RhoA mediates flow-induced endothelial sprouting in a 3-D tissue analogue of angiogenesis.

Endothelial cells (ECs) integrate signals from the local microenvironment to guide their behaviour. RhoA is involved in vascular endothelial growth factor (VEGF)-driven angiogenesis, but its role in mechanotransduction during sprouting has not been established. Using dominant negative cell transfections in a microfluidic device that recapitulates angiogenic sprouting, we show that endothelial cells respond to interstitial flow in a RhoA-dependent manner while invading a 3-D extracellular matrix. Furthermore, RhoA regulates flow-induced, but not VEGF gradient-induced, tip cell filopodial extensions. Thus, RhoA pathways mediate mechanically-activated but not VEGF-induced endothelial morphogenesis.

Mechanical compression drives cancer cells toward invasive phenotype.

Uncontrolled growth in a confined space generates mechanical compressive stress within tumors, but little is known about how such stress affects tumor cell behavior. Here we show that compressive stress stimulates migration of mammary carcinoma cells. The enhanced migration is accomplished by a subset of "leader cells" that extend filopodia at the leading edge of the cell sheet. Formation of these leader cells is dependent on cell microorganization and is enhanced by compressive stress. Accompanied by fibronectin deposition and stronger cell-matrix adhesion, the transition to leader-cell phenotype results in stabilization of persistent actomyosin-independent cell extensions and coordinated migration. Our results suggest that compressive stress accumulated during tumor growth can enable coordinated migration of cancer cells by stimulating formation of leader cells and enhancing cell-substrate adhesion. This novel mechanism represents a potential target for the prevention of cancer cell migration and invasion.