Figure 7. Treatment of old mice with DEN/PB initiates early liver proliferation and liver cancer via fast elimination of the ph-S193 isoform of C/EBPα.

(A) Activation of gankyrin by DEN/PB in livers of old mice causes an early elimination of C/EBPα protein. Expression of C/EBPα, gankyrin, and cdc2 was examined by Western blotting with nuclear extracts from 3 mice of each age group. Positions of 42-kDa and 30-kDa isoforms of C/EBPα are shown. The membranes were reprobed with β-actin. (B) Levels of C/EBPα and gankyrin were calculated as ratios to β-actin. (C) Levels of gankyrin mRNA and C/EBPα mRNA were examined by RT-PCR and shown as ratios to β-actin mRNA. Bar graphs show a summary of 3 independent experiments. (D) DNA synthesis is increased in livers of old mice at 12 weeks after DEN/PB treatments. Left image shows a typical picture of BrdU staining of young and old livers. Arrows show BrdU-positive hepatocytes. Original magnification, ×63. Bar graphs present a summary of 3 experiments with 3 animals of each age group. (E) A typical picture of liver tumors in old mice at 20 weeks after DEN/PB treatments. Arrows show tumor nodules. (F) Liver body ratios in young and old animals at 20 weeks after DEN treatments. Data shown are mean ± SD.