UBD and head and neck squamous cell carcinoma: UBA6 is a dual‐activity E1s enzyme that activates both ubiquitin and the ubiquitin‐like protein FAT10, which targets proteins for rapid proteasomal degradation.[37] However, we observed no significant effect of squamocin treatment on FAT10 modification in these two HNSCC cell lines (Figure S6C, Supporting Information).