by immunofluorescent colabelling in UACL and normal gastrointestinal epithelia.

RESULTS

MUC5AC and TFF1 were colocalised in distal ductular and surface elements of the UACL and in foveolar cells of the stomach, whereas MUC6 and TFF2 were colocalised to acinar and proximal ductular structures in the UACL, in the fundus and deep antral glands of the stomach, and in Brunner's glands of the duodenum. MUC5B was found sporadically throughout the UACL and gastric body. MUC2 was absent from the UACL, Brunner's glands, and stomach. MUC2 and TFF3 were colocalised throughout the large and small bowel mucosa.

CONCLUSIONS

The UACL has a unique profile of mucin gene expression. Coordinated localisation of trefoil peptides and mucins in UACL and normal gastrointestinal epithelia suggests they may assist each others' functions in protection and repair of gastrointestinal mucosa.

Polymorphism of human mucin genes in chest disease: possible significance of MUC2

Most of the genes that encode epithelial mucins are highly polymorphic due to variations in the length of domains of tandemly repeated (TR) coding sequence, the part of the apomucin that is heavily glycosylated. We report here for the first time a difference in the distribution of MUC TR length alleles in chest disease. We examined the distribution of the length alleles of those MUC genes whose expression we have confirmed in the bronchial tree in an age- and sex-matched series of 50 pairs of atopic patients with and without asthma. There was no significant difference in the distribution of alleles of MUC1, MUC4, MUC5AC, and MUC5B. MUC2, however, showed a highly significant difference in distribution. The atopic, nonasthmatic individuals showed an allele distribution that was very different from all our other patient and control groups, this group showing a longer mean allele length. The observations suggest that longer MUC2 alleles may help protect atopic individuals from developing asthma, though the effect may be due to a linked gene. The biological significance of this variation with respect to susceptibility to asthma will merit further investigation, and it will also be important to substantiate this finding on an independent data set.

Retinoic acid-dependent transforming growth factor-beta 2-mediated induction of MUC4 mucin expression in human pancreatic tumor cells follows retinoic acid receptor-alpha signaling pathway

The MUC4 mucin is considered as the homologue of rat sialomucin complex (SMC, rat Muc4) due to its similar structural organization. Like SMC, MUC4 may also exist as two subunits: a mucin type unit known as MUC4alpha and a growth factor-like transmembrane subunit, MUC4beta. The expression of MUC4 in normal human pancreas is not detectable, but it is highly expressed in pancreatic tumor cells. In the present study, we investigated the regulation of MUC4 expression in human pancreatic tumor cells CD18/HPAF, exhibiting a high level of MUC4 transcripts and protein. When these cells were adapted to grow in the serum-free medium (CD18/HPAF-SF), the MUC4 expression was undetectable. Among several serum constituents, all-trans-retinoic acid (RA) induced the expression of MUC4 transcripts in a concentration- and time-dependent manner. The RA-mediated increase in the level of the MUC4 transcript coincided with an increased expression of transforming growth factor-beta2 (TGF-beta2) transcript. The antagonist of the retinoic acid receptor (RAR)-alpha (Ro41-5253) abrogated the expression of MUC4 and TGF-beta2 induced by RA. The exogenous addition of TGF-beta2 also increased the MUC4 expression. The TGF-beta-neutralizing antibody blocked the RA-induced as well as TGF-beta2-mediated MUC4 expression. In conclusion, induction of MUC4 expression in pancreatic carcinoma by RA is mediated through the RAR-alpha signaling pathway, and TGF-beta2 may serve as an interim mediator of this regulated expression.

Role of fucosyltransferases in the association between apomucin and Lewis antigen expression in normal and malignant gastric epithelium

BACKGROUND

In normal gastric epithelium, MUC5AC is detected in superficial epithelium associated with Lewis type 1 antigens and MUC6 is detected in antral glands with Lewis type 2. Therefore, the stomach constitutes an excellent model to examine the role of glycosyltransferases in determining the specificity of apomucin glycosylation.

AIMS

To determine the molecular basis of this association and to examine changes in expression of gastric and intestinal apomucins and their association with Lewis antigens during the gastric carcinogenesis process.

