A lysosome‐to‐nucleus signalling mechanism senses and regulates the lysosome via mTOR and TFEB (2012)
Figure 2

mTORC1 regulates TFEB. (A) Lysosomal stress inhibits mTOR signalling. Immunoblotting of protein extracts isolated from HeLa cells treated overnight as indicated. Membranes were probed with antibodies against p‐T202/Y204‐ERK1/2, ERK1/2, p‐T389‐S6K, and S6K to measure ERK and mTORC1 activities. (B) Torin 1 induces TFEB dephosphorylation and nuclear translocation. FLAG immunoblotting of cytosolic and nuclear fractions isolated from TFEB–3 × FLAG HeLa cells starved in amino acid‐free media and subsequently stimulated as indicated for at least 3 h. Correct subcellular fractionation was verified with H3 and tubulin antibodies. (C) Effects of ERK and mTOR inhibitors on TFEB nuclear translocation. TFEB–GFP HeLa cells were seeded in 96‐well plates, cultured for 12 h, and then treated with the indicated concentrations of the ERK inhibitor U0126, or the mTOR inhibitors Rapamycin, Torin 1, and Torin 2. After 3 h at 37°C, cells were processed and images were acquired using the OPERA automated confocal microscope (Perkin‐Elmer). Scale bars represent 30 μm. (D) Dose–response curves of the effects of ERK and mTOR inhibitors on TFEB nuclear translocation. TFEB–GFP HeLa cells were seeded in 384‐well plates, cultured for 12 h, and treated with 10 different concentrations of the ERK inhibitor U0126, or the mTOR inhibitors Rapamycin, Torin 1, and Torin 2 ranging from 2.54 nM to 50 μM. The graph shows the percentage of nuclear translocation at the different concentrations of each compound (in log of the concentration). The EC50 for each compound was calculated using Prism software (see Materials and methods for details). (E) Immunofluorescence of HEK‐293T cells treated with DMSO or Torin 1 and stained with antibodies against endogenous TFEB and the lysosomal protein RagC (green and red, respectively, in the merge). DAPI is included in the merge. Scale bars represent 10 μM. (F) Rag GTPase knockdown induces TFEB nuclear translocation. HeLa cells stably expressing TFEB–3 × FLAG were infected with lentiviruses encoding Short hairpin (Sh‐) RNAs targeting luciferase (control) or RagC and RagD mRNAs. In all samples, 96 h post infection, cells were left untreated (N=normal media), starved (S=starved media) or treated with Torin 1 (T=Torin 1) for 4 h and then subjected to nuclear/cytosolic fractionation. TFEB localization was detected with a FLAG antibody, whereas tubulin and H3 were used as controls for the cytosolic and nuclear fraction, respectively; levels of S6K phosphorylation were used to test RagC and RagD knockdown efficiency. (G) Loss of mTORC2 does not affect TFEB phosphorylation. Mouse embryonic fibroblasts (MEFs) isolated from Sin1−/− or control embryos (E14.5) were infected with a retrovirus encoding TFEB–3 × FLAG; 48 h post infection, cells were treated with Torin 1 (T) for 4 h where indicated, subjected to nuclear/cytosolic fractionation and immunoblotted for FLAG, tubulin, and H3. (H) Binding of TFEB to mTORC1. HEK‐293T cells that express TFEB–3 × FLAG were lysed and subjected to FLAG immunoprecipitation followed by immunoblotting for mTOR, the mTORC1 subunit raptor and the mTORC2 components rictor and Sin1. FLAG–Rap2A served as negative control.