Expression of Tn, sialosyl-Tn, and T antigens in human colon cancer

Mucin glycoproteins are major secretory products of the colon and contain O-linked oligosaccharides synthesized on a polypeptide backbone. The initial step in the synthesis of O-linked oligosaccharides is the addition of N-acetylgalactosamine to serine or threonine residues forming the Tn antigen. This substance can then receive additional carbohydrate residues such as sialic acid to form sialosyl-Tn antigen, or galactose to form T antigen. In the colon, the T antigen is an oncodevelopmental cancer-associated antigen but little is known about Tn and sialosyl-Tn expression. The present comparative immunohistochemical study was performed to analyze the expression of these antigens in fetal, normal adult, and malignant colorectal tissues with an aim toward elucidating whether Tn and sialosyl-Tn are also oncodevelopmental colon cancer-associated antigens and to gain insight into the earliest steps of mucin glycosylation in colonocytes. We used three reagents to detect Tn antigen (two monoclonal antibodies ETn1.01 and CU-1, and one lectin Vicia villosa), two reagents to detect sialosyl-Tn (monoclonal antibodies TKH2 and B72.3) and one to detect T antigen (monoclonal antibody AH9-16). Except for occasional reactivity with VVA and CU-1, cells of normal colonic mucosa did not express Tn, sialosyl-Tn, or T antigens. However, in the transitional mucosa immediately adjacent to cancer, all three antigens were expressed (ranging from 35 to 67% of cases depending upon the reagent). In colon cancers, the percentage of cases expressing each antigen were as follows: Tn 72-81%, sialosyl-Tn 93-96%, and T 71%. Unlike T antigen, which was preferentially expressed by moderately well- and well-differentiated adenocarcinomas, both Tn and sialosyl-Tn antigens were expressed by most histological subsets of colon cancers, including poorly differentiated adenocarcinomas and mucinous (colloid and signet ring cell type) carcinomas. The majority of cancers expressed both Tn and sialosyl-Tn, usually in association with T antigen. Only one cancer lacked all three antigens. Fetal colonic mucosal cells expressed all three antigens, particularly in goblet cell mucin. These results indicate that like T antigen, Tn and sialosyl-Tn are oncodevelopmental cancer-associated antigens in the colon. Moreover, Tn and sialosyl-Tn antigens appear to be useful markers of poorly differentiated adenocarcinomas and mucinous carcinomas: two histological subsets that often fail to express other cancer-associated antigens and that are often associated with a poor clinical outcome.(ABSTRACT TRUNCATED AT 400 WORDS)     

Mucin oligosaccharide biosynthesis in human colonic cancerous tissues and cell lines.

BACKGROUND. The Tn, sialosyl-Tn, and T antigens are carbohydrate-associated antigens that represent initial steps in mucin O-linked glycosylation. Previous immunohistochemical studies have shown that these three antigens are rarely, if ever, expressed in normal colonic mucosa; however, most colonic cancerous tissues express these structures. Little is known about the factors that control the expression of these antigens in colonic tissues or cell lines. One hypothesis is that cancers have increased levels of the glycosyltransferase activities responsible for synthesizing these antigens. METHODS. The current study analyzed antigen expression by immunohistochemistry and glycosyltransferase enzyme activities for Tn, sialosyl-Tn, and T antigens in colonic tissues and cell lines to (1) compare values between normal and cancerous tissues and (2) correlate these results with tumor stage, histologic findings, and location. RESULTS. All nine colonic cancer cell lines expressed Tn antigen; sialosyl-Tn and T antigens were expressed by the more mucin-producing cell lines. Sialosyl-Tn transferase activity was higher in the more mucinous cell lines; T transferase activity was higher in those with less mucin. In paired specimens of normal and cancerous tissues, levels of each of the three glycosyltransferases were similar. In cancerous tissues, enzyme activity did not correlate with tumor location, stage, or histologic type. There also was no correlation between glycosyltransferase activity and expression of the relevant antigen. CONCLUSIONS. Thus, because normal and malignant colonic tissues have comparable levels of Tn, sialosyl-Tn, and T glycosyltransferases, the absence of these antigens in normal mucosa apparently is related to other factors such as antigen masking.     

