Altered mucin core peptide expression in acute and chronic cholecystitis.

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

MUC4 and MUC5B transcripts are the prevalent mucin messenger ribonucleic acids of the human endocervix.

Mucins secreted by the endocervical epithelium protect the surfaces of the reproductive tract epithelium from pathogen penetrance and modulate sperm entry into the uterus. Three large gel-forming mucins, MUCs 5AC, 5B, and 6, are expressed by the endocervical epithelium, as is MUC4, a relatively uncharacterized mucin for which only tandem repeat sequence has been reported. We sought to determine the relative abundance of each of these mucin gene transcripts and to relate their expression to blood progesterone and estradiol. Samples were obtained from six subjects at successive stages in the menstrual cycle. Primers to nontandem repeat sequences of MUCs 4, 5AC, 5B, and 6 were used in semiquantitative reverse transcription-polymerase chain reaction to determine relative abundance of each mucin gene in relation to beta2-microglobulin message control. In order to design primers from a nontandem repeat region of MUC4 so that MUC4 message levels could be quantitated, we obtained approximately 2.7-kilobase nontandem repeat sequence 5' to the tandem repeat sequence of a MUC4 genomic clone. The sequence showed lack of cysteine-rich D-domains and was rich in serine and threonine. Semiquantitative polymerase chain reaction analyses indicated that the principal mucin transcripts of human endocervix are MUC4 and MUC5B, with MUC4 predominant in 15 of 21 samples. When correlated with plasma steroid levels, message levels of both MUC4 and MUC5B were inversely related to progesterone levels.

Variable number tandem repeat polymorphism of the mucin genes located in the complex on 11p15.5.

A family of four genes that encode major secreted mucins (MUC6, MUC2, MUC5AC and MUC5B) map to within 400 kb on chromosome 11p15.5. These genes contain long stretches of tandem repeats of sequence that encode serine- and threonine-rich domains but that otherwise show no similarity from gene to gene, and regions of unique sequence domains that do show evidence of sequence homology. We have previously reported the existence of polymorphism in three of these genes but the extent and nature of this allelic variation is now described here in detail. Variable number tandem repeat polymorphisms of MUC6, MUC2 and MUC5AC are predicted to encode mucin polypeptides that differ in length. In the case of MUC2 and MUC6 these length differences are substantial (up to twofold). MUC5B in contrast does not show common allele length variation. Three MUC2 mutations are reported, none of which are associated with the meiotic recombinations previously observed in this region of chromosome 11.

The MUC6 secretory mucin gene is expressed in a wide variety of epithelial tissues.

Secretory mucins play an important role in the cytoprotection of epithelial surfaces and are used as tumour markers in a variety of cancers. The MUC6 secretory mucin was originally isolated from a gastric cDNA library. The aim was to determine the specific type and location of MUC6 mucin gene expression in a wide range of human adult and fetal epithelial tissues. In situ hybridization, RNA analysis, and immunohistochemistry were used to quantify and localize mucin gene expression. The data obtained show that MUC6 is highly expressed in gastric mucosa, duodenal Brunner's glands, gall bladder, seminal vesicle, pancreatic centroacinar cells and ducts, and periductal glands of the common bile duct; focal expression is seen in basal endometrial and endocervical glands. MUC6 epitopes were also highly expressed in 7/10 pancreatic cancers and 7/10 cholangiocarcinomas and focally expressed in 4/10 endocervical adenocarcinomas. Expression of MUC6 occurs early in fetal development and was observed in Brunner's glands and pancreatic ducts at 18-19 weeks and in gastric glands at 20 weeks' gestation. The tissue distribution of the MUC6 secretory mucin indicates that it may function to protect epithelial tissues from a wide range of substances. Expression of MUC6 is frequently preserved in pancreatic and bile duct adenocarcinomas, but it is only sparsely expressed in endocervical carcinomas.

The carboxyl-terminal sequence of the human secretory mucin, MUC6. Analysis Of the primary amino acid sequence.

