Gradual reduction of BUBR1 protein levels results in premature sister-chromatid separation then in aneuploidy

Abstract

Biallelic and heterozygous mutations of the BUB1B gene have been reported in mosaic variegated aneuploidy (MVA), a rare disorder characterized by constitutional mosaic aneuploidies associated to severe intrauterine growth retardation, microcephaly and, in most cases, to premature chromatid separation (PCS), highlighting the key role of human BUBR1 in chromosome segregation. To study the consequences of gradual reduction of the BUBR1 protein levels, inhibition of BUB1B expression in model cells was induced using short hairpin RNAs (shRNAs). We obtained stable shRNA-transduced HeLa cells displaying a gradient of residual BUBR1 protein (8.5, 10, 14, 58, and 77%), mimicking the situation of patients' cells harboring one or two BUB1B mutations. Induction of PCS was detected in all transduced cells and its level was correlated to the decrease of BUBR1. Aneuploidy was clearly detected in cells with residual BUBR1 below 50%. Our data demonstrate that the function of the human BUBR1 protein in the spindle checkpoint is remarkably dosage-dependent and that the biological consequences of BUB1B expression reduction on premature chromatid separation and aneuploidy depend on the residual amount of BUBR1. This provides a biological explanation for the mode of inheritance of PCS, which is dominant, and of MVA, which can be recessive in some families and result from the combination of a null allele associated to a common hypomorphic allele in others.

BubR1 is a spindle assembly checkpoint protein regulating meiotic cell cycle progression of mouse oocyte

“…20 Also, it has been demonstrated that the function of the human BubR1 protein in the spindle checkpoint is remarkably dosage-dependent and its gradual reduction results in premature sister chromatid separation. 21 Different from mitosis, meiosis undergoes two successive divisions with only one round of DNA replication, thereby producing Myc-δBubR1 mRNA translated successfully (Fig. 5A).…”

Clinical impact of aneuploidy on gastric cancer patients

“…In the fi rst study, which described mutations of Bub1 in colorectal cancer [4], no direct correlation was found with cancer disease [33], except for the gene Bub1B, which has been identifi ed as mutated in the disease Mosaic variegated aneuploidy, which is a rare recessive condition characterised by childhood cancer and constitutional mosaicism for chromosomal gains and losses [34][35][36]. However, some mutations have been described in mitotic checkpoint proteins that could be involved in the develop- Fig.…”

Physiological Relevance of Cell Cycle Kinases

“…These individuals are predisposed to develop childhood cancer including rhabdomyosarcoma, Wilms tumor, or leukemia (117). Cell lines derived from MVA patients with biallelic mutations have an impaired mitotic checkpoint, chromosome alignment defects, and low overall BubRl abundance, resulting in premature sister-chromatid separation and aneuploidy (29,315). Both Bubl and …”