Reactive oxygen species mediate Cr(VI)-induced S phase arrest through p53 in human colon cancer cells

Compounds that contain chromate (Cr(VI)) are well-known carcinogens that are present in both industrial settings and the environment. The mechanism of carcinogenesis associated with these compounds is not well understood. This study focused on Cr(VI)-induced cell cycle arrest in human colon adenocarcinoma DLD1 cells. Treatment of the cells with Cr(VI) at 2.5 μM caused a growth arrest at the S phase. An increase in Cr(VI) concentration enhanced the growth arrest. Superoxide dismutase did not alter the Cr(VI)-induced S phase arrest. Catalase inhibited S-cell growth, indicating that H₂ O₂ is an important mediator in Cr(VI)-induced S phase arrest. Electron spin resonance spin-trapping measurements showed that incubation of cells with Cr(VI) generated hydroxyl radical (^•OH). Catalase inhibited ^•OH generation, indicating that H₂ O₂ was generated from cells stimulated by Cr(VI) and that H₂ O₂ functioned as a precursor of ^•OH radical generation. p53, an oxidative response transcription factor, was activated upon Cr(VI) stimulation. Inhibition of p53 by introducing small hairpin RNA decreased S phase arrest induced by Cr(VI). These results support the following conclusions: (1) reactive oxygen species (ROS) are generated in Cr(VI)-stimulated DLD1 cells; (2) among the ROS generated, H₂ O₂ played a major role in causing S phase arrest in DLD1 cells; and (3) ROS mediated S phase arrest through a p53-dependent pathway.