Scientists Identify the Enzyme That Shatters Chromosomes in One in Four Cancers, Revealing a New Target for Drug Resistance
UC San Diego researchers identify N4BP2 as the molecular trigger behind chromothripsis, the catastrophic chromosome-shattering event that drives treatment resistance in roughly a quarter of human cancers.
Overview
A research team led by UC San Diego has identified the enzyme responsible for one of the most violent forms of genomic destruction in cancer. The enzyme, called N4BP2, enters fragile cellular compartments and shatters the chromosomes trapped inside, unleashing dozens to hundreds of genetic alterations in a single catastrophic event known as chromothripsis. The discovery, published in Science, provides the first direct molecular explanation for how this process begins and opens a potential new avenue for combating treatment-resistant tumors.
Approximately one in four human cancers shows evidence of chromothripsis, according to UC San Diego. The rate is even higher in certain tumor types: virtually all osteosarcomas and many aggressive brain cancers display the hallmarks of chromosome shattering.
What We Know
Chromothripsis occurs when errors during cell division trap individual chromosomes inside small, fragile compartments called micronuclei. When a micronucleus ruptures, the chromosome inside becomes exposed to the cell’s cytoplasm. What happens next had remained a mystery for more than a decade.
To find the answer, the research team — led by senior author Don Cleveland and first author Ksenia Krupina at UC San Diego, with collaborators Jonas Koeppel and Peter J. Campbell at the University of Cambridge and the Wellcome Trust Sanger Institute — conducted an unbiased screen of all 204 known and putative human nucleases, as reported by ScienceDaily. That screen identified N4BP2, a previously uncharacterized cytoplasmic endonuclease, as the enzyme that enters ruptured micronuclei and fragments the exposed DNA.
The evidence for N4BP2’s role is unusually direct. When the researchers eliminated the enzyme from brain cancer cells, chromosome shattering dropped dramatically. Conversely, when they forced N4BP2 into the nuclei of otherwise healthy cells, intact chromosomes broke apart, according to SciTechDaily. “N4BP2 isn’t just correlated with chromothripsis. It is sufficient to cause it,” said Krupina, as quoted by ScienceDaily.
The fragmented chromosomes are then stitched back together in random order by the cell’s DNA repair machinery, generating the massive structural rearrangements characteristic of chromothripsis. The study also found that this process gives rise to extrachromosomal DNA (ecDNA) — circular DNA fragments that sit outside chromosomes and are increasingly recognized as drivers of drug resistance and rapid tumor progression.
An analysis of more than 10,000 human cancer genomes confirmed the clinical relevance: tumors with elevated N4BP2 expression showed markedly increased chromothripsis patterns and structural rearrangements, according to UC San Diego.
What We Don’t Know
While the study establishes N4BP2 as a key initiator, it remains unclear whether additional nucleases contribute to chromosome fragmentation in specific cancer contexts. The researchers screened all known human nucleases, but the interplay between N4BP2 and the broader DNA damage response is not yet fully mapped.
It is also unknown whether blocking N4BP2 in established tumors would meaningfully slow cancer progression. The enzyme’s normal cellular function — presumably outside of the aberrant micronuclei context — has not been well characterized, raising questions about potential side effects of therapeutic inhibition.
No drug candidates targeting N4BP2 have been disclosed. The pathway from identifying a molecular target to developing a viable therapeutic typically spans many years, and it remains to be seen whether the enzyme is druggable in the traditional pharmacological sense.
Why It Matters
Chromothripsis and ecDNA have emerged as two of the most important mechanisms by which aggressive cancers evolve rapidly and evade treatment. Until now, they were largely treated as separate phenomena. This study links them mechanistically, placing N4BP2 at the very start of a cascade that produces both chromosome shattering and the circular DNA fragments that help tumors amplify oncogenes on demand.
“By finding what breaks the chromosome, we now have a new intervention point for slowing cancer evolution,” said Cleveland, as quoted by ScienceDaily.
Krupina, who is joining the University of Iowa’s Holden Comprehensive Cancer Center as an assistant professor, plans to expand investigations into the molecular mechanisms of N4BP2 and identify additional factors involved in chromosome shattering following nuclear envelope rupture. The research was funded by multiple National Institutes of Health grants.