H-ferritin subunit overexpression in erythroid cells reduces the oxidativestress response and induces multidrug resistance properties

The labile iron pool (LIP) of animal cells has been implicated in cell iron regulation and as a key component of the oxidative-stress response. A majo r mechanism commonly implied in the downregulation of LIP has been the indu ced expression of ferritin (FT), particularly the heavy subunits (H-FT) tha t display ferroxidase activity. The effects of H-FI on LIP and other physio logical parameters were studied in murine erythroleukemia (MEL) cells stabl y transfected with H-FT subunits. Clones expressing different levels of H-F T displayed similar concentrations of total cell iron (0.3 +/- 0.1 mmol/L) and of reduced/total glutathione. However, with increasing H-FT revels the cells expressed lower levels of LIP and reactive oxygen species (ROS) and e nsuing cell death after iron toads and oxidative challenges. These results provide direct experimental support for the alleged roles of H-FT as a regu lator of labile cell iron and as a possible attenuator of the oxidative cel l response. H-FT overexpression was of no apparent consequence to the cellu lar proliferative capacity. However, concomitant with the acquisition of ir on and redox regulatory capacities, the H-FT-transfectant cells commensurat ely acquired multidrug resistance (MDR) properties. These properties were i dentified as increased expression of MDR1 mRNA (by reverse transcription po lymerase chain reaction [RT-PCR]), P-glycoprotein (Western immunoblotting), drug transport activity (verapamil-sensitive drug efflux), and drug cytoto xicity associated with increased MDR1 or PgP Although enhanced MDR expressi on per se evoked no significant changes in either LIP revels or ROS product ion, it might be essential for the survival of H-FT transfectants, possibly by expediting the export of cell-generated metabolites. (C) 1999 by The Am erican Society of Hematology.