Background: DNA microarray global gene expression analysis is a useful approach in the search for tumor biomarkers. We have used Affymetrix Global gene expression U-133 oligonucleotide chips and SAGE with immunohistochemical validation to identify markers of gastric carcinoma.

Design: We compared the global gene expression profiles of 7 gastric adenocarcinomas and 4 gastric cancer cell lines with the profiles of 8 samples of normal gastric mucosa. We compared the findings to the SAGE expression profiles of 3 gastric cancers and validated the results using immunohistochemistry (IHC).

Results: Claudin genes 3, 4 and 7 were overexpressed in gastric carcinomas and in gastric cancer cell lines when compared to normal mucosa. SAGE tag counts of Claudins 4 and 7 were also significantly higher in tumors. By IHC, 8/11 intestinal type cancers were positive for Claudin 3 while 10/11 tumors were positive for Claudins 4 and 7. All 10 cases of diffuse gastric cancer were Claudin 4 positive, while 4/11 and 5/11 were positive for Claudins 3 and 7 respectively. Areas of intestinal metaplasia adjacent to tumors in section also showed strong IHC staining for Claudins 3, 4 and 7.

Conclusion: Claudins 3, 4 and 7 are overexpressed in gastric adenocarcinomas of both the intestinal and diffuse types. In addition, Claudins 3,4 and 7 may serve as markers of intestinal metaplasia. These findings have potential for clinical application in the imaging and targeted therapy of precancerous upper gastrointestinal lesions.

Background: Claudin proteins are components of tight intercellular junctions that are important in the formation of intercellular barriers. We previously identified up-regulation of Claudins 3, 4 and 7 in invasive gastric adenocarcinoma using Affymetrix Global Gene Expression U-133 oligonucleotide gene chips and immunohistochemical (IHC) analysis. We noted that while normal gastric mucosa was negative for Claudin 3, 4 and 7 expression, regions of intestinal metaplasia and epithelial dysplasia showed positivity for these proteins. We hypothesized that Claudin 3, 4 and 7 would be similarly overexpressed in esophageal intestinal metaplasia and adenocarcinoma.

Design: Claudin 3, 4 and 7 gene expression was analyzed by Affymetrix U-133 microarrays in 3 cases of esophageal adenocarcinoma and 3 cases of normal esophagus. The results were further investigated by IHC using tissue microarrays (TMAs) constructed from esophageal resection specimens. TMAs contained squamous mucosa (44 cases), gastric mucosa (40 cases), non-dysplastic Barrett mucosa (BE, 16 cases), low-grade dysplasia (16 cases), high-grade dysplasia (26 cases), adenocarcinoma (58 cases), lymph node (27 cases), liver and lung metastases (1 each). Claudin protein staining was scored on a semiquanitiative scale of 0+ - 4+.

Results: Claudins 4 and 7 mRNA was expressed in four cases of normal esophagus but Claudin 3 was not. Claudins 3 message was however overexpressed in 3 cases of esophageal adenocarcinoma, as were Claudins 4 and 7. By IHC, squamous mucosa displayed 0-2+ staining in most cases with all three Claudin antibodies, although 3 cases had 3+ staining for Claudin 4. The majority of gastric mucosa was negative for expression of Claudins 3,4 and 7 (36/40, 37/40, and 20/35 cases respectively), however there was 1+ staining in 3, 6, and 11 cases respectively, 2+ staining in 0, 2, and 4 cases, and 3+ staining in 0, 2, and 0 cases. In contrast, Claudin 4 showed 3-4+ staining in 13/14 BE, 41/42 cases of dysplasia, 54/58 carcinomas and in 27/29 metastatic lesions. Claudin 3 showed 3-4 + positivity in 8/16 BE, in 18/40 cases of dysplasia, 30/58 cases of carcinoma, and in 15/27 metastases. Claudin 7 showed 3-4 + positivity in 14/16 BE, in 30/42 cases of dysplasia, 36/58 cases of carcinoma, and in 17/27 metastases.

Concludions: The findings suggest that Claudins, in particular Claudin 4 may provide targets for the diagnosis and directed therapy of esophageal carcinoma and its precursors.