Preparation and characterization of monoclonal antibodies directed to the tumor-associated O-linked sialosyl-2----6 alpha-N-acetylgalactosaminyl (sialosyl-Tn) epitope

Two monoclonal antibodies, TKH1 and TKH2, directed toward the sialosyl-Tn structure (NeuAc alpha 2----6GalNAc alpha 1----O-Ser or Thr), which display a remarkable immunohistological tumor specificity, were generated by immunization with ovine submaxillary mucin. The reactivity of these antibodies was monitored by solid phase enzyme-linked immunosorbent assay with different native and glycosidase-treated mucins and glycoproteins. Binding of the antibody to ovine submaxillary mucin glycoprotein was strongly inhibited by the O-linked disaccharide NeuAc alpha 2----6GalNAc alpha 1----O-serine, less strongly by NeuAc alpha 2----6GalNAc beta 1----O-propyl, and weakly by the monosaccharide GalNac. The reactivity was compared with previously established anti-Tn antibodies B72.3, NCC-Lu-35, and NCC-Lu-81. The antibody B72.3 was prepared previously after immunization with metastatic breast adenocarcinoma and its epitope was claimed to be GalNAc alpha 1----O-Ser (or - Thr) by Springer and associates [Springer, G.F., et al. In: T. Dao, et al. (eds.), Tumor Markers and Their Significance in the Management of Breast Cancer, pp. 47-70. New York: A.R. Liss, 1986]. The antibody was found to show very similar reactivity as that of TKH1/TKH2, and its reactivity to ovine submaxillary mucin was inhibited specifically by NeuAc alpha 2----6GalNAc alpha 1----O-serine, indicating that the antibody is clearly directed to sialosyl-Tn antigen. Immunohistological study of the distribution of this antigen in various normal human tissues and carcinomas by TKH1/TKH2 antibodies, as well as B72.3 and monoclonal antibodies NCC-Lu-35/81, which are directed to GalNAc alpha 1----O-Ser or Thr (Tn), was performed. The sialosyl-Tn antigen was not found in normal tissue except for a weak expression in Leydig cells of the testis, goblet cells of the colon, and parietal cells of the stomach. In contrast, the sialosyl-Tn antigen was strongly expressed in a large number of adenocarcinomas. As expected from the specificity studies, B72.3 shows the same reactivity as TKH1 and TKH2. Thus, both sialosyl-Tn (NeuAc alpha 2----6GalNAc alpha 1----O-Ser/Thr) and Tn (GalNAc alpha 1----O-Ser/Thr) are good tumor markers, and combined use of antibodies directed to these structures might be useful in the screening and classification of cancer.     

Effect of benzyl-alpha-GalNAc, an inhibitor of mucin glycosylation, on cancer-associated antigens in human colon cancer cells.

Many cancer-associated antigens are present on mucin glycoproteins. These include peripheral antigens such as sialyl Lea and sialyl Lex and core region carbohydrate antigens such as T, Tn, and Sialyl Tn. We have recently described an inhibitor of mucin glycosylation, benzyl-alpha-GalNAc. The purpose of this study was to determine its effect on expression of mucin carbohydrate antigens. HM7 colon cancer cells were treated for 2 days in culture with 2 mM benzyl-alpha-GalNAc. This treatment did not affect viability or doubling time, but inhibited synthesis of [3H]glucosamine-labeled mucins. There was also secretion of benzyl-oligosaccharides and a decrease in the proportion of long oligosaccharides on 3H-labeled mucins. Mucins were purified from spent media by gel filtration and assayed for binding of monoclonal antibodies and lectins. Mucins from benzyl-alpha-GalNAc-treated cells had increased binding of peanut agglutinin (specific for T antigen, Gal beta 3GalNAc) and Vicia villosa agglutinin B4 (specific for Tn antigen, GalNAc alpha-Thr/Ser), but decreased binding of monoclonal antibodies 19-9, SNH3, and 91.9H (specific for sialyl Lea, sialyl Lex, and sulfomucin, respectively). Treatment of the cells with benzyl-alpha-GalNAc also decreased their binding to E-selectin (ELAM-1), which recognizes sialyl Lea and sialyl Lex. Thus, benzyl-alpha-GalNAc treatment, which decreases the level of peripheral carbohydrate carbohydrate antigens on mucins with accumulation of core region antigens, may be useful in modifying the immunological and biological properties of colon cancer cells.     

