Muc13, a novel human cell surface mucin expressed by epithelial and hemopoietic cells

Alterations in glycosylation as biomarkers for cancer detection

Glycoconjugates constitute a major class of biomolecules which include glycoproteins, glycosphingolipids and proteoglycans. Glycans are involved in several physiological and pathological conditions, such as host-pathogen interactions, cell differentiation, migration, tumour invasion and metastisation, cell trafficking and signalling. Cancer is associated with glycosylation alterations in glycoproteins and glycolipids. This review describes various aspects of protein glycosylation with the focus on alterations associated with human cancer. The application of these glycosylation modifications as biomarkers for cancer detection in tumour tissues and serological assays is summarised.

Autoproteolysis of the SEA module of rMuc3 C-terminal domain modulates its functional composition

rMuc3 is a typical transmembrane mucin and contains a 174 amino acid domain called an SEA module in its C-terminal domain which is cleaved in eukaryotic cells. However, the mechanism by which the rMuc3 SEA module is proteolyzed and its biological significance has to be elucidated. In this study, we showed that the rMuc3 C-terminal domain was cleaved at LSKGSIVV motif within SEA module in prokaryotic cells, the time-dependence of the cleavage was found in the purified rMuc3 C-terminal domain carrying a mutated LSKASIVV motif expressed in bacteria. Thus, the cleavage of rMuc3 SEA module depended on autoproteolysis. The autoproteolysis of the SEA module of rMuc3 C-terminal domain played a critical role in the migration and invasion of the LoVo human colon cancer cells with rMuc3 C-terminal domain in vitro. The rMuc3 C-terminal domain induced a significant activation of HER/ErbB2 phosphorylated form (py1248) in LoVo cells. Inhibition of the phosphorylation by gefitinib (ZD1839) did attenuate migration and invasion of LoVo cells with rMuc3 C-terminal domain. Thus, rMuc3 C-terminal domain undergoes autoproteolysis at its SEA module, which maintains its availability for the potentiation of the signaling process that is modulated by HER/ErbB2 phosphorylation to promote the migration and invasion of LoVo cells.

Gene expression profiling of metaplastic lineages identifies CDH17 as a prognostic marker in early stage gastric cancer

BACKGROUND & AIMS

Intestinal metaplasia (IM) and spasmolytic polypeptide-expressing metaplasia (SPEM) are precursors to gastric carcinogenesis. We sought to identify molecular biomarkers of gastric metaplasias and gastric cancer by gene expression profiling of metaplastic lesions from patients.

METHODS

Complementary DNA microarray analysis was performed on IM and SPEM cells isolated from patient samples using laser capture microdissection. Up-regulated transcripts in metaplastic lesions were confirmed by immunostaining analysis in IM, SPEM, and gastric cancer tissues. Proteins that were highly expressed specifically in gastric cancer tissues were analyzed for their association with survival in a test set (n = 450) and a validation set (n = 502) of samples from gastric cancer patients.

RESULTS

Compared with normal chief cells, 858 genes were differentially expressed in IM or SPEM samples. Immunostaining was detected for 12 proteins, including 3 new markers of IM (ACE2, LGALS4, AKR1B10) and 3 of SPEM (OLFM4, LYZ, DPCR1). Of 13 proteins expressed in IM or SPEM, 8 were expressed by 17%-50% of human gastric cancer tissues (MUC13, OLFM4, CDH17, KRT20, MUC5AC, LGALS4, AKR1B10, REG4). Expression of CDH17 or MUC13 correlated with patient survival in the test and validation sets. Multivariate analysis showed that CDH17 was an independent prognostic factor in patients with stage I or node-negative disease.

CONCLUSIONS

We identified several novel biomarkers for IM, SPEM, and gastric cancer using gene expression profiling of human metaplastic lesions. Expression of CDH17 and MUC13 was up-regulated in gastric cancer tissues. CDH17 is a promising prognostic marker for early stage gastric cancer.

Membrane-bound mucins: the mechanistic basis for alterations in the growth and survival of cancer cells

Mucins (MUC) are high molecular weight O-linked glycoproteins whose primary functions are to hydrate, protect, and lubricate the epithelial luminal surfaces of the ducts within the human body. The MUC family is comprised of large secreted gel forming and transmembrane (TM) mucins. MUC1, MUC4, and MUC16 are the well-characterized TM mucins and have been shown to be aberrantly overexpressed in various malignancies including cystic fibrosis, asthma, and cancer. Recent studies have uncovered the unique roles of these mucins in the pathogenesis of cancer. These mucins possess specific domains that can make complex associations with various signaling pathways, impacting cell survival through alterations of cell growth, proliferation, death, and autophagy. The cytoplasmic domain of MUC1 serves as a scaffold for interaction with various signaling proteins. On the other hand, MUC4 mediates its effect by stabilizing and enhancing the activity of growth factor receptor ErbB2. MUC16, previously known as CA125, is a well-known serum marker for the diagnosis of ovarian cancer and has a key role in stimulation and dissemination of ovarian cancer cells by interacting with mesothelin and galectin. Therefore, herein we discuss the function and divergent mechanisms of MUC1, MUC4, and MUC16 in carcinogenesis in the context of alteration in cell growth and survival.

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.

Mucins in ovarian cancer diagnosis and therapy

Ovarian cancer is the most lethal gynecologic malignancy and the five-year survival rate is only 35% after diagnosis. Epithelial ovarian cancer is a highly metastatic disease characterized by widespread peritoneal dissemination and ascites. The death incidences from ovarian cancer could be significantly lowered by developing new methods for the early diagnosis and treatment of this fatal disease. Several potential markers have been identified recently. However, mucins are the most promising markers for ovarian cancer diagnosis. Mucins are large extracellular, heavily glycosylated proteins and their aberrant expression has been implicated in the pathogenesis of a variety of cancers, including ovarian cancer. This review will summarize known facts about the pathological and molecular characteristics of ovarian cancer, the current status of ovarian cancer markers, as well as general information about mucins, the putative role of mucins in the progression of ovarian cancer and their potential use for the early diagnosis and treatment of this disease.

Mucins in cancer: function, prognosis and therapy

Epithelia are protected from adverse conditions by a mucous barrier. The secreted and transmembrane mucins that constitute the mucous barrier are largely unrecognized as effectors of carcinogenesis. However, both types of mucins are intimately involved in inflammation and cancer. Moreover, diverse human malignancies overexpress transmembrane mucins to exploit their role in signalling cell growth and survival. Mucins have thus been identified as markers of adverse prognosis and as attractive therapeutic targets. Notably, the findings that certain transmembrane mucins induce transformation and promote tumour progression have provided the experimental basis for demonstrating that inhibitors of their function are effective as anti-tumour agents in preclinical models.

