However, in HPV-negative cell lines (C33A HPV-negative cervical cancer cells and U2OS osteosarcoma cells), HP1γ overexpression had no effect on the protein levels of UBE2L3 and p53 (Supplementary Fig. S12A) as well as the expression of p53 target genes (Supplementary Fig. S12B). Here, TP53 is linked to osteosarcoma.