Hemin-Enhanced Resistance of Human Leukemia Cells to Oxidative Killing: Antisense Determination of Ferritin Involvement

Human HL-60 cells exhibited a strong hyperresistance to the lethal effects of photodynamic activity (singlet oxygen) or glucose oxidase activity (hydrogen peroxide) 16–20 h after being exposed to hemin (ferriprotoporphyrin IX). Hyperresistance was accompanied by the overproduction of immunodetectable ferritin, predominantly the heavy (H) subunit, which exhibits ferroxidase activity. Cells that had been enriched in apoferritin via pinocytotic uptake showed similar hyperresistance to both types of oxidative challenge. On the other hand, preincubating cells with hemin in the presence of a phosphorothioate-linked antisense oligodeoxynucleotide against H-ferritin mRNA resulted in a strong diminution in both hyperresistance and H-ferritin induction. No effects were seen when a scrambled order oligodeoxynucleotide of the same base composition was used, confirming that the antisense oligomer had specifically inhibited H-ferritin translation. These results indicate that induced ferritin played a crucial role in the observed cytological responses. Enhanced oxidant resistance is attributed to the ability of this ferritin to rapidly sequester and incapacitate redox-active iron.