PP1 promotes cyclin B destruction and the metaphase-anaphase transition by dephosphorylating CDC20

Ubiquitin-dependent proteolysis of cyclin B and securin initiates sister chromatid segregation and anaphase. The anaphase promoting complex/cyclosome (APC/C) and its co-activator CDC20 form the main ubiquitin E3 ligase for these proteins. APC/CCDC20 is regulated by CDK1-cyclin B and counteracting PP1 and PP2A family phosphatases through modulation of both activating and inhibitory phosphorylations. Here we report that PP1 promotes cyclin B destruction at the onset of anaphase by removing specific inhibitory phosphorylation in the N-terminus of CDC20. Depletion or chemical inhibition of PP1 stabilises cyclin B and results in a pronounced delay at the metaphase-to-anaphase transition after chromosome alignment. This requirement for PP1 is lost in cells expressing CDK1-phosphorylation defective CDC206A mutants. These CDC206A cells show a normal spindle checkpoint response, but once all chromosomes have aligned rapidly degrade cyclin B and enter into anaphase in the absence of PP1 activity. PP1 therefore facilitates the metaphase-to-anaphase by promoting APC/CCDC20-dependent destruction of cyclin B in human cells.