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mTORC2 Is Involved in the Induction of RSK Phosphorylation by Serum or Nutrient Starvation

Po-Chien Chou1, Swati Rajput1, Xiaoyun Zhao2

  • 1Department of Biochemistry and Molecular Biology, Rutgers-Robert Wood Johnson Medical School, Piscataway, NJ 08854, USA.

Cells
|July 2, 2020
PubMed

Insights

Mechanistic target of rapamycin (mTOR) complex 2 is crucial for optimal p90 ribosomal S6 kinase (RSK) phosphorylation at its hydrophobic motif site, influencing RSK substrate specificity and nutrient response.

Area of Science:

  • Cellular metabolism
  • Signal transduction pathways
  • Protein kinase regulation

Background:

  • Cells maintain metabolic homeostasis by adjusting to nutrient availability.
  • Mechanistic target of rapamycin (mTOR) complex 2 (mTORC2) phosphorylates AGC kinases, including Akt and PKC, at their hydrophobic motif (HM) sites, regulating cell growth and metabolism.
  • p90 ribosomal S6 kinase (RSK) phosphorylation at its homologous HM site (Ser380) is linked to mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) activation.

Purpose of the Study:

  • To investigate the role of mTORC2 in RSK phosphorylation at the Ser380 site.
  • To determine if mTOR catalytic activity is required for RSK phosphorylation.
  • To explore the potential scaffolding function of mTORC2 in RSK phosphorylation and its impact on substrate specificity.

Main Methods:

  • Cellular assays to assess RSK phosphorylation.
  • Nutrient manipulation (withdrawal, glycolysis inhibition).
  • Pharmacological inhibition of mTOR.
  • Co-localization studies of RSK and SIN1β.
  • Analysis of RSK substrate phosphorylation (CCTβ subunit).

Main Results:

  • Optimal RSK phosphorylation at Ser380 requires an intact mTORC2.
  • RSK Ser380 phosphorylation is enhanced under conditions of nutrient withdrawal or glycolysis inhibition, which increase mTORC2 activity.
  • mTOR catalytic activity is not essential for RSK Ser380 phosphorylation.
  • RSK and SIN1β co-localize at the membrane, suggesting mTORC2 may act as a scaffold.
  • Phosphorylation of the CCTβ subunit, an RSK substrate, is impaired in the absence of mTORC2.

Conclusions:

  • mTORC2 plays a critical role in regulating RSK phosphorylation at the hydrophobic motif site.
  • mTORC2-mediated RSK phosphorylation influences RSK substrate specificity.
  • RSK activity and its response to nutrient fluctuations are modulated by mTORC2.
Keywords:
AGC kinasesCCT/TRiCCCTβMAPK/ERKRSKchaperoninmTORC2metabolismnutrientsp90 ribosomal s6 kinasestarvation

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