Aberrant expression of a human mucin gene (MUC5AC) in rectosigmoid villous adenoma.

BACKGROUND & AIMS: Rectosigmoid villous adenomas (RVAs) account for approximately 10% of all colorectal tumors. They have distinct pathological features, including abundant mucus secretion, possible malignant transformation, and multiple recurrences after conservative treatment. The aim of this study was to determine the nature of any changes in mucin gene expression in RVAs. METHODS: In situ hybridization was used to examine mucin messenger RNA expression in a series of 22 patients with an RVA. Five normal rectal and colonic mucosae and five rectal adenocarcinomas were used as controls. RESULTS: In the 22 RVAs, we found an overexpression of MUC2 and an aberrant expression of MUC5AC. This MUC5AC expression was more intense in RVAs with low-grade dysplasia than in those cases with high-grade dysplasia. Moreover, in 4 cases, it was detected at a distance from the tumor in areas previously considered as normal by endoscopic and histological examination. CONCLUSIONS: MUC5AC seems to be a specific marker for RVAs and thus may be useful for the early detection of RVA recurrences after endoscopic laser treatment.

In situ hybridization shows distinct patterns of mucin gene expression in normal, benign, and malignant pancreas tissues.

BACKGROUND & AIMS: Northern blotting and immunohistochemistry have shown cell-specific patterns of mucin gene expression in the pancreas and alterations associated with neoplastic transformation. The aim of this study was to determine the presence of mucin transcripts at the single cell level in tissue samples from normal pancreas and benign and malignant pancreatic proliferative lesions. METHODS: In situ hybridization with 35S-labeled oligonucleotides was performed on sections of paraffin-embedded tissues. RESULTS: Acinar cells express only MUC1. Normal pancreatic ducts show homogeneous expression of MUC1 and MUC5B and heterogenous expression of MUC3. MUC2, MUC4, and MUC5AC are generally undetectable in all cells of normal pancreas tissue. Pancreas cancers generally express MUC1, MUC3, MUC4, MUC5B and MUC5AC. Obstructive chronic pancreatitis adjacent to pancreas cancers shows the same pattern of mucin gene expression as normal ducts. In areas of papillary hyperplasia, altered expression of MUC3, MUC5B, and MUC5AC is observed. CONCLUSIONS: In situ hybridization has confirmed that neoplastic transformation of the exocrine pancreas is accompanied by changes in mucin gene expression. Although this type of change is not restricted to cancer cells, the findings of this study suggest that analysis of mucin gene expression may be of value in the differential diagnosis of pancreatic lesions.

Expression of human mucous proteinase inhibitor in respiratory tract: a study by in situ hybridization.

Human mucous proteinase inhibitor (MPI) is present in bronchial secretions, where it participates in the protection of lung structures against degradation by leukocyte elastase. The protein has been localized by immunohistochemical studies and immunogold labeling essentially in the serous cells of the submucosal glands and also in the surface epithelial cells of central and peripheral airways. However, until now no gene expression study has been performed at the tissue level. In this study, in situ hybridization was used to precisely study MPI mRNA expression in bronchial tissue sections with a specific radiolabeled oligonucleotide probe. By light microscopy, MPI gene expression was localized exclusively in the serous and seromucinous acini of the submucosal glands of large airways. The MPI gene was expressed in submucosal glands of normal and carcinomatous tissue sections, whereas it was not expressed in bronchial and bronchiolar surface epithelia.

Characterization of the human mucin gene MUC5AC: a consensus cysteine-rich domain for 11p15 mucin genes?

To date five human mucin cDNAs (MUC2, 5A, 5B, 5C and 6) mapped to 11p15.3-15.5, so it appears that this chromosome region might contain several distinct gene loci for mucins. Three of these cDNAs, MUC5A, B and C, were cloned in our laboratory and previously published. A common number, 5, was recommended by the Human Gene Mapping Nomenclature Committee to designate them because of their common provenance from human tracheobronchial mucosa. In order to define whether they are products of the same gene locus or distinct loci, we describe in this paper physical mapping of these cDNAs using the strategy of analysis of CpG islands by pulse-field gel electrophoresis. The data suggest that MUC5A and MUC5C are part of the same gene (called MUC5AC) which is distinct from MUC5B. In the second part of this work, complete sequences of the inserts corresponding to previously described (JER47, JER58) and novel (JER62, JUL32, MAR2, MAR10 and MAR11) cDNAs of the so-called MUC5AC gene are presented and analysed. The data show that in this mucin gene, the tandem repeat domain is interrupted several times with a subdomain encoding a 130 amino acid cysteine-rich peptide in which the TR3A and TR3B peptides previously isolated by Rose et al. [Rose, Kaufman and Martin (1989) J. Biol. Chem., 264, 8193-8199] from airway mucins are found. A consensus peptide sequence for these subdomains involving invariant positions of most of the cysteines is proposed. The consensus nucleotide sequence of this subdomain is also found in the MUC2 gene and in the MUC5B gene, two other mucin genes mapped to 11p15. The functional significance for secreted mucins of these cysteine-rich subdomains and the modular organization of mucin peptides are discussed.

