A recent paper reported USP15 as a DUB antagonizing ubiquitination of GS.[37] However, in our study, USP15 knockout did not decrease GS protein in GBM cells (Figure S4G, Supporting Information), whereas genetic ablation of USP9X decreased GS in GBM and ovarian cancer (Figure 3I; Figure S4D,E, Supporting Information). Here, USP15 is linked to ovarian cancer.