YBX1 and breast cancer: Five cell lines were used, including 4 transduced with the FUCCI (F) cell cycle reporter constructs [33]: A549/F lung cancer cells with wild-type (wt) TP53 [34]; HT1080/F fibrosarcoma cells with wtTP53 [35] and the variant HT1080-6TG (6TG/F) with mutant TP53 [36]; the spontaneously immortalized IIICF/c/F skin fibroblast line from a Li Fraumeni patient [37]; and MDA-MB-231 breast cancer cells with mutant TP53. Cells were transfected with control (si-Ctrl) or YB-1 siRNA (si-YB-1) and Western blotted to confirm YB-1 depletion (Figure S1a).