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

In silico identification and comparative analysis of differentially expressed genes in human and mouse tissues

Background

Screening for differentially expressed genes on the genomic scale and comparative analysis of the expression profiles of orthologous genes between species to study gene function and regulation are becoming increasingly feasible. Expressed sequence tags (ESTs) are an excellent source of data for such studies using bioinformatic approaches because of the rich libraries and tremendous amount of data now available in the public domain. However, any large-scale EST-based bioinformatics analysis must deal with the heterogeneous, and often ambiguous, tissue and organ terms used to describe EST libraries.

Results

To deal with the issue of tissue source, in this work, we carefully screened and organized more than 8 million human and mouse ESTs into 157 human and 108 mouse tissue/organ categories, to which we applied an established statistic test using different thresholds of the p value to identify genes differentially expressed in different tissues. Further analysis of the tissue distribution and level of expression of human and mouse orthologous genes showed that tissue-specific orthologs tended to have more similar expression patterns than those lacking significant tissue specificity. On the other hand, a number of orthologs were found to have significant disparity in their expression profiles, hinting at novel functions, divergent regulation, or new ortholog relationships.

Conclusion

Comprehensive statistics on the tissue-specific expression of human and mouse genes were obtained in this very large-scale, EST-based analysis. These statistical results have been organized into a database, freely accessible at our website , for easy searching of human and mouse tissue-specific genes and for investigating gene expression profiles in the context of comparative genomics. Comparative analysis showed that, although highly tissue-specific genes tend to exhibit similar expression profiles in human and mouse, there are significant exceptions, indicating that orthologous genes, while sharing basic genomic properties, could result in distinct phenotypes.

Laboratory findings in tear fluid analysis

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

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

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.

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

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

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.

Effect of retinoic acid on gene expression in human conjunctival epithelium: secretory phospholipase A2 mediates retinoic acid induction of MUC16

PURPOSE

How vitamin A contributes to the maintenance of the wet-surfaced phenotype at the ocular surface is not well understood. This study sought to identify vitamin A-responsive genes in ocular surface epithelia using gene microarray analysis of cultures of a human conjunctival epithelial (HCjE) cell line grown with all-trans-retinoic acid (RA). The analysis showed that secretory phospholipase A(2) group IIA (sPLA(2)-IIA) was the gene most upregulated by RA, followed by the membrane-associated mucin MUC16 at a later time point. Since eicosanoids, the product of arachidonic acid generated by the PLA(2) family, have been shown to increase mucin production, this study sought to determine whether sPLA(2) mediates the RA induction of MUC16.

METHODS

HCjE cells were cultured with or without RA for 3, 6, 24, and 48 hours. Complementary RNA prepared from RNA of the HCjE cells was hybridized to human gene chips and analyzed using commercial software. Microarray data on mucin expression were validated by real-time PCR. To investigate whether sPLA(2) is associated with RA-induced MUC16 upregulation, HCjE cells were incubated with RA and the broad-spectrum PLA(2) inhibitor aristolochic acid (ArA) or the specific sPLA(2)-IIA inhibitor LY315920, followed by analysis of MUC16 mRNA and protein by real-time PCR and Western blot analysis.

RESULTS

After RA addition, 28 transcripts were upregulated and 6 downregulated by more than twofold (P < 0.01) at both 3 and 6 hours (early phase). Eighty gene transcripts were upregulated and 45 downregulated at both 24 and 48 hours (late phase). Group IIA sPLA(2), significantly upregulated by 24 hours, and MUC16 were the most upregulated RNAs by RA at 48 hours. sPLA(2) upregulation by RA was confirmed by Western blot analysis. When HCjE cells were incubated with RA plus ArA or specific inhibitor of sPLA(2)-IIA, LY315920, the RA-induced MUC16 mRNA was significantly reduced (P < 0.01).

CONCLUSIONS

The RA-associated upregulation of membrane-associated mucin MUC16 at late phase appears to be through sPLA(2)-IIA. Upregulation of this hydrophilic membrane-associated mucin may be one of the important mechanisms by which vitamin A facilitates maintenance of the wet-surfaced phenotype on the ocular surface.

Expression of mucin genes in the human testis and its relationship to spermatogenesis

In this study we investigate the expression pattern of mucin genes in the human testis and evaluate the relationship between the expression of mucin genes and impaired spermatogenesis in the human testis. Thirty human testis tissues were collected from patients undergoing diagnostic testicular biopsy to investigate the cause of infertility. One part of the tissue underwent histological observation, and the other part of the tissue was subjected to semiquantitative RT-PCR of mucin genes, that is, mucin1, 2, 3, 4, and 9. The relative amount of mucin mRNAs was calculated by densitometry using glyceraldehydes-3-phosphate dehydrogenase (GAPDH) as an internal control. The samples were histologically diagnosed as either obstructive azoospermia with normal spermatogenesis (n = 13) or non-obstructive azoospermia with impaired spermatogenesis (n = 17). In the human testis with normal spermatogenesis, mRNA expression of mucin1, 9, 13 and GAPDH were found, but RT-PCR products of mucin 2, 3 and 4 were not detected. In the testis with impaired spermatogenesis, however, RT-PCR product of mucin1 was not found. There was no difference in the other mucin mRNA expression patterns between the testis with either normal or impaired spermatogenesis. To our knowledge, this study is the first that has detected the mRNA of mucin9 and 13 in human testis. This study also shows that mucin1 expression might be closely related to spermatogenesis. Our findings should be substantiated by more direct evidence, such as mucin protein expression and localization.

