Plk1-mediated stabilization of 53BP1 through USP7 regulates centrosome positioning to maintain bipolarity.

Although 53BP1 has been established well as a mediator in DNA damage response, its function in mitosis is not clearly understood. We found that 53BP1 is a mitotic-binding partner of the kinases Plk1 and AuroraA, and that the binding with Plk1 increases the stability of 53BP1 by accelerating its interaction with the deubiquitinase USP7. Depletion of 53BP1 induces mitotic defects such as chromosomal missegregation, misorientation of spindle poles and the generation of extra centrosomes, which is similar phenotype to USP7-knockdown cells. In addition, 53BP1 depletion reduces the levels of p53 and centromere protein F (CENPF), interacting proteins of 53BP1. These phenotypes induced by 53BP1 depletion were rescued by expression of wild-type or phosphomimic mutant 53BP1 but not by expression of a dephosphomimic mutant. We propose that phosphorylation of 53BP1 at S380 accelerates complex formation with USP7 and CENPF to regulate their stability, thus having a crucial role in proper centrosome positioning, chromosomal alignment, and centrosome number.