β1 Integrin–FAK–Piezo1 signalling axis drives in-situ stiffening mediated ECM remodelling and invasion of 3D breast epithelium

Stiffening of tissue is a hallmark of cancer progression, driving invasive phenotypes through complex interactions between cells and their extracellular matrix (ECM). However, the mechanisms linking mechanical cues to ECM remodelling and invasion remain incompletely understood. Here, using an in-situ stiffening model that allows for modulation of ECM stiffness around fully formed normal mammary acini embedded in their native ECM microenvironment, we identify critical steps in basement membrane (BM) and stromal ECM remodelling during invasion and discover the molecular mechanisms driving this process. We find that stiffening of the ECM around normal mammary acini results in rapid loss and degradation of laminin (LN) and upregulation of the fibronectin (FN) secretion around the acini. This priming phase is followed by the onset of invasion which requires localized upregulation of LN production and ECM remodelling. Mechanistically, ECM production and remodelling as well as invasion is mediated by β1 integrin–FAK signalling, which activates mechanosensitive ion channels (MSCs). Further, we identify Piezo1 as the MSC downstream of β1 integrin–FAK that drives BM disruption and stromal ECM remodelling. Taken together, our results identify the mechanisms by which stiffness can trigger invasive phenotypes from normal tissues.