Mechanical stress on the Focal Contact Facilitates Endocytosis of Integrins in Endothelial Cells

Abstract

Effects of mechanical stress on integrin clusters at focal contacts (FCs) were examined in cultured human umbilical vein endothelial cells (HUVECs). HUVECs were stained with an Alexa-antibody against an extracellular domain of the β1 integrin for live imaging of β1 integrins. Localized mechanical stimulus was applied to the FCs at the basal membrane by displacing a fibronectin coated glass bead that was attached on the apical cell surface and connected to the basal FCs via stress fibres. When the bead was displaced to stretch the connected stress fibers, integrin clusters at the basal membrane started to disappear within 1 min. Many clathrin positive integrin-containing vesicles were observed in the cytosol after the integrin disappearance, suggesting facilitated endocytosis of integrins. The mechano-induced integrin endocytosis was inhibited by external Ca²⁺ depletion or PAO (100 nM, for 5 min), a blocker of tyrosine phosphatase. These results suggest that mechanical stress on FCs facilitates the clathrin-dependent endocytosis of integrins via increased intracellular Ca²⁺ probably by activated SA channels and tyrosine dephosphorylation of focal proteins. We also observed FCs disappearance when an entire HUVEC was cyclically stretched. [Jpn J Physiol 54 Suppl:S72 (2004)]