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E-cadherin is a central molecule in the process of gastric carcinogenesis and its posttranslational modifications by N-glycosylation have been described to induce a deleterious effect on cell adhesion associated with tumor cell invasion. However, the role that site-specific glycosylation of E-cadherin has in its defective function in gastric cancer cells needs to be determined. Using transgenic mice models and human clinical samples, we demonstrated that N-acetylglucosaminyltransferase V (GnT-V)-mediated glycosylation causes an abnormal pattern of E-cadherin expression in the gastric mucosa. In vitromodels further indicated that, among the four potential N-glycosylation sites of E-cadherin, Asn-554 is the key site that is selectively modified with β1,6 GlcNAc-branched N-glycans catalyzed by GnT-V. This aberrant glycan modification on this specific asparagine site of E-cadherin was demonstrated to affect its critical functions in gastric cancer cells by affecting E-cadherin cellular localization, cis-dimer formation, molecular assembly and stability of the adherens junctions and cell–cell aggregation, which was further observed in human gastric carcinomas. Interestingly, manipulating this site-specific glycosylation, by preventing Asn-554 from receiving the deleterious branched structures, either by a mutation or by silencing GnT-V, resulted in a protective effect on E-cadherin, precluding its functional dysregulation and contributing to tumor suppression.

The cadherin/catenin complex regulates cellular adhesion and motility and is believed to function as an invasion suppressor system. Several studies have identified alterations in the expression profiles of those molecules in different histotypes of thyroid carcinoma. The diffuse sclerosing variant (DSV) of papillary thyroid carcinoma (PTC) is a rare, highly invasive variant of PTC in which an impairment of cell-cell adhesion may play a major role. In an attempt to progress in the understanding of the clinicopathological features of DSV, this study examined eight cases of DSV, 18 cases of classical PTC and a control group of normal thyroid by immunohistochemistry (E-, P- and N-cadherins and β-, γ- and α-catenins). The E-cadherin gene was also studied by polymerase chain reaction/single strand conformation polymorphism (PCR/SSCP) and methylation-specific PCR (MSP). In contrast to classical PTC, which showed heterogeneous loss of E-cadherin expression, in almost every case of DSV a pronounced reduction was observed in its membranous expression, accompanied by a relocation to the cytoplasm. Inactivation of the E-cadherin/catenin complex appears to occur in DSV via two different pathways: E-cadherin alteration either through mutation (one out of the eight cases) or through methylation of the E-cadherin gene promoter (three out of five cases); and β- and/or γ-catenin alterations (three of the eight cases). Methylation of the E-cadherin gene promoter, abnormalities of E-cadherin expression and alterations of γ-catenin were also detected in classical PTC. In DSV, as in classical PTC, there is neo-expression of P-cadherin in areas of squamous metaplasia and no N-cadherin expression. In conclusion, abnormalities of the E-cadherin/catenin complex appear to be more pronounced in DSV than in classical PTC. It remains to be shown whether or not such differences are associated with the more aggressive behaviour of DSV compared with classical PTC. Copyright © 2001 John Wiley & Sons, Ltd.

Twin studies are an important tool in medical genetics for the evaluation of the relative roles of genetic and non-genetic factors in several diseases. Familial amyloidotic polyneuropathy type I (FAP-I), TTR Met 30, was present in two sets of proven monozygotic (MZ) twins, one from Majorca and the other from Portugal. Monozygosity was established by analysis of DNA polymorphisms. Both pairs were discordant for age at onset and some clinical manifestations of FAP-I. We reviewed the differences in age at onset and clinical features in both sets and in two other pairs of presumed MZ twins with FAP-I and compared them with those in MZ twin pairs with other Mendelian disorders, such as neurofibromatosis type 1, Huntington's disease, facioscapulohumeral muscular dystrophy, and myotonic dystrophy. We conclude that, in addition to the postulated modifying genes, there must be a significant contribution from non-genetic factors to the phenotypic variability of FAP-I (age at onset and clinical expression), either because of enviromental differences or stochastic events during (or after) the twinning process.

Families with autosomal dominant inherited predisposition to gastric cancer have been described. More recently, germline E-cadherin/CDH1 mutations have been identified in hereditary diffuse gastric cancer kindred. The need to have protocols to manage and counsel these families in the clinic led a group of geneticists, gastroenterologists, surgeons, oncologists, pathologists, and molecular biologists to convene a workshop to produce consensus statements and guidelines for familial gastric cancer. Review of the available cancer pathology from people belonging to families with documented germline E-cadherin/CDH1 mutations confirmed that the gastric cancers were all of the diffuse type. Criteria to define the different types of familial gastric cancer syndromes were agreed. Foremost among these criteria was that review of histopathology should be part of the evaluation of any family with aggregation of gastric cancer cases. Guidelines for genetic testing and counselling in hereditary diffuse gastric cancer were produced. Finally, a proposed strategy for clinical management in families with high penetrance autosomal dominant predisposition to gastric cancer was defined.