Immunohistochemical study of mucin carbohydrates and core proteins in hepatolithiasis and cholangiocarcinoma

The expression of mucin carbohydrates [Tn, sialosyl-Tn(STn), and T antigens] and core proteins [MUCI-apomucin-related antigen (ARA) and MUC2-ARA] was examined immunohisto-chemically in tissues from 40 patients with hepatolithiasis and 26 patients with intrahepatic bile-duct carcinoma. Tn and STn antigens were expressed in most of the carcinomas, and were also often expressed in the atypical bile-duct epithelium of the patients with hepatolithiasis or carcinoma, whereas they were rarely or never expressed in the normal bile duct, suggesting that they are effective tumor markers. T antigen was less useful as a marker for intrahepatic bile-duct carcinoma or the atypical epithelium, because it was expressed in normal bile-duct of some cases. Regarding the expression of ARAs in the carcinomas, non-invasive bile-duct cyst adenocarcinomas with favorable prognosis either expressed no MUCI-ARA with [DF3(-), MUSE11(-) and 139H2(-)] staining pattern or expressed MUCI-ARA with [DF3(-), MUSE11(+) and 139H2(+)] staining pattern. However these tumors often expressed MUC2-ARA with [anti-MRP(+) and CCP58(+)] staining pattern. In contrast, most invasive non-papillary cholangiocarcinomas with poor prognosis expressed MUCI-ARA with [DF3( + ), MUSE 11(+) and 139H2(+)] staining pattern, but expressed no MUC2-ARA with [anti-MRP(-) and CCP58(-)] staining pattern. These results suggests that different apomucins are produced by bile-duct cystadenocarcinomas and cholangiocarcinomas with differing prognosis. Furthermore, expression of Tn and STn antigens is a useful indicator of malignancy in the intrahepatic duct. © 1993 Wiley-Liss, Inc.     

Expression of Mucin Carbohydrates and Core Proteins in Carcinomas of the Ampulla of Vater: Their Relationship to Prognosis

We examined the expression of carbohydrate antigens which are associated with the earliest steps in mucin glycosylation (Tn and sialosyl-Tn) and the expression of the mucin core protein antigens associated with MUC1 gene product (DF3 antigen) as well as MUC2 gene product (intestinal-MRP antigen) in tissues from 38 patients with carcinoma of the ampulla of Vater, in order to determine whether these mucin antigens are available as tumor markers or not, and to evaluate whether their expression is correlated with the biological behavior of the carcinomas or not. DF3 antigen showed a relatively high expression rate (61%) in the carcinoma tissues, but was rarely expressed in the non-neoplastic epithelium around the carcinomas in the region of the ampulla of Vater, Tn and sialosyl-Tn antigens showed high expression rates in the carcinoma tissues (86% and 84% each), whereas they showed rare or no expression in the non-neoplastic epithelium around the carcinomas, except for highly restricted expression in the duodenal villous epithelium. The patients with positive DF3 expression in the carcinoma showed significantly poorer survival than those with negative DF3 expression (P<0.05), whereas the patients with positive intestinal-MRP expression in the carcinoma showed significantly more favorable survival than those with negative intestinal-MRP expression (P<0.05). The expression rate of DF3 antigen was significantly higher in the cases with deep invasion into the pancreas (89%) than in those with no or minimal invasion (52%) (P<0.05). In contrast, the expression rate of intestinal-MRP antigen was significantly higher in the cases with no or minimal invasion into the pancreas (38%) than in those with deep invasion (0%) (P<0.05). In conclusion, the expression of DF3, Tn and sialosyl-Tn antigens is an effective histopathological indicator for carcinomas in the area of the ampulla of Vater, and the expression of DF3 and intestinal-MRP antigens is a useful indicator of the prognosis of the patients.     

Characterization of mucin antigens recognized by monoclonal antibodies raised against human colon cancer cells

Two monoclonal antibodies, MLS 102, which recognizes cancer-associated mucin antigens, and MLS 103, which recognizes normal mucin, were used to isolate, by immunoaffinity chromatography, the corresponding antigens from cell lysates and spent medium of a human colorectal carcinoma cell line, LS 180. The MLS 102 antigen contained serine, threonine, and proline as major amino acids. The carbohydrate chains of the MLS 102 antigen were composed of O-linked NeuAc alpha 2----6GalNAc (56%), N-acetylgalactosamine (25%), and longer oligosaccharide chains. The MLS 103 antigen differed from the MLS 102 antigen in both amino acid and carbohydrate composition. Most O-linked oligosaccharides of the MLS 103 antigen were longer than the disaccharide found in the MLS 102 antigen. Immunostaining of LS 180 cells using MLS 102 and MLS 103 revealed that the cells are heterogeneous with respect to the expression of the antigens.     

