Apafant

The postmitochondrial events of apoptosis include activation of the caspases. Cytochrome c binds to the protein Apaf-1 in the cytosol, resulting in the recruitment and activation of caspase-9, which in turn activates cas-pase-3 (Figs 35-4, 35-5). Fourteen different mammalian caspases have been identified and each may play a key role... 

Fig. 12 Variation of rate coefficients ( oh°) w lh ApAf for proton transfer from substituted malonate monoanions to hydroxide ion...

Wang, X., 1997, Cytochrome c and dATP-dependent formation of Apaf-l/caspase-9 complex initiates an apoptotic protease cascade. Cell 91 479-489. 

It is now well estahlished that activation of the caspase cascade is an indispensable and sufficient process in the execution phase of apoptosis (Nunez et al, 1998). As for mitochondria-mediated apoptosis, cytochrome c released from the mitochondrial inner membrane is well known to play an important role in the activation of caspase 9, one of the upstream proteases in the cascade (Zou et al, 1997). For activation of caspase 9, cytochrome c or apoptotic protease activating factor 2 (Apaf 2) induces the formation of the complex between Apaf 1 and caspase 9. The resultant activated caspase 9 then activates caspase 3, which in turn leads to the genomic DNA fragmentation and apoptotic cell death. 

Li, P., Nijhawan, D., Budihardjo, 1., Srinivasula, S.M., Ahmad, M., Alnemri, E.S., and Wang, X,. 1997, Cytochrome c and dATP-dependent formation of Apaf-l/caspase-9 complex initiates an apoptotic protease cascade. Cell 91 479-489. 

Recently Imai et al (1999) cloned a novel protein, FLASH, that contains a region with stmctural similarity to Apaf-1 and a duplicated domain similar to the DEDs of caspase-8. This region, designated DRD (DED-recruiting domain), would allow its interaction with caspase-8 and FADD and its recruitment to the DISC, where it is thought to participate in caspase-8 activation. 

Saleh, A., Srinivasula, S. M., Acharya, S., Fishel, R., and Alnemri, E. S., 1999, Cytochrome c and dATP-mediated oligomerization of Apaf-1 is a prerequisite for procaspase-9 activation. JBiol Chem 274 17941-17945. 

Caspase-8 activates the effector caspases either directly, or indirectly by promoting the cytochrome c (see p. 140) from mitochondria. Once in the cytoplasm, cytochrome c binds to and activates the protein Apaf-1 (not shown) and thus triggers the caspase cascade. Apoptotic signals can also come from the cell nucleus. If irreparable DNA damage is present, the p53 protein (see p. 394)—the product of a tumor suppressor gene—promotes apoptosis and thus helps eliminate the defective cell. 

In aminoglycoside-treated animals, the cells can be led to canonical apop-totic death through activation of caspases. Caspase-9 forms an apoptosome complex with cytochrome c and APAF-1 and leads to apoptosis through activation of caspase-3. Aminoglycosides activate caspases in auditory structures conversely, inhibition of caspase activity successfully blocks neomycin-induced vestibulotoxicity. In contrast, apoptotic markers were essentially absent in a mouse model of chronic kanamycin ototoxicity where death of auditory sensory cells ensued via cathepsins. The activation of cathepsin D was accompanied by the nuclear translocation of endonuclease G, necrotic cleavage of PARP, and activation of p,-calpain, all facets of necrotic cell death. 

Figure 14-8. Overview of pathways that regulate programmed cell death. Apoptosis may occur in response to signaling through either the extrinsic pathway or the intrinsic pathway. In each case, proteolytic cleavage activates an initiator caspase, caspase 8 or 9, either of which can cleave an effector caspase such as caspase 3. Apaf-1 is part of a large complex called the apoptosome that mediates the intrinsic pathway. Binding of an extracellular death ligand to its cell-surface receptor activates the extrinsic pathway.

