A. b-AP15 showing cytotoxic effect on NB cells. Six NB cell lines IMR-32, NGP, SK-N-BE2, SH-SY5Y, SK-N-AS, and LAN-6 were incubated with serial dilutions of b-AP15 or medium alone for 72 hours. Cell Counting Kit-8 (CCK-8) assay was used to determine cell viability. B. IC50 values of six cell lines tested were measured based on CCK-8 assay. C. Morphological changes of six NB cell lines after incubation with serial dilutions of b-AP15 for 72 hours were shown. D. Two USP14-knockdown cells, NGP and SH-SY5Y, were harvested, and subjected to immunoblotting with anti-Lys48-linked specific antibody. Same amounts of lysates were performed Coomassie Blue staining as loading controls. E. NGP and SH-SY5Y cells were treated with b-AP15 (1 μM) for the indicated time points. Cell lysates were subjected to immunoblotting as the above. F, G. USP14 knockdown NGP and SH-SY5Y (F) cells or b-AP15 treated NB cells (G) were subjected to immunoblotting with anti-HSP40, HSP70, and USP14 antibodies.