Signal cross talks for sustained MAPK activation and cell migration: the potential role of reactive oxygen species

Signal transduction exerted by the microenvironment around the primary tumor locus may trigger tumor metastasis especially at the migration stage. Sustained mitogen activated protein kinase (MAPK) signaling involved in uncontrolled tumor cell migration rely on the cross talks between integrin, receptor tyrosine kinase (RTK) and protein kinase C (PKC). The molecular mechanisms for cross talking between these migration-related signal cascades leading to sustained cell migration are reviewed, focusing on the focal adhesion scaffold protein paxillin as the platform for signal integration. We proposed reactive oxygen species (ROS) as the critical signal messenger sustaining these signal cascades. For the cross talk of integrin with RTK, ROS may suppress paxillin-associated protein tyrosine phosphatase (PTP-PEST) relieving its negative regulatory effects. For the cross talk of integrin with PKC, PKC itself may phosphorylate integrin or paxillin-associated focal adhesion proteins to induce generation of ROS which may reactivate PKC. In the future, ROS will be validated as the promising therapeutic targets for prevention of tumor metastasis.