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.