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An AMPKα2-specific phospho-switch controls lysosomal targeting for activation

Kaitlin R Morrison1, William J Smiles2, Naomi X Y Ling2

  • 1Flinders Health and Medical Research Institute, Flinders University, Adelaide, SA 5042, Australia.

Cell Reports
|February 16, 2022
PubMed

Insights

AMP-activated protein kinase (AMPK) alpha2-S345 phosphorylation is crucial for lysosomal targeting and activation, particularly under nutrient starvation. This alpha2-specific mechanism enables AMPK activation independently of cellular energy levels.

Area of Science:

  • Cellular Metabolism
  • Molecular Biology
  • Signal Transduction

Background:

  • AMP-activated protein kinase (AMPK) and mechanistic target of rapamycin complex 1 (mTORC1) are key metabolic regulators.
  • mTORC1 reciprocally phosphorylates AMPK alpha-isoforms at specific serine residues (S345/7).
  • The functional significance of this reciprocal phosphorylation, particularly isoform-specific roles, remains incompletely understood.

Purpose of the Study:

  • To investigate the isoform-specific regulatory role of AMPK alpha-S345/7 phosphorylation by mTORC1.
  • To elucidate the cellular localization and activation mechanisms of AMPK in response to altered phosphorylation states.
  • To determine the impact of alpha2-S345 phosphorylation loss on cellular growth under nutrient stress.

Main Methods:

  • Genetic manipulation to abolish alpha2-S345 phosphorylation.
  • Pharmacological inhibition of mTORC1 using torin1.
  • Mass spectrometry for quantitative phosphoproteomics.
  • Cellular localization studies using immunofluorescence.
  • Analysis of MEF cell growth under amino acid starvation.

Main Results:

  • Loss of alpha2-S345 phosphorylation, but not alpha1-S347, relieves mTORC1 suppression of AMPK signaling.
  • Dephosphorylation of alpha2-S345, unlike alpha1-S347, transiently targets AMPK to lysosomes for LKB1-mediated activation.
  • Alpha2-S345 exhibits higher basal phosphorylation stoichiometry than alpha1-S347 and retains partial phosphorylation after prolonged mTORC1 inhibition.
  • Loss of alpha2-S345 phosphorylation impairs MEF cell growth during amino acid starvation.

Conclusions:

  • AMPK alpha2-S345 phosphorylation is a critical regulator of AMPK activation at lysosomes, independent of cellular energy status.
  • This alpha2-specific mechanism provides a novel pathway for nutrient-sensing and cellular adaptation.
  • Targeting this pathway could offer therapeutic strategies for metabolic disorders.
Keywords:
AMPKenergy homeostasiskinaselysosomemTORC1metabolic signalingphosphorylation

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