The Mouse Alpha-Albumin (Afamin) Promoter Is Differentially Regulated by Hepatocyte Nuclear Factor 1α and Hepatocyte Nuclear Factor 1β

Abstract

Alpha-albumin (AFM), a member of the albumin gene family that also includes albumin, alpha-fetoprotein, and vitamin D-binding protein, is expressed predominantly in the liver and activated at birth. Here, we identify two hepatocyte nuclear factor 1 (HNF1)-binding sites in the AFM promoter that are highly conserved in different mammals. These two sites bind HNF1a and HNF1b. The distal site (centered at À132, relative to AFM exon 1) is more important than proximal site (centered at À58), based on HNF1 binding and mutational analysis in transfected cells. Our data indicate that HNF1a is a more potent activator of AFM promoter than is HNF1b. However, HNF1b can act in a dominant manner to inhibit HNF1a-dependent transactivation of the AFM promoter when both proteins are expressed together. This suggests that the differential timing with which the albumin family genes are activated in the liver may be influenced by their responsiveness to HNF1a and HNF1b. Our comparison of HNF1-binding sites in the promoters in the albumin family of genes indicates that the primordial albumin-like gene contained two HNF1 sites; one of these sites was lost from the albumin promoter, but both sites still are present in other members of this gene family.

Pericentral activity of alpha-fetoprotein enhancer 3 and glutamine synthetase upstream enhancer in the adult liver are regulated by β-catenin in mice

“…[26][27][28][29][30] Previous studies indicated that the 3.2-kb region upstream of the rat GS gene (À3,150 to þ59) could confer pericentral expression of a linked reporter gene in Tg mice. 31 To test whether the upstream enhancer of the rat GS gene exhibited pericentral activity by itself, this enhancer was cloned as a 400-basepair (bp) fragment (as previously defined 21 and which will be referred to as RGS e ) and fused to the heterologous human b-globin promoter linked to the mouse H-2D d reporter gene (bgl-D d ). We have used bgl-D d extensively to monitor gene expression in cells and Tg mice; this cassette is inactive in all mouse tissues, but is highly responsive to linked enhancers.…”

“…Protein concentrations were determined using the bicinchoninic acid (BCA) protein assay (Pierce, Rockville, IL). Labeling of annealed oligonucleotides (Table 1) (Integrated DNA Technologies, Inc., Coralville, IA) with 32 P and electrophoretic mobility shift assay (EMSAs) were carried out as previously described 21…”

Afamin — A pleiotropic glycoprotein involved in various disease states

“…Two hepatocyte nuclear factor 1 (HNF1)-binding sites binding HNF1α and HNF1β have been identified in the afamin promoter. Expression studies in mice suggest that the different responsiveness of albumin gene family members is crucial for their liver expression [11]. More recently, a microarray study showed increased expression of transcription factor islet-1 levels (which is associated with increased β-cell function) to increase afamin expression 35-fold [12].…”

Diagnosis, management, and prognosis of HNF1B nephropathy in adulthood

“…Activity of either partner may differentially affect the target genes. 29 Should this occur in humans, and if both patients carried a point mutation, a dominant-negative effect of HNF1A/HNF1B heterodimers could account for the phenotype. Alternatively, interacting genes may participate in phenotypic heterogeneity.…”