The DNA-PKcs-primary cilia axis maintains ionizing radiation-induced senescence in tumor cells

Senescence is a cellular response closely associated with genotoxic stress and plays a critical role in determining cell fate following irradiation exposure. Primary cilia, which are sensory organelles on the cell surface, detect and transmit diverse signaling cues. However, the relationship between primary cilia and senescence in long-term cell fate decisions after ionizing radiation (IR) remains poorly understood. Here, we show that the DNA-dependent protein kinase catalytic subunit (DNA-PKcs) colocalizes with centromeres during various stages of mitosis, whereas during interphase, phosphorylated DNA-PKcs (p-DNA-PKcs) is confined to the nucleus in tumor cells. Following irradiation exposure, primary cilia are formed and persistently maintained at high levels in senescent tumor cells. Inhibition of DNA-PKcs enhances primary cilia formation, whereas combined inhibition with siDNA-PKcs and irradiation reduces cilia generation. Moreover, chloral hydrate-induced primary cilia removal results in senescent cell death and decreases p-DNA-PKcs protein expression. Notably, treatment with the apoptosis inducer ABT263 also leads to increased cell death and decreased incidence of primary cilia. Inhibition of either primary cilia or DNA-PKcs further enhances the radiosensitivity of tumor cells. These findings suggest that DNA-PKcs contributes to primary cilia formation after irradiation and plays a critical role in both the induction and maintenance of cellular senescence.