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.