Lumen signaling complexes containing Cdc42, Par3, Par6b, Jam-B, Jam-C, MT1-MMP, and α₂β₁ integrin control EC lumen and tube formation in 3D collagen matrices. (A-D) ECs were siRNA-treated for Luciferase (control), Jam-B plus Jam-C, Par3, MT1-MMP, α₂ integrin, or Jam-C alone and transfected with MT1-MMP-S, S-GFP-Cdc42, or JamB wt-S adenoviral vectors. They were suspended in 3D collagen matrices and allowed to undergo morphogenesis for 16 hours, followed by the preparation of detergent lysates and incubation with S-protein agarose beads as described.¹⁶  Eluates were analyzed for MT1-MMP, Cdc42, Jam-B, Jam-C, α₂ integrin, Par3, and Par6b. (E) Schematic diagram showing the interactive relationships of the lumen signaling complex which controls EC lumen and tube formation in 3D collagen matrices.