Molecular mediators of αvβ3-induced endothelial cell survival

The alpha(v)beta(3) integrin interaction with the extracellular matrix (ECM) plays an essential role in inhibiting apoptosis in endothelial cells. We have recently shown that alpha(v)beta(3) ligation on rat aortic endothelial cells (RAECs) specifically activates the transcription factor nuclear factor kappa B (NF-kappa B) and promotes cell survival. Inhibiting NF-kappa B nuclear translocation abolished the protective effect of alpha(v)beta(3) ligands. Here, we report that ligation of alpha(v)beta(3) by its ligand, osteopontin (OPN), induces the phosphorylation and activation of inhibitory kappa B kinase beta (IKK beta) and promotes the specific degradation of inhibitory kappa B alpha (I kappa B alpha) in RAECs. Overexpression of a dominant negative (DN) IKK beta protein prevents I kappa B alpha phosphorylation, NF-kappa B activation, and inhibits the protective effects of OPN. The NF-kappa B-inducing kinase (NIK) has been shown to be one of the upstream kinases involved in IKK activation. OPN-mediated NF-kappa B activity is increased upon NIK wild-type (WT) overexpression and blocked following NIK DN overexpression. In addition, NIK -/- mouse embryonic fibroblasts (MEFs) plated on OPN display reduced NF-kappa B activity and decreased I kappa B alpha phosphorylation compared to NIK +/+ MEFs. Finally, functional inhibition of integrin beta(3)-dependent NF-kappa B signaling decreases OPN-induced I kappa B alpha, IKK beta and NIK phosphorylation. These studies for the first time show that the alpha(v)beta(3)-NF-kappa B-dependent endothelial survival pathway is dependent on IKB alpha, IKK beta, and NIK. Copyright (c) 2006 S. Karger AG, Basel.