Glycoconjugates constitute a major class of biomolecules which include glycoproteins, glycosphingolipids and proteoglycans. Glycans are involved in several physiological and pathological conditions, such as host-pathogen interactions, cell differentiation, migration, tumour invasion and metastisation, cell trafficking and signalling. Cancer is associated with glycosylation alterations in glycoproteins and glycolipids. This review describes various aspects of protein glycosylation with the focus on alterations associated with human cancer. The application of these glycosylation modifications as biomarkers for cancer detection in tumour tissues and serological assays is summarised.

Intestinal metaplasia (IM) is part of a stepwise sequence of alterations of the gastric mucosa, leading ultimately to gastric cancer, and is strongly associated with chronic Helicobacter pylori infection. The molecular mechanisms underlying the onset of IM remain elusive. The aim of this study was to assess the putative involvement of two intestine-specific transcription factors, CDX1 and CDX2, in the pathogenesis of gastric IM and gastric carcinoma. Eighteen foci of IM and 46 cases of gastric carcinoma were evaluated by immunohistochemistry for CDX1 and CDX2 expression. CDX1 was expressed in all foci of IM and in 41% of gastric carcinomas; CDX2 was expressed in 17/18 foci of IM and in 54% of gastric carcinomas. In gastric carcinomas, a strong association was observed between the expression of CDX1 and CDX2, as well as between the intestinal mucin MUC2 and CDX1 and CDX2. No association was observed between the expression of CDX1 and CDX2 and the histological type of gastric carcinoma. In conclusion, these results show that aberrant expression of CDX1 and CDX2 is consistently observed in IM and in a subset of gastric carcinomas. The association of CDX1 and CDX2 with expression of the intestinal mucin MUC2, both in IM and in gastric carcinoma, indirectly implies that CDX1 and CDX2 may be involved in intestinal differentiation along the gastric carcinogenesis pathway.

SUMMARYTo investigate the expression of MUC6 mucin in gastric carcinomas, we generated a novel monoclonal antibody (MAb CLH5) using an MUC6 synthetic peptide. MAb CLH5 reacted exclusively with the MUC6 peptide and with native and deglycosylated mucin extracts from gastric tissues. MAb CLH5 immunoreactivity was observed in normal gastric mucosa restricted to pyloric glands of the antrum and mucopeptic cells of the neck zone of the body region. In a series of 104 gastric carcinomas, 31 (29.8%) were immunoreactive for MUC6. The expression of MUC6 was not associated with histomorphological type or with clinicopathological features of the carcinomas. Analysis of the co-expression of MUC6 with other secreted mucins (MUC5AC and MUC2) in 20 gastric carcinomas revealed that different mucin core proteins are co-expressed in 55% of the cases. MUC6 was co-expressed and co-localized with MUC5AC in 45% and with MUC2 in 5% of the cases. Expression of MUC2 alone was observed in 25% of the cases. All carcinomas expressing MUC2 mucin in more than 50% of the cells were of the mucinous type according to the WHO classification. The co-expression of mucins was independent of the histomorphological type and stage of the tumors. In conclusion, we observed, using a novel well-characterized MAb, that MUC6 is a good marker of mucopeptic cell differentiation and is expressed in 30% of gastric carcinomas, independent of the clinicopathological features of the cases. Furthermore, we found that co-expression and co-localization of mucins in gastric carcinomas is independent of histomorphology and staging. Finally, we observed that intestinal mucin MUC2 is expressed as the most prominent mucin of the mucins tested in mucinous-type gastric carcinomas.

