SELENITE INDUCTION OF DNA STRAND BREAKS AND APOPTOSIS IN MOUSE LEUKEMIC L1210 CELLS

The effects of selenite on DNA integrity, cell viability, and long-ter m proliferative potential of mouse leukemic L1210 cells were examined in this study. Selenite treatment resulted in concentration-dependent increases in DNA single-strand breaks and double-strand breaks, as det ected by a modified filter elution assay. A time-course experiment sho wed that DNA single-strand breaks preceded DNA double-strand breaks. A garose gel electrophoresis of DNA extracted from selenite-treated cell s displayed a nucleosomal fragmentation pattern that is characteristic of apoptotic cell death. The involvement of a Ca2+,Mg2+-dependent end onuclease responsible for DNA double-strand fragmentation was implied by the observation that two inhibitors of endonuclease activity, i.e. aurintricarboxylic acid and zinc, blocked selenite-induced DNA double- strand breaks. These inhibitors also prevented selenite-induced cell d eath as defined by loss of ability to exclude trypan blue dye. Selenit e treatment severely impaired the colony-forming ability of cells capa ble of trypan blue exclusion. The induction of DNA strand breaks and c ommitment to apoptosis may explain the selenite-mediated growth inhibi tion and loss of long-term proliferative potential.