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. 2017 May 18;66(4):517-532.e9.
doi: 10.1016/j.molcel.2017.04.027.

Bromodomain Protein BRD4 Is a Transcriptional Repressor of Autophagy and Lysosomal Function

Jun-Ichi Sakamaki  1 , Simon Wilkinson  1 , Marcel Hahn  2 , Nilgun Tasdemir  3 , Jim O'Prey  1 , William Clark  1 , Ann Hedley  1 , Colin Nixon  1 , Jaclyn S Long  1 , Maria New  4 , Tim Van Acker  4 , Sharon A Tooze  4 , Scott W Lowe  5 , Ivan Dikic  6 , Kevin M Ryan  7
Affiliations

Bromodomain Protein BRD4 Is a Transcriptional Repressor of Autophagy and Lysosomal Function

Jun-Ichi Sakamaki et al. Mol Cell. .

Abstract

Autophagy is a membrane-trafficking process that directs degradation of cytoplasmic material in lysosomes. The process promotes cellular fidelity, and while the core machinery of autophagy is known, the mechanisms that promote and sustain autophagy are less well defined. Here we report that the epigenetic reader BRD4 and the methyltransferase G9a repress a TFEB/TFE3/MITF-independent transcriptional program that promotes autophagy and lysosome biogenesis. We show that BRD4 knockdown induces autophagy in vitro and in vivo in response to some, but not all, situations. In the case of starvation, a signaling cascade involving AMPK and histone deacetylase SIRT1 displaces chromatin-bound BRD4, instigating autophagy gene activation and cell survival. Importantly, this program is directed independently and also reciprocally to the growth-promoting properties of BRD4 and is potently repressed by BRD4-NUT, a driver of NUT midline carcinoma. These findings therefore identify a distinct and selective mechanism of autophagy regulation VSports手机版. .

Keywords: AMPK; BRD4; BRD4-NUT; G9a/EHMT2/KMT1C; SIRT1; autophagy; hMOF/KAT8; lysosomes; selective autophagy; transcriptional regulation of autophagy V体育安卓版. .

