Transcriptional targets of DAF-16 insulin signaling pathway protect C. elegans from extreme hypertonic stress

Am J Physiol Cell Physiol. 2005 Feb;288(2):C467-74. doi: 10.1152/ajpcell.00451.2004. Epub 2004 Oct 20.

Abstract

All cells adapt to hypertonic stress by regulating their volume after shrinkage, by accumulating organic osmolytes, and by activating mechanisms that protect against and repair hypertonicity-induced damage. In mammals and nematodes, inhibition of signaling from the DAF-2/IGF-1 insulin receptor activates the DAF-16/FOXO transcription factor, resulting in increased life span and resistance to some types of stress. We tested the hypothesis that inhibition of insulin signaling in Caenorhabditis elegans also increases hypertonic stress resistance. Genetic inhibition of DAF-2 or its downstream target, the AGE-1 phosphatidylinositol 3-kinase, confers striking resistance to a normally lethal hypertonic shock in a DAF-16-dependent manner. However, insulin signaling is not inhibited by or required for adaptation to hypertonic conditions. Microarray studies have identified 263 genes that are transcriptionally upregulated by DAF-16 activation. We identified 14 DAF-16-upregulated genes by RNA interference screening that are required for age-1 hypertonic stress resistance. These genes encode heat shock proteins, proteins of unknown function, and trehalose synthesis enzymes. Trehalose levels were elevated approximately twofold in age-1 mutants, but this increase was insufficient to prevent rapid hypertonic shrinkage. However, age-1 animals unable to synthesize trehalose survive poorly under hypertonic conditions. We conclude that increased expression of proteins that protect eukaryotic cells against environmental stress and/or repair stress-induced molecular damage confers hypertonic stress resistance in C. elegans daf-2/age-1 mutants. Elevated levels of solutes such as trehalose may also function in a cytoprotective manner. Our studies provide novel insights into stress resistance in animal cells and a foundation for new studies aimed at defining molecular mechanisms underlying these essential processes.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Caenorhabditis elegans / physiology*
  • Caenorhabditis elegans Proteins / genetics
  • Caenorhabditis elegans Proteins / metabolism*
  • Forkhead Transcription Factors
  • Genes, Helminth / physiology*
  • Hypertonic Solutions
  • Insulin / genetics*
  • Insulin / metabolism
  • Oligonucleotide Array Sequence Analysis
  • Osmotic Pressure
  • Signal Transduction / physiology*
  • Somatomedins / genetics*
  • Somatomedins / metabolism
  • Transcription Factors / genetics
  • Transcription Factors / metabolism*
  • Transcription, Genetic
  • Trehalose / pharmacology

Substances

  • Caenorhabditis elegans Proteins
  • Forkhead Transcription Factors
  • Hypertonic Solutions
  • Insulin
  • Somatomedins
  • Transcription Factors
  • daf-16 protein, C elegans
  • Trehalose