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. 2011 Nov 11;30(24):4908-20.
doi: 10.1038/emboj.2011.413.

Inhibition of autophagy by TAB2 and TAB3

Alfredo Criollo  1 , Mireia Niso-Santano, Shoaib Ahmad Malik, Mickael Michaud, Eugenia Morselli, Guillermo Mariño, Sylvie Lachkar, Alexander V Arkhipenko, Francis Harper, Gérard Pierron, Jean-Christophe Rain, Jun Ninomiya-Tsuji, José M Fuentes, Sergio Lavandero, Lorenzo Galluzzi, Maria Chiara Maiuri, Guido Kroemer
Affiliations

Inhibition of autophagy by TAB2 and TAB3

Alfredo Criollo et al. EMBO J. .

Abstract

Autophagic responses are coupled to the activation of the inhibitor of NF-κB kinase (IKK). Here, we report that the essential autophagy mediator Beclin 1 and TGFβ-activated kinase 1 (TAK1)-binding proteins 2 and 3 (TAB2 and TAB3), two upstream activators of the TAK1-IKK signalling axis, constitutively interact with each other via their coiled-coil domains (CCDs) VSports手机版. Upon autophagy induction, TAB2 and TAB3 dissociate from Beclin 1 and bind TAK1. Moreover, overexpression of TAB2 and TAB3 suppresses, while their depletion triggers, autophagy. The expression of the C-terminal domain of TAB2 or TAB3 or that of the CCD of Beclin 1 competitively disrupts the interaction between endogenous Beclin 1, TAB2 and TAB3, hence stimulating autophagy through a pathway that requires endogenous Beclin 1, TAK1 and IKK to be optimally efficient. These results point to the existence of an autophagy-stimulatory 'switch' whereby TAB2 and TAB3 abandon inhibitory interactions with Beclin 1 to engage in a stimulatory liaison with TAK1. .

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Conflict of interest statement (VSports app下载)

The authors declare that they have no conflict of interest.

