Erythropoietin-dependent suppression of the expression of the beta subunits of the interleukin-3 receptor during erythroid differentiation

To clarify how erythroid cells lose their response to interieukin-3 (IL-3), we analyzed the expression of the alpha (alpha (IL-3)) and beta (beta (IL- 3)/beta (com)) subunits of its receptor in a panel of murine cell lines imm ortalized at different stages of hemopoietic differentiation. The panel was composed by the mast cell line 32D and by its granulo-monocytic (32D GM), granulocytic (32D G), and erythroid (32D Epo1.1 and Epo) subclones. The 32D Epo cells grow only in erythropoietin (EPO) while the Epo1.1 subclone grow s in either EPO or IL-3. The phenotype of these cells is that of early (exp ression of globins and erythroid-specific carbonic anhydrase II) and late ( also expression of the erythroid-specific band 4.1 mRNA) erythroblasts when they grow in IL-3 or EPO, respectively. All the cell lines expressed compa rable levels of alpha (IL-3). In contrast, the expression of beta (IL-3)/be ta (com) was restricted to cells growing in IL-3 and was barely detectable in 32D Epo and 32D Epo1.1 cells growing in EPO. When switched from EPO to I L-3, 32D Epo1.1 cells expressed 10 times more beta (IL-3)/beta (com) by rap idly activating (within 1 h) their transcription rate. When reexposed to EP O, 32D Epo1.1. cells first expressed (1-6 h) more beta (IL-3)/beta (com) (2 times) but suppressed such an expression at later time points (by 48 h). T he beta (IL-3)/beta (com) mRNA half-life was also different when 32D Epo1.1 cells grew in EPO or IL-3 (2-3 h vs >5 h, respectively). These results ind icate that EPO specifically induces transcriptional and posttranscriptional downmodulation of beta (IL-3)/beta (com) expression in late erythroid cell s. (C) 2000 Academic Press.