DNA end joining becomes less efficient and more error-prone during cellular senescence

^*Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX 77030; and ^†Department of Cellular and Structural Biology, Sam and Ann Barshop Center for Longevity and Aging Studies, University of Texas Health Science Center, San Antonio, TX 78245

Edited by Thomas D. Petes, University of North Carolina, Chapel Hill, NC (received for review February 2, 2004)

Abstract

Accumulation of somatic mutations is thought to contribute to the aging process. Genomic instability has been shown to increase during aging, suggesting an aberrant function of DNA double-strand break (DSB) repair. Surprisingly, DSB repair has not been examined with respect to cellular senescence. Therefore, we have studied the ability of young, presenescent, and senescent normal human fibroblasts to repair DSBs in transfected DNA by using a fluorescent reporter substrate. We have found that the efficiency of end joining is reduced up to 4.5 fold in presenescent and senescent cells, relative to young cells. Sequence analysis of end junctions showed that the frequency of precise ligation was higher in young cells, whereas end joining in old cells was associated with extended deletions. These results indicate that end joining becomes inefficient and more error-prone during cellular senescence. Furthermore, the ability to use microhomologies for end joining was compromised in senescent cells, suggesting that young and senescent cells may use different end joining pathways. We hypothesize that inefficient and aberrant end joining is a likely mechanism underlying the age-related genomic instability and higher incidence of cancer in the elderly.

Footnotes

↵ ‡ To whom correspondence should be addressed at: Department of Biochemistry and Molecular Biology, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030. E-mail: gorbunov{at}bcm.tmc.edu.
This paper was submitted directly (Track II) to the PNAS office.
Abbreviations: DSB, double-strand break; NHEJ, nonhomologous end joining; FACS, fluorescence-activated cell sorter; PD, population doubling.