Expression profile of malignant and nonmalignant lesions of esophagus and stomach: differential activity of functional modules related to inflammation and lipid metabolism

Adenocarcinomas of stomach and esophagus are frequently associated with preceding inflammatory alterations of the normal mucosa. Whereas intestinal metaplasia of the gastric mucosa is associated with higher risk of malignization, Barrett's disease is a risk factor for adenocarcinoma of the esophagus. Barrett's disease is characterized by the substitution of the squamous mucosa of the esophagus by a columnar tissue classified histopathologically as intestinal metaplasia. Using cDNA microarrays, we determined the expression profile of normal gastric and esophageal mucosa as well as intestinal metaplasia and adenocarcinomas from both organs. Data were explored to define functional alterations related to the transformation from squamous to columnar epithelium and the malignant transformation from intestinal metaplasia to adenocarcinomas. Based on their expression profile, adenocarcinomas of the esophagus showed stronger correlation with intestinal metaplasia of the stomach than with Barrett's mucosa. Second, we identified two functional modules, lipid metabolism and cytokine, as being altered with higher statistical significance. Whereas the lipid metabolism module is active in samples representing intestinal metaplasia and inactive in adenocarcinomas, the cytokine module is inactive in samples representing normal esophagus and esophagitis. Using the concept of relevance networks, we determined the changes in linear correlation of genes pertaining to these two functional modules. Exploitation of the data presented herein will help in the precise molecular characterization of adenocarcinoma from the distal esophagus, avoiding the topographical and descriptive classification that is currently adopted, and help with the proper management of patients with Barrett's disease.

Ultrastructure of the human periovulatory cervical mucus

Two main types of cervical mucus have been described during the menstrual cycle: oestrogenic and progestative. Each category shows diverse morphological and functional features from the reproductive point of view. Traditionally, this change has been approached by analysing morphological patterns. In fact, a mesh model has been described for cervical mucus, structurally composed of fibrillar subunits with a parallel orientation, together with another model in a characteristic network shape with canalicular units, but the real model is not clear. The objective of our work was to study the different morphological structures of the mucus, as related to the day of follicular rupture (considered as day 0) determined by ultrasound. Cervical mucus samples were obtained from the cervical canal with an ASPIRETTEtrade mark from day -4 to day +1 of the menstrual cycle. Samples were fixed and dried by critical point. The ultrastructure was examined with scanning electron microscopy. The presence of three types of oestrogenic and one type of progestative cervical mucus was confirmed in this period. Our paper shows different types of ultrastructure in the oestrogenic mucus in relation to ovulation, which would help to understand the interaction between male gametes and cervical mucus in migration through the female genital tract.

Major secretory mucin expression in chronic sinusitis

OBJECTIVE

The aim of this study was to investigate mucin expression in chronic sinusitis compared to that in normal nasal mucus.

STUDY DESIGN AND SETTING

Sinus mucus samples were collected during functional endoscopic sinus surgery (FESS). The expression of 3 airway mucins, MUC2, MUC5AC, and MUC5B, was determined by ELISA.

RESULTS

The 3 mucins are expressed in chronic sinusitis and in normal nasal mucus. MUC5AC and MUC5B represent a major component in sinus mucins while MUC5B and MUC2 predominated in normal nasal mucin. In sinus mucins, upregulation of MUC5AC was associated with downregulation of MUC2 and vice versa. This inverse relationship was strengthened in the presence of nasal polyps.

CONCLUSION

At least 3 mucins are expressed at various levels in chronic sinusitis. An inverse relationship was identified between expression of MUC5AC and MUC2. Large prospective studies are required to unravel the complexities of sinus mucus in chronic sinusitis.

SIGNIFICANCE

Mucins may be used as markers for assessment of disease severity and may also help as prognostic indicators following medical or surgical treatment.

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

BACKGROUND

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

AIMS

To investigate the prognostic significance of MUC4 expression in IDC.

METHODS

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

RESULTS

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

CONCLUSIONS

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

Mucin gene expression in nasal polyps

CONCLUSIONS

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

OBJECTIVE

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

MATERIAL AND METHODS

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

RESULTS

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

Amino acid sequence of alpha-subunit in hen egg white ovomucin deduced from cloned cDNA

The primary amino acid sequence of alpha-subunit in ovomucin (OVM) from hen thick egg white was determined. The 2087 amino acid residues with a relative molecular mass of 230.9 kDa along the full length of the alpha-subunit were represented. The alpha-subunit contains domains, arranged from the N- to C-terminals in the following order: D1-D2-D'-D3-R (central region)-D4-C1-CK (Cystine-knot), in a manner similar to the arrangement of D, C and CK domains in human pre-pro-von Willebrand factor (hpp-vWF) and hMUC2. The alpha-subunit showed identities on amino acid sequences with hpp-vWF and hMUC2 at 33 and 41% in the N-terminal region and 30 and 38% in the C-terminal region, respectively. The numbers and positions of cysteine residues were highly conserved among alpha-subunit, hpp-vWF and hMUC2. However, R showed no virtual sequence homology with the corresponding regions in two proteins. It was estimated that alpha-subunit was not part of a large peptide of OVM, but was independently synthesized from beta-subunit.

