Cholesterol-rich plasma membrane microdomains regulate integrin mediated mechanotransduction

Focal adhesions and caveolae have been identified as important sites for shear-sensitive mechanotransduction. Interestingly, recent findings propose significant crosstalk exists between these microdomains. To test whether co-regulation of these distinct mechanosensors constitutes a relevant mechanotransduction mechanism, we exposed BAEC to 10 dynes/cm² of laminar shear stress and examined the interaction of proteins associated with these sites. Shear stress stimulated the recruitment of the α1/caveolin-1/Fyn/Shc complex to the β1 integrin where caveolin-1 functions as a scaffold for signal progression. Additionally, shear-induced β1 integrin activation resulted in caveolin-1 phosphorylation and subsequent binding of Csk, an integrin localized protein and inhibitor of Src kinases. These data suggest caveolin-1 functions to both positively and negatively regulate integrin associated signaling. To test the importance of lipid raft organization in these signaling events we used p-cyclodextrin, a cholesterol chelator; to disrupt lipid rafts, including caveolae, at the plasma membrane. In our studies, cholesterol depletion blocked shear-induced phosphorylation of caveolin-1 and its increased association with Csk. However, cyclodextrin alone activated the β1 integrin complex and enhanced the shear-induced recruitment of α1/caveolin-1/Fyn/Shc. Together these data strongly implicate cholesterol rich microdomains, such as caveolae, as key coordination sites for the regulation of integrin mechanotransduction.