COP1 and Familial prostate cancer: Reasoning that the dosage of ETS protein is crucial in ETS-drive prostate cancer tumorigenesis, we created a low dosage (ETV4WT) level and a high dosage (ETV4AAA) level of ETV4 protein through increased ETV4 protein stability by mutating the conserved ExxVPD motifs responsible for COP1 degradation (22, 24).