Hepatic HNF4alpha deficiency induces periportal expression of glutamine synthetase and other pericentral enzymes.
In liver, most genes are expressed with a porto-central gradient. The transcription factor hepatic nuclear-factor4alpha (HNF4alpha) is associated with 12% of the genes in adult liver, but its involvement in zonation of gene expression has not been investigated. A putative HNF4alpha-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 HNF4alpha-specific antiserum. Chromatin-immunoprecipitation assays of HNF4alpha-deficient (H4LivKO) and control (H4Flox) livers with HNF4alpha antiserum precipitated the GS upstream enhancer DNA only from H4Flox liver. Identical results were obtained with a histone-deacetylasel (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 beta1 (TRbeta1) were exclusively expressed in pericentral hepatocytes. In H4LivKO liver, this pericentral expression remained unaffected, but the genes were additionally expressed in the periportal hepatocytes, albeit at a lower level. The expression of the periportal enzyme phosphoenolpyruvate carboxykinase had declined in HNF4alpha-deficient hepatocytes. GS-negative cells, which were present as single, large hepatocytes or as groups of small cells near portal veins, did express HNF4alpha. Clusters of very small GS- and HNF4alpha-negative, and PCNA- and OV6-positive cells near portal veins were contiguous with streaks of brightly HNF4alpha-positive, OV6-, PCNA-, and PEPCK-dim cells.


CONCLUSIONS
Our findings show that HNF4alpha suppresses the expression of pericentral proteins in periportal hepatocytes, possibly via a HDAC1-mediated mechanism. Furthermore, we show that HNF4alpha deficiency induces foci of regenerating hepatocytes.
Stanulović
Vesna S
VS
AMC Liver Center, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.
Kyrmizi
Irene
I
Kruithof-de Julio
Marianna
M
Hoogenkamp
Maarten
M
Vermeulen
Jacqueline L M
JL
Ruijter
Jan M
JM
Talianidis
Iannis
I
Hakvoort
Theodorus B M
TB
Lamers
Wouter H
WH
D000818:Animals; D001483:Base Sequence; D004247:DNA / Q000378:metabolism; D004742:Enhancer Elements, Genetic / Q000235:genetics; D005974:Glutamate-Ammonia Ligase / Q000235:genetics / Q000378:metabolism*; D051557:Hepatocyte Nuclear Factor 4 / Q000235:genetics / Q000378:metabolism*; D022781:Hepatocytes / Q000378:metabolism; D008099:Liver / Q000166:cytology / Q000378:metabolism*; D008115:Liver Regeneration / Q000502:physiology; D051379:Mice; D018345:Mice, Knockout; D008969:Molecular Sequence Data; D009953:Ornithine-Oxo-Acid Transaminase / Q000235:genetics / Q000378:metabolism*; D019764:Phosphoenolpyruvate Carboxykinase (ATP) / Q000378:metabolism; D018809:Proliferating Cell Nuclear Antigen / Q000378:metabolism; D051381:Rats; D037042:Thyroid Hormone Receptors beta / Q000235:genetics / Q000378:metabolism*
D051557:Hepatocyte Nuclear Factor 4; C496593:Hnf4a protein, mouse; D018809:Proliferating Cell Nuclear Antigen; D037042:Thyroid Hormone Receptors beta; D004247:DNA; D009953:Ornithine-Oxo-Acid Transaminase; D019764:Phosphoenolpyruvate Carboxykinase (ATP); D005974:Glutamate-Ammonia Ligase