Specific Ablation of the Apoptotic Functions of Cytochrome c Reveals a Differential Requirement for Cytochrome c and Apaf-1 in Apoptosis

Abstract

As components of the apoptosome, a caspase-activating complex, cytochrome c (Cyt c) and Apaf-1 are thought to play critical roles during apoptosis. Due to the obligate function of Cyt c in electron transport, its requirement for apoptosis in animals has been difficult to establish. We generated "knockin" mice expressing a mutant Cyt c (KA allele), which retains normal electron transfer function but fails to activate Apaf-1. Most KA/KA mice displayed embryonic or perinatal lethality caused by defects in the central nervous system, and surviving mice exhibited impaired lymphocyte homeostasis. Although fibroblasts from the KA/KA mice were resistant to apoptosis, their thymocytes were markedly more sensitive to death stimuli than Apaf-1(-/-) thymocytes. Upon treatment with gamma irradiation, procaspases were efficiently activated in apoptotic KA/KA thymocytes, but Apaf-1 oligomerization was not observed. These studies indicate the existence of a Cyt c- and apoptosome-independent but Apaf-1-dependent mechanism(s) for caspase activation.

Caspase function in programmed cell death

“…Following irradiation, KA thymocytes undergo apoptosis and caspase activation in the absence of apoptosome formation, suggesting the existence of an apoptosome-independent mechanism of caspase activation in thymocytes. 80 The KA mice confirm that cytochrome c is essential for Apaf-1 activation, and also provide evidence for alternative pathways of caspase activation.…”

“…80 Interestingly, while the fibroblasts from the KA mice are resistant to apoptosis, their thymocytes are more sensitive to apoptosis than the apaf-1-null thymocytes. Following irradiation, KA thymocytes undergo apoptosis and caspase activation in the absence of apoptosome formation, suggesting the existence of an apoptosome-independent mechanism of caspase activation in thymocytes.…”

SMAC/Diablo mediates the proapoptotic function of PUMA by regulating PUMA-induced mitochondrial events

“…Recently, studies carried out using genetically engineered animals indicate that these proteins are required for apoptosis under certain conditions. For example, knock-in of a cytochrome c mutant that fails to activate Apaf-1 in mice abrogates caspase activation and apoptosis in fibroblasts (Hao et al, 2005). Knockout of AIF in mice inhibited neuronal cell death (Yu et al, 2002).…”

Neural precursor cells possess multiple p53-dependent apoptotic pathways

“…21 Using NPCs prepared from mice with gene disruptions of p53, bax and bak, apaf-1, or caspase-9, we investigated whether the molecular requirements for STSinduced death were similar to the requirements for genotoxic injury-induced death. Our results indicate that specific death stimuli activate selective upstream signaling molecules that converge at the level of p53, which leads to Bax/Bakdependent caspase activation and NPC death through either transcription-dependent or -independent mechanisms.…”