page 955). Unlike other Raf-1 functions, this one doesn't require Raf-1 kinase activity, a theme the researchers think will be recurrent in future Raf-1 biology.When Raf-1 is knocked out in the epidermis of animals carrying conditional Raf-1 alleles, the epidermal structure remains normal. However, wounds heal slowly in the absence of Raf-1, despite normal cell proliferation in the epidermis. In culture, Raf-1–deficient cells do not migrate normally and appear rounded and contracted with dense cortical actin structures.
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.