Inhibition of iron uptake in HL60 cells by 2-formylpyridine monothiosemicarbazonato Cu(II).
The electron paramagnetic resonance (EPR) signal of the tyrosyl radical attributed to ribonucleoside diphosphate reductase decreases after treatment of promyelocytic leukemic HL60 cells with 2-formylpyridine thiosemicarbazonato copper(II) (CuL). According to EPR studies, CuL forms adducts with both histidine and cysteine-like Lewis bases associated with isolated membranes from HL60 cells. After the addition of CuL, the EPR signal for the cysteine-like adduct decreases substantially over a 15-min period. The reduction of signal is consistent with oxidation of thiols as shown by an analysis of sulfhydryl content. It is hypothesized that receptor-mediated transferrin internalization is inhibited by oxidation of critical thiols. Since the uptake of 59Fe-transferrin is greatly inhibited by the treatment of HL60 cells with CuL, the reduced uptake of iron by cells, in the presence of CuL, may lead to decreased iron availability for the activity of the M2 subunit of ribonucleotide reductase and a subsequent decrease in the tyrosyl radical signal of the enzyme. Moreover, the intact subunit M2 is no longer detected by EPR, even after the addition of excess iron.
Narasimhan
J
J
National Biomedical Electron Spin Resonance Center, Medical College of Wisconsin, Milwaukee 53226.
Antholine
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Chitambar
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Petering
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D001693:Biological Transport, Active / Q000187:drug effects; D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals; D006801:Humans; D007501:Iron / Q000378:metabolism*; D009942:Organometallic Compounds / Q000494:pharmacology*; D010084:Oxidation-Reduction; D012262:Ribonucleoside Diphosphate Reductase / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism; D013438:Sulfhydryl Compounds / Q000378:metabolism; D014168:Transferrin / Q000378:metabolism; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000378:metabolism; D014443:Tyrosine
D005609:Free Radicals; D009942:Organometallic Compounds; D013438:Sulfhydryl Compounds; D014168:Transferrin; D014443:Tyrosine; C031471:2-formylpyridine thiosemicarbazonato copper(II); D007501:Iron; D012262:Ribonucleoside Diphosphate Reductase