Figures

Figure 1
Figure 1
Identification of novel Beclin 1 interactors. (A) Beclin 1 (BCN1) interactors identified by yeast two-hybrid technology. Proteins binding to BCN1 are listed and their interacting domains are indicated by black bars. Numbers refer to amino-acid positions. (B) Identification of TAB2 and TAB3 fragments interacting with BCN1 in the yeast two-hybrid system. Blue lines depict the fragments of TAB2 or TAB3 that were found to interact with BCN1 (numbers on the right refer to the amount of yeast clones identified for each fragment). The minimal domain required for the interaction is referred to as Beclin-binding domain (BBD). (C) Constructs derived from TAB2 and TAB3 used in this study. (D, E) Co-immunoprecipitation of TAB2 or TAB3 with BCN1. The indicated constructs, namely HA-tagged and T7-tagged TAB2, and TAB3 constructs in (D) and (E), respectively, and Flag-tagged Beclin 1 (Flag–BCN1) were transfected into HeLa cells alone or in combination. Twenty-four hours later, TAB2 and TAB3 were immunoprecipitated with antibodies specific for HA (D) or T7 (E) and the precipitate was separated by SDS–PAGE and revealed with an antibody specific for Flag. (F) Immunoprecipitation of endogenous BCN1 with endogenous TAB2 or TAB3. HeLa cells were subjected to autophagy induction with starvation conditions, 1 μM rapamycin or 30 μM pifithrin α (PFTα) for the indicated time and then processed for TAB2 or TAB3 immunoprecipitation followed by the immunodetection of BCN1, TAK1, TAB2 and TAB3. Results in (E) and (F) are representative for three independent experiments.
Figure 2
Figure 2
Reduced interaction between Beclin 1, TAB and TAB3 in conditions of autophagy induction. (A, B) Inhibition of autophagy by dominant-negative (DN) TAK1. HeLa cells were co-transfected with a GFP–LC3-encoding construct plus pcDNA3.1 (empty vector), or plasmids for the expression of WT TAK1 (TAK1WT) or the DN TAK1K63W mutant. One day later, cells were either left untreated (control) or driven into autophagy by starvation or by the administration of 1 μM rapamycin or 30 μM pifithrin α (PFTα), followed by immunoblotting for the detection of TAK1 and endogenous LC3 (A) or immunofluorescence microscopy for the quantification of cells with cytosolic GFP–LC3 puncta (GFP–LC3VAC cells) (B) (mean values±s.d., n=3; *P<0.01 versus control cells). GAPDH levels were monitored to ensure equal loading. (C, D) Inhibition of autophagy by knockdown of VPS34, Beclin 1 (BCN1) and TAK1. siRNAs that effectively deplete VPS34, BCN1 and TAK1 were co-transfected with a GFP–LC3-encoding plasmid in HeLa cells. Autophagy was then induced as in (A) and the frequency of GFP–LC3VAC cells (mean values±s.d., n=3; *P<0.01 versus control cells) was determined. (E, F) The same setting shown in (C, D) was performed with U2OS cells and FYVE–RFP (mean values±s.d., n=3; *P<0.01, **P<0.001 versus control cells).
Figure 3
Figure 3
Induction of autophagosomes by depletion of TAB2 or TAB3. (A, B) Detection of autophagic GFP–LC3+ puncta. HeLa or U2OS cells stably expressing GFP–LC3 were transfected with siRNAs targeting TAK1, TAB1, TAB2 or TAB3 or with a control siRNA (siUNR). One day later, the subcellular localization and abundance of GFP–LC3 or immunostained TAB2 or TAB3 was determined by epifluorescence microscopy. Representative images are shown in (A) (HeLa cells) and quantitative results (mean values±s.d., n=3; *P<0.01 versus siUNR-transfected cells) are depicted in (B) (U2OS cells). (C) Lipidation of LC3 induced by TAB2 or TAB3 knockdown. Representative immunoblots showing the conversion of non-lipidated LC3 (LC3-I) to its lipidated variant (LC3-II) as well as SQSTM1/p62 protein levels are shown. GAPDH levels were monitored to ensure equal loading. (D, E) Quantification of autophagosomes and autophagolysosomes by transmission electron microscopy. Representative images of HeLa cells transfected with siUNR or with TAB2- or TAB3-targeting siRNAs are shown in (D), and quantitative results are depicted in (E) (mean values±s.d., n=3; *P<0.01 versus siUNR-transfected cells). (F) Epistatic analysis of the effects of TAB2 and TAB3 depletion on autophagy. HeLa cells stably expressing GFP–LC3 were transfected with siRNAs specific for TAB2 or TAB3 and/or with cDNAs coding for full-length HA-tagged TAB2 (HA–TAB2) or TAB3 (HA–TAB3). Twenty-four hours later, the frequency of cells exhibiting >5 GFP–LC3+ cytosolic puncta (GFP–LC3VAC cells) was determined. Results are mean values±s.d. (n=3; *P<0.01 versus siUNR-transfected cells). (G) U2OS cells stably expressing FYVE–RFP were transfected with siUNR, or with siRNAs specific for TAB2, TAB3, VPS34, Beclin 1 (BCN1) and TAK1, in the indicated combinations. Forty-eight hours later, the percentage of cells with RFP–FYVE+ puncta cells was determined. Results are mean values±s.d. (n=3; *P<0.01 versus siUNR-transfected cells).
Figure 4
Figure 4
