| Budget Amount *help |
¥3,300,000 (Direct Cost: ¥3,300,000)
Fiscal Year 2001: ¥1,300,000 (Direct Cost: ¥1,300,000)
Fiscal Year 2000: ¥2,000,000 (Direct Cost: ¥2,000,000)
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| Research Abstract |
In this study, the relation between β-catenin alteration and expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase (COX)-2 was examined in AOM-induced rat colon carcinogenesis. K-ras gene mutations were also investigated. Mutation analysis by PCR-single strand conformation polymorphism method and direct sequencing demonstrated the β-catenin gene to be frequently mutated from the stage of dysplastic aberrant crypt foci(ACF),the early stage of colon carcinogenesis. K-ras was frequently mutated in hyperplastic ACF, indicating that Kras may play an important role in the formation of ACF. Immunohistochernical staining showed alteration of cellular localization of β-catenin in all dysplastic ACF, adenomas and adenocarcinomas examined. iNOS expression was also observed in most of these lesions in which β-catenin alterations were observed. Neither iNOS expression nor β-catenin alterations were observed in any hyperplastic ACF. COX-2 expression in stromal elements was found even in normal colon mucosa, and increased in adenomas and adenocarcinomas, while epithelial cells were only positive in large adenocarcinomas. These results show that β-catenin alterations may be related to induction of iNOS expression, these being early events in AOM-induced colon tumorigenesis which may play important roles in causing dysplastic changes. Mutations in the p-catenin gene were also very frequently found in mouse colon tumors induced by AOM, while K-ras mutations were rare, suggesting that K-ras activation may be not essential for tumor development. However, in a cell culture system, transfection of the K-ras gene with an activating mutation enhanced iNOS expression induced by IL-lβ and LPS. Therefore, K-ras is also suggested to play an important role in colon tumorigenesis by enhancing iNOS expression.
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