Mucins and mucin binding proteins in colorectal cancer

Mucins are high-molecular weight epithelial glycoproteins with a high content of clustered oligosaccharides O-glycosidically linked to tandem repeat peptides rich in threonine, serine, and proline. There are two structurally and functionally distinct classes of mucins: secreted gel-forming mucins (MUC2, MUC5AC, MUC5B, and MUC6) and transmembrane mucins (MUC1, MUC3A, MUC3B, MUC4, MUC12, MUC17), although the products of some MUC genes do not fit well into either class (MUC7, MUC8, MUC9, MUC13, MUC15, MUC16).MUC1 mucin, as detected immunologically, is increased in expression in colon cancers, which correlates with a worse prognosis. Expression of MUC2 secreted gel-forming mucin is generally decreased in colorectal adenocarcinoma, but preserved in mucinous carcinomas, a distinct subtype of colon cancer associated with microsatellite instability. Another secreted gel-forming mucin, MUC5AC, a product of normal gastric mucosa, is absent from normal colon, but frequently present in colorectal adenomas and colon cancers.The O-glycosidically linked oligosaccharides of mucins can be described in terms of core type, backbone type, and peripheral structures. Colon cancer mucins have differences in both core carbohydrates and in peripheral carbohydrate structures that are being investigated as diagnostic and prognostic markers, and also as targets for cancer vaccines. Colon cancer mucins typically have increases in three core structures: Tn antigen (GalNAcThr/Ser), TF antigen (Gal3GalNAc) and sialyl Tn (NeuAc6GalNAc). The type 3 core (GlcNAc3GalNAc) predominant in normal colonic mucin is lacking in colon cancer mucins. There are cancer-associated alterations in the peripheral carbohydrates of colonic mucins including a decrease in O-acetyl-sialic acid and a decrease in sulfation. There are, however, cancer-associated increases in sialyl LeX and related structures on mucins and other glycoproteins that can serve as ligands for selectins, increasing the metastatic capacity of colon cancer cells. The endogenous galactoside-binding protein galectin-3, which is expressed at higher levels in colon cancers than normal colon, binds to colon cancer mucin as well as other glycoproteins. Interference of the binding of selectins and galectin-3 to mucin may show therapeutic or preventative promise for colon cancer.     

Structural variations of blood group A antigens in human normal colon and carcinomas

The blood group A determinant is carried by four basic carrier carbohydrate chains. This paper reports the expression of blood group A variants, as determined by immunohistology with highly specific monoclonal anti-A antibodies, in 18 adenocarcinomas of the distal colon, 4 specimens of normal proximal mucosa from group A persons, and 5 specimens of fetal colonic mucosa. Monoclonal antibodies directed to type 1 chain A, type 1 chain ALeb, type 2 chain A, type 2 chain ALey, and type 3 chain A (repetitive A) were used. In normal mucosa, type 1 chain A and ALeb were expressed in proximal regions. Type 1 chain A was expressed in columnar cells, whereas type 1 chain ALeb was found in goblet cells. Type 2 and type 3 chain A structures were not found in normal adult mucosa. All types of A antigens were detected in adenocarcinomas from the distal colon as well as in normal fetal mucosa. In fetal mucosa, type 1 chain A and ALeb antigens and type 3 chain A antigens were expressed in columnar cells, whereas type 2 chain A and Ley and type 1 chain ALeb antigens were found in goblet cells. The results indicate that blood group A antigens with type 1, 2, and 3 carriers are present in fetal mucosa and adenocarcinomas of distal colon, while epithelial mucosa of normal adult colon is characterized by the exclusive expression of type 1 chain A antigens.     

Type III intestinal metaplasia and carcinoma express an identical carbohydrate-epitope revealed by a novel monoclonal antibody (2D11)

A monoclonal antibody (2D11, IgG2b) obtained by immunizing mice with a mucin fraction of the human gastric mucosa reacted specifically to intestinal metaplasia of human gastric mucosa and fetal intestinal mucosa but not to normal adult gastric, small intestinal or colonic mucosa in immunohistochemical staining. The results of Western blotting indicated that 2D11 recognized the high molecular weight glycoprotein(s) (mucin) of the stomach. Treatment of the antigens with sodium periodate abolished their reactivity to 2D11, and digestion of the antigens with beta-galactosidase reduced their reactivity to 2D11. Digestion of the antigens with pronase had no effect, however, suggesting that 2D11 recognizes the oligosugar moiety but not the peptide moiety of the antigens. Further immunohistochemical investigation showed that the reactivity of 2D11 was restricted to the Type IotaIotaIota intestinal metaplasia that is identified by a characteristic staining pattern with the high iron diamine-Alcian blue stain. 2D11 also reacted in high frequency to adenocarcinomas of the stomach (66.7%), pancreas (66.7%) and gallbladder (50.0%), but in low frequency to those in lung (8.3%) and colon (11.1%). It is of interest that 2D11 reacted to very restricted regions of the gastric adenocarcinomas. All monoclonal antibodies to mucin polypeptides (MUC1, 2, 3, 5AC and 6) examined stained intestinal metaplasia and carcinomas in a different pattern from 2D11 in immunohistochemistry. These facts indicate that Type IotaIotaIota intestinal metaplasia and carcinomas express carbohydrate chains identical to those expressed in the fetal intestinal mucosa, suggesting that both of them are closely related to fetal intestinal mucosa.     

