Folate deficiency induces mitotic aberrations and chromosomal instability by compromising the spindle assembly checkpoint in cultured human colon cells

Folates comprise the essential B9 vitamin that act as cofactors and cosubstrates in one-carbon metabolism for both biosynthesis and methylation of DNA and RNA. Folate deficiency (FD) has been shown to induce chromosomal instability (CIN), yet the underlying mechanisms are poorly understood. Here, we used human NCM460 colon mucosal cells as a model to investigate the effect of FD on spindle assembly checkpoint (SAC), a cell-cycle regulatory pathway preventing CIN during mitosis. Cells were maintained in medium containing 1.36 (FD) and 2260 nM (control, FC) folate for 21 days. CIN was measured by cytokinesis-block micronucleus assay; mitotic infidelity was determined by aberrant mitosis analysis; SAC activity was assessed by nocodazole-challenge assay, and the expression of core SAC genes was examined by real-time quantitative PCR (RT-qPCR). We found that, relative to FC, FD significantly induced CIN in a time-dependent way (P < 0.01). Mitotic cells cultured in FD medium had significant higher frequencies of misalignment, misegregation and spindle multipolarity than those cultured in FC medium (P < 0.01). FD-induced SAC impairment and overriding, resulting premature mitotic exit and cell multinucleation (P < 0.05). Moreover, FD deregulated the expression of several key SAC genes (P < 0.01). Overall, these data are the first to demonstrate that FD substantially compromises SAC network which predisposes cells to mitotic aberrations and CIN. These results establish a new link between folate metabolism and SAC signalling, two pathways that are highly relevant for tumorigenesis.