[An analysis of the iron related proteins during erythroid differentiation in K562 cells]

Intracellular iron homeostasis is modulated by ferritin and transferrin receptor (TfR). And the biosynthesis of both proteins is regulated post-transcriptionally by the interaction of specific cytoplasmic protein, termed iron responsive elements-binding protein (IRE-BP) with specific sequences, termed iron responsive elements (IRE), located in the 5' untranslated region (UTR) of the ferritin mRNA or 3'UTR of TfR mRNA. In spite of the important role of IRE/IRE-BP interaction for cellular iron metabolism, the role of it for erythroid differentiation is not yet well known. In this study, the author investigated the time sequential change of IRE-BP, ferritin and TfR mRNA expression and the binding activity of IRE-BP with IRE during erythroid differentiation of human erythroleukemic cells (K 562). During erythroid differentiation of K 562 cells by Na-butyrate, analysis using reverse transcription-polymerase chain reaction indicated that TfR mRNA expression was little changed. The addition of excess iron (as 100 micrograms/ml holo transferrin) caused reduction of the level of TfR mRNA, however, the iron chelator defferoxamine caused its increase. IRE-BP mRNA was slightly increased at the early period of erythroid differentiation and unaffected by iron or iron chelator treatment. Affinity binding signal of IRE and IRE-BP detected by gel retardation assay was also increased at the early period of erythroid differentiation. The addition of iron or iron chelator both caused marked increase in the binding activity of IRE-BP at 48 hr after Na-butyrate treatment. These results suggest that IRE/IRE-BP inter-action may play a possible role in the erythroid differentiation of K562 cells.