Hepatic HNF4α deficiency induces periportal expression of glutamine synthetase and other pericentral enzymes

Abstract

In liver, most genes are expressed with a porto-central gradient. The transcription factor hepatic nuclear-factor4␣ (HNF4␣) is associated with 12% of the genes in adult liver, but its involvement in zonation of gene expression has not been investigated. A putative HNF4␣-response element in the upstream enhancer of glutamine synthetase (GS), an exclusively pericentral enzyme, was protected against DNase-I and interacted with a protein that is recognized by HNF4␣-specific antiserum. Chromatin-immunoprecipitation assays of HNF4␣-deficient (H4LivKO) and control (H4Flox) livers with HNF4␣ antiserum precipitated the GS upstream enhancer DNA only from H4Flox liver. Identical results were obtained with a histone-deacetylase1 (HDAC1) antibody, but antibodies against HDAC3, SMRT and SHP did not precipitate the GS upstream enhancer. In H4Flox liver, GS, ornithine aminotransferase (OAT) and thyroid hormone-receptor ␤1 ( T he development and maintenance of liver architecture and function is regulated by liver-enriched transcription factors. 1 One of these, hepatic nuclear factor 4␣ (HNF4␣; NR2A1) is expressed at high levels in liver, kidney, intestine, and pancreas 2,3 and binds to the promoter of 12% of genes that are expressed in adult liver. 4 HNF4␣ is an orphan member of the nuclear-receptor superfamily. 2 Depending on chain length and degree of saturation, 5 fatty acyl-coenzyme A thioesters may act as agonistic or antagonistic factors, but whether or not these thioesters function as ligands remains unsettled. 2,[6][7][8] Transcriptional regulation by HNF4␣ is accomplished by interactions with coactivator or corepressor mediators (e.g., GRIP1, SRC-1, CBP/p300, SMRT). 6,7,9,10 The resulting coactivator or corepressor complexes have intrinsic histone acetyltransferase (HAT) and histone deacetylase (HDAC) activity, respectively. Histone modifications play an important role in the regulation of the

Suppression of Hepatocyte Proliferation by Hepatocyte Nuclear Factor 4α in Adult Mice

“…This response is transitory in nature because microarray analysis indicated that changes in cell cycle control and other genes involved in hepatocyte proliferation were associated with the Hnf4a F/F;AlbERT2cre knock-out and not with the Alb-Hnf4a Ϫ/Ϫ mice in which only small regenerating foci of hepatic periportal oval cells were observed previously (42). This latter finding was confirmed in the present study using BrdU incorporation.…”

The acyl-CoA thioesterase I is regulated by PPARα and HNF4α via a distal response element in the promoter

“…As both of these receptors have a positive effect on the Acot1 promoter, one would expect that the addition of activated PPARa and HNF4a may result in a synergistic increase in promoter activity. However, transcriptional regulation by HNF4a is accomplished by interactions with various coactivators or corepressors, such as histone deacetylase 1 (a corepressor), and a very recent study by Stanulovic et al (29) showed that both HNF4a and histone deacetylase 1 are present on an upstream enhancer element of the glutamine synthetase promoter, which results in the suppression of glutamine synthetase expression in liver periportal areas. Therefore, the competition between HNF4a and PPARa for binding to the Acot1 DR1 is likely a complicated interplay between coactivators, corepressors, and ligand availability.…”

“…6A), although some weak signal was detected in the knockout liver extracts. This may be attributable to the fact that HNF4a is a conditional liver-specific knockout and there is some very low amount of HNF4a protein present in the nucleus (29). EMSA was also performed using in vitrotranslated HNF4a, and binding to the DR1 was competed out using a 50-fold molar excess of cold probe and supershifted using an HNF4a antibody (Fig.…”

Morphogenetic competence of HNF4α-deficient mouse hepatic cells

“…Clonal proliferation of positive nuclei can occasionally be observed at e18.5 in null livers (Fig. 6A and see also [19]). …”