Surprises from Raf-1 Knockout

Ehrenreiter et al. explored the signaling roles of the Raf-1 protein kinase by creating mice that lacked Raf-1 expression in the epidermis. Although Raf-1 can function in activation of mitogen-activated protein kinases, phosphorylation of ERK was not altered in the keratinocytes lacking Raf-1. Instead, a critical role of Raf-1 in wound healing and cell migration was revealed. The development of the epidermis was normal in the knockout animals, but wound healing in vivo was strongly inhibited, as was keratinocyte migration in Boyden chamber assays. The defects were similar to those observed in cells lacking Rok-α (Rho-associated kinase, also called ROCK-II). Indeed Rok-α activity was increased in the knockout cells, and treatment of knockout fibroblasts with a Rok inhibitor or transfection with a catalytically inactive mutant of Rok-α restored normal morphology and migration of the cells. Rok-α was also mislocalized to the plasma membrane in the cells lacking Raf-1. Endogenous Raf-1 and Rok-α were shown to interact by immunoprecipitation of the proteins together from migrating wild-type cells. A catalytically inactive form of Raf-1 could also rescue the knockout cells, indicating that the physical presence of Raf-1, rather than its kinase activity, was required. K. Ehrenreiter, D. Piazzolla, V. Velamoor, I. Sobczak, J. V. Small, J. Takeda, T. Leung, M. Baccarini, Raf-1 regulates Rho signaling and cell migration. J. Cell Biol. 168 , 955-964 (2005). [Abstract] [Full Text]