PLK4 phosphorylation of CP110 is required for efficient centriole assembly.

Centrioles are assembled during S phase and segregated into 2 daughter cells at the end of mitosis. The initiation of centriole assembly is regulated by polo-like kinase 4 (PLK4), the major serine/threonine kinase in centrioles. Despite its importance in centriole duplication, only a few substrates have been identified, and the detailed mechanism of PLK4 has not been fully elucidated. CP110 is a coiled-coil protein that plays roles in centriolar length control and ciliogenesis in mammals. Here, we revealed that PLK4 specifically phosphorylates CP110 at the S98 position. The phospho-resistant CP110 mutant inhibited centriole assembly, whereas the phospho-mimetic CP110 mutant induced centriole assembly, even in PLK4-limited conditions. This finding implies that PLK4 phosphorylation of CP110 is an essential step for centriole assembly. The phospho-mimetic form of CP110 augmented the centrosomal SAS6 level. Based on these results, we propose that the phosphorylated CP110 may be involved in the stabilization of cartwheel SAS6 during centriole assembly.