Activated AKT/PKB signaling in C. elegansuncouples temporally distinct outputs of DAF-2/insulin-like signaling

Authors:
Open Access
Publisher website
Google Scholar
Abstract
Background: In the nematode,Caenorhabditis elegans, a conserved insulin-like signaling pathway controls larval development, stress resistance and adult lifespan. AGE-1, a homolog of the p110 catalytic subunit of phosphoinositide 3-kinases (PI3K) comprises the major known effector pathway downstream of the insulin receptor, DAF-2. Phospholipid products of AGE-1/PI3K activate AKT/PKB kinase signaling via PDK-1. AKT/PKB signaling antagonizes nuclear translocation of the DAF-16/FOXO transcription factor. Reduced AGE-1/PI3K signaling permits DAF-16 to direct dauer larval arrest and promote long lifespan in adult animals. In order to study the downstream effectors of AGE-1/PI3K signaling inC. elegans, we conducted a genetic screen for mutations that suppress the constitutive dauer arrest phenotype ofage-1(mg109)animals.Results: This report describes mutations recovered in a screen for suppressors of the constitutive dauer arrest (daf-C) phenotype ofage-1(mg109). Two mutations corresponded to alleles ofdaf-16. Two mutations were gain-of-function alleles in the genes,akt-1andpdk-1, encoding phosphoinositide-dependent serine/threonine kinases. A fifth mutation,mg227, located on chromosome X, did not correspond to any known dauer genes, suggesting thatmg227may represent a new component of the insulin pathway. Genetic epistasis analysis by RNAi showed that reproductive development inage-1(mg109);akt-1(mg247)animals was dependent on the presence ofpdk-1. Similarly, reproductive development inage-1(mg109);pdk-1(mg261)animals was dependent onakt-1. However, reproductive development inage-1(mg109); mg227animals required onlyakt-1, andpdk-1activity was dispensable in this background. Interestingly, whilemg227suppressed dauer arrest inage-1(mg109)animals, it enhanced the long lifespan phenotype. In contrast,akt-1(mg247)andpdk-1(mg261)did not affect lifespan or stress resistance, while bothdaf-16alleles fully suppressed these phenotypes.Conclusion: A screen for suppressors of PI3K mutant phenotypes identified activating mutations in two known pathway components, providing insights into their regulation. In particular, the interdependence ofakt-1andpdk-1, even in activated forms, supports the existence of AGE-1-independent pathways for these phospholipid-dependent kinases. Phenotypic analysis of these alleles shows that the larval and adult outputs of AGE-1/PI3K are fully separable in these mutants.

This publication has 40 references indexed in Scilit: