Rapid Cellular Signalling and Dose Dependent Cellular Pathways Induced in HPV-G Cells Exposed to Medium Borne Factors

The aim of this thesis was to investigate rapid signalling events and dose dependent activation of cellular pathways in unirradiated human keratinocyte (HPV-G) cells exposed to bystander signal molecules in vivo and in vitro. HPV-G cells were exposed to irradiated cell conditioned medium (ICCM) ranging from 5mGy to 5Gy ICCM. Cellular events investigated included intercellular calcium, reactive oxygen species (ROS), mitochondrial membrane potential, cytochrome c release, caspase 3 and 8 activity, Bcl-2 expression and mitochondrial proliferation. Apoptosis levels and clonogenic survival were also determined in order to understand the cellular outcome of the activated pathways. It was found that exposure of HPV-G cells to ICCM induces rapid signalling events, hence eliminating the role of protein transcription in the initial response to the ICCM signal. Downstream cellular responses were observed to occur in a Bcl-2/caspase dependent manner, with the mitochondria being a pivotal organelle in both pathways. The in vivo studies showed that the response of tissue/cells to radiation is strongly controlled by genetic factors. This study has shown the rapid activation of cellular responses to low dose radiation and therefore stresses the need for an increased knowledge of radiation induced bystander effects.