Mechanisms of autophagy induced by depletion of TAB2 or TAB3. (A–D) Impact of bafilomycin A1 (BafA1) on the induction of GFP–LC3+ puncta by TAB2 and TAB3 depletion. HeLa cells stably expressing GFP–LC3 were transfected with a control siRNA (siUNR) or with siRNAs targeting TAB2 and TAB3 for 24 h. During the last 12 h of this period, BafA1 was optionally added. After fixation and permeabilization, LAMP2 was detected by immunofluorescence. Representative confocal microphotographs for the TAB2 siRNA are shown (A), together with the profiles of colocalization of fluorescent signals (B) along the indicated direction (α–ω). Columns in (C) represent the percentage of colocalization of GFP–LC3 and LAMP2 (mean values±s.d.; *P<0.01 versus siUNR-transfected cells), as quantified in at least 50 cells for each condition. The frequency (mean±s.d.) of cells with >5 GFP–LC3+ cytosolic puncta (GFP–LC3VAC cells) is plotted in (D). (E) Impact of BafA1 on LC3 lipidation. MEFs with the indicated genotypes were cultured in complete medium supplemented with BafA1 for 12 h and the proportion of LC3-I/LC3-II was determined by immunoblotting. GAPDH levels were monitored to ensure equal loading. (F, G) Impact of autophagy-relevant proteins and of the TAK1-IKK signalling axis on GFP–LC3 aggregation induced by the depletion of TAB2 or TAB3. HeLa cells stably expressing GFP–LC3 were transfected with siUNR or with siRNAs targeting the indicated proteins, alone or in combination, and 48 h later GFP–LC3VAC cells were quantified (mean values±s.d., n=4; *P<0.01 versus siUNR-transfected cells). (H) Inhibition of autophagy by dominant-negative (DN) TAK1. HeLa cells stably expressing GFP–LC3 were co-transfected with pcDNA3.1 (empty vector) or with plasmids encoding WT (TAK1WT) or a DN TAK1 variant (TAK1K63W) together with the indicated siRNAs for 24 h, followed by the quantification of GFP–LC3VAC cells (mean values±s.d., n=3, *P<0.01 versus siUNR-, pcDNA3.1-transfected cells).
Figure 5
Figure 5
Inhibition of autophagy by full-length TAB2 and TAB3 but induction by their C-terminal fragments. (A) Effects of full-length TAB2 and TAB3 or their deletion mutants (as in Figure 1C) on autophagy. HeLa cells stably expressing GFP–LC3 were transfected with pcDNA3.1 (empty vector) or with plasmids encoding the indicated TAB2 and TAB3 variants for 24 h, then driven into autophagy by starvation or by the administration of 1 μM rapamycin or 30 μM pifithrin α (PFTα) for 4 h. Finally, the frequency (mean±s.d., n=3) of cells with >5 GFP–LC3+ cytosolic puncta (GFP–LC3VAC cells) was assessed (*P<0.01 versus control cells transfected with the same plasmid; #P<0.01 versus pcDNA3.1-transfected cells treated with the same pro-autophagic trigger). (B) U2OS cells stably expressing FYVE–RFP were co-transfected with pcDNA3.1 or with vectors encoding TAB2C or TAB3C together with a control siRNA (siUNR) or with siRNAs specific for VPS34, Beclin 1 (BCN1) or TAK1 for 24 h, followed by the quantification of cells exhibiting FYVE–RFP+ dots (FYVE–RFP+). Results are mean values±s.d. (n=3; *P<0.01 versus siUNR-, pcDNA3.1-transfected cells). (C) Inhibition of the interaction between endogenous TAB2, TAB3 and BCN1 by C-terminal fragments of TAB2 and TAB3. Forty-eight hours after transfection with pcDNA3.1 or plasmids coding for the indicated proteins, cells were lysed, TAB2 or TAB3 was immunoprecipitated and BCN1 was immunodetected. GAPDH levels were monitored to ensure equal loading. This experiment has been done three times, yielding comparable results. (D) Mechanisms of autophagy induction by the Beclin-binding domain (BBD)-containing C-terminal fragments of TAB2 and TAB3. HeLa cells were transfected with pcDNA3.1, TAB2C- or TAB3C-encoding plasmids in combination with the indicated siRNAs for 24 h, followed by the quantification of GFP–LC3VAC cells (mean values±s.d., n=3; *P<0.01 versus siUNR-, pcDNA3.1-transfected cells).
Figure 6
Figure 6
Induction of autophagy by a Beclin 1 fragment that disrupts the interaction between endogenous Beclin 1, TAB2 and TAB3. (A) Determination of the TAB-binding domain (TBD) within Beclin 1 (BCN1). Yeast two-hybrid technology was used to screen for positive (+) or negative interactions (−) between BCN1 fragments and full-length TAB2. (B) Schematic presentation of the constructs used in subsequent experiments (BBD, Beclin-binding domain). (C) Confirmation of the TBD by immunoprecipitation. The indicated constructs were transfected into HeLa cells, followed by lysis, immunoprecipitation of HA-tagged full-length TAB2 or TAB3 and detection of His-tagged constructs. (D, E) Inhibition of the interaction between endogenous BCN1, TAB2 and TAB3 by a BCN1 fragment corresponding to the TBD. HeLa cells were transfected with pcDNA3.1 (empty vector) or with plasmids encoding the TBD or a His-tagged Beclin 1 variant lacking the TBD (His–BCN1ΔTBD), followed by co-immunoprecipitation of endogenous TAB2 (D) or TAB3 (E) and detection of BCN1. (F) Induction of autophagy by the TBD. HeLa cells stably expressing GFP–LC3 were transfected with pcDNA3.1 or constructs encoding the indicated BCN1 variants. After 24 h, Flag-tagged proteins were detected by immunoblotting and the frequency of cells with >5 GFP–LC3+ cytosolic puncta (GFP–LC3VAC cells) was assessed (mean values±s.d., n=3; *P<0.01, **P<0.001 versus pcDNA3.1-transfected cells). (G, H) Mechanisms of autophagy induction by the TBD. (G) U2OS cells stably expressing RFP–FYVE were transfected pcDNA3.1 or plasmids for the expression of TBD, BCN1 or BCN1ΔTBD in combination with a control siRNA (siUNR) or siRNAs that effectively deplete VPS4, BCN1 and TAK1. Forty-eight hours later, the percentage of cells exhibiting FYVE–RFP+ dots (FYVE–RFP+) was assessed. (G). Alternatively, HeLa cells stably expressing GFP–LC3 were transfected with pcDNA3.1 or with a TBD-encoding plasmids plus siUNR or siRNAs specific the indicated proteins. Forty-eight hours later, the percentage of GFP–LC3VAC cells was determined (H). Results are mean values±s.d. (n=3, *P<0.01 versus siUNR-, pcDNA3.1-transfected cells). (I) Inhibition of TBD-induced autophagy by dominant-negative (DN) TAK1. Cells were co-transfected pcDNA3.1 or vectors encoding WT TAK1 (TAK1WT) or a DN TAK1 variant (TAK1K63W) alone or together with a TBD-encoding plasmid for 24 h, followed by the quantification of GFP–LC3VAC cells (mean values±s.d., n=3; *P<0.01 versus pcDNA3.1-transfected cells).
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