BAK1 (BCL2-antagonist/killer 1)

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BAK1 (BCL2-antagonist/killer 1)

Written	2010-02	Grant Dewson, Ruth Kluck
		The Walter, Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville 3050, Melbourne, Australia

(Note : for Links provided by Atlas : click)

Identity

Other alias	BAK
	BAK-LIKE
	BCL2L7
	Bcl2-L-7
	CDN1
	MGC117255
	MGC3887
LocusID (NCBI)	578
Atlas_Id	752
Location	6p21.31 [Link to chromosome band 6p21]
Location_base_pair	Starts at and ends at bp from pter
Local_order	Orientation: minus strand. Located approximately 380 kb centromeric to the human major histocompatibility complex (MHC) class II region.

Fusion genes
(updated 2017)

Data from Atlas, Mitelman, Cosmic Fusion, Fusion Cancer, TCGA fusion databases with official HUGO symbols (see references in chromosomal bands)

Note

The BAK1 gene produces the Bak protein, a pro-apoptotic protein from the Bcl-2 protein family. Either Bak or Bax is required to permeabilize the mitochondrial outer membrane during the mitochondrial (intrinsic) pathway of apoptotic cell death. Bak is a single-pass membrane protein that localises to the mitochondrial outer membrane in healthy cells, while Bax moves to mitochondria during apoptosis. Both Bak and Bax convert to the activated, pro-apoptotic form by undergoing a large conformational change before oligomerising to form apoptotic pores in the mitochondrial outer membrane. Pore formation allows the release of cytochrome c, Smac and other proteins that promote protease (caspase) activity to kill the cell. Thus, Bak/Bax pore formation is a major point of no return in cell death. The activation of Bak (and Bax) is initiated when the cell up-regulates the pro-apoptotic BH3-only members of the Bcl-2 family. Bak activation is blocked if sufficient prosurvival (anti-apoptotic) Bcl-2 family members (e.g. Bcl-xL, Mcl-1, Bcl-2 and A1) are present to sequester the BH3-only proteins and also perhaps the activated Bak and Bax proteins. As cancer cells often express high levels of these prosurvival proteins, several agents that target the prosurvival proteins are being developed as novel cancer therapeutics.

DNA/RNA

Description	The BAK1 gene, with 7748 bases in length, and contains 6 exons. The first exon is non-coding, and most of the largest, final exon is untranslated.
Transcription	The BAK1 gene transcribes a 211 aa protein Bak. A possible 101 aa splice variant, called BAK-like, contains BH1, BH2 and TM domains, but no BH3 domain, with a 2.4 kb transcript of BAK-like detected in most human tissues and exhibiting pro-apoptotic activity. Two other human BAK1 mRNA variants are present in GenBak but may not be expressed: the BakM variant would be 190 aa and lack 21 amino acids in the linker region between alpha-helices 1 and 2; another would be 153 aa with the stop codon upstream of a splice junction and therefore predicted to be subject to nonsense-mediated mRNA decay. However in mice, a similar 151 aa N-Bak that contains only the BH3 domain is reportedly expressed in neurons.
Pseudogene	There are two pseudogenes: Bak2 (chromosome 20) and Bak3 (chromosome 11).

Protein

Note	The BAK1 gene encodes for a 23409 Da protein, named Bak. The Bak cDNA was isolated by three groups by virtue of its protein product interacting with the adenovirus E1B 19K protein, or its homology to the BH1 and BH2 domains of Bcl-2. The BH3 domain of Bak is essential for its binding to a hydrophobic surface groove on the prosurvival proteins Bcl-xL and Mcl-1. The Bak BH3 domain is also important for binding to a similar hydrophobic groove in another activated Bak molecule to form Bak oligomers and the formation of pores.



	The human Bak protein is 211 aa in length. Bcl-2 homology (BH) domains indicate regions of sequence homology with other Bcl-2 family members, with the BH3 domain being present in all members. The structure of non-activated Bak is similar to that of the prosurvival Bcl-2 family members, with alpha helices 1-9 indicated. The oligomerization domain is important for homo-oligomerization and pore formation, while the transmembrane domain anchors Bak in the mitochondrial outer membrane.

