Notch1 inhibits differentiation of hematopoietic cells by sustaining GATA-2 expression

Notch signaling is involved in cell fate decisions in many systems includin g hematopoiesis. It has been shown that expression of an activated form of Notch1 (aNotch1) in 32D mouse myeloid progenitor cells inhibits the granulo cytic differentiation induced by granulocyte colony-stimulating factor (G-C SF). Results of the current study show that aNotch1, when expressed in F5-5 mouse erythroleukemia cells, also inhibits erythroid differentiation. Comp arison of the expression levels of several transcription factors after stim ulation for myeloid and erythroid differentiation, in the presence or absen ce of aNotch1, revealed that aNotch1 did not change its regulation pattern with any of the transcription factors examined, except for GATA-2, despite its inhibitory effect on differentiation. GATA-2 was down-regulated when th e parental 32D and FS-5 were induced to differentiate into granulocytic and erythroid lineages, respectively. In these induction procedures, however, the level of GATA-2 expression was sustained when aNotch1 was expressed. To ascertain whether maintenance of GATA-2 is required for the Notch-induced inhibition of differentiation, the dominant-negative form of GATA-3 (DN-GAT A); which acted also against GATA-2, or transcription factor PU.1, which wa s recently shown to be the repressor of GATA-2, was introduced into aNotch1 -expressing 32D (32D/aNotch1) cells that do not express GATA family protein s other than GATA2. Both DN-GATA and PU.1 reversed the phenotype of 32D/aNo tch1 inducing its differentiation when G-CSF was added. Furthermore, enforc ed expression of HES-1, which is involved in Notch signaling, delayed diffe rentiation of 32D, and again this phenotype was neutralized by DN-GATA. The se results indicate that GATA-2 activity is necessary for the Notch signali ng in hematopoietic cells. (Blood. 2001; 98:3283-3289) (C) 2001 by The Amer ican Society of Hematology.