Specialized replication mechanisms maintain genome stability at human centromeres

The high incidence of whole-arm chromosome aneuploidy and translocations in tumors suggests instability of centromeres, unique loci built on repetitive sequences and essential for chromosome separation. The causes behind this fragility and the mechanisms preserving centromere integrity remain elusive. We show that replication stress, hallmark of pre-cancerous lesions, promotes centromeric breakage in mitosis, due to spindle forces and endonuclease activities. Mechanistically, we unveil unique dynamics of the centromeric replisome distinct from the rest of the genome. Locus-specific proteomics identifies specialized DNA replication and repair proteins at centromeres, highlighting them as difficult-to-replicate regions. The translesion synthesis pathway, along with other factors, acts to sustain centromere replication and integrity. Prolonged stress causes centromeric alterations like ruptures and translocations, as observed in ovarian cancer models experiencing replication stress. This study provides unprecedented insights into centromere replication and integrity, proposing mechanistic insights into the origins of centromere alterations leading to abnormal cancerous karyotypes. [Display omitted] •Human centromeres are hotspots for ruptures under replication stress•Centromeres harbor specialized replication dynamics required for their integrity•Locus-specific proteomics reveals centromeres as difficult-to-replicate regions•Whole-arm chromosomal translocations arise from prolonged replication stress Scelfo, Angrisani, et al. delve into the causes of centromere fragility—frequent in cancer—unveiling specialized replication dynamics crucial for centromeres’ integrity. They spotlight centromeres as challenging replication sites with dedicated factors required for replication and stability. Replication stress prompts centromeric alterations, rupture, and whole-arm chromosome translocations.