Prostaglandin E2 induces MUC8 gene expression via a mechanism involving ERK MAPK/RSK1/cAMP response element binding protein activation in human airway epithelial cells

MUC8 gene expression is overexpressed in nasal polyp epithelium and is also increased by treatment with inflammatory mediators in nasal epithelial cells. These data suggest that MUC8 may be one of important mucin genes expressed in human airway. However, the mechanisms of various inflammatory mediator-induced MUC8 gene expression in normal nasal epithelial cells remain unclear. We examined the mechanism by which prostaglandin E(2) (PGE2), an arachidonic acid metabolite, increases MUC8 gene expression levels. Here, we show that ERK mitogen-activated protein kinase is essential for PGE2-induced MUC8 gene expression in normal human nasal epithelial cells and that p90 ribosomal S 6 protein kinase 1 (RSK1) mediates the PGE2-induced phosphorylation of cAMP-response element binding protein. Our results also indicate that cAMP-response element at the -803 region of the MUC8 promoter is an important site of PGE2-induced MUC8 gene expression. In conclusion, this study gives insights into the molecular mechanism of PGE2-induced MUC8 gene expression in human airway epithelial cells.

Gallbladder mucin plays a role in gallstone formation

Mucin is a high-molecular-weight glycoprotein that is synthesized, stored, and secreted by epithelial mucosal cells, especially goblet cells. Mucin proteins are derived from many different genes, termed MUC genes. Several lines of evidence point to a biological role for mucin in cholesterol gallstone formation. Mucin serves as a pronucleating agent in experimental and human gallstone disease, and the hydrophobic binding sites in the polypeptide core of mucin may provide a favorable environment for nucleation of cholesterol monohydrate from supersaturated bile. Mucin hypersecretion is prominent in many animal models of gallstone formation, thus contributing by its pronucleating quality to gallstone formation. According to some research, mucin hypersecretion may also contribute to the formation of brown pigment stones. This may be explained in part by the findings that lipopolysaccharides derived from certain bacteria are effective stimulants of mucin secretion. Aspirin and nonsteroidal anti-inflammatory drugs inhibit gallbladder mucin secretion and prevent gallstone formation in animal models. Expanding our knowledge on mucin research may improve our understanding of the natural history of gallstone formation and enable the development of new treatment strategies.

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

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

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

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

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

Mucus production after transposition of intestinal segments into the urinary tract

Following transposition into the urinary tract, intestinal segments continue to produce mucus and problems related to excessive production do not to diminish with time. Currently, 20 human mucin genes have been described and their protein products partially or fully characterised. As the use of transposed intestinal segments in urology increases, there is now a need for a better understanding of mucins at the gene and protein levels. There is also a need for urologists to be aware of the many complications related to excess mucus production. Whilst effective therapeutic measures to reduce mucus production and its related complications remain elusive, it is now clear that without such effective mucoregulatory agents the quality of life of patients will continue to be less than satisfactory. This review describes the biology of mucus and the problems related to continued production following transposition of intestinal segments into the urinary tract. Difficulties related to quantification of urinary mucus, in addition to the structural and mucin gene changes that occur in transposed segments, are addressed.

Characterization of a novel human UDP-GalNAc transferase, pp-GalNAc-T15

We have cloned, expressed and characterized a novel member of the human UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferase (pp-GalNAc-T) family, pp-GalNAc-T15. The pp-GalNAc-T15 transcript was ubiquitously expressed in human tissues. Recombinant pp-GalNAc-T15 transferred N-acetylgalactosamine (GalNAc) toward a panel of mucin-derived peptide substrates in vitro. Although pp-GalNAc-T15 showed significantly less catalytic activity than pp-GalNAc-T2, T15 transferred up to seven GalNAcs to the Muc5AC peptide, while T2 transferred up to five GalNAcs. These results clearly indicated that pp-GalNAc-T15 is a novel member of the human pp-GalNAc-T family with unique catalytic activity.

Correlation between MUC5AC expression and the prognosis of patients with adenocarcinoma of the uterine cervix

BACKGROUND

Mucin expression shows some correlation with prognosis in patients with various cancers. However, few studies have been conducted on adenocarcinomas of the uterine cervix.

METHODS

An immunohistochemical study with a monoclonal anti-MUC5AC antibody, 45M1, was performed on 47 adenocarcinomas of the uterine cervix and on 40 specimens of normal endocervical epithelium. The correlations between clinicopathologic variables and MUC5AC expression were evaluated in the cervical adenocarcinomas.

RESULTS

A significant reduction of MUC5AC expression was evident in the adenocarcinomas of the cervix in comparison with that in the normal endocervical epithelium (53.2% vs. 100%; P <.001). MUC5AC expression was correlated with paracervical invasion and histological type. Patients with negative MUC5AC expression showed poorer survival than those with positive MUC5AC expression (P =.03). However, multivariate analysis revealed that only the depth of invasion was an independent prognostic variable.

