A375 human
malignant melanoma cells undergo mitotic arrest-associated apoptosis when treated with pharmacological concentrations of
sodium arsenite, a chemotherapeutic for
acute promyelocytic leukemia. Our previous studies indicated that decreased
arsenite sensitivity correlated with reduced mitotic spindle checkpoint function and reduced expression of the checkpoint
protein BUBR1. In the current study,
arsenite induced
securin and
cyclin B stabilization, BUBR1 phosphorylation, and spindle checkpoint activation.
Arsenite also increased activating
cyclin dependent kinase 1 (CDK1) Thr(161) phosphorylation but decreased inhibitory Tyr15 phosphorylation. Mitotic arrest resulted in apoptosis as indicated by colocalization of mitotic phospho-
Histone H3 with active
caspase 3. Apoptosis was associated with BCL-2 Ser70 phosphorylation. Inhibition of CDK1 with
roscovitine in
arsenite-treated mitotic cells inhibited spindle checkpoint maintenance as inferred from reduced BUBR1 phosphorylation, reduced
cyclin B expression, and diminution of mitotic index.
Roscovitine also reduced BCL-2 Ser70 phosphorylation and protected against apoptosis, suggesting mitotic arrest caused by hyperactivation of CDK1 directly or indirectly leads to BCL-2 phosphorylation and apoptosis. In addition, suppression of BUBR1 with
siRNA prevented
arsenite-induced mitotic arrest and apoptosis. These findings provide insight into the mechanism of
arsenic's chemotherapeutic action and indicate a functional spindle checkpoint may be required for
arsenic-sensitivity.