Multipolar Spindle Pole Coalescence Is a Major Source of Kinetochore Mis-Attachment and Chromosome Mis-Segregation in Cancer Cells

Abstract

Many cancer cells display a CIN (Chromosome Instability) phenotype, by which they exhibit high rates of chromosome loss or gain at each cell cycle. Over the years, a number of different mechanisms, including mitotic spindle multipolarity, cytokinesis failure, and merotelic kinetochore orientation, have been proposed as causes of CIN. However, a comprehensive theory of how CIN is perpetuated is still lacking. We used CIN colorectal cancer cells as a model system to investigate the possible cellular mechanism(s) underlying CIN. We found that CIN cells frequently assembled multipolar spindles in early mitosis. However, multipolar anaphase cells were very rare, and live-cell experiments showed that almost all CIN cells divided in a bipolar fashion. Moreover, fixed-cell analysis showed high frequencies of merotelically attached lagging chromosomes in bipolar anaphase CIN cells, and higher frequencies of merotelic attachments in multipolar vs. bipolar prometaphases. Finally, we found that multipolar CIN prometaphases typically possessed γ-tubulin at all spindle poles, and that a significant fraction of bipolar metaphase/early anaphase CIN cells possessed more than one centrosome at a single spindle pole. Taken together, our data suggest a model by which merotelic kinetochore attachments can easily be established in multipolar prometaphases. Most of these multipolar prometaphase cells would then bi-polarize before anaphase onset, and the residual merotelic attachments would produce chromosome mis-segregation due to anaphase lagging chromosomes. We propose this spindle pole coalescence mechanism as a major contributor to chromosome instability in cancer cells.

CUX1, a haploinsufficient tumour suppressor gene overexpressed in advanced cancers

“…Normal cells do not thrive when tetraploid, because the presence of multiple centrosomes induces the formation of a multipolar mitotic spindle [78][79][80] . Multipolar divisions lead to catastrophic chromosome missegregation, and the progeny of such divisions are almost invariably non-viable 79 .…”

“…Increased p110 CUX1 expression, however, activates a transcriptional programme that reinforces the spindle assembly checkpoint and delays mitosis until centrosomes have clustered to enable bipolar mitosis 19 . However, the passage through a multipolar intermediate before centrosome clustering enriches for merotelic chromosome attachments, leading to chromosome missegregation and the rapid generation of aneuploid populations from which tumorigenic cells emerge 19,78,79 . Strikingly, mammary tumours that …”

Let's huddle to prevent a muddle: centrosome declustering as an attractive anticancer strategy

“…6,61,62 Centrosome clustering allows the formation of a 'pseudo-bipolar' mitotic spindle as depicted in Figure 1a, which averts multipolarity, the varying degrees of which are depicted in Figures 1b-e. A closer look at this clustering phenomenon has uncovered the formation of a transient multipolar spindle intermediate before the centrosome clustering mechanism engages. 63,64 During this brief multipolar state, there is accumulation of merotelic kinetochore-microtubule attachments (i.e., attachment of microtubules from two different spindle poles to the same kinetochore), which are poorly sensed by the SAC mechanism. Merotelic attachments can severely compromise genomic integrity and promote CIN by causing both structural and numerical karyotypic abnormalities.…”

“…Clustering may confer survival advantages and promote malignancy by predisposing the cell to CIN via merotelic microtubule-kinetochore attachment and genome missegregation. 63,64 When 'low-grade' (i.e., survivable) missegregation results in the loss of a gene that promotes faithful chromosome segregation and maintenance (or gain of another copy of a gene that disturbs these processes), then the cell acquires CIN -essentially, the ability to shuffle its genome until a stable, malignant phenotype is procured. 131 By contrast, in the absence of clustering, supernumerary centrosomes result in spindle multipolarity, which may cause aneuploidy of a mortally high grade.…”

Le fuseau mitotique, le centrosome et le cancer : trouvez l’intrus !

“…Si ce défaut n'est pas détecté par le SAC, la ségrégation devient aléatoire et peut engendrer des retards dans la ségrégation des chromatides soeurs. On sait que les attachements mérotéliques sont une source majeure d'aneuploïdie dans les cellules de mammifères [11,16,17] (Figure 3). D'un point de vue moléculaire, le phénomène de regroupement des centrosomes est très mal compris.…”