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Background & Aims: Anecdotally, patients in safety net health care systems have difficulty completing screening and diagnostic colonoscopies, but this is poorly characterized. It is important to understand this phenomenon to improve low rates of colorectal cancer screening in vulnerable populations and to ensure that patients with signs and symptoms complete medically indicated colonoscopic evaluations. Methods: We performed a 6-month retrospective review of outpatient endoscopy laboratory scheduling and procedure logs and electronic medical records at Denver Health Medical Center (DHMC), a large safety net health care system, to describe rates and sociodemographic predictors of colonoscopy nonattendance and inadequate (fair/poor) bowel preparation. Predictor variables included patient age, gender, race/ethnicity, procedure indication, and insurance type. Results: The nonattendance rate was 41.7% for all scheduled outpatient colonoscopies without difference between screening and diagnostic procedures. Consistent with non–safety net systems, the rate of inadequate bowel preparation was 30.2%; however, the rate of poor bowel preparation that absolutely precluded an exam was 9.9%. Correctional care patients had markedly higher rates of nonattendance and inadequate bowel preparation compared with other groups. Conclusions: A very large proportion of patients scheduled for colonoscopy in a large safety net health care system do not attend their procedures, and among those who do, there is a high rate of inadequate bowel preparation leading to incomplete and aborted evaluations. Interventions are needed to promote the more efficient use of a limited and expensive resource and to achieve higher rates of screening and medically indicated diagnostic colonoscopies in vulnerable patient populations.

Mucin-type glycoproteins are the major structural proteins in gastric mucus. Stomach mucin proteins include MUC5AC, synthesized by surface foveolar or pit cells, and MUC6, synthesized by neck and gland cells. The aim of this study was to determine the spatial distribution of these mucin proteins within the extracellular mucous coat. Double-labeling immunoflourescence/confocal microscopy was used in histologically normal surgical resection specimens. Intralumenal mucin within antral glands consisted entirely of MUC6 protein. Intralumenal mucin within the gland isthmus region consisted of an irregular mixture of MUC5AC and MUC6. The mucous layer on the gastric surface consisted primarily of MUC5AC extending in layered sheets with MUC6 protein layered in between. The laminated appearance of the surface mucus was present in both H. pylori-infected and noninfected specimens. These data indicate that MUC5AC and MUC6 proteins remain segregated within the mucous gel in a laminated linear arrangement. The physical stratification of mucin proteins may confer increased strength to the mucous layer or represent independent and redundant protection.

The complete genomic organization of the two mucin genes MUC2 and MUC6 was obtained by comparison of new and published mRNA sequences with newly available human genomic sequence. The two genes are located 38.5 kb apart in a head-to-head orientation within a gene complex on chromosome 11p15.5. The N-terminal organization of MUC6 is highly similar to that of MUC2, containing the D1, D2, D', and D3 Von Willebrand factor domains followed by the large tandem repeat domains located in exons 31 and 30, respectively. MUC6 has a much smaller C-terminal domain (101 amino acids) encoded by 2 exons containing only the CK domain, compared with MUC2, which has a C-terminal domain of 859 amino acids containing the D4, C, D, and CK domains, encoded by 19 exons. The gene structures agreed partially but not completely with predictions from gene prediction programs.

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.

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.

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 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.

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 in 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.

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.

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.

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.

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.

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 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.

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.

Concomitant differentiation and partial inhibition of proteasome trigger cell death in a neuroblastoma cell line (NBP2). Neither induction of differentiation nor partial inhibition of proteasome alone affects the viability of NBP2 cells. We wanted to identify genes whose expression alters under concomitant conditions and may account for cell death.We used gel electrophoresis to analyze total genomic DNA for the detection of DNA fragmentation. Affymetrix Murine Genome U74A version 2 microarray was used to screen for approximately 6,000 functionally characterized genes and approximately 6,000 expressed sequence tags (ESTs). Real time PCR (RT-PCR) was performed to provide an accurate assessment of changes in gene expression.Concomitant differentiation and partial inhibition of proteasome trigger apoptosis, characterized by genomic DNA fragmentation in NBP2 cells. We found that the expression of 41 genes changed 2.5-fold or more primarily under concomitant conditions midway through apoptosis. Based on real time PCR, the expression of galectin-3, glycosylated 96, a leucine zipper protein (LRG-21), and endothelial cell activated protein C receptor (EPCR) increased between 50-500-fold, whereas the expression of Polo serine/threonine kinase, N-myc, and Histone H2A.1 decreased ranging from 8 to 37 fold. Altered expression of galectin-3, EPCR, and LRG-21 was detected as early as 2-8 h post simultaneous conditions.We identified new genes that might be involved in apoptotic events in neuroblastoma cells.