During the process of apoptosis, several mitochondrial proteins are released into the cytoplasm, including AIF and cytochrome C for the activation of proteases (L4). AIF, a tlavoprotein, can induce apoptotic morphological changes of the nucleus in a caspase-independent manner (M7, S8). Cytochrome C probably executes apoptosis by interaction with cytoplasmic protein Apaf-1 and direct activation of caspases (L2). Since the release of AIF and cytochrome C is regulated by the proteins of the Bcl-2 family, Bcl-2 can inhibit apoptosis by retention of cytochrome C in the mitochondria (T6). 

Caspase-9 Apaf-3, ICE-LAP6, Mch6 Apoptosis Caspase-3... 

In this model, cellular stress mediates the release of cytochrome C from the mitochondrion. The proapoptotic proteins Bax and BH3 proteins support the release of cytochrome C, while the antiapoptotic Bcl2 protein has an inhibitory effect. Cytosolic cytochrome C binds to the cofactor Apaf 1, which then associates via its CARD motif with procaspase 9 to a complex termed apopto-some. In this complex, procaspase 9 is processed to the mature caspase which subsequently activates downstream effector caspases and commits the cell to death. 

Jazirehi AR, Gan XH, De Vos S et al. Rituximab (anti-CD20) selectively modifies Bcl-xL and apoptosis protease aetivating faetor-1 (Apaf-1) expression and sensitizes human non-Hodgkin s lymphoma B eell lines to paelitaxel-indueed apoptosis. Mol Cancer T/zer 2003 2 1183-1193. 

Bcl-2 and related cytoplasmic proteins are key regulators of apoptosis [26], Anti-apoptotic proteins such as Bcl-2 and Bc1-Xl prevent apoptosis in response to numerous stimuli. During the apoptotic process, cytochrome c is released from mitochondria, but the release can be inhibited by the presence of Bcl-2 on the organelles [27]. The released cytochrome c forms an essential part of die apoptosome, which is composed of cytochrome c, Apaf-1, and procaspase-9 [28]. The complex formation results in activation of caspase-9, which leads to the stimulation of caspase-3. Bcl-XL has recently been reported to bind to Apaf-1 [29], It may inhibit the association of Apaf-1 with procaspase-9 and thereby prevent caspase activation. 

Figure 7.21 The cascade of events in the liver following a toxic dose of paracetamol. Hsp10, Hsp 60 are heat shock proteins, which have a protective function, cyt c is ctyochrome c. TNF-a, EGR-1, and GM-CSF are all genes involved with apoptosis, c-fos, APAF-1, and c-myc are also genes.

Moreover, the inductive contribution of a p deuterium to the IE on amine basicity was estimated.31 The inductive effect on pK due to an sp2-sp3 C-C bond, with a dipole moment of 0.35 D, as in propene, can be assigned as 0.95, the ApAf between allylamine and methylamine. Above, in connection with the structural question of the extent to which IEs affect dipole moments, dCu dco is 0.5 pm and dfi/dd is 0.004e. These combine to a ApAT on deuteration of 0.001, which is much smaller than the measured IEs in Table 5. An inductive contribution does exist, but it is negligible. 

The principal function of cyt. c is to form complexes through a defined interface with protein partners in our cells. This is most established for eukaryotic cytochrome c within the mitochondrial electron transport chain (ETC), a process required for carrying out the oxidative phosphorylation of ATP.4 Formation of a complex with cyt. c reductase (an electron-donor protein from complex III) and cyt. c oxidase (an electron-acceptor protein from complex IV) leads to the transfer of electrons between otherwise separated proteins. More recently cyt. c has been found to play a critical role in the process of apoptosis or programmed cell death This in turn has led to a resurgence of interest in all aspects of cyt. c research.5 Again protein-protein interactions have been shown be essential with mitochrondrial cyt. c binding to such proteins as APAF-1 to form the multi-protein species known as the apoptosome that is now thought to be a requirement for apoptosis.6,7... 

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