Cytochrome c, and apoptosis

Mitochondrial permeability transition involves the opening of a larger channel in the inner mitochondrial membrane leading to free radical generation, release of calcium into the cytosol and caspase activation. These alterations in mitochondrial permeability lead eventually to disruption of the respiratory chain and dqDletion of ATP. This in turn leads to release of soluble intramito-chondrial membrane proteins such as cytochrome C and apoptosis-inducing factor, which results in apoptosis. 

The involvement of mitochondria in the pro-apoptotic effects of carotenoids has been clearly demonstrated by the fact that P-carotene induces the release of cytochrome c from mitochondria and alters the mitochondrial membrane potential (Aym) in different tumor cells (Palozza et al., 2003a). Moreover, the highly polar xanthophyll neoxanthin has been reported to induce apoptosis in colon cancer cells by a mechanism that involves its accumulation into the mitochondria and a consequent loss of mitochondrial transmembrane potential and releas of cytochrome c and apoptosis-inducing factor (Terasaki et al., 2007). 

Several different changes in mitochondria occur during apoptosis. These include a change in membrane potential (usually depolarization), increased production of reactive oxygen species, potassium channel activation, calcium ion uptake, increased membrane permeability and release of cytochrome c and apoptosis inducing factor (AIF) [25]. Increased permeability of the mitochondrial membranes is a pivotal event in apoptosis and appears to result from the formation of pores in the membrane the proteins that form such permeability transition pores (PTP) may include a voltage-dependent anion channel (VDAC), the adenine nucleotide translocator, cyclophilin D, the peripheral benzodiazepine receptor, hexokinase and... 

Sustained elevations in intracellular Ca levels promote mitochondrial Ca uptake, which decreases the mitochondrial membrane potential and blocks the electron transport chain leading to ATP depletion. Large increases in mitochondrial Ca uptake also increase mitochondrial membrane permeability (Dubinsky and Levi, 1998) resulting in the release of proapoptotic factors such as cytochrome c and apoptosis inducing factor (AIL) (Luetjens et al, 2000). Cytochrome c binds to apoptotic protease-activation factor 1 (APAFl) and procaspase-9, forming a multiprotein complex known as the apoptosome that activates the caspase cascade. The apoptosome activates caspase-9, which in turn activates caspase-3. Caspase-3 activates caspase-activated DNase (CAD), resulting in DNA fragmentation, characteristic of apoptosis. 

Movsesyan VA, Stoica BA, Faden AI (2004) MGLuR5 activation reduces beta-amyloid-induced cell death in primary neuronal cultures and attenuates translocation of cytochrome c and apoptosis-inducing factor. J Neurochem 89 1528-1536... 

BH3 domain) of the BH3-only proteins binds to other Bcl-2 family members thereby influencing their conformation. This interaction facilitates the release of cytochrome C and other mitochondrial proteins from the intermembrane space of mitochondria. Despite much effort the exact biochemical mechanism which governs this release is not yet fully understood. The release of cytochrome C facilitates the formation of the apoptosome, the second platform for apoptosis initiation besides the DISC. At the apoptosome which is also a multi-protein complex the initiator caspase-9 is activated. At this point the two pathways converge. 

Mailer What is clear is that we can take an egg extract, add cytochrome C and induce apoptosis quickly. If the inhibitor is there it is not very dominant. 

Colquhoun and Schumacher [98] have shown that y-linolcnic acid and eicosapentaenoic acid, which inhibit Walker tumor growth in vivo, decreased proliferation and apoptotic index in these cells. Development of apoptosis was characterized by the enhancement of the formation of reactive oxygen species and products of lipid peroxidation and was accompanied by a decrease in the activities of mitochondrial complexes I, III, and IV, and the release of cytochrome c and caspase 3-like activation of DNA fragmentation. Earlier, a similar apoptotic mechanism of antitumor activity has been shown for the flavonoid quercetin [99], Kamp et al. [100] suggested that the asbestos-induced apoptosis in alveolar epithelial cells was mediated by iron-derived oxygen species, although authors did not hypothesize about the nature of these species (hydroxyl radicals, hydrogen peroxide, or iron complexes ). 

