Alterations of the transforming growth factor-beta signaling pathway in hepatocellular carcinomas induced endogenously and exogenously in rats

To elucidate involvement of the transforming growth factor-beta (TGF-beta) signaling pathway in endogenous and exogenous liver carcinogenesis, we inve stigated mutations of TGF-beta receptor type II (TGF-beta RII), Smad2 and S mad4 genes, and expression of TGF-beta RII in hepatocellular carcinomas (HC Cs) induced by a choline-deficient L-amino acid-defined (CDAA) diet and by N-nitrosodiethylamine (DEN), Male Fischer 344 rats received a CDAA diet con tinuously and HCCs were sampled after 75 weeks. Administration of DEN was f ollowed by partial hepatectomy (PH), with colchicine to induce cell cycle d isturbance and a selection pressure regimen, HCCs being obtained after 32 w eeks. Total RNAs were extracted from individual HCCs and mutations in TGF-b eta RII, Smad2 and Smad4 were investigated by reverse transcription (RT)-po lymerase chain reaction (PCR)-restriction-single-strand conformation polymo rphism (SSCP) analysis followed by sequencing analysis, Mutations of Smad2 were detected in 2 out of 12 HCCs (16.7%) induced by the CDAA diet, a GGT-t o-GGC transition (Gly to Gly) at codon 30 and a TCT-to-GCT (Ser to Ala) tra nsversion at codon 118, without any TGF-beta RII or Smad4 alterations, No m utations of TGF-beta RII, Smad2 and Smad4 were encountered in eleven HCCs i nduced by the exogenous carcinogen. Semi-quantitative RT-PCR revealed reduc ed expression of TGF-beta RII in 2 HCCs (16.7%) without Smad2 mutations out of 12 HCCs induced by the CDAA diet and none of II induced by DEN, These r esults suggest that the TGF-beta signaling pathway may be disturbed in endo genous liver carcinogenesis in rats.