Characterization of activating signal cointegrator-2 as a novel transcriptional coactivator of the xenobiotic nuclear receptor constitutive androstane receptor.
Activating signal cointegrator-2 (ASC-2) is a recently isolated transcriptional coactivator protein for a variety of different transcription factors, including many members of the nuclear receptor superfamily. In this report, we demonstrate that ASC-2 also serves as a coactivator of the xenobiotic nuclear receptor constitutive androstane receptor (CAR). First, transcriptional activation by CAR was enhanced by cotransfected ASC-2 in CV-1 and HeLa cells. In contrast, CAR transactivation was significantly impaired in HepG2 cells stably expressing specific small interfering RNA directed against ASC-2. Consistent with these results, chromatin immunoprecipitation experiments revealed that ASC-2 is recruited to the known CAR target genes in a ligand-dependent manner. Secondly, CAR specifically interacted with the first LXXLL motif of ASC-2, and these interactions were stimulated by CAR agonist 1,4-bis[2-(3,5-dichloropyridyloxy)]benzene and repressed by CAR inverse agonist androstanol, suggesting that this motif may mediate the interactions of ASC-2 and CAR in vivo. In support of this idea, DN1, a fragment of ASC-2 encompassing the first LXXLL motif, suppressed CAR transactivation, and coexpressed ASC-2 but not other LXXLL-type coactivators such as thyroid hormone receptor-associated protein 220 reversed this repression. Finally, CAR was recently found to play a pivotal role in effecting the severe acetaminophen-induced liver damage. Interestingly, transgenic mice expressing DN1 were resistant to the acetaminophen-induced hepatotoxicity and expression of a series of the known CAR target genes was specifically repressed in these transgenic mice. Taken together, these results strongly suggest that ASC-2 is a bona fide coactivator of the xenobiotic nuclear receptor CAR and mediate the specific xenobiotic response by CAR in vivo.
Choi
Eunho
E
Division Diabetes, Endocrinology & Metabolism, Department of Medicine, Baylor College of Medicine, Houston, TX 77030, USA.
Lee
Seunghee
S
Yeom
Seon-Yong
SY
Kim
Geun Hyang
GH
Lee
Jae Woon
JW
Kim
Seung-Whan
SW
D000082:Acetaminophen / Q000378:metabolism / Q000633:toxicity*; D020816:Amino Acid Motifs; D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases / Q000235:genetics; D047369:Chromatin Immunoprecipitation; D000090702:Constitutive Androstane Receptor; D065702:Cytochrome P-450 CYP2B6; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics; D005786:Gene Expression Regulation; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D008099:Liver / Q000187:drug effects*; D051379:Mice; D008822:Mice, Transgenic; D056918:Nuclear Receptor Coactivators; D010089:Oxidoreductases, N-Demethylating / Q000235:genetics; D025941:Protein Interaction Mapping; D034622:RNA Interference; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics / Q000378:metabolism*; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D015262:Xenobiotics / Q000378:metabolism / Q000633:toxicity
D000090702:Constitutive Androstane Receptor; D047908:Intracellular Signaling Peptides and Proteins; C486559:NCOA6 protein, human; D056918:Nuclear Receptor Coactivators; D018160:Receptors, Cytoplasmic and Nuclear; D015534:Trans-Activators; D014157:Transcription Factors; D015262:Xenobiotics; D000082:Acetaminophen; D003577:Cytochrome P-450 Enzyme System; D001189:Aryl Hydrocarbon Hydroxylases; C585599:CYP2B6 protein, human; C104464:CYP3A protein, human; D065702:Cytochrome P-450 CYP2B6; D051544:Cytochrome P-450 CYP3A; D010089:Oxidoreductases, N-Demethylating