Effect of extracellular hemin on hemoglobin and ferritin content of erythroleukemia cells

Abstract

Mouse (MEL) and human (K-562) erythroleukemia cell lines can be induced to undergo erythroid differentiation, including hemoglobin (Hb) synthesis, by extra cellular hemin. In order to study the effect of extracellular hemin on intracellular ferritin and Hb content, we have used Mossabauer spectroscopy to measure the amount of ⁵⁷Fe incorporated into ferritin or Hb and a fluorescent enzyme-linked immunosorbent assay (ELISA) to measure the ferritin protein content. When K-562 cells were cultured in the presence of a ⁵⁷Fe source either as transferrin or citrate, in the absence of a differentiation inducer, all the intracellular ⁵⁷Fe was detected in ferritin. When the cells were cultured in the presence of ⁵⁷Fe-hemin, ⁵⁷Fe was found in both ferritin and Hb. ⁵⁷Fe in ferritin increased rapidly, and after 2 days it reached a plateau at 5 × 10⁻¹⁴g/cell. ⁵⁷Fe in Hb increased linearly with time and reached the same value after 12 days. Addition of other iron sources such as iron-saturated transferrin, iron citrate, or iron ammonium citrate caused a much lower increase in ferritin protein content as compared to hemin. When K-562 cells were induced by ⁵⁷Fe-hemin in the presence of ⁵⁶Fe-transferrin, ⁵⁷Fe was found to be incorporated in equal amounts into both ferritin and Hb. However, when the cells were induced by ⁵⁶Fe-hemin in the presence of ⁵⁷Fe-transferrin, ⁵⁷Fe was incorporated only into ferritin, but not into Hb, which contained ⁵⁶Fe iron. These results indicate that in K-562 cells, when hemin is present in the culture medium it is preferentially incorporated into Hb, regardless of the availability of other extra-or intracellular iron sources such as transferrin in ferritin. In MEL cells induced to differentiate by dimethylsulfoxide (DMSO) a different pattern of iron incorporation was observed; ⁵⁷Fe from both transferrin and hemin was found to incorporate in ferritin as well as in Hb.