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 G(2) phase using Hoechst 33342 and released from synchrony in the presence or absence of 5 μM sodium arsenite. RESULTS: Mitotic index analysis demonstrated that arsenite treatment delayed exit from G(2) in 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 G(2) phase synchrony showed that arsenite induced inhibitor of DNA binding-1 (ID1) differentially in p53((+))and p53((−)) cells. Immunoblotting con-firmed 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.