The available information favours a greater impact of environmental exposures on intestinal type gastric cancer, and risk factors for the cardia and distal stomach cancers also appear to be different. We aimed to estimate the association between fruit and vegetable intake and gastric cancer, by location and histological type. We performed a population-based case-control study and a meta-analysis of studies addressing this issue. Incident cases (n=305) were identified in two large teaching hospitals (Porto, Portugal), and controls were randomly sampled among city dwellers (n=1129). Published studies were searched through PubMed, and effects were combined with random effects meta-analysis. In our case-control study, the odds ratio (OR) for the comparison of the highest vs. lowest tertile of fruit consumption was 0.47 [95% confidence interval (CI): 0.21-1.05] for cardia, 0.53 (95% CI: 0.35-0.80) for non-cardia cancer, 0.36 (95% CI: 0.20-0.62) for intestinal, and 1.00 (95% CI: 0.53-1.90) for the diffuse histological type. For vegetables, the corresponding OR was 0.59 (95% CI: 0.26-1.35), 0.85 (95% CI: 0.58-1.26), 0.95 (95% CI: 0.57-1.57), and 0.60 (95% CI: 0.32-1.14). In meta-analysis, considering fruit consumption (highest vs. lowest category), the combined OR was 0.58 (95% CI: 0.38-0.89) for cardia, 0.61 (95% CI: 0.44-0.84) for non-cardia, 0.49 (95% CI: 0.33-0.72) for intestinal type, and 0.82 (95% CI: 0.57-1.20) for diffuse type. Vegetables also decreased the risk of cardia (OR=0.63, 95% CI: 0.50-0.79), non-cardia (OR=0.75, 95% CI: 0.59-0.95), intestinal (OR=0.61, 95% CI: 0.44-0.86), and diffuse type (OR=0.67, 95% CI: 0.44-1.01). Fruit or vegetable intake was associated with a decreased risk of gastric cancer regardless of the anatomical location and the histological type, although dietary intake had a more clear-cut protective effect on intestinal type cancers.

In intestinal metaplasia and 30% of gastric carcinomas, MUC2 intestinal mucin and the intestine-specific transcription factors Cdx-1 and Cdx-2 are aberrantly expressed. The involvement of Cdx-1 and Cdx-2 in the intestinal development and their role in transcription of several intestinal genes support the hypothesis that Cdx-1 and/or Cdx-2 play important roles in the aberrant intestinal differentiation program of intestinal metaplasia and gastric carcinoma. To clarify the mechanisms of transcriptional regulation of the MUC2 mucin gene in gastric cells, pGL3 deletion constructs covering 2.6 kb of the human MUC2 promoter were used in transient transfection assays, enabling us to identify a relevant region for MUC2 transcription in all gastric cell lines. To evaluate the role of Cdx-1 and Cdx-2 in MUC2 transcription we performed co-transfection experiments with expression vectors encoding Cdx-1 and Cdx-2. In two of the four gastric carcinoma cell lines and in all colon carcinoma cell lines we observed transactivation of the MUC2 promoter by Cdx-2. Using gel shift assays we identified two Cdx-2 binding sites at ؊177/؊171 and ؊191/؊187. Only simultaneous mutation of the two sites resulted in inhibition of Cdx-2-mediated transactivation of MUC2 promoter, implying that both Cdx-2 sites are active. Finally, stable expression of Cdx-2 in a gastric cell line initially not expressing Cdx-2, led to induction of MUC2 expression. In conclusion, this work demonstrates that Cdx-2 activates the expression of MUC2 mucin gene in gastric cells, inducing an intestinal transdifferentiation phenotype that parallels what is observed both in intestinal metaplasia and some gastric carcinomas.There is consistent data indicating that in human stomach as well as in other organs mucin genes are expressed in a regulated cell-and tissue-specific manner and that altered mucin gene expression occurs in cancer and precancerous lesions (1). In normal gastric mucosa most studies show little or no expression of the intestinal mucin MUC2 (2-9). In intestinal metaplasia, a preneoplastic lesion of the stomach characterized by the transdifferentiation of the gastric mucosa to an intestinal phenotype, there are alterations in the mucin expression pattern including de novo expression of MUC2, mostly in goblet cells (10). Thirty percent of gastric carcinomas, including all carcinomas of the mucinous type, also aberrantly express MUC2 intestinal mucin (11, 12). The molecular mechanisms responsible for the regulation of MUC2 transcription and expression are beginning to be elucidated. The structure of MUC2 promoter was characterized (13, 14) and MUC2 expression was reported to be regulated by methylation of the promoter (15-17) and by the Sp1 family of transcription factors (13,18,19). It has also been described that MUC2 is transcriptionally activated by p53 (20) and, in tracheobronchial epithelial cells, by lipopolysaccharide from Pseudomonas aeruginosa (21, 22) and epidermal growth factor (19). However, information on MUC2 transcriptional regulation in gas...