Endogenous endonuclease-induced DNA fragmentation: an early event in cell-mediated cytolysis.

Abstract

Within minutes of exposure of target cells to cytotoxic T lymphocytes, their nuclear DNA begins to be fragmented. This phenomenon precedes 5"Cr release by at least an hour. DNA fragmentation occurs only when appropriately sensitized cytotoxic T cells are used and is not merely a result of cell death because killing of target cells by heating, freeze/thawing, or lysing with antibody and complement did not yield DNA fragments. Agarose gel electrophoresis of target cell DNA showed discrete multiples of an approximately 200-base-pair subunit, suggesting that fragmentation was the result of activation of a specific endonuclease. A similar pattern of DNA fragments is observed during glucocorticoid-induced killing of mouse thymocytes. The endonuclease in that case is inhibited by zinc ions, and we find that Zn2+ also inhibits DNA fragmentation and 51Cr release induced by cytotoxic T cells, suggesting a final common biochemical pathway for both types of cell death.

The transcriptional repressor ICER and cAMP-induced programmed cell death

“…Cells treated with PGE1 show high sensitivity with an IC 50 of 0.2 mM (Figure 1c). PGE 1 also causes DNA fragmentation (Figure 1d lower panel) typical of apoptosis as described in other cells (Duke et al, 1983;McConkey et al, 1990).…”

Extracellular ATP as a trigger for apoptosis or programmed cell death.

“…The morphological changes associated with ATP-induced apoptosis are blocked in thymocytes by the inhibitors of macromolecular assembly, cycloheximide and actinomycin D. Likewise, ATP-mediated DNA fragmentation in EL4 cells is suppressed by inhibitors of transcription as well as by zinc, an endonuclease inhibitor (6,8,10). The extent of fragmentation is not directly proportional to the ATP concentration, however, as the fragmentation decreases when the ATP concentration is increased beyond 0.5 mM.…”

How apoptosis got the immune system in shape

“…In the 1980s the field was divided by two opposing hypotheses, one advocating colloid osmotic lysis as a result of pore formation in the target cell similar to complementmediated lysis [73], and the other supporting active induction of programmed cell death, the concept of which was just making its debut in the world of immunology. The first concrete evidence for killing by apoptosis rather than passive osmotic lysis came from a study that observed rapid DNA fragmentation by an endogenous endonuclease after exposure of target cells to CTL [74]. Earlier studies using electron microscopy had described extensive nuclear changes and surface blebbing in target cells, results that had, in retrospect, hinted at apoptosis [75].…”