Altered expression of beta-catenin, inducible nitric oxide synthase and cyclooxygenase-2 in azoxymethane-induced rat colon carcinogenesis

Activation of the beta-catenin/T cell factor-mediated transcription pathway through mutations of the APC or beta-catenin gene is suggested to play an important role in colon carcinogenesis and there is great interest in the t arget genes. We have described the frequent mutation and an altered cellula r localization of beta-catenin in rat colon adenocarcinomas induced by azox ymethane (AOM), along with up-regulation of inducible nitric oxide synthase (iNOS) and cyclooxygenase (COX)-2, In the present study, the relation betw een beta-catenin alteration and expression of iNOS and COX-2 in AOM-induced rat colon carcinogenesis was examined in hyperplastic and dysplastic type aberrant crypt, adenoma and adenocarcinoma samples. K-ras gene mutations we re also investigated. Mutation analysis by the PCR-single strand conformati on polymorphism method and direct sequencing demonstrated the beta-catenin gene to be mutated in two of three dysplastic aberrant crypt foci (ACF), tw o of six adenomas and 20 of 26 adenocarcinomas, while K-ras was mutated in seven of 10 hyperplastic ACP and seven of 26 adenocarcinomas. Immunohistoch emical staining showed an alteration in cellular localization of beta-caten in in all dysplastic ACF, adenomas and adenocarcinomas examined. iNOS expre ssion was also observed in all but one of the lesions in which beta-catenin alterations were observed. Neither iNOS expression nor beta-catenin altera tions were observed in any hyperplastic ACF COX-2 expression in stromal ele ments was found even in normal colon mucosa and increased in adenomas and a denocarcinomas, while epithelial cells were only positive in large adenocar cinomas. These results show that beta-catenin alterations may be related to induction of iNOS expression, these being early events in AOM-induced colo n tumorigenesis which may play important roles in causing dysplastic change s.