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Executioner Caspases (Caspase 3, Caspase 6 and Caspase 7) Once initiator caspases are activated, they produce a chain reaction, activating several other executioner caspases. Executioner caspases degrade over 600 cellular components [19] in order to induce the morphological changes for apoptosis. Examples of caspase cascade during apoptosis:
Overview of signal transduction pathways involved in apoptosis. Cell death is the event of a biological cell ceasing to carry out its functions. This may be the result of the natural process of old cells dying and being replaced by new ones, as in programmed cell death, or may result from factors such as diseases, localized injury, or the death of the organism of which the cells are part.
Caspase-9 is an enzyme that in humans is encoded by the CASP9 gene.It is an initiator caspase, [5] critical to the apoptotic pathway found in many tissues. [6] Caspase-9 homologs have been identified in all mammals for which they are known to exist, such as Mus musculus and Pan troglodytes.
During apoptosis, the apoptotic effector caspase, caspase-3, cleaves ICAD and thus causes CAD to become activated. [7] A nucleosome, consisting of DNA (grey) wrapped around a histone tetramer (coloured). In apoptotic DNA fragmentation, the DNA is cleaved in the internucleosomal linker region, which is the part of the DNA not wrapped around the ...
Caspase-7 is a member of the caspase (cysteine aspartate protease) family of proteins, and has been shown to be an executioner protein of apoptosis. Sequential activation of caspases plays a central role in the execution-phase of cell apoptosis .
[13] [16] In each case, caspase 9 activation leads to the activation of a full caspase cascade and subsequent cell death. It has been suggested that the evolutionary reason for the multimeric protein complex activating the caspase cascade is to ensure trace amounts of cytochrome c do not accidentally cause apoptosis. [7]
Finally, perforin creates a pore in the membrane, and releases the caspases which leads to the activation of caspase 3. This initiator caspase may cause the cleaving of inactive caspase 3, causing it to become cleaved caspase 3. This is the final molecule needed to trigger cell death. [14]
APO-1-mediated apoptosis can be inhibited by a variety of factors, including the viral caspase inhibitors CrmA and p35, as well as viral FLICE-inhibitory proteins known as v-FLIPs. When in the presence of APO-1, v-FLIPs preferentially bind and prevent procaspase-8 from being recruited; as such, apoptosis is stalled.