BH3 Domains other than Bim and Bid Can Directly Activate Bax/Bak

Du, Han; Wolf, Jacob; Schafer, Blanca; Moldoveanu, Tudor; Chipuk, Jerry E.; Kuwana, Tomomi

doi:10.1074/jbc.m110.167148

Cited by 145 publications

(139 citation statements)

References 44 publications

(65 reference statements)

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“…In Jurkat and SKW6.4 cells, the tolerance for BIK, BMF or NOXA is similar to that of BIM EL or PUMA (Figures 3k and l), consistent with claims that BIK, BMF and NOXA might also be direct activators in at least some contexts. 2,20,23,52 In contrast, the tolerance for BAD is much higher than the tolerance for BIM and PUMA in all cell lines examined (Figures 3k, 3l, 5b and c). This difference between BAD and the other BH3-only proteins was particularly evident in cells with relatively low expression of BCL2 and BCLX L (Figures 3k and l).…”

Section: Discussionmentioning

confidence: 83%

Measurement of BH3-only protein tolerance

et al. 2017

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The BCL2 family of proteins regulates cellular life and death decisions. Among BCL2 family members, BH3-only proteins have critical roles by neutralizing antiapoptotic family members, as well as directly activating BAX and BAK. Despite widespread occurrence of BH3-only protein upregulation in response to various stresses, this process is rarely quantified. Moreover, it is unclear whether all BH3-only proteins are equipotent at inducing cell death. Here we show that BH3-only proteins increase as much as 15-to 20-fold after various treatments and define a parameter, termed BH3-only tolerance, which measures how many copies of a particular BH3-only protein can be expressed before the majority of cells in a population undergo apoptosis. We not only assess the relative contributions of anti-and proapoptotic BCL2 family members to BH3-only tolerance, but also illustrate how the study of this parameter can be used to understand cellular sensitivity to anticancer drugs and new combinations. These observations provide a new quantitative framework for assessing apoptotic susceptibility under various conditions.

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Section: Discussionmentioning

confidence: 83%

Measurement of BH3-only protein tolerance

et al. 2017

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“…Within the BH3-only proteins, Bim and tBid are termed activators, as they have been observed to directly bind to Bax and Bak 267 , whereas Noxa and Bad are referred to as sensitizers as they have only been found to bind the pro-survival proteins 266 . There is debate as to whether Puma acts as an activator or sensitizer protein, as it has been found to bind weakly with the effector proteins 271 , as has the Bmf BH3-peptide 272 . The Bmf and Puma peptides bound weakly to the effector proteins, but were apparently sufficient such that in the absence of Bid and Bim, they could initiate cytochrome c release 272 .…”

Section: The Bcl-2 Familymentioning

confidence: 99%

“…There is debate as to whether Puma acts as an activator or sensitizer protein, as it has been found to bind weakly with the effector proteins 271 , as has the Bmf BH3-peptide 272 . The Bmf and Puma peptides bound weakly to the effector proteins, but were apparently sufficient such that in the absence of Bid and Bim, they could initiate cytochrome c release 272 . In the direct model, the activators are essential for the activation of MOMP, however Bid -/-Bim -/-mice display normal apoptosis.…”

Section: The Bcl-2 Familymentioning

confidence: 99%

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Role of the pro-survival molecule Bfl-1 in melanoma

Hind

Carter

Harris

et al. 2015

The International Journal of Biochemistry & Cell Biology

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Melanoma, the cancer derived from the melanocytes of the skin, is becoming an ever more common cancer in the ageing population of the developed world and displays an intrinsic resistance to current therapies. This chemo resistance makes metastatic melanoma an extremely difficult cancer to treat leading to a 5 year survival rate of just 20%. As such, it is important to unearth new potential drug targets to increase the prospects for melanoma patients.Bfl-1 is a pro-survival protein of the Bcl-2 family of apoptosis regulating proteins. It has been found to be over-expressed in a small subset of chemo resistant tumours, including melanoma. Accordingly, I characterised the molecule in melanoma cells and determined its role in protecting these cells from chemotherapy-induced apoptosis. I elucidated the expression profile and half-lives of the protein and mRNA across a panel of melanoma cell-lines and healthy melanocytes. I also confirmed, using pathway specific inhibitors, that Bfl-1 was transcriptionally regulated by the NFB pathway and concluded through pulsechase experiments that Bfl-1 protein was degraded, at least in part, by the proteasome. Subcellular fractionation and indirect immunofluorescence techniques elucidated that Bfl-1 was located mostly at the mitochondria in both resting and apoptotic cells, with a diffuse level present throughout the cytoplasm. As well as characterising the protein in both melanoma cells and healthy primary melanocytes, I determined its role in the resistance of these cells to apoptosis. Over-expressed Bfl-1 was found to protect melanoma cells from apoptosis caused by a range of chemotherapeutic agents in A375 melanoma cells, which naturally expressed very low levels of Bfl-1. Further, knock down of Bfl-1 using siRNA technology in melanoma cells revealed the dependence of these cells on Bfl-1 for their resistance to certain chemotherapeutic agents currently used in melanoma treatment, including the MEK inhibitor PD901. All together, this research contributes to our understanding of Bfl-1 and highlights it as a potentially important therapeutic target in metastatic melanoma.

