BubR1 Is Essential for Thio-Dimethylarsinic Acid-Induced Spindle Assembly Checkpoint and Mitotic Cell Death for Preventing the Accumulation of Abnormal Cells

Abstract

Thio-dimethylarsinic acid (thio-DMA) was detected in human urine after exposure to inorganic arsenic and arsenosugars consumed by marine algae. Our previous studies have shown that thio-DMA disturbed the cell cycle progression and arrested cells in mitosis, though the biological significance or the mechanism by which thio-DMA-induced mitotic phase accumulation occurs is yet to be understood. In this study, we showed that thio-DMA promotes the phosphorylation of BubR1 protein, which is one of the constituents of the spindle assembly checkpoint (SAC) complex and accumulates in the cell in mitotic phase. Binding of Mad2 to CDC20, also known as the marker of the mitotic checkpoint complex (MCC) formation during the activation of SAC, was enhanced and mitotic associated cell death by apoptosis was promoted in HeLa cells but not in HepG2 cells. Basal BubR1 protein level in HepG2 was 10-times lower than that of HeLa cells. Consequently, BubR1 knockdown HeLa cells were generated by small interfering RNA (siRNA) technique. The MCC formation and mitotic arrest induced by thio-DMA were completely inhibited in BubR1 knockdown cells. Moreover, BubR1 knockdown cells could survive in the medium containing higher concentrations of thio-DMA with some abnormalities such as larger cell size, huge nucleus, multiple nuclei, and abnormal DNA contents. Especially, cyclin B1 negative tetraploid cells, which signify interphase cells with tetraploid, increased and survived after 48-72 h treatment with thio-DMA. Thus, these results suggest that BubR1mediated SAC activation and MCC formation are one of the defense systems for preventing the accumulation and survival of abnormal cells induced by thio-DMA.

Phosphodiesterase Type 5 Inhibitors Synergize Vincristine in Killing Castration-Resistant Prostate Cancer Through Amplifying Mitotic Arrest Signaling

“…Kita et al reported that BubR1 knockdown in Hela cells showed reduced formation of mitotic checkpoint complex and mitotic arrest induced by thio-dimethylarsinic acid. The mitotic index was significantly decreased associated with almost completely abolished cyclin B1 protein expression in the BubR1 knockdown cells, leading to an increased cell survival when exposed to thio-dimethylarsinic acid ( 39 ). Our data were consistent with this notion showing that sildenafil significantly amplified vincristine-mediated BubR1 phosphorylation and mitotic index, increasing cyclin B1 protein levels and ultimately sensitizing cell apoptosis.…”