Expression	BAK1 mRNA is expressed widely in different tissues as an approximately 2.4 kb transcript. Highest mRNA levels are in the heart and skeletal muscle.
Localisation	The Bak protein is inserted in the mitochondrial outer membrane in healthy cells, while its close homologue Bax translocates to mitochondria after an apoptotic stimulus. A small proportion of Bak has also been detected at the endoplasmic reticulum membrane.
Function	Bak (or Bax) is required to form pores in the mitochondrial outer membrane during apoptotic cell death. The killing activity of Bak is regulated by other members of the Bcl-2 family. For example, certain BH3-only proteins (Bim and Bid) are reported to directly bind Bak to convert it into the activated conformation, while the prosurvival proteins (e.g. Bcl-xL and Mcl-1) can sequester activated Bak and so prevent Bak homo-oligomerization and pore formation. The role of Bak at the ER membrane is unclear.
Homology	Human Bak shares 99.5% amino acid identity with Pan troglodytes, 91.9% identity with Canis lupus familiaris, 86.2% with Bos taurus, 77.2% with Rattus norvegicus. BAK1 is not found in the Danio rerio genome. Human Bak has 53% amino-acid sequence identity with the BH1 and BH2 domains of Bcl-2. Over the full sequence, Bak is 25, 33 and 19% identical to Bcl-2, Bcl-xL and Bax, respectively.

Mutations

Note	Several Bak single point mutations have been associated with autoimmune diseases, aortic aneurysms, and cervical, colorectal and gastric cancers, although the causal relationship is not clear. In addition, around 200 SNPs, with unknown clinical association have been reported in Entrez SNP database.
Somatic	Somatic mutations were increased in uterine cervical carcinoma (6 from 42) compared with non-neoplastic tissue (0 from 32). While an early study reported somatic mutations in 17% of samples of colorectal and gastric cancers in Korean patients, a later study reported no somatic mutations in 192 colorectal and gastric cancers.

Implicated in

Note

Entity	Lymphoma and leukemia
Note	Lymphomas and leukemias have high levels of Bcl-2 prosurvival proteins that prevent Bak (and Bax) from inducing apoptosis. New anti-cancer therapies that target prosurvival proteins can activate Bak (or Bax) to re-instate apoptotic cell death. In one example, a new drug, GX15-070, was found to induce apoptosis in mantle cell lymphoma cell lines by binding to Mcl-1 and assist in Bak activation (Pérez-Galán et al., 2007). This drug is in clinical trials for refractory chronic lymphocytic leukemia (Storey, 2008), and is presumably acting by indirectly activating Bak (or Bax).


Entity	Gastric and colorectal cancer
Note	The first report of Bak mutations being associated with gastrointestinal cancers was of missense BAK1 mutations in 3 of 24 gastric cancers and 2 of 20 colorectal cancers, with mutations observed only in advanced-stage cancers (Kondo et al., 2000). In another study, BAK1 mutations were also rare (3/107) in patients with gastric adenocarcinomas, and were each associated with late stage disease (Kim et al., 2003). However, no somatic mutations were found in 192 patients with colorectal and gastric cancers, and the rare single-nucleotide substitutions (4/129) were also found in the corresponding normal tissue samples (Sakamoto et al., 2004).


Entity	Uterine cervical carcinoma
Note	Possible role for Bak mutation in uterine cervical carcinoma was reported (Wani et al., 2003). In a study of 42 patients, 6 missense (M60V, D30N, D57N, V74M, I80T and V191A) and one silent mutations in the coding region of BAK1 were found, with no mutations detected in 32 non-neoplastic cervix tissue samples. Mutations were associated with late-stage disease and with resistance to chemotherapy, but were not statistically significant due to sample size.


Entity	Melanoma
Note	In patients with superficial-spreading melanoma high Bak levels corresponded to improved survival (10-year survival of 62%), while low Bak correlated with low survival (10-year survival of 10%) (Fecker et al., 2006). Bax levels correlated in a similar way.


Entity	Autoimmune diseases
Note	Severe autoimmune disease occurs in adult mice following deletion of both Bak and its close relative Bax (Takeuchi et al., 2005). The mice accumulate excess memory B- and T-cells in lymphoid and mesenchymal organs, leading to hepato-splenomegaly, lymphadenopathy, and thymic selection impairment. In humans, similar deletion of two copies of BAK1 (and BAX) does not occur, however less marked changes in Bak protein levels, as well as BAK1 mutations, have been associated with autoimmune disease in rare cases (see below).


