title: Regulation of mTORC1 complex assembly and signaling by GRp58/ERp57.
abstract: The mammalian target of rapamycin (mTOR) regulates cell growth and survival via two different multiprotein complexes, mTORC1 and mTORC2. The assembly of these serine-threonine kinase multiprotein complexes occurs via poorly understood molecular mechanisms. Here, we demonstrate that GRp58/ERp57 regulates the existence and activity of mTORC1. Endogenous mTOR interacts with GRp58/ERp57 in different mammalian cells. In vitro, recombinant GRp58/ERp57 preferentially interacts with mTORC1. GRp58/ERp57 knockdown reduces mTORC1 levels and phosphorylation of 4E-BP1 and p70(S6K) in response to insulin. In contrast, GRp58/ERp57 overexpression increases mTORC1 levels and activity. A redox-sensitive mechanism that depends on GRp58/ERp57 expression activates mTORC1. Although GRp58/ERp57 is known as an endoplasmic reticulum (ER) resident, we demonstrate its presence at the cytosol, together with mTOR, Raptor, and Rictor as well as a pool of these proteins associated to the ER. In addition, the presence of GRp58/ERp57 at the ER decreases in response to insulin or leucine. Interestingly, a fraction of p70(S6K), but not 4E-BP1, is associated to the ER and phosphorylated in response to serum, insulin, or leucine. Altogether, our results suggest that GRp58/ERp57 is involved in the assembly of mTORC1 and positively regulates mTORC1 signaling at the cytosol and the cytosolic side of the ER.
authors.affiliation: Departamento de Farmacología CINVESTAV-IPN, Av. Instituto Politécnico Nacional 2508, Col. San Pedro Zacatenco, 07360, Apartado postal 14-740, 07000 Mexico D.F., Mexico.
authors.forename: Iliana
authors.initials: I
authors.lastname: Ramírez-Rangel
authors.forename: Ismael
authors.initials: I
authors.lastname: Bracho-Valdés
authors.forename: Aleida
authors.initials: A
authors.lastname: Vázquez-Macías
authors.forename: Jorge
authors.initials: J
authors.lastname: Carretero-Ortega
authors.forename: Guadalupe
authors.initials: G
authors.lastname: Reyes-Cruz
authors.forename: José
authors.initials: J
authors.lastname: Vázquez-Prado
mesh_terms: D049109:Cell Proliferation; D003600:Cytosol / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D000076222:Mechanistic Target of Rapamycin Complex 1; D046912:Multiprotein Complexes; D011485:Protein Binding; D019704:Protein Disulfide-Isomerases / Q000235:genetics / Q000378:metabolism*; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism
chemical_list: D046912:Multiprotein Complexes; D011506:Proteins; C546842:MTOR protein, human; D000076222:Mechanistic Target of Rapamycin Complex 1; D058570:TOR Serine-Threonine Kinases; D019704:Protein Disulfide-Isomerases; C085868:PDIA3 protein, human