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Phenobarbital regulates nuclear expression of HNF‐4α in mouse and rat hepatocytes independent of CAR and PXR
Author(s) -
Bell Aaron W.,
Michalopoulos George K.
Publication year - 2006
Publication title -
hepatology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.488
H-Index - 361
eISSN - 1527-3350
pISSN - 0270-9139
DOI - 10.1002/hep.21234
Subject(s) - pregnane x receptor , phenobarbital , constitutive androstane receptor , nuclear receptor , hepatocyte nuclear factor 4 , hepatocyte nuclear factors , hepatocyte , chemistry , endocrinology , gene expression , medicine , drug metabolism , biology , metabolism , biochemistry , transcription factor , gene , in vitro
Phenobarbital is a lipophilic molecule used as a sedative and antiepileptic drug that elicits a multitude of effects in the liver, including gross liver enlargement, hepatocyte hypertrophy, and induced expression of drug‐metabolizing enzymes and other liver‐specific genes. The constitutive androstane receptor (CAR; NR1I3) and to a lesser extent the pregnane X receptor (PXR; NR1I2) are responsible for mediating induction of many phenobarbital‐responsive genes. However, CAR‐mediated transcriptional control of some genes is critically dependent on hepatocyte nuclear factor 4 alpha (HNF‐4α; NR2A1), which itself regulates multiple liver‐specific genes involved in hepatic growth, metabolism, and differentiation. We studied the effects of phenobarbital on HNF‐4α expression in hepatocytes and provide evidence that HNF‐4α nuclear expression is regulated in response to phenobarbital. Real‐time polymerase chain reaction analyses revealed that HNF‐4α mRNA is modestly up‐regulated by phenobarbital. In addition, nuclear expression of HNF‐4α protein is significantly elevated 3 hours after the administration of phenobarbital in wild‐type, CAR −/− , and CAR −/− /PXR −/− mice. In vitro analysis revealed that phenobarbital‐induced HNF‐4α expression is both time‐ and dose dependent. In addition, the phosphatase inhibitor okadaic acid and the Ca 2+ /calmodulin‐dependent protein kinase II inhibitor KN62 block nuclear induction of HNF‐4α by phenobarbital. Furthermore, HNF‐4α nuclear expression is enhanced by inhibition of cyclic AMP–dependent protein kinase A. In conclusion , induced nuclear expression of HNF‐4α and CAR is an integral part of the phenobarbital response, aimed at coordinated regulation of genes involved in drug metabolism and detoxification as well as maintenance of liver function. (H EPATOLOGY 2006;44:186–194.)