Apoptosis is a morphologically defined form of programmed cell death (PCD) that is mediated by the activation of members of the caspase family. Analysis of death-receptor signaling in lymphocytes has revealed that caspase-dependent signaling pathways are also linked to cell death by nonapoptotic mechanisms, indicating that apoptosis is not the only form of PCD. Under physiological and pathological conditions, cells demonstrate a high degree of flexibility in cell-death responses, as is reflected in the existence of a variety of mechanisms, including necrosis-like PCD, autophagy (or type II PCD), and accidental necrosis. In this review, we discuss recent data suggesting that canonical apoptotic pathways, including death-receptor signaling, control caspase-dependent and -independent cell-death pathways.Key words: apoptosis, necrosis, nonapoptotic programmed cell death, death receptors, ceramides.
Hedgehog Inhibition Promotes a Switch from Type II to Type I Cell Death Receptor Signaling in Cancer Cells