The Alleviating Effects Of Genistein On Ionizing Radiation-induced DNA Damage And Its Molecular Mechanisms

With the rapid development of radiotherapy,nuclear industry and more people using mobile phone and computer,there are more and more opportunities for exposure to radiation. Radiation has become the forth largest pollution following air,water and noise pollution. How to alleviate radiation-induced damages has become the key issue for radiotherapy in clinic and in people’s daily life.Genistein(GEN) is one of the main components of soy isoflavones, which has a variety of biologically activity such as antioxidant and estrogen, etc. In recent years, studies have shown that GEN has radioprotective effects, but its molecular mechanisms are less studied. This paper focuses on the study of alleviating effects of GEN on ionizing radiation-induced damage and its mechanism as follows:Firstly,we have proven that GEN could significantly improve the cell proliferation and alleviated DNA damage in previous study in our group. Hence, we further to observe GEN’s impacts on cell cycle and apoptosis after human hepatocytes L-02 irradiated with X ray. The results revealed that low concentrations of GEN(1μM, 5μM) could reduce cell apoptosis, and enhanced G2/M arrest at 24 and 48 h after irradiation.Secondly,our preliminary animal and cell experiment has shown that GEN could regulate the expression of some endoplasmic reticulum stress(ERS) genes and DNA damage repair genes at mRNA level. Here,we further to detect the expression of some important genes at protein level with Western blotting. The results suggested that low concentrations of GEN(1μM, 5μM) could up-regulate the expression of HERPUD1, which is cell apoptosis related protein; HHR23 A and HHR23 B were upregulated at different time point after irradiation, which are DNA damage repair proteins.Thirdly,DNA Damage Signaling Pathway chip was utilized to detect the impacts of GEN on the expression of other DNA damage repair related genes. The results showed that 5μM GEN group significantly increased the expression level of HUS1 and PMS2, and lowered the expression of MPG at 48 h after irradiation, which is another patyway of GEN promoting DNA damage repair and reduced cell radiosensitivity.Finally, we found that GEN could significantly increase the expression of HERPUD1(ER stress protein) in our previous cell and animal experiments, therefore we selected HERPUD1 as our target gene to further study whether it is one of the key genes related with GEN’s radiation protection bio-activity. L-02 cells were stably transfected with RNAi HERPUD1 to silence its expression,then cell proliferation,cell apoptosis,cell cycle and DNA damage were detected at different time points after irradiation. The results indicated that the silencing of HERPUD1 inhibited L-02 cell proliferation,significantly enhanced DNA damage at 24 h and 72 h after irradiation,increased L-02 cell apoptosis,and induced G0/G1 arrest after ionizing radiation. That suggests that HERPUD1 is one of the key proteins of GEN exerting its bio-activity of alleviating ionizing radiation-induced apoptosis and promoting DNA repair.