METHODS

Fucosyltransferase (FUT1, FUT2, FUT3) and mucin (MUC5AC, MUC6) transcripts were detected using reverse transcription-polymerase chain reaction. Apomucin (MUC2, MUC4, MUC5AC, MUC6) and Lewis antigen (types 1 and 2) expression were analysed using single and double immunohistochemistry and in situ hybridisation.

RESULTS

In the normal stomach, FUT1 is exclusively detected associated with MUC6; FUT2 is only detected when MUC5AC is present. This co-regulation is lost in gastric tumours, as is differential expression of MUC5AC and MUC6 in normal gastric epithelial cells. In gastric tumours, especially those with the intestinal phenotype, MUC2 and MUC4 genes are upregulated, and gastric-type and intestinal-type mucins are coexpressed. These changes are early events in the gastric carcinogenesis process, as they are detected in intestinal metaplasia.

CONCLUSIONS

The glycosylation pattern found in normal gastric epithelium is dictated by the specific set of fucosyltranferases expressed by the cells rather than by the apomucin sequence. The development of intestinal metaplasia and gastric cancer is associated with the appearance of cellular phenotypes that are absent from normal epithelium.

MUC1 in carcinoma-host interactions

Many carcinoma-associated markers are glycoconjugates whose expression undergoes temporal or spatial regulation. Mucin-1 (MUC1), discovered through monoclonal antibody technology, is a well-documented example of such a molecule and influences numerous pathophysiological behaviors, such as the invasion and metastasis of carcinoma cells. Levels of MUC1 expression in carcinomas correlate with the clinical stage of the cancer and inversely correlate with the survival prospects of patients. The MUC1 immune response is known to provide a protective host defense mechanism against cancer. The multiple functions of MUC1 in carcinoma-host interactions are believed to be dependent on the polymorphic nature of MUC1, particularly its glycosylation status.

Altered mucin core peptide expression in acute and chronic cholecystitis

Human mucin genes include membrane-bound mucins (MUC1, MUC3, MUC4) and secretory mucins (MUC2, MUC5AC, MUC5B, MUC6). Our aim was to determine mucin gene expression in human gallbladder cell lines, normal gallbladder from liver donors (N = 7) and surgical specimens with mild chronic cholecystitis (N = 29), chronic cholecystitis (N = 48), and acute and chronic cholecystitis (N = 27). MUC1 mRNA was ubiquitous; however, only rare MUC1 immunoreactivity was detected. MUC3, MUC5AC, MUC5B, and MUC6 mRNA were present in all gallbladder specimens and cell lines examined. Prominent MUC3, MUC5AC, MUC5B, and MUC6 immunoreactivity was present in 86-100% of normal gallbladders. The frequency of MUC5AC reactivity was decreased in specimens with acute cholecystitis (P < 0.05). In contrast, MUC2-reactivity was absent in normal gallbladder and present in 53.8% of acute cholecystitis specimens (P < 0.05). Surface epithelium is characterized by MUC3, MUC5AC, and MUC5B, whereas deeper mucosal folds display MUC5B and MUC6 immunoreactivity. Gallbladder epithelium demonstrates a unique and diverse pattern of mucin core proteins that becomes altered with increasing degrees of inflammation.

Lack of mucin MUC5AC field change expression associated with tubulovillous and villous colorectal adenomas

BACKGROUND

MUC5AC is a secreted mucin aberrantly expressed by polypoid colorectal adenomas. It has been hypothesised that the "normal" surrounding colorectal mucosa expresses MUC5AC as a field change phenomenon that can be used to predict adenoma recurrence following resection.

AIM

To determine if there is a field change of de novo MUC5AC expression in histologically normal rectal mucosa adjacent to villous and tubulovillous adenomas, and thus whether MUC5AC expression can be used as a marker of early tumour recurrence.

METHODS

In a prospective cohort study paired mucosal biopsies of adenomatous and macroscopically "normal" mucosa were obtained from 11 patients with villous and 11 patients with tubulovillous adenomas who underwent primary resection for purpose of cure. The tissues were studied to determine MUC5AC gene expression by immunohistochemistry and in situ hybridisation. Patients were followed up by flexible sigmoidoscopy to detect the presence of early local recurrence.

