Fig. 6.
Activation of the cyclin D1-CDK4–E2F1 pathway to increase thyroid tumor cell proliferation of the ThrbPV/+-PTU mice. Thyroid extracts (25 μg) from mice with the genotypes indicated (n = 4 for each genotype) were analyzed for key cell cycle regulators as shown by Western blotting. Markedly elevated protein abundance of cyclin D1 (A), CDK4 (B), and E2F1 (C) were observed in the thyroids of ThrbPV/+-PTU mice (lanes 13–16) as compared with the WT-PTU mice (lanes 5–8). No apparent signals were observed in either the WT (lanes 1–4) or untreated ThrbPV/+mice (lanes 9–12). GAPDH (D) was used as the loading control.