Radiation induces autophagic cell death via the p53/DRAM signaling pathway in breast cancer cells

Abstract

Autophagy is known to play a role in the response of breast cancer cells to radiation therapy. However,the mechanisms that mediate the process of autophagy and contribute to radiation-induced cell death and cell survival remain to be fully characterized. Therefore,in this study,the functional role of autophagy in radiation-induced cytotoxicity in breast cancer cells was investigated. After MCF-7 cells were exposed to various doses of radiation,increased monodansylcadaverine (MDC) staining and a greater deposition of LC3-positive puncta were observed. Expression of the autophagy-related proteins,Beclin 1 and LC3-II,were also found to be upregulated. Radiation-induced autophagic cell death was partially abrogated following the administration of 3-methyladenine (3-MA) and in knockdown experiments of Atg5 and Beclin 1. In the gene microarray analysis performed after irradiation,a number of differentially expressed genes were identified. In particular,upregulation of both the mRNA and protein levels of the autophagy-related genes,DRAM and TIGAR,were detected. However,inhibition of autophagy by 3-MA reduced the radiation-induced upregulation of LC3-II and DRAM. Conversely,silencing of p53 downregulated the expression of LC3-II and DRAM following radiation. Silencing of DRAM reversed the upregulation of LC3-II and DRAM following radiation,partially blocked radiation-induced cell death,and no significant change in p53 expression was detected. Based on these results,the p53/DRAM signaling pathway appears to contribute to radiation-induced autophagic cell death in MCF-7 breast cancer cells.