Expression of Glutathione S-Transferase, E-Cadherin, and Catenins during N,N-Diethylnitrosamine-Induced Hepatocarcinogenesis in Rat Liver

ABSTRACT

N,N-Diethylnitrosamine (DEN) has been proved to have carcinogenic potential in the initiation or promotion stage and the transformed cells proliferate to form preneoplastic nodules which are positive for placental form of glutathione S-transferase (GST-P). E-Cadherin, a member of the cadherin family, is expressed in epithelial cells. To evaluate the role of adhesion molecules (E-Cadherin, alpha-catenin, and beta-catenin), which have not been well understood in carcinogenesis, we investigated the changes of E-cadherin, alpha-Catenin and beta-Catenins by immunohistochemistry and immunoblotting in DEN-induced hepatocarcinogenesis of rat liver. In addition, the sequential analysis of histopathology and the expression of GST-P were also examined. Immunoreactive areas for GST-P were gradually increased from early period of carcinogenesis and strong GST-P positive foci were noted in various lesions, especially in the clear cell and eosinophilic cell nodules. Immunohistochemically, the E-Cadherin expression was increased in DEN-treated preneoplastic nodules in 4 and 10 weeks and hepatocellular carcinomas displayed relatively reduced expression compared with the hyperplastic nodules. But alpha- and beta-catenin expression was increased in hyperplastic nodules and hepatocellular carcinomas. Immunoblotting studies revealed that the level of alpha-catenin (cytosol and membranous fraction) was overexpressed in hyperplastic nodules as well as hepatocellular carcinomas, which showed markedly increased expression. The membranous fraction of beta-catenin was markedly increased in 10 weeks of DEN treatment and slightly reduced in hepatocellular carcinomas. These findings suggest that during DEN-induced hepatocarcinogenesis, the clear cell and eosinophilic cell nodules expressing GST-P in their cytoplasm are early transformed cell nodules. The altered expression of E-Cadherin and catenins is closely related with tumor propagation. Loss or reduced expression of E-cadherin may play a role in the progression of late hyperplastic nodule to hepatocellular carcinoma in DEN-induced rat hepato carcinogenesis.