Two human diffuse gastric carcinoma cell lines were established in vitro from xenografted tumours serially passaged in nude mice. Of 12 primary diffuse gastric carcinomas, 7 were successfully xenografted in nude mice (58.3%). Short-term primary cultures were achieved in all the xenografted lines. However, only 2 of the 7 short-term primary cultures were established as long-term cultures (GP202 and GP220). GP202 cells are larger than GP220 cells, show less abundant intercellular junctions at the ultrastructural level and grow in culture as a compact thin monolayer. The GP220 cells grow preferentially in small clusters attached to the monolayer, with a subpopulation of floating cells. Both lines have cells containing small mucin vacuoles in the cytoplasm and cells displaying a typical signet-ring shape. GP202 cells grow as solid tumours in nude mice but GP220 cells do not give rise to tumours. The flow cytometry and karyotype analysis showed aneuploidy in GP202 cells, with many numerical and structural chromosomal abnormalities, and diploidy in GP220 cells, with several structural chromosomal abnormalities. The CDw75 and Tn antigens are more prominently expressed in GP202 cells than in GP220 cells. T antigen is only expressed in GP202 cells, whereas only GP220 cells express EGFR. Sialosyl-Tn is not expressed in either of the cell lines. The gastric cancer cell lines described in this paper represent a valuable addition to the small number of diffuse gastric cancer cell lines currently available and also provide a good model for further in vitro and in vivo studies of gastric carcinogenesis.

BACKGROUND & AIMS:Microsatellite instability (replication error [RER]- positive phenotype) is a frequent genetic alteration in gastric carcinomas. The clinical relationship between RER-positive and RER- negative gastric tumors is poorly characterized. The aim of this study was to investigate the relationship between the number of altered microsatellite loci and the clinicopathologic features of gastric carcinoma. METHODS:Five or 6 microsatellite loci were analyzed in 61 gastric carcinomas using polymerase chain reaction. RESULTS:Twenty-one carcinomas (34.4%) had microsatellite instability: 7 at 1 locus, 2 at 2 loci, and 12 at multiple loci. The comparison between the three groups (with none, 1 or 2, and more than 2 RER-positive loci) showed that RER- negative carcinomas and carcinomas with 1 or 2 RER-positive loci share features that differ from those of carcinomas with multiple RER- positive loci. The latter were all of the intestinal or atypical subtype and had lower DNA content, more prominent lymphoid infiltration, and less prevalent nodal metastases than carcinomas in the other two groups. The patients with carcinomas showing multiple RER- positive loci had a better prognosis. CONCLUSIONS:The finding of microsatellite instability in a single or few loci does not qualify a case as a mutator phenotype from a clinical standpoint. Gastric tumors with multiple RER-positive loci have a particular clinicopathologic profile leading to a better outcome. (Gastroenterology 1996 Jan;110(1):38-44)

The role of the retinoblastoma gene (RB1) in human gastric carcinogenesis is yet to be clarified. We report on the analysis of RB1 structure and protein (pRB) expression in gastric carcinomas using Southern blotting, Western blotting and immunohistochemistry. The relationship between pRB expression and cell proliferation was assessed by a proliferation marker (PCNA) in a subset of cases. Non-neoplastic mucosas were studied, as controls, by the same methodology. We found a close relationship between pRB expression and PCNA in non-neoplastic mucosas as well as in gastric carcinomas. All tumours were immunohistochemically positive for pRB, although with a variable proportion of non-immunoreactive cells. Carcinomas of the diffuse type showed absence of pRB expression in a larger proportion of neoplastic cells than carcinomas of the intestinal type (P < 0.05). Analysis of the RB1 structure using probe p68RS2.0 revealed allelic imbalance in 29% of informative cases. No homozygous deletions and/or rearrangements were detected with p68RS2.0 and cDNA probes. Western analysis revealed no abnormal patterns of pRB. Our data therefore suggest that major alterations affecting the RB1 gene are rather infrequent in human gastric carcinomas.

We carried out an immunohistochemical study and DNA analysis of 30 gastric carcinomas to evaluate p53 overexpression and allelic loss at 17p. The immunohistochemical study demonstrated immunoreactivity for p53 protein in four cases. Allelic loss for the pYNZ22.1 marker was detected in nine cases. In total, ten cases showed immunoreactivity for p53 protein, allelic loss, or both. The study of nine of these cases by constant denaturant gel electrophoresis revealed p53 mutations in three cases. We conclude that the prevalence of mutations of p53 in our series is similar to what has recently been observed in other cases of gastric cancer, but lower than in colon carcinomas.

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