Entity	Sjogren's syndrome
Note	The Bak protein and its gene mutation may participate in the pathology and susceptibility of Sjogren's syndrome, as Bak was over-expressed in patient autoimmune lesions (Anaya et al., 2005). In a later study three polymorphisms in BAK1 were associated with Sjogren's syndrome (Delgado-Vega et al., 2009).


Entity	Coeliac disease
Note	A significant increase in Bak mRNA and protein levels was found in the intestinal lesions of patients with untreated coeliac disease (Chernavsky et al., 2002). The increase in Bak and in apoptosis of enterocytes may be due to increased IFN-gamma signalling.


Entity	Graves' disease
Note	Differential expression of Bak (and Bcl-2 and Bax) was associated with apoptosis in thyrocytes and lymphoid follicles, implicating Bak in the pathology of Grave's disease (Hiromatsu et al., 2004).


Entity	Multiple sclerosis
Note	Bak mRNA levels were increased in the autoimmune lesions of patients with multiple sclerosis (Banisor and Kalman, 2004).


Entity	Ataxia telangiectasia
Note	BAK1 mutations were observed in 8 of 50 patients with ataxia telangiectasia, and were each a silent mutation in exon 2 in codon 14 (TGC>TGT), while none of the healthy controls had such an alteration (Isaian et al., 2009).


Entity	Transient platelet loss
Note	Bak can be activated to kill platelets as a side effect of new anti-cancer treatments (Mason et al., 2007; Oltersdorf et al., 2005). The small molecule ABT-737 is a BH3-mimetic that binds specifically to prosurvival proteins (Bcl-2, Bcl-xL, Bcl-w) that are commonly over-expressed in cancers. As platelets contain Bcl-xL as the predominant prosurvival protein guarding Bak, ABT-737 causes Bak activation and transient loss of platelets.


Entity	Age-related hearing loss
Note	In mice, Bak-mediated apoptosis exacerbated age-related hearing loss (Someya et al., 2009; Someya et al., 2007). Moreover, hearing loss was decreased if Bak was deleted, if mice were kept on a calorie restriction diet, or given oral supplementation with antioxidants. In keeping with oxidative stress was proposed to induce Bak expression in primary cells from cochlear cells.


Entity	Aortic aneurysms
Note	A possible role for Bak mutation in aortic aneurysms was evident in a study of 31 patients with abdominal aortic aneurysms (Gottlieb et al., 2009). Two single nucleotide polymorphisms (R42H and V52A) in the BAK1 gene were present in both diseased (31 cases) and healthy aortic tissue (5 cases), but not in matching blood samples. The authors propose that multiple variants of a gene such as BAK1 might pre-exist within disease-susceptible tissues, and can be selected for during disease progression.

To be noted

The Bak protein plays a role in many diseases due to its central role in apoptotic cell death. However, most Bak dysregulation is not due to mutations in Bak, but rather to altered expression or mutation of Bak regulators (e.g. Bcl-xL and Mcl-1). If Bak (and its homologue Bax) fail to activate and form a pore in mitochondria, the cell may survive when it was meant to die, and so contribute to cancer. In the opposite scenario, if Bak (or Bax) is activated inappropriately and mitochondria are permeabilized, excessive cell death can occur, for example, in neurodegenerative disease, autoimmune disease, and platelet loss following anti-cancer treatments. Agents that can trigger Bak-mediated apoptosis in a non-targeted way include most anti-cancer agents, while agents that may trigger Bak (and Bax) indirectly by targeting Bcl-2, Bcl-xL, Bcl-w, Mcl-1 and A1, include antisense, antibody and small molecule approaches (Storey, 2008).

	Nomenclature
	Cards
Atlas	BAK1ID752ch6p21.txt
Aliases
	Genomic and cartography
	Gene and transcription
RefSeq transcript (Entrez)
RefSeq genomic (Entrez)
SOURCE (Princeton)	Expression in : [Datasets] [Normal Tissue Atlas] [carcinoma Classsification] [NCI60]
BioGPS (Tissue expression)	578
	Protein : pattern, domain, 3D structure
Domain families : Pfam (Sanger)
Domain families : Pfam (NCBI)
	Protein Interaction databases
	Ontologies - Pathways
	Clinical trials, drugs, therapy
	Miscellaneous
canSAR (ICR)	(select the gene name)
Other database	Bcl-2 Family Database
Other database	Deathbase
	Probes
	Litterature

REVIEW articles	automatic search in PubMed
Last year publications	automatic search in PubMed