Exit from Arsenite-Induced Mitotic Arrest Is p53 Dependent

Background: Arsenic is both a human carcinogen and a chemotherapeutic agent, but the mechanism of neither arsenic-induced carcinogenesis nor tumor selective cytotoxicity is clear. Using a model cell line in which p53 expression is regulated exogenously in a tetracycline-off system (TR9-7 cells), our laboratory has shown that arsenite disrupts mitosis and that p53-deficient cells [$p53^{(-)}$], in contrast to p53-expressing cells [$p53^{(+)}$], display greater sensitivity to arsenite-induced mitotic arrest and apoptosis. Objective: Our goal was to examine the role p53 plays in protecting cells from arsenite-induced mitotic arrest. Methods:$p53^{(+)}$and$p53^{(-)}$cells were synchronized in G2phase using Hoechst 33342 and released from synchrony in the presence or absence of 5 μ M sodium arsenite. Results: Mitotic index analysis demonstrated that arsenite treatment delayed exit from G2in$p53^{(+)}$and$p53^{(-)}$cells. Arsenite-treated$p53^{(+)}$cells exited mitosis normally, whereas$p53^{(-)}$cells exited mitosis with delayed kinetics. Microarray analysis performed on mRNAs of cells exposed to arsenite for 0 and 3 hr after release from G2phase synchrony showed that arsenite induced inhibitor of DNA binding-1 (ID1) differentially in$p53^{(+)}$and$p53^{(-)}$cells. Immunoblotting confirmed that ID1 induction was more extensive and sustained in$p53^{(+)}$cells. Conclusions: p53 promotes mitotic exit and leads to more extensive ID1 induction by arsenite. ID1 is a dominant negative inhibitor of transcription that represses cell cycle regulatory genes and is elevated in many tumors. ID1 may play a role in the survival of arsenite-treated$p53^{(+)}$cells and contribute to arsenic carcinogenicity.