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FJ
EXPRESS SUMMARY ARTICLE The Full-length version of this article is also available, published online August 12, 2005 as doi:10.1096/fj.04-2447fje. |
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Buck Institute for Age Research, Novato, California, USA
1 Correspondence: Buck Institute for Age Research, 8001 Redwood Blvd., Novato, CA 94945, USA. E-mail: gmccoll{at}buckinstitute.org
SPECIFIC AIMS
We have begun to examine the role of DNA repair processes in life span determination and stress responses in adult C. elegans where somatic cells are in a postmitotic state. We examined cku-70 and cku-80, the C. elegans orthologs of mammalian Ku70 and Ku80 by knocking down expression using RNA interference (RNAi). Our aims were to 1) investigate the DNA repair phenotypes for cku-70 and cku-80; 2) examine the roles of cku-70 and cku-80 in life span determination; and 3) determine the role of cku-70 and cku-80 in adult stress responses.
PRINCIPAL FINDINGS
1. cku-70 and cku-80 are required for wild-type response to genotoxic stress
Reduced CKU-70 or CKU-80 functions in C. elegans renders worms sensitive to DNA damage from methyl methane sulfonate (MMS), a DNA-alkylating agent and mutagen. Exposure of fertile adult worms to increasing doses of MMS resulted in an increasing proportion of eggs that failed to develop. Furthermore, reduction of either CKU-70 or CKU-80 activity significantly increased this sensitivity, consistent with their roles in DNA repair processes.
Impaired DNA repair processes and possible lowered genomic stability following cku-70(RNAi) or cku-80(RNAi) did not reduce overall fertility.
2. Reduced cku-70 activity does not alter wild-type life span but increases daf-2 mutant life span and reduces daf-16 mutant life span
Reduction of cku-70 activity did not alter wild-type life span (Fig. 1
) and only slightly increased (mean increase 
14%) rrf-3(pk1426) life span, which show increased sensitivity to RNAi compared with wild-type. Further examination of cku-70(RNAi) revealed that life span of daf-2(e1370) was significantly increased (mean increase 35%), while daf-16(m26) life span was marginally but significantly decreased (mean decrease 11%). In the double mutant, daf-16(m26); daf-2(e1370) no life span difference was detected. In contrast, cku-80(RNAi) did not alter rrf-3(pk1426) or daf-2(e1370) life span.
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3. Reduced cku-70 activity increases thermotolerance in a DAF-16 dependent manner
Wild-type thermotolerance was significantly increased following cku-70(RNAi), consistent with roles observed in mammalian cells. However, we found this increase to be daf-16-dependent, such that daf-2(e1370) thermotolerance was also significantly increased, but not in either daf-16(m26) or daf-16(m26); daf-2(e1370) genetic backgrounds. No effect on thermotolerance was observed following cku-80(RNAi). This suggests that CKU-70 and CKU-80 also have distinct functions in C. elegans and that regulation of thermotolerance is not a function of a CKU-70/80 heterodimer.
CONCLUSIONS AND SIGNIFICANCE
The mammalian Ku heterodimer has important roles in DNA double strand break repair, telomere maintenance, cell cycle checkpoint-arrest, tumor suppression, and cellular stress resistance. However, Ku functions in postmitotic tissues are not defined. To investigate the evolutionarily conserved functions of Ku we knocked down expression by RNAi of Ku genes in C. elegans (cku-70 and cku-80). We found that C. elegans cku-70 is required for resistance to genotoxic stress, modulates cytotoxic stress responses, and influences aging. The later effects are dependent upon an IGF-1/insulin-like signaling pathway previously shown to affect life span. Reduction of CKU-70 activity amplifies the aging phenotype of IGF-1/Insulin-like signaling mutants: long-lived insulin receptor daf-2 mutations become even longer lived and short-lived forkhead transcription factor daf-16 mutants are even shorter lived. These observations support the view that organismal stress resistance determines life span and CKU-70 modulates these effects.
This study has identified a single gene outside of the insulin-like signaling pathway that amplifies the aging phenotype in both a negative and positive direction depending on genetic background (Fig. 2
). We describe an interesting interplay between DNA repair and aging. Processes intended to reduce the risks of tumor formation may, as a by-product, shorten maximal life span.
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FOOTNOTES
To read the full text of this article, go to http://www.fasebj.org/cgi/doi/10.1096/fj.04-2447fje;
This article has been cited by other articles:
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