c-myc amplification in pre-malignant and malignant lesions induced in rat liver by the resistant hepatocyte model

We have investigated by restriction fragment analysis genomic abnormalities involving the c-myc gene in DNA isolated from adenomas and hepatocellular carcinomas (HCCs). Adenomas and HCCs were induced by the “resistant hepatocyte” protocol in diethylnitrosamine-initiated male F344 rats. Southem- blot analysis of EcoRI-restricted DNA from normal liver, early and late adenomas, I2 weeks (EAs) and 30 weeks (Us) after initiation, and HCCs, showed 2 bands of 18 and 3.2 kb hybridizing with c-myc, in all tissues. c-rnyc amplification occurred in almost all HCCs, and in the majority of EAs and Us. These results were confirmed by dilution analysis. c-myc amplification was also seen in adenomas and HCCs by Southem analysis with Hindlll-restricted DNA, and in HCCs by differential PCR. c-myc mRNA increase occurred in all adenomas and HCCs, but it was higher in the lesions showing gene amplification. Moreover, a 13-kb DNA extraband, hybridizing with c-myc, was found in the Hindlll-restricted DNA from HCCs, but not in normal liver and adenomas, and a 7. I -kb extra band was present in EcoRI-digested DNA from one LA EcoRI-restricted DNA from some adenomas exhibited a decrease in intensity of the 18-kb fragment, and an increase in intensity of the 3.2-kb fragment. No alteration in banding pattern occurred in the B-actin gene in adenomas. These results provide evidence of amplification and some other rearrangements involving the c-myc gene, in pre-malignant and malignant liver lesions, induced by the RH protocol. and suaest a role of c-myc rearraniement inthe prog-mion of adenoias to malignancy.