Conjunctival mucin mRNA expression in contact lens wear

PURPOSE

To investigate the influence of the water content in non-ionic hydrogel contact lenses (HCL) on the mRNA levels of human conjunctival mucin genes (MUCs).

METHODS

Sixteen healthy subjects with no history of contact lenses wear were selected and randomized into two equal groups. Group 1 subjects wore low water content (38%, Soflens 38) non-ionic HCLs. Group 2 wore high water content (66%, Soflens 66) non-ionic HCLs. Conjunctival impression cytology was applied to the superior bulbar conjunctiva of both eyes before, 6 months, and 1 year after HCL fitting, and 15 days after discontinuation of wearing. Total RNA was isolated, retrotranscribed, and amplified by conventional polymerase chain reaction (PCR) and by quantitative real time PCR to study the mRNA levels of MUCs and to analyze variations during the study period. Time- and HCL-dependent variations in mRNA expression were analyzed using Student's test.

RESULTS

From the known MUCs, transcripts from MUC1, MUC2, MUC4, MUC5AC, MUC7, MUC13, MUC15, MUC16, and MUC17 genes were detected in all subjects before HCL fitting. Except for MUC2, the expression of some MUC genes significantly increased whereas others significantly decreased at either the 6- and 12-month period. Statistically significant differences between both HCL groups (p < 0.001) were found in the MUC4, MUC13, and MUC15 mRNA expression after 1 year of wear and after the 15 days without HCL wear. However, these differences were not clearly related to the water content of the lenses.

CONCLUSIONS

Low and high water content non-ionic HCLs induced different changes in the mRNA levels of several MUCs, but the water content was not related to the changes. Recovery to basal levels of conjunctival MUC mRNA expression after wearing HCL lenses for a year takes longer than 15 days for some MUCs.

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.

The membrane-bound mucins: From cell signalling to transcriptional regulation and expression in epithelial cancers

The membrane-bound mucins belong to an ever-increasing family of O-glycoproteins. Based on their structure and localization at the cell surface they are thought to play important biological roles in cell-cell and cell-matrix interactions, in cell signalling and in modulating biological properties of cancer cells. Among them, MUC1 and MUC4 mucins are best characterized. Their altered expression in cancer (overexpression in the respiratory, gastro-intestinal, urogenital and hepato-biliary tracts) indicates an important role for these membrane-bound mucins in tumour progression, metastasis, cancer cell resistance to chemotherapeutics drugs and as specific markers of epithelial cancer cells. Some mechanisms responsible for MUC1 and MUC4 role in tumour cell properties have been deciphered recently. However, much remains to be done in order to understand the molecular mechanisms and signalling pathways that control the expression of membrane-bound mucins during the different steps of tumour progression toward adenocarcinoma and evaluate their potential as prognostic/diagnostic markers and as therapeutic tools. In this review we focus on the molecular mechanisms and signalling pathways known to control the expression of membrane-bound mucins in cancer. We will discuss the mechanisms of regulation at the promoter level (including genetic and epigenetic modifications) that may be responsible for the mucin altered pattern of expression in epithelial cancers.

Mucin gene expression in bile of patients with and without gallstone disease, collected by endoscopic retrograde cholangiography

AIM: To investigate the pattern of mucin expression and concentration in bile obtained during endoscopic retrograde cholangiography (ERC) in relation to gallstone disease.

METHODS: Bile samples obtained at ERC from 29 consecutive patients, 17 with and 12 without gallstone disease were evaluated for mucin content by gel filtration on a Sepharose CL-4B column. Dot blot analysis for bile mucin apoproteins was performed with antibodies to Mucin 1 (MUC1), MUC2, MUC3, MUC5AC, MUC5B and MUC6. Staining intensity score (0-3) was used as a measure of antigen expression.

RESULTS: MUC1, MUC2, MUC3, MUC5AC, MUC5B and MUC6 were demonstrated in 34.4%, 34.4%, 51.7%, 51.7%, 55.1% and 27.5% of bile samples, respectively. The staining intensity scores were 0.62 ± 0.94, 0.58 ± 0.90, 0.79 ± 0.97, 1.06 ± 1.22, 1.20 ± 1.26 and 0.41 ± 0.73, respectively. Mean mucin concentration measured in bile by the Sepharose CL-4B method was 22.8 ± 24.0 mg/mL (range 3.4-89.0 mg/mL). Mean protein concentration was 8.1 ± 4.8 mg/mL (range 1.7-23.2 mg/mL).

CONCLUSION: High levels of MUC3, MUC5AC and MUC5B are expressed in bile aspirated during ERC examination. A specific pattern of mucin gene expression or change in mucin concentration was not found in gallstone disease.

Role of matrix metalloproteinase-9 in lipopolysaccharide-induced mucin production in human airway epithelial cells

Matrix metalloproteinases (MMPs) have been found to be involved in the pathogenesis of inflammatory airway diseases. However, the role of MMPs in lipopolysaccharide (LPS)-induced mucin overproduction remains unclear. We explored the role of MMP-9 in LPS-induced MUC5AC production and the effect of doxycycline on MUC5AC production. The study showed that LPS induced transcription and protein expression of both MMP-9 and MUC5AC in NCI-H292 cells and in primary human epithelial cells, and the increased MUC5AC level were associated with increased MMP-9 transcripts, protein and activity. However, the increase of MUC5AC transcripts and protein were diminished after cells had been treated with doxycycline, MMP-9 siRNA or EGFR inhibitor. Doxycycline inhibited MMP-9 transcription, protein production and activity, while LPS-induced increase of MMP-9 transcription was inhibited by EGFR inhibitor, p38 MAPK and JNK inhibitor. The LPS-induced phosphorylation of p38 MAPK and JNK were inhibited by EGFR inhibitor. These results suggested that LPS-induced MUC5AC production may be partially mediated by MMP-9 activation and EGFR-p38 MAPK/JNK signaling pathway. Doxycycline may play a therapeutic role in LPS-induced mucus hypersecretion.

Drainage post-thyroglossal duct remnant surgery: Possible source and analysis

Objective: To establish the distance between tongue base salivary tissue and hyoid. Also, to identify protein differences between thyroglossal duct (TGD) remnants and salivary tissue in order to distinguish drainage source post Sistrunk surgery.

