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Mol. Cell. Biol., 04 1995, 2135-2144, Vol 15, No. 4
DL Galson, T Tsuchiya, DS Tendler, LE Huang, Y Ren, T Ogura and HF Bunn
The erythropoietin (Epo) gene is regulated by hypoxia-inducible cis- acting
elements in the promoter and in a 3' enhancer, both of which contain
consensus hexanucleotide hormone receptor response elements which are
important for function. A group of 11 orphan nuclear receptors, transcribed
and translated in vitro, were screened by the electrophoretic mobility
shift assay. Of these, hepatic nuclear factor 4 (HNF-4), TR2-11, ROR alpha
1, and EAR3/COUP-TF1 bound specifically to the response elements in the Epo
promoter and enhancer and, except for ROR alpha 1, formed DNA-protein
complexes that had mobilities similar to those observed in nuclear extracts
of the Epo-producing cell line Hep3B. Moreover, both anti-HNF-4 and
anti-COUP antibodies were able to supershift complexes in Hep3B nuclear
extracts. Like Epo, HNF-4 is expressed in kidney, liver, and Hep3B cells
but not in HeLa cells. Transfection of a plasmid expressing HNF-4 into HeLa
cells enabled an eightfold increase in the hypoxic induction of a
luciferase reporter construct which contains the minimal Epo enhancer and
Epo promoter, provided that the nuclear hormone receptor consensus DNA
elements in both the promoter and the enhancer were intact. The
augmentation by HNF- 4 in HeLa cells could be abrogated by cotransfection
with HNF-4 delta C, which retains the DNA binding domain of HNF-4 but lacks
the C- terminal activation domain. Moreover, the hypoxia-induced expression
of the endogenous Epo gene was significantly inhibited in Hep3B cells
stably transfected with HNF-4 delta C. On the other hand, cotransfection of
EAR3/COUP-TF1 and the Epo reporter either with HNF-4 into HeLa cells or
alone into Hep3B cells suppressed the hypoxia induction of the Epo
reporter. These electrophoretic mobility shift assay and functional
experiments indicate that HNF-4 plays a critical positive role in the
tissue-specific and hypoxia-inducible expression of the Epo gene, whereas
the COUP family has a negative modulatory role.
Copyright © 1995, American Society for Microbiology
The orphan receptor hepatic nuclear factor 4 functions as a transcriptional activator for tissue-specific and hypoxia-specific erythropoietin gene expression and is antagonized by EAR3/COUP-TF1
Department of Medicine, Brigham & Women's Hospital, Boston, Massachusetts 02115.
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