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Mol. Cell. Biol., 10 1995, 5453-5460, Vol 15, No. 10
V Vallet, B Antoine, P Chafey, A Vandewalle and A Kahn
Transcription of hepatocyte-specific genes requires the interaction of
their regulatory regions with several nuclear factors. Among them is the
hepatocyte nuclear factor 3 (HNF3) family, composed of the HNF3 alpha, HNF3
beta, and HNF3 gamma proteins, which are expressed in the liver and have
very similar fork head DNA binding domains. The regulatory regions of
numerous hepatocyte-specific genes contain HNF3 binding sites. We examined
the role of HNF3 proteins in the liver- specific phenotype by turning off
the HNF3 activity in well- differentiated mhAT3F hepatoma cells. Cells were
stably transfected with a vector allowing the synthesis of an HNF3 beta
fragment consisting of the fork head DNA binding domain without the
transactivating amino- and carboxy-terminal domains. The truncated protein
was located in the nuclei of cultured hepatoma cells and competed with
endogenous HNF3 proteins for binding to cognate DNA sites. Overproduction
of this truncated protein, lacking any transactivating activity, induced a
dramatic decrease in the expression of liver-specific genes, including
those for albumin, transthyretin, transferrin, phosphoenolpyruvate
carboxykinase, and aldolase B, whereas the expression of the L-type
pyruvate kinase gene, containing no HNF3 binding sites, was unaltered.
Neither were the concentrations of various liver-specific transcription
factors (HNF3, HNF1, HNF4, and C/EBP alpha) affected. In partial
revertants, with a lower ratio of truncated to full-length endogenous HNF3
proteins, previously extinguished genes were re-expressed. Thus, the
transactivating domains of HNF3 proteins are needed for the proper
expression of a set of liver- specific genes but not for expression of the
genes encoding transcription factors found in differentiated hepatocytes.
Copyright © 1995, American Society for Microbiology
Overproduction of a truncated hepatocyte nuclear factor 3 protein inhibits expression of liver-specific genes in hepatoma cells
Institut National de la Sante et de la Recherche Medicale U129, Institut Cochin de Genetique Moleculaire, Universite Rene Descartes, Paris, France.
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