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

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.