Discover how rolling-translated EGFR variants sustain signaling in glioblastoma through circular RNA mechanisms
Imagine a car parking brake that instead of stopping the vehicle, actually jams the accelerator pedal to the floor. This mechanical nightmare mirrors a biological reality inside the most common and aggressive form of brain cancer—glioblastoma (GBM). For decades, scientists have known that in over 50% of glioblastoma cases, a molecular switch called the epidermal growth factor receptor (EGFR) gets stuck in the "on" position, relentlessly driving cancer growth 1 . Yet drugs designed to target this receptor have consistently failed in clinical trials, leaving researchers baffled.
The solution to this medical mystery emerged from an unexpected place—not from studying the EGFR protein itself, but from investigating a strange, circular form of genetic material that encodes a previously unknown protein. This discovery, published in Neuro-Oncology, reveals how cancer cells exploit a novel biological mechanism to keep their growth signals active, and opens promising new avenues for treatment 1 2 . This article will explore the fascinating story of how scientists discovered "rolling-translated EGFR" (rtEGFR) and how this finding is reshaping our understanding of glioblastoma.
To understand this breakthrough, we first need to venture into the once-overlooked realm of circular RNAs (circRNAs). Unlike traditional linear RNA molecules that resemble straight lines with clear start and end points, circRNAs form continuous loops without beginning or end.
"For years, scientists believed circRNAs were simply 'genomic junk' without important functions," explains researchers from Sun Yat-sen University 9 . "Their stable circular structures resist digestion by RNase R, and they accumulate in the brain in a conservative form wherein neurons seldom undergo mitosis."
These circular molecules were initially thought to function merely as sponges that soak up other cellular components. However, recent discoveries have revealed something remarkable—some circRNAs can actually serve as blueprints for proteins, despite their circular configuration 9 .
Continuous loop without 5' cap or 3' poly-A tail
Resistant to degradation by RNase R enzyme
How can a looped molecule be read by the cellular machinery designed for linear templates? The answer lies in two special features:
Internal Ribosome Entry Site: Special sequences that can directly recruit protein-making ribosomes without needing a start signal at the beginning of a linear molecule 9
Chemical tags that can similarly attract the protein-making machinery 9
These features allow circRNAs to bypass the normal rules of protein production, creating an assembly line that can theoretically run indefinitely around their circular track.
The research team from Sun Yat-sen University made a crucial observation: one specific circRNA derived from the EGFR gene was highly abundant in glioblastoma tissues compared to normal brain cells 1 2 . This circRNA, dubbed circ-EGFR, seemed to be particularly important in the most aggressive brain tumors.
Circ-EGFR is highly abundant in glioblastoma tissues
Confirmed circular nature using multiple methods
Identified protein products using custom antibodies and mass spectrometry
Tested function in cells and animal models
First, they needed to verify that circ-EGFR was truly circular. Using:
To read the genetic sequence of circ-EGFR 2
To visualize the circular molecules 2
To confirm the precise back-splicing sequence 2
All three methods consistently confirmed they were dealing with a genuine circRNA.
Next, the team needed to determine whether this circRNA could actually produce a protein. They employed:
Created to recognize the predicted protein product 2
A sophisticated technology that identifies proteins based on their molecular weight and chemical properties 2
These methods revealed something extraordinary—circ-EGFR was producing not one, but multiple related proteins of different sizes (35, 40, 55, and 70 kilodaltons) 9 .
To understand what this protein does, the researchers:
The most remarkable finding emerged when the team deciphered how circ-EGFR produces proteins. Unlike typical RNA translation that starts at point A and ends at point Z, circ-EGFR contains what scientists call an "infinite open reading frame" (iORF) 1 .
