RAC1 and melanoma: As a substrate of Hace1, Rho GTPase Rac1 can be ubiquitylated at lysine 147 by HACE1.10 Many studies have indicated that Rac1 is involved in regulating various biological processes, including cell motility, cell–cell contact, protein translation, and cell growth.11,12 A previous study evidenced that HACE1 ubiquitylated optineurin, thereby suppressing in vitro and in vivo growth of lung cancer cells by activating the autophagy.13 On the other hand, HACE1 also displayed pro-invasive properties in melanoma cells.14 However, its biological function in glioma remains to be determined.