RB1 and cancer: Knockdown of PTEN in CKS2-KD cells did not impair CKS2 protein level, but partially rescued cancer-associated phenotypes including cell proliferation, colony formation and EdU staining (Fig. 5E–H), suggesting that PTEN act downstream of CKS2. To validate that PTEN was indeed downstream of RB-E2F1, we observed that E2F1 knockdown had the same effect of CKS2 depletion on PTEN protein levels in Y79 cells (Fig. 5D, I).