Regulation of expression of murine transferrin receptor 2

Complementary and genomic DNA for the murine transferrin receptor 2 (TfR2) were cloned and mapped to chromosome 5. Northern blot analysis showed that high levels of expression of murine TfR2 occurred in the liver, whereas expression of TfR1 in the liver was relatively low. During liver development, TfR2 was up-regulated and TfR1 was down-regulated. During erythrocytic differentiation of murine erythroleukemia (MEL) cells induced by dimethylsulfoxide, expression of TfR1 increased, whereas TfR2 decreased. In MEL cells, expression of TfR1 was induced by desferrioxamine, an iron chelator, and it was reduced by ferric nitrate. In contrast, levels of TfR2 were not affected by the cellular iron status. Reporter assay showed that GATA-1, an erythroid-specific transcription factor essential for erythrocytic differentiation at relatively early stages, enhanced TfR2 promoter activity. Interestingly, FOG-1, a cofactor of GATA-1 required for erythrocyte maturation, repressed the enhancement of the activity by GATA-1. Also, CCAAT-enhancer binding protein, which is abundant in liver, enhanced the promoter activity. Thus, tissue distribution of TfR2 was consistent with the reporter assays. Expression profiles of TfR2 were different from those of TfR1, suggesting unique functions for TfR2, which may be involved in iron metabolism, hepatocyte function, and erythrocytic differentiation.