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International audience; Integrin-linked kinase (ILK) and cytoplasmic adaptors of the PINCH and parvin families form a ternary complex, termed IPP, that localizes to integrin adhesions. We show here that deletion of the genes encoding ILK or PINCH1 similarly blocks maturation of focal adhesions to tensin-rich and phosphotyrosine-poor fibrillar adhesions (FBs) by downregulating expression or recruitment of tensin and destabilizing alpha5beta1-integrin-cytoskeleton linkages. As IPP components are interdependent for integrin targeting and protein stability, functional dissection of the complex was achieved by fusing ILK, PINCH, parvin or their individual motifs to the cytoplasmic tail of beta3 integrin, normally excluded from FBs. Using this novel gain-of-function approach, we demonstrated that expression of the C-terminal kinase domain of ILK can restore tensin recruitment and prompt focal-adhesion maturation in IPP-null cells. Debilitating mutations in the paxillin- or ATP-binding sites of ILK, together with alpha-parvin silencing, revealed a determinant role for ILK-parvin association, but not for direct paxillin binding, in this function. We propose a model in which the C-terminal domain of ILK promotes integrin sorting by reinforcing alpha5beta1-integrin-actin linkage and controls force transmission by targeting tensin to maturing adhesions.

International audience; Integrins play a key role in regulating endothelial cell survival, migration and differentiated function during angiogenic blood-vessel remodeling. Integrin-linked kinase (ILK) is a multidomain protein that interacts with the cytoplasmic tail of integrin beta subunits and is thought to participate in integrin-mediated signal transduction. We report here that attenuation of ILK expression in cultured bovine aortic endothelial cells by RNA interference had marked effects on surface distribution of alpha5beta1 integrin and the organization of cell-matrix adhesions characterized by the disappearance of fibrillar (3D-like) adhesions that are rich in alpha5beta1 and paxillin, and associated fibrillar fibronectin matrix. This defect was not caused by a decrease in fibronectin mRNA levels or by intracellular retention of the protein. Adhesion to surface-adsorbed matrix proteins based on beta1 and beta3 integrin was enhanced following ILK depletion, whereas cell spreading, migration and multilayer alignment into capillary-like structures on Matrigel were impaired. We conclude that ILK is an important regulator of the endothelial phenotype and vascular network formation by directing the assembly and/or maturation of alpha5beta1-competent matrix-forming adhesions.