Caspases 3 and 7: Key Mediators of Mitochondrial Events of Apoptosis

Abstract

The current model of apoptosis holds that upstream signals lead to activation of downstream effector caspases. We generated mice deficient in the two effectors, caspase 3 and caspase 7, which died immediately after birth with defects in cardiac development. Fibroblasts lacking both enzymes were highly resistant to both mitochondrial and death receptor-mediated apoptosis, displayed preservation of mitochondrial membrane potential, and had defective nuclear translocation of apoptosis-inducing factor (AIF). Furthermore, the early apoptotic events of Bax translocation and cytochrome c release were also delayed. We conclude that caspases 3 and 7 are critical mediators of mitochondrial events of apoptosis.Mitochondria play a central role in apoptosis. Mitochondrial outer membrane permeabilization (MOMP) leads to release of proapoptotic factors such as cytochrome c and AIF (1). Furthermore, loss of mitochondrial membrane potential (Δψ m ) is thought to contribute to cell death by disruption of normal mitochondrial function (2, 3). Interaction of members of the Bcl-2 family of proteins regulates MOMP, the key event of cytochrome c release into the cytoplasm (3, 4). What is less clear, however, is the precise role of caspase proteases in mitochondrial events of apoptosis. Although upstream caspases, such as caspase 2 and caspase 8, affect mitochondrial events in both death-receptor and mitochondrial pathways of apoptosis, either directly or through interaction with Bcl-2 family members, the role of presumed downstream "effector" caspases in this process is less clear (5, 6). Therefore, we studied the two highly related effectors, caspase 3 and caspase 7, to elucidate their functions in apoptosis.* To whom correspondence should be addressed. richard.flavell@yale.edu. We generated caspase 7 −/− mice ( fig. S1), which were born in ratios consistent with Mendelian inheritance. They had normal appearance, organ morphology, and lymphoid development. When caspase 7 −/− mouse embryonic fibroblasts (MEFs) were treated with inducers of apoptosis, they exhibited a slight survival advantage as compared with wild-type MEFs. Apoptosis caused by a range of insults in other caspase 7 −/− cells proceeded normally, however, including the death of activated T cells following stimulation of the T cell receptor, thymocyte apoptosis, Fas-mediated death of B cells, and Fas-mediated death of hepatocytes ( fig. S2). Supporting Online MaterialCaspase 3, which is structurally similar to caspase 7, might compensate for the lack of caspase 7, which would lead to this relatively mild antiapoptotic phenotype (7,8). Thus, we bred caspase 7 −/− mice to caspase 3 −/− mice previously described by our laboratory (9). The embryonic stem cells containing the mutation were from the 129/SvJ genetic background. Mice derived from these embryonic stem cells were backcrossed six generations onto the C57BL/6 background. We obtained no live caspase 3 −/− /caspase 7 −/− double-knockout (DKO) mice when progeny were genotyped at an age of 10 to 14 days. DKO mic...

Major apoptotic mechanisms and genes involved in apoptosis

“…Despite there are limited information about caspase-6 and -7 rather than caspase-3, it is known that while caspase-3 suppression results in the inhibition of apoptosis, suppression of caspase-6 and -7 do not significantly affect the apoptotic process [48]. Furthermore, caspase-3 was reported to be crucial for PARP cleavage and DNA fragmentation which are hallmarks of apoptosis [49]. However, some studies showed that under the conditions that both caspase-3 and caspase-7 were knocked out, the cells could undergo cell death in an alternative manner via necrosis.…”

“…However, some studies showed that under the conditions that both caspase-3 and caspase-7 were knocked out, the cells could undergo cell death in an alternative manner via necrosis. Studies with caspase-3/caspase-7 double-knockout thymocytes and mouse embryonic fibroblasts showed that thymocytes remain sensitive to Fas-mediated apoptosis, whereas fibroblasts become resistant [49,50].…”

pRb/E2F-1-mediated caspase-dependent induction of Noxa amplifies the apoptotic effects of the Bcl-2/Bcl-xL inhibitor ABT-737

“…However, executioner caspases were found to be required for full-blown Bax activation and mitochondrial permeabilisation in response to diverse stimuli. 19 In addition, when caspase activity is blocked, subsets of mitochondria remain refractory to permeabilisation and allow cells to survive to death stimuli. 20,21 Thus, caspase activity might also amplify the apoptotic process upstream of mitochondria, and fuel signals initiated by inhibition of some Bcl-2 homologs by ill-characterized mechanisms.…”

Apoptosome dependent caspase-3 activation pathway is non-redundant and necessary for apoptosis in sympathetic neurons

“…Recently, it has been reported that MEFs derived from mice either deficient for caspase-9 or doubly deficient for caspase-3 and caspase-7 show a delay in cytochrome c release following UV irradiation, implicating a role for caspase feedback at the mitochondria in regulating cytochrome c release. 30 In contrast, in sympathetic neurons, which are dependent solely on caspase-3 for effector caspase activity, deletion of caspase-3 did not alter the kinetics of cytochrome c release following NGF deprivation (Supplementary Figure 2). These results suggest that the role for caspase-mediated feedback on mitochondrial release of cytochrome c may be cell type or stimulus specific.…”