HIERARCHY AND POSITIVE-NEGATIVE INTERPLAYS OF THE HEPATOCYTE NUCLEAR FACTORS HNF-1, HNF-3 AND HNF-4 IN THE LIVER-SPECIFIC ENHANCER FOR THE HUMAN ALPHA-1-MICROGLOBULIN BIKUNIN PRECURSOR
P. Rouet et al., HIERARCHY AND POSITIVE-NEGATIVE INTERPLAYS OF THE HEPATOCYTE NUCLEAR FACTORS HNF-1, HNF-3 AND HNF-4 IN THE LIVER-SPECIFIC ENHANCER FOR THE HUMAN ALPHA-1-MICROGLOBULIN BIKUNIN PRECURSOR, Nucleic acids research, 23(3), 1995, pp. 395-404
Alpha-1-microglobulin and bikunin are two plasma glycoproteins encoded
by an alpha-1-microglobulin/bikunin precursor (AMBP) gene. The strict
liver-specific expression of the AMBP gene is controlled by a potent
enhancer made of six clustered boxes numbered 1-6 that have been repor
ted to be proven or potential binding sites for the hepatocyte-enriche
d nuclear factors HNF-1, -4, -3, -1, -3, -4, respectively. In the pres
ent study, electromobility shift assays of wild-type or mutated probes
demonstrated that the boxes 1-5 have a binding capacity for their cog
nate HNF protein. Box 5 is also a target for another, as yet unidentif
ied, factor. A functional analysis of the wild-type or mutated enhance
r, driving its homologous promoter and a reporter CAT gene in the HepG
2 hepatoma cell line, demonstrated that all six boxes participate in t
he enhancer activity, with the primary influence of box 4 (HNF-1) and
box 2 (HNF-4). A similar analysis in the HNF-free CHO cell line co-tra
nsfected with one or several HNF factors further demonstrated various
interplays between boxes: box 3 (HNF-3 alpha and beta) has a negative
influence over the major HNF-4 box 2 as well as a positive influence o
ver the major HNF-1 box 4.