Laminin-binding Integrins Regulate Angiogenesis by Distinct and Overlapping Mechanisms in Organotypic Cell Culture Models

Endothelial cells engage extracellular matrix and basement membrane components through integrin-mediated adhesion to promote angiogenesis. Our previous studies demonstrated that endothelial expression of laminin-411 and laminin-511 as well as α6 integrins is required for endothelial sprouting and tube formation in organotypic angiogenesis assays. These studies demonstrated that α6 integrins promote migration and regulate the expression of ANGPT2 and CXCR4 and that α6-dependent regulation of CXCR4 contributes to endothelial morphogenesis in our assays. However, these studies did not identify specific roles for the α6β1, α6β4, or α3β1 laminin-binding integrins. Here, we employ RNAi technology to parse the contributions of these integrins. We demonstrate that α6β4 promotes migration, sprouting, and tube formation, and also positively regulates the expression of ANGPT2, but does not promote CXCR4 expression, suggesting that α6β1 functions in this regulation. Additionally, we show that α3β1 regulates endothelial sprouting and tube formation, but is not required for migration in our assays or for the expression of ANGPT2 or CXCR4. Integrin α3β1 promotes the expression of NRP1 and ID1 RNAs, both of which are known to promote angiogenesis. Taken together, our results indicate that laminin-binding integrins play distinct roles during endothelial morphogenesis and do not compensate for one another in organotypic culture.