TP53 and osteosarcoma: These siRNAs, as well as non-target#1 siRNA (negative control, C) and a p53 siRNA (positive control, p53), were transiently transfected into p53-null MG63 osteosarcoma cell line infected with a retroviral vector encoding p53R273H (MG-R273H, Supplementary Figure S1) or U2OS osteosarcoma cell line endogenously expressing wtp53, followed by western blotting for p53 (Figure 2A).