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Characterization of a transferrin-independent uptake system for iron in HeLa cells

J Biol Chem. 1990 Feb 25;265(6):3139-45.

Abstract

HeLa cells incubated in serum-free medium accumulated 59Fe ("non-transferrin iron") when incubated with either 59Fe-citrate, 59Fe-nitrilotriacetate, or 59Fe dissolved in Tricine ascorbate. Accumulation of iron was time-, concentration-, and Ca2+-dependent and was saturable. Uptake of non-transferrin (non-Tf) iron was transferrin-independent because of the fact that uptake occurred at pH 5.5, a pH at which transferrin binds iron poorly and at which transferrin is not internalized by cells. Uptake of non-Tf iron was less affected than uptake of transferrin iron by 1) exposure of cells to trypsin, a maneuver that cleaves Tf receptors, or 2) incubation of cells with phenylarsine oxide, an agent that inhibits both fluid- and receptor-mediated internalization. After exposure of cells to non-Tf iron at 37 degrees C, most of the cell-associated radioactivity was recovered in heme and ferritin, demonstrating that iron gained access to intracellular compartments and was not simply adsorbed to the cell surface. Uptake of non-Tf iron could be partially blocked by Cu2+ in a dose-dependent manner, while the accumulation of transferrin-bound iron was unaffected by Cu2+. Other transition metals, such as Zn2+, Cd2+, and Mn2+ were able to inhibit the uptake of non-Tf iron to different degrees. The accumulation of 109Cd was inhibited by incubation of cells with non-Tf iron, Cu2+, or Mn2+. The extent of inhibition was concentration- and metal-dependent. A number of cultured cell lines including HeLa, human skin fibroblasts, and Chinese hamster ovary cells demonstrated uptake of non-Tf iron and 109Cd. Additionally, an endosome acidification mutant of Chinese hamster ovary cells, which exhibited an increase in non-Tf iron uptake, also exhibited an increase in the uptake of Cd2+. These observations suggest that the characteristics of the non-Tf iron transport system in HeLa cells are similar if not identical to those reported for perfused rat liver (Wright, T. L., Brissot, P., Ma, W.-L., and Weisiger, P. A. (1986) J. Biol. Chem. 261, 10909-10914) and suggest the existence of a family of transition metal transport systems, each with a different metal specificity.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Arsenicals / pharmacology
  • Binding, Competitive
  • Biological Transport
  • Cadmium / metabolism
  • Egtazic Acid / pharmacology
  • HeLa Cells / drug effects
  • HeLa Cells / metabolism
  • Humans
  • Hydrogen-Ion Concentration
  • Iron / metabolism*
  • Kinetics
  • Temperature
  • Transferrin / metabolism
  • Trypsin / pharmacology

Substances

  • Arsenicals
  • Transferrin
  • Cadmium
  • oxophenylarsine
  • Egtazic Acid
  • Iron
  • Trypsin