title: Nuclear receptor CAR represses TNFalpha-induced cell death by interacting with the anti-apoptotic GADD45B.
abstract: BACKGROUND
  Phenobarbital (PB) is the most well-known among numerous non-genotoxic carcinogens that cause the development of hepatocellular carcinoma (HCC). PB activates nuclear xenobiotic receptor Constitutive Active/Androstane Receptor (CAR; NR1I3) and this activation is shown to determine PB promotion of HCC in mice. The molecular mechanism of CAR-mediated tumor promotion, however, remains elusive at the present time. Here we have identified Growth Arrest and DNA Damage-inducible 45beta (GADD45B) as a novel CAR target, through which CAR represses cell death.
  
  
  RESULTS
  PB activation of nuclear xenobiotic receptor CAR is found to induce the Gadd45b gene in mouse liver throughout the development of HCC as well as in liver tumors. Given the known function of GADD45B as a factor that represses Mitogen-activated protein Kinase Kinase 7 - c-Jun N-terminal Kinase (MKK7-JNK) pathway-mediated apoptosis, we have now demonstrated that CAR interacts with GADD45B to repress Tumor Necrosis Factor alpha ( TNFalpha)-induced JNK1 phosphorylation as well as cell death. Primary hepatocytes, prepared from Car(+/+), Car(-/-), Gadd45b(+/+) and Gadd45b(-/-) mice, were treated with TNFalpha and Actinomycin D to induce phosphorylation of JNK1 and cell death. Co-treatment with the CAR activating ligand TCPOBOP (1,4 bis[2-(3,5-dichloropyridyloxy)]benzene) has resulted in repression of both phosphorylation and cell death in the primary hepatocytes from Car(+/+) but not Car(-/-) mice. Repression by TCPOBOP was not observed in those prepared from Gadd45b(-/-) mice. In vitro protein-protein interaction and phosphorylation assays have revealed that CAR interacts with MKK7 and represses the MKK7-mediated phosphorylation of JNK1.
  
  
  CONCLUSIONS
  CAR can form a protein complex with GADD45B, through which CAR represses MKK7-mediated phosphorylation of JNK1. In addition to activating the Gadd45b gene, CAR may repress death of mouse primary hepatocytes by forming a GADD45B complex and repressing MKK7-mediated phosphorylation of JNK1. The present finding that CAR can repress cell death via its interaction with GADD45B provides an insight for further investigations into the CAR-regulated molecular mechanism by which PB promotes development of HCC.
authors.affiliation: Laboratory of Reproductive and Developmental Toxicology, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, North Carolina, United States of America.
authors.forename: Yukio
authors.initials: Y
authors.lastname: Yamamoto
authors.forename: Rick
authors.initials: R
authors.lastname: Moore
authors.forename: Richard A
authors.initials: RA
authors.lastname: Flavell
authors.forename: Binfeng
authors.initials: B
authors.lastname: Lu
authors.forename: Masahiko
authors.initials: M
authors.lastname: Negishi
mesh_terms: D000818:Animals; D000943:Antigens, Differentiation / Q000378:metabolism*; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism*; D016923:Cell Death; D000090702:Constitutive Androstane Receptor; D022781:Hepatocytes / Q000166:cytology* / Q000378:metabolism; D008099:Liver; D048688:MAP Kinase Kinase 7 / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D048055:Mitogen-Activated Protein Kinase 8 / Q000378:metabolism*; D010634:Phenobarbital / Q000494:pharmacology; D010766:Phosphorylation; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism / Q000502:physiology*; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*; D000097642:GADD45 Proteins
chemical_list: D000943:Antigens, Differentiation; D051017:Apoptosis Regulatory Proteins; D000090702:Constitutive Androstane Receptor; D048688:MAP Kinase Kinase 7; D048055:Mitogen-Activated Protein Kinase 8; D010634:Phenobarbital; D018160:Receptors, Cytoplasmic and Nuclear; D014409:Tumor Necrosis Factor-alpha; C490125:Gadd45b protein, mouse; D000097642:GADD45 Proteins; C000716328:Nr1i3 protein, mouse
references.citation: Oncogene. 1991 Jan;6(1):165-7
references.pmid: 1899477
references.citation: Mol Endocrinol. 2005 Jun;19(6):1646-53
references.pmid: 15831521
references.citation: Mol Cell Biol. 1998 Oct;18(10):5652-8
references.pmid: 9742082
references.citation: Biochem J. 2007 Nov 1;407(3):373-81
references.pmid: 17635106
references.citation: Cancer Res. 2004 Oct 15;64(20):7197-200
references.pmid: 15492232
references.citation: Nature. 1978 Feb 2;271(5644):456-8
references.pmid: 24178
references.citation: J Biol Chem. 2003 Mar 28;278(13):11344-50
references.pmid: 12551939
references.citation: Genes Dev. 2004 Apr 1;18(7):830-50
references.pmid: 15082532
references.citation: Cell. 2006 Feb 10;124(3):601-13
references.pmid: 16469705
references.citation: Science. 1993 Feb 19;259(5098):1161-5
references.pmid: 8382376
references.citation: Nature. 2004 Sep 23;431(7007):461-6
references.pmid: 15329734
references.citation: Cell. 2003 Jan 24;112(2):181-92
references.pmid: 12553907
references.citation: J Clin Invest. 2008 May;118(5):1911-23
references.pmid: 18382767
references.citation: Mol Pharmacol. 2002 Jan;61(1):1-6
references.pmid: 11752199
references.citation: Nature. 2000 Oct 19;407(6806):920-3
references.pmid: 11057673
references.citation: Blood. 1994 Aug 15;84(4):1036-42
references.pmid: 8049423
references.citation: Nat Immunol. 2004 Jan;5(1):38-44
references.pmid: 14691480
references.citation: Mol Cell Biol. 2004 Sep;24(18):7931-40
references.pmid: 15340055
references.citation: J Biol Chem. 2007 Jun 29;282(26):19029-41
references.pmid: 17485467
references.citation: Hepatology. 2004 Oct;40(4):981-8
references.pmid: 15382178
references.citation: Nat Cell Biol. 2004 Feb;6(2):146-53
references.pmid: 14743220
references.citation: Mol Pharmacol. 2003 Nov;64(5):1069-75
references.pmid: 14573755
references.citation: Nature. 2001 Nov 15;414(6861):308-13
references.pmid: 11713530
references.citation: J Biol Chem. 2003 Jan 24;278(4):2701-12
references.pmid: 12421825
references.citation: Mol Cell Biol. 1994 Apr;14(4):2361-71
references.pmid: 8139541
references.citation: Hepatology. 2005 Nov;42(5):1118-26
references.pmid: 16231353
references.citation: J Immunol. 1994 Aug 15;153(4):1778-88
references.pmid: 8046244
references.citation: J Biol Chem. 2007 Mar 30;282(13):9768-9776
references.pmid: 17267396
references.citation: Mol Endocrinol. 2003 Jul;17(7):1268-82
references.pmid: 12663745
references.citation: J Biol Chem. 1999 Mar 5;274(10):6043-6
references.pmid: 10037683