Endothelial lumen signaling complexes control 3D matrix–specific tubulogenesis through interdependent Cdc42- and MT1-MMP–mediated events

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Abstract
Here, we define an endothelial cell (EC) lumen signaling complex involving Cdc42, Par6b, Par3, junction adhesion molecule (Jam)–B and Jam-C, membrane type 1–matrix metalloproteinase (MT1-MMP), and integrin α2β1, which coassociate to control human EC tubulogenesis in 3D collagen matrices. Blockade of both Jam-B and Jam-C using antibodies, siRNA, or dominant-negative mutants completely interferes with lumen and tube formation resulting from a lack of Cdc42 activation, inhibition of Cdc42-GTP–dependent signal transduction, and blockade of MT1-MMP–dependent proteolysis. This process requires interdependent Cdc42 and MT1-MMP signaling, which involves Par3 binding to the Jam-B and Jam-C cytoplasmic tails, an interaction that is necessary to physically couple the components of the lumen signaling complex. MT1-MMP proteolytic activity is necessary for Cdc42 activation during EC tube formation in 3D collagen matrices but not on 2D collagen surfaces, whereas Cdc42 activation is necessary for MT1-MMP to create vascular guidance tunnels and tube networks in 3D matrices through proteolytic events. This work reveals a novel interdependent role for Cdc42-dependent signaling and MT1-MMP–dependent proteolysis, a process that occurs selectively in 3D collagen matrices and that requires EC lumen signaling complexes, to control human EC tubulogenesis during vascular morphogenesis.

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