Mechanism Of Intracellular And Intercellular Communication Regulating Radiation-induced DNA Damage

Radiation-induced DNA and chromosomal damage have always been the focus of radiobiology.Radiation can not only cause damage to irradiated cells,but can also cause damage to unirradiated bstander cells.Signal communication played an important role in regulating the generation of damage.In this paper,the mechanism of signal communication in radiation-induced cellular DNA and chromosome damage was studied from two aspects:intracellular and intercellular communication.The core of this paper was as follows:1.Intracellular signaling was rapidly activated when cells were irradiated,and,this process played an important role in regulating radiation-induced DNA damage.In this paper,we studied the DNA damage and the mechanism of intracellular signal communication in irradiated normal human fibroblasts.Heme oxygenase 1(HO-1),which was reported to induce anti-inflammatory activity,was upregulated in irradiated cells.Pre-treatment with HO-1 inhibitor protoporphyrin IX zinc(?)exacerbated double strands break formation following exposure to fusion radiation.The expression of cyclooxygenase-2(COX-2)contributed to the upregulation of HO-1,as demonstrated by the result that its inhibitor NS-398 blocked the induction of HO-1 in irradiated cells.It was further clarified that the ATM DNA damage response was activated.It stimulated the phosphorylation of p38 mitogen-activated protein kinase,which was responsible for the upregulation of COX-2 and HO-1.The present results provided novel information on fusion radiation induced biological effects and potential targets for decreasing the health risks.2.Two kinds of intercellular signal communication methods regulated the damage of unirradiated cells:(1)Gap junction was an important pathway for intercellular communication.Connexin43(Cx43)was the most abundant connexin molecule composed of gap junctions.Regulation of Cx43 expression and modification was an effective way to regulate gap junction communication.Src affected Cx43 activity through multiple pathways,however,it was unclear how Src regulated Cx43 to affect intercellular communication and ultimately regulated the generation of DNA damage in bystander cells.In our study,we demonstrated that Cx43 on Tyr265 was phosphorylated by activated Src in a-irradiation HepG2 cells,with the total expression of Cx43 unchanged.After inhibition of the phosphorylation of Cx43 in irradiated cells,the frequency of y-H2AX foci formation in adjacent non-irradiated bystander cells was significantly enhanced.Our further studies showed that autophagy regulated the activity of Src and phosphorylation of Cx43,and the level of autophagy was correlated with the radiation-induced reactive oxygen species(ROS).These results suggested that ROS and autophagy migh play an important role in regulating the Src-Cx43 pathway to affect the production of DNA damage in bystander cells.Our findings give new insights for Cx43-mediated gap junction intercellular communication,as well as the underlying mechanism of radiation-induced bystander effects.(2)Secretion factor was another important pathway for intercellular communication.Nuclear high mobility group box-1 protein(HMGB1)acted as a DNA chaperone with DNA binding and bending activities,when secreted in culture medium.it acted as a signal molecule involved in intercellular communication.Our studies found that HMGB1,secreted by irradiated cells,inhibitd the production of damage in bystander cells.And,the release was regulated by the antioxidant transcription factor NRF2.Further studies found that NRF2 negatively regulated the expression of PCAF.Knockdown of NRF2 led to up-regulation of PCAF,and PCAF acetylated HMGB1 to promote its transfer from nucleus to cytoplasm.In addition,irradiation activated PARP-1 via ROS,further increased the release of HMGB1 by NRF2 knockdown cells.Studies of bystander cells shown that HMGB1 in culture medium inhibited the production of chromosomal damage in bystander cells via the TLR4/p65 pathway.This study demonstrated that HMGB 1-mediated intercellular communication inhibitd the production of chromosomal damage in bystander cells.These results revealed that cell signaling played an important role in the regulation of radiation-induced DNA damage and provided a new understanding of radiation-induced cell damage.