Noticeably, we found that in addition to post-transcriptional regulation of Bmi1 expression by PTC-209 [22], the proteasomal degradation might be partially responsible for PTC-209-mediated Bmi1 downregulation in HNSCC as evidenced by the attenuation of Bmi1 loss by MG132 addition following PTC-209 treatment and increased ubiquitination of Bmi1 after PTC-209 exposure. This evidence concerns the gene BMI1 and head and neck squamous cell carcinoma.