Cells depleted of Ska arrest at metaphase. Chromosome-associated APC/C shows high ubiquitylation activity. Ska complex helps to localize APC/C on chromosomes. Forced localization of Ska complex to kinetochores enhances APC/C localization to chromosomes and promotes APC/C activity.

The mitotic checkpoint maintains genomic stability by ensuring that chromosomes are accurately segregated during mitosis. When the checkpoint is activated, the mitotic checkpoint complex (

BackgroundProteins functioning in the same biological pathway tend to be transcriptionally co-regulated or form protein-protein interactions (PPI). Multiple spatially and temporally regulated events are coordinated during mitosis to achieve faithful chromosome segregation. The molecular players participating in mitosis regulation are still being unravelled experimentally or using in silico methods.ResultsAn extensive literature review has led to a compilation of 196 human centromere/kinetochore proteins, all with experimental evidence supporting the subcellular localization. Sixty-four were designated as “core” centromere/kinetochore components based on peak expression and/or well-characterized functions during mitosis. By interrogating and integrating online resources, we have mined for genes/proteins that display transcriptional co-expression or PPI with the core centromere/kinetochore components. Top-ranked hubs in either co-expression or PPI network are not only enriched with known mitosis regulators, but also contain candidates whose mitotic functions are not yet established. Experimental validation found that KIAA1377 is a novel centrosomal protein that also associates with microtubules and midbody; while TRIP13 is a novel kinetochore protein and directly interacts with mitotic checkpoint silencing protein p31comet.ConclusionsTranscriptional co-expression and PPI network analyses with known human centromere/kinetochore proteins as a query group help identify novel potential mitosis regulators.

Background: How MPS1 kinase functions during mitotic checkpoint signaling is not fully understood. Results: C-MAD2 expression rescues premature mitotic exit caused by MPS1 inhibition without localizing at kinetochores. Conclusion: MPS1 functions primarily to enhance C-MAD2 production and subsequent formation of the mitotic checkpoint complex. Significance: The results underscore the importance of MPS1 kinase in maintaining kinetochore localization and catalytic efficiency of the MAD1⅐C-MAD2 core.

OTSSP167 was recently characterized as a potent inhibitor for maternal embryonic leucine zipper kinase (MELK) and is currently tested in Phase I clinical trials for solid tumors that have not responded to other treatment. Here we report that OTSSP167 abrogates the mitotic checkpoint at concentrations used to inhibit MELK. The abrogation is not recapitulated by RNAi mediated silencing of MELK in cells. Although OTSSP167 indeed inhibits MELK, it exhibits off-target activity against Aurora B kinase in vitro and in cells. Furthermore, OTSSP167 inhibits BUB1 and Haspin kinases, reducing phosphorylation at histones H2AT120 and H3T3 and causing mislocalization of Aurora B and associated chromosomal passenger complex from the centromere/kinetochore. The results suggest that OTSSP167 may have additional mechanisms of action for cancer cell killing and caution the use of OTSSP167 as a MELK specific kinase inhibitor in biochemical and cellular assays.