title: Proton-assisted amino acid transporter PAT1 complexes with Rag GTPases and activates TORC1 on late endosomal and lysosomal membranes.
abstract: Mammalian Target of Rapamycin Complex 1 (mTORC1) is activated by growth factor-regulated phosphoinositide 3-kinase (PI3K)/Akt/Rheb signalling and extracellular amino acids (AAs) to promote growth and proliferation. These AAs induce translocation of mTOR to late endosomes and lysosomes (LELs), subsequent activation via mechanisms involving the presence of intralumenal AAs, and interaction between mTORC1 and a multiprotein assembly containing Rag GTPases and the heterotrimeric Ragulator complex. However, the mechanisms by which AAs control these different aspects of mTORC1 activation are not well understood. We have recently shown that intracellular Proton-assisted Amino acid Transporter 1 (PAT1)/SLC36A1 is an essential mediator of AA-dependent mTORC1 activation. Here we demonstrate in Human Embryonic Kidney (HEK-293) cells that PAT1 is primarily located on LELs, physically interacts with the Rag GTPases and is required for normal AA-dependent mTOR relocalisation. We also use the powerful in vivo genetic methodologies available in Drosophila to investigate the regulation of the PAT1/Rag/Ragulator complex. We show that GFP-tagged PATs reside at both the cell surface and LELs in vivo, mirroring PAT1 distribution in several normal mammalian cell types. Elevated PI3K/Akt/Rheb signalling increases intracellular levels of PATs and synergistically enhances PAT-induced growth via a mechanism requiring endocytosis. In light of the recent identification of the vacuolar H(+)-ATPase as another Rag-interacting component, we propose a model in which PATs function as part of an AA-sensing engine that drives mTORC1 activation from LEL compartments.
authors.affiliation: Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom.
authors.forename: Margrét H
authors.initials: MH
authors.lastname: Ögmundsdóttir
authors.forename: Sabine
authors.initials: S
authors.lastname: Heublein
authors.forename: Shubana
authors.initials: S
authors.lastname: Kazi
authors.forename: Bruno
authors.initials: B
authors.lastname: Reynolds
authors.forename: Shivanthy M
authors.initials: SM
authors.lastname: Visvalingam
authors.forename: Michael K
authors.initials: MK
authors.lastname: Shaw
authors.forename: Deborah C I
authors.initials: DC
authors.lastname: Goberdhan
mesh_terms: D026905:Amino Acid Transport Systems / Q000378:metabolism*; D000596:Amino Acids / Q000494:pharmacology; D000818:Animals; D004331:Drosophila melanogaster / Q000166:cytology / Q000254:growth & development / Q000378:metabolism; D004705:Endocytosis / Q000187:drug effects; D011992:Endosomes / Q000187:drug effects / Q000378:metabolism*; D005260:Female; D020558:GTP Phosphohydrolases / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D007425:Intracellular Membranes / Q000187:drug effects / Q000378:metabolism*; D008247:Lysosomes / Q000187:drug effects / Q000378:metabolism*; D000076222:Mechanistic Target of Rapamycin Complex 1; D020559:Monomeric GTP-Binding Proteins / Q000378:metabolism; D046912:Multiprotein Complexes; D009479:Neuropeptides / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D011485:Protein Binding / Q000187:drug effects; D011506:Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D000076205:Ras Homolog Enriched in Brain Protein; D015398:Signal Transduction / Q000187:drug effects; D027981:Symporters / Q000378:metabolism*; D058570:TOR Serine-Threonine Kinases
chemical_list: D026905:Amino Acid Transport Systems; D000596:Amino Acids; D020558:GTP Phosphohydrolases; D000076222:Mechanistic Target of Rapamycin Complex 1; D020559:Monomeric GTP-Binding Proteins; D046912:Multiprotein Complexes; D009479:Neuropeptides; D019869:Phosphatidylinositol 3-Kinases; D011506:Proteins; D051057:Proto-Oncogene Proteins c-akt; D000076205:Ras Homolog Enriched in Brain Protein; D027981:Symporters; D058570:TOR Serine-Threonine Kinases; C490211:RHEB protein, human; C475905:SLC36A1 protein, human