Effect of Hydroxyurea on Cellular Iron Metabolism in Human Leukemic CCRF-CEM Cells: Changes in Iron Uptake and the Regulation of Transferrin Receptor and Ferritin Gene Expression following Inhibition of DNA Synthesis1

Hydroxyurea inhibits cellular proliferation through action on ribonucleotide reducÃ-ase,an iron-dependent enzyme responsible for the synthesis of deoxyribonucleotides. Whereas previous investigations have examined the interaction of hydroxyurea with this enzyme, the action of hydroxyurea on other aspects of iron metabolism has not been studied in detail. In our study, incubation of CCRF-CEM cells with hydroxyurea resulted in an inhibition of ribonucleotide reducÃ-ase activity/DNA synthesis within 4 h and produced a parallel decrease in the uptake of iron by cells. In contrast, iron uptake by hydroxyurea-resistant CCRF-CEM cells was not inhibited by hydroxyurea. After 6 h, hydroxyurea produced an increase in the activity of the iron-regulatory protein, a cytoplasmic mRNA-binding protein responsible for regulating the translation of transferrin receptor and ferritin mRNAs. After 24 h, hydroxyurea-treated cells displayed a 1.5-fold increase in transferrin receptor inKN V and protein and a signif icant decrease in ferritin levels. The hydroxyurea-induced increase in transferrin receptor was abrogated by transferrin-iron. In contrast to hydroxyurea, inhibition of DNA synthesis by 1-ß-D-arabinofuranosylcytosine produced a decrease in transferrin receptor expression. Our studies suggest that iron uptake by CCRF-CEM cells is closely linked to ribonu cleotide reductase activity rather than to transferrin receptor number. Inhibition of ribonucleotide reductase/DNA synthesis by hydroxyurea results in a decrease in iron uptake by cells and an increase in the activity of the iron-regulatory protein, which, in turn, is responsible for the hydroxyurea-induced increase in transferrin receptor and decrease in ferritin synthesis.