Distribution of blood group antigens A, B, H, Lewisa, and Lewisb in human normal, fetal, and malignant colonic tissue

In humans, most blood group substances (BGS) are expressed throughout the fetal colon but are absent from the distal portion of adult colon. Cancers of the distal colon frequently reexpress BGS thereby suggesting that these antigens behave as oncofetal antigens at this organ site. We used a sensitive immunoperoxidase method with monoclonal antibodies directed against blood groups A, B, O (H), Lewisa and Lewisb to systematically evaluate BGS expression in fetal colon, normal adult colon from immediate autopsies of kidney donors, mucosa adjacent to cancer (transitional mucosa) and colorectal cancer tissues. In normal colon, BG-A, B, H, and Lewisb were expressed in proximal but not distal colon, whereas Lewisa was distributed uniformly throughout the colon. In colon cancer, and fetal colon, the proximal-distal gradient of BG-A, B, H, and Lewisb expression was abolished because of enhanced distal expression of these antigens. In cancer tissues, three patterns of altered BGS expression emerged: (a) incompatible expression of BG-A or BG-B (over 50% of patients); (b) deletion of BGS; and (c) precursor BG-H accumulation (80% of 25 tumors). BGS staining of transitional mucosa closely resembled that of the adjacent tumor except that no examples of BGS deletion were encountered in transitional mucosa. The goblet cell secretory vacuole accounted for most of the BGS expression in normal colon, but cancer cells demonstrated differentiation-dependent antigenic expression such that well-differentiated tumors expressed BGS on cell apical membranes and glandular contents, but poorly differentiated cancers exhibited diffuse cytoplasmic staining. These findings confirm the oncofetal nature of BGS in distal colon cancer, and provide immunohistochemical evidence for a diverse repertoire of altered antigen expression in colon cancer. Further investigation is needed to elucidate the possible genetic and biochemical mechanisms involved.     

Simple mucin-type cancer associated antigens are pre-cancerous biomarkers during 1,2-dimethylhydrazine-induced rat colon carcinogenesis

The simple mucin-type truncated O-glycans Tn (GalNAc-O-Ser/Thr) and sialyl-Tn (STn) antigens are useful diagnostic markers for human colon cancer. We herein report the characterization of 1,2-dimethylhidrazine (DMH)-induced colon cancer in rats as a new model for the study of aberrant O-glycosylation products during carcinogenesis. Evaluated by immunohistochemistry, both anti-Tn and anti-STn MAbs revealed no staining of normal colonic mucosa. On the contrary, Tn and STn were expressed by the first lesions detected following carcinogen administration (aberrant crypt foci), observing the most intense and uniform pattern in crypts with severe dysplasia. Adenocarcinomas with non-secreting components showed moderately and strong stain, but mucin-secreting carcinomas were mildly stained. The biochemical characterization of soluble Tn glycoproteins from ascitic fluids of rats with colon cancer revealed that Tn is bearing high molecular weight glycoproteins (containing sialic acid and/or GlcNAc and GalNAc), which migrated as two major components (one of approximately 220 kDa and other>500 kDa). Evaluated by CsCl gradient ultracentrifugation and perchloric acid precipitation, it was shown that Tn is carried for mucins. These results indicate that Tn and STn are pre-cancerous biomarkers in colon of rats treated with DMH. This model of rat colon cancer could be useful to study in vivo the temporal sequence of molecular events responsible for the deregulation of O-glycosylation pathways during colon carcinogenesis, and could contribute to improve the evaluation of diagnostic and therapeutic strategies based on the utilization of Tn and STn antigens.     

Human urinary bladder carcinoma glycoconjugates expressing T-(Gal beta(1-3)GalNAc alpha 1-O-R) and T-like antigens: a comparative study using peanut agglutinin and poly- and monoclonal antibodies.