RESULTS

10 villous adenomas showed mature MUC5AC glycoprotein and all 11 expressed MUC5AC mRNA. Five tubulovillous adenomas showed mature MUC5AC glycoprotein and 10 expressed MUC5AC mRNA. Neoexpression of the MUC5AC mucin gene was not detected in any of the mucosal biopsies taken adjacent to either villous or tubulovillous adenomas, even in three patients with early, locally recurrent disease.

CONCLUSIONS

Aberrant MUC5AC gene expression is not a "field change" in the colorectal mucosa in patients with rectal adenomas and therefore cannot be used to predict local recurrence of villous and tubulovillous adenomas.

Induction of mucin gene expression in human colonic cell lines by PMA is dependent on PKC-epsilon

Treatment of HT-29 cells with phorbol 12-myristate 13-acetate (PMA), an activator of protein kinase C (PKC), induces MUC2 expression. To investigate the role of PKC in regulating mucin genes in intestinal cells, we examined the regulation of MUC1, MUC2, MUC5AC, MUC5B, and MUC6 expression in two human mucin-producing colonic cell lines, T84 and HT29/A1. T84 and HT29/A1 cells (at 80-90% confluency) were exposed to 100 nM PMA for 0, 3, and 6 h. Twofold or greater increases in mRNA levels for MUC2 and MUC5AC were observed in both cell lines during this time period, whereas the levels of MUC1, MUC5B, and MUC6 mRNAs were only marginally affected. These results indicated that PKC differentially regulates mucin gene expression and that it may be responsible for altered mucin expression. Our previous results suggested that the Ca(2+)-independent PKC-epsilon isoform appeared to mediate PMA-regulated mucin exocytosis in these cell lines. To determine if PKC-epsilon was also involved in MUC2/MUC5AC gene induction, HT29/A1 cells were stably transfected with either a wild-type PKC-epsilon or a dominant-negative ATP-binding mutant of PKC-epsilon (PKC-epsilon K437R). Overexpression of the dominant-negative PKC-epsilon K437R blocked induction of both mucin genes, whereas PMA-induced mucin gene expression was not prevented by overexpression of wild-type PKC-epsilon. PMA-dependent MUC2 mucin secretion was also blocked in cells overexpressing the dominant-negative PKC-epsilon K437R. On the basis of these observations, PKC-epsilon appears to mediate the expression of two major gastrointestinal mucins in response to PMA as well as PMA-regulated mucin exocytosis.

Secretory low-molecular-weight phospholipases A2 and their specific receptor in bile ducts of patients with intrahepatic calculi: factors of chronic proliferative cholangitis

Intrahepatic calculi is characterized by an intractable course and frequent recurrences, requiring multiple operative interventions. Chronic proliferative cholangitis, an active and long-standing inflammation of the stone-containing bile ducts with the hyperplasia of epithelia and the proliferation of the duct-associated mucus glands, may underlie the complex nature of the disease. In terms of the pathophysiology, interest has been focused on the role of secretory low-molecular-weight phospholipases A2 (sPLA2s) as inflammatory mediators or factors modulating cell functions via their specific sPLA2-receptor, and also on the production and secretion of altered mucin molecules from the inflamed bile ducts. In search of factors involving chronic proliferative cholangitis, the sPLA2 isoforms in the bile such as the pancreatic-type sPLA2 (group IB sPLA2) and the arthritic-type sPLA2 (group IIA sPLA2), were assayed to correlate protein masses of the sPLA2s with alterations in biliary composition. Furthermore, the steady-state messenger RNA (mRNA) levels of the sPLA2s, the membrane-bound sPLA2-receptor, cystic fibrosis transmembrane conductance regulator (CFTR), and mucin core polypeptide (MUC) genes in the bile ducts were assayed by reverse- transcriptase polymerase chain reaction (RT-PCR). Immunoreactive sPLA2-IB and sPLA2-IIA levels were significantly higher in the bile from the stone-containing hepatic ducts (2315 +/- 677 for sPLA2-IB; 281 +/- 42 for sPLA2-IIA ng/dL, mean +/- SEM; n = 20) than in the ductal bile from gallbladder stone patients (609 +/- 92, P <.01; 22 +/- 2, P <.01; n = 24). The increased sPLA2 levels were associated with a concomitant increase in lysophosphatidylcholine, prostaglandin E2 (PGE2), and total mucin concentrations. The affected bile ducts showed an increased mRNA level of sPLA2-IB and sPLA2-IIA compared with the ducts from control subjects, in whom the mRNAs of the sPLA2-receptor and other sPLA2 isoforms, such as groups V and X sPLA2s, were coincidently expressed. Reflecting the increased amounts of total biliary mucins, the affected ducts showed an increase in mRNA levels of CFTR as well as MUC2, MUC3, MUC5AC, MUC5B, and MUC6 compared with the ducts from control subjects. In intrahepatic calculi, an enhanced expression of the sPLA2s and their possible cross-talk via sPLA2-receptor may be of pathophysiological significance for the chronic proliferative cholangitis, in association with the enhanced CFTR expression and the alterations in mucin gene expression in the bile ducts, probably through potentiating arachidonate metabolism with associated biliary alterations favoring growth of preexisting stones and even further progressions.