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Graphical abstract
Figure 1
Figure 1
BRD4 Silencing Enhances Autophagic Flux (A) Drosophila S2R+ cells expressing GFP-LC3 were transfected with double-stranded RNA (dsRNA) targeting control luciferase (Luc) or Fs(1)h. (B and C) KP-4 cells transfected with control or BRD4 siRNA for 72 hr were subjected to western blot analysis (B) and stained for LC3B (C). The number of LC3 puncta normalized to cell number is shown. CON: n = 94 cells, BRD4 1: n = 97 cells, BRD4 2: n = 74 cells. Scale bars, 50 μm. (D) Immunohistochemistry of small intestinal sections from transgenic mice harboring inducible renilla luciferase or BRD4 shRNA. Sections were stained for LC3 (upper) and BRD4 (lower). Cytoplasmic signal in BRD4 panels is due to non-specific staining. Scale bars, 50 μm. (E) KP-4 cells transfected with BRD4 siRNA were treated with 10 μM CQ for 4 hr. (F) KP-4 cells transfected with BRD4 siRNA were stained for WIPI2. The number of WIPI2 puncta normalized to cell number is shown. CON: n = 119 cells, BRD4 1: n = 107 cells, BRD4 2: n = 109 cells. Scale bars, 20 μm. (G) KP-4 cells stably expressing RFP-GFP-LC3 were transfected with BRD4 siRNA. Scale bars, 50 μm. (H) KP-4 cells were treated with 500 nM JQ1 for 9 hr in the presence or absence of CQ (10 μM, 4 hr). (I) KP-4 cells overexpressing BRD4 were treated with 10 μM CQ for 4 hr. (J) TY-82 cells transfected with NUT siRNA for 5 days were treated with 10 μM CQ for 8 hr. BRD4-NUT was detected using NUT antibody. All data are shown as mean ± SD. ∗p < 0.01. See also Figure S1.
Figure 2
Figure 2
BRD4 Is a Negative Regulator of Autophagy Gene Expression (A and B) KP-4 cells transfected with control or BRD4 siRNA were subjected to RNA-seq and gene ontology analyses (A) and RT-qPCR analysis (B). (C) RT-qPCR analysis of KP-4 cells treated with DMSO, 500 nM JQ1, 500 nM I-BET151, or 500 nM OTX015 for 9 hr. (D) RT-qPCR analysis of KP-4 cells treated with 500 nM JQ1 for the indicated time. (E) RT-qPCR analysis of KP-4 cells overexpressing BRD4. All data are shown as mean ± SD. In (A)–(D), n = 3 independent experiments; in (E), data are representative of two independent experiments performed in triplicate. ∗p < 0.01, ∗∗p < 0.05. See also Figure S2.
Figure 3
Figure 3
BRD4 Knockdown Enhances Lysosomal Function (A) RT-qPCR analysis of KP-4 cells transfected with control or BRD4 siRNA. (B–D) KP-4 cells transfected with BRD4 siRNA were subjected to western blot analysis with antibodies against lysosomal proteins (B) and stained with LAMP1 antibody (C), LysoTracker Red (100 nM, 2 hr) (D, upper panels), and Magic Red CTSB (1 hr) (D, lower panels). Area of LAMP1+, LysoTracker+, and Magic Red CTSB+ area normalized to cell number is shown (C, CON: n = 115 cells, BRD4: n = 130 cells; D upper, CON: n = 66 cells, BRD4 1: n = 52 cells, BRD4 2: n = 50 cells; D lower, CON: n = 164 cells, BRD4 1: n = 109 cells, BRD4 2: n = 53 cells). Scale bars, 50 μm. (E) Hexosaminidase activity was measured using lysates from control and BRD4 knockdown KP-4 cells. (F and G) RT-qPCR analysis of TY-82 cells transfected with NUT siRNA for 72 hr (F) or treated with 500 nM JQ1 for 9 hr (G). (H) KP-4 cells were transfected with BRD4 and/or MiT/TFE (TFEB, TFE3, MITF) siRNAs and treated with 10 μM CQ for 4 hr. All data are shown as mean ± SD. In (A) and (F), n = 3 independent experiments. In (E), n = 4 independent experiments. In (G), data are representative of two independent experiments performed in triplicate. ∗p < 0.01, ∗∗p < 0.05. See also Figure S3.
Figure 4
Figure 4
Starvation Leads to BRD4 Dissociation from Autophagy Gene Promoters (A and B) KP-4 cells were starved for 4 hr followed by chromatin immunoprecipitation (ChIP) assay with BRD4 antibody (A) and RT-qPCR analysis (B). (C) KP-4 cells infected with Cas9/hMOF sgRNA were subjected to ChIP assay with BRD4 antibody. (D) KP-4 cells were starved for 4 hr followed by ChIP assay with H4K16Ac antibody. (E and F) KP-4 cells infected with Cas9/SIRT1 sgRNA were starved for 4 hr followed by ChIP assay with BRD4 antibody (E) and RT-qPCR analysis (F). Western blot shows efficient SIRT1 depletion in Cas9/SIRT1 sgRNA-infected cells. (G and H) KP-4 cells infected with Cas9/AMPKα1 and α2 sgRNAs were starved for 4 hr followed by immunoprecipitation with DBC1 antibody (G) and RT-qPCR analysis (H). All data are shown as mean ± SD. In (A)–(F) and (H), n = 3 independent experiments. ∗p < 0.01, ∗∗p < 0.05, N.S., no significance. See also Figure S4.
Figure 5
Figure 5
BRD4 Represses Autophagy Gene Expression through G9a (A) Cell extracts from KP-4 cells were subjected to immunoprecipitation with G9a (upper) and BRD4 (lower) antibodies. (B) KP-4 cells were starved for 4 hr followed by immunoprecipitation with BRD4 antibody. (C–F) KP-4 cells were treated with 500 nM JQ1 for 9 hr (C and E). KP-4 cells harboring inducible control or BRD4 shRNA were treated with 500 ng/mL doxycycline (DOX) for 4 days (D and F). ChIP assays were performed using G9a (C and D) and H3K9diMe (E and F) antibodies. (G and H) KP-4 cells infected with shRNA targeting G9a were transfected with BRD4 siRNA followed by RT-qPCR (G) and western blot (H). (I) KP-4 cells overexpressing BRD4 were infected with shRNA targeting G9a. All data are shown as mean ± SD. In (C)–(G), n = 3 independent experiments. ∗p < 0.01, ∗∗p < 0.05, N.S., no significance. See also Figure S5.
Figure 6
Figure 6
Effect of BRD4 Silencing on Stimulus-Dependent and Selective Autophagy (A–F) Cells transfected with BRD4 siRNA were starved for 1–5 hr (KP-4 cells, A), treated with 500 nM rapamycin for 24 hr (KP-4 cells, B), starved of glucose for 4 hr (KP-4 cells, C), cultured under hypoxic (1% O2) conditions for 48 hr (SUIT2 cells, D), treated with 100 mM Trehalose for 4 hr (KP-4 cells, E), or treated with 500 nM 4-Hydroxytamoxifen (4-OHT) for 48 hr (IMR90 ER-HRas G12V cells, F). (G) KP-4 cells harboring rtTA and Tre-tight-HTT Q94-CFP were transfected with BRD4 siRNA. At 12 hr after transfection, cells were treated with 1 μg/mL DOX for 10 hr. At 48 hr after removal of DOX, cells were separated into Triton X-100 soluble and insoluble fractions. (H) KP-4 cells transfected with BRD4 siRNA were infected with Salmonella enterica serovar Typhimurium. The number of Salmonella was determined by performing colony-forming unit assays at 2, 6, and 8 hr after infection and normalized to the numbers at 2 hr. Data are shown as mean ± SEM; n = 4 independent experiments. (I) KP-4 cells expressing YFP-parkin were transfected with BRD4 siRNA followed by treatment with 1 μM Antimycin A and 1 μM Oligomycin for 8 hr. See also Figure S6.
Figure 7
Figure 7
BRD4 Knockdown Sustains mTOR Activity during Starvation and Confers Resistance to Starvation-Induced Cell Death (A and B) KP-4 cells transfected with BRD4 siRNA were starved of amino acids (A). Cells pre-treated with CQ (10 μM, 4 hr) were subjected to amino acid starvation for 2 hr in the presence of CQ (B). (C) KP-4 cells infected with Cas9/ATG5 sgRNA were transfected with BRD4 siRNA and subjected to amino acid starvation for 2 hr. (D and E) KP-4 cells infected with Cas9/ATG5 sgRNA were transfected with BRD4 siRNA. Following 48 hr starvation, percentage of subG1 cells (D) and cell number (E) were determined (n = 3 independent experiments). (F and G) KP-4 cells transfected with BRD4 siRNA were starved for 48 hr in the presence or absence of 10 μM CQ. Percentage of dead (F) and surviving (G) cells was determined by trypan blue exclusion test (n = 4 independent experiments). All data are shown as mean ± SD. ∗p < 0.01, N.S., no significance. See also Figure S7.
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