Cellular distributions of molecules with altered expression specific to the tumor promotion process from the early stage in a rat two-stage hepatocarcinogenesis model

A global gene expression profiling specific to the early process of tumor promotion by fenbendazole (FB) or phenobarbital (PB) in a rat two-stage hepatocarcinogenesis model revealed 33 genes to show altered expression in common with both chemicals. The immunohistochemical distribution of transferrin receptor (Tfrc), nuclear receptor subfamily 0, group B, member 2 (Nr0b2) and minichromosome maintenance deficient 6 (MCM6), included in the altered expression profile, were therefore examined in FB- and PB-induced proliferative lesions at both early and late stages of tumor promotion. In addition, immunoexpression of transforming growth factor beta receptor (TGF beta R) I, TGF beta RII, phosphatase and tensin homolog deleted on chromosome 10 ( PTEN) and phosphorylated phosphatase and tensin homolog deleted on chromosome 10 ( pPTEN) was also examined. In the early stage, most hepatocellular foci positive for glutathione S-transferase placental form (GST-P) showed co-expression of TGF beta RI and lack of PTEN and pPTEN, some GST-P-positive foci co-expressing Tfrc and Nr0b2. In the late stage, selective expression of TGF beta RI, but not TGF beta RII, was also observed in many adenomas and carcinomas consistently expressing GST-P. Nr0b2 was variably expressed in the proliferative lesions, irrespective of the carcinogenic stage. Like the GST-P- positive foci, adenomas and carcinomas consistently lacked PTEN and pPTEN. Expression of Tfrc and MCM6 was increased in parallel with the carcinogenic stage. In conclusion, loss of PTEN and dysregulation of transforming growth factor b signaling can be considered to be involved in rat hepatocarcinogenesis from early stages. Selective expression of Tfrc in proliferative lesions suggests an involvement of changes in iron homeostasis during the process of tumor promotion/progression driven by FB or PB.