Knockout of STUB1 using two independent sgRNAs led to a marked increase in CTSL protein levels in HNSCC cell lines HN8 and FaDu (Figure 4A), whereas CTSL mRNA levels remained unchanged (Figure S2H), indicating that STUB1 negatively regulates CTSL at the post‐transcriptional level. The gene discussed is STUB1; the disease is head and neck squamous cell carcinoma.