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. 2012 Aug 10;47(3):359-70.
doi: 10.1016/j.molcel.2012.05.040. Epub 2012 Jun 27.

"V体育平台登录" Bim inhibits autophagy by recruiting Beclin 1 to microtubules

Shouqing Luo  1 , Moises Garcia-Arencibia, Rui Zhao, Claudia Puri, Pearl P C Toh, Oana Sadiq, David C Rubinsztein
Affiliations

Bim inhibits autophagy by recruiting Beclin 1 to microtubules

Shouqing Luo et al. Mol Cell. .

Abstract

Bim is a proapoptotic BH3-only Bcl-2 family member. In response to death stimuli, Bim dissociates from the dynein light chain 1 (DYNLL1/LC8), where it is inactive, and can then initiate Bax/Bak-mediated mitochondria-dependent apoptosis. We found that Bim depletion increases autophagosome synthesis in cells and in vivo, and this effect is inhibited by overexpression of cell death-deficient Bim. Bim inhibits autophagy by interacting with Beclin 1, an autophagy regulator, and this interaction is facilitated by LC8. Bim bridges the Beclin 1-LC8 interaction and thereby inhibits autophagy by mislocalizing Beclin 1 to the dynein motor complex. Starvation, an autophagic stimulus, induces Bim phosphorylation, which abrogates LC8 binding to Bim, leading to dissociation of Bim and Beclin 1. Our data suggest that Bim switches locations between apoptosis-inactive/autophagy-inhibitory and apoptosis-active/autophagy-permissive sites. VSports手机版.

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Graphical abstract
Figure 1
Figure 1
Bim Physically Interacts with Beclin 1 Independently of the Bim BH3 Domain (A) Bcl-xL was cotransfected into HeLa cells with empty vector (IP negative control), Beclin 1-Flag, Beclin 1-Flag/HA-Bim(EL), Beclin 1-Flag/HA-Puma, Beclin 1-Flag/HA-Noxa, or Beclin 1-Flag/Bad. Anti-Flag (M2) was used for immunoprecipitation, and proteins were detected with anti-Bcl-xL, anti-HA, or anti-Bad, anti-Flag (Rabbit). (B) HA-Bim (wild-type) was cotransfected into Bax/Bak double-knockout (DKO) mouse embryonic fibroblasts (MEFs) with empty vector (IP negative control) or Beclin 1-Flag. Immunoprecipitations were performed as in (A). (C) Beclin 1-Flag was cotransfected into Bax/Bak DKO MEFs with empty vector (IP negative control) or HA-Bim (wild-type). Anti-HA was used for immunoprecipitation. ∗, antibody heavy chain. (D) HeLa cell lysates were subjected to GFP antibody (negative control) and anti-Bim antibody immunoprecipitation. Proteins were detected with anti-Beclin 1 and anti-Bim. ∗∗, antibody heavy chain; ∗, antibody light chain. (E) Bcl-xL was cotransfected into HeLa cells with empty vector (IP negative control), wild-type HA-Bim(EL), or HA-Bim L152E F159E [Bim(EL)EE]. Anti-Bim was used for immunoprecipitation. ∗, antibody light chain. (F) HeLa cells were transfected with vector, wild-type HA-Bim, or HA-BimEE. Lysates were probed with the indicated antibodies. HeLa cells treated with staurosporine (STS) for 5 hr were a positive control. Note that wild-type Bim causes apoptosis, which reduces its levels compared to BimEE. (G) Vector, wild-type Bim(EL), or Bim(EL) L152E F159E (BimEE) was transfected into HeLa cells. Transfection efficiency was >90%. After 20 hr, cell viability was determined by measurement pf ATP levels. Data are shown as mean ± SD. ∗∗∗p < 0.001. (H) HeLa cells were transfected with vector/GFP (3:1), wild-type HA-Bim/GFP (3:1), or HA-BimEE/GFP (3:1) (to ensure that Bim-transfected cells also contain GFP). After 16 hr, cells were stained with Annexin V-APC and analyzed by FACS. The percentage of APC and GFP double-positive cells/GFP-positive cells are shown. Data are shown as mean ± SD. ∗∗∗p < 0.001. (I) Bim(EL)/Bcl-xL were cotransfected into HeLa cells with empty vector (IP negative control) or Beclin 1-Flag; Bim(EL)-EE/Bcl-xL were also cotransfected into HeLa cells with Beclin 1-Flag. Anti-Flag (M2) was used for immunoprecipitation. Data are shown as mean ± SD. NS, not significant. (J) BimEL-EE (EL)/vector (IP negative control), BimEL-EE (EL)/Beclin 1-Flag, BimL-EE (L)/Beclin 1-Flag, and BimS-EE (S)/Beclin 1-Flag were transfected into HeLa cells. Anti-Flag was used for immunoprecipitation. Data are shown as mean ± SD. ∗∗∗p < 0.001; NS, not significant. See also Figure S1.
