USP15 and glioblastoma: The antagonistic actions between ubiquitin ligases and DUBs are responsible for protein homeostasis as exemplified that USP13-FBXL14 regulated reversible ubiquitination of c-Myc in glioblastoma stem cells [59], and USP15-SMURF2 cooperatively modulated TGF-β receptor in glioblastoma [60].