Apoptosis and other effects of radiation in normal human urothelial cells
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In this paper, an attempt is made to identify endpoints that might be of potential use in the quantification of radiation effects in human tissues. Irradiated cultures of cells that are not selected for clonogenic survival but are left in situ to grow after irradiation show a wide variety of morphological and biochemical abnormalities. These include nuclear fragmentation and other evidence of programmed cell death, but they also include a considerable amount of lysis, necrosis, and persistent abnormal growth and function, which are expressed in the progeny of irradiated cells. Induction of proteins associated with stress or shock responses, growth and cell cycle control, and control of apoptosis are also seen and may persist. The dose dependence of these various responses is documented, because it probably determines to a large extent the outcome of radiation exposure in terms of whether a cell dies, divides normally, or develops genomic instability, mutation, and ultimate carcinogenic progression of the progeny. Clearly, a cell that dies presents no further threat to the organism, nor does a fully repaired cell. Therefore, a major challenge facing radiation protection research is to define the population at risk of surviving with damage. The results show that there is a variation in response to radiation between different patient cultures that is detectable in an explant culture system of primary normal human urothelium. The growth pattern and protein expression postirradiation is consistent with apoptosis being a major determinant of low dose response to radiation. This form of death appears to be suppressed at higher doses and, in the majority of subjects, results in the presence of a highly abnormal population of cells, even though the population size is the same whether their progenitors were irradiated or not.