USP4 and cancer: B-AP15 contributes to the selective inhibition of USP4 and UCHL5, and restrains the cell proliferation of various cancers, including lung cancer, CRC, BC, myeloma, prostate cancer, and liver cancer (D'Arcy et al., 2011; Tian et al., 2014; Cai et al., 2017; Ding et al., 2018).