Ezrin's 'dormant' form turns out to be an active driver of bone cancer metastasis

For decades, the protein ezrin had a simple biography. In its open form, anchored at the cell membrane, it was active - helping cells move, adhere, and communicate. In its closed form, floating in the cell's interior, it was dormant. A molecular wallflower.

That biography turns out to be wrong.

A team at Georgetown University's Lombardi Comprehensive Cancer Center has discovered that closed ezrin is anything but inactive. It binds directly to RNA, influences how genes are translated into proteins, and - most alarmingly - can single-handedly restore metastatic behavior in osteosarcoma cells. The finding, published March 17, 2026, in Science Signaling, fundamentally rewrites what researchers thought they knew about one of cancer's most important proteins.

A protein with a secret life

Osteosarcoma is the most common bone cancer in children and young adults, with about 1,000 new cases diagnosed annually in the United States. Roughly half occur in patients under 18. When caught early, five-year survival rates range from 60% to 75%. But once the cancer metastasizes, survival plummets to between 5% and 30%. Those metastatic cases are precisely where treatment has been most difficult - and where ezrin plays a central role.

Ezrin was already known to be important in osteosarcoma metastasis. But researchers assumed the action was all happening at the membrane, where open ezrin connects the cell's internal skeleton to its outer surface. The closed form? Just the inactive reserve pool, waiting to be activated.

The Georgetown team, led by Aykut Uren, devised an elegant experiment to test that assumption. Because ezrin naturally pivots between open and closed states, it is nearly impossible to study one form without interference from the other. So the researchers created osteosarcoma cells that produced no ezrin at all, then reintroduced two mutant versions: one locked permanently open, the other locked permanently closed. They implanted these cells into zebrafish to observe their metastatic behavior.

Closed ezrin restores the ability to spread

The results overturned the conventional model. Closed ezrin, far from being dormant, was able to restore metastatic behavior in osteosarcoma cells that had been stripped of the protein entirely. It did this through a mechanism no one had previously suspected: direct binding to RNA.

These RNA interactions allowed closed ezrin to influence gene translation - shaping which proteins the cell produces and in what quantities. The net effect was to support the molecular machinery of cancer cell growth and spread. "We now know that ezrin's closed form is not inactive at all," Uren said. "It's performing essential RNA-related functions that help cancer cells spread."

This dual functionality may explain why ezrin has been such a potent driver of metastasis across multiple cancer types and why targeting it therapeutically has proven so frustrating. If you only block the open form at the membrane, the closed form continues working inside the cell - and vice versa.

Small molecules that target both forms

The good news is that Uren's lab has already identified small molecules capable of inhibiting both open and closed states of ezrin. These compounds have shown promise in cultured osteosarcoma cells and in multiple mouse models. The next challenge is improving the drugs' binding properties and solubility before any consideration of human testing.

That is a significant gap. Moving from cell culture and mouse models to clinical trials involves years of optimization, toxicity testing, and regulatory hurdles. And the complexity of ezrin's role - active in two different forms through two different mechanisms - means that any drug will need to disrupt both functions without causing unacceptable side effects in healthy tissues where ezrin performs normal duties.

Rewriting the textbook on a familiar protein

The broader significance extends beyond osteosarcoma. Ezrin is implicated in multiple cancer types, and if its closed form is universally active as an RNA-binding protein, the entire field's understanding of this protein family needs revision. The finding also highlights how basic research assumptions - in this case, that a protein's closed conformation equals inactivity - can persist for decades and shape therapeutic strategies that may be incomplete.

For the roughly 500 children and adolescents diagnosed with osteosarcoma each year in the U.S., the clinical implications are still distant. But the discovery of a new molecular mechanism underlying metastasis - and the existence of small molecules that can target it - represents a path that did not exist before this study.