Relationship of ROS and NO in X　ray Induced Bystander Effects in HeLa Cells

Key words: 
• bystander effect /
• reactive oxygen species /
• nitric oxide /
• inducible nitric oxide synthase /
• X ray

Abstract: Accumulating evidence indicates that irradiated cells can release signals which induce a series of biological responses in nonexposed cells. This is known as irradiationinduced bystander effects. Both reactive oxygen species(ROS) and nitric oxide(NO) play important roles in bystander effects. In this study， we determined the relationship of ROS and NO in the signaling pathway of bystander effects. HeLa cells were treated with or without dimethye sulfoxide(DMSO) before Xray irradiation， and micronuclei formation as well as cell proliferation rate was detected in both irradiated and bystander cells. In addition， we also detected inducible nitric oxide synthase(iNOS) expression and NO level in irradiated cells using Western blotting and DAFFM DA fluorescent probe， respectively. Our results showed that micronuclei were induced in irradiated and bystander cells while DMSO treatment significantly suppressed the formation of micronuclei in both of them. We also found that when cells were irradiated their proliferation rate was suppressed while DMSO treatment eliminated this inhibition effect. In contrast， the cells received conditioned medium from irradiated cells proliferated more quickly than the cells received medium from non irradiated cells while DMSO treatment reduced the difference. Finally， we found that irradiated cells had higher level of iNOS and NO compared to nonirradiated controls， whereas DMSO treatment decreased their levels. These results suggest that ROS is the upstream signal of NO in Xray induced bystander effects in HeLa cells.