PU.1 Is Degraded in Differentiation of Erythrocytes Through a Proteasome-Dependent Pathway

The transcription factor PU.1 regulates erythrocyte differentiation. We previously reported that F5-5 erythroblasts differentiate into erythrocytes in response to activin by degrading PU.1, and that inhibiting PU.1- degradation suppresses F5-5 cell differentiation into erythrocytes. These findings suggest that regulating PU.1 degradation is critical for terminal differentiation of erythrocytes. Here, we investigate the mechanism underlying PU.1 degradation during successive differentiation of erythrocytes. Using 2D-MS proteomic analysis, we show that proteasome subunits and proteins required for degradation by proteasomes immunoprecipitate with PU.1 in response to activin. Furthermore, a proteasome inhibitor, lactacystin, partially suppresses differentiation of F5-5 cells into erythrocytes in response to activin, and partially inhibits PU.1 degradation. Our results indicate that degradation of PU.1 necessary for erythrocyte differentiation occurs, in part, through the proteasome pathway.