Starts at point A, ends at point Z
Continuous loop with no natural endpoint
Since the molecule has no natural end point, the cellular machinery can continue reading around the circle multiple times, like a train on a circular track. Through a process called "programmed -1 ribosomal frameshifting" (-1PRF), the translation periodically jumps to a different reading frame, bypassing what would normally be stop signals 1 . This creates a series of repeating amino acid sequences that form a complex, multi-unit protein structure the researchers named "rolling-translated EGFR" (rtEGFR) 1 .
| Protein Band | Molecular Weight | Composition | Detection Method |
|---|---|---|---|
| Band 1 | 35 kD | Basic repeating unit | Western blot 9 |
| Band 2 | 40 kD | Modified repeating unit | Western blot 9 |
| Band 3 | 55 kD | Multimeric complex | Western blot 9 |
| Band 4 | 70 kD | Larger multimeric complex | Western blot 9 |
So what does rtEGFR actually do in cancer cells? The experiments revealed that rtEGFR doesn't simply mimic normal EGFR—it plays a more sophisticated role:
By keeping EGFR at the cell surface, rtEGFR blocks the natural process that would normally remove and break down activated EGFR 1
This results in prolonged growth signaling, even when the cell should be turning these signals off 1
| Cellular Process | Normal Conditions | With rtEGFR Present | Experimental Method |
|---|---|---|---|
| EGFR membrane localization | Regulated | Sustained | Immunofluorescence 1 |
| EGFR endocytosis | Normal | Attenuated | EGFR degradation assay 2 |
| EGFR degradation | Proceeds normally | Significantly reduced | Ubiquitination assay 2 |
| Downstream signaling | Transient | Persistent | Phosphorylation analysis 1 |
The clinical significance of these findings became clear when the researchers examined patient data. Glioblastoma patients with high levels of circ-EGFR had significantly worse outcomes than those with low levels 1 . This suggests that rtEGFR production represents a new mechanism that cancer cells use to resist treatment and maintain their aggressive growth.
| Research Tool | Application | Function in Discovery |
|---|---|---|
| RNAase R | RNA digestion | Linear RNA removal to isolate circRNAs 2 |
| Lentivirus vectors | Gene delivery | Create stable cell lines with modified circ-EGFR expression 2 |
| Custom antibodies | Protein detection | Specifically recognize rtEGFR protein products 2 |
| Mass spectrometer | Protein identification | Confirm rtEGFR amino acid sequences 2 |
| Patient-derived xenografts | In vivo modeling | Study rtEGFR function in biologically relevant models 2 |
The discovery of rtEGFR represents more than just a scientific curiosity—it opens concrete possibilities for improving glioblastoma treatment. Since rtEGFR is found in cancer cells but not in normal brain tissue, it represents an ideal therapeutic target 1 2 . The researchers demonstrated that removing rtEGFR made tumor cells more vulnerable to existing EGFR-targeted therapies, suggesting combination approaches could be more effective.
This research also highlights the broader potential of circRNA-encoded proteins in cancer biology. As the Sun Yat-sen University team notes, multiple circRNAs have been found to encode functional proteins in glioblastoma, with some acting as tumor suppressors and others as cancer promoters 9 :
Encodes SHPRH-146aa which protects a full-length tumor suppressor protein from degradation 9
Produces AKT3-174aa that limits AKT phosphorylation and suppresses tumor growth 9
Encodes FBXW7-185aa that promotes the degradation of the oncogene c-Myc 9
These discoveries collectively suggest we're witnessing the emergence of a new layer of biological regulation in cancer, one that has been hidden in circular RNAs.
The story of rtEGFR teaches us a valuable lesson about scientific progress—sometimes breakthroughs require us to think in circles rather than straight lines. For decades, cancer researchers focused predominantly on linear forms of genetic information, while an entire world of circular molecules remained in the shadows.
"You spin me right 'round"—indeed, sometimes the most profound answers come not from moving forward, but from going in circles 1 .
This discovery not only explains why previous EGFR-targeted therapies have struggled, but also provides new direction for developing more effective treatment strategies. As research in this field advances, targeting rtEGFR may eventually help improve outcomes for patients facing this devastating disease.
The journey from dismissing circRNAs as "genomic junk" to recognizing them as sources of functional proteins illustrates how much we still have to learn about the complexity of cancer biology.