PT  - JOURNAL ARTICLE
AU  - Satu Arpiainen
AU  - Françoise Raffalli-Mathieu
AU  - Matti A. Lang
AU  - Olavi Pelkonen
AU  - Jukka Hakkola
TI  - Regulation of the <em>Cyp2a5</em> Gene Involves an Aryl Hydrocarbon Receptor-Dependent Pathway
AID  - 10.1124/mol.104.008078
DP  - 2005 Apr 01
TA  - Molecular Pharmacology
PG  - 1325--1333
VI  - 67
IP  - 4
4099  - http://molpharm.aspetjournals.org/content/67/4/1325.short
4100  - http://molpharm.aspetjournals.org/content/67/4/1325.full
SO  - Mol Pharmacol2005 Apr 01; 67
AB  - We have investigated the role of the aryl hydrocarbon receptor (AHR) in the regulation of the Cyp2a5 gene. The C57BL/6 and DBA/2 mouse strains with a genetically determined difference in AHR function were used to study the CYP2A5 induction by typical AHR ligands, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and 3-methylcholanthrene. The CYP2A5 mRNA up-regulation in these mouse strains showed a difference in response, typical for AHR-regulated genes, both by TCDD in cultured primary hepatocytes and by 3-methylcholanthrene in vivo. In primary hepatocytes, TCDD caused a 3-fold elevation of the CYP2A5 protein level and a similar induction of the CYP2A5-catalyzed coumarin 7-hydroxylation activity. In reporter gene assays, the Cyp2a5 promoter region -3033 to +10 mediated a 2- to 5-fold induction of luciferase activity by TCDD treatment in primary hepatocytes and in Hepa-1 hepatoma cells with an intact AHR/AHR nuclear translocator (ARNT) complex. In Hepa-1 variant cell lines with deficiencies in the AHR/ARNT complex, the absence of ARNT abolished the induction. A putative AHR response element (XRE) was identified in the Cyp2a5 promoter at the position -2514 to -2492 and found to interact with the AHR/ARNT heterodimer. Transfection experiments combined with mutation of the XRE site indicated that the site partly mediates the TCDD induction of Cyp2a5. An additional AHR-dependent mechanism also regulates the proximal promoter of the Cyp2a5 gene. In conclusion, our studies showed that AHR ligands up-regulate Cyp2a5 transcriptionally by an AHR/ARNT-dependent mechanism and established Cyp2a5 as a novel AHR-regulated gene.