Besides, Geng et al. discovered that a p21-activated kinase 5 (PAK5)/PAK5-aspartyl aminopeptidase (DNPEP)/USP4 axis can be involved in breast cancer progression in which higher level of PAK5 and USP4 expression predicted a worse OS and USP4 can be degradation through hydrolysis pathway regulated by phosphorylated DNPEP [94]. Here, USP4 is linked to breast cancer.