Methods/Setting: The anterior neck block was obtained from 10 adult cadavers with no known neck pathology. The distance between the normal salivary tissue and hyoid was measured histologically. Immunohistochemistry (IHC) was then performed on 20 archived tissue blocks from pediatric patients post Sistrunk surgery to identify the presence of amylase, MUC5AC (tracheobronchial mucin), and MUC7 (salivary mucin) within the excised specimen.

Results: Average distance between salivary tissue and the hyoid within adult human cadavers was 3.3 mm (range, 1.0-4.2 mm). IHC revealed all excised TGD remnants contained amylase and MUC5AC but none contained MUC7. Both amylase and MUC7 were present within adjacent salivary tissues.

Conclusions: Salivary tissue of the tongue base normally resides an average of 3.3 mm from the hyoid within the adult population. Biochemical analysis showed MUC5AC was specific for TGD remnants while MUC7 was specific for salivary tissue. Amylase does not distinguish between the two tissues.

Expression and functions of transmembrane mucin MUC13 in ovarian cancer

MUC13, a transmembrane mucin, is normally expressed in gastrointestinal and airway epithelium. Its aberrant expression has been correlated with gastric colon and cancer. However, the expression and functions of MUC13 in ovarian cancer are unknown. In the present study, the expression profile and functions of MUC13 were analyzed to elucidate its potential role in ovarian cancer diagnosis and pathogenesis. A recently generated monoclonal antibody (clone PPZ0020) was used to determine the expression profile of MUC13 by immunohistochemistry using ovarian cancer tissue microarrays and 56 additional epithelial ovarian cancer (EOC) samples. The expression of MUC13 was significantly (P < 0.005) higher in cancer samples compared with the normal ovary/benign tissues. Among all ovarian cancer types, MUC13 expression was specifically present in EOC. For the functional analyses, a full-length MUC13 gene cloned in pcDNA3.1 was expressed in a MUC13 null ovarian cancer cell line, SKOV-3. Here, we show that the exogenous MUC13 expression induced morphologic changes, including scattering of cells. These changes were abrogated through c-Jun NH(2) kinase (JNK) chemical inhibitor (SP600125) or JNK2 siRNA. Additionally, a marked reduction in cell-cell adhesion and significant (P < 0.05) increases in cell motility, proliferation, and tumorigenesis in a xenograft mouse model system were observed upon exogenous MUC13 expression. These cellular characteristics were correlated with up-regulation of HER2, p21-activated kinase 1, and p38 protein expression. Our findings show the aberrant expression of MUC13 in ovarian cancer and that its expression alters the cellular characteristics of SKOV-3 cells. This implies a significant role of MUC13 in ovarian cancer.

Cadherin-catenin adhesion system and mucin expression: a comparison between young and older patients with gastric carcinoma

BACKGROUND

Young patients are thought to develop gastric carcinomas with a molecular genetic profile that is distinct from that of gastric carcinomas occurring at a later age. The aim of this study was to compare the clinicopathological features and expression patterns of the markers E-cadherin and beta-catenin, and mucins (MUC1, MUC2, MUC5AC, and MUC6) in young and older patients.

METHODS

The clinicopathological features and overall survival data of 62 young patients (age <or=40 years) with gastric cancer were retrospectively reviewed from hospital records and compared with the data for 453 older patients (age >40 years). A tissue microarray method and immunohistochemistry were used in order to analyze marker expression in paraffin-embedded tissue blocks obtained from both groups.

RESULTS

The young group presented a higher percentage of diffuse-type tumors in comparison to the older group (P<0.01). The rates of positivity for E-cadherin and beta-catenin membranous expression patterns and mucin (MUC2, MUC5AC and MUC6) positivity were higher in the young group (P<0.01). Although young patients showed a lower frequency of alterations in marker expression and had significantly better survival rates than the older patients, neither age nor the marker expression pattern were found to be independent prognostic factors of survival. Only stage, tumor size, and tumor location persisted as prognostic factors for patients with gastric cancer.

CONCLUSION

Biological markers of cellular adhesion and gastric differentiation were differently expressed in young and older patients. Our findings support the hypothesis that young patients develop carcinomas with a different genetic pathway compared to the pathway of tumors occurring at a later age, and we suggest further investigations to assess the prognostic relevance of the markers to specific subgroups.

Molecular aspects of mucoadhesive carrier development for drug delivery and improved absorption

Although the oral route remains the most favored route of drug administration, major scientific obstacles prevent the effective and efficient delivery of low-molecular-mass drugs, peptides and proteins that exhibit poor solubility and permeability. Mucoadhesive dosage forms and the associated drug carriers have the ability to interact at a molecular level with the mucus gel layer that lines the epithelial surfaces of the major absorptive regions of the body. This interaction provides an increased residence time of the therapeutic formulation while localizing the drug at the site of administration. Such local, non-specific targeting leads to an increase in both oral absorption and bioavailability. Fundamental understanding of the biological processes encountered along the gastrointestinal tract can provide a sufficient engineer of carriers that are capable to provide this increase in residence time. Here we discuss the theoretical framework for achieving mucoadhesive systems as related to biomaterials science and the structure of the biomaterials used.

Mucin dynamics in intestinal bacterial infection

BACKGROUND

Bacterial gastroenteritis causes morbidity and mortality in humans worldwide. Murine Citrobacter rodentium infection is a model for gastroenteritis caused by the human pathogens enteropathogenic Escherichia coli and enterohaemorrhagic E. coli. Mucin glycoproteins are the main component of the first barrier that bacteria encounter in the intestinal tract.

METHODOLOGY/PRINCIPAL FINDINGS

Using Immunohistochemistry, we investigated intestinal expression of mucins (Alcian blue/PAS, Muc1, Muc2, Muc4, Muc5AC, Muc13 and Muc3/17) in healthy and C. rodentium infected mice. The majority of the C. rodentium infected mice developed systemic infection and colitis in the mid and distal colon by day 12. C. rodentium bound to the major secreted mucin, Muc2, in vitro, and high numbers of bacteria were found in secreted MUC2 in infected animals in vivo, indicating that mucins may limit bacterial access to the epithelial surface. In the small intestine, caecum and proximal colon, the mucin expression was similar in infected and non-infected animals. In the distal colonic epithelium, all secreted and cell surface mucins decreased with the exception of the Muc1 cell surface mucin which increased after infection (p<0.05). Similarly, during human infection Salmonella St Paul, Campylobacter jejuni and Clostridium difficile induced MUC1 in the colon.

