Unique and overlapping transcriptional roles of arylhydrocarbon receptor nuclear translocator (Arnt) and Arnt2 in xenobiotic and hypoxic responses.
Arnt and the homologous Arnt2 share a high degree of sequence similarity and are believed to function as obligate common partners for a number of basic helix-loop-helix (bHLH)-PAS transcription factors including arylhydrocarbon receptor (AhR) and HIFalpha. Genetic disruption of both Arnt and Arnt2 demonstrated both unique and overlapping functions in response to environmental stimuli and during mouse development. Either stably or transiently expressed Arnt/Arnt2 wild type and various mutants or chimeric constructs in Hepa1-c4 cells exhibit similar levels of hypoxic response element-driven reporter gene expression and the induction of endogenous Glut-1 through binding with HIFalpha in response to hypoxia. In contrast, we observed clear functional differences in the ability of Arnt and Arnt2 to induce xenobiotic response element-driven reporter and endogenous CYP1A1 gene expression. In contrast with Arnt, Arnt2 was practically incapable of interacting with ligand-activated AhR to induce the expression of target genes for xenobiotic-metabolizing enzymes in response to xenobiotics. The differential binding of AhR by Arnt and Arnt2 can be ascribed to a single His/Pro amino acid difference in the PASB region of Arnt and Arnt2, suggesting that the PASB/PASB interaction between bHLH-PAS transcription factors plays a selective role for their specific partner molecule.
Sekine
Hiroki
H
Center for Tsukuba Advanced Research Alliance and Institute of Basic Medical Sciences, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba 305-8577, Japan.
Mimura
Junsei
J
Yamamoto
Masayuki
M
Fujii-Kuriyama
Yoshiaki
Y
D000595:Amino Acid Sequence; D000818:Animals; D051784:Aryl Hydrocarbon Receptor Nuclear Translocator / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D051792:Basic Helix-Loop-Helix Proteins; D001665:Binding Sites; D015687:Cell Hypoxia / Q000235:genetics / Q000502:physiology; D002460:Cell Line; D019363:Cytochrome P-450 CYP1A1 / Q000235:genetics; D015870:Gene Expression; D051379:Mice; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary; D018336:Receptors, Aryl Hydrocarbon / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D014158:Transcription, Genetic; D015262:Xenobiotics / Q000378:metabolism / Q000633:toxicity
D051784:Aryl Hydrocarbon Receptor Nuclear Translocator; D051792:Basic Helix-Loop-Helix Proteins; D019363:Cytochrome P-450 CYP1A1; D018336:Receptors, Aryl Hydrocarbon; D011994:Recombinant Proteins; D015262:Xenobiotics; C484722:Ahr protein, mouse; C497397:Arnt protein, mouse; C099817:Arnt2 protein, mouse