SIN1/MIP1 maintains rictor-mTOR complex integrity and regulates Akt phosphorylation and substrate specificity

Cell. 2006 Oct 6;127(1):125-37. doi: 10.1016/j.cell.2006.08.033. Epub 2006 Sep 7.

Abstract

Mammalian target of rapamycin (mTOR) controls cell growth and proliferation via the raptor-mTOR (TORC1) and rictor-mTOR (TORC2) protein complexes. Recent biochemical studies suggested that TORC2 is the elusive PDK2 for Akt/PKB Ser473 phosphorylation in the hydrophobic motif. Phosphorylation at Ser473, along with Thr308 of its activation loop, is deemed necessary for Akt function, although the regulatory mechanisms and physiological importance of each phosphorylation site remain to be fully understood. Here, we report that SIN1/MIP1 is an essential TORC2/PDK2 subunit. Genetic ablation of sin1 abolished Akt-Ser473 phosphorylation and disrupted rictor-mTOR interaction but maintained Thr308 phosphorylation. Surprisingly, defective Ser473 phosphorylation affected only a subset of Akt targets in vivo, including FoxO1/3a, while other Akt targets, TSC2 and GSK3, and the TORC1 effectors, S6K and 4E-BP1, were unaffected. Our findings reveal that the SIN1-rictor-mTOR function in Akt-Ser473 phosphorylation is required for TORC2 function in cell survival but is dispensable for TORC1 function.

Publication types

  • Research Support, N.I.H., Extramural
  • 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*
  • Cells, Cultured
  • Fibroblasts / cytology
  • Fibroblasts / metabolism
  • Forkhead Box Protein O1
  • Forkhead Box Protein O3
  • Forkhead Transcription Factors / genetics
  • Forkhead Transcription Factors / metabolism
  • Gene Silencing
  • Humans
  • Mice
  • Mice, Inbred C57BL
  • Mice, Knockout
  • Multiprotein Complexes
  • Phosphoproteins / genetics
  • Phosphoproteins / metabolism
  • Phosphorylation
  • Protein Kinases / genetics
  • Protein Kinases / metabolism*
  • Proteins / genetics
  • Proteins / metabolism
  • Proto-Oncogene Proteins c-akt / genetics
  • Proto-Oncogene Proteins c-akt / metabolism*
  • Rapamycin-Insensitive Companion of mTOR Protein
  • Regulatory-Associated Protein of mTOR
  • Signal Transduction / physiology
  • Substrate Specificity
  • TOR Serine-Threonine Kinases
  • Threonine / metabolism
  • Transcription Factors / genetics
  • Transcription Factors / metabolism

Substances

  • Adaptor Proteins, Signal Transducing
  • CRTC1 protein, human
  • CRTC2 protein, human
  • Carrier Proteins
  • FOXO1 protein, human
  • FOXO3 protein, human
  • Forkhead Box Protein O1
  • Forkhead Box Protein O3
  • Forkhead Transcription Factors
  • MAPKAP1 protein, human
  • Multiprotein Complexes
  • Phosphoproteins
  • Proteins
  • RICTOR protein, human
  • RPTOR protein, human
  • Rapamycin-Insensitive Companion of mTOR Protein
  • Regulatory-Associated Protein of mTOR
  • Transcription Factors
  • Threonine
  • Protein Kinases
  • MTOR protein, human
  • TOR Serine-Threonine Kinases
  • mTOR protein, mouse
  • Proto-Oncogene Proteins c-akt