Mucin gene expression during differentiation of human airway epithelia in vitro. Muc4 and muc5b are strongly induced

Mucus hypersecretion is characteristic of chronic airway diseases. However, regulatory mechanisms are poorly understood. Human airway epithelial cells grown on permeable supports at the air-liquid interface (ALI) develop a mucociliary morphology resembling that found in vivo. Such cultures provide a model for studying secretory cell lineage, differentiation, and function, and may provide insight regarding events leading to mucus hypersecretion. The mucin gene expression profile of well-differentiated human airway epithelial cells in culture has not yet been established. We compared expression of all the currently described mucin genes in poorly differentiated (conventional cultures on plastic) and well-differentiated (ALI) human nasal and bronchial epithelial cells. Differentiation-dependent upregulation of MUC3, MUC5AC, MUC5B, and MUC6 messenger RNA (mRNA) was demonstrated using reverse transcriptase-polymerase chain reaction (RT-PCR). Northern blot analysis showed a similar increase for MUC4 and demonstrated that induction of MUC4 and MUC5B expression depended on retinoic acid. MUC1, MUC2, MUC7, and MUC8 mRNAs were also detected by RT-PCR, but these genes did not appear to be strongly regulated as a function of differentiation. Mucin gene expression was similar in bronchial and nasal cells. Thus, mucociliary differentiation of human airway epithelia in vitro entails upregulation of several mucin genes.

Malignant and other properties of human colon carcinoma cells after suppression of sulfomucin production in vitro

Although the loss of sulfomucins was known as an indicator of carcinogenesis and malignant progression of colonic epithelia, it was not known whether the loss was directly related to the malignant behavior of colon carcinoma cells. We have studied the biological properties of LS174T human colon carcinoma cells before and after suppression of sulfomucin production. Incorporation of [35S]-sulfate into high molecular weight mucins decreased after carcinoma cell treatment with 1.5% dimethylsulfoxide (DMSO) for 8 days. The amounts of sulfomucin determined using a sulfomucin-specific monoclonal antibody (mAb 91.9H), in Western blot and flowcytometric analyses, also decreased. In addition, the levels of MUC2 and MUC5B mucin gene expression measured by RT-PCR were reduced after DMSO-treatment, whereas the levels of MUC1, MUC5AC, and MUC6 mucin gene expression were not. The DMSO-treated cells were tested in vitro and in vivo for their properties. Differences were not detected in their anchorage-independent growth, anchorage-dependent growth, E-selectin-dependent cell adhesion or sensitivity to interleukin (IL)-2-activated lymphocyte cytolysis. When untreated or DMSO-treated LS174T cells were injected intrasplenically into nude mice, the treated cells lacking certain cell surface sulfomucins formed fewer metastatic colonies in the liver. These results suggest that the loss of sulfomucins by colonic epithelial cells during progression is not directly related to the enhanced malignant behavior.

