A new study in Science Immunology has uncovered a previously unrecognized mechanism by which cancer cells may evade immune detection, identifying the RNA helicase DDX6 as a key regulator of RNA editing and innate immune suppression.
The research, led by Larry Ng, PhD, of the Cancer Science Institute of Singapore, found that DDX6 represses a specific form of double-stranded RNA (dsRNA) editing that would otherwise stabilize dsRNA molecules and promote immune activation. When DDX6 was depleted, dsRNA accumulated, triggering innate immune signaling, increasing immune cell infiltration, and reshaping the tumor microenvironment in both patient-derived organoids and mouse models.
The findings provide new insight into how tumors exploit RNA-editing pathways to suppress immune responses and suggest that targeting DDX6 could represent a new strategy for cancer immunotherapy.
“Our cells are equipped with this double-stranded RNA sensing mechanism,” Ng explained. “It is actually a mechanism against viruses.” Cells contain specialized sensors that recognize dsRNA, a molecular pattern commonly associated with viral infection. Activation of these sensors triggers inflammatory responses, including type I interferon signaling, that help eliminate infected cells.
However, dsRNA is not exclusively produced by viruses. Normal cells also generate endogenous RNA transcripts capable of forming double-stranded structures. To prevent inappropriate immune activation, cells rely on RNA-editing enzymes such as adenosine deaminase acting on RNA 1 (ADAR1), which modify dsRNA molecules and reduce their ability to activate immune sensors.
“What RNA editing does is to actually prevent this autoimmunity from happening,” Ng said. “Editing marks our own RNA with this modification, so it will help to prevent the recognition by the sensors.”
This protective mechanism becomes particularly important in cancer. Tumor cells often exhibit extensive chromosomal instability, producing abundant abnormal RNA transcripts and dsRNA structures that could otherwise trigger immune responses.
“Cancers actually have a lot of these double-stranded RNA structures due to chromosomal instability,” Ng said. “But they survive.” According to Ng, tumors accomplish this by co-opting RNA-editing pathways that normally protect healthy cells. “What they do is that they actually hijack this editing function to help them survive,” he said. “If we could target or prevent this editing from happening, we can actually reactivate the covert RNA sensing, and this might help to trigger tumor cell death.”
The study focused on DDX6, an RNA helicase previously linked to cancer development but not fully understood in the context of immune regulation. Ng and colleagues discovered that DDX6 interacts directly with ADAR1 and suppresses a specific category of ADAR1-mediated RNA editing events.
The finding challenges a longstanding assumption in the RNA-editing field.
For years, researchers believed that RNA editing primarily suppresses immune activation by destabilizing dsRNA structures, making them less recognizable to innate immune sensors. Ng’s study reveals that some RNA-editing events have the opposite effect.
“Not all of this editing can actually prevent the recognition of these RNA structures,” Ng said. “It actually helps to stimulate the interferon response.”
These editing events appear to stabilize dsRNA rather than destabilize it, promoting activation of innate immune pathways. DDX6 suppresses these immunostimulatory editing events, thereby preventing immune activation.
“DDX6 actually helps to prevent this potent editing event from happening—this immunostimulatory RNA editing event,” Ng said.
The discovery represents what Ng described as a significant shift in understanding RNA editing biology. “For a very long time, people in the RNA editing field think that editing actually helps to prevent the recognition of double-stranded RNA structures,” he said. “But in this paper we showed that not all of these editing events can actually destabilize. Some of them can help to stabilize.”
The biological consequences of DDX6 suppression were evident in both normal tissues and tumors. Mice lacking DDX6 accumulated dsRNA and developed widespread interferon activation, demonstrating the protein’s importance in preventing excessive innate immune responses in healthy cells.
Within tumors, however, DDX6-mediated suppression appeared to benefit cancer cells by limiting immune activation. “The immune activation actually will result in cell death,” Ng said. “Too much activation is not good for cancer.”
The researchers found that reducing DDX6 levels promoted dsRNA-driven innate immune responses and increased immune cell infiltration within tumors. Nevertheless, Ng emphasized that the study was designed primarily to investigate innate immunity rather than directly demonstrate enhanced antitumor immune activity.
“We see increased immune cell infiltration, and there is evidence of immune cell activation,” he said. “But whether or not this increased immune cell infiltration is causing the tumor to shrink, I do not have the definite evidence yet.”
Instead, the data support a role for DDX6 in shaping the tumor microenvironment. “It remodels the tumor microenvironment toward the more inflamed state,” Ng said.
Additional studies, including T-cell killing assays and other functional experiments, will be required to determine whether DDX6 inhibition directly enhances immune-mediated tumor destruction.
The broader significance of the work lies in its contribution to understanding how RNA editing influences immunity. “I feel it’s more about the mechanism that I found on how DDX6 behaves or functions as an immune suppressor,” Ng said.
