Tenascin-C and SF/HGF produced by myofibroblasts in vitro provide convergent proinvasive signals to human colon cancer cells through RhoA and Rac

Myofibroblasts are present at the invasion front in colon cancer. In an attempt to understand their putative proinvasive activity, we have developed an in vitro model. Myofibroblasts isolated from colon cancer tissue or obtained through transdifferentiation of colon fibroblasts by transforming growth factor (TGF)-beta stimulate invasion of colon cancer cells into collagen type I and Matrigel. We identified two convergent proinvasive agents secreted by myofibroblasts: namely scatter factor/hepatocyte growth factor (SF/HGF) and the TGF-beta-upregulated extracellular matrix glycoprotein tenascin-C (TNC), each of which is necessary though not sufficient for invasion. Myofibroblast-stimulated invasion into collagen type I is characterized by a change from a round, nonmigratory morphotype with high RhoA and low Rac activity to an elongated, migratory morphotype with low RhoA and high Rac activity. RhoA inactivation is determined by the epidermal growth factor (EGF)-like repeats of TNC through EGF-receptor signaling that confers a permissive and priming signal for the proinvasive activity of SF/HGF that activates Rac via c-Met. We confirmed the validity of this mechanism by using pharmacological modulators and dominant negative or constitutive active mutants that interfere with RhoA-Rho kinase and Rac signaling. Our in vitro results point to a new putative proinvasive signal for colon cancer cells provided by myofibroblasts in the tumor stroma.