CONCLUSIONS

MUC5AC expression was suppressed in adenocarcinoma of the uterine cervix. Absence of MUC5AC expression seems correlated with worse survival.

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.

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.

Combined status of MUC1 mucin and surfactant apoprotein A expression can predict the outcome of patients with small-size lung adenocarcinoma

AIM

Lung cancer is still a disease of high mortality, despite advanced diagnostic techniques. Here, we aim to report a unique method to predict the recurrence and outcome of patients with pulmonary adenocarcinomas.

METHODS AND RESULTS

Immunohistochemical expression of MUC1 mucin and surfactant apoprotein A (SP-A) was examined in 185 cases of surgically removed lung adenocarcinomas of non-bronchioloalveolar type smaller than 30 mm. Staining results were evaluated semiquantitatively, and the expression of MUC1 and SP-A was compared in each case. There were 140/185 (76%) cases showing MUC1 expression higher than SP-A expression (MUC1>SP-A), and 45/185 (24%) cases showing MUC1 expression lower than or equal to SP-A expression (MUC1<or =SP-A). Recurrence was observed in 24% (34/140) of the patients with a MUC1>SP-A pattern, but in 7% (3/45) of the patients with a MUC1< or =SP-A pattern after the median observation period of 41 months (1-99 months) (P < 0.01). The MUC1>SP-A group showed higher recurrence and worse survival than the MUC1<or =SP-A group by Kaplan-Meier's method (P < 0.01 and P < 0.005). Even in the patients with apparently favourable prognostic factors (well-differentiated adenocarcinoma or no lymph node metastasis), recurrence and survival were different between the two groups.

CONCLUSIONS

A high MUC1/SP-A ratio is strongly associated with a poor outcome in patients with small-size lung adenocarcinoma.

Levels of mucin gene expression in normal human conjunctival epithelium in vivo

PURPOSE

Conjunctival impression cytology (CIC) samples were used to determine the mean and normal range of mRNA levels of human MUC1, MUC2, MUC4, MUC5AC, and MUC7 mucin genes.

METHODS

Real time PCR was performed to determine normal mRNA levels in CIC samples of 24 male and 19 female healthy donors. Correlation coefficients between gene expression levels were obtained.

RESULTS

All five mucin genes were expressed in the CIC samples. MUC1 and MUC4 were present at the highest level and MUC2 was at the lowest. There were no gender differences. Significant positive correlations existed between MUC2 and MUC4 and between MUC2 and MUC7 levels.

CONCLUSIONS

Normal levels and ranges of mRNAs for MUC1, MUC2, MUC4, MUC5AC and MUC7 conjunctival mucin genes have been established for the first time. These data may serve as the normal threshold values for future comparisons in different experimental and pathological conditions involving the ocular surface.

MUC1 and MUC2 expression in pancreatic ductal carcinoma obtained by fine-needle aspiration

BACKGROUND

Mucins are high molecular weight glycoproteins that are produced by various epithelial cells including those found in the pancreas. MUC1 and MUC2 are two well characterized mucin antigens. The objective of the current study was to examine the pattern of phenotypic expression of MUC1 and MUC2 in pancreatic lesions obtained by fine-needle aspiration biopsy (FNA) and to determine the utility of MUC1 and MUC2 as markers for pancreatic ductal carcinoma.

METHODS

Thirty-nine cell blocks of pancreatic FNA obtained under endoscopic ultrasound guidance were retrieved from the archives and immunostained with a monoclonal antibody directed against MUC1 and MUC2. These cell blocks were taken from 39 patients (16 females and 23 males) who had a median age of 64 years. Eleven FNAs were taken from patients with reactive/inflammatory conditions. The remaining 28 FNAs included 24 ductal carcinomas, 2 neuroendocrine tumors, 1 lymphoma sample, and 1 sarcoma sample. The presence of immunoreactivity, irrespective of the level of intensity or the percentage of cells, was considered as positive for MUC1 and MUC2 expression. Follow-up included correlation with pathology materials obtained at surgery and review of medical records.

RESULTS

Twenty-three of 24 pancreatic ductal carcinomas (96%) demonstrated positive staining with MUC1. Twenty-one positive cases demonstrated either apical or diffuse membranous staining with variable cytoplasmic staining. The remaining two positive cases showed only cytoplasmic staining. One of the 11 cases of chronic pancreatitis and benign conditions demonstrated weak apical membranous MUC1 staining in the acinic cells. The difference between the two groups was statistically significant (P < 0.001, using the Fisher exact test). Three pancreatic ductal carcinomas and one chronic pancreatitis specimen demonstrated cytoplasmic staining with MUC2; the difference between the two groups was not found to be statistically significant. None of the nonductal neoplasms demonstrated expression of either MUC1 or MUC2. The sensitivity and specificity of MUC1 as a marker for pancreatic ductal carcinomas were 96% and 94%, respectively.

CONCLUSIONS

MUC1 is overexpressed in pancreatic ductal carcinoma with a predominantly membranous and variable cytoplasmic staining pattern. The results of the current study suggest that the phenotypic expression of MUC1 can be used as an ancillary marker for diagnosing pancreatic ductal carcinoma in cytologic preparations. Conversely, MUC2 does not appear to be a useful marker for recognizing pancreatic ductal carcinoma in FNA specimens.

