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A disorder-related variant (E420K) of a PP2A-regulatory subunit (PPP2R5D) causes constitutively active AKT-mTOR

Cinta M Papke1, Kali A Smolen2, Mark R Swingle1

  • 1Department of Biochemistry and Molecular Biology, University of South Alabama, Mobile, Alabama, USA.

The Journal of Biological Chemistry
|January 22, 2021
PubMed

Insights

PPP2R5D-related disorder involves intellectual disability and is caused by genetic variants. This study found the E420K variant activates AKT-mTOR signaling, increasing cell size, which rapamycin treatment can reduce.

Area of Science:

  • Genetics and Molecular Biology
  • Cellular Signaling
  • Rare Disease Etiology

Background:

  • PPP2R5D-related disorder is a rare genetic condition presenting in early childhood with intellectual disability, hypotonia, autism-spectrum disorder, macrocephaly, and dysmorphic features.
  • The disorder arises from de novo heterozygous dominant missense variants in the PPP2R5D gene, which encodes a regulatory subunit of protein phosphatase 2A (PP2A).

Purpose of the Study:

  • To elucidate the molecular mechanisms underlying PPP2R5D-related disorder by investigating the functional consequences of a specific missense variant.
  • To identify altered signaling pathways and protein interactions resulting from the PPP2R5D E420K variant.

Main Methods:

  • Utilized CRISPR-single-base editing to generate HEK-293 cells with the specific PPP2R5D c.1258G>A (E420K) variant.
  • Performed unbiased quantitative proteomic and phosphoproteomic analyses using isobaric tandem mass tag (TMT) labeling and LC-MS3.
  • Conducted orthogonal validation studies and tested the efficacy of rapamycin treatment.

Main Results:

  • Identified heterozygous-dominant alterations in kinase/phosphatase signaling pathways in cells harboring the E420K variant.
  • Discovered a novel interaction between PPP2R5D and AKT, leading to constitutively active AKT-mTOR signaling.
  • Observed increased cell size and uncoordinated cellular growth in E420K-variant cells, which were ameliorated by rapamycin treatment, including reduced RPS6 phosphorylation.

Conclusions:

  • The E420K variant in PPP2R5D disrupts normal cellular signaling by activating the AKT-mTOR pathway, contributing to the pathogenesis of PPP2R5D-related disorder.
  • Inhibition of mTOR1 shows therapeutic potential by suppressing hyperphosphorylation and excessive cell growth associated with the disorder.
  • The study presents a robust methodological framework for investigating the molecular basis of genetic disorders using advanced genomic and proteomic techniques.
Keywords:
AKT-mTORJordan’s syndromePP2APPP2R5DPPP2R5D-intellectual disabilityPPP2R5D-related neurodevelopmental disorderphosphatase

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