Sposi N M, Cianetti L, Tritarelli E, Pelosi E, Militi S, Barberi T, Gabbianelli M, Saulle E, Kühn L, Peschle C, Testa U
Department of Hematology-Oncology, Istituto Superiore di Sanità, Rome, Italy.
Eur J Biochem. 2000 Dec;267(23):6762-74. doi: 10.1046/j.1432-1033.2000.01769.x.
We have investigated the expression of transferrin receptor (TfR) iron regulatory protein-1 (IRP-1) and iron regulatory protein-2 (IRP-2) in liquid suspension culture of purified hematopoietic progenitor cells (HPCs) induced by a growth factor stimulus to proliferation and unilineage differentiation/maturation through the erythroid, granulocytic, monocytic and megakaryocytic lineages. In initial HPC differentiation, TfR expression is induced in both erythroid and granulopoietic cultures. In late HPC differentiation (i.e. starting from day 5 of culture) and then differentiated precursor maturation, the TfR gene is highly expressed in the erythroid lineage, whereas it is sharply downmodulated in the granulopoietic, monocytopoietic and megakaryocytic series. The elevated TfR expression in erythroid cells is: (a) mediated through a high rate of TfR gene transcription; (b) modulated by intracellular iron levels; (c) mediated by TfR mRNA stabilization through the iron regulatory protein (IRP), in that IRP-1 activity is high in erythroid lineage as compared to the levels observed in other hemopoietic lineages; and (d) dependent on exogenous erythropoietin (Epo) (this is indicated by the marked TfR and IRP-1/IRP-2 downmodulation after Epo starvation). Interestingly, analysis of IRP-1 and IRP-2 expression during hemopoietic differentiation showed that: (a) IRP-1 expression was maintained during all steps of erythroid differentiation, while it was lost in the other hemopoietic lineages; (b) IRP-2 expression was observed during all stages of hemopoietic differentiation in all four lineages. However, IRP-1 and IRP-2 expression and activity are induced when monocytes, which express only low levels of IRP-1 and IRP-2, are induced to maturation to macrophages. These studies indicate that: (a) in normal erythropoiesis, the hyperexpression of TfR, starting from early erythroid HPC differentiation, is Epo-dependent and mediated via transcriptional and post-transcriptional mechanisms; (b) in the granulopoietic, monocytopoietic and megakaryocytic pathways, the TfR is first induced and then downmodulated (the latter phenomenon is mediated via transcriptional suppression of the TfR gene and IRP inactivation).
我们研究了转铁蛋白受体（TfR）、铁调节蛋白-1（IRP-1）和铁调节蛋白-2（IRP-2）在纯化的造血祖细胞（HPC）液体悬浮培养中的表达情况。这些造血祖细胞在生长因子刺激下，通过红系、粒系、单核系和巨核系进行增殖和单系分化/成熟。在造血祖细胞的初始分化阶段，红系和粒系培养中均诱导了TfR的表达。在造血祖细胞晚期分化（即从培养第5天开始）以及随后分化的前体细胞成熟过程中，TfR基因在红系中高表达，而在粒系、单核系和巨核系中则急剧下调。红系细胞中TfR表达升高的原因如下：（a）通过TfR基因的高转录率介导；（b）受细胞内铁水平调节；（c）通过铁调节蛋白（IRP）使TfR mRNA稳定来介导，因为与其他造血系中观察到的水平相比，IRP-1在红系中的活性较高；（d）依赖于外源性促红细胞生成素（Epo）（这通过Epo饥饿后TfR和IRP-1/IRP-2的显著下调表明）。有趣的是，对造血分化过程中IRP-1和IRP-2表达的分析表明：（a）IRP-1在红系分化的所有阶段均维持表达，而在其他造血系中则消失；（b）在所有四个系的造血分化的所有阶段均观察到IRP-2的表达。然而，当仅表达低水平IRP-1和IRP-2的单核细胞被诱导成熟为巨噬细胞时，IRP-1和IRP-2的表达及活性会被诱导。这些研究表明：（a）在正常红细胞生成过程中，从早期红系造血祖细胞分化开始，TfR的过表达是Epo依赖性的，并通过转录和转录后机制介导；（b）在粒系、单核系和巨核系途径中，TfR首先被诱导，然后下调（后一种现象通过TfR基因的转录抑制和IRP失活介导）。