MUC1: a multifunctional cell surface component of reproductive tissue epithelia

MUC1 is a large, transmembrane mucin glycoprotein expressed at the apical surface of a variety of reproductive tract epithelia. Functions attributed to MUC1 include those generally associated with mucins such as lubrication and hydration of cell surfaces as well as protection from microorganisms and degradative enzymes. In addition, MUC1 is an effective inhibitor of both cell-cell and cell-extracellular matrix interactions in both normal and malignant contexts. Moreover, a series of recent studies has shown that the highly conserved cytoplasmic tail of MUC1 interacts specifically with a series of important signal transducing molecules including beta-catenin, Grb2 and erbB family members. MUC1 expression in normal epithelia can be quite dynamic, varying in response to steroid hormone or cytokine influences. Following malignant transformation, MUC1 often becomes highly overexpressed, loses its apical restriction, and displays aberrant glycosylation and altered mRNA splice variants. Regulation of MUC1 expression can occur at the transcriptional level. In addition, post-translational regulation of cell surface expression occurs via the activity of cell surface proteases or "sheddases" that release soluble forms of the large ectodomains. This review will briefly summarize studies of MUC1 expression and function in reproductive tissues with particular emphasis on the uterus. In addition, current knowledge of the mechanisms of MUC1 gene regulation, metabolic processing and potential signal transducing functions will be presented.

MUC4 is a novel prognostic factor of intrahepatic cholangiocarcinoma-mass forming type

Complete surgical resection of the tumor is the sole approach to improve the cure rate of patients with intrahepatic cholangiocarcinoma-mass forming type (ICC-MF). Although patients are treated by curative resection, many of them show poor outcome. Mucin (MUC)4 expression has been implicated as a marker for diagnosis and progression of pancreatic adenocarcinomas, but there is no study of the relationship between MUC4 expression and patient's prognosis in ICC-MF. In the present study, we examined the expression profile of MUC4 in ICC-MF tissue from 27 patients using immunohistochemistry. MUC4 was expressed in the carcinoma tissues of 10 (37%) of the 27 ICC-MF tumors, whereas it was not expressed in normal liver tissue. Because MUC4 is an intramembrane ligand for receptor tyrosine kinase ErbB2 and is related with regulation of p27, we also compared the MUC4 expression with ErbB2 and p27 expressions in ICC-MFs. The patients with MUC4 and ErbB2 double positive expression showed a short survival period compared to non-expressing patients. MUC4 and p27 showed no relationship. The univariate analysis showed that tumor size, intrahepatic metastasis, lymph node metastasis, MUC4 expression, and MUC1 expression were statistically significant risk factors affecting the outcome of the patients with ICC-MF. The multivariate analysis demonstrated that MUC4 expression, as well as surgical margin, were statistically significant independent risk factors. In conclusion, the results suggest that expression of MUC4 in ICC-MF is a new independent factor for poor prognosis and is a useful marker to predict the outcome of the patients with ICC-MF.

Human epithelium from conjunctival impression cytology expresses MUC7 mucin gene

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Initiation of transcription of the MUC3A human intestinal mucin from a TATA-less promoter and comparison with the MUC3B amino terminus

Human intestinal mucin genes MUC3A and MUC3B are members of a membrane mucin gene family residing at chromosome 7q22. In this paper, we utilized genomic and cDNA cloning to elucidate the sequence of the 5'-region of the MUC3A gene including the gene promoter and the amino terminus coding sequence. Following its 21-residue signal peptide, the amino terminus of the mucin consists of a 233-residue Thr-, Ser-, and Pro-rich nonrepetitive sequence that is contiguous with its hypervariable domain of 375-residue repeats. RNase protection analysis and 5'-GeneRacer PCR indicated that MUC3A gene transcripts initiate from multiple start sites along a region spanning approximately 180 bases. The 5'-flanking region of the gene had promoter activity when fused to a luciferase reporter gene in all of the tested cell lines. This region contained binding sites for several transcription factors, including those implicated in the regulation of intestinal genes, but lacked a cognate TATA box. These features of the gene promoter may enable the gene to be expressed at variable levels in several cell types with different repertoires of transcription factors. We also utilized 5'-GeneRacer PCR to determine the sequence of the 5'-terminus of the MUC3B message. The amino termini of the MUC3A and MUC3B mucins are 91% conserved at the amino acid level. Thus, MUC3A and MUC3B have highly conserved amino and carboxyl termini, suggesting a recent duplication of the entire ancestral gene. It remains to be determined whether other members of the 7q22 membrane mucin gene family have amino-terminal domains similar to MUC3A and MUC3B.

