SKP2 and neoplasm: Cellular senescence and apoptosis are major mechanisms of tumor suppression.26 Cellular senescence was observed in Skp2-deficient MEF cells in an ARF-p53-independent manner.27 Sgt1 interacts with Skp1,8, 18 which interacts with Skp2.28 Our analysis found no significant difference in HRas-induced senescence and apoptosis between Sgt1+/−p53−/− MEF cells and Sgt1+/+p53−/− MEF cells (Supplementary Figures S4B and S4C).