CONCLUSION

Major changes in both the cell-surface and secreted mucins occur in response to intestinal infection.

MUC1 and the MUCs: A Family of Human Mucins with Impact in Cancer Biology

Mucins represent a family of glycoproteins characterized by repeat domains and a dense O-glycosylation. During the last two decades, the gene and peptide structures of various mucins as well as their glycosylation states were partly elucidated. Characteristic tumor-associated alterations of the expression patterns and glycosylation profiles were observed in biochemical, immunochemical, and histological studies and are discussed in the light of efforts to use the most prominent member in this family, MUC1, as a tumor target in anti-tumor strategies. Within this context the present review, focusing on MUC1, describes recent work on the regulation of mucin biosynthesis by cytokines and hormones, the role of mucins in cell adhesion, and their interaction with the immune system. Important aspects of clinical diagnostics based on mucin antigens are discussed, including the application of tumor serum assays and the significance of numerous studies revealing correlations between the expression of peptide cores or mucin-associated carbohydrates and clinicopathological parameters like tumor progression and prognosis.

Signal pathway of 17beta-estradiol-induced MUC5B expression in human airway epithelial cells

MUC5B is a major mucin of the human respiratory tract, and it is not clear how MUC5B expression is regulated in various airway diseases. The goal of this study was to determine the mechanisms by which 17beta-estradiol induces MUC5B gene expression in airway epithelial cells. It was found that E2, a sex hormone, stimulates MUC5B gene overexpression by interaction with estrogen receptor alpha (ERalpha) and by acting through extracellular signal-regulated kinase 1/2 (ERK1/2)-mitogen-activated protein kinase (MAPK). Pretreatment with ER antagonist ICI 182,780 blocked both E2-induced ERK1/2-MAPK activation and MUC5B gene expression. It was also found that the activation of p90 ribosomal S 6 protein kinase 1 (RSK1), cAMP-response element-binding protein (CREB), and cAMP-response element (CRE) (-956 region of the MUC5B promoter)-responsive signaling cascades via ERK1/2 MAPK are crucial aspects of the intracellular mechanisms that mediate MUC5B gene expression. Taken together, these studies give additional insights into the molecular mechanism of hormone-induced MUC5B gene expression and enhance our understanding of abnormal mucin secretion in response to hormonal imbalances.

In silico strategy for detection of target candidates for antibody therapy of solid tumors

In contrast to earlier attempts for the identification of target candidates suitable for monoclonal antibody (mAb) based cancer therapies we concentrated on highly selective lineage-specific genes additionally preserved or even overexpressed in orthotopic cancers. In a script aided workflow we reduced all human entries of the RefSeq mRNA database to those encoding transmembrane domain bearing gene products and subjected them to BLAST analysis against the human EST database. All BLAST results were validated in a gene centric way allowing two types of data curation prior to expression profiling of matching ESTs in selected healthy tissues: (i) exclusion of questionable ESTs arising e.g. from genomic contamination and (ii) elimination of erroneously predicted mRNAs as well as transcripts with only weak EST coverage. The impact of such stringent input control on accuracy of prediction is underlined by RT-PCR confirmation of predicted tissue distribution patterns for a number of selected candidates.

Higher gastric mucin secretion and lower gastric acid output in first-degree relatives of gastric cancer patients

BACKGROUND

Patients infected by Helicobacter pylori who have first-degree relatives with gastric cancer have an 8-fold increased risk of developing gastric cancer themselves. Mucins are high-molecular-weight glycoproteins that play a cardinal role in the protective mechanism of the gastric epithelium.

AIM

To study gastric acid and mucin secretion in dyspeptic patients with and without a family history of gastric cancer and H. pylori infection.

MATERIALS AND METHODS

Twenty-six dyspeptic patients underwent esophago-gastro-duodenoscopy, gastric biopsies, and acid and mucin secretory tests. The sample was divided by family history of gastric cancer and H. pylori status.

RESULTS

Patients who were infected by H. pylori had a significantly higher degree of inflammation than those who were not. H. pylori-positive patients with a positive family history had a lower basal and maximal gastric acid output than infected patients with no family history and noninfected controls, and a higher basal and maximal mucin output than infected patients with no family history. MUC5AC was the major mucin species expressed in gastric juice.

CONCLUSIONS

In patients with relatives with gastric cancer, H. pylori infection is associated with a more severe inflammatory reaction consisting of decreased gastric acid secretion and increased mucin secretion.

Mucins in the mucosal barrier to infection

The mucosal tissues of the gastrointestinal, respiratory, reproductive, and urinary tracts, and the surface of the eye present an enormous surface area to the exterior environment. All of these tissues are covered with resident microbial flora, which vary considerably in composition and complexity. Mucosal tissues represent the site of infection or route of access for the majority of viruses, bacteria, yeast, protozoa, and multicellular parasites that cause human disease. Mucin glycoproteins are secreted in large quantities by mucosal epithelia, and cell surface mucins are a prominent feature of the apical glycocalyx of all mucosal epithelia. In this review, we highlight the central role played by mucins in accommodating the resident commensal flora and limiting infectious disease, interplay between underlying innate and adaptive immunity and mucins, and the strategies used by successful mucosal pathogens to subvert or avoid the mucin barrier, with a particular focus on bacteria.

Identification of Fn14/TWEAK receptor as a potential therapeutic target in esophageal adenocarcinoma

Given the poor survival rate and efficacy of current therapy for esophageal adenocarcinoma (EAC), there is a need to identify and develop new therapeutic targets for treatment. Microarray analysis (Affymetrix U133A GeneChips, Robust Multi-Chip Analysis) was used to expression profile 11 normal squamous and 18 Barrett's esophagus biopsies, 7 surgically resected EACs and 3 EAC cell lines. Two hundred transcripts representing potential therapeutic targets were identified using the following criteria: significant overexpression in EAC by analysis of variance (p = 0.05, Benjamini Hochberg false discovery rate); 3-fold increase in EAC relative to normal and Barrett's esophagus and expression in at least 2 of the 3 EAC cell lines. From the list of potential targets we selected TNFRSF12A/Fn14/TWEAK receptor, a tumor necrosis factor super-family receptor, for further validation based on its reported role in tumor cell survival and potential as a target for therapy. Fn14 protein expression was confirmed in SEG-1 and BIC-1 cell lines, but Fn14 was not found to affect tumor cell survival after exposure to chemotherapeutics as expected. Instead, a novel role in EAC was discovered in transwell assays, in which modulating Fn14 expression affected tumor cell invasion. Fn14's potential as a therapeutic target was further supported by immunohistochemistry on a tissue microarray of patient samples that showed that Fn14 protein expression increased with disease progression in EAC.

