Scientists at the University of California, San Diego have pinpointed the enzyme that launches chromothripsis—a sudden, massive shattering and re‑assembly of chromosomes that fuels rapid tumor evolution and treatment resistance. Their findings, published in Science, reveal how this chaotic event starts and why it matters for the most aggressive cancers.
Unlike the slow accumulation of single‑point mutations, chromothripsis can generate dozens or hundreds of genetic changes in a single episode, giving cancer cells a swift evolutionary boost. Roughly one in four tumors shows evidence of this phenomenon, with nearly all osteosarcomas and many brain cancers displaying especially high levels.
How N4BP2 Triggers DNA Breakage in Micronuclei
During cell division, misplaced chromosomes can become trapped inside tiny, fragile structures called micronuclei. When these micronuclei rupture, the enclosed DNA is exposed to nucleases—enzymes that cut DNA strands. Until now, the specific nuclease responsible for the cascade remained unknown.
Using an imaging‑based screen that examined every known and predicted human nuclease, the team discovered that N4BP2 uniquely enters micronuclei and slices the DNA inside. Removing N4BP2 from brain‑cancer cells sharply reduced chromosome shattering, while forcing the enzyme into the nucleus caused intact chromosomes to fragment—even in otherwise healthy cells.
Connection to Aggressive Tumors and Extrachromosomal DNA
Analysis of more than 10,000 cancer genomes showed that tumors with high N4BP2 activity also harbored extensive chromothripsis and large‑scale structural rearrangements. These cancers frequently contain extrachromosomal DNA (ecDNA), circular DNA fragments that carry oncogenes and drive rapid growth and drug resistance.
The study suggests that ecDNA is not a separate event but a downstream product of chromothripsis, placing N4BP2 at the very start of a cascade that creates some of the most unstable cancer genomes. Targeting N4BP2 or its downstream pathways could therefore blunt the genomic chaos that enables tumors to adapt, recur, and evade therapy.
Funding for the work came from multiple National Institutes of Health grants.