The distribution of MUC6 suggests that its primary function is protection of vulnerable epithelial surfaces from damaging effects of constant exposure to a wide range of endogenous caustic or proteolytic agents. A combination of genomic, cDNA. and 3' rapid amplification of cDNA ends techniques was used to isolate the carboxyl-terminal end of MUC6. The 3' nontandem repeat region contained 1083 base pairs of coding sequence (361 amino acids) followed by 632 base pairs of 3'-untranslated region. The coding sequence consists of two distinct regions; region 1 contained the initial 270 amino acids (62% Ser-Thr-Pro with no Cys residues), and region 2 contained the COOH-terminal 91 amino acids (22% Ser-Thr-Pro with 12% Cys). Although region 1 had no homology to any sequences in GenBank, region 2 had approximately 25% amino acid homology to the COOH-terminal regions of human mucins MUC2, -5, and -5B and von Willebrand factor. The shortness of region 2 would leave little of the peptide backbone exposed to a potentially hostile environment. Antibody studies suggest that MUC6 in its native form exists as a disulfide-bonded multimer. The conservation of the 11 cysteine positions in region 2 suggests the importance of this short region to mucin polymerization.

Mucin genes expressed by human female reproductive tract epithelia.

Recent characterizations of mucins at the molecular level indicate that at least eight mucin genes are expressed by epithelia of mucosal surfaces. The purpose of this study was to determine whether these cloned mucins, designated MUC1, MUC2, MUC3, MUC4, MUC5AC, MUC5B, MUC6, and MUC7, are expressed by epithelia of the female reproductive tract. Northern blot analysis, in situ hybridization, and immunohistochemistry were performed using RNA and tissue from surgically removed human reproductive tract specimens including endocervix, ectocervix, vagina, endometrium, and fallopian tube. Complementary DNA to the tandem repeat regions of MUCs 1, 2, 3, 5AC, 5B, and 6; oligonucleotides to the tandem repeat regions of MUCs 4, 6, and 7; and antibodies that recognize unique mucin tandem repeats were used. The data demonstrate that the endocervical epithelium expresses five mucin genes: MUCs 1, 4, 5AC, 5B, and 6. The ectocervical and vaginal epithelia express MUCs 1 and 4, although vaginal expression of MUC4 appears patchy. Endometrial epithelium expresses MUC1 and low amounts of MUC6. MUC6 immunoreactivity was detected only is scattered endometrial glands located in the basalis region in specimens from pre- and postmenopausal women. The only mucin detected in the fallopian tube was MUC1. These data indicate that the endocervical epithelium expresses multiple mucin genes and that the stratified epithelia of the ectocervix and vagina also produce mucins that may function in reproductive processes and protection of the reproductive tract tissues.

Alteration in mucin gene expression and biological properties of HT29 colon cancer cell subpopulations.

Previous studies from our laboratory have shown that HT29 cells selected by adaptation to methotrexate (HT29-MTX) express mature mucins that differ in their immunoreactivity to antibodies against gastric mucin and in the level of one of two major gastric mucin MUC5AC (MUC5) mRNA compared with parental HT29 cells. In this study, we examined the expression of another major gastric mucin, MUC6 mRNA, as well as that of MUC2, -3 and -5 mRNAs in HT29-MTX cells. We also examined their relationship to mucin-related antigen expression and biological properties of the cells such as adhesion to matrigel and E-selectin and in vitro invasiveness, liver colonising activity and degree of differentiation of nude mouse xenograft. Slot blot and Northern analysis revealed markedly increased levels of MUC5 mRNA but no change in MUC6 mRNA level in HT29-MTX cells compared with parental HT29 cells which express barely detectable levels of MUC6 mRNA. A nuclear run-on study showed that MUC5 mRNA was up-regulated at the transcriptional level. The marked increase in MUC5 mRNA was associated with a significant increase in the expression of human gastric mucin and apomucin antigens in HT29-MTX cells. When the adhesive capacity of two cell lines was compared, HT29-MTX cells showed significantly lower adhesion to E-selectin consistent with their lower expression of sialyl Le(x) and sialyl Le(a) antigens compared with HT29 cells. HT29-MTX cells also showed lower adhesive capacity to matrigel than HT29 cells. Interestingly, HT29-MTX cells exhibited significantly decreased liver colonisation capacity in nude mice following splenic vein injection. Furthermore, nude mouse xenograft tumours produced by HT29-MTX cells exhibited a significantly greater degree of differentiation, consisting of mucin-secreting glands than those produced by HT29 cells. In conclusion, these results indicate a shift of predominantly colonic-type mucins to the gastric type, specifically the surface epithelial cell type (MUC5) but not the mucous neck cell or antral gland type (MUC6) in HT29-MTX cells and strongly suggest that altered regulation of mucin genes and the degree of differentiation in cancer cells may be responsible for the altered biological behaviour of these cells.

