Abstract
The secretory pathway is a sophisticated endomembrane machinery designed to transport and deliver proteins and lipids to intracellular organelles and the extracellular space. While the molecular components of the secretory pathway are well understood, less is known about their regulation, especially by mechanical cues. Here, it is reported that substrate stiffness stimulates conventional secretion. A molecular pathway is unravelled that links a mechanical cue through proto-oncogene tyrosine-protein kinase Src (Src) and focal adesion kinase (FAK) kinases to promote the trafficking of secretory proteins out of the Golgi apparatus and prevent their post-Golgi lysosomal degradation. Phosphoproteomic analysis revealed the Golgi-specific Brefeldin A resistance factor 1 (GBF1) as a key downstream mechano-responsive regulator, whose phosphorylation state orchestrates post-Golgi cargo sorting, directing proteins either toward secretion or to lysosomes. Finally, AMP-activated protein kinase (AMPK) is identified as a stiffness-dependent upstream regulator of GBF1 phosphorylation. Together, the data reveal a molecular regulatory loop in which matrix stiffness positively regulates cellular secretion via the Src-FAK-AMPK-GBF1 axis, which can have relevant medical implications in conditions like cancer and fibrosis and their treatment.