Cyclic strain induces reorganization of integrin α5β1 and α2β1 in human umbilical vein endothelial cells

Abstract

Cyclic strain has been shown to modulate endothelial cell (EC) morphology, proliferation, and function. We have recently reported that the focal adhesion proteins focal adhesion kinase (pp125(IAK)) and paxillin, are tyrosine phosphorylated in EC exposed to strain and these events regulate the morphological change and migration induced by cyclic strain. Integrins are also localized on focal adhesion sites and have been reported to induce tyrosine phosphorylation of pp125(IAK) under a variety of stimuli. To study the involvement of different integrins in signalling induced by cyclic strain, we first observed the redistribution of α and β integrins in EC subjected to 4 h cyclic strain. Human umbilical vein endothelial cells (HUVEC) seeded on either fibronectin or collagens surfaces were subjected to 10% average strain at a frequency 60 cycles/min. Confocal microscopy revealed that β1 integrin reorganized in a linear pattern parallel with the long axis of the elongated cells creating a fusion of focal adhesion plaques in EC plated on either fibronectin (a ligand for α5β1) or collagen (a ligand for α2β1) coated plates after 4 h exposure cyclic strain β1 integrin, which is a vitronectin receptor, did not redistribute in EC exposed to cyclic strain. Cyclic strain also led to a reorganization of α5 and α2 integrins in a linear pattern in HUVEC seeded on fibronectin or collagen, respectively. The expression of integrins α5, α2, and β1 did not change even after 24 h exposure to strain when assessed by immunoprecipitation of these integrins. Cyclic strain-induced tyrosine phosphorylation of pp125(IAK) occurred concomitant with the reorganization of β1 integrin. We concluded that α5β1 that α5β1 and α2β1 integrins play an important role in transducing mechanical stimuli into intracellular signals.