THE EFFECT OF REDOX-RELATED SPECIES OF NITROGEN MONOXIDE ON TRANSFERRIN AND IRON UPTAKE AND CELLULAR PROLIFERATION OF ERYTHROLEUKEMIA (K562) CELLS

The iron-responsive element-binding protein (IRE-BP) modulates both fe rritin mRNA translation and transferrin receptor (TfR) mRNA stability by binding to specific mRNA sequences called iron-responsive elements (IREs). The regulation of IRE-BP in situ could possibly occur either t hrough its Fe-S cluster and/or via free cysteine sulphydryl groups suc h as cysteine 437 (Philpott et al, J Biol Chem 268:17655, 1993; and Hi rling et al, EMBO J 13:453, 1994). Recently, nitrogen monoxide (NO) ha s been shown to have markedly different biologic effects depending on its redox state (Lipton et al, Nature 364:626, 1993). Considering this fact, it is conceivable that the NO group, as either the nitrosonium ion (NO+) or nitric oxide (NO.), may regulate IRE-BP activity by S-nit rosylation of key sulphydryl groups or via ligation of NO. to the Fe-S cluster, respectively. This hypothesis has been examined using the NO + generator, sodium nitroprusside (SNP); the NO. generator, S-nitroso- N-acetylpenicillamine (SNAP); and the NO./peroxynitrite (ONOO-) genera tor, 3-morpholinosy-dnonimine hydrochloride (SIN-1). Treatment of K562 cells for 18 hours with SNP (1 mmol/L) resulted in a pronounced decre ase in both the RNA-binding activity of IRE-BP and the level of TfR mR NA. In addition, Scatchard analysis showed a marked decrease in the nu mber of specific Tf-binding sites, from 590,000/cell (control) to 170, 000/cell (test), and there was also a distinct decrease in Fe uptake. Furthermore, SNP did not decrease cellular viability or proliferation. In contrast, the NO. generator, SNAP (1 mmol/L), increased RNA-bindin g activity of IRE-BP, the level of TfR mRNA, and the number of TfRs in K562 cells. Moreover, both SNAP (1 mmol/L) and SIN-1 (0.5 mmol/L) red uced cellular proliferation. The results are discussed in context of t he possible physiologic role of redox-related species of NO in regulat ing iron metabolism. (C) 1995 by The American Society of Hematology.