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. 2012 Aug 10;47(3-8):359–370. doi: 10.1016/j.molcel.2012.05.040

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© 2012 ELL & Excerpta Medica.

Open Access under CC BY 3.0 license

PMC Copyright notice

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.