PIP3-binding proteins promote age-dependent protein aggregation and limit survival in C. elegans

Oncotarget. 2016 Aug 2;7(31):48870-48886. doi: 10.18632/oncotarget.10549.

Abstract

Class-I phosphatidylinositol 3-kinase (PI3KI) converts phosphatidylinositol 4,5-bisphosphate (PIP2) to phosphatidylinositol 3,4,5-triphosphate (PIP3). PIP3 comprises two fatty-acid chains that embed in lipid-bilayer membranes, joined by glycerol to inositol triphosphate. Proteins with domains that specifically bind that head-group (e.g. pleckstrin-homology [PH] domains) are thus tethered to the inner plasma-membrane surface where they have an enhanced likelihood of interaction with other PIP3-bound proteins, in particular other components of their signaling pathways. Null alleles of the C. elegans age-1 gene, encoding the catalytic subunit of PI3KI, lack any detectable class-I PI3K activity and so cannot form PIP3. These mutant worms survive almost 10-fold longer than the longest-lived normal control, and are highly resistant to a variety of stresses including oxidative and electrophilic challenges. Traits associated with age-1 mutation are widely believed to be mediated through AKT-1, which requires PIP3 for both tethering and activation. Active AKT complex phosphorylates and thereby inactivates the DAF-16/FOXO transcription factor. However, extensive evidence indicates that pleiotropic effects of age-1-null mutations, including extreme longevity, cannot be explained by insulin like-receptor/AKT/FOXO signaling alone, suggesting involvement of other PIP3-binding proteins. We used ligand-affinity capture to identify membrane-bound proteins downstream of PI3KI that preferentially bind PIP3. Computer modeling supports a subset of candidate proteins predicted to directly bind PIP3 in preference to PIP2, and functional testing by RNAi knockdown confirmed candidates that partially mediate the stress-survival, aggregation-reducing and longevity benefits of PI3KI disruption. PIP3-specific candidate sets are highly enriched for proteins previously reported to affect translation, stress responses, lifespan, proteostasis, and lipid transport.

Keywords: longevity; oxidative stress resistance; phosphatidylinositol 3,4,5-triphosphate (PIP3); phosphatidylinositol 3-kinase; protein aggregation.

MeSH terms

  • Animals
  • Caenorhabditis elegans / physiology*
  • Catalytic Domain
  • Codon, Nonsense
  • Computer Simulation
  • Hydrogen Peroxide
  • Ligands
  • Lipids / chemistry
  • Membrane Proteins / metabolism*
  • Mutation
  • Phosphatidylinositol 3-Kinases / metabolism*
  • Phosphatidylinositol 4,5-Diphosphate / metabolism*
  • Phosphatidylinositol Phosphates / metabolism*
  • Protein Binding
  • RNA Interference
  • Thermodynamics

Substances

  • Codon, Nonsense
  • Ligands
  • Lipids
  • Membrane Proteins
  • Phosphatidylinositol 4,5-Diphosphate
  • Phosphatidylinositol Phosphates
  • phosphatidylinositol 3,4,5-triphosphate
  • Hydrogen Peroxide
  • Phosphatidylinositol 3-Kinases