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Bcl-2-associated X protein

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Title: Bcl-2-associated X protein  
Author: World Heritage Encyclopedia
Language: English
Subject: Apoptosis, Peripheral membrane protein, Gossypol, Bcl-2, Catechin, Fas ligand, Apoptosome, Monocrotophos, Phospholipid scramblase, BH3 interacting-domain death agonist
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Bcl-2-associated X protein

BCL2-associated X protein
Available structures
PDB Ortholog search: RCSB
BAX Gene
RNA expression pattern

Apoptosis regulator BAX also known as bcl-2-like protein 4 is a protein that in humans is encoded by the BAX gene.[1]

BAX is a member of the Bcl-2 gene family. Apoptosis regulator BAX promotes apoptosis by binding to and antagonizing the Bcl-2 protein.[1]

The BAX gene was the first identified pro-apoptotic member of the Bcl-2 protein family.[2] Bcl-2 family members share one or more of the four characteristic domains of homology entitled the Bcl-2 homology (BH) domains (named BH1, BH2, BH3 and BH4), and can form hetero- or homodimers.[2][3] Bcl-2 proteins act as anti- or pro-apoptotic regulators that are involved in a wide variety of cellular activities.

Orthologs of the BAX gene [4] have been identified in most mammals for which complete genome data are available. Certain members of BAX, such as Bcl-2, Bcl-xl and Mcl1 are anti-apoptotic, whilst others are pro-apoptotic. BAX is a pro-apoptotic Bcl-2 protein containing BH1, BH2 and BH3 domains.


In healthy mammalian cells, the majority of BAX is found in the cytosol, but upon initiation of apoptotic signaling, Bax undergoes a conformation shift. Upon induction of apoptosis, BAX becomes organelle membrane-associated, and in particular, mitochondrial membrane associated.[5][6][7][8][9]

BAX is believed to interact with, and induce the opening of the mitochondrial voltage-dependent anion channel, VDAC.[10] Alternatively, growing evidence also suggests that activated BAX and/or Bak form an oligomeric pore, MAC in the outer membrane.[11] This results in the release of cytochrome c and other pro-apoptotic factors from the mitochondria, often referred to as mitochondrial outer membrane permeabilization, leading to activation of caspases.[12] This defines a direct role for BAX in mitochondrial outer membrane permeabilization, a role common to the Bcl-2 proteins containing the BH1, BH2 and BH3 domains.

Role in Cancer

The expression of BAX is upregulated by the tumor suppressor protein p53, and BAX has been shown to be involved in p53-mediated apoptosis.[13][14][15] The p53 protein is a transcription factor[13][14][15] that, when activated as part of the cell's response to stress, regulates many downstream target genes, including BAX. Wild-type p53 has been demonstrated to upregulate the transcription of a chimeric reporter plasmid utilizing the consensus promoter sequence of BAX approximately 50-fold over mutant p53.[13][14][15] Thus it is likely that p53 promotes BAX's apoptotic faculties in vivo as a primary transcription factor. However, p53 also has a transcription-independent role in apoptosis. In particular, p53 interacts with Bax, promoting its activation as well as its insertion into the mitochondrial membrane.[13][14][15]

Binding of HA-BAD to BCL-xL and concomitant disruption of BAX:BCL-xL interaction was found to partly reverse paclitaxel resistance in human ovarian cancer cells.[16]


Bcl-2-associated X protein has been shown to interact with:

See also


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