OVEREXPRESSION OF PU.1 INDUCES GROWTH AND DIFFERENTIATION INHIBITION AND APOPTOTIC CELL-DEATH IN MURINE ERYTHROLEUKEMIA-CELLS

PU.1 is a member of the ets family of transcription factors and is exp ressed in Friend virus-induced murine erythroleukemia (MEL) cells as a consequence of proviral integration into the PU.1/Spi-1 locus. After induction of MEL cell differentiation by treatment with dimethylsulfox ide (DMSO), expression of the PU.1/Spi-1 gene decreased before inducti on of beta-globin gene expression. Overexpression of PU.1 by using a z inc-inducible expression plasmid in MEL cells resulted in unexpected g rowth inhibition of the transfectants, When PU.1-overexpressing transf ectants were treated with DMSO, growth inhibition became much pronounc ed and apoptosis was induced, Expression of the beta-globin gene was n ot induced under this condition. Neither growth inhibition nor apoptos is was induced in MEL cells after expression of mutant PU.1 proteins w ith a deletion of the activation domain or the DNA-binding Ets domain irrespective of the presence of DMSO. Interestingly, beta-globin gene expression was not induced in the transfectants expressing the former mutant, whereas it was induced in those expressing the latter one in t he presence of DMSO. These results indicate that overexpression of PU. 1 in MEL cells results in growth and differentiation inhibition and, i n conjunction with DMSO treatment, apoptotic cell death. These results also suggest that the activation domain and the Ets domain of PU.1 co ntribute differently to induction of these effects. (C) 1997 by The Am erican Society of Hematology.