Fas ligand and interleukin-ip), the neurotransmitter glutamate and thrombin. Like tumor necrosis factor (TNF) receptors, Fas is coupled to downstream death effector proteins that ultimately induce caspase activation (Ch. 22). Fas and TNF receptors recruit proteins called FADD and TRADD respectively FADD and TRADD then activate caspase-8, which, in turn, activates caspase-3 (Fig. 35-4). Calcium ion influx mediates neuronal apoptosis induced by glutamate receptor activation calcium induces mitochondrial membrane permeability transition pore opening, release of cytochrome c and caspase activation. Interestingly, in the absence of neurotrophic factors some neurotrophic factor receptors can activate apoptotic cascades, the low-affinity NGF receptor being one example of such a death receptor mechanism [23],... 

Goldstein, J.C., Waterhouse, N.J., Juin, P., Evan, G.I., and Green, D.R., 2000, The coordinate release of cytochrome c during apoptosis is rapid, complete and kinetically invariant. Nature Cell Biology 2 156-162. 

Li, P.F., Dietz, R., and von Harsdorf, R., 1999, P53 regulates mitochondrial membrane potential through reactive oxygen species and induces cytochrome c-independent apoptosis blocked by Bcl-2, EMBO J. 18 66027-6036. 

The cytosolic targets of cathepsin D have not been ascertained. However, since we found that inhibition of cathepsin D prevented both release of cytochrome c and activation of caspase-3-like caspases, we suggest that cathepsin D exerts its effect upstream of both the release of cytochrome c from mitochondria and the onset of the caspase cascade. Cathepsin B seems to be of minor importance in this system, because we observed that the activity of cathepsin B decreased and the cathepsin B inhibitor CA074-Me had no influence on the rate of apoptosis (Kagedal et al 2001). 

Roberg, K., 2001, Relocalization ofcathepsin D and cytochrome c early in apoptosis revealed by immunoelectron microscopy. Lab. Invest. 81 149-158 Roberg, K., Johansson, U., and OUinger, K., 1999, Lysosomal release of cathepsin D precedes relocation of cytochrome c and loss of mitochondrial transmembrane potential during apoptosis induced by oxidative stress. Free Radio. Biol. Med. 27 1228-1237 Roberg, K. and OUinger, K., 1998, Oxidative stress causes relocation of the lysosomal... 

Apoptosis Damage to mitochondria can also result in the release of cytochrome c and other factors into the cytosol, which can initiate the process of apoptosis. If a sufficient number of cells in a tissue or organ is lost, the function of the organ or tissue can be impaired, so that it would be less... 

Intrinsic system Apoptosis is initiated due to changes to the mitochondria during which the inner membrane becomes permeable to large molecules, probably as a result of a decrease in the membrane potential. This can result from intracellular damage (e.g. accumulation of Ca ions), lack of oxygen or fuel. This results in release of cytochrome c and other proteins from the mitochondria which stimulate apoptosis. In fact, these apoptotic proteins plus cytochrome c form a complex, the apoptosome, which activates an initiator caspase. 

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. 

Fig. 1. Proposed mechanism of action of rituximab associated with the apoptosis pathway. Binding of rituximab with the CD20 antigen up-regulates the production of interleukin-10 (IL-10). The IL-10 autocrine loop down-regulates the expression of the bcl-2 protein, which inhibits the intrinsic pathway (or mitochondrial mediated pathway) of apoptosis. The mitochondrial pathway is induced by intracellular stress signals. The translocation of the bcl-2 protein into the mitochondria leads to the activation of caspase 9 via release of cytochrome c and apoptotic protease-activating factor 1. The other pathway, the extrinsic pathway (or death receptor mediated pathway) activates caspase 8. Subsequently, caspase 8 or 9 activates caspase 3, leading to programmed cell death (apoptosis).

Figure 32-4 Sketch illustrating only a few of the many aspects of apoptosis in a mammalian cell. Emphasis here is on the death receptor pathways and cytochrome c-activated apoptosis. A third pathway is initiated by stress in endoplasmic reticulum membranes. In addition, attack by cytolytic T cells sometimes causes apoptosis by action of a granzyme on protein Bid or via a death receptor. Objects in scheme are not drawn to a single scale.

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