Volume 272, Number 39,
Issue of September 26, 1997
pp. 24300-24307
©1997 by The American Society for Biochemistry and Molecular Biology, Inc.
Thrombopoietin-induced Expression of the Glycoprotein IIb Gene
Involves the Transcription Factor PU.1/Spi-1 in UT7-Mpl Cells
(Received for publication, May 6, 1997, and in revised form, July 17, 1997)
Alexandre
Doubeikovski
,
George
Uzan
§
,
Zinaida
Doubeikovski
,
Marie-Hélène
Prandini
¶
,
Françoise
Porteu
,
S.
Gisselbrecht
and
I.
Dusanter-Fourt
From 
INSERM U363, Institut Cochin de
Génétique Moléculaire, Hopital Cochin, 27 rue du
Faubourg Saint-Jacques, 75014 Paris, France, § INSERM U268,
Hopital Paul Brousse, 94807 Villejuif Cedex, France, and
¶ Commissariat à l'Energie Atomique, 17 avenue des
Martyres, 38054 Grenoble Cedex 9, France
Thrombopoietin (TPO) is the major regulator of
proliferation and differentiation of megakaryocytes and their
progenitors. These actions can be reproduced in the human
megakaryoblastic cell line UT7 into which the murine TPO receptor,
c-Mpl, was introduced. In these cells, TPO enhanced the expression of
the specific megakaryocytic marker integrin glycoprotein (GP) IIb-IIIa
while decreasing the expression of erythroid genes (Porteu, F., Rouyez,
M.-C., Cocault, L., Benit, L., Charon, M., Picard, F., Gisselbrecht,
S., Souyri, M., and Dusanter-Fourt, I. (1996) Mol. Cell. Biol.
16, 2473-2482). We have now analyzed the effect of TPO on the
transcriptional activity of the GPIIb promoter in these cells. Using
transient transfection assays of a series of human GPIIb promoter
fragments, we delineated a TPO-responsive element within the previously
reported enhancer region of the promoter. Although this enhancer
included GATA- and Ets-binding sites (EBSs), we found that only EBS
514 was important for TPO response. We identified PU.1/Spi-1 as the endogenous Ets transcription factor that strongly and preferentially interacted with this enhancer EBS. This factor did not interact with
other proximal EBSs in the GPIIb promoter. We next showed that TPO
induced a strong and selective increase of PU.1/Spi-1 expression and
DNA binding activity in UT7-Mpl cells. In contrast, TPO did not affect
the expression of Ets-1/2 while weakly increasing the levels of Fli-1.
Overexpression of PU.1/Spi-1 was further shown to enhance GPIIb
promoter activity in the absence and presence of TPO. Overall, our data
indicated that, in UT7-Mpl cells, TPO increased the transcriptional
activity of a GPIIb gene in part due to an enhanced expression of an
unexpected transcription factor, the Ets family PU.1/Spi-1 factor. To
our knowledge, this is the first evidence of a role for the PU.1/Spi-1
factor in the regulation of megakaryocytic genes.
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