Abstract
Complex signaling events control tumor invasion in three-dimensional (3D) extracellular matrices. Recent evidence suggests that cells utilize both matrix metalloproteinase (MMP)-dependent and MMP-independent means to traverse 3D matrices. Herein, we demonstrate that lysophosphatidic-acid-induced HT1080 cell invasion requires membrane-type-1 (MT1)-MMP-mediated collagenolysis to generate matrix conduits the width of a cellular nucleus. We define these spaces as single-cell invasion tunnels (SCITs). Once established, cells can migrate within SCITs in an MMP-independent manner. Endothelial cells, smooth muscle cells and fibroblasts also generate SCITs during invasive events, suggesting that SCIT formation represents a fundamental mechanism of cellular motility within 3D matrices. Coordinated cellular signaling events are required during SCIT formation. MT1-MMP, Cdc42 and its associated downstream effectors such as MRCK (myotonic dystrophy kinase-related Cdc42-binding kinase) and Pak4 (p21 protein-activated kinase 4), protein kinase Calpha and the Rho-associated coiled-coil-containing protein kinases (ROCK-1 and ROCK-2) coordinate signaling necessary for SCIT formation. Finally, we show that MT1-MMP and Cdc42 are fundamental components of a co-associated invasion-signaling complex that controls directed single-cell invasion of 3D collagen matrices.