Abstract
Bortezomib, a proteasome inhibitor, proved potent in the treatment of recurrent multiple myeloma or mantle cell lymphoma. However, slow progress was made when it was applied to treat solid tumors. We discovered that different head and neck squamous cell carcinoma (HNSCC) cell lines had significantly different sensitivities to bortezomib, and also demonstrated that individual relatively sensitive HNSCC cell lines had fewer ΔNp63α expressions. Based on these findings, we speculated that ΔNp63α may be a key factor in the resistance of HNSCC cells to bortezomib. ΔNp63α knockdown made HNSCC more sensitive to bortezomib, while ΔNp63α overexpression made it more resistant. RNA sequencing (RNA-seq) analysis of ΔNp63α-knockdown cells revealed clear alterations in the subset of genes that were associated with oxidative stress and antioxidant defense. The gene CYGB was downregulated significantly. CHIP-seq detection showed that CYGB was the transcriptional regulatory site of ΔNp63α. CHIP-PCR showed evidence of ΔNp63α binding. The detection of the dual-luciferase reporter gene demonstrated that ΔNp63α significantly enhanced the CYGB promoter activity. Furthermore, we confirmed that CYGB plays a role in clearing excess ROS induced by bortezomib to inhibit HNSCC apoptosis. Consequently, ΔNp63α regulated the expression of CYGB in HNSCC. CYGB was the target of transcription regulation of ΔNp63α. It reduced apoptosis by clearing excess ROS produced by bortezomib, and thus exerted drug resistance.