Regulation of cell death

We begin our discourse on cell death with a summary of the tools and the components of the machinery that carry out the CD programme. We shall see that, despite a bewildering variety of new names, regulation of the apoptosis pathways has basic features in common with other cellular signalling pathways. 

The apoptotic machinery is controlled, like the cell cyde, by internal and external signals. External signals are received by receptors. The receptors that trigger apoptosis are called death receptors. Alfhou they may participate in other cellular signal transduction pathways, when they interact with death ligands they activate death effectors. The effectors are the caspases, a family of C5 teine proteases which eventually destroy the cell. 

Like other receptors, death receptors are activated by binding ligands. The activated death receptor-ligand complex is linked with its death domain (DD) to a homologous DED (death effector region), repeated in tandem, and recruits a zymogen form of a protease, pro-caspase 8 (Fig. 13.1). But the linker is, like other linkers, versatile. 

1 The CD95-liganded death receptor with the intracellular death domains (DDs) binds to the death effector domain (DED) which links the receptor-ligand complex to the procaspase 8. Cell denotes the cell boundary. (Based on the information in Rg. 1 of ref. 5 and reproduced with permission of the authors and Science.) 

Decoy receptors divertthe ligand and prevent apoptosis 

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