The E3/E4 ubiquitin ligase UFD-2 mediates negative feedback on Raf protein stability

Signaling by the kinase cascade comprised of Raf, MEK, and ERK is critical for animal development; moreover, its inappropriate activation is commonly found in human malignancies. In a genetic screen for factors that control signaling by the Caenorhabditis elegans Raf ortholog LIN-45, we found that it is negatively regulated by the E3/E4 ubiquitin ligase UFD-2. Both UFD-2 and its partner, the ATP-dependent unfoldase CDC-48, were required for degradation of LIN-45 protein. Our structure-function studies showed that disruption of LIN-45 domains that mediate protein interactions and complex formation, including the Ras binding domain, cysteine-rich domain, or C-terminus, allow for UFD-2-independent degradation. We propose a model whereby UFD-2 mediates a novel step of Raf degradation, by acting with the CDC-48 unfoldase machinery to extract Raf from multiprotein complexes.