Even though similar observations have been found in another study using 92.1 uveal melanoma cells [59], reduced H2AK119ub levels could not be seen in MP38 cells, which displayed low basal activity of PRC1. Additionally, Desai et al. observed a decrease in H2AK119ub upon treatment with PRT4165 for up to 36 h in undifferentiated KIND-1 (embryonic stem) cells, which displayed high RING1 protein levels, while BMI1 protein levels were rather low [60]. Here, PRC1 is linked to uveal melanoma.