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Unformatted text preview: from caspase-8 cleavage of the proapoptotic BH3-only protein Bid,
leading to Bid activation, permeabilization of mitochondria, and activation
of caspase-9, thus amplifying the caspase cascade initiated by direct activation of caspase-8 at cell death receptors. Alternative Pathways of Programmed Cell Death
Although apoptosis is the most common form of regulated or programmed
cell death, recent research has shown that programmed cell death can also
occur by alternative, non-apoptotic mechanisms. One of these alternative
pathways of regulated cell death is autophagy. As discussed in Chapter 8,
autophagy provides a mechanism for the gradual turnover of the cell’s
components by the uptake of proteins or organelles into vesicles
(autophagosomes) that fuse with lysosomes (see Figure 8.45). In addition,
autophagy promotes cell survival under conditions of nutrient deprivation.
Under conditions of starvation, activation of autophagy serves to increase
the degradation of cellular proteins and organelles, generating energy and
allowing their components to be reutilized for essential functions.
In other circumstances, however, autophagy provides an alternative to
apoptosis as a pathw...
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