Complete sequence of the human mucin MUC4: a putative cell membrane-associated mucin

The MUC4 gene, which encodes a human epithelial mucin, is expressed in various epithelial tissues, just as well in adult as in poorly differentiated cells in the embryo and fetus. Its N-terminus and central sequences have previously been reported as comprising a 27-residue peptide signal, followed by a large domain varying in length from 3285 to 7285 amino acid residues. The present study establishes the whole coding sequence of MUC4 in which the C-terminus is 1156 amino acid residues long and shares a high degree of similarity with the rat sialomucin complex (SMC). SMC is a heterodimeric glycoprotein complex composed of mucin (ascites sialoglycoprotein 1, ASGP-1) and transmembrane (ASGP-2) subunits. The same organization is found in MUC4, where the presence of a GlyAspProHis proteolytic site may cleave the large precursor into two subunits, MUC4alpha and MUC4beta. Like ASGP-2, which binds the receptor tyrosine kinase p185(neu), MUC4beta possesses two epidermal growth factor-like domains, a transmembrane sequence and a potential phosphorylated site. MUC4, the human homologue of rat SMC, may be a heterodimeric bifunctional cell-surface glycoprotein of 2.12 micrometers. These results confer a new biological role for MUC4 as a ligand for ErbB2 in cell signalling.

Respiratory carcinoma cell lines. MUC genes and glycoconjugates

Lung carcinoma cell lines are being used in many laboratories to study various airway epithelial functions, including mucin gene expression. To identify model systems for investigating regulation of MUC5/5AC gene expression and secretion of MUC5/5AC mucins in airway epithelial cells, we evaluated the expression of several mucin genes in six carcinoma cell lines of respiratory tract origin. RNA was extracted from A549, Calu-3, NCI H292, Calu-6, RPMI 2650, and A-427 cells; MUC1, MUC2, MUC4, MUC5/5AC, and MUC5B messenger RNA (mRNA) expression was determined. By Northern analyses, all cell lines expressed MUC1 mRNA, whereas MUC2 mRNA was not detectable in any of the cell lines. RPMI 2650 cell lines expressed only MUC1 mRNA. NCI-H292 cells expressed MUC4 and low levels of MUC5/5AC mRNA. Calu-3 and A549 cells expressed MUC5/5AC mRNA; A549 cells also expressed MUC5B mRNA. Glycoconjugates secreted by lung carcinoma cells were also examined. By wheat germ lectin analysis, Calu-3, H292, and A549 cells secreted high molecular weight glycoproteins having N-acetylglucosamine and/or sialic acid moieties. Western blot analyses with an anti-MUC5:TR-3A antibody demonstrated that Calu-3 and A549 cells secreted MUC5/5AC mucins. All six carcinoma cell lines secreted large, radiolabeled, sulfated macromolecules; the majority were proteoglycans that were digested by hyaluronidase. However, Calu-3 cells also secreted sulfated high molecular-weight glycoproteins that were immunoprecipitated by anti-MUC5:TR-3A antibody. These studies demonstrated that Calu-3 and A549 cell lines expressed high and moderate amounts of MUC5/5AC mRNA and MUC5/5AC mucins, whereas H292 cells expressed lesser amounts. These cell lines should prove useful for studies of MUC5/5AC gene expression and MUC5/5AC biosynthesis, trafficking, and secretions in airway epithelial cells.

Abnormalities in mucin gene expression in Crohn's disease

Alterations in the structure and/or quantity of mucins could alter the barrier function of mucus and play a role in initiating and maintaining mucosal inflammation in Crohn's disease. To investigate the hypothesis of a mucin gene defect in Crohn's disease, we analyzed the expression of the different mucin genes in the ileal mucosa of patients with Crohn's disease and controls. mRNA expression levels were assessed by a quantitative dot blot analysis and compared (i) between healthy and involved ileal mucosa of patients with Crohn's disease and (ii) between healthy mucosa of patients with Crohn's disease and controls. Expression of the different mucin genes was heterogeneous among controls and patients with Crohn's disease, except for MUC6 in controls. Nevertheless, MUC1 mRNA expression was significantly decreased in the involved ileal mucosa of patients with Crohn's disease when compared to the healthy mucosa (p = 0.02). Moreover, the expression levels of MUC3, MUC4, and MUC5B were significantly lower in both healthy and involved ileal mucosa of patients with Crohn's disease compared to controls (p < or = 0.05). The decrease of expression levels of some mucin genes (more particularly MUC3, MUC4, and MUC5B) in both healthy and involved ileal mucosa suggests a primary or very early mucosal defect of these genes in CD.