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UCSC Genome Browser Gene Interaction Graph
Gene interactions and pathways from curated databases and text-mining
Autophagy 2011, PMID: 21460630

ULK1 inhibits mTORC1 signaling, promotes multisite Raptor phosphorylation and hinders substrate binding.

Dunlop, Elaine A; Hunt, David K; Acosta-Jaquez, Hugo A; Fingar, Diane C; Tee, Andrew R

Protein synthesis and autophagy work as two opposing processes to control cell growth in response to nutrient supply. The mammalian/mechanistic target of rapamycin complex 1 (mTORC1) pathway, which acts as a master regulator to control protein synthesis, has recently been shown to inhibit autophagy by phosphorylating and inactivating ULK1, an autophagy regulatory protein. ULK1 also inhibits phosphorylation of a mTORC1 substrate, S6K1, indicating that a complex signaling interplay exists between mTORC1 and ULK1. Here, we demonstrate that ULK1 induces multisite phosphorylation of Raptor in vivo and in vitro. Using phospho-specific antibodies we identify Ser855 and Ser859 as being strongly phosphorylated by ULK1, with moderate phosphorylation of Ser792 also observed. Interestingly, ULK1 overexpression also increases phosphorylation of Raptor Ser863 and the mTOR autophosphorylation site, Ser2481 in a mTORC1-dependent manner. Despite this evidence for heightened mTORC1 kinase activity following ULK1 overexpresssion, mTORC1-mediated phosphorylation of S6K1 and 4E-BP1 is significantly inhibited. ULK1 expression has no effect on protein-protein interactions between the components of mTORC1, but does reduce the ability of Raptor to bind to the substrate 4E-BP1. Furthermore, shRNA knockdown of ULK1 leads to increased phosphorylation of mTORC1 substrates and decreased phosphorylation of Raptor at Ser859 and Ser792. We propose a new mechanism whereby ULK1 contributes to mTORC1 inhibition through hindrance of substrate docking to Raptor. This is a novel negative feedback loop that occurs upon activation of autophagy to maintain mTORC1 inhibition when nutrient supplies are limiting.

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Text Mining Data

mTORC1 ⊣ ULK1: " ULK1 inhibits mTORC1 signaling, promotes multisite Raptor phosphorylation and hinders substrate binding "

Raptor ⊣ mTORC1: " ULK1 inhibits mTORC1 signaling, promotes multisite Raptor phosphorylation and hinders substrate binding "

Raptor → ULK1: " Here, we demonstrate that ULK1 induces multisite phosphorylation of Raptor in vivo and in vitro "

ULK1 — mTORC1: " Interestingly, ULK1 overexpression also increases phosphorylation of Raptor Ser863 and the mTOR autophosphorylation site, Ser2481 in a mTORC1 dependent manner "

ULK1 — mTORC1: " Interestingly, ULK1 overexpression also increases phosphorylation of Raptor Ser863 and the mTOR autophosphorylation site, Ser2481 in a mTORC1 dependent manner "

S6K1 → mTORC1: " Despite this evidence for heightened mTORC1 kinase activity following ULK1 overexpresssion, mTORC1 mediated phosphorylation of S6K1 and 4E-BP1 is significantly inhibited "

4E-BP1 → mTORC1: " Despite this evidence for heightened mTORC1 kinase activity following ULK1 overexpresssion, mTORC1 mediated phosphorylation of S6K1 and 4E-BP1 is significantly inhibited "

4E-BP1 → ULK1: " ULK1 expression has no effect on protein-protein interactions between the components of mTORC1, but does reduce the ability of Raptor to bind to the substrate 4E-BP1 "

mTORC1 ⊣ ULK1: " We propose a new mechanism whereby ULK1 contributes to mTORC1 inhibition through hindrance of substrate docking to Raptor "

Manually curated Databases

  • IRef Biogrid Interaction: RPS6 — RPS6KB1 (direct interaction, enzymatic study)
  • IRef Biogrid Interaction: RPTOR — ULK1 (direct interaction, enzymatic study)
  • IRef Biogrid Interaction: RPTOR — ULK1 (physical association, affinity chromatography technology)
  • IRef Biogrid Interaction: MLST8 — ULK1 (physical association, affinity chromatography technology)
  • IRef Biogrid Interaction: ULK1 — ATG13 (direct interaction, enzymatic study)
  • IRef Biogrid Interaction: EIF4EBP1 — MTOR (direct interaction, enzymatic study)
  • IRef Biogrid Interaction: ULK1 — MTOR (physical association, affinity chromatography technology)
In total, 6 gene pairs are associated to this article in curated databases