Matrix-specific Suppression of Integrin Activation in Shear Stress Signaling

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Abstract
Atherosclerotic plaque develops at sites of disturbed flow. We previously showed that flow activates endothelial cell integrins, which then bind to the subendothelial extracellular matrix (ECM), and, in cells on fibronectin or fibrinogen, trigger nuclear factor-kappaB activation. Additionally, fibronectin and fibrinogen are deposited into the subendothelial ECM at atherosclerosis-prone sites at early times. We now show that flow activates ECM-specific signals that establish patterns of integrin dominance. Flow induced alpha2beta1 activation in cells on collagen, but not on fibronectin or fibrinogen. Conversely, alpha5beta1 and alphavbeta3 are activated on fibronectin and fibrinogen, but not collagen. Failure of these integrins to be activated on nonpermissive ECM is because of active suppression by the integrins that are ligated. Protein kinase A is activated specifically on collagen and suppresses flow-induced alphavbeta3 activation. Alternatively, protein kinase Calpha is activated on fibronectin and mediates alpha2beta1 suppression. Thus, integrins actively cross-inhibit through specific kinase pathways. These mechanisms may determine cellular responses to complex extracellular matrices.