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An interconnected hierarchical model of cell death regulation by the BCL-2 family

Nature Cell Biology volume 17, pages 1270–1281 (2015)Cite this article

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Abstract

Multidomain pro-apoptotic BAX and BAK, once activated, permeabilize mitochondria to trigger apoptosis, whereas anti-apoptotic BCL-2 members preserve mitochondrial integrity. The BH3-only molecules (BH3s) promote apoptosis by either activating BAX–BAK or inactivating anti-apoptotic members. Here, we present biochemical and genetic evidence that NOXA is a bona fide activator BH3. Using combinatorial gain-of-function and loss-of-function approaches in Bid−/−Bim−/−Puma−/−Noxa−/− and Bax−/−Bak−/− cells, we have constructed an interconnected hierarchical model that accommodates and explains how the intricate interplays between the BCL-2 members dictate cellular survival versus death. BID, BIM, PUMA and NOXA directly induce stepwise, bimodal activation of BAX–BAK. BCL-2, BCL-XL and MCL-1 inhibit both modes of BAX–BAK activation by sequestering activator BH3s and ‘BH3-exposed’ monomers of BAX–BAK, respectively. Furthermore, autoactivation of BAX and BAK can occur independently of activator BH3s through downregulation of BCL-2, BCL-XL and MCL-1. Our studies lay a foundation for targeting the BCL-2 family for treating diseases with dysregulated apoptosis.

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Figure 1: NOXA directly activates BAX and BAK independently of BID, BIM and PUMA.
Figure 2: Noxa deficiency further protects Bid−/−Bim−/−Puma−/− mouse embryonic fibroblasts or small intestine from apoptosis.
Figure 3: Quadruple deficiency of Bid, Bim, Puma and Noxa abrogates apoptosis in transformed MEFs triggered by growth factor deprivation and ER stress but not genotoxic stress.
Figure 4: DNA damage activates BAX- and BAK-dependent mitochondrial apoptosis in transformed Bid−/−Bim−/−Puma−/−Noxa−/− QKO MEFs.
Figure 5: BAX and BAK can be autoactivated by DNA damage independently of activators BID, BIM, PUMA and NOXA through downregulation of BCL-2, BCL-XL and MCL-1.
Figure 6: BCL-XL is superior to BCL-2 and MCL-1 in preventing DNA damage-induced apoptosis owing to its dual inhibition of BAX and BAK as well as higher protein stability.
Figure 7: A schematic diagram depicting the interconnected hierarchical model in which the BCL-2 family proteins regulate mitochondrion-dependent cell death.

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Acknowledgements

We apologize to all of the investigators whose research could not be appropriately cited owing to space limitation. We thank H.-F. Chen and S. Han for technical assistance. This work was supported by grants to E.H.C. from the NIH (R01CA125562) and the American Cancer Society (118518-RSG-10-030-01-CCG), and to E.G. from the NIH (R01CA178394) This work was also supported by the NIH P30CA008748.

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Authors and Affiliations

  1. Human Oncology and Pathogenesis Program, Memorial Sloan Kettering Cancer Center, New York, New York 10065, USA

    Hui-Chen Chen, Masayuki Kanai, Akane Inoue-Yamauchi, Ho-Chou Tu, Yafen Huang, Shugaku Takeda, Po M. Chan, Yogesh Tengarai Ganesan, Chung-Ping Liao, James J. Hsieh & Emily H. Cheng

  2. Department of Medicine, University of Chicago, Chicago, Illinois 60637, USA

    Decheng Ren

  3. Department of Pharmacological Sciences, Stony Brook University, Stony Brook, New York 11794, USA

    Hyungjin Kim

  4. Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York 10461, USA

    Denis E. Reyna & Evripidis Gavathiotis

  5. Department of Medicine, Memorial Sloan Kettering Cancer Center, New York, New York 10065, USA

    James J. Hsieh

  6. Department of Pathology, Memorial Sloan Kettering Cancer Center, New York, New York 10065, USA

    Emily H. Cheng

  7. Department of Pathology and Laboratory Medicine, Weill Cornell Medical College, Cornell University, New York, New York 10065, USA

    Emily H. Cheng

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Contributions

H.-C.C. designed and conducted experiments, and analysed data. E.H.C. designed research, analysed data and supervised the project. H.-C.T., M.K., Y.H., H.K., A.I.-Y., Y.T.G. and D.E.R. conducted experiments. J.J.H. and E.G. supervised some experiments. H.C.T., D.R., P.M.C., S.T. and C.-P.L. generated essential reagents.

