14-3-3s Contributes to Radioresistance By Regulating DNA Repair and Cell Cycle via PARP1 and CHK2

14-3-3s has been implicated in the development of chemo and radiation resistance and in poor prognosis of multiple human cancers. While it has been postulated that 14-3-3s contributes to these resistances via inhibiting apoptosis and arresting cells in G2-Mphase of the cell cycle, the molecular basis of this regulation is currently unknown. In this study, we tested the hypothesis that 14-3-3s causes resistance to DNA-damaging treatments by enhancing DNA repair in cells arrested in G2-M phase following DNA-damaging treatments. We showed that 14-3-3s contributed to ionizing radiation (IR) resistance by arresting cancer cells in G2-Mphase following IR and by increasing non-homologous end joining (NHEJ) repair of the IR-induced DNA double strand breaks (DSB). The increased NHEJ repair activity was due to 14-3-3s-mediated upregulation of PARP1 expression that promoted the recruitment of DNA-PKcs to the DNA damage sites for repair of DSBs. On the other hand, the increased G2-M arrest following IR was due to 14-3-3s-induced Chk2 expression. Implications: These findings reveal an important molecular basis of 14-3-3s function in cancer cell resistance to chemo/radiation therapy and in poor prognosis of human cancers. (C) 2017 AACR.