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Department of Pediatrics, Yale University, New Haven, Connecticut 06520-8064
The
divergent homeobox gene Hex is expressed in both developing
and mature liver. A putative Hex binding site was identified in the promoter region of the liver-specific Na+-bile acid
cotransporter gene (ntcp), and we hypothesized that Hex regulates the ntcp promoter through this
site. Successive 5'-deletions of the ntcp promoter in a
luciferase reporter construct transfected into Hep G2 cells confirmed a
Hex response element (HRE) within the ntcp
promoter (nt
733/
714). Moreover, p-CMHex transactivated a
heterologous promoter construct containing HRE multimers (p4xHRELUC),
whereas a 5-bp mutation of the core HRE eliminated transactivation. A
dominant negative form of Hex (p-Hex-DN) suppressed basal luciferase activity of p-4xHRELUC and inhibited activation of this construct by p-CMHex. Interestingly, p-CMHex transactivated the HRE in Hep G2 cells but not in fibroblast-derived COS cells, suggesting the possibility that Hex protein
requires an additional liver cell-specific factor(s) for full activity. Electrophoretic mobility shift assays confirmed that liver and Hep G2
cells contain a specific nuclear protein that binds the native HRE. We
have demonstrated that the liver-specific ntcp gene promoter
is the first known target of Hex and is a useful tool for
evaluating function of the Hex protein.
transcriptional regulation; liver
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