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Correspondence to Emily H. Cheng.

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Integrated supplementary information

Supplementary Figure 2 Triple deletion of Bid, Bim, and Puma fails to completely block intrinsic apoptosis in mouse embryonic fibroblasts.

E1A/Ras-transformed wild-type (WT), Bid−/−Bim−/−, Bim−/−Puma−/−, or Bid−/−Bim−/−Puma−/− MEFs were untreated, or cultured in the absence of serum or glucose, or in the presence of tunicamycin, thapsigargin or etoposide. Cell death was quantified by annexin-V staining at the indicated times (mean ± s.d., n = 3 independent experiments). ∗, P < 0.05; ∗∗, P < 0.01; ∗∗∗, P < 0.001 (Student’s t-test).

Supplementary Figure 3

(a) Reticulocyte lysates abrogates the cytochrome c releasing activity of NOXA. Isolated wild-type mitochondria were incubated with IVTT mouse NOXA generated using wheat germ extract (WGE) in the absence or presence of reticulocyte lysates (R) or IVTT mouse NOXA generated using reticulocyte lysates (R) in the absence or presence of wheat germ extract (WGE) at 30 °C for 30 min, after which the release of cytochrome c was quantified by ELISA assays (mean ± s.d., n = 3 independent experiments). (b) Isolated wild-type mitochondria were incubated with IVTT mouse tBID generated using wheat germ extract (WGE) in the absence or presence of reticulocyte lysates (R) at 30 °C for 30 min, after which the release of cytochrome c was quantified by ELISA assays (mean ± s.d., n = 3 independent experiments). (c) The expression of Noxa mRNA is comparable in wild-type and Bid−/−Bim−/−Puma−/− MEFs. The mRNA levels of Noxa in primary wild-type or Bid−/−Bim−/−Puma−/− MEFs were assessed by qRT-PCR. Data were normalized against GAPDH (mean ± s.d., n = 3 independent experiments). (d) Bid−/−Bim−/−Puma−/− TKO and Bid−/−Bim−/−Puma−/−Noxa−/− QKO mice display persistence of interdigital webs. Ventral views of paws from WT, Bid−/−Bim−/−Puma−/− TKO, and Bid−/−Bim−/−Puma−/−Noxa−/− QKO mice at 6 to 8 weeks of age. Representative images from at least 20 mice are shown. (e) Bid−/−Bim−/−Puma−/− TKO and Bid−/−Bim−/−Puma−/−Noxa−/− QKO mice fail to develop external vaginal introituses. Photographs of vaginal openings from WT, Bid−/−Bim−/−Puma−/− TKO, and Bid−/−Bim−/−Puma−/−Noxa−/− QKO mice at 6 to 8 weeks of age. Arrows point to external vaginal region. Representative images from at least 6 mice are shown. (f) Noxa expression is lower both at the basal level and in response to genotoxic stress in T-cells than transformed mouse embryonic fibroblasts. The mRNA levels of Noxa in the indicated cells untreated or treated with etoposide for 6 h were assessed by qRT-PCR. Data were normalized against 18S rRNA (mean ± s.d., n = 3 independent experiments). ∗∗, P < 0.01 (Student’s t-test).

Supplementary Figure 4 Total body irradiation-induced apoptosis in spleen was greatly reduced in both Bid−/−Bim−/−Puma−/− and Bid−/−Bim−/−Puma−/−Noxa−/− mice.

(a) Apoptosis in the spleens of wild-type, Bid−/−Bim−/−Puma−/− TKO, or Bid−/−Bim−/−Puma−/−Noxa−/− QKO mice at 8 to 17 weeks of age at 4 h after 18 Gy total body irradiation was assessed by TUNEL staining. Representative light microscopy images from two independent experiments are shown (brown, magnification 200×). Scale bars, 50 μm. (b) Wild-type, Bid−/−Bim−/−Puma−/− TKO, or Bid−/−Bim−/−Puma−/−Noxa−/− QKO mice at 8 to 10 weeks of age were unirradiated (n = 3 for each genotype) or irradiated with 5 Gy total body irradiation (n = 3 for each genotype). 3 days later, total numbers of splenocytes and CD4+ splenocytes were assessed. The percentage of survival was defined as the numbers of viable cells from irradiated mice divided by those from unirradiated ones with the same genotypes (mean ± s.d., n = 3 for each genotype). ∗∗, P < 0.01 (Student’s t-test).

