Suppression of p53R2 gene expression with specific siRNA sensitizes HepG2 cells to doxorubicin.

INTRODUCTION: p53R2 is a p53-inducible protein that contributes to DNA repair by providing dNTPs in response to DNA damage. The roles of p53R2 in cancer cells and malignancies still remain controversial. Herein, we examined the effects of p53R2 silencing on HepG2 human hepatocellular carcinoma (HHC) cell line (wild-type p53) viability, apoptosis and cell cycle arrest in the presence and absence of doxorubicin.

METHODS: Cell transfection was performed using a liposomal approach. Gene silencing was determined by quantitative real-time PCR and western blot analysis. To evaluate the cell growth rate after transfection, trypan blue dye exclusion assay was employed. The cytotoxicity of the doxorubicin and p53R2 siRNA as single agents or in combination against HepG2 cell was analyzed by MTT assay and the drug combination effects was evaluated by calculating the combination index. The effects of treatments on different stages of cell cycle were analyzed by flow cytometry using propidium iodide (PI) and induction of apoptosis was assessed using DNA-histone ELISA.

RESULTS: We found that silencing of p53R2 alone had a strong effect on growth inhibition and spontaneous apoptosis in HepG2 cells. p53R2 siRNA synergistically enhanced the cytotoxic effect of doxorubicin. Furthermore, when used in combination with doxorubicin (0.4μM), a significant increase in the rate of apoptosis was observed (P<0.05). Moreover, cell cycle at S and G2/M phases progressed at a lower rate after p53R2 combination treatment compared with doxorubicin mono-therapy.

CONCLUSION: These findings suggest that siRNA-mediated silencing of p53R2 has great potential as a therapeutic tool and adjuvant in chemotherapy.