Figure 2
Figure 2
Autophagosome Levels in Bim-Depleted and -Overexpressing Cells (A) Bim−/− and Bim+/+ MEFs were cultured in 6-well dishes. Cells were treated with vehicle or Bafilomycin A1 (Baf) for 4 hr. Blots were probed with the indicated antibodies. LC3-II/tubulin in wild-type control MEFs is set as 1. The relative value of LC3-II/tubulin in Bim-knockout MEFs is shown (n = 5). Data are mean ± SD. ∗∗∗p < 0.001. (B) HeLa cells were transfected with control siRNA and Bim siRNA. After 48 hr, cells were treated with vehicle or Baf for 4 hr. Blots were probed with the indicated antibodies and analyzed as described in (A). ∗∗∗p < 0.001. (C) Bim−/− and Bim+/+ MEFs were transfected with GFP-LC3. The percentages of cells with GFP-LC3 vesicles were assessed. Data are shown as mean ± SD. ∗∗p < 0.01. (D) HeLa cells were transfected with control plasmid (pMKO)/GFP-LC3 or pMKO-BimshRNA/GFP-LC3 (to ensure that GFP-LC3-positive cells also contain BimshRNA or control plasmid, the ratio of pMKO or pMKO-BimshRNA/GFP-LC3 is 3:1). The percentages of cells with GFP-LC3 vesicles were assessed. Data are shown as mean ± SD. ∗∗∗p < 0.001. (E) HeLa cells were transfected with control plasmid (pMKO) or pMKO-BimshRNA. Blots were probed with the indicated antibodies. Data are shown as mean ± SD. ∗∗∗p < 0.001. (F) HeLa cells were transfected with control plasmid (pMKO)/GFP-PX or pMKO-BimshRNA/GFP-PX (3:1). The percentages of cells with GFP-vesicles were assessed. Data are shown as mean ± SD. ∗∗p < 0.01. (G) DFCP1-GFP cells were transfected with control siRNA or Bim siRNA. The numbers of GFP puncta were assessed. Data are shown as mean ± SD.∗p < 0.05. Images represent DFCP1-GFP vesicles in cells transfected with control siRNA and Bim siRNA. Arrows mark DFCP1-GFP puncta. (H) HeLa cells were treated with control siRNA or Bim siRNA. Blots were probed with the indicated antibodies. Data are shown as mean ± SD. ∗∗p < 0.01. (I) Bim(EL)/control siRNA, Bim(EL)/Bim siRNA, Bim(EL)EE/control siRNA, Bim(EL)EE/Bim siRNA, vector/control siRNA, and vector/Bim siRNA were transfected into HeLa cells. Blots were probed with the indicated antibodies. Data are shown as mean ± SD. ∗∗p < 0.01. (J) HeLa cells were transfected with control plasmid or Bim(EL)EE. Blots were probed with the indicated antibodies. Data are shown as mean ± SD. ∗∗p < 0.01. (K) Bax/Bak DKO MEFs were transfected with control plasmid /GFP-LC3, wild-type Bim(EL)/GFP-LC3 (3:1), or Bim (EL) EE/GFP-LC3. The percentages of cells with GFP-LC3 vesicles were assessed. Data are shown as mean ± SD. ∗∗p < 0.01. (L) Two independent control vector (pcDNA3) or Bim(EL)EE stably expressing HeLa cell clones were transfected with GFP-LC3 respectively. The percentages of cells with GFP-LC3 vesicles were assessed. Data are shown as mean ± SD. ∗∗∗p < 0.001. (M) HeLa cells were transfected with control plasmid/GFP-PX or Bim(EL)EE/GFP-PX (3:1). The percentages of cells with GFP-vesicles were assessed. Data are shown as mean ± SD. ∗∗p < 0.01. Fluorescent microscope images show GFP-PX vesicles. See also Figure S2.
