ΔNp63 Regulates Radioresistance in Human Head and Neck Squamous Carcinoma Cells

Radiation therapy is commonly used to treat head and neck squamous cell carcinoma (HNSCC); however, recurrence results from the development of radioresistant cancer cells. Therefore, it is necessary to identify the underlying mechanisms of radioresistance in HNSCC. Previously, we showed that the inhibition of karyopherin- beta 1 (KPNB1), a factor in the nuclear transport system, enhances radiation-induced cytotoxicity, specifically in HNSCC cells, and decreases the localization of SCC-specific transcription factor Delta Np63. This suggests that Delta Np63 may be a KPNB1-carrying nucleoprotein that regulates radioresistance in HNSCC. Here, we determined whether Delta Np63 is involved in the radioresistance of HNSCC cells. Cell survival was measured by a colony formation assay. Apoptosis was assessed by annexin V staining and cleaved caspase-3 expression. The results indicate that Delta Np63 knockdown decreased the survival of irradiated HNSCC cells, increased radiation-induced annexin V+ cells, and cleaved caspase-3 expression. These results show that Delta Np63 is involved in the radioresistance of HNSCC cells. We further investigated which specific karyopherin-alpha (KPNA) molecules, partners of KPNB1 for nuclear transport, are involved in nuclear Delta Np63 expression. The analysis of nuclear Delta Np63 protein expression suggests that KPNA1 is involved in nuclear Delta Np63 expression. Taken together, our results suggest that Delta Np63 is a KPNB1-carrying nucleoprotein that regulates radioresistance in HNSCC.