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Mol. Cell. Biol., Apr 1997, 1913-1922, Vol 17, No. 4
GF Spath and MC Weiss
The capacity of the liver-enriched transcription factor hepatocyte nuclear
factor 4 (HNF4) to direct redifferentiation of dedifferentiated rat
hepatoma cells was investigated by stable transfection of epitope- tagged
HNF4 cDNA into H5 variant cells. HNF4-producing cells expressed the
previously silent HNF1 gene and showed activation of some hepatic
functions, including alpha1-antitrypsin, beta-fibrinogen, and
transthyretin, but not of the endogenous HNF4 gene. Expression of the other
hepatocyte-enriched transcription factors was not modified. Treatment of
the HNF4tag-expressing cells with dexamethasone induced expression of the
transgene by 10-fold, resulting in enhanced expression of target genes of
both glucocorticoid hormones and HNF4. The set of activated hepatic genes
was extended by treatment of cells with the demethylating agent
5-azacytidine followed by selection in dexamethasone-containing
glucose-free medium. Some of the colonies that developed reexpressed the
entire set of hepatic functions tested. Fusion of HNF4tag-producing H5
cells with well-differentiated Fao cells showed that only those hybrids
which maintained expression of HNF4tag were protected from complete
extinction, including that of the Fao HNF4 gene. Thus, H5 cells must
produce an extinguisher of the HNF4 gene. In addition, this result implies
that HNF4 itself, or its target HNF1, is a positive regulator of HNF4. In
conclusion, HNF4tag expression overcomes repression of the hepatic
phenotype of the H5 cell without abolishing its potential to extinguish an
active genome. Taken together, these results predict that expression of
HNF4 should be sufficient to establish heritable expression of many
parameters of the hepatic differentiated state.
Copyright © 1997, American Society for Microbiology
Hepatocyte nuclear factor 4 expression overcomes repression of the hepatic phenotype in dedifferentiated hepatoma cells
Unite de Genetique de la Differenciation, URA 1149, Centre National de la Recherche Scientifique, Institut Pasteur, Paris, France.
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