Expression cloning of gastric mucin complementary DNA and localization of mucin gene expression.

BACKGROUND & AIMS: Secretory mucins play an important role in gastric cytoprotection and are derived from a heterogeneous family of genes. The aim of this study was to determine the specific type and location of mucin gene expression in the human stomach. METHODS: Expression cloning was performed by screening a human gastric complementary DNA expression library with antisera against deglycosylated gastric mucin. RNA analysis and immunohistochemistry were used to quantify and localize mucin gene expression. RESULTS: Sequencing of positive clones revealed two clones containing tandem repeats. The first contained a 169-amino acid repeat and was named MUC6 (as previously described). The second contained the same 8-amino acid repeat consensus sequence (APTTSTTS) as complementary DNAs previously isolated from a tracheobronchial complementary DNA library and was labeled MUC5 (or MUC5AC). RNA analysis indicated that the gastric epithelium contains high levels of MUC5 and MUC6 messenger RNA with little or no MUC2, MUC3, and MUC4 messenger RNA. Immunohistochemical analysis showed that surface mucous cells of the cardia, fundus, and antrum expressed MUC5 peptide. In contrast, MUC6 peptide expression was limited to mucous neck cells of the fundus, antral-type glands of the antrum and cardia, and Brunner's glands of the duodenum. CONCLUSIONS: MUC5 and MUC6 represent major secretory mucins in the stomach and are localized to distinct cell types.

Mucin gene expression in normal, preneoplastic, and neoplastic human gastric epithelium.

Mucins synthesized by malignant cells may contribute (via decreased cellular adhesion and immune recognition) to cancer invasion and metastases. Human mucins are derived from a heterogeneous family of genes, labeled MUC1-6. Our aim was to determine the pattern of mucin gene expression in normal, preneoplastic (intestinal metaplasia), and malignant gastric specimens. Probes and antibodies for specific mucin tandem repeat sequences were used for RNA and immunohistochemical analysis. Normal stomach mucosa was characterized by expression of MUC1, MUC5, and MUC6 mRNA and immunoreactive protein, without MUC2, MUC3, and MUC4 gene expression. In contrast, high levels of MUC2 and MUC3 mucin mRNA and immunoreactive protein were found in specimens with intestinal metaplasia. Gastric cancers exhibited markedly altered secretory mucin mRNA levels compared with adjacent normal mucosa, with decreased levels of MUC5 and MUC6 mRNA and increased levels of MUC3 and MUC4 mRNA. Overall, immunoreactive MUC1 mucin was detected in 72% of 33 gastric cancers, and secretory mucin core peptides were expressed in 34% (MUC2), 45% (MUC3), 19% (MUC5), and 57% (MUC6) of these specimens. Coexpression of multiple (three or more) mucin core proteins occurred in 15 of 25 (60%) advanced (stages III and IV) cancers compared with 1 of 8 (12.5%) early (stages I and II) cancers (P < 0.048). We conclude that human gastric epithelium has a unique mucin gene pattern, which becomes markedly altered in preneoplastic and neoplastic specimens. Increased mucin gene heterogeneity in gastric adenocarcinomas is associated with advanced cancer stage.

Screening for colorectal cancer.

In the past few years, knowledge of the clinical, biologic, and molecular genetic characteristics of colorectal cancer has greatly increased. Although the most cost-effective approach remains to be identified, screening for colorectal cancer can decrease mortality due to this disease by detecting cancers at earlier stages and allowing the removal of adenomas, thus preventing the subsequent development of cancer. Molecular studies that have helped define the genetic basis for this disease hold great promise for the development of better and more powerful methods to identify populations at risk. Individually, these technological, clinical, and basic-science advances are exciting; together, they promise to move us closer to the goal of substantially reducing mortality due to colorectal cancer.

