# The Extracellular Matrix Regulates Invasion in Fusion-Negative Rhabdomyosarcoma via YAP–PIEZO1 Signaling Axis

## TL;DR

This study shows how the density of the extracellular matrix affects the spread of fusion-negative rhabdomyosarcoma through a signaling pathway involving YAP and PIEZO1, offering a new treatment target.

## Contribution

The study identifies a novel YAP–PIEZO1 signaling axis linking extracellular matrix density to cancer invasion in fusion-negative rhabdomyosarcoma.

## Key findings

- High extracellular matrix density activates YAP, which increases PIEZO1 expression and calcium influx to promote invasion.
- Pharmacological inhibition of the YAP–PIEZO1 axis reduces invasive potential in fusion-negative rhabdomyosarcoma cells.
- Elevated PIEZO1 expression correlates with poorer survival in patients with fusion-negative rhabdomyosarcoma.

## Abstract

Fusion-negative rhabdomyosarcoma (FNRMS) is the prevalent subtype of rhabdomyosarcoma, the most common pediatric soft-tissue sarcoma. Its invasion often leads to recurrence and poor prognosis. This study investigates how the density of the extracellular matrix, surrounding cancer cells in the tissue, influences FNRMS invasion. We found that high extracellular matrix density activates the protein YAP, which directly triggers the expression of the mechanical sensor PIEZO1. This sensor allows calcium to enter the cells, providing a signal that facilitates invasion. Pharmacological inhibition of this axis successfully reduced the invasive potential, highlighting a novel therapeutic vulnerability for FNRMS patients.

Background: Fusion-negative rhabdomyosarcoma (FNRMS) represents the most prevalent subtype of rhabdomyosarcoma, the most common pediatric soft-tissue sarcoma. Although its invasion is a leading cause of recurrence and poor prognosis, its underlying mechanism remains unclear. We investigated how extracellular matrix density regulates FNRMS progression via mechano-transduction. Methods: We used three-dimensional spheroid invasion assays with FNRMS cells embedded in varying collagen concentrations. Mechanistic insights were gained through immunofluorescence, sequencing reanalysis, calcium live-cell imaging, and pharmacological inhibition of the YAP–PIEZO1 axis. Results: High extracellular matrix density significantly enhanced invasive spreading, correlating with increased YAP nuclear localization. YAP overexpression was sufficient to promote invasive spreading, while its inhibition attenuated the matrix-enhanced phenotype. We identified PIEZO1 as a direct transcriptional target of YAP. High extracellular matrix density stimulated PIEZO1-dependent calcium influx, which was required for invasion. Furthermore, elevated PIEZO1 expression was significantly associated with poorer overall survival in FNRMS patients. Targeting YAP effectively suppressed both calcium flux and invasion. Conclusions: Our findings establish a YAP–PIEZO1 axis linking extracellular matrix density to FNRMS invasion. This mechanosensitive pathway represents a potential therapeutic vulnerability in aggressive FNRMS.