CO alters the methylation status of histone H3. Cell lysates (25 µg protein per lane) from U937 cells were treated with CO-releasing molecule (CORM) for 4 h was separated by SDS-PAGE and performed western blot analyses with several antibodies recognized with distinct methylated residue of histone H3 described in Materials and Methods. The expression level of histone H3 protein was determined as an internal control. The data show a representative set from 3 independent experiments.