Cellular signaling in cell death.

Apoptosis is a process of selective cell deletion involving endogenous endonuclease activation that mediates most examples of programmed cell death. Recent work has demonstrated that the process is regulated within the dying cell by signal transduction pathways, including increases in cytosolic ionized calcium concentrations, activation of protein kinases A and C, and stimulation of the nuclear enzyme poly(adenosine 5'-diphosphate-ribose) polymerase. In addition, oncogenes, tumor suppressor genes, and transcription factors also regulate induction of cell death. Evidence also indicates that apoptosis mediates a number of instances of pathologic cell death and, in some of these examples, the biochemical mechanisms responsible appear to mimic the cell-signaling mechanisms controlling the process in physiologic situations.