Supplementary Figure 5

(a) Immunoblot analyses of siRNA- or shRNA-mediated knockdown. SV40-transformed Bid−/−Bim−/−Puma−/−Noxa−/− MEFs infected with retrovirus expressing shRNA against the indicated genes, or transfected with the indicated siRNA, were harvested at 72 h later and analyzed with immunoblots using the indicated antibodies. SV40-transformed Bid−/−Bim−/−Puma−/−Noxa−/− MEFs were sequentially infected with retrovirus expressing HA-tagged BIK or BMF and retrovirus expressing shRNA against luciferase, Bik, or Bmf. The expression of HA-tagged BIK or BMF was assessed by an anti-HA immunoblot. (b) SV40-transformed Bid−/−Bim−/−Puma−/−Noxa−/− MEFs infected with retrovirus expressing shRNA again luciferase, Bmf, or Bik, were harvested at 72 h later. The mRNA levels of Bmf or Bik were assessed by qRT-PCR. Data were normalized against GAPDH (mean ± s.d., n = 3 independent experiments). (c) SV40-transformed Bid−/−Bim−/−Puma−/−Noxa−/− MEFs transfected with scrambled siRNA (siScr) or siRNA against Hrk were harvested at 72 h later. The mRNA levels of Hrk were assessed by qRT-PCR. Data were normalized against GAPDH (mean ± s.d., n = 3 independent experiments). (d) SV40-transformed Bid−/−Bim−/−Puma−/−Noxa−/− MEFs transfected with scrambled siRNA (siScr) or siRNA against Hrk were untreated or treated with etoposide for 2 days. Cell death was quantified by annexin-V staining (mean ± s.d., n = 3 independent experiments). ∗∗, P < 0.01; ∗∗∗, P < 0.001 (Student’s t-test).

Supplementary Figure 6

(a) SV40-transformed wild-type MEFs, untreated or treated with etoposide, tunicamycin (TC), or thapsigargin (TG), were subjected to immunoblot analysis using the indicated antibodies. (b) CD4+ T cells purified from the spleens of two wild-type mice were untreated or treated with etoposide for 18 h, and subjected to immunoblot analysis using the indicated antibodies. (c) SV40-transformed Bid−/−Bim−/−Puma−/−Noxa−/− QKO MEFs, untreated or treated with etoposide, or irradiated with 20 Gy γ-irradiation or UV-C, were subjected to immunoblot analysis using the indicated antibodies. (d) SV40-transformed wild-type, Bid−/−Bim−/−Puma−/− TKO, Bid−/−Bim−/−Puma−/−Noxa−/− QKO, or Bax−/−Bak−/− DKO MEFs were untreated or irradiated with 20 Gy γ-irradiation. Cell death was quantified by annexin-V staining at the indicated times (mean ± s.d., n = 3 independent experiments). (e) Knockdown of Bcl-2, Bcl-xL or Mcl-1 does not sensitize QKO cells to overexpression of BAD, BMF, BIK or HRK. SV40-transformed Bid−/−Bim−/−Puma−/−Noxa−/− QKO MEFs were transfected with scrambled siRNA (siScr) or siRNA against Bcl-2, Bcl-xL or Mcl-1. After 2 days, cells were infected with retrovirus expressing GFP or the indicated BH3-only proteins. Cell death was quantified by annexin-V staining at 30 h (mean ± s.d., n = 3 independent experiments). (f) SV40-transformed wild-type or Bid−/−Bim−/−Puma−/− TKO MEFs stably expressing GFP, HA-BCL-2, HA-BCL-XL or HA-MCL-1 were subjected to anti-HA immunoprecipitation in 0.2% NP-40 lysis buffer. The input (5%) and immunoprecipitates were analyzed by anti-BAX, anti-BAK, and anti-HA immunoblots. ∗∗, P < 0.01; ∗∗∗, P < 0.001 (Student’s t-test).

Supplementary Figure 7 A schematic depicts activation of BAX and BAK upon DNA damage.

Supplementary Figure 8 Full scans of immunoblots.

In some experiments, membranes were cut prior to probing each strip with a separate antibody.

Supplementary Table 1 Bid−/−Bim−/−Puma−/− and Bid−/−Bim−/−Puma−/−Noxa−/− mice display persistent interdigital webs and imperforate vagina.
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Chen, HC., Kanai, M., Inoue-Yamauchi, A. et al. An interconnected hierarchical model of cell death regulation by the BCL-2 family. Nat Cell Biol 17, 1270–1281 (2015). https://doi.org/10.1038/ncb3236

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