GATA-1 DOMINANTLY ACTIVATES A PROGRAM OF ERYTHROID GENE-EXPRESSION INFACTOR-DEPENDENT MYELOID FDCW2 CELLS

Erythrocyte development has previously been shown to depend upon the e xpression of the lineage-restricted trans-acting factor GATA-1, Despit e predicted roles for this factor during early development, GATA-1-def icient cells in chimeric mice and embryonic stem cell cultures mature to a late proerythroblast stage and express at least certain genes tha t normally are thought to be regulated by GATA-1 (including erythroid Kruppel-like factor [EKLF] and the erythropoietin [Epo] receptor), Opp ortunities to test roles for GATA-1 in erythroid gene activation in th ese systems therefore are limited, In the present study, in an alterna te approach to test the function of GATA-1, GATA-1 has been expressed together with the Epo receptor in myeloid FDCW2 cells and the resultin g effects on cytokine-dependent proliferation and erythroid gene expre ssion have been assessed, GATA-1 expression at low levels delayed FDCW 2ER cell cycle progression at the G(1) phase specifically during Epo-i nduced mitogenesis, Upon expression of GATA-1 at increased levels, pro liferation in response to Epo, interleukin-3 (IL-3), and stem cell fac tor was attenuated and endogenous GATA-1, EKLF and beta(maj)-globin ge ne expression was activated. Friend of GATA-1 (FOG) transcript levels also were enhanced, and ets-1 and c-mpl but not Epo receptor gene expr ession was induced, Finally, in FDCW2 cells expressing increased level s of GATA-1 and a carboxyl-terminally truncated Epo receptor, Epo (wit h respect to IL-3 as a control) was shown to markedly promote globin t ranscript expression. Thus, novel evidence for select hierarchical rol es for GATA-1 and Epo in erythroid lineage specification is provided.