The Greatwall kinase safeguards the genome integrity by affecting the kinome activity in mitosis.

Progression through mitosis is balanced by the timely regulation of phosphorylation and dephosphorylation events ensuring the correct segregation of chromosomes before cytokinesis. This balance is regulated by the opposing actions of CDK1 and PP2A, as well as the Greatwall kinase/MASTL. MASTL is commonly overexpressed in cancer, which makes it a potential therapeutic anticancer target. Loss of Mastl induces multiple chromosomal errors that lead to the accumulation of micronuclei and multilobulated cells in mitosis. Our analyses revealed that loss of Mastl leads to chromosome breaks and abnormalities impairing correct segregation. Phospho-proteomic data for Mastl knockout cells revealed alterations in proteins implicated in multiple processes during mitosis including double-strand DNA damage repair. In silico prediction of the kinases with affected activity unveiled NEK2 to be regulated in the absence of Mastl. We uncovered that, RAD51AP1, involved in regulation of homologous recombination, is phosphorylated by NEK2 and CDK1 but also efficiently dephosphorylated by PP2A/B55. Our results suggest that MastlKO disturbs the equilibrium of the mitotic phosphoproteome that leads to the disruption of DNA damage repair and triggers an accumulation of chromosome breaks even in noncancerous cells.

CoA synthase regulates mitotic fidelity via CBP-mediated acetylation.

The temporal activation of kinases and timely ubiquitin-mediated degradation is central to faithful mitosis. Here we present evidence that acetylation controlled by Coenzyme A synthase (COASY) and acetyltransferase CBP constitutes a novel mechanism that ensures faithful mitosis. We found that COASY knockdown triggers prolonged mitosis and multinucleation. Acetylome analysis reveals that COASY inactivation leads to hyper-acetylation of proteins associated with mitosis, including CBP and an Aurora A kinase activator, TPX2. During early mitosis, a transient CBP-mediated TPX2 acetylation is associated with TPX2 accumulation and Aurora A activation. The recruitment of COASY inhibits CBP-mediated TPX2 acetylation, promoting TPX2 degradation for mitotic exit. Consistently, we detected a stage-specific COASY-CBP-TPX2 association during mitosis. Remarkably, pharmacological and genetic inactivation of CBP effectively rescued the mitotic defects caused by COASY knockdown. Together, our findings uncover a novel mitotic regulation wherein COASY and CBP coordinate an acetylation network to enforce productive mitosis.

The Tumor Suppressor Cdkn3 Is Required for Maintaining the Proper Number of Centrosomes by Regulating the Centrosomal Stability of Mps1.

Supernumerary centrosomes promote the assembly of abnormal spindles in many human cancers. The observation that modest changes in the centrosomal levels of Mps1 kinase can cause centrosome overduplication in human cells suggests the existence of a regulatory system that may tightly control its centrosomal stability. Here, we show that Cdkn3, a Cdk-associated phosphatase, prevents Mps1-mediated centrosome overduplication. We identify Cdkn3 as a direct binding partner of Mps1. The interaction between Mps1 and Cdkn3 is required for Mps1 to recruit Cdkn3 to centrosomes. Subsequently, Mps1-bound Cdkn3 forms a regulatory system that controls the centrosomal levels of Mps1 through proteasome-mediated degradation and thereby prevents Mps1-mediated centrosome overduplication. Conversely, knockdown of Cdkn3 stabilizes Mps1 at centrosomes, which promotes centrosome overduplication. We suggest that Mps1 and Cdkn3 form a self-regulated feedback loop at centrosomes to tightly control the centrosomal levels of Mps1, which prevents centrosome overduplication in human cells.