Molecular cloning, genomic structure, and expression analysis of MUC20, a novel mucin protein, up-regulated in injured kidney

Immunoglobulin A nephropathy (IgAN) is the most common primary glomerulonephritis in the world. Here, we identify a cDNA encoding a novel mucin protein, shown previously to be up-regulated in IgAN patients, from a human kidney cDNA library. This protein contains a mucin tandem repeat of 19 amino acids consisting of many threonine, serine, and proline residues and likely to be extensively O-glycosylated; thus, this gene was classified in the mucin family and named MUC20. The human MUC20 gene contains at least four exons and is localized close to MUC4 on chromosome 3q29. We found variations in repeat numbers in the mucin tandem domain, suggesting polymorphism of this region. Northern blot and reverse transcription-PCR analyses revealed that human MUC20 mRNA was expressed most highly in kidney and moderately in placenta, colon, lung, prostate, and liver. Immunohistochemical analysis of human kidney revealed that MUC20 protein was localized in the proximal tubules. Immunoblotting analysis of MUC20 proteins produced in Madin-Darby canine kidney and HEK293 cells indicated the localization of MUC20 protein in a membrane fraction and extensive posttranslational modification. Immunoelectron microscopy of MUC20-producing Madin-Darby canine kidney cells demonstrated that MUC20 protein was localized on the plasma membrane. Expression of MUC20 mRNA in a human kidney cell line was up-regulated by tumor necrosis factor-alpha, phorbol 12-myristate 13-acetate, or lipopolysaccharide. Two species of MUC20 mRNA (hMUC20-L and hMUC20-S), resulting from alternative transcription, were identified in human tissue, whereas only one variant was observed in mouse tissues. Mouse MUC20 mRNA was expressed in the epithelial cells of proximal tubules, and the expression increased dramatically with the progression of lupus nephritis in the kidney of MRL/MpJ-lpr/lpr mice. Moreover, the expression of mouse MUC20 was augmented in renal tissues acutely injured by cisplatin or unilateral ureteral obstruction. These characteristics suggest that the production of MUC20 is correlated with development and progression of IgAN and other renal injuries.

Prognostic value of serum MUC5AC mucin in patients with cholangiocarcinoma

BACKGROUND

The authors recently showed that MUC5AC mucin, which is expressed aberrantly in tumor tissue, is present in significant concentrations in serum from patients with cholangiocarcinoma. Subsequently, determination of serum MUC5AC had high sensitivity and specificity for cholangiocarcinoma. In this study, the possible association between serum MUC5AC mucin and the clinical findings of the patients and their prognostic value were explored.

METHODS

The expression of MUC5AC mucin in serum samples from 179 patients with histologically confirmed cholangiocarcinoma were determined using immunoblotting.

RESULTS

Detection of serum MUC5AC was associated with patients with blood group Type A, larger-sized tumors (> 5 cm), and advanced-stage disease. Patients who had positive serum MUC5AC status had a significantly poorer prognosis (median survival, 127 days; 95% confidence interval [95% CI], 107-180 days) compared with patients who had negative serum MUC5AC status (median survival, 329 days; 95% CI, 199-458 days; P < 0.001). Multivariate analysis with adjustment for all covariates showed that patients who had positive serum MUC5AC status had a 2.5-fold higher risk of death compared with patients who had negative serum MUC5AC status (P < 0.001).

CONCLUSIONS

Serum MUC5AC was associated with tumor burden. The determination of serum MUC5AC may be predictive of poor patient outcome and may be useful in selecting possible treatment options for patients with cholangiocarcinoma. Cancer 2003;98:1438-43.

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

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

Clarithromycin inhibits overproduction of muc5ac core protein in murine model of diffuse panbronchiolitis

Long-term treatment of macrolide antibiotics is considered an effective treatment for diffuse panbronchiolitis (DPB). Although hypersecretion is a common feature of this disease, and it is known that macrolides inhibit mucin production, the mechanism of the effect on mucin production is unclear. The aim of our study was to determine the production of muc5ac core protein, a major core protein of mucin in airway secretion, and the effect of clarithromycin treatment on such production in a mouse model mimicking DPB. Alcian blue-periodic acid-Schiff-positive cells were detected in the lungs of Pseudomonas aeruginosa-infected mice. Western blots of these mice showed muc5ac glycoprotein at day 1 and increased progressively from day 4 to day 14 after inoculation of bacteria. Clarithromycin (10 mg. kg-1. day-1 for 7 days) significantly reduced the muc5ac expression at both the mRNA and protein levels. To investigate the role of molecules upstream in muc5ac regulation, we examined the role of mitogen-activated protein kinase. Extracellular signal-regulated kinase 1/2 phosphorylation increased in the infected lung and decreased after treatment. Our results suggest that overproduction of muc5ac plays an important role in the pathogenesis of DPB and that clinical improvement following macrolide therapy seems to involve, at least in part, its inhibition of mucin overproduction, through modulation of intracellular signal transduction.

