Regulation of Alpha‐fetoprotein expression in the mouse liver by HNF1 and NF1

Abstract

Alpha‐fetoprotein (AFP) is highly expressed in the fetal liver but silenced at birth. A G‐A substitution at −119 of the human AFP promoter was associated with persistent AFP expression in the adult liver. The −119 region harbors overlapping sites for Hepatocyte Nuclear Factor 1 (HNF1) and Nuclear Factor I (NFI); the G‐A substitution increases HNF1 binding. This overlapping HNF1/NFI site is conserved in other mammals, including the mouse. In this study, we have used a combination of biochemical, tissue culture, and transgenic mouse studies to explore further the role of this HNF1/NFI site in AFP regulation. Transient co‐transfections in Hep3B hepatoma cells indicate that HNF1 activates while NFI represses the AFP promoter. EMSAs indicate that HNF1 and NF1 compete for binding to this site. Transgenes regulated by the wild‐type AFP promoter are expressed at low levels in the adult liver. Transgenes with a GG‐AA mutation (similar to the G‐A human mutation) are more active in the adult liver. In EMSAs, the GG‐AA mutation enhances HNF1 binding and reduces NF1 binding. Our data indicate that HNF1 and NFI compete for binding to the AFP promoter and this competition is involved in postnatal AFP repression..