阪口 政清

Using 2-dimensional gel electrophoresis, we previously demonstrated that the S100C protein remarkably decreased after immortalization of normal human fibroblasts, and that this protein caused growth inhibition of human tumor cells when forcibly expressed in these cells, suggesting that S100C plays a significant role in tumor suppression. The present study was carried out to determine what type of human tissues express S100C protein, and, subsequently, whether the S100C content in these tissues changes after normal cells have been transformed into cancer cells. We found that ductal cells in various tissues were positively stained with the S100C protein. In comparison, epithelial cells in digestive organs such as the stomach, small intestine, and colon were not stained as strongly. When 14 pairs of human normal and cancerous tissues were stained with the antibody, decreases in the staining levels of S100C were observed in 6 kinds of cancerous tissues--from the bronchus, mammary duct, renal tubule, prostate, uterus, and testis--in comparison with staining in their normal counterparts. These results suggest that S100C is a new tumor marker protein, the expression of which significantly decreases after malignant transformation of human tissues.

We have recently shown that a new therapeutic modality using the REIC/Dkk-3 gene (Ad-REIC) is effective against various human cancers, including those of prostate, testis and breast origins. The aim of the present study was to examine the sensitivity of bladder cancers to Ad-REIC and to clarify the molecular mechanisms that determine sensitivity/resistance. We found that 2 human bladder cancer cell lines, T24 and J82, are resistant to Ad-REIC. In T24 and J82 cells, the ER stress response and activation of JNK were observed in a manner similar to that in the sensitive PC3 cells. Translocation of Bax to mitochondria occurred in PC3 cells but not in T24 and J82 cells. Bcl-2 was remarkably overexpressed in T24 and J82 compared with the expression levels in sensitive cell lines. Treatment of T24 and J82 cells with a Bcl-2 inhibitor sensitized the cells to Ad-REIC-induced apoptosis. The results indicate that some human bladder cancers are resistant to apoptosis induced by overexpression of REIC/Dkk-3, which is at least in part due to up-regulation of Bcl-2. These results provide a basis for possible use of Bcl-2 as a marker of sensitive cancers and to try to sensitize resistant cancers to Ad-REIC by down-regulation of Bcl-2.