CUL4B and osteosarcoma: In addition, the same amount of CUL4B-Flag protein pulled down much more DDB1 and RBX1 protein in U2OS and Saos-2 osteosarcoma cells than in hFOB1.19 cells (Fig. 2A), suggesting that DDB1 and RBX1 are also upregulated in osteosarcoma cells.