ANALYSIS OF THE THROMBOPOIETIN RECEPTOR (MPL) PROMOTER IMPLICATES GATA AND ETS PROTEINS IN THE COREGULATION OF MEGAKARYOCYTE-SPECIFIC GENES

The MPL gene codes for the thrombopoietin receptor, whose ligand speci fically controls megakaryocytic differentiation. To understand the mol ecular basis for the megakaryocyte-specific expression of MPL, we anal yzed the promoter of this gene. A 200 bp fragment is sufficient for hi gh-level specific expression. This fragment can bind several trans-act ing factors in vitro, including GATA-1 and members of the Ets family. GATA-1 binds with low affinity to a unique GATA motif at -70 in the MP L promoter, and destruction of this site yields only a modest decrease in expression level in HEL cells. Ets proteins also bind with low aff inity to two sites. One is located at position -15 and its destruction reduces expression to 50%; the other is located immediately downstrea m of the GATA motif and plays a crucial role in expression of the prom oter in HEL cells, as its inactivation reduces expression to 15%. Furt hermore, GATA-1 and two Ets proteins, Ets-1 and Fli-1, can trans-activ ate the MPL promoter in heterologous cells. The effects of GATA-1 and these two Ets proteins are additive, Together with our previous result s on the glycoprotein Ilb (GpIIb) promoter, this study indicates a mol ecular basis for the coregulation of early markers of megakaryocyte di fferentiation. (C) 1996 by The American Society of Hematology.