Subcellular proteomics of cell differentiation: quantitative analysis of the plasma membrane proteome of Caco-2 cells

Human colorectal carcinoma (Caco-2) cells undergo in culture spontaneous enterocytic differentiation, characterized by polarization and appearance of the functional apical brush border membrane. To provide insights into the biology of differentiation, we have performed a comparative proteomic analysis of the plasma membranes from proliferating cells (PCs) and the apical membranes from differentiated cells (DCs). Proteins were resolved by SDS-PAGE, in-gel digested and analyzed by RP-LC and MS/MS. Alternatively, proteins were digested in solution, and tryptic peptides were labeled with isotopic tags and analyzed by 2-D LC followed by MS/MS. Among the 1125 proteins identified in both proteomes, 76 were found to be significantly increased in the membranes of DCs and 61 were increased in PCs. Majority of the proteins increased in the apical membranes were metabolic enzymes, proteins involved in the maintenance of cellular structure, transmembrane transporters, and proteins regulating vesicular transport. In contrast, majority of the proteins increased in the membranes of PCs were involved in gene expression, protein synthesis, and folding. Both groups contained many novel proteins with yet to be identified functions, which could provide potential new markers of the intestinal cells or of colorectal cancer.

Improved in vitro model systems for gastrointestinal infection by choice of cell line, pH, microaerobic conditions, and optimization of culture conditions

BACKGROUND

Commonly used in vitro infection cultures do not mimic the human gastrointestinal tract with regard to pH and microaerobic conditions. Furthermore, despite the importance of mucin-Helicobacter interactions, the cell lines used have not been selected for appropriate mucin expression. To make in vitro studies more applicable to human disease, we have developed coculture methods taking these factors into account.

MATERIALS AND METHODS

Nine human gastrointestinal epithelial cell lines (MKN1, MKN7, MKN28, MKN45, KATO3, HFE145, PCAA/C11 Caco-2, and LS513) were investigated. Expression and glycosylation of mucins (MUC1, 2, 3, 4, 5AC, 5B, 6, 12, 13, and 16) were determined by immunohistochemistry. We analyzed the effect of microaerobic conditions and acidic pH on cell proliferation, viability, and apoptosis.

RESULTS

Microaerobic culture, which is more physiological for the bacteria, did not adversely affect mammalian cell viability, proliferation, or induce apoptosis The cell lines varied in mucin expression, with MKN7 and MKN45 being most similar to gastric mucosa and Caco-2 and LS513 to intestinal mucosa, although none exactly matched normal mucosa. However, changes in culture conditions did not cause major changes in the mucin expression within cell lines.

CONCLUSIONS

Culture conditions mimicking the natural environment and allowing the bacterial cells to thrive had no effect on cell viability or apoptosis, and very little influence on mucin expression of human gastrointestinal cells. Thus, it is feasible, using the simple methods we present here, to substantially improve bacterial-mammalian cell in vitro coculture studies to make them more reflective of human infection.

Gallbladder inflammation is associated with increase in mucin expression and pigmented stone formation

Mucin is a high molecular weight glycoprotein that plays an important role in protecting the gallbladder epithelium from the detergent effect of bile. However, it also participates in gallstone formation. There is little information about a possible relationship between gallbladder inflammation and mucin expression or gallbladder stones' characteristics. The aims of this study were to investigate stone characteristics and patterns of mucin expression in the gallbladder epithelium and bile of gallstone patients, in relation to inflammation. Gallbladder bile and tissue samples from 21 patients were obtained at surgery. Mucin content was evaluated by gel filtration on a Sepharose CL-4B column. Dot blot for bile mucin apoproteins and immunohistochemistry staining for gallbladder mucosal mucin apoproteins were performed with antibodies to MUC2, MUC3, MUC5AC, MUC5B and MUC6. Staining intensity score (0-3) was used for assessment of antigen expression and the level of inflammation. Gallstone cholesterol content was determined in 16 patients. MUC 5AC and MUC 5B were demonstrated in 95.4 and 100% of gallbladder bile samples, respectively. Immunohistochemistry staining with antibodies to MUC 2, MUC 3, MUC 5AC, MUC 5B and MUC 6 were positive in 0, 100, 85.7, 100 and 95.4% of the gallbladder mucosal samples, respectively. Pigmented brown stones were associated with a higher level of gallbladder inflammation. Mucin species expressed in gallbladder epithelium are MUC3, MUC5AC, MUC5B and MUC6. MUC5AC and MUC5B are secreted into bile. Inflammation of the gallbladder is accompanied by a higher level of MUC5AC expression and is associated with pigmented brown stones.

Mucin expression profile in pancreatic cancer and the precursor lesions

In this review article, we demonstrate the mucin expression profile in normal tissue, invasive ductal carcinoma (IDC), two subtypes of intraductal papillary-mucinous neoplasm (IPMN dark cell type and IPMN clear cell type), pancreatic intraepithelial neoplasia (PanIN), and mucinous cystic neoplasm (MCN) of the pancreas. In MUC1, there are various glycoforms, such as poorly glycosylated MUC1, sialylated MUC1, and fully glycosylated MUC1. IDCs showed high expression of all the glycoforms of MUC1. IPMNs dark cell type showed no expression or low expression of all the glycoforms of MUC1. IPMNs clear cell type showed low expression of poorly glycosylated MUC1, but expression of sialylated MUC1 and fully glycosylated MUC1. Expression of MUC2 was negative in IDCs, high in IPMNs dark cell type and low in IPMNs clear cell type. MUC5AC was highly expressed in IDCs, IPMNs dark cell type, and IPMNs clear cell type. MUC6 expression was higher in IPMNs clear cell type than in IDCs and IPMNs dark cell type. Our recent study demonstrated that high expression of MUC4 in IDCs is correlated with a poor outcome for patients. In PanINs, expression of both MUC5AC and MUC6 are an early event, whereas up-regulation of MUC1 is a late event. MCNs do not look as if they will show a specific mucin expression profile according to the literature review.

