Erythropoietin-Dependent Suppression of the Expression of the β Subunits of the Interleukin-3 Receptor during Erythroid Differentiation

To clarify how erythroid cells lose their response to interleukin-3 (IL-3), we analyzed the expression of the α (αIL-3) and β (βIL-3/βcom) subunits of its receptor in a panel of murine cell lines immortalized 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 grows in either EPO or IL-3. The phenotype of these cells is that of early (expression 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 comparable levels of αIL-3. In contrast, the expression of βIL-3/βcom 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 IL-3, 32D Epo1.1 cells expressed 10 times more βIL-3/βcom by rapidly activating (within 1 h) their transcription rate. When reexposed to EPO, 32D Epo1.1 cells first expressed (1–6 h) more βIL-3/βcom (2 times) but suppressed such an expression at later time points (by 48 h). The βIL-3/βcom 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 indicate that EPO specifically induces transcriptional and posttranscriptional downmodulation of βIL-3/βcom expression in late erythroid cells.