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Mol. Cell. Biol., May 1997, 2790-2797, Vol 17, No. 5
E Ktistaki and I Talianidis
Chicken ovalbumin upstream promoter transcription factors (COUP-TFs)
strongly inhibit transcriptional activation mediated by nuclear hormone
receptors, including hepatocyte nuclear factor 4 (HNF-4). COUP-TFs repress
HNF-4-dependent gene expression by competition with HNF-4 for common
binding sites found in several regulatory regions. Here we show that
promoters, such as the HNF-1 promoter, which are recognized by HNF- 4 but
not by COUP-TFs are activated by COUP-TFI and COUP-TFII in conjunction with
HNF-4 more than 100-fold above basal levels, as opposed to about 8-fold
activation by HNF-4 alone. This enhancement was strictly dependent on an
intact HNF-4 E domain. In vitro and in vivo evidence suggests that COUP-TFs
enhance HNF-4 activity by a mechanism that involves their physical
interaction with the amino acid 227 to 271 region of HNF-4. Our results
indicate that in certain promoters, COUP- TFs act as auxiliary cofactors
for HNF-4, orienting the HNF-4 activation domain in a more efficient
configuration to achieve enhanced transcriptional activity. These findings
provide new insights into the regulatory functions of COUP-TFs, suggesting
their involvement in the initial activation and subsequent high-level
expression of hepatic regulators, as well as in the positive and negative
modulation of downstream target genes.
Copyright © 1997, American Society for Microbiology
Chicken ovalbumin upstream promoter transcription factors act as auxiliary cofactors for hepatocyte nuclear factor 4 and enhance hepatic gene expression
Institute of Molecular Biology and Biotechnology, Foundation for Research and Technology Hellas, Herakleion, Crete, Greece.
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