ZUP1 and neoplasm: Furthermore, we found that the p53 accumulation is mainly due to its cytoplasmic retention by UCHL1, depending on its DUB activity, which is responsible for the tumor suppressive function of UCHL1. Thus, UCHL1, acts as a functional tumor suppressor by inhibiting cell proliferation and inducing apoptosis, but is epigenetically-silenced in breast cancer.