Aging
Navigate
Submit an Article
Research Paper|Volume 2, Issue 9|pp 582—596

ATM-independent, high-fidelity nonhomologous end joining predominates in human embryonic stem cells

Bret R. Adams1,2, Amy J. Hawkins1, Lawrence F. Povirk3,4, Kristoffer Valerie1,2,4
  • 1Departments of Radiation Oncology, Virginia Commonwealth University, Richmond, VA 23298, USA
  • 2Biochemistry and Molecular Biology, Virginia Commonwealth University, Richmond, VA 23298, USA
  • 3Pharmacology and Toxicology, Virginia Commonwealth University, Richmond, VA 23298, USA
  • 4the Massey Cancer Center, Virginia Commonwealth University, Richmond, VA 23298, USA
Received: August 27, 2010Accepted: September 10, 2010Published: September 11, 2010
https://doi.org/10.18632/aging.100197

Copyright: © 2010 Adams et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Abstract

We recently demonstrated that human embryonic stem cells (hESCs) utilize homologous recombination repair (HRR) as primary means of double-strand break (DSB) repair. We now show that hESCs also use nonhomologous end joining (NHEJ). NHEJ kinetics were several-fold slower in hESCs and neural progenitors (NPs) than in astrocytes derived from hESCs. ATM and DNA-PKcs inhibitors were ineffective or partially effective, respectively, at inhibiting NHEJ in hESCs, whereas progressively more inhibition was seen in NPs and astrocytes. The lack of any major involvement of DNA-PKcs in NHEJ in hESCs was supported by siRNA-mediated DNA-PKcs knockdown. Expression of a truncated XRCC4 decoy or XRCC4 knock-down reduced NHEJ by more than half suggesting that repair is primarily canonical NHEJ. Poly(ADP-ribose) polymerase (PARP) was dispensable for NHEJ suggesting that repair is largely independent of backup NHEJ. Furthermore, as hESCs differentiated a progressive decrease in the accuracy of NHEJ was observed. Altogether, we conclude that NHEJ in hESCs is largely independent of ATM, DNA-PKcs, and PARP but dependent on XRCC4 with repair fidelity several-fold greater than in astrocytes.