Functional genomics as a window on radiation stress signaling.

Exposure to ionizing radiation, as well as other stresses, results in the activation of complex signal transduction pathways, which eventually shape the response of cells and organisms. Some of the important pathways responding to radiation include the ATM/P53 pathway, MAPK cascades and NF-kappaB activation, as well as signaling events initiated at the cell membrane and within the cytoplasm. Alterations in gene expression play roles both as intermediaries in signaling and as downstream effector genes. Differences in cell type, interindividual genetic differences and crosstalk occurring between signaling pathways may help to channel radiation stress signals between cell cycle delay, enhanced DNA repair, and apoptosis. These differences may in turn help determine the likelihood of late effects of radiation exposure, including carcinogenesis and fibrosis. The tools of the postgenomic era enable high-throughput studies of the multiple changes resulting from the interplay of radiation signaling pathways. Gene expression profiling, in particular shows great promise, both in terms of insight into basic molecular mechanisms and for the future hope of biomarker development and individual tailoring of cancer therapy.