A dynamic network model of mTOR signaling reveals TSC-independent mTORC2 regulation

Sci Signal. 2012 Mar 27;5(217):ra25. doi: 10.1126/scisignal.2002469.

Abstract

The kinase mammalian target of rapamycin (mTOR) exists in two multiprotein complexes (mTORC1 and mTORC2) and is a central regulator of growth and metabolism. Insulin activation of mTORC1, mediated by phosphoinositide 3-kinase (PI3K), Akt, and the inhibitory tuberous sclerosis complex 1/2 (TSC1-TSC2), initiates a negative feedback loop that ultimately inhibits PI3K. We present a data-driven dynamic insulin-mTOR network model that integrates the entire core network and used this model to investigate the less well understood mechanisms by which insulin regulates mTORC2. By analyzing the effects of perturbations targeting several levels within the network in silico and experimentally, we found that, in contrast to current hypotheses, the TSC1-TSC2 complex was not a direct or indirect (acting through the negative feedback loop) regulator of mTORC2. Although mTORC2 activation required active PI3K, this was not affected by the negative feedback loop. Therefore, we propose an mTORC2 activation pathway through a PI3K variant that is insensitive to the negative feedback loop that regulates mTORC1. This putative pathway predicts that mTORC2 would be refractory to Akt, which inhibits TSC1-TSC2, and, indeed, we found that mTORC2 was insensitive to constitutive Akt activation in several cell types. Our results suggest that a previously unknown network structure connects mTORC2 to its upstream cues and clarifies which molecular connectors contribute to mTORC2 activation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptor Proteins, Signal Transducing / genetics
  • Adaptor Proteins, Signal Transducing / metabolism
  • Animals
  • Carrier Proteins / genetics
  • Carrier Proteins / metabolism
  • Cell Line
  • Computer Simulation
  • Gene Knockdown Techniques
  • HeLa Cells
  • Humans
  • Immunoblotting
  • Immunoprecipitation
  • Insulin / metabolism
  • Insulin / pharmacology
  • Models, Biological*
  • Multiprotein Complexes / genetics
  • Multiprotein Complexes / metabolism
  • Phosphatidylinositol 3-Kinases / metabolism
  • Phosphorylation / drug effects
  • Protein Binding
  • Rapamycin-Insensitive Companion of mTOR Protein
  • Regulatory-Associated Protein of mTOR
  • Ribosomal Protein S6 Kinases, 70-kDa / metabolism
  • Signal Transduction / drug effects
  • Signal Transduction / physiology*
  • Software
  • TOR Serine-Threonine Kinases / genetics
  • TOR Serine-Threonine Kinases / metabolism*
  • Tuberous Sclerosis Complex 1 Protein
  • Tuberous Sclerosis Complex 2 Protein
  • Tumor Suppressor Proteins / genetics
  • Tumor Suppressor Proteins / metabolism

Substances

  • Adaptor Proteins, Signal Transducing
  • Carrier Proteins
  • Insulin
  • Multiprotein Complexes
  • RICTOR protein, human
  • RPTOR protein, human
  • Rapamycin-Insensitive Companion of mTOR Protein
  • Regulatory-Associated Protein of mTOR
  • TSC1 protein, human
  • TSC2 protein, human
  • Tuberous Sclerosis Complex 1 Protein
  • Tuberous Sclerosis Complex 2 Protein
  • Tumor Suppressor Proteins
  • Phosphatidylinositol 3-Kinases
  • MTOR protein, human
  • TOR Serine-Threonine Kinases
  • Ribosomal Protein S6 Kinases, 70-kDa