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

// Srinivas Ayyadevara 1,2,3 , Meenakshisundaram Balasubramaniam 1,2 , Jay Johnson 2 , Ramani Alla 1,3 , Samuel G. Mackintosh 4 and Robert J. Shmookler Reis 1,2,3,4 1 McClellan Veterans Medical Center, Central Arkansas Veterans Healthcare Service, Little Rock, AR, USA 2 BioInformatics Program, University of Arkansas for Medical Sciences and University of Arkansas at Little Rock, Little Rock, AR, USA 3 Reynolds Institute on Aging/Department of Geriatrics, University of Arkansas for Medical Sciences, Little Rock, AR, USA 4 Department of Biochemistry & Molecular Biology, University of Arkansas for Medical Sciences, Little Rock, AR, USA Correspondence to: Robert J. Shmookler Reis, email: // Srinivas Ayyadevara, email: // Keywords : phosphatidylinositol 3-kinase; phosphatidylinositol 3,4,5-triphosphate (PIP3); longevity; oxidative stress resistance; protein aggregation Received : March 28, 2016 Accepted : June 20, 2016 Published : July 12, 2016 Abstract Class-I phosphatidylinositol 3-kinase (PI3K I ) converts phosphatidylinositol 4,5-bisphosphate (PIP 2 ) to phosphatidylinositol 3,4,5-triphosphate (PIP 3 ). PIP 3 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 PIP 3 -bound proteins, in particular other components of their signaling pathways. Null alleles of the C. elegans age-1 gene , encoding the catalytic subunit of PI3K I , lack any detectable class-I PI3K activity and so cannot form PIP 3 . 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 PIP 3 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 PIP 3 -binding proteins. We used ligand-affinity capture to identify membrane-bound proteins downstream of PI3K I that preferentially bind PIP 3 . Computer modeling supports a subset of candidate proteins predicted to directly bind PIP 3 in preference to PIP 2 , and functional testing by RNAi knockdown confirmed candidates that partially mediate the stress-survival, aggregation-reducing and longevity benefits of PI3K I disruption. PIP 3 -specific candidate sets are highly enriched for proteins previously reported to affect translation, stress responses, lifespan, proteostasis(definition), and lipid transport.