Repression of ferritin expression increases the labile iron pool, oxidative stress, and short-term growth of human erythroleukemia cells

Or Kakhlon,Yosef Gruenbaum,Zvi Ioav Cabantchik

doi:10.1182/blood.v97.9.2863

Abstract

AbstractThe role of ferritin expression on the labile iron pool of cells and its implications for the control of cell proliferation were assessed. Antisense oligodeoxynucleotides were used as tools for modulating the expression of heavy and light ferritin subunits of K562 cells. mRNA and protein levels of each subunit were markedly reduced by 2-day treatment with antisense probes against the respective subunit. Although the combined action of antisense probes against both subunits reduced their protein expression, antisense repression of one subunit led to an increased protein expression of the other. Antisense treatment led to a rise in the steady-state labile iron pool, a rise in the production of reactive oxygen species after pro-oxidative challenges and in protein oxidation, and the down-regulation of transferrin receptors. When compared to the repression of individual subunits, co-repression of each subunit evoked a more than additive increase in the labile iron pool and the extent of protein oxidation. These treatments had no detectable effects on the long-term growth of cells. However, repression of ferritin synthesis facilitated the renewal of growth and the proliferation of cells pre-arrested at the G1/S phase. Renewed cell growth was significantly less dependent on external iron supply when ferritin synthesis was repressed and its degradation inhibited by lysosomal antiproteases. This study provides experimental evidence that links the effect of ferritin repression on growth stimulation to the expansion of the labile iron pool.

Highlights

H-FT evoked a reduction in labile iron pool (LIP) and thereby affected related cellular properties, growth and proliferation were modified only at very high levels of H-FT expression.[3,7]
Sequences of the human FT mRNA (H and L subunits), approximately 20 bp long, were screened by the software package GCG to trace for potential AS-ODNs
H-FT and L-FT levels were lowered to approximately 25% to 50% of the levels found in cells incubated with the reversed or inverted sequence (IN-ODN) of the AS-ODN, comparable to those attained with 50 ␮M Desferrioxamine treatment (DFO) for 24 hours

Summary

Introduction

H-FT evoked a reduction in LIP and thereby affected related cellular properties, growth and proliferation were modified only at very high levels of H-FT expression.[3,7] These and other studies based on H-FT–transfected cells raise some questions about the significance of strategies based on FT overexpression for understanding FT involvement in the control of cell growth. Recent studies[10,11,12,13] suggested a link between the repression of H-FT expression and the promotion of cell proliferation by oncogenes such as c-myc[14,15] and E1A.10-13,16. Earlier studies with c-myc showed the opposite, namely that stimulation of growth correlated with H-FT expression.[17] Recent studies[10,11,12,13] suggested a link between the repression of H-FT expression and the promotion of cell proliferation by oncogenes such as c-myc[14,15] and E1A.10-13,16 earlier studies with c-myc showed the opposite, namely that stimulation of growth correlated with H-FT expression.[17]

Methods

Results

Conclusion