Calcium-activated DNA fragmentation kills immature thymocytes.
Glucocorticoid hormones kill immature thymocytes by activating a self-destructive process that involves extensive DNA fragmentation. It has been demonstrated that thymocyte suicide is dependent on an early, sustained increase in cytosolic Ca2+ concentration, and new protein synthesis, but the biochemical lesion that leads to cell death has not been established. To determine whether endonuclease activation or activation of another Ca2+-dependent process could mediate cell killing, we treated thymocytes with the glucocorticoid methylprednisolone in the presence of inhibitors of various Ca2+-dependent degradative enzymes. The role of poly(ADP-ribose) polymerase, an enzyme known to be activated by DNA damage, was also assessed. Glucocorticoid-induced chromatin cleavage and cell killing were blocked by the endonuclease inhibitor aurintricarboxylic acid, whereas inhibitors of other Ca2+-dependent degradative processes or of poly(ADP-ribose) polymerase did not abrogate cell death. In addition, stimulation of thymocyte DNA fragmentation by the Ca2+ ionophore A23187 resulted in cell killing that could be blocked by the endonuclease inhibitor. Together, our results suggest that thymocyte suicide is caused by extensive Ca2+-stimulated DNA fragmentation.
McConkey
D J
DJ
Department of Toxicology, Karolinska Institutet, Stockholm, Sweden.
Hartzell
P
P
Nicotera
P
P
Orrenius
S
S
D000818:Animals; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology*; D002470:Cell Survival; D004249:DNA Damage; D005938:Glucocorticoids / Q000494:pharmacology; D008297:Male; D013950:Thymus Gland / Q000166:cytology / Q000187:drug effects / Q000502:physiology*
D005938:Glucocorticoids; D000001:Calcimycin; D002118:Calcium