Hashimoto Yutaka, Shirane Michiko, Nakayama Keiichi I
Department of Molecular and Cellular Biology, Medical Institute of Bioregulation, Kyushu University, Fukuoka, Japan.
Department of Molecular Biology, Graduate School of Pharmaceutical Science, Nagoya City University, Nagoya, Japan.
Genes Cells. 2018 Jun;23(6):418-434. doi: 10.1111/gtc.12583. Epub 2018 Apr 27.
Mammalian/mechanistic target of rapamycin complex 1 (mTORC1) responds to growth factors and nutrient availability. Amino acids induce the recruitment of mTORC1 to the lysosomal membrane and its consequent activation, but the molecular mechanism of such activation has remained unclear. We have now examined the role of TMEM55B, a lysosomal protein of unknown molecular function, in this process on the basis of the results of proteomics and immunofluorescence analyses showing that TMEM55B interacts with many proteins that participate in mTORC1 activation including components of the vacuolar-type proton ATPase (V-ATPase) and Ragulator complexes at the lysosomal membrane. The amino acid-induced phosphorylation of the mTORC1 substrates S6K and 4E-BP was attenuated in TMEM55B-depleted cells compared with control cells. Depletion of TMEM55B was also found to evoke lysosomal stress as showed by translocation of the transcription factor TFEB to the nucleus. Furthermore, recruitment of the V1 domain subcomplex of V-ATPase to lipid rafts was abrogated in TMEM55B-depleted cells. Collectively, our results suggest that TMEM55B contributes to assembly of the V-ATPase complex in lipid rafts of the lysosomal membrane and to subsequent activation of mTORC1.
哺乳动物雷帕霉素靶蛋白复合物1（mTORC1）对生长因子和营养物质的可利用性作出反应。氨基酸可诱导mTORC1募集至溶酶体膜并随之激活，但这种激活的分子机制仍不清楚。基于蛋白质组学和免疫荧光分析结果，我们现在研究了溶酶体蛋白TMEM55B（分子功能未知）在此过程中的作用，这些结果表明TMEM55B与许多参与mTORC1激活的蛋白质相互作用，包括溶酶体膜上的液泡型质子ATP酶（V-ATP酶）和Ragulator复合物的组分。与对照细胞相比，在TMEM55B缺失的细胞中，氨基酸诱导的mTORC1底物S6K和4E-BP的磷酸化减弱。还发现，TMEM55B的缺失会引发溶酶体应激，转录因子TFEB易位至细胞核即表明了这一点。此外，在TMEM55B缺失的细胞中，V-ATP酶的V1结构域亚复合物向脂筏的募集被消除。总体而言，我们的结果表明，TMEM55B有助于溶酶体膜脂筏中V-ATP酶复合物的组装以及随后mTORC1的激活。
