UBE2I and cancer: Strikingly, SS was the most sensitive subtype of cancer to knocking down UBE2I (UBC9), SUMO2 (the most widely expressed SUMO in humans20), PIAS1, SAE1 and UBA2 (SAE2) (Supplementary Fig. 1A–E), molecules encompassing the entire SUMOylation process (Supplementary Fig. 1F) and pointing to a selective dependency of SS on this posttranslational modification (PTM).