Radiosensitization of esophageal carcinoma cells by knockdown of RNF2 expression

Radiotherapy has been widely used for the treatment of cancer patients, especially for esophageal cancer patients. Ring finger protein 2 (RNF2) plays an important role in promoting the growth of cancer cells after exposure to irradiation. The present study aims to characterize the proliferative effects of RNF2 on cancer cells, and its mechanisms on the growth of esophageal cancer cells. We demonstrate that expression of RNF2 was markedly upregulated in esophageal cancer cell lines and surgically resected cancer specimens. In addition, RNF2 expression level is positively correlated with the presence of tumor size, lymph node metastases and negatively correlated with patient survival rates, suggesting that it plays an important role in the progression of esophageal cancer. Furthermore, the expression of RNF2 at both mRNA and protein levels in esophageal cancer ECA109 and TE13 cells was detected by real-time PCR and western blot assay after shRNA targeting RNF2. Co-immunoprecipitation (Co-IP) assay and western blot analysis were employed to detect the interaction between RNF2 and r-H2AX, H2AK119ub, and the expression of proteins associated with cell cycle and apoptosis, respectively. We used flow cytometry assay to analyze cell cycle and apoptosis of transfected cells, and further examined cellular growth in vitro and in vivo. shRNA targeting RNF2 gene and protein downregulated RNF2 expression after transfection for 24 h. The proliferation of tumor cells in RNF2-shRNA group was suppressed after radiotherapy. In addition, the interaction of RNF2, H2AK119ub, r-H2AX was increased after exposure to IR, followed by increasing apoptosis rates and inducing the arrest at G0/G1 phase after irradiation and shRNA targeting RNF2. Expression of the short-hairpin RNA is also correlated with the upregulation of p16 and Bax, and the downregulation of cyclin D2, cyclin-dependent kinase (CDK)-4, H2AX and Bcl-2. RNF2 gene knockdown induces radiosensitivity of esophageal cancer cells in vitro and significantly inhibits the growth of tumor cells. The mechanisms include inducing the cell cycle arrest at G0/G1 phase and promoting apoptosis.