Radio-Adaptive Response: A Novel Chromosomal Response in Chinese Hamster Cells in Vitro
When exposed to various DNA damaging stresses, a variety of prokaryotic and eukaryotic cells exhibit induction of an adaptation mechanism. The adaptive response was first reported by Samson and Cairns (1977) in Escherichia coli as an inducibile form of DNA repair acting on alkylation damage, in which the bacterial cells that had been exposed to low levels of alkylating agents became less susceptible to the subsequent high doses of the same and other compounds. In this adaptive response, the induction of adaptation proteins, DNA glycosylase and DNA alkyltransferase are involved (Karran et al. 1979; Evensen and Seeberg 1982), which is distinct from the SOS response, another inducible effect resulting from DNA damage (Jeggo et al. 1977). An analogous adaptive response has also been observed in some higher mammalian systems (e.g., Samson and Schwartz 1980; Laval and Laval 1984) and in higher plants (Rieger et al. 1982). Interestingly, the adaptive response has been recently found to occur in human lymphocytes exposed to low doses of ionizing radiation (Olivieri et al. 1984; Shadley and Wolff, 1987; Sankaranarayanan et al. 1989). A pretreatment with “conditioning” or “adapting” low doses of either tritium β-mys or X-rays resulted in a reduction in the yield of chromosomal aberrations induced by a subsequent (“challenge”) higher dose. Such a clastogenic radio-adaptive response has also been observed in the induction of micronuclei and sister chromatid exchanges (SCEs) in proliferative Chinese hamster V79 cells (Ikushima 1987, 1989), and of chromosomal aberrations in Vicia faba root tip cells (Heindorff et al. 1987). It is now clear that the radio-adaptive response can occur in cells from a rather universal range of eukaryotes. While the network of the adaptive response to alkylating agents in bacteria is well understood at the molecular level (for a review, see Lindahl et al. 1988), very little is known about the mechanisms responsible for the radio-adaptive response in higher eukaryotes.
KeywordsThymidine Tritium Mitomycin Bleomycin Uridine
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