Figure 3
Figure 3
Autophagy Is Increased in Bim-Knockout Mice (A) Lysates from spleen-derived T cells of wild-type (Bim+/+) and Bim-knockout (Bim−/−) mice were immunoblotted and probed with indicated antibodies. Statistics were from three knockout and control mice. Data are shown as mean ± SD. ∗∗∗p < 0.001. (B) T cells from Bim+/+ and Bim−/− mice were cultured with/without Baf for 4 hr preceding harvest, immunoblotted, and probed with the indicated antibodies. (C) Spleen-derived T cells from Bim+/+ or Bim−/− mice were stained with rabbit anti-LC3 antibody. Representative confocal images and quantification from triplicates (n = 100–110) are shown. Data are shown as mean ± SD. ∗∗∗p < 0.0001. (D) Bim+/+ and Bim−/− mouse liver lysates were immunoblotted and probed with the indicated antibodies (n = 3). Data are shown as mean ± SD. ∗∗p < 0.01. (E) Bim+/+ and Bim−/− mouse liver lysates were immunoblotted and probed with the indicated antibodies (n = 3). Data are shown as mean ± SD. ∗∗∗p < 0.001. (F) RNA from Bim wild-type or Bim-knockout mouse livers was analyzed by qRT-PCR for p62/beta-actin mRNA. The mean ± SD from three mice per group is shown. NS, not significant. See also Figure S3.
Figure 4
Figure 4
The Effect of Bim on Autophagy Is Beclin 1 Dependent (A) HeLa cells were treated with control siRNA, Bim siRNA + control siRNA, control siRNA + Beclin 1 siRNA, or Bim siRNA + Beclin 1 siRNA. Blots were probed as indicated. Data are shown as mean ± SD. ∗∗p < 0.01. (B) HeLa cells were treated with control siRNA, Bim siRNA + control siRNA, control siRNA + Beclin 1 siRNA, or Bim siRNA + Beclin 1 siRNA. After 24 hr, cells were transfected with GFP-PX for 24 hr. GFP-PX vesicles were assessed with a confocal microscope. Data are shown as mean ± SD. ∗∗p < 0.01. Arrows label cells with increased number/size of GFP-PX vesicles. (C) GFP-mRFP-LC3 HeLa cells were treated with control, Bim siRNA, or Bcl-2 siRNA and then analyzed with Cellomics microscope. Data are shown as mean ± SD. ∗∗∗p < 0.001. (D) GFP-mRFP-LC3 stable HeLa cells were treated with control siRNA, Bim siRNA + control siRNA, control siRNA + Beclin 1 siRNA, or Bim siRNA + Beclin 1 siRNA and then analyzed with Cellomics microscope and matching confocal images are shown. Data are shown as mean ± SD. ∗∗∗p < 0.001. See also Figure S4.
Figure 5
Figure 5
Starvation-Induced BimT116 Phosphorylation Disrupts the Bim-Beclin- 1 Interaction (A) Bim(EL)EE/empty vector (IP negative control) or Bim(EL)EE/Beclin 1-Flag (in duplicate) were transfected into HeLa cells. After 20 hr, one set of cells with Bim(EL)EE/Beclin 1-Flag were starved in HBSS for 2 hr. Anti-Flag antibody (M2) was used for immunoprecipitation, and blots were probed as indicated. Data are shown as mean ± SD. ∗∗∗p < 0.001. (B) Panel i: HeLa cells were treated with control siRNA or Bim siRNA. After 48 hr, one set of transfections were starved in HBSS for 2 hr. Blots were probed as indicated. LC3-II/tubulin ratio of siRNA-transfected cells is set as 1 (n = 3). Data are shown as mean ± SD. ∗∗∗p < 0.001; NS, not significant. Panel ii: HeLa cells were treated with control siRNA or Bim siRNA. After 48 hr, one set of transfections were treated with Baf for 2 hr; one set of transfections were starved and treated with Baf for 2 hr. Blots were probed as indicated and analyzed as in (Bi). ∗∗p < 0.01; NS, not significant. (C) HeLa cells were transfected with control plasmid /GFP-LC3 (3:1), or Bim(EL)EE/GFP-LC3 (3:1). After 20 hr, one set of transfected cells were starved in HBSS for 2 hr and then fixed. The percentages of cells with GFP-LC3 vesicles were assessed. Data are shown as mean ± SD. ∗∗p < 0.01. NS, not significant. (D) BimS-Beclin 1 binding is not sensitive to HBSS starvation. BimEL-EE (EL)/vector (IP negative control), BimEL-EE (EL)/Beclin 1-Flag (two replicates), BimL-EE (L)/Beclin 1-Flag (two replicates) or BimS-EE (S)/Beclin 1-Flag (two replicates) were transfected into HeLa cells. After 20 hr, one of EL-Beclin 1-Flag transfections, one of L-Beclin-Flag transfections and one of S-Beclin 1-Flag transfections were subjected to 2 hr HBSS starvation. Anti-Flag (M2) was used for immunoprecipitation. (E) HBSS starvation increases Bim T116 phosphorylation. Bim(EL)EE