Mucin gene expression in the human endocervix.

In the human uterine endocervix, five out of the six human mucin genes investigated (MUC 2, MUC 3, MUC 4, MUC 5AC, MUC 5B and MUC 6) are expressed, whereas in some other mucosae the hybridization pattern demonstrates the expression of only two or three of these genes. The most intense labelling by in-situ hybridization is obtained significantly with MUC 4, predominantly during the luteal phase. The expression of the MUC 4 gene appears to be influenced by the oestro-progesterone ratio. During the ovulatory cycle, there are only a few differences concerning the variations of expression of all other MUC genes.

Expression of human mucin genes in respiratory, digestive, and reproductive tracts ascertained by in situ hybridization.

In recent years considerable advances have been made in our knowledge of the peptide moiety of human mucins through cDNA cloning. In many diseases disorders in mucin biosynthesis are observed, which result either from changes in the synthesis of the carbohydrate side chains or from differences in the relative expression of the different apomucins, each of which may affect physical properties of the viscous gel. We describe in situ hybridization studies on healthy human mucosae with five different oligonucleotide probes corresponding to each of the human genes known to date that encode secreted mucins, i.e., MUC 2, 3, 4 (HGM nomenclature) and 5B, 5C (proposed name). These genes present a nucleic tandem repeat organization. The choice of oligonucleotide probes was made to amplify the signal by hybridization of many small probes on the same mRNA molecules. A characteristic pattern of mucin gene expression was observed for each mucosa.

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

A human tracheobronchial lambda gt 11 cDNA library was screened using antiserum prepared against the deglycosylated protein backbone of human tracheobronchial mucins. Two cDNAs, designated JER 28 and 57, obtained from this immunoscreening, were used to isolate two other cDNA clones, JUL 7 and JUL 10, from a human tracheobronchial lambda gt 10 cDNA library. These four clones (561, 1830, 1631 and 991 bp), which mapped to chromosome 11p15, were all found to contain degenerate 87-base-pair tandem repeats which encode non-repetitive peptides. Numerous deletions or insertions in an otherwise virtually perfect 87-base-pair tandem repeat create many shifts in reading frame which completely destroy the repetitive peptide structure. The peptide is composed of alternate hydrophobic and hydrophilic domains which probably differ in the extent to which they are glycosylated. The mRNAs are expressed both in the respiratory and in the digestive tracts. These human mucin probes may be important in assessing the abnormal mucins associated with inflammatory diseases or carcinoma from human mucosae.

Structural features of the core proteins of human airway mucins ascertained by cDNA cloning.

Tracheobronchial secretions are one of the most important elements of the mucociliary system that protects the respiratory mucosa. They contain bronchial mucus, which is composed of a group of macromolecules secreted by the goblet cells of the epithelium and the submucosal glands. Bronchial mucins are the most characteristic molecules of this mucus. They form a group of complex, polydispersed O-linked glycoproteins containing sugars, which make up 80% of their weight. The protein core of human airway mucin has been difficult to sequence by traditional technologies because of its high content of serine and threonine residues linked to numerous oligosaccharide chains. We therefore prepared a lambda gt11 cDNA library from one sample of human tracheobronchial mucosa and screened this library with a polyclonal antibody directed against the apopeptides of human bronchial mucins. We obtained 20 positive clones that were sequenced. These sequences were classified into three different types. The use of the nucleotide probes from these clones in Northern blot analysis showed that the RNA messages were extremely polydispersed. At the current time, four of these probes allow us to map human tracheobronchial mucins genes to at least three different chromosomes. These results suggest that the peptide moiety of the human airway mucin is very heterogeneous.

Molecular cloning and chromosomal localization of a novel human tracheo-bronchial mucin cDNA containing tandemly repeated sequences of 48 base pairs.

A lambda gt11 cDNA library constructed from human tracheo-bronchial mucosa was screened with a polyclonal antiserum raised to chemically deglycosylated pronase glycopeptides from human bronchial mucins. Out of 20 positives clones, one partial cDNA clone was isolated and allowed to map a novel human tracheo-bronchial mucin gene. It contains 48 nucleotide tandem repeats quite perfectly identical which encodes a protein containing about 50% of hydroxy amino-acids. This clone hybridized to polydisperse messages produced by human tracheo-bronchial and human colonic mucosae. The gene (proposed name MUC 4) from which cDNA is derived maps to chromosome 3.