Cells lacking Raf-1 (bottom) migrate poorly.
This suggests that either Rho or its downstream effector, Rok-α kinase, is hyperactive. Biochemical experiments showed that Raf-1 was required for Rok-α inhibition in keratinocytes and fibroblasts, and that inhibition of Rok-α activity overcame Raf-1 deficiency. Kinase-dead Raf-1 mutations also rescue the defect, indicating that Raf-1 regulates Rok-α via protein–protein interaction rather than by modifying the target.
Raf-1 is a weak kinase, even when phosphorylating its favored targets such as MEK, so a kinase-independent function is novel but not entirely unexpected. Ehrenreiter et al. think Raf-1 regulates Rok-α by targeting it to proper compartments in the cell and predict that similar functions will be found in other Raf-1 pathways. They are now mapping the Raf-1 domains responsible for Rok-α regulation.