High Yields of Lethal Mutations in Somatic Mammalian Cells that Survive Ionizing Radiation

Abstract

When mammalian cells are irradiated in vitro, the component cells of a normal-appearing survivor colony or clone are commonly thought to have proliferative capacity equivalent to that of the unirradiated cells. We have found, however, that cells appearing in survivor colonies may carry heritable lethal defects which come to light, perhaps only after numerous successful divisions, in the form of plating efficiencies that are reduced below those of unirradiated cells in a dose-dependent manner. We regard these heritable defects as signs of the induction of lethal mutations, which, like non-lethal mutations, may require many generations before they are expressed. This effect has been noted in two very dissimilar mammalian cell lines, one a primary culture from adult tissue, the other an immortal cell line. We suggest that induction of lethal mutations may occur also in somatic cells in vivo; this would account for the well-known observation that previously irradiated but apparently healed tissue is subsequently proved to be extraordinarily sensitive to subsequent exposure to irradiation or cytotoxic drugs. The results of our experiments in vitro suggest that current methods of estimating mutation or transformation yields may yield underestimates. If lethal mutations are induced also in vivo, interpretations of the results of fractionation experiments on normal tissues may have to be reconsidered.

Delayed chromosomal instability induced by DNA damage.

“…Although the observed induction of gross chromosome rearrangements in these clones did not influence the reciprocal exchange of homologous DNA sequences between sister chromatids, it is reasonable to assume that delayed chromosomal instability plays a significant role in gene mutation (7,16,32,40), gene amplification (17,18,33,38,50), cellular transformation (26,28), teratogenesis (15,35), and even carcinogenesis (13,30) after exposure of cells to DNA-damaging agents.…”

“…Some examples are delayed reproductive cell death in cells surviving X irradiation (6-9, 32, 40), delayed mutation in cells exposed to the alkylating agent ethyl methanesulfonate (44) or to X irradiation (7,32,40), and delayed chromosomal instability in cells surviving exposure to ionizing radiation (20,23,26,39). In all cases the cells initially survived exposure to the DNA damage and were capable of reproductive cell proliferation.…”

Effects of hTERT on metal ion-induced genomic instability

“…This phenomenon, usually characteristic of radiation exposure (Seymour et al, 1986;Kadhim et al, 1992), resulted in a persistent reduction in clonogenic survival and increase in chromosome aberrations in the distant progeny of cells which appeared to have completely recovered from the exposure. Genomic instability induced by agents other than metals is influenced by telomerase including hTERT and/or telomeres in a number of species including yeast, plants, mice and cultured human cells (Sabatier et al, 1994;Blasco et al, 1997;Hackett et al, 2001;Cui et al, 2002).…”

Radiation-induced genomic instability and bystander effects: inter-related nontargeted effects of exposure to ionizing radiation

“…In addition, it has been apparent for many years that radiation-induced cytotoxicity, defined as loss of reproductive potential, may be delayed for up to six generations of cell replication (Puck and Marcus, 1956;Elkind and Sutton, 1959;Trott and Hug, 1970) with death occurring randomly among the progeny cells (Thompson and Suit, 1969). More recently, the progeny of irradiated cells have been shown to exhibit an enhanced death rate and loss of reproductive potential that persists for many generations and possibly indefinitely in established cell lines (Seymour et al, 1986;Gorgojo and Little, 1989;Little et al, 1990;Seymour and Mothersill, 1992;Brown and Trott, 1994;. The terms lethal mutations and delayed reproductive death are used interchangeably for this delayed death phenotype.…”