Assay of mucins in human tear fluid

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

Prognostic Significance of the MUC1 and MUC4 Expressions in Thyroid Papillary Carcinoma

OBJECTIVES

The aim of the present study was to examine the expressions of mucin genes MUC1 and MUC4 and to evaluate the difference of their expressions in normal thyroid tissue, follicular adenoma, and papillary carcinoma. Furthermore, we aimed to estimate their prognostic significance in papillary carcinoma.

METHODS

We performed semiquantitative reverse-transcription polymerase chain reaction for determining the MUC1 and MUC4 mRNA expressions, and immunohistochemical staining was performed to determine the MUC1 and MUC4 protein expressions in 22 normal thyroid tissues, 22 follicular adenomas, and 15 papillary carcinomas. The semiquantitative scoring of the immunohistochemical staining was compared with the prognostic factors for thyroid carcinoma to evaluate the prognostic significance in 87 papillary carcinoma patients.

RESULTS

The MUC1 mRNA of the papillary carcinoma tissue showed an increased expression level compared with the other tissues. However, the expression level of MUC4 mRNA was weak in all the specimens, and this was not significantly different among the three groups. MUC1 immunoreactivity was more intense in papillary carcinoma but not in the other tissues. MUC4 was not expressed in all thyroid tissues. The expression of MUC1 was significantly associated with tumor size, extrathyroidal spread, and TNM stage (P < .05).

CONCLUSIONS

Up-regulation of MUC1 may play a more important role than that of MUC4 in the development of thyroid papillary carcinoma, and it may have some significance as a prognostic factor.

The MUC13 cell surface mucin is highly expressed by human colorectal carcinomas

Mucins are complex mucosal glycoproteins that can be highly expressed by adenocarcinomas, having diagnostic, therapeutic, and biological significance. MUC13 encodes a cell surface membrane-anchored mucin expressed in the normal gastrointestinal tract, trachea, and kidney as well as colorectal, esophageal, gastric, pancreatic, and lung cancers. MUC13 protein expression was determined immunohistochemically in 99 sporadic colorectal cancers, assessing proportion of tumor cells stained, stain intensity, and localization. In normal colon, intense apical membrane and variable cytoplasmic MUC13 staining was present in both goblet and columnar cells, with strongest reactivity in the upper crypts and surface epithelium. All cancers showed staining of most tumor cells, being most conspicuous in the apical membranes of gland spaces. Left-sided tumors had a higher overall proportion of MUC13-positive tumor cells than right-sided tumors (P < .05), and high staining intensity was more frequent in adenocarcinomas (81%) than mucinous tumors (50%) (P < .05). Poorly differentiated and late-stage tumors were more likely to have high-intensity cytoplasmic staining (P < or = .025). Basolateral cell membranes were stained in 24% of cases, being more common in poorly differentiated tumors (55%) than well or moderately differentiated tumors (16%) (P < or = .001). Partial or full circumferential MUC13 staining was frequently observed in areas of tumor budding. Although MUC13 immunoreactivity was not predictive of patient outcome, there was a trend toward poorer outcome in patients with tumors showing basolateral MUC13. In summary, MUC13 was expressed abundantly by all colorectal cancers, with the highest expression in more poorly differentiated tumors.

Mucin overproduction in chronic inflammatory lung disease

Mucus overproduction and hypersecretion are commonly observed in chronic inflammatory lung disease. Mucins are gel-forming glycoproteins that can be stimulated by a variety of mediators. The present review addresses the mechanisms involved in the upregulation of secreted mucins. Mucin induction by neutrophil elastase, bacteria, cytokines, growth factors, smoke and cystic fibrosis transmembrane conductance regulator malfunction are also discussed.

Gastric-type well-differentiated adenocarcinoma and pyloric gland adenoma of the stomach

Since 1985, when gastric-type well-differentiated adenocarcinomas were demonstrated in hyperplastic polyps of the stomach, we have studied phenotypic expression in gastrointestinal epithelial lesions. The recent discovery of MUC genes coding core proteins of mucin has improved research on the phenotypic expression of gastrointestinal neoplasms. The disease entity of gastric-type well-differentiated adenocarcinoma has recently been accepted, especially in Japan and Europe. This entity has often become a clinicopathological subject of discussion, because its biological behavior is possibly highly malignant, in spite of the difficulty in making endoscopic and histopathological diagnoses. Even under these circumstances, the term "gastric adenoma" usually means flat adenoma of the intestinal type. Gastric-type adenomas have been regarded as exceptional until recently. Although gastric-type adenomas could theoretically be classified into foveolar type and pyloric-gland type, foveolar-type adenoma is, in practice, difficult to distinguish from gastric-foveolar-type adenocarcinoma. In 2003, we first reported systematic clinicopathological analyses of pyloric gland adenoma, demonstrating its unstable and precancerous nature. In this article, we review and discuss the clinicopathological and molecular pathological aspects of gastric-type well-differentiated adenocarcinomas and pyloric gland adenomas, mainly based on our published and unpublished data.

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

RATIONALE

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

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

The inhibitory effect of the leukotriene receptor antagonist on leukotriene D4-induced MUC2/5AC gene expression and mucin secretion in human airway epithelial cells

OBJECTIVES

Mucin gene expression and mucin production are markedly increased in inflammatory airway disorders such as asthma, chronic bronchitis and rhinosinusitis. Cytokines, lipopolysaccharides and other inflammatory mediators such as prostaglandin and leukotriene are related to the secretion and production of mucin. However, the relationship of leukotrienes with mucin genes expression is not clear. The aim of this study is to evaluate MUC2/5AC gene expression and mucin secretion by the leukotriene receptor in human airway epithelial cells.

METHODS

The effect of leukotriene D(4) and the leukotriene receptor antagonist, pranlukast hydrate (ONO-1078) on the regulation of MUC2/5AC gene expression and mucin secretion were observed in human airway NCI-H292 epithelial cells. The mRNA levels of MUC2/5AC and the amount of mucin were determined by reverse transcription-polymerase chain reaction (RT-PCR) and immunoassay.

RESULTS

Leukotriene D(4) upregulated MUC2/5AC gene expression and mucin secretion in a dose dependent pattern. Pranlukast hydrate (ONO-1078, 100 microM) downregulated the leukotriene D(4)-induced MUC2/5AC gene expression and mucin secretion.

CONCLUSION

These results suggest that the leukotriene receptor system is one of the mechanisms related to MUC2/5AC gene expression and mucin secretion in the human airway epithelium.

