Cooperativity between the Ras-ERK and Rho-Rho kinase pathways in urokinase-type plasminogen activator-stimulated cell migration

Binding of the urokinase-type plasminogen activator (uPA) to its receptor activates diverse cell signaling pathways. How these signals are integrated so that cell physiology is altered remains unclear. In this study, we demonstrated that migration of MCF-7 breast cancer cells and HT-1080 fibrosarcoma cells on serum-coated surfaces is stimulated by agents that activate ERK, including uPA, epidermal growth factor, and constitutively active MEK1. The promigratory activity of these agents was entirely blocked not only by the MEK-specific antagonist PD098059, but also by antagonists of the Rho-Rho kinase pathway, including Y-27632 and dominant-negative RhoA (RhoA-N19). uPA did not significantly increase the level of GTP-bound RhoA, suggesting that the constitutive activity of the Rho-Rho kinase pathway may be sufficient to support ERK-stimulated cell migration. Paradoxically, Y-27632 and RhoA-N19 increased ERK phosphorylation in MCF-7 cells, providing further evidence that ERK activation alone does not promote cell migration when Rho kinase is antagonized. When MCF-7 cell migration was stimulated by ERK-independent processes such as expression of the beta(3) integrin subunit or changing the substratum to type I collagen, Y-27632 and RhoA-N19 failed to inhibit the response. This study supports a model in which the Ras-ERK and Rho-Rho kinase pathways cooperate to promote cell migration. Neutralizing either pathway is sufficient to block the response to agents that stimulate cell migration by activating ERK.