ERYTHROPOIETIN EXERTS TRANSCRIPTIONAL AND TRANSLATIONAL CONTROL OVER GLOBIN-SYNTHESIS IN J2E CELLS

The J2E erythroid cell line, generated by transforming fetal liver cel ls, terminally differentiates in response to erythropoietin (epo). The cells expressed both adult and embryonic globin genes, although consi derably more adult globin was produced, and transcripts for both speci es rose following exposure to epo. A 6-fold increase in transcription of the adult alpha and beta(maj) globin genes was observed after hormo nal stimulation, which resulted in a substantial accumulation of mRNA. In addition, a modest but transient rise in translation enabled a 6-f old elevation in globin protein to occur. Concurrently, the total heme content rose markedly, enhancing hemoglobin synthesis 10-fold. The pr osthetic group complexed entirely with globin proteins, and the hemogl obin produced was present as fully functional oxyhemoglobin, capable o f gaseous exchange. We concluded, therefore, that hemoglobin synthesis in epo-induced J2E cells normally results from the coordinate stimula tion of heme and globin synthesis. However, some mutant clones emerged where concomitant increases in globin and heme were not observed. Des pite similar profiles for the appearance of hemoglobin and equivalent amounts of the oxygen carrier, several noticeable differences in globi n synthesis were detected between epo-induced J2E cells and DMSO-stimu lated murine erythroleukemia cells, i.e., the types of globin genes ex pressed, patterns of mRNA and protein production, and translation rate s. These results demonstrate that the J2E cells provide a useful model system for investigating the molecular mechanisms of epo-initiated he moglobin synthesis.