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| inhibitor of apoptosis ： ウィキペディア英語版 |
inhibitor of apoptosis
Apoptosis, or programmed cell death, is a highly regulated process used by many multi cellular organisms. Like any regulated process, apoptosis is subject to either activation or inhibition by a variety of chemical factors. Apoptosis can be triggered through two main pathways; extrinsic and intrinsic. The extrinsic pathway mostly involves extracellular signals triggering intracellular apoptosis mechanisms by binding to and sending signals from the outside of the cell. Intrinsic pathways involved internal cell signaling primarily through the mitochondria. Inhibitors of apoptosis are a group of proteins that mainly act on the intrinsic pathway that block programmed cell death, which can oftentimes lead to cancer or other effects for the cell. Many of these inhibitors act to block caspases, a family of cysteine proteases that play an integral role in apoptosis. Some of these inhibitors include the Bcl-2 family, viral inhibitor crmA, and IAP's.
==Bcl-2==
Bcl-2 is an oncogene that is part of the Bcl-2 family of proteins that can either inhibit or promote apoptosis. The Bcl-2 family is characterized by the Bcl-2 homologous domains BH1, BH2, BH3, and BH4, the combinations of which determine its role in the apoptosis process. Members of the family that inhibit apoptosis include Bcl-2 itself, Bcl-XL, and Bcl-w, which possess all four of the domains. Studies have shown that the Bcl-2 oncogene may inhibit apoptosis in two ways; either by directly controlling the activation of caspases, or by disrupting the channels that allow proapoptotic factors from leaving the mitochondria.
Regarding the activation a caspases, there exists a gene called ''ced-9'' in ''C. elegans'' that protects against cell death that is a part of the Bcl-2 family. ''ced-9'' encodes for a protein that is structurally similar to Bcl-2, that has been shown to function quite similarly in inhibiting apoptosis. In ''C. elegans'', the ''ced-9'' protein binds to another protein ''ced-4'', a homolog of APAF-1 in humans, and prevents it from activating caspase ''ced-3'', which is necessary for killing of the cell. (). In humans APAF-1 actually doesn't interact with Bcl-2; rather is activated by cytochrome c, the release of which from the mitochondria is regulated by Bcl-2. BAX and BAK are multidomain proapoptoic members of the Bcl-2 family that lie in the cytosol and the mitochondria, respectively. After several stimuli leading to cell death are activated, BAX also moves to the mitochondria where it carries out its functions there. Bcl-2 and Bcl-xl have been found to sequester BH3 domain molecules in the mitochondria, which prevents the activation of BAX and BAK. ()
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