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“…4,5 They are activated by BH3-only proteins binding to the α2-α5 surface groove, [6][7][8][9][10][11][12] or for Bax, to the α1/α6 'rear pocket'. 13 Binding triggers dissociation of the latch domain (α6-α8) from the core domain (α2-α5), together with exposure of N-terminal epitopes and the BH3 domain.…”

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confidence: 99%

Bak apoptotic pores involve a flexible C-terminal region and juxtaposition of the C-terminal transmembrane domains

et al. 2015

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Bak and Bax mediate apoptotic cell death by oligomerizing and forming a pore in the mitochondrial outer membrane. Both proteins anchor to the outer membrane via a C-terminal transmembrane domain, although its topology within the apoptotic pore is not known. Cysteine-scanning mutagenesis and hydrophilic labeling confirmed that in healthy mitochondria the Bak α9 segment traverses the outer membrane, with 11 central residues shielded from labeling. After pore formation those residues remained shielded, indicating that α9 does not line a pore. Bak (and Bax) activation allowed linkage of α9 to neighboring α9 segments, identifying an α9:α9 interface in Bak (and Bax) oligomers. Although the linkage pattern along α9 indicated a preferred packing surface, there was no evidence of a dimerization motif. Rather, the interface was invoked in part by Bak conformation change and in part by BH3:groove dimerization. The α9:α9 interaction may constitute a secondary interface in Bak oligomers, as it could link BH3:groove dimers to high-order oligomers. Moreover, as high-order oligomers were generated when α9:α9 linkage in the membrane was combined with α6:α6 linkage on the membrane surface, the α6-α9 region in oligomerized Bak is flexible. These findings provide the first view of Bak carboxy terminus (C terminus) membrane topology within the apoptotic pore. Mitochondrial permeabilization during apoptosis is regulated by the Bcl-2 family of proteins. 1-3 Although the Bcl-2 homology 3 (BH3)-only members such as Bid and Bim trigger apoptosis by binding to other family members, the prosurvival members block apoptosis by sequestering their pro-apoptotic relatives. Two remaining members, Bak and Bax, form the apoptotic pore within the mitochondrial outer membrane (MOM).Bak and Bax are globular proteins comprising nine α-helices. 4,5 They are activated by BH3-only proteins binding to the α2-α5 surface groove, 6-12 or for Bax, to the α1/α6 'rear pocket'. 13 Binding triggers dissociation of the latch domain (α6-α8) from the core domain (α2-α5), together with exposure of N-terminal epitopes and the BH3 domain. 6,7,14-16 The exposed BH3 domain then binds to the hydrophobic groove in another Bak or Bax molecule to generate symmetric homodimers. 6,7,14,17,18 In addition to dimerizing, parts of activated Bak and Bax associate with the lipid bilayer. 19 In Bax, the α5 and α6 helices may insert into the MOM, 20 although recent studies indicate that they lie in-plane on the membrane surface, with the hydrophobic α5 sandwiched between the membrane and a BH3:groove dimer interface. 7,[21][22][23] The dimers can be linked via cysteine residues placed in α6, 18,24,25 and more recently via cysteine residues in either α3 or α5, 6,21 allowing detection of the higherorder oligomers associated with pore formation. 26,27 However, whether these interactions are required for high-order oligomers and pore formation remains unclear.Like most Bcl-2 members, Bak and Bax are targeted to the MOM via a hydrophobic C-terminal region. The C terminus targets Bak to the...

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BH3 Domains other than Bim and Bid Can Directly Activate Bax/Bak

Cited by 145 publications

References 44 publications

Measurement of BH3-only protein tolerance

Measurement of BH3-only protein tolerance

Role of the pro-survival molecule Bfl-1 in melanoma

Bak apoptotic pores involve a flexible C-terminal region and juxtaposition of the C-terminal transmembrane domains

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