T- and T-like antigens on glycoproteins and glycolipids were examined in extracts of human urinary bladder tumors and normal tissue by Western blot analysis and reagent binding to thin layer chromatograms. Three different anti-T-reagents were used: peanut (Arachis hypogaea) lectin (PNA) and mono- and polyclonal antibodies specific for T-antigen (Gal beta(1-3)GalNAc alpha 1-O-R). Immunodetection with the T-specific reagents in nitrocellulose replicas of bladder tumor glycoproteins, separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, demonstrated tumor-specific T-antigen-bearing glycoproteins compared to normal urothelial glycoproteins. In addition, a remarkable difference in binding was found between the immunological reagents and PNA lectin. PNA showed major reactivity to a 28-kD glycoprotein extracted from tumors. Monoclonal anti-T-antibody (clone HH8) showed major reactivity with an M(r) 34,000 glycoprotein, and polyclonal anti-T-antibody showed major reactivity with an M(r) 36,000 glycoprotein. PNA agarose column affinity-purified tumor glycoproteins did not bind the antibodies. Glycoproteins, M(r) 28,000 and 34,000, were shown to be O-linked by stepwise deglycosylation. In solid phase monosaccharide inhibition tests, galactose followed by N-acetyl-galactosamine were the most potent monosaccharides inhibiting binding to immobilized bladder tumor glycoproteins. None of the anti-T-reagents reacted with glycolipids extracted from tumor tissue. It is concluded that PNA lectin, in addition to the T-disaccharide, reacts with other protein-anchored carbohydrate structures in carcinomas.     

Mucin gene expression in colonic tissues and cell lines.

Complementary DNA clones encoding four different mucin core peptides have been isolated. However, the expression of these mucin genes in the colon has not been systematically studied. The present investigation used Northern blot analysis to study the expression of MUC1, MUC2, MUC3, and MUC4 mRNA in paired normal and cancerous colonic tissues, and nine colon cancer cell lines. Results were correlated with the clinicopathological features of the tumors and with the immunohistochemical expression of several carbohydrate tumor-associated antigens that may reside on mucins. MUC1 mRNA was expressed in all colonic tissues, and levels in paired normal and cancer tissues were similar in most cases. MUC2 and MUC3 mRNAs were expressed in both normal and cancer tissues, but levels were often decreased in the cancers. MUC4 mRNA was present in normal mucosa with comparable or sometimes greater expression in cancers. There was no apparent correlation between the expression of any particular mucin gene or pattern of mucin genes and the site, stage, or histological type of tumor. In addition, the expression of mucin-associated carbohydrate antigens did not correlate with any individual mucin gene or group of mucin genes. In colon cancer cell lines all four MUC genes were expressed rather weakly or not at all. These results indicate that the human colon expresses a broad repertoire of mucin genes which are differentially regulated in malignancy. Whether this differential regulation of mucin genes affect the behavior of the tumor and results in the altered glycosylation commonly seen in these requires further investigation.     

Role of the human ST6GalNAc-I and ST6GalNAc-II in the synthesis of the cancer-associated sialyl-Tn antigen

The Sialyl-Tn antigen (Neu5Acalpha2-6GalNAc-O-Ser/Thr) is highly expressed in several human carcinomas and is associated with carcinoma aggressiveness and poor prognosis. We characterized two human sialyltransferases, CMP-Neu5Ac:GalNAc-R alpha2,6-sialyltransferase (ST6GalNAc)-I and ST6GalNAc-II, that are candidate enzymes for Sialyl-Tn synthases. We expressed soluble recombinant hST6GalNAc-I and hST6GalNAc-II and characterized the substrate specificity of both enzymes toward a panel of glycopeptides, glycoproteins, and other synthetic glycoconjugates. The recombinant ST6GalNAc-I and ST6GalNAc-II showed similar substrate specificity toward glycoproteins and GalNAcalpha-O-Ser/Thr glycopeptides, such as glycopeptides derived from the MUC2 mucin and the HIVgp120. We also observed that the amino acid sequence of the acceptor glycopeptide contributes to the in vitro substrate specificity of both enzymes. We additionally established a gastric cell line, MKN45, stably transfected with the full length of either ST6GalNAc-I or ST6GalNAc-II and evaluated the carbohydrate antigens expression profile induced by each enzyme. MKN45 transfected with ST6GalNAc-I showed high expression of Sialyl-Tn, whereas MKN45 transfected with ST6GalNAc-II showed the biosynthesis of the Sialyl-6T structure [Galbeta1-3 (Neu5Acalpha2-6)GalNAc-O-Ser/Thr]. In conclusion, although both enzymes show similar in vitro activities when Tn antigen alone is available, whenever both Tn and T antigens are present, ST6GalNAc-I acts preferentially on Tn antigen, whereas the ST6GalNAc-II acts preferentially on T antigen. Our results show that ST6GalNAc-I is the major Sialyl-Tn synthase and strongly support the hypothesis that the expression of the Sialyl-Tn antigen in cancer cells is due to ST6GalNAc-I activity.     

