ERYTHROPOIETIN TRIGGERS A BURST OF GATA-1 IN NORMAL HUMAN ERYTHROID-CELLS DIFFERENTIATING IN TISSUE-CULTURE

GATA-1 is a central transcription-activator of erythroid differentiati on. In the present work we have studied the kinetics of its expression and activity during development of normal human erythroid progenitors , grown in primary cultures. In response to the addition of erythropol etin (Epo), the cells undergo proliferation and differentiation in a s ynchronized fashion. This recently developed experimental system allow s biochemical dissection of erythroid differentiation in a physiologic al meaningful environment. No DNA-binding activity of GATA-1 could be detected before the addition of Epo, although a very low level of mRNA was observed. Following Epo addition there was a sharp parallel rise in both mRNA and DNA-binding activity, consistent with positive autore gulation of the GATA-1 gene. After reaching a peak on day 7-9, both mR NA and protein activity decreased. The binding activity of the ubiquit ous factor SP1 showed a biphasic pattern; its second peak usually coin cided with the GATA-1 peak, suggesting that SP1 also plays a specific role in erythroid maturation. The highest activity of GATA-1 per eryth roid cell was found on day 6-8, immediately preceding the major rise i n globin gene mRNA and in the number of hemoglobinized cells. The resu lts imply that a high level of GATA-1 activity is necessary for globin gene expression and erythroid maturation, suggesting that a requireme nt for a threshold concentration of GATA-1 is part of the mechanism th at determines the final steps of erythroid maturation.