Chromosomal translocations in human cells are generated by canonical nonhomologous end-joining

Area of Science:

• Genetics
• Molecular Biology
• Cancer Research

Background:

• Chromosomal translocations are hallmarks of human cancers.
• Nonhomologous end-joining (NHEJ) is a primary DNA repair pathway.
• Canonical NHEJ (c-NHEJ) and alternative NHEJ (alt-NHEJ) are distinct subtypes of this repair process.

Purpose of the Study:

• To investigate the mechanisms of translocation joining in human cells.
• To determine the role of canonical NHEJ (c-NHEJ) in generating chromosomal translocations.
• To compare translocation formation in human versus mouse cells.

Main Methods:

• Introduction of DNA double-strand breaks (DSBs) on two chromosomes using designer nucleases (ZFNs, TALENs, CRISPR/Cas9).
• Analysis of translocation junctions in human cells deficient for c-NHEJ components (LIG4, XRCC4).
• Assessment of translocation junction characteristics, including deletions and microhomology.

Main Results:

• Human cells deficient for LIG4 or XRCC4 exhibited altered translocations with longer deletions and more microhomology, suggesting alt-NHEJ involvement.
• Contrary to mouse models, human translocations were found to be primarily generated by c-NHEJ.
• Cancer-associated translocations induced by CRISPR/Cas9 also depended on c-NHEJ.

Conclusions:

• Human cells utilize c-NHEJ for generating chromosomal translocations, a mechanism distinct from mouse cells.
• This species-specific difference in DNA repair pathways has significant implications for understanding cancer development.
• The findings highlight the importance of considering species-specific differences in genomic rearrangement mechanisms in cancer research.