Background & Aims: Early onset colorectal cancer (CRC) is an important feature of hereditary nonpolyposis colorectal cancer (HNPCC). We sought to compare rates of genetically defined HNPCC among individuals with early onset CRC drawn from a high-risk clinic and a population-based cancer registry. Methods: Probands with CRC diagnosed before 36 years of age were enrolled from a high-risk CRC clinic at the University of California, San Francisco (UCSF), and a population-based Kaiser Permanente (KP) Health Plan cancer registry. Probands provided cancer family histories and tumors for microsatellite instability (MSI) testing and MSH2/MLH1 protein immunostaining. Germline MSH2 and MLH1 mutational analysis was performed. Results: Forty-three probands were enrolled from UCSF and 23 from KP. The UCSF and KP probands had similar median age of onset of CRC (30 vs. 31 years) and the percentage with any personal or family history of another HNPCC-related cancer (70% vs. 74%). However, 28 of 40 (70%) of the UCSF tumors were MSI-H compared with 6 of 18 (33%) of KP tumors (P = 0.01), and 13 germline MSH2 or MLH1 mutations were found in the UCSF group compared with 0 in the KP group (P = 0.0001). In a multivariate analysis, institution (P = 0.002) and the total number of colorectal cancers in the family (P = 0.0001) were independent predictors of MSH2 or MLH1 mutation. Conclusions: Family history of cancer is an important feature of HNPCC, even among individuals with early onset CRC. Caution must be undertaken when extrapolating data regarding HNPCC from high-risk clinic populations to the general population. GASTROENTEROLOGY 2002;122:940-947

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.

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.

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.

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.

Advances in the understanding of biochemical and molecular processes associated with cellular growth and differentiation, as well as colonic carcinogenesis hold promise for the development of new diagnostic and therapeutic modalities for this disease. Altered glycosylation of cell surface and secreted glycoconjugates appear to be useful markers in differentiating normal from malignant colonic tissue. New information regarding deletion and inappropriate expression of several blood group-related carbohydrate antigens as well as the synthesis of unique cancer-related carbohydrate structures has been derived from the use of monoclonal antibody technology, and may lead to more sensitive and specific screening tests and targeted therapies. Several glycoprotein markers for colon cancer have been studied whose diagnostic accuracy may surpass the limited sensitivity and specificity of traditional markers such as CEA. Colorectal cancers contain numerous quantitative and qualitative differences in metabolic and synthetic enzyme activities compared with normal colonic mucosa, which may be of potential importance in designing chemotherapeutic regimens or for following disease activity. Other cancer-associated markers, such as increases in orthinine decarboxylase activity and crypt cell labeling reflect abnormal proliferative activity and may be correlated with premalignant states. Studies of protooncogene expression and certain chromosomal deletions will provide insight into mechanisms of carcinogenesis and may also serve to define high-risk individuals. It is likely that as the biochemical and molecular mechanisms underlying malignancy are further delineated, cancer-associated markers will be defined that will improve diagnostic and more importantly, therapeutic efficacy.

A human small intestine lambda gt11 cDNA library was screened using antisera prepared against the deglycosylated protein backbone of human colon cancer xenograft mucin. Three cDNAs were isolated from this screening, designated SMUC 40-42. These cDNAs were all found to contain tandem repeats of 69 nucleotides which encoded a threonine- and proline-rich protein consensus sequence of PTTTPITTTTTVTPTPTPTGTQT. RNA blots probed with one of these cDNAs, SMUC 41, exhibited large, polydisperse hybridization bands at approximately 7,600 bases. Band intensities were strongest when human small intestine, colon, and colon cancer poly(A)+ RNA was used. In vitro translation of poly(A)+ RNA from human small intestine, colon, and colon cancer cells produced a 162,000-dalton peptide that was immunoprecipitated with antibodies to deglycosylated mucin. SMUC 41 was also used to probe DNA blots, which indicated the presence of restriction fragment length polymorphisms in the intestinal mucin gene. These findings may be important in assessing the abnormal mucins found associated with several human diseases.