Integrin‐Piezo1 Axis Drives ECM Remodeling and Invasion of 3D Breast Epithelium

Abstract Stiffening of tissue is a hallmark of cancer progression, promoting invasive phenotypes through altered cell‐extracellular matrix (ECM) interactions. However, how fully formed epithelial structures respond to mechanical cues within their native ECM environment remains poorly understood. Here, using a 3D in situ stiffening hydrogel system that enables modulation of stiffness around mature normal mammary acini, it uncovers critical steps in ECM remodeling and invasion of epithelial structures and discover molecular mechanisms driving this process. Stiffening around mature acini triggers two temporally distinct phases of epithelial remodeling, a rapid priming phase involving basement membrane (laminin, LN) disruption and fibronectin (FN) secretion, followed by a delayed invasion phase characterized by FN remodeling and LN re‐deposition that coincides with acinar proliferation and invasion. Mechanistically, it is shown that these changes are mediated by α3β1‐ and α5β1‐integrin–focal adhesion kinase (FAK) signaling, which in turn activates the mechanosensitive ion channel Piezo1 to regulate ECM composition, remodeling, and acinar invasion. Together, the findings reveal how mature epithelial structures dynamically respond to mechanical stiffening to create an invasive niche, offering new insights into how tissue architecture and stiffness synergize to drive breast cancer progression.