Lewis x is highly expressed in normal tissues: A comparative immunohistochemical study and literature revision

An immunohistochemical analysis was employed to determine the expression of carbohydrate antigens associated to mucins in normal epithelia. Tissue samples were obtained as biopsies from normal breast (18), colon (35) and oral cavity mucosa (8). The following carbohydrate epitopes were studied: sialyl-Lewis x, Lewis x, Lewis y, Tn hapten, sialyl-Tn and Thomsen-Friedenreich antigen. Mucins were also studied employing antibodies against MUC1, MUC2, MUC4, MUC5AC, MUC6 and also normal colonic glycolipid. Statistical analysis was performed and Kendall correlations were obtained. Lewis x showed an apical pattern mainly at plasma membrane, although cytoplasmic staining was also found in most samples. TF, Tn and sTn haptens were detected in few specimens, while sLewis x was found in oral mucosa and breast tissue. Also, normal breast expressed MUC1 at a high percentage, whereas MUC4 was observed in a small number of samples. Colon specimens mainly expressed MUC2 and MUC1, while most oral mucosa samples expressed MUC4 and MUC1. A positive correlation between MUC1VNTR and TF epitope (τ=0.396) was found in breast samples, while in colon specimens MUC2 and colonic glycolipid versus Lewis x were statistically significantly correlated (τ=0.28 and τ=0.29, respectively). As a conclusion, a defined carbohydrate epitope expression is not exclusive of normal tissue or a determined localization, and it is possible to assume that different glycoproteins and glycolipids may be carriers of carbohydrate antigens depending on the tissue localization considered.     

Characterization of a prostate carcinoma mucin-like antigen (PMA)

A recently identified, high m.w. human tumor antigen, reactive with monoclonal antibody (MAb) PD41 and designated prostate mucin antigen (PMA), was found to have expression highly restricted to prostate carcinomas. Both biochemical and immunological characteristics of this antigen and its relationship to other tumor-associated mucins and various species of submaxillary mucins were evaluated. Immunohistochemical examination of submaxillary tissues revealed differential expression of this antigen and other human tumor-associated mucins, with MAb PD41 expression found only in bovine submaxillary gland serous cells. Neuraminidase treatment enhanced antibody binding by 50%, suggesting partial masking of the PD41 epitope by sialic acid. Antigenicity was reduced by treatment with alkaline-borohydride, sodium metaperiodate, β-galactosidase, O-glycanase, and various proteolytic enzymes. MAb PD41 antibody binding also could be significantly reduced by selected lectins and sugars suggesting that the immunodominant carbohydrate involved in the epitope was an O-linked oligosaccharide containing N-acetyl galactosamine as a major component. This antigen was further distinguished from T, Tn, or Sialyl-Tn antigens and blood group carbohydrate antigens by radioimmunometric analyses. Cross-blocking and double determinant RIA experiments also showed a distinction between the PD41 epitope and several well-characterized tumor-associated mucin antigens such as MUCI, CEA, M344, OCI25, and AR3 as well as bovine submaxillary core protein. Our results indicate that the PD41-reactive epitope is a non-acidic O-linked carbohydrate or glycopeptide epitope with restricted expression in prostate carcinomas and bovine submaxillary glands. This expression is distinct from other mucin-like tumor-associated antigens identified in human prostate carcinomas. © 1995 Wiley-Liss, Inc.     