Mucin gene expression in rhinitis syndromes

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

Cysteine-rich domains of muc3 intestinal mucin promote cell migration, inhibit apoptosis, and accelerate wound healing

BACKGROUND & AIMS

Muc3 intestinal mucin contains an extracellular cysteine-rich domain with 2 epidermal growth factor (EGF)-like motifs. The aim of this study was to determine the functional properties of Muc3 proteins.

METHODS

Glutathione S-transferase-fusion proteins containing both Muc3 EGF-like domains (m3EGF1,2) or truncated versions (m3EGF1 and m3EGF2) were purified from Escherichia coli. Mouse colon (young adult mouse colon) and human A431 and LoVo cells were examined for migration and tyrosine phosphorylation in response to recombinant proteins. LoVo cells were transfected with a human MUC3A transmembrane-EGF1,2 construct and a stable clone was isolated (LhM3c14). Endogenous MUC3A in LoVo was inhibited by specific small interfering RNA transfection. Apoptosis was quantitated by nuclear morphology or terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate biotin nick-end labeling assay. Colitis was induced in mice by oral 5% dextran sodium sulfate or rectal 5% acetic acid, followed by enema treatments.

RESULTS

m3EGF1,2 stimulated cell migration in all cell lines, but did not induce proliferation. Migration was inhibited by a tyrosine phosphorylation inhibitor, genistein, but not by the EGF receptor inhibitor, tyrphostin (AG1478). Inhibition of endogenous MUC3A in LoVo reduced baseline migration. Tyrosine phosphorylation of ErbB receptors was not observed after treatment of cells with m3EGF1,2. LoVo cells pretreated with m3EGF1,2 and transfected LhM3c14 cells showed reduced apoptosis in response to tumor necrosis factor alpha or Fas-receptor stimulation. Administration of m3EGF1,2 per rectum significantly reduced mucosal ulceration and apoptosis in experimental acute colitis. Truncated proteins m3EGF1 and m3EGF2 had no effect.

CONCLUSIONS

The Muc3 mucin cysteine-rich domain plays an active role in epithelial restitution, and represents a potential novel therapeutic agent for intestinal wound healing.

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.

The expression of MUC4 and MUC5AC is related to the biologic malignancy of intraductal papillary mucinous neoplasms of the pancreas

OBJECTIVE

Intraductal papillary mucinous neoplasms (IPMNs) of the pancreas show heterogeneous proliferations with latent malignancy. Mucins (MUC) are high-molecular-weight glycoproteins, with an aberrant expression profile in various malignancies. Recently, MUC4 and MUC5AC expressions have been demonstrated to correlate with the unfavorable and the favorable prognosis of pancreatic duct cell carcinoma, respectively. However, little is known about these mucin expressions in IPMNs.

METHODS

To clarify the role of MUC4 and MUC5AC expressions in IPMNs, the expression profiles of MUC4 and MUC5AC were investigated in 50 lesions from 17 specimens with 16 IPMNs by immunohistochemistry, using each of their specific antibodies.

RESULTS

The expression of MUC4 was found in the lesions ranging from adenoma to cancer lesions of IPMNs, whereas it was undetectable in normal and hyperplastic lesions. Frequent expression of MUC4 is found in the higher grade of IPMNs (borderline and cancer lesions; 16/18 lesions, 94%). The differences were independently significant (P < 0.001) when the cutoff point was set between adenoma and borderline IPMNs. Similarly, frequent expression of MUC5AC was detected in the lesions from adenoma to cancer of IPMNs (32/34, 94%), whereas no intense expression was detected in normal or hyperplastic lesions. The significant difference was found when the cutoff point was set between hyperplasia and adenoma of IPMNs (P < 0.001).

CONCLUSIONS

These results indicated that the expressions of MUC4 and MUC5AC are potential markers to distinguish adenoma or above malignant lesions of IPMNs from lesser malignant ones, respectively.

Cleavage in the GDPH sequence of the C-terminal cysteine-rich part of the human MUC5AC mucin

MUC5AC is the main gel-forming mucin expressed by goblet cells of the airways and stomach where it protects the underlying epithelia. We expressed the C-terminal cysteine-rich part of the human MUC5AC mucin in CHO-K1 cells (Chinese-hamster ovary K1 cells) where it formed disulfide-linked dimers in the ER (endoplasmic reticulum). After reducing the disulfide bonds of these dimers, not only the expected monomers were found, but also two smaller fragments, indicating that the protein was partially cleaved. The site of cleavage was located at an Asp-Pro bond situated in a GDPH (Gly-Asp-Pro-His) sequence found in the vWD4 (von Willebrand D4) domain. This sequence is also found in the human MUC2 mucin, previously shown to be cleaved at the same site by a slow, non-enzymatic process triggered by a pH below 6 [Lidell, Johansson and Hansson (2003) J. Biol. Chem. 278, 13944-13951]. In contrast with this, the cleavage of MUC5AC started already in the neutral ER. However, it continued and was slightly accelerated at a pH below 6.5, a pH found in the later parts of the secretory pathway. The cleavage generated a reactive group in the new C-terminus that could link the protein to a primary amine. No cleavage of MUC5AC has so far been reported. By using an antibody reacting with the C-terminal cleavage fragment, we could verify that the cleavage occurs in wild-type MUC5AC produced by HT-29 cells. The cleavage of MUC5AC and the generation of the reactive new C-terminus could contribute to the adherent and viscous mucus found at chronic lung diseases such as asthma and cystic fibrosis, characterized by mucus hypersecretion and lowered pH of the airways.

An inventory of mucin genes in the chicken genome shows that the mucin domain of Muc13 is encoded by multiple exons and that ovomucin is part of a locus of related gel-forming mucins

Background

Mucins are large glycoproteins that cover epithelial surfaces of the body. All mucins contain at least one PTS domain, a region rich in proline, threonine and serine. Mucins are also characterized by von Willebrand D (VWD) domains or SEA domains. We have developed computational methods to identify mucin genes and proteins based on these properties of the proteins. Using such methods we are able to characterize different organisms where genome sequence is available with respect to their mucin repertoire.

Results

We have here made a comprehensive analysis of potential mucins encoded by the chicken (Gallus gallus) genome. Three transmembrane mucins (Muc4, Muc13, and Muc16) and four gel-forming mucins (Muc6, Muc2, Muc5ac, and Muc5b) were identified. The gel-forming mucins are encoded within a locus similar to the corresponding human mucins. However, the chicken has an additional gene inserted between Muc2 and Muc5ac that encodes the the α-subunit of ovomucin, a protein similar to Muc2, but it is lacking a PTS domain. We also show that the β-subunit of ovomucin is the orthologue of human MUC6. The transmembrane Muc13 gene is in chicken as well as in mammals adjacent to the HEG (heart of glass) gene. HEG has PTS, EGF and transmembrane domains like Muc13, suggesting that these two proteins are evolutionary related. Unlike previously known mucins, the PTS domain of Muc13 is encoded by multiple exons, where each exon encodes a repeat unit of the PTS domain.

