Targeting of β-Catenin Reverses Radioresistance of Cervical Cancer with the <i>PIK3CA</i> -E545K Mutation

Abstract

This study aims to explore whether E545K, the most common hotspot mutation of <i>PIK3CA</i> in cervical cancer, confers radioresistance to cervical cancer cells, to demonstrate the underling mechanism, and to develop the effective targets. SiHa and MS751 cells with <i>PIK3CA</i>-WT and <i>PIK3CA</i>-E545K were established by lentiviral transfection. The radiosensitivity was assessed by colony formation, cell cycle, cell apoptosis, DNA damage, and repair assay. The growth and immunohistochemical assay of xenograft tumor-related toxicity were evaluated <i>in vivo</i> It was indicated that more cells with <i>PIK3CA</i>-E545K arrested in S phase. Irradiation (IR) led to more survival percentage, less apoptosis, fewer pH2A.X foci, and higher expression of Chk1/2 in SiHa and MS751 cells bearing <i>PIK3CA</i>-E545K. Mechanically, AKT/GSK3β/β-catenin pathway was highly activated, and more β-catenin was found accumulated in nucleus in cells with <i>PIK3CA</i>-E545K after IR. Furthermore, targeting β-catenin by shRNA or XAV939 enhanced IR sensitivity in cells with <i>PIK3CA</i>-WT and <i>PIK3CA</i>-E545K, whereas it was more notably in the latter. β-Catenin shRNA and XAV939 increased IR-mediated inhibition of colony formation with highly activated p53/bcl2/bax pathway. XAV939 enhanced IR-caused apoptosis, DNA damage, overcame S-phase arrest, DNA repair and reversed β-catenin nuclear accumulation in MS751 cells with <i>PIK3CA</i>-E545K. <i>In vivo</i>, XAV939 enhanced the radiosensitivity of cervical cancer xenografts with <i>PIK3CA</i>-E545K with invisible viscera toxicity. The findings demonstrate that cervical cancer cells with <i>PIK3CA</i>-E545K are resistant to IR by enhancing the expression and nuclear accumulation of β-catenin. Targeting β-catenin reverses the radioresistance, which suggests possible areas for preclinical research on β-catenin inhibition for strengthening the radiosensitivity of cervical cancer.