or BimEE(EL)-T116A were transfected into HeLa cells. After 20 hr, one set of Bim(EL)EE transfections and one of Bim(EL)EE-T116A were starved for 2 hr in HBSS. Blots were probed with the indicated antibodies. (F) Bim T116 phosphorylation disables Bim-Beclin 1 interaction. Bim(EL)EE /vector (IP negative control), Bim(EL)EE/Beclin 1-Flag (in duplicate), or Bim(EL)EE-T116E (phospho-mimic, designated as T116E here)/Beclin-Flag (in duplicate) were transfected into HeLa cells. After 20 hr, one set of Bim(EL)EE/Beclin 1-Flag transfections and one of Bim(EL)EE-T116E/Beclin 1-Flag transfections were starved for 2 hr in HBSS (Starv). Anti-Flag (M2) was used for immunoprecipitation. (G) HeLa cells were transfected with control plasmid /GFP-LC3, Bim(EL)-EE/GFP-LC3 (3:1), or Bim(EL)-EE T116E/GFP-LC3 (3:1). After 20 hr, one set of transfected cells were starved in HBSS for 2 hr and the cells were then fixed. The percentages of cells with GFP-LC3 vesicles were assessed. Data are shown as mean ± SD. ∗∗p < 0.01; NS, not significant. See also Figure S5.
Figure 6
Figure 6
LC8 Promotes the Bim-Beclin 1 Interaction (A) Bim-147 does not bind to Beclin 1. Beclin 1-Flag/vector (IP negative control), Beclin 1-Flag/Myc-BimEL-1-147aa (Myc-147), or Beclin 1-Flag/Myc-BimEL-ΔBH3 (Myc-ΔBH3) were transfected into HeLa cells. Anti-Myc (Rabbit) was used for immunoprecipitation. (B) Bim-147 is competent for LC8 binding. LC8/vector (IP negative control), LC8/Myc-BimEL-1-147aa (Myc-147), or LC8/Myc-BimEL-ΔBH3 (Myc-ΔBH3) were transfected into HeLa cells. Anti-Myc (Rabbit) was used for immunoprecipitation. (C) Mutating LC8 binding consensus sites within Bim disrupts the Bim-LC8 interaction. Bim(EL)EE/vector (IP negative control), Bim(EL)EE/Myc-LC8, Bim(EL)EE-S109A, S113A, T114A (AAA)/ Myc-LC8, or Bim(EL)EE-T116E/ Myc-LC8 were transfected into HeLa cells. Anti-Myc (Rabbit) was used for immunoprecipitation. Data are shown as mean ± SD. ∗∗∗p < 0.001. (D) Mutating LC8 binding consensus sites within Bim disrupts the Bim-Beclin 1 interaction. Bim(EL)EE/vector (IP negative control), Bim(EL)EE/Beclin 1-Flag, Bim(EL)EE-S109A, S113A, T114A (AAA)/Beclin 1-Flag, or Bim(EL)EE-T116E/Beclin 1-Flag were transfected into HeLa cells. Anti-Flag (M2) was used for immunoprecipitation. Data are shown as mean ± SD. ∗∗∗p < 0.001. (E) Bim-S does not bind to LC8. BimEL-EE (EL)/vector (IP negative control), BimEL-EE (EL)/Myc-LC8, BimL-EE (L)/Myc-LC8, or BimS-EE (S)/Myc-LC8 were transfected into HeLa cells. Anti-Myc (Rabbit) was used for immunoprecipitation. (F) Model of LC8 promoting Beclin 1-Bim interaction. In nutrients, LC8 binds the Bim consensus sequence (DKSTQTP). This enables a transition of the Bim C terminus from a disordered state to α helices and a β sheet (Barbar, 2008), which favors the Bim-Beclin 1 interaction. In starvation conditions, Bim is phosphorylated at T116 within the consensus sequence (DKSTQpTP) leading to its dissociation from LC8 (Lei and Davis, 2003). Bim returns to the disordered state, which binds to Beclin 1 less effectively. Grey boxes, higher degree of disorder; white box, lower degree of disorder (Barbar, 2008). (G) LC8 enhances Bim-Beclin 1 interaction in vitro. His-Bim, His-LC8 and GST-Beclin 1 were expressed in BL21(DE3) E. coli and purified. Two micrograms of His-Bim was combined with 2 μg GST without or with 1 μg His-LC8 (as controls); 2 μg His-Bim was combined with 2 μg GST-Beclin 1 without or with 1 μg His-LC8. The mixtures were incubated in buffer A for 3 hr. Glutathione beads were then used to pull down GST or GST-Beclin 1. The pulldown products were detected with anti-Bim and anti-Beclin 1. (H) LC8 siRNA knockdown reduces the Bim-Beclin 1 interaction. Control siRNA or LC8 siRNA were transfected into HeLa cells. After 48 hr, HA-Bim(EL)EE/vector (IP negative control) or HA-Bim(EL)EE/Beclin 1-Flag was transfected into control siRNA transfected HeLa cells; HA-Bim(EL)EE/Beclin 1-Flag was transfected into LC8 siRNA-transfected HeLa cells. Anti-Flag (M2) was used for immunoprecipitation. Note that in the presence of BimEE, endogenous LC8 was pulled down by Beclin 1 when cells were treated with control siRNA. Data are shown as mean ± SD. ∗∗∗p < 0.001. See also Figure S6.