Conclusion

We report new mucin homologues in chicken and this information will aid in understanding the evolution of mucins in vertebrates. The fact that ovomucin, a protein not found in mammals, was located in the same locus as other gel-forming mucins provides strong support that these proteins are evolutionary related. Furthermore, a relationship of HEG and the transmembrane Muc13 is suggested on the basis of their biochemical properties and their presence in the same locus. Finally, our finding that the chicken Muc13 is distributed between multiple exons raises the interesting possibility that the length of the PTS domain could be controlled by alternative splicing.

Increased levels of mucins in the cystic fibrosis mouse small intestine, and modulator effects of the Muc1 mucin expression

The mouse model (Cftr(tm1UNC)/Cftr(tm1UNC)) for cystic fibrosis (CF) shows mucus accumulation and increased Muc1 mucin mRNA levels due to altered splicing (Hinojosa-Kurtzberg AM, Johansson MEV, Madsen CS, Hansson GC, and Gendler SJ. Am J Physiol Gastrointest Liver Physiol 284: G853-G862, 2003). However, it is not known whether Muc1 is a major mucin contributing to the increased mucus and why CF/Muc1-/- mice show lower mucus accumulation. To address this, we have purified mucins from the small intestine of CF mice using guanidinium chloride extraction, ultracentrifugation, and gel filtration and analyzed them by slot blot, gel electrophoresis, proteomics, and immunoblotting. Normal and CF mice with wild-type (WT) Muc1 or Muc1-/- or that are transgenic for human MUC1 (MUC1.Tg, on a Muc1-/- background) were analyzed. The total amount of mucins, both soluble and insoluble in guanidinium chloride, increased up to 10-fold in the CF mice compared with non-CF animals, whereas the CF mice lacking Muc1 showed intermediate levels between the CF and non-CF mice. However, the levels of Muc3 (orthologue of human MUC17) were increased in the CF/Muc1-/- mice compared with the CF/MUC1.Tg animals. The amount of MUC1 mucin was increased several magnitudes in the CF mice, but MUC1 did still not appear to be a major mucin. The amount of insoluble mucus of the large intestine was also increased in the CF mice, an effect that was partially restored in the CF/Muc1-/- mice. The thickness of the firmly adherent mucus layer of colon in the Muc1-/- mice was significantly lower than that of WT mice. The results suggest that MUC1 is not a major component in the accumulated mucus of CF mice and that MUC1 can influence the amount of other mucins in a still unknown way.

Rôles physiologiques des mucines dans la barrière colique

Colonic mucus is a key element of colonic barrier as it is located at the frontier between luminal microflora and colonic mucosa itself. Colonic mucus is mainly composed of high molecular weight glycoproteins called mucins that can be either secreted or membrane-linked. The expression of various colonic mucins is altered in colorectal cancers or inflammations. The aim of this review is to highlight the crucial role played by colonic mucins in the maintenance of colonic barrier integrity, both because they are part of the protective mucus layer, and because they individually exert specific functions involved in epithelial barrier, like cell growth and differentiation, immunomodulation, signal transduction or cell adhesion.

The front line of enteric host defense against unwelcome intrusion of harmful microorganisms: mucins, antimicrobial peptides, and microbiota

The intestinal tract is a complex ecosystem that combines resident microbiota and the cells of various phenotypes with complex metabolic activities that line the epithelial wall. The intestinal cells that make up the epithelium provide physical and chemical barriers that protect the host against the unwanted intrusion of microorganisms that hijack the cellular molecules and signaling pathways of the host and become pathogenic. Some of the organisms making up the intestinal microbiota also have microbicidal effects that contribute to the barrier against enteric pathogens. This review describes the two cell lineages present in the intestinal epithelium: the goblet cells and the Paneth cells, both of which play a pivotal role in the first line of enteric defense by producing mucus and antimicrobial peptides, respectively. We also analyze recent insights into the intestinal microbiota and the mechanisms by which some resident species act as a barrier to enteric pathogens. Moreover, this review examines whether the cells producing mucins or antimicrobial peptides and the resident microbiota act in partnership and whether they function individually and/or synergistically to provide the host with an effective front line of defense against harmful enteric pathogens.

Enzymatic large-scale synthesis of MUC6-Tn glycoconjugates for antitumor vaccination

In cancer, mucins are aberrantly O-glycosylated, and consequently, they express tumor-associated antigens such as the Tn determinant (alpha-GalNAc-O-Ser/Thr). As compared with normal tissues, they also exhibit a different pattern of expression. In particular, MUC6, which is normally expressed only in gastric tissues, has been detected in intestinal, pulmonary, colorectal, and breast carcinomas. Recently, we have shown that the MCF7 breast cancer cell line expresses MUC6-Tn glycoproteins in vivo. Cancer-associated mucins show antigenic differences from normal mucins, and as such, they may be used as potential targets for immunotherapy. To develop anticancer vaccines based on the Tn antigen, we prepared several MUC6-Tn glycoconjugates. To this end, we performed the GalNAc enzymatic transfer to two recombinant MUC6 proteins expressed in Escherichia coli, using UDP-N-acetylgalactosamine: polypeptide N-acetylgalactosaminyltransferases (ppGalNAc-Ts), which catalyze in vivo the Tn antigen synthesis. We used either a mixture of ppGalNAc-Ts from MCF7 breast cancer cell extracts or a recombinant ppGalNAc-T1. In both cases, we achieved the synthesis of MUC6-Tn glycoconjugates at a semi-preparative scale (mg amounts). These glycoproteins displayed a high level of Tn antigens, although the overall density depends on both enzyme source and protein acceptor. These MUC6-Tn glycoconjugates were recognized by two anti-Tn monoclonal antibodies that are specific to human cancer cells. Moreover, the MUC6-Tn glycoconjugate glycosylated using MCF7 extracts as the ppGalNAc-T source was able to induce immunoglobulin G (IgG) antibodies that recognized a human tumor cell line. In conclusion, the large-scaled production of MUC6 with tumor-relevant glycoforms holds considerable promise for developing effective anticancer vaccines, and further studies of their immunological properties are warranted.