Mammalian EAK-7 activates alternative mTOR signaling to regulate cell proliferation and migration

Sci Adv. 2018 May 9;4(5):eaao5838. doi: 10.1126/sciadv.aao5838. eCollection 2018 May.

Abstract

Nematode EAK-7 (enhancer-of-akt-1-7) regulates dauer formation and controls life span; however, the function of the human ortholog mammalian EAK-7 (mEAK-7) is unknown. We report that mEAK-7 activates an alternative mechanistic/mammalian target of rapamycin (mTOR) signaling pathway in human cells, in which mEAK-7 interacts with mTOR at the lysosome to facilitate S6K2 activation and 4E-BP1 repression. Despite interacting with mTOR and mammalian lethal with SEC13 protein 8 (mLST8), mEAK-7 does not interact with other mTOR complex 1 (mTORC1) or mTOR complex 2 (mTORC2) components; however, it is essential for mTOR signaling at the lysosome. This phenomenon is distinguished by S6 and 4E-BP1 activity in response to nutrient stimulation. Conventional S6K1 phosphorylation is uncoupled from S6 phosphorylation in response to mEAK-7 knockdown. mEAK-7 recruits mTOR to the lysosome, a crucial compartment for mTOR activation. Loss of mEAK-7 results in a marked decrease in lysosomal localization of mTOR, whereas overexpression of mEAK-7 results in enhanced lysosomal localization of mTOR. Deletion of the carboxyl terminus of mEAK-7 significantly decreases mTOR interaction. mEAK-7 knockdown decreases cell proliferation and migration, whereas overexpression of mEAK-7 enhances these cellular effects. Constitutively activated S6K rescues mTOR signaling in mEAK-7-knocked down cells. Thus, mEAK-7 activates an alternative mTOR signaling pathway through S6K2 and 4E-BP1 to regulate cell proliferation and migration.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cell Line
  • Cell Movement
  • Cell Proliferation
  • Conserved Sequence
  • Evolution, Molecular
  • Humans
  • Intracellular Membranes / metabolism
  • Lysosomes / metabolism
  • Protein Tyrosine Phosphatases / chemistry
  • Protein Tyrosine Phosphatases / genetics
  • Protein Tyrosine Phosphatases / metabolism*
  • Ribosomal Protein S6 Kinases, 90-kDa / metabolism
  • Signal Transduction*
  • TOR Serine-Threonine Kinases / chemistry
  • TOR Serine-Threonine Kinases / genetics
  • TOR Serine-Threonine Kinases / metabolism*

Substances

  • Ribosomal Protein S6 Kinases, 90-kDa
  • Rps6ka1 protein, mouse
  • TOR Serine-Threonine Kinases
  • Protein Tyrosine Phosphatases