Rita Enhances Radiosensitivity Mainly Via S100a9 Through A P53-Independent Way In Squamous Cell Cervical Cancer Cells

This study is to explore the relationship among small-molecule reactivation of p53 and induction of tumor cell apoptosis (RITA), p53 and S100A9, and its impact on radiotherapy (RT) on squamous cell cervical cancer cells. Several published p53 mutations were introduced into Caski cells. Expression of wild type p53 (wtp53) was measured. Caski cells under different p53 status were respectively treated with RITA, radiotherapy (RT), RITA+RT, with untreated cells as the control. Cell apoptosis, proliferation and invasion were measured with or without S100A9 knockdown. We found that mup53 273 R-H but not mup53 183 S-A could inhibit the expression of wtp53. RITA alone or in synergy with RT induced apoptosis and inhibition of cell proliferation and invasion in Caski cells. The effects were not significantly affected by knockdown of p53 by p53-shRNA or mup53 273 R-H. On the other hand, the expression of S100A9 at both the RNA and the protein levels was significantly enhanced by RITA and wtp53, and inhibited by p53 273 R-H and p53-shRNA but not p53 183 S-A. Knockdown of S100A9 abolished RITA-induced apoptosis and inhibition of cell proliferation and invasion in the RITA group and markedly decreased the enhancing effect of RITA on RT in the RITA+RT group. Promoter/luciferase reporter assays revealed that while wtp53 significantly enhanced the S100A9 gene promoter activity, mup53 273 R-H but not mup53 183 S-A significantly inhibited it. Although having no significant effect on the S100A9 gene promoter activity, RITA markedly increased the stability of S100A9 mRNA in Caski cells. RITA alone or in synergy with RT induces apoptosis and inhibition of cell proliferation and invasion in Caski cells mainly through inducing the expression of S100A9 by increasing its mRNA stability. This is a p53-independent mechanism that does not rely on p53-induced transactivation of the S100A9 gene promoter/transcription. It adds new insights into the pharmacological potential of RITA alone or in combination with radiotherapy on treatment of cervical cancer.