Comparison of nonhomologous end joining and homologous recombination in human cells

Abstract

The two major pathways for repair of DNA double-strand breaks (DSBs) are homologous recombination (HR) and nonhomologous end joining (NHEJ). HR leads to accurate repair, while NHEJ is intrinsically mutagenic. To understand human somatic mutation it is essential to know the relationship between these pathways in human cells. Here we provide a comparison of the kinetics and relative contributions of HR and NHEJ in normal human cells. We used chromosomally integrated fluorescent reporter substrates for real-time in vivo monitoring of the NHEJ and HR. By examining multiple integrated clones we show that the efficiency of NHEJ and HR is strongly influenced by chromosomal location. Furthermore, we show that NHEJ of compatible ends (NHEJ-C) and NHEJ of incompatible ends (NHEJ-I) are fast processes, which can be completed in approximately 30 min, while HR is much slower and takes 7h or longer to complete. In actively cycling cells NHEJ-C is twice as efficient as NHEJ-I, and NHEJ-I is three times more efficient than HR. Our results suggest that NHEJ is a faster and more efficient DSB repair pathway than HR.

Loss of p21Sdi1 expression in senescent cells after DNA damage accompanied with increase of miR-93 expression and reduced p53 interaction with p21Sdi1 gene promoter

“…It has been reported that DNA double strand breaks (DSBs) are repaired by nonhomologous end joining (NHEJ) and homologous recombinational repair (HRR), and NHEJ is faster and more efficient than HRR in human cells [16]. The activity of NHEJ varies depending on cell cycle phase (G1 < S < G2/M) in which the damage is inflicted [17] and Ku protein is significantly reduced in senescent 0006-291X/$ -see front matter Ó 2011 Elsevier Inc. All rights reserved.…”

Alternative NHEJ Pathway Components Are Therapeutic Targets in High-Risk Neuroblastoma

“…Digestion with HindIII in NHEJ plasmid leaves compatible broken DNA ends, whereas ISceI digestion produces incompatible ends. The rationale for selecting two distinct restriction sites was that radiation and chemotherapy medications cause nonspecific DSBs that are more likely to have incompatible ends, therefore NHEJ-I-SceI may resemble repair occurring after cancer therapies (15). NHEJ and HR reporters have been validated by plasmid rescue and sequencing studies (27,28).…”

“…S1; refs. 15,27,28). Restriction enzymes, including Hind III, I-SceI, or BsrG1 induced DSB in reporter cassettes, which were utilized to quantify DSB repair activity in neuroblastoma cells of varying cytogenetic phenotypes.…”

“…Compared with HR, NHEJ is functional throughout the cell cycle and restores chromosomal continuity without sequence homology (14,15). There are two major processes of NHEJ that differ with respect to repair factors and end-joining fidelity.…”

A recombination-based method to characterize human BRCA1 missense variants

“…The choice may be dictated by genome composition. In large repetitive genomes of plants and animals overly efficient HR may lead to deleterious genomic rearrangements, such that NHEJ may be a safer choice [32]. This is the main reason why we measured the effect of BRCA1 missense variants on NHEJ in a plasmid random integration assay.…”