Induction of MUC8 gene expression by interleukin-1 beta is mediated by a sequential ERK MAPK/RSK1/CREB cascade pathway in human airway epithelial cells

Mucins are the major components of the mucus layer that covers and protects the respiratory, digestive, and reproductive tracts. Our previous studies showed that MUC8 gene expression was overexpressed in in vivo polyp epithelium in chronic sinusitis and was also increased by treatment with inflammatory mediators in an in vitro culture condition. However, the mechanisms by which the inflammatory mediators-induced MUC8 gene expression in normal nasal epithelial cells evolved remain unclear. We examined the mechanism by which the important proinflammatory mediator, interleukin (IL)-1 beta, increases MUC8 gene expression levels. We found that pharmacologic and genetic inhibition of ERK MAPK pathway abolished IL-1 beta-induced MUC8 gene expression in normal human nasal epithelial cells. Moreover, the overexpression of wide-type or of the dominant-negative mutant of p90 ribosomal S6 protein kinase 1 (RSK1) enhanced or suppressed, respectively, IL-1 beta-induced MUC8 gene expression. RSK1 was found to directly phosphorylate cAMP-response element-binding protein (CREB), and this event led to the stimulation of subsequent CRE-mediated gene transcription. In conclusion, IL-1 beta was found to induce MUC8 gene expression via a sequential ERK/RSK1/CREB pathway in human airway epithelial cells.

mRNA of MUC2 is stimulated by IL-4, IL-13 or TNF-alpha through a mitogen-activated protein kinase pathway in human colon cancer cells

MUC2 mucin is a secretory glycoprotein which is produced from the intestinal goblet cells and is a major component of the intestinal epithelial mucus. The biological function of MUC2 mucin is considered to be the protection of intestinal epithelial surface, whereas the regulatory mechanism of MUC2 mucin production in immune response is not completely understood. We have studied the effects of cytokines, IL-4, IL-13 and TNF-alpha, on the regulation of MUC2 mRNA in the human colonic cancer cell lines, LS174T and HT29. The quantitative reverse transcription-polymerase chain reaction showed that single addition of IL-4, IL-13 and TNF-alpha to cell culture induced about two-fold increase of MUC2 mRNA level in LS174T cells. Interleukin-4 and IL-13 activated phosphorylation of mitogen-activated protein kinase in LS174T cells. A specific inhibitor of mitogen-activated protein kinase pathway, U0126, totally inhibited the increase of MUC2 mRNA by IL-4 or IL-13 in those cells. Therefore, mitogen-activated protein activation of kinase is required for the increase of MUC2 mRNA by IL-4 or IL-13 in LS174T cells. In contrast to LS174T cells, only TNF-alpha increased MUC2 mRNA through a mitogen-activated protein kinase pathway in HT29 cells that express low levels of MUC2 mRNA. These findings sustain a novel phenomenon that MUC2 mRNA expression is differently controlled by IL-4, IL-13, or TNF-alpha in LS174T and HT29 cells, whereas the mitogen-activated protein kinase pathway plays a role in the MUC2 mRNA expression induced by those cytokines in both cell lines.

Mutagenesis of a Gly-Ser cleavage site in MUC1 inhibits ectodomain shedding

MUC1 mucin is a type 1 transmembrane glycoprotein dimer of extracellular and membrane-bound subunits. The two non-covalently associated subunits are produced from a single polypeptide chain by proteolysis at a Gly-Ser peptide bond in the endoplasmic reticulum prior to localization on the cell surface. However, once expressed on the surface, the extracellular subunit is shed from cells in the absence of the membrane-associated subunit. Previous studies implicated a cellular metalloproteinase mediating MUC1 ectodomain shedding, but no reports have delineated the site of metalloproteinase cleavage or directly assessed the role of the Gly-Ser bond in shedding. Therefore, we performed site-directed mutagenesis of the Gly-Ser site and determined the effects on MUC1 proteolysis and shedding. Ser-->Ala substitution blocked MUC1 cleavage and inhibited shedding. Equal amounts of wild type and mutant MUC1 were expressed on the cell surface, indicating that lack of shedding of the mutant molecule was not due to reduced surface localization. We conclude that the Gly-Ser peptide bond is required for MUC1 shedding.

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

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

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

AIMS

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Novel MUC1 splice variants contribute to mucin overexpression in CFTR-deficient mice

A cystic fibrosis (CF) mouse expressing the human mucin MUC1 transgene (CFM) reverted the CF/Muc1(-/-) phenotype (little mucus accumulated in the intestine) to that of CF mice expressing mouse Muc1, which exhibited increased mucus accumulation. Western blots and immunohistochemical analysis showed that the MUC1 protein was markedly increased in CFM mice in which it was both membrane bound and secreted into the intestinal lumen. Studies to determine the reason for increased levels of the extracellular domain of MUC1 mucin identified mRNA and protein of two novel splice variants and the previously described secreted MUC1 lacking the cytoplasmic tail (MUC1/SEC). Novel MUC1 splice variants, CT80 and CT58, were both transmembrane proteins with cytoplasmic tails different from the normal MUC1. The MUC1-CT80 and MUC1/SEC forms are found expressed mainly in the CFM mice intestines. Thus MUC1 expression is increased, and it appears that alternate cytoplasmic tails may change its role in signaling. MUC1 could be an important contributor to the CF intestinal phenotype.

