SUMO1 and liver cancer: Moreover, the precipitated protein complexes included more SUMOylated Mettl3-Flag in liver cancer cells expressing Mettl3-Flag, SUMO1, and scramble siRNA than in cells expressing Mettl3-Flag, SUMO1, and Ubc9 siRNA, indicating that UBC9 is required for Mettl3 SUMOylation (Figure 1A).