CD9 expression in gastric cancer and its significance

BACKGROUND: The tetraspanin transmembrane protein CD9 is known to be involved in cell adhesion, proliferation, and cell motility. Previous studies have reported that reduced expression of CD9 is related to aggressive behavior of cancer cells. However, the cause-and-effect relationship between the CD9 expression level and the state of malignancy remains unclear. Here, we investigated the connection between the CD9 expression level and the state of malignancy in gastric cancers. MATERIALS AND METHODS: The expression of CD9 was examined in primary and metastatic gastric carcinoma tissues. In total, specimens from 78 patients were used for immunohistological staining and specimens from 57 patients were subjected to Northern blotting. Paired samples of tumor/normal tissues obtained from five cases of gastric cancer were used for Western blotting. RESULTS: CD9 expression was observed at both the message level and the protein level in primary gastric carcinoma tissues, lymph node metastatic tissues, and peritoneal dissemination tissues. Contrary to previous reports for other cancers, CD9 expression was intensified in cancerous areas of gastric cancers in comparison with noncancerous areas in the same patient. When analyzed by the malignancy status based on the clinicopathological diagnosis, there was a tendency that CD9 expression was observed in severe vessel invasion, active lymph node metastasis, and advanced stage. CONCLUSIONS: CD9 expression was rather intensified in gastric cancer tissue in comparison with normal tissues. CD9 expression was more prominent in advanced gastric cancer.