Abstract
Hemodynamic shear stress regulates endothelial phenotype through activation of Notch1 signaling, yet the mechanistic basis for this activation is unclear. Here, we establish a fluid shear stress-dependent mechanism of Notch1 activation that is distinct from canonical ligand trans-endocytosis. Application of laminar flow triggers the rapid spatial polarization of full-length Notch1 heterodimers into downstream membrane microdomains. Unlike canonical transactivation, this response occurs independently of ligand redistribution, and Notch1 receptors are cis-endocytosed into the receptor-bearing cell within polarized microdomains prior to proteolytic activation. We discover that the Notch1 intracellular domain (ICD) critically orchestrates receptor polarization and proteolytic activation in response to flow but is dispensable for canonical ligand transactivation. Shear stress increases ICD interaction with annexin A2 and caveolar proteins which control Notch1 endocytosis and proteolytic compartmentalization. These findings define a flow-specific Notch1 mechanotransduction pathway linking receptor polarization and endocytosis with proteolytic activation and establish new mechanisms regulating Notch receptor activation.