Colorectal cancer. A new look at an old problem.

This discussion was selected from the weekly staff conferences in the Department of Medicine, University of California, San Francisco. Taken from a transcription, it has been edited by Nathan M. Bass, MD, PhD, Associate Professor of Medicine, under the direction of Lloyd H. Smith Jr. MD, Professor of Medicine and Associate Dean in the School of Medicine.

Localization of mucin (MUC2 and MUC3) messenger RNA and peptide expression in human normal intestine and colon cancer.

BACKGROUND/AIMS: Several studies have reported Northern blot data showing that mucin is expressed in a tissue-specific manner. To determine whether expression is limited to specific cell types within these tissues requires histological analysis. METHODS: Both immunocytochemistry and in situ hybridization were used to identify cell types expressing the MUC2 and MUC3 mucins in the human small intestine, colon, and colon carcinoma. RESULTS: In the normal small intestine and colon, an antibody recognizing the MUC2 apomucin stained goblet cells. In contrast, an antibody recognizing the MUC3 apomucin stained both goblet and absorptive cells. Consistent with this, in situ hybridization showed MUC2 messenger RNA (mRNA) only in goblet cells and MUC3 mRNA in both goblet and absorptive cells. In several samples of moderately well-differentiated colon cancer, MUC2 and MUC3 showed distinct patterns of expression, but the expression level of each was reduced compared with levels in normal tissue; there was considerable tumor-to-tumor and cell-to-cell variability using both mucin antibodies and complementary DNA probes. CONCLUSIONS: Individual mucin genes have distinct patterns of expression within mucin-producing tissues, suggesting that the various mucin gene products play distinct functional roles.

Molecular cloning of human intestinal mucin (MUC2) cDNA. Identification of the amino terminus and overall sequence similarity to prepro-von Willebrand factor.

Secretory mucins consist of a protein backbone that is catenated by disulfide bonds, heavily O-glycosylated, and packaged into storage granules prior to release from cells. In this paper, we identify and sequence cDNAs that encode the amino terminus of the MUC2 protein, a major form of mucin found in human intestines and airways. The protein sequence was found to contain a repetitive element of approximately 350 amino acids with considerable sequence similarity to the D domains of prepro-von Willebrand factor. A total of four of these D domains were found to be present in the MUC2 protein, three in the amino-terminal region, and one in the carboxyl-terminal region. Prepro-von Willebrand factor contains four D domains itself, and the overall positioning of the D domains in the two proteins is similar. Prepro-von Willebrand factor contains a 741 residue pro-protein that has been implicated in both the disulfide-linked oligomerization of von Willebrand factor and its packaging into secretory vacuoles. A similar region is present in the MUC2 amino terminus sequence, suggesting that the mechanisms involved in the polymerization and packaging of MUC2 may parallel those already described for von Willebrand factor.

Human gastric mucin. Identification of a unique species by expression cloning.

Gastric mucin is a large glycoprotein which is thought to play a major role in the protection of the gastrointestinal tract from acid, proteases, pathogenic microorganisms, and mechanical trauma. In this paper we describe the isolation by expression cloning and characterization of cDNAs which code for human gastric mucin. The cDNA sequence is characterized by a tandem repeat region whose individual repeat unit is 507 base pairs (169 amino acids) long. The translated sequence is rich in threonine, serine, and proline (31, 18, and 15%, respectively) and contains a relatively large amount of histidine (7.1%) and alanine (5.6%). RNA blot analysis shows a polydisperse pattern which is characteristic of mucins. Expression of this gene is highest in the stomach and gall bladder, with weaker expression in the terminal ileum and right colon. This expression pattern is different from other human mucins and indicates that this gene codes for a unique mucin. Fluorescence in situ hybridization techniques have localized this gene to chromosome 11p15.4-11p15.5. This is the third mucin to be localized to the 11p15 region and suggests a clustering of secretory mucin genes. We propose that this gene for human gastric mucin be called MUC6.

