Tumor necrosis factor-alpha (TNF) is a cytokine that participates in a variety of physiologic processes, most notably the inflammatory response, which results in host defense and the deleterious effects of chronic inflammation. Recent data indicate that TNF is produced and released by normal monocytes and human tumor cells following ionizing radiation exposure. The radiobiological significance of TNF is that it produces radioprotection that is specific for hematopoietic cells, but sensitizes human tumor cells and fibroblasts to killing by x-irradiation These findings have potential clinical implications, because of the direct effects of TNF and the enhanced cell killing by the interaction between TNF and radiation. Preliminary data indicates that TNF gene induction following x-irradiation occurs primarily at the level of transcription. X-ray induced TNF transcription is blocked when protein kinase C (PKC) is inhibited or depleted implicating this signaling pathway in radiation-induced TNF production. We propose to study the mechanisms of radiation-induced TNF transcription by using deletion analysis of the TNF gene promoter. We propose to study the role of PKC in the transcriptional activation of TNF following irradiation by transfecting the gene encoding different isoforms of PKC into cell variants that are deficient in PKC. We will also study the mechanisms of radiation-induced PKC activation by analyzing known PKC signalling pathways. Determining the signalling pathways that initiate radiation-mediated TNF transcription will identify means to attenuate TNF production during radiotherapy and the potentially associated adverse sequelae.
