TP53 and liver cancer: In the same cells, we assessed the expression of p21, a downstream target of p53 protein, and observed an increase of p21 in the p53 wild-type liver cancer cell lines HepG2 (Fig. 3a) and Sk-hep-1 (Supplementary Fig. S3g), but not in the p53 null liver cancer cell line Hep3B (Fig. 3b).