THE UPTAKE OF INORGANIC IRON COMPLEXES BY HUMAN-MELANOMA CELLS

The human melanoma cell line, SK-MEL-28, expresses high levels of melanotransferrin. The uptake of inorganic iron (Fe) complexes compared to transferrin-bound Fe by these cells has been investigated to determine whether melanotransferrin has a role in Fe uptake. The mechanisms of Fe uptake have been characterised using Fe-59 complexes of citrate, nitrilotriacetate, desferrioxamine, and Fe-59 added to Eagle's minimum essential medium (MEM) and compared with human transferrin (Tf) labelled with Fe-59 and iodine-125. Iron uptake from the Fe complexes of citrate, nitrilotriacetate and MEM were similar, and far greater than that from Tf at the same Fe concentration (2.5-mu-M). Ammonium chloride and a monoclonal antibody to the transferrin receptor (42/6), had no effect on the uptake of Fe from inorganic Fe complexes, suggesting that receptor-mediated endocytosis of Tf was not involved. The monoclonal antibody, 96.5, specific for melanotransferrin did not alter total Fe uptake but slightly increased the proportion of Fe internalised, possibly due to the modulation of the antigen by the antibody. However, from the time required for modulation to occur (approximately 2 h), the small increase in internalisation observed and the fact that no increase in total cell Fe occurred, it is suggested that melanotransferrin has little role in Fe uptake.