An autocatalytic cleavage in the C terminus of the human MUC2 mucin occurs at the low pH of the late secretory pathway

During purification of a recombinant MUC2 C terminus expressed in CHO-K1 cells, the protein was partly cleaved when buffers with a pH of 6.0 were used. When buffers with higher pH values were used, less cleavage was found. Disulfide bonds held the two fragments generated together as these were only observed after reduction. Edman sequencing of the C-terminal 110-kDa fragment revealed that the cleavage had occurred at an Asp-Pro bond, a site described previously to generate the so-called "link peptide" after disulfide bond reduction. In vitro studies on the conditions for cleavage showed that it occurred in a time-dependent manner at a pH below 6.0. Furthermore, the reaction was not enzyme-mediated as it occurred in pure preparations of the MUC2 C terminus and was not inhibited by protease inhibitors. When expressed in the mucin producing cell line LS 174T, the C terminus was cleaved to a higher extent compared with the CHO-K1 cells. Neutralizing the secretory pathway with either NH(4)Cl or bafilomycin A1 inhibited this cleavage. Altogether, our results suggest that the cleavage is an autocatalytic reaction that occurs in the acidic environment of the late secretory pathway. Furthermore, the cleavage produced a new, reactive C terminus that has the potential to attach the mucin to itself or other molecules. Because a pH below 6 can be reached in the late secretory pathway and on mucosal surfaces, the cleavage and possible cross-linking are likely to be of biological importance.

Anti-tumor immunity in mice induced by synthetic polypeptides of MUC5AC and MUC6 apomucins

AIM: To evaluate the immune response and anti-tumor activity induced by synthetic polypeptides of MUC5AC and MUC6 apomucins in mice.

METHODS: The cellular and humoral immunity induced by MUC5AC and MUC6 synthetic polypeptides were examined in mouse, proliferation of lymphocyte and cytotoxicity of T lymphocytes were assessed by 3H-TDR incorporation assay.

RESULTS: The conjugated MUC5AC and MUC6 synthetic polypeptides could induce B cells in mice to produce high titre antibodies against the immunized peptides and delayed-type hypersensitivity. But they could not induce significant proliferation of lymphocyte and specific cytotoxic T-lymphocytes (CTL) in vitro against 7901 gastric cancer cells. This may be caused by the experimental design, inefficient epitope of synthetic polypeptides, or MHC restriction.

CONCLUSION: MUC5AC-KLH and MUC6-KLH synthetic polypeptide conjugates can induce cellular and humoral immunity other than cytotoxic T lymphocytes of anti-tumor effect.

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

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

Cloning and characterization of a novel UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferase, pp-GalNAc-T14

A novel member of the human UDP-N-acetyl-D-galactosamine:polypeptide N-acetylgalactosaminyltransferase (pp-GalNAc-T) gene family was cloned and designated pp-GalNAc-T14. This type II membrane protein contains all motifs that are conserved in the pp-GalNAc-T family proteins and forms a subfamily with pp-GalNAc-T2 on the phylogenetic tree. Quantitative real time PCR analysis revealed significantly high expression of the pp-GalNAc-T14 transcript in kidney, although the transcripts were ubiquitously expressed in all tissues examined. Furthermore, the recombinant pp-GalNAc-T14 transferred GalNAc to a panel of mucin-derived peptide substrates such as Muc2, Muc5AC, Muc7, and Muc13 (-58). Our results provide evidence that pp-GalNAc-T14 is a new member of the pp-GalNAc-T family and suggest that pp-GalNAc-T14 may be involved in the O-glycosylation in kidney.

The MUC gene family: their role in diagnosis and early detection of pancreatic cancer

The early diagnosis of pancreatic cancer, as well as distinguishing between chronic pancreatitis and malignant pancreatic disease, remains still a clinical problem. Presently, there is no specific tumor marker for diagnosing pancreatic cancer. Mucin-associated marker like CA 19-9 are the most widely available pancreatic cancer tumor marker, but its value as a screening marker is limited by its reduced specificity. Mucins (MUCs) are heavily glycosylated, high molecular weight glycoproteins with an aberrant expression profile in various malignancies. This review considers briefly the potential use of the mucin expression pattern in diagnosis of pancreatic neoplasm. The overview will point out the present knowledge about changes in the mucin gene expression in pancreatic intraepithelial neoplasia (PanINs) as precursor lesions and in pancreatic adenocarcinoma, compared to normal pancreas and chronic pancreatitis and the potential role for differentiating chronic pancreatitis from pancreatic cancer.Furthermore, the potential use of MUCs in the diagnosis and differentiation of intraductal papillary-mucinous neoplasm's (IPMNs) will be discussed.

The MUC gene family: their role in diagnosis and early detection of pancreatic cancer

The early diagnosis of pancreatic cancer, as well as distinguishing between chronic pancreatitis and malignant pancreatic disease, remains still a clinical problem. Presently, there is no specific tumor marker for diagnosing pancreatic cancer. Mucin-associated marker like CA 19-9 are the most widely available pancreatic cancer tumor marker, but its value as a screening marker is limited by its reduced specificity.

Mucins (MUCs) are heavily glycosylated, high molecular weight glycoproteins with an aberrant expression profile in various malignancies.

This review considers briefly the potential use of the mucin expression pattern in diagnosis of pancreatic neoplasm. The overview will point out the present knowledge about changes in the mucin gene expression in pancreatic intraepithelial neoplasia (PanINs) as precursor lesions and in pancreatic adenocarcinoma, compared to normal pancreas and chronic pancreatitis and the potential role for differentiating chronic pancreatitis from pancreatic cancer.

Furthermore, the potential use of MUCs in the diagnosis and differentiation of intraductal papillary-mucinous neoplasm's (IPMNs) will be discussed.

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.