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Iron accumulation and iron-regulatory protein activity in human hepatoma (HepG2) cells

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Abstract

Iron may populate distinct hepatocellular iron pools that differentially regulate expression of proteins such as ferritin and transferrin receptor (TfR) through iron-regulatory mRNA-binding proteins (IRPs), and may additionally regulate uptake and accumulation of non-transferrin-bound iron (NTBI). We examined iron-regulatory protein (IRP) binding activity and ferritin/TfR expression in human hepatoma (HepG2) cells exposed to iron at different levels for different periods. Several iron-dependent RNA-binding activities were identified, but only IRP increased with β-mercaptoethanol. With exposures between 0 and 20 μg/ml iron, decreases in IRP binding accompanied large changes in TfR and ferritin expression, while chelation of residual iron with deferoxamine (DFO) caused a large increase in IRP binding with little additional effect on TfR or ferritin expression. Cellular iron content increased beyond 4 days of exposure to iron at 20 μg/ml, when IRP binding, TfR, and ferritin had all reached stable levels. However, iron content of the cells plateaued by 7 days, or decreased with 24 h exposure to very high concentrations (>50 μg/ml) of iron. These results indicate that iron-replete HepG2 cells exhibit a narrow range of maximal responsiveness of the IRP-regulatory mechanism, whose functional response is blunted both by excessive iron exposure and by removal of iron from a chelatable pool. HepG2 cells are able to limit iron accumulation upon higher or prolonged exposure to NTBI, apparently independent of the IRP mechanism. (Mol Cell Biochem 265: 37–45, 2004)

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  1. Laboratory Medicine and Pathobiology, University of Toronto, 1 King's College Circle, Toronto, Ont., Canada

    Zvezdana Popovic & Douglas M. Templeton

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  1. Zvezdana Popovic
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Popovic, Z., Templeton, D.M. Iron accumulation and iron-regulatory protein activity in human hepatoma (HepG2) cells. Mol Cell Biochem 265, 37–45 (2004). https://doi.org/10.1023/B:MCBI.0000044313.19574.c6

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