SCFFbxw5 targets MCAK in G2/M to facilitate ciliogenesis in the following cell cycle

The microtubule depolymerase Kif2C/MCAK plays important roles in various cellular processes and is frequently overexpressed in different cancer types. Despite the importance of its correct abundance, remarkably little is known about how MCAK levels are regulated in cells. Using comprehensive screening on protein microarrays, we identified 161 candidate substrates of the multi-subunit ubiquitin E3 ligase SCFFbxw5, including MCAK. In vitro reconstitution assays demonstrate that MCAK and its closely related orthologs Kif2A and Kif2B become efficiently polyubiquitylated by neddylated SCFFbxw5 and Cdc34, without requiring preceding modifications. In cells, SCFFbxw5 targets MCAK for proteasomal degradation specifically during G2/M. While this seems largely dispensable for mitotic progression, loss of Fbxw5 leads to increased MCAK levels at basal bodies, which impair formation of primary cilia in the following G1. We have thus identified a novel regulatory event of ciliogenesis that occurs already within the G2/M phase of the preceding cell cycle.