ERYTHROPOIETIN UP-REGULATES THE EXPRESSION OF ITS OWN RECEPTOR IN TF-1 CELL-LINE

In the erythroleukemia cell line TF-1, recombinant human erythropoieti n (rHEpo), but not c-kit ligand, enhanced the number of cells expressi ng the erythropoietin receptor (EpoR), as measured by flow-cytometric analysis of binding of the biotin-labeled Epo. Moreover,I-125-Epo bind ing and Scatchard analyses, indicated that TF-1 cells, maintained in s tandard conditions with IL-3, and those stimulated with c-kit ligand, bear a single class of EpoR. On the other hand, cells cultured in the presence of rHEpo had a higher number of receptors than IL-3 or c-kit ligand-stimulated cells, and had two binding sites with different affi nities for the ligand. EpoR mRNA expression was higher in cells expose d to rHEpo than in IL-3 or c-kit-stimulated cells. This difference may have been dependent on either a higher level of transcription or an i ncreased stability of mRNA. The observed changes of EpoR in rHEpo stim ulated TF-1 cell line could cooperate, together with the alteration of the gene (3' end deletion), in the occurrence of the erythroleukemic process. Changes induced in EpoR by rHEpo were not accompanied by an i ncrease in the expression of glycophorin A or globin chain mRNAs. This may suggest that rHEpo is unable to induce erythroid differentiation in TF-1 cells. The results also indicate that this cell line could be a model for the investigation of the role of transcription factor(s) i n the expression of EpoR, and for the study of the mechanism(s) underl ying the changes in the number and affinity of the cell receptors. (C) 1998 Elsevier Science Ltd. All rights reserved.