The human MUC2 intestinal mucin has cysteine-rich subdomains located both upstream and downstream of its central repetitive region.

The human MUC2 mucin is a large secretory glycoconjugate that coats the epithelia of the intestines, airways, and other mucus membrane-containing organs. Previous work has shown that this mucin contains an extended tandem repeat-containing domain rich in Thr and Pro. In the present work we describe two additional regions of this mucin located both upstream and downstream of the tandem repeat array. The carboxyl-terminal domain contains 984 residues and can be divided into mucin-like (139 residues) and cysteine-rich (845 residues) subdomains. This latter subdomain exhibits varying degrees of sequence similarity to a wide range of mucins and mucin-like proteins including those isolated from rats, pigs, cows, and frogs. We also report here the sequence of 1270 residues lying immediately upstream of the tandem repeats. This region contains a repetitive, mucin-like subdomain and a second cysteine-rich stretch of more than 700 residues. Both cysteine-rich subdomains of this mucin have sequence similarity with von Willebrand factor, a serum protein that exists as a disulfide-linked polymer. This suggests that these cysteine-rich subdomains are important in the catenation of mucin monomers into oligomers, the structures that confer viscoelasticity upon mucus.

Molecular cloning of rat intestinal mucin. Lack of conservation between mammalian species.

We have prepared antisera to deglycosylated rat intestinal mucin and used it to obtain immunoreactive clones from a rat jejunum cDNA library. Four of these clones were sequenced, and all were found to be partial cDNAs that contained 18-base pair tandem repeats characteristic of a mucin. These cDNAs encoded a repetitive peptide with a consensus sequence of TTTPDV. Thus, they bear little resemblance to either of the two human intestinal mucin cDNAs isolated previously (Gum, J. R., Byrd, J. C., Hicks, J. W., Toribara, N. W., Lamport, D. T. A., and Kim, Y. S. (1989) J. Biol. Chem. 264, 6480-6487 and Gum, J. R., Hicks, J. W., Swallow, D. M., Lagace, R. E., Byrd, J. C., Lamport, D. T. A., Siddiki, B., and Kim, Y. S. (1990) Biochem. Biophys. Res. Commun. 171, 407-415). One of these rat mucin clones, designated RMUC 176, was chosen for further analysis. This clone recognized a band of approximately 9 kilobases when used to probe RNA blots. A strong hybridization band was present using rat small intestine and colon RNA but was not detectable when RNA isolated from heart, liver, or kidney was tested. The RMUC 176 clone and the two previously isolated human intestinal mucin cDNA clones were used to probe blots prepared from BamHI-digested DNA of various species. Here, the human probes detected fragments present only in human and chimpanzee DNA, whereas the RMUC 176 clone recognized fragments only in rat and mouse DNA. Thus, the repetitive portions of intestinal mucin genes are apparently not well conserved between phylogenetically distant species.

MUC-2 human small intestinal mucin gene structure. Repeated arrays and polymorphism.

MUC-2, the first described intestinal mucin gene, has become important as a prototype for secreted mucins in several organ systems. However, little is known about its protein backbone structure and hence its role in diseases such as colon cancer, ulcerative colitis, and cystic fibrosis, which are known to have mucin abnormalities. Studies in this manuscript show that MUC-2 contains two distinct regions with a high degree of internal homology, but the two regions bear no significant homology to each other. Region 1 consists mostly of 48-bp repeats which are interrupted in places by 21-24-bp segments. Several of these interrupting sequences show similarity to each other, creating larger composite repeat units. Region 1 has no length polymorphisms. Region 2 is composed of 69-bp tandem repeats arranged in an uninterrupted array of up to 115 individual units. Southern analysis of genomic DNA samples using TaqI and HinfI reveals both length and sequence polymorphisms which occur within region 2. The sequence polymorphisms have different ethnic distributions, while the length polymorphisms are due to variable numbers of tandem repeats.

The structure of human intestinal apomucins.

