Analysis of radiation- and chemical-induced bystander effects in normal human lymphoblastoid cells

My Ph.D. dissertation work has focused on studying the signaling pathways involved in bystander effects induced by chemicals and ionizing radiation. Bystander effects have been studied extensively using ionizing radiation; however few studies have evaluated the ability of other agents, such as chemicals, to induce similar effects. Radiation-induced bystander effects refer to damage seen in cells that have not been directly exposed to radiation. Mitogen-activated protein kinase (MAPK) pathways have been shown to play an important role in radiation-induced bystander effects. These pathways have also been shown to be involved in general stress responses. I thus hypothesized that bystander effects are not restricted to radiation and that other DNA damaging agents could also induce these effects, and that the bystander effects induced by these various agents would all predominantly involve the same MAPK pathways.;Bystander effects were evaluated in normal lymphoblastoid cells exposed to chemicals or radiation using the micronucleus assay. These findings indicated that the chemicals mitomycin C and phleomycin were capable of inducing bystander effects in the cell lines used. We also confirmed the occurrence of radiation-induced bystander effects in these cell lines.;The involvement of MAPK proteins in bystander effects were evaluated by measuring the phosphorylation levels of MAPK proteins and caspase 3/7 activity following MAPK inhibition. The results indicated a transient, initial, increase in protein phosphorylation. Inhibition of the proteins resulted in an initial decrease followed by a return to basal levels or an increase in caspase activity.;The expression changes of MAPK target genes were evaluated in the next part of my project. The genes chosen were specific targets of each of the three MAPK pathways. The results indicated changes in gene expression in response to chemical- and radiation-induced bystander effects.;Overall, this work provides strong evidence for the occurrence of bystander effects by agents other than ionizing radiation and indicates the involvement of common signaling pathways in chemical- and radiation-induced bystander effects. An understanding of the molecular mechanisms involved in bystander effects might help us develop more efficient cancer treatment regimens that could focus on amplifying the tumor cell killing signals, will limiting the damage to naive bystander cells.