ROCK signaling mediates the adoption of different modes of migration and invasion in human mammary epithelial tumor cells

For the invasive migration of tumor cells, at least two mechanisms are currently discussed: (1) the mesenchymal mode depending on extracellular proteolysis and (2) the proteolysis-independent amoeboid mode depending on the activity of the Rho kinase ROCK. The ability of tumor cells to switch between different modes of motility has been shown to limit the efficiency of agents aimed to reduce invasion. Here we show by combining 2D and 3D migration assays that human mammary tumor cells exhibited a strongly reduced migration velocity as compared to their normal counterparts indicating that high invasiveness is not necessarily correlated with high migratory capacity in 2D assays. This reduced migration was apparently due to significant differences in actin organization, decreased persistence of lamellipodia by 50% and increased cell substrate adhesion. These differences resulted from a 2.5-fold higher activity of ROCK and were mediated by its downstream effectors myosin light chain kinase and cofilin. Thus, inhibition of ROCK activity caused a marked increase in 2D migration efficiency by 40%, without, however, affecting 3D invasion. A massive reduction of invasion by 60% was achieved by the simultaneous inhibition of the ROCK-dependent amoeboid and the extracellular proteolysis-dependent mesenchymal mode. These results may point to a new efficient strategy for blocking tumor cell invasion in vivo.