© The Author 2008. Published by Oxford University Press on behalf of the Society of Toxicology. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org
Why Does ARNT2 Behave Differently from ARNT?
Department of Pathology and Laboratory Medicine, Jonsson Comprehensive Cancer Center, and Molecular Toxicology Program, University of California at Los Angeles, California 90095
1 To whom correspondence should be addressed at the University of California—Los Angeles, Pathology, BOX 951732, 10833 Le Conte Ave, 13-244 Factor Bldg, Los Angeles, CA 90095-1732. Fax: (300) 794-9272. E-mail: ohank@mednet.ucla.edu.
Received February 8, 2008; accepted February 10, 2008
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The aryl hydrocarbon receptor nuclear translocator (ARNT) is a member of the bHLH PAS (basic helix–loop–helix Period/ARNT/Single-minded) family of transcription factors. It is the obligatory dimerization partner for many other members of this family, including the aryl hydrocarbon receptor (AHR) and hypoxia-inducible factors 1
and 2 (HIF-1/2). Agonists for AHR include a variety of environmentally important toxicants, including 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), and polycyclic aromatic hydrocarbons (PAHs) such as 3-methylcholanthrene (3MC) and benzo[a]pyrene (BAP). The mechanism of transcriptional activation by AHR is best understood for the CYP1A1 gene. After binding ligand, AHR translocates into the nucleus and dimerizes with ARNT. The AHR/ARNT heterodimer then binds to specific regulatory sequences, termed xenobiotic response elements (XREs), in the enhancer regions of CYP1A1 (and other responsive genes). Transcriptional coactivators the associated with the AHR/ARNT dimer as it resides on the enhancer region. These coactivators in turn direct the recruitment of
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