Monoclonal antibody directed against colon cancer mucin has high specificity for malignancy

Exposure of core carbohydrate structures such as NeuAc alpha2–6GalNAc-Ser/Thr (sialosyl-Tn) in mucus glycoproteins is often associated with malignant transformation in a number of different tissues. Reagents that specifically identify such structures would be useful in the diagnosis of cancer. Monoclonal antibody JT10e has been produced against mucins from xeno-grafts of LS174T colon cancer cells but also reacts with mucins of pancreatic cancer xenografts. The following data suggest that JTlOe reacts with sialosyl-Tn: (I) reactivity with bovine and ovine submaxillary mucins; (2) reactivity sensitive to neuramini-dase or mild acid; (3) inhibition of reactivity by NeuAc and NeuAc alpha2–6 lactose; and (4) lack of reactivity with other glycoproteins with related carbohydrate structures but no sialosyl-Tn. JTlOe is distinguishable from 2 other antibodies which react with sialosyl-Tn, B72.3 and TKH2 because JT10e: (a) did not react with normal gastric tissue while B72.3 and TKH2 did; (b) was only partially inhibited by TKH2 and not at all by B72.3; (c) did not react with Tn antigen while B72.3 did; and (d) bound more strongly to pancreatic cancer mucins than did either B72.3 or TKH2. JT10e reacted with a high percentage of malignant colonic, pancreatic, gastric and mammary tissues but not with the corresponding normal tissues. A high percentage of patients with colonic, pancreatic, gastric, mammary and lung cancers had elevated blood levels of JT10e antigen. A number of colonic cancer patients had elevated JT10e antigen levels without corresponding elevations in CA19–9 levels. These results suggest that JT10e antibody could be used in conjunction with other mucin markers to improve the identification of malignancy in colon, and to study the structure of oligosaccha-rides in cancer mucins.     

B3GNT3 expression suppresses cell migration and invasion and predicts favorable outcomes in neuroblastoma

Aberrant expression of the simple mucin‐type carbohydrate antigens such as T, Tn, sialyl‐T and sialyl‐Tn is associated with poor prognosis in several cancers. β1,3‐N‐acetylglucosaminyltransferase‐3 (B3GNT3), a member of the β3GlcNAcT family, is responsible for forming extended core 1 (T antigen) oligosaccharides. The role of B3GNT3, which is expressed in various tissues including human fetal brain, in regulating neuroblastoma (NB) formation and cell behaviors remains unclear. Here, we showed that increased B3GNT3 expression evaluated using immunohistochemistry in NB tumor tissues correlated well with the histological grade of differentiation as well as a favorable Shimada's subset of pathology. Univariate and multivariate analyses revealed that positive B3GNT3 expression in tumor tissues predicted a favorable prognosis in NB patients independent of other prognostic markers. B3GNT3 overexpression suppresses T antigen formation and malignant phenotypes including migration and invasion of SK‐N‐SH cells, whereas B3GNT3 knockdown enhances these phenotypes of SK‐N‐SH cells. Moreover, B3GNT3 expression decreased phosphorylation of focal adhesion kinase (FAK), Src, paxillin, Akt and ERK1/2. We conclude that B3GNT3 predicts a favorable cancer behavior of NB and suppresses malignant phenotypes by modulating mucin‐type O‐glycosylation and signaling in NB cells.     

Aberrant expression of MUC5AC and MUC6 gastric mucin genes in colorectal polyps

Altered mucin glycosylation and the de novo appearance of gastric mucin antigens have been described in colonic adenomas. The purpose of our study was to determine if expression of the gastric mucin genes MUC5AC and MUC6 occurs in colorectal adenomas and whether this correlates with histopathologic criteria of malignant potential. Immunohistochemical staining using antibodies against MUC5AC and MUC6 tandem repeat synthetic peptides was performed on specimens of normal colon mucosa (n = 26), hyperplastic polyps (n = 9) and adenomatous polyps (n = 111). Mucin mRNA levels were determined using RNase protection assays using riboprobes corresponding to unique non‐repetitive sequences. MUC5AC and MUC6 staining were rarely detected and of low intensity in normal colon and hyperplastic polyps. The number of immunoreactive polyps and intensity of MUC5AC and MUC6 staining were greatest in larger adenomas of moderate villous histology and dysplasia. MUC5AC and MUC6 staining tended to decrease in highly villous polyps with severe dysplasia. Increased MUC5AC mRNA levels were found in 26/45 of adenomas tested compared with 0/9 normal colon specimens. MUC6 mRNA levels were found in 20/45 of adenomas compared with 1/9 normal colon specimens. MUC5AC and MUC6 mRNA were present more frequently and at higher levels in polyps with intermediate stages of size, villous histology and dysplasia. We conclude that aberrant expression of MUC5AC and MUC6 mucin genes is likely responsible for an expanded repertoire of mucin antigen expression in colorectal neoplasia. Int. J. Cancer 80:210–218, 1999. Published 1999 Wiley‐Liss, Inc.