Elevated MPS1 converts the fibrous corona into a source of chromosomal instability in colon cancer

Chromosomal instability (CIN), characterised by recurrent chromosome mis-segregation, fuels intratumour heterogeneity and tumour evolution. Yet, its proximal molecular causes remain ill-defined. Tumour-scale genomic and transcriptomic analyses associate MPS1 overexpression with CIN in colon carcinomas. Consistently, CIN ⁺ patient-derived colon cancer cells (PCCCs) display elevated MPS1, frequent merotelic kinetochore-microtubule attachments and lagging chromosomes that are suppressed by partial MPS1 inhibition. Conversely, ectopic MPS1 overexpression in otherwise stable near-diploid cells phenocopies these defects, inducing micronuclei formation and karyotypic divergence. Mechanistically, MPS1 overactivity maintains ROD phosphorylation at Thr13/Ser15, continuously sustaining fibrous corona assembly despite mature end-on attachments. 3D-STED microscopy reveals split-interface configurations in which microtubules from opposing poles engage the canonical outer-kinetochore surface and a spatially distinct corona domain, explaining how merotely forms and persists into anaphase. Disrupting corona assembly restores chromosome segregation fidelity in MPS1-overexpressing RPE-1 cells and in CIN ⁺ PCCCs. Together, our findings establish MPS1 overexpression as a driver of CIN and uncover how oncogenic transcriptional rewiring of mitotic signalling converts a transient microtubule-capture structure into a pathological source of merotely and chromosome mis-segregation in colon cancer.