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Mol. Cell. Biol., Mar 1996, 778-791, Vol 16, No. 3
SC Power and S Cereghini
vHNF1 (also termed HNF1 beta) is a member of the hepatocyte nuclear fa ctor
1 (HNF1; also termed HNF1 alpha) family of homeodomain-containing
transcription factors that interact with a sequence motif found in the
regulatory regions of a large number of genes expressed mainly in the
liver. It has been suggested that vHNF1 plays a role in early
differentiation of specialized epithelia of several endoderm- and
mesoderm-derived organs, with HNF1 playing a role in later stages. In
support of this idea, expression of vHNF1 but not HNF1 is induced upon
treatment of the embryonal carcinoma cell line F9 with retinoic acid. We
have cloned and analyzed the vHNF1 promoter to gain a better understanding
of the regulation of vHNF1 expression and how it relates to the expression
of HNF1. We have identified five sites of DNA-protein interaction within
the first 260 bp upstream of the transcription start site, which involve at
least three different families of transcription factors. Two sites, a
distal DR-1 motif and a proximal octamer motif, are the most important for
promoter activity. The DR-1 motif interacts with several members of the
steroid hormone receptor superfamily including HNF4, COUP-TFI/Ear3,
COUP-TFII/Arp1, and RAR alpha/RXR alpha heterodimers. The vHNF1 promoter is
transactivated by COUP-TFI/Ear3 and COUP-TFII/Arp1 and, unlike the HNF1
promoter, is virtually unaffected by HNF4. Interestingly, the proximal
octamer site and not the DR-1 site is required for COUP-TFI/Ear3 and
COUP-TFII/Arp1 transactivation of the vHNF1 promoter. COUP-TFI/Ear3 does
not bind directly to this proximal octamer site. We present evidence of an
interaction between COUP- TFI/Ear3 and the octamer-binding proteins in
vitro and in the cell, suggesting that COUP-TFI and COUP-TFII activate the
vHNF1 promoter via an indirect mechanism.
Copyright © 1996, American Society for Microbiology
Positive regulation of the vHNF1 promoter by the orphan receptors COUP- TF1/Ear3 and COUP-TFII/Arp1
URA Centre National de la Recherche Scientifique, Institut Pasteur, Paris, France.
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