A quantitative and semiautomated method for determining misaligned and lagging chromosomes during mitosis

Centrosomal Protein 55 Regulates Chromosomal Instability in Cancer Cells by Controlling Microtubule Dynamics

Centrosomal Protein 55 (CEP55) exhibits various oncogenic activities; it regulates the PI3K-Akt-pathway, midbody abscission, and chromosomal instability (CIN) in cancer cells. Here, we analyzed the mechanism of how CEP55 controls CIN in ovarian and breast cancer (OvCa) cells. Down-regulation of CEP55 reduced CIN in all cell lines analyzed, and CEP55 depletion decreased spindle microtubule (MT)-stability in OvCa cells. Moreover, recombinant CEP55 accelerated MT-polymerization and attenuated cold-induced MT-depolymerization. To analyze a potential relationship between CEP55-controlled CIN and its impact on MT-stability, we identified the CEP55 MT-binding peptides inside the CEP55 protein. Thereafter, a mutant with deficient MT-binding activity was re-expressed in CEP55-depleted OvCa cells and we could show that this mutant did not restore reduced CIN in CEP55-depleted cells. This finding strongly indicates that CEP55 regulates CIN by controlling MT dynamics.

Contribution of CENP-F to FOXM1-Mediated Discordant Centromere and Kinetochore Transcriptional Regulation

Proper chromosome segregation is required to ensure chromosomal stability. The centromere (CEN) is a unique chromatin domain defined by CENP-A and is responsible for recruiting the kinetochore (KT) during mitosis, ultimately regulating microtubule spindle attachment and mitotic checkpoint function. Upregulation of many CEN/KT genes is commonly observed in cancer. Here, we show that although FOXM1 occupies promoters of many CEN/KT genes with MYBL2, FOXM1 overexpression alone is insufficient to drive the FOXM1-correlated transcriptional program. CENP-F is canonically an outer kinetochore component; however, it functions with FOXM1 to coregulate G2/M transcription and proper chromosome segregation. Loss of CENP-F results in altered chromatin accessibility at G2/M genes and reduced FOXM1-MBB complex formation. We show that coordinated CENP-FFOXM1 transcriptional regulation is a cancer-specific function. We observe a small subset of CEN/KT genes including CENP-C, that are not regulated by FOXM1. Upregulation of CENP-C in the context of CENP-A overexpression leads to increased chromosome missegregation and cell death suggesting that escape of CENP-C from FOXM1 regulation is a cancer survival mechanism. Together, we show that FOXM1 and CENP-F coordinately regulate G2/M genes, and this coordination is specific to a subset of genes to allow for maintenance of chromosome instability levels and subsequent cell survival.

Contribution of CENP-F to FOXM1-mediated discordant centromere and kinetochore transcriptional regulation

Proper chromosome segregation is required to ensure genomic and chromosomal stability. The centromere is a unique chromatin domain present throughout the cell cycle on each chromosome defined by the CENP-A nucleosome. Centromeres (CEN) are responsible for recruiting the kinetochore (KT) during mitosis, ultimately regulating spindle attachment and mitotic checkpoint function. Upregulation of many genes that encode the CEN/KT proteins is commonly observed in cancer. Here, we show although that FOXM1 occupies the promoters of many CEN/KT genes with MYBL2, occupancy is insufficient alone to drive the FOXM1 correlated transcriptional program. We show that CENP-F, a component of the outer kinetochore, functions with FOXM1 to coregulate G2/M transcription and proper chromosome segregation. Loss of CENP-F results in alteration of chromatin accessibility at G2/M genes, including CENP-A, and leads to reduced FOXM1-MBB complex formation. The FOXM1-CENP-F transcriptional coordination is a cancer-specific function. We observed that a few CEN/KT genes escape FOXM1 regulation such as CENP-C which when upregulated with CENP-A, leads to increased chromosome misegregation and cell death. Together, we show that the FOXM1 and CENP-F coordinately regulate G2/M gene expression, and this coordination is specific to a subset of genes to allow for proliferation and maintenance of chromosome stability for cancer cell survival.

Phosphorylation of CENP-R by Aurora B regulates kinetochore-microtubule attachment for accurate chromosome segregation

Error-free mitosis depends on accurate chromosome attachment to spindle microtubules via a fine structure called the centromere that is epigenetically specified by the enrichment of CENP-A nucleosomes. Centromere maintenance during mitosis requires CENP-A-mediated deposition of constitutive centromere-associated network that establishes the inner kinetochore and connects centromeric chromatin to spindle microtubules during mitosis. Although previously proposed to be an adaptor of retinoic acid receptor, here, we show that CENP-R synergizes with CENP-OPQU to regulate kinetochore-microtubule attachment stability and ensure accurate chromosome segregation in mitosis. We found that a phospho-mimicking mutation of CENP-R weakened its localization to the kinetochore, suggesting that phosphorylation may regulate its localization. Perturbation of CENP-R phosphorylation is shown to prevent proper kinetochore-microtubule attachment at metaphase. Mechanistically, CENP-R phosphorylation disrupts its binding with CENP-U. Thus, we speculate that Aurora B-mediated CENP-R phosphorylation promotes the correction of improper kinetochore-microtubule attachment in mitosis. As CENP-R is absent from yeast, we reasoned that metazoan evolved an elaborate chromosome stability control machinery to ensure faithful chromosome segregation in mitosis.

Kinetochore life histories reveal an Aurora-B-dependent error correction mechanism in anaphase

Chromosome mis-segregation during mitosis leads to aneuploidy, which is a hallmark of cancer and linked to cancer genome evolution. Errors can manifest as "lagging chromosomes" in anaphase, although their mechanistic origins and likelihood of correction are incompletely understood. Here, we combine lattice light-sheet microscopy, endogenous protein labeling, and computational analysis to define the life history of >104 kinetochores. By defining the "laziness" of kinetochores in anaphase, we reveal that chromosomes are at a considerable risk of mis-segregation. We show that the majority of lazy kinetochores are corrected rapidly in anaphase by Aurora B; if uncorrected, they result in a higher rate of micronuclei formation. Quantitative analyses of the kinetochore life histories reveal a dynamic signature of metaphase kinetochore oscillations that forecasts their anaphase fate. We propose that in diploid human cells chromosome segregation is fundamentally error prone, with an additional layer of anaphase error correction required for stable karyotype propagation.