Human intestinal mucins are large glycoconjugates (greater than 1,000,000 D) that coat the epithelium, serving to lubricate and protect. Apart from this physiologic function, mucins are important in that they are frequently altered in cancer; thus, they have potential usefulness as tumor markers. We have isolated mucins from human LS174T colon cancer cells and small intestine, deglycosylated these highly purified glycoconjugates, produced polyclonal antibodies to the apomucins, and used these antibodies to isolate two different types of cDNA clones that encode different apomucins. The first class of cDNA clones was isolated using antibodies to deglycosylated LS174T mucin. These cDNA, designated SMUC or MUC2, contain 69 nucleotide tandem repeats that encode a repetitive peptide that is extremely rich in threonine and proline. Northern blots using MUC2 cDNA as probes exhibit large (7,600 bases) and polydisperse hybridization bands. This gene is polymorphic within the human population and is located on chromosome 11. The second class of cDNA was isolated using antibodies to deglycosylated small intestinal mucin. These cDNA, designated SIB or MUC3, have 51 nucleotide tandem repeats that encode a threonine- and serine-rich repetitive peptide. This mucin also is encoded by a large, polydisperse message, but it is clearly distinct from MUC2 as it is located on chromosome 7. Both the MUC2 and MUC3 mucins are expressed in colonic tumors; however, the level of their expression is quite variable. Thus, at least two mucins are expressed by the human gastrointestinal tract. Elucidation of the regulation of these two genes will be important in understanding the physiology and pathophysiology of the human intestine.

Mucin production by human colonic carcinoma cells correlates with their metastatic potential in animal models of colon cancer metastasis.

Patients with mucinous colorectal cancers characteristically present with advanced disease, however, the relationship between mucin production by colon cancer cells and their metastatic potential remains unclear. We therefore sought to define the relationship between mucin production by human colon cancer cells and metastatic ability by employing animal models of colon cancer metastasis. LS LiM 6, a colon carcinoma cell line with high liver metastasizing ability during cecal growth in nude mice produced twofold more metabolically labeled intracellular mucin and secreted four- to fivefold more mucin into the culture medium compared to poorly metastatic parental line LS174T. This was accompanied by a similar elevation in poly(A)+ RNA detected by blot hybridization with a human intestinal mucin cDNA probe, and increases in mucin core carbohydrate antigens determined immunohistochemically. Variants of LS174T selected for high (HM 7) or low (LM 12) mucin synthesizing capacity also yielded metastases after cecal growth and colonized the liver after splenic-portal injection in proportion to their ability to produce mucin. Inhibition of mucin glycosylation by the arylglycoside benzyl-alpha-N-acetyl-galactosamine greatly reduced liver colonization after splenic-portal injection of the tumor cells. These data suggest that mucin production by human colon cancer cells correlates with their metastatic potential and affects their ability to colonize the liver in experimental model systems.

Heterogeneity in the induction and expression of carcinoembryonic antigen-related antigens in human colon cancer cell lines.

Sodium butyrate induces morphological and biochemical changes consistent with a more differentiated phenotype in some colon cancer cell lines. These changes include increased expression of carcinoembryonic antigen (CEA) and other oncodevelopmental markers. We utilized domain-specific probes and polyclonal antibodies against CEA-related antigens to study sodium butyrate-induced expression of the CEA gene family in a villous adenoma-derived cell line, which is nontumorigenic in nude mice (VACO 235), and two colonic carcinoma cell lines known to respond to sodium butyrate exposure by phenotypic differentiation (HT-29 and LS 174T). The induction begins as quickly as 24 h after exposure and occurs primarily at a transcriptional level, although some translational control is also evident. No evidence was found for gene amplification, rearrangement, or methylation to account for the mechanism of this transcriptional control. [35S]Cysteine pulse-labeled cell lysate immunoblots and polyadenylated RNA blot hybridization suggest that increases in mRNA transcript and CEA-related glycoprotein levels are primarily due to increased synthesis rather than decreased degradation. A considerable amount of heterogeneity is seen in the biosynthesis of the CEA-related glycoproteins, with each cell line showing a distinct pattern of CEA-related antigen expression from a limited number of mRNA transcripts.