Noncoding regulatory mutations contribute to the aberrant gene expression profile of neuroblastomas

Cancer begins when the instructions inside a cell go wrong, causing it to grow out of control. For decades, scientists have looked for these errors by reading the protein-coding sections of the genome, the parts of DNA that act as blueprints for building the body's machinery. However, in a specific and deadly childhood cancer called neuroblastoma, which forms in the adrenal glands or along the spine, these traditional blueprints often appear surprisingly clean. Researchers have found very few recurring mistakes in the protein-making genes of high-risk tumors. This silence in the coding regions suggests that the true culprits might be hiding elsewhere, in the vast stretches of DNA that do not code for proteins but instead act as switches, dimmers, and volume controls for the genes. These noncoding regions determine when and how strongly a gene is turned on or off, and if they are damaged, the cell's behavior can change just as drastically as if a blueprint were torn up.

A team of researchers at the University of Alabama at Birmingham set out to find these hidden errors in neuroblastoma. They focused on a phenomenon called allele-specific expression, which occurs when a cell uses one copy of a gene differently than the other. In a healthy person, the two copies of a gene usually produce similar amounts of protein. But in cancer, if a mutation disrupts the switch controlling one copy, that copy might be silenced or overactive while the other remains normal. By comparing the activity of these gene pairs in tumor samples against healthy adrenal tissue, the scientists could pinpoint which genes were being mismanaged by the cancer. They then asked a critical question: were these mismanaged genes being driven by large-scale chromosomal losses or gains, which are common in this disease, or were they being driven by tiny, specific mutations in the noncoding regulatory switches?

The researchers analyzed genetic data from 156 children with neuroblastoma and compared it to 220 samples of normal adrenal tissue. They identified 1,363 genes that showed this specific pattern of mismanagement only in the tumors. These genes were not random; they were heavily involved in the development of the sympathetic nervous system and the adrenergic cell state, which is the specific identity that neuroblastoma cells often adopt. While many of these mismanaged genes were indeed linked to large chromosomal errors, the team discovered a significant group that lived in regions of the genome with normal copy numbers. This finding was crucial because it proved that something other than large-scale chromosomal damage was causing these genes to malfunction.

Digging deeper into these copy-number-neutral regions, the scientists found that the mismanaged genes were surrounded by a higher density of somatic mutations—new genetic errors that arise in the tumor but are not inherited. These mutations were not scattered randomly; they were concentrated in open chromatin regions, which are the parts of the DNA that are accessible and active in neuroblastoma cells. The researchers then used computer models to predict how these mutations affected the binding sites for transcription factors, the proteins that act as master switches to turn genes on or off. They found that these mutations frequently disrupted the binding sites for a specific transcription factor called GATA3.

GATA3 is a key regulator that helps maintain the adrenergic identity of neuroblastoma cells. The study showed that when the noncoding mutations broke the GATA3 binding sites near certain genes, those genes often belonged to the GATA3 regulatory network. One notable example was a gene called KMT2C, which acts as a tumor suppressor. The researchers found that tumors with mutations in the noncoding regions near KMT2C, which disrupted GATA3 binding, had significantly lower levels of the KMT2C protein. This suggests that the cancer cells were using these tiny, noncoding mutations to turn off a protective gene, effectively disarming the cell's natural defenses.

The study concludes that noncoding regulatory mutations are a major, yet often overlooked, driver of neuroblastoma. By focusing on how genes are expressed rather than just looking for broken protein blueprints, the researchers uncovered a new layer of genetic complexity. They demonstrated that these tumors often rely on subtle changes to the switches that control gene activity, particularly those governed by GATA3, to drive their growth and survival. This work provides a new map for understanding how neuroblastoma develops and suggests that future treatments might need to target these regulatory switches, not just the protein-coding genes.