Figure 7
Figure 7
Bim Suppresses Autophagy by Mediating the LC8-Beclin 1 Interaction (A) HeLa cells were transfected with vector (vec) /GFP-LC3, BimEL-EE (EL)/GFP-LC3, BimL-EE (L)/GFP-LC3, BimS-EE (S)/GFP-LC3, or BimEL-EE-AAA (AAA)/GFP-LC3 (3:1). The percentages of cells with GFP-LC3 vesicles were assessed. Data are shown as mean ± SD. ∗∗∗p < 0.001; ∗∗p < 0.01; NS, not significant. Note that BimEL-EE-S109A, S113A, T114A is designated as BimEL-EE-AAA. (B) Bim bridges the Beclin 1-LC8 interaction. Dynein light chain1 (Myc-LC8)/empty vectors (IP negative control), Myc-LC8/Beclin 1-Flag/empty vector, Myc-LC8/Beclin 1-Flag/BimEL-EE (EL), Myc-LC8/Beclin 1-Flag/BimL-EE (L), Myc-LC8/Beclin 1-Flag/BimS-EE (S), and Myc-LC8/Beclin 1-Flag/BimEL-EE-S109A, S113A, T114A (AAA) were transfected into HeLa cells. Anti-Flag (M2) was used for immunoprecipitation. (C) Starvation reduces the ability of Bim to bridge the Beclin 1-LC8 interaction. Myc-LC8/empty vectors (IP negative control), Myc-LC8/Beclin 1-Flag/empty vector, or Myc-LC8/Beclin 1-Flag/HA-BimEL-EE (HA-Bim) (two replicates) were transfected into HeLa cells. After 20 hr, one set of cells with Myc-LC8/Beclin 1-Flag/HA-HA-Bim was starved in HBSS for 2 hr. Anti-Flag (M2) antibody was used for immunoprecipitation. (D) HeLa cells were cultured with DMEM with 10% serum (Control) or starved (Starve) in HBSS for 2 hr. The fixed cells were stained with Beclin 1 and tubulin antibodies and analyzed by confocal microscopy. White boxes show the areas where Beclin 1 is enriched. Yellow boxes show enlarged areas. (E) HeLa cells were treated with control siRNA or LC8 siRNA. After 24 hr, cells were split. Vector/GFP-LC3 or Bim(EL)EE/GFP-LC3 (3:1) were transfected into the control siRNA-transfected or LC8 siRNA-transfected cells. The percentages of cells with GFP-LC3 vesicles were assessed. Data are shown as mean ± SD. ∗∗p < 0.01; NS, not significant. (F) HeLa cells were treated with control siRNA, Bim siRNA, or LC8 siRNA for 48 hr. Cells were then fixed in 37°C, 4% PFA for 10 min. Cells were stained with Beclin 1 and tubulin antibodies and analyzed by confocal microscopy. White boxes/triangle show areas where Beclin 1 is enriched. Yellow boxes show enlarged areas. Colocalizations were quantified from images in 12–15 cells with Volocity program (Colocalization coefficient Mx). Data are shown as mean ± SD. ∗∗∗p < 0.001. (G) Bim inhibits autophagy. In normal conditions, LC8 recruits Beclin 1 to the microtubule-based dynein motor complex via Bim, thereby inhibiting autophagosome formation (Bim possesses autophagy-inhibitory activity). Under stress conditions (e.g., nutrient starvation), Bim phosphorylation at T116 by JNK leads to its dissociation from LC8, and this dissociation triggers the dissociation of Bim-Beclin 1. The Beclin 1-Vps34 can then localize to isolation membranes (IMs) to enable autophagosome synthesis. Free Bim can induce apoptosis. See also Figure S7.
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