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Molecular and Cellular Biology, July 2005, p. 5317-5328, Vol. 25, No. 13
0270-7306/05/$08.00+0     doi:10.1128/MCB.25.13.5317-5328.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Aryl Hydrocarbon Receptor-Mediated Transcription: Ligand-Dependent Recruitment of Estrogen Receptor {alpha} to 2,3,7,8-Tetrachlorodibenzo- p-Dioxin-Responsive Promoters

Jason Matthews,1*,{dagger} Björn Wihlén,1,{dagger} Jane Thomsen,1 and Jan-Åke Gustafsson1,2

Department of Biosciences at Novum, Karolinska Institutet, Novum S-14157,1 Department of Medical Nutrition, Karolinska Institutet, Novum S-14186, Huddinge Sweden2

Received 1 September 2004/ Returned for modification 30 November 2004/ Accepted 21 March 2005

Using chromatin immunoprecipitation assays, we studied the 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-mediated recruitment of the aryl hydrocarbon receptor (AhR) and several coregulators to the CYP1A1 promoter. AhR displayed a time-dependent recruitment, reaching a peak at 75 min and maintaining promoter occupancy for the remainder of the time course. Recruitment of AhR was followed by TIF2/SRC2, which preceded CBP, histone H3 acetylation, and RNA polymerase II (RNAPII). Simultaneous recruitment to the enhancer and the TATA box region suggests the formation of a large multiprotein complex bridging the two promoter regions. Interestingly, estrogen receptor {alpha} (ER{alpha}) displayed a TCDD- and time-dependent recruitment to the CYP1A1 promoter, which was increased by cotreatment with estradiol. Transfection in HuH7 human liver cells confirmed previously reported ER{alpha} enhancement of AhR activity. In contrast, TCDD did not induce the recruitment of ER{alpha} to the estrogen-responsive pS2 promoter, and after 120 min of cotreatment with estradiol, ER{alpha} is still present on the CYP1A1 promoter but no longer at pS2. RNA interference studies with T47D cells support a role for ER{alpha} in TCDD-dependent CYP1A1 expression. Our data suggest that ER{alpha} acts as a coregulator of AhR-mediated transcriptional activation and that the recruitment of ER{alpha} by AhR represents a novel mechanism AhR-ER{alpha} cross talk.

* Corresponding author. Mailing address: Department of Biosciences at Novum, Karolinska Institutet, Huddinge 14157, Sweden. Phone: 46-8-6083339. Fax: 46-8-7745538. E-mail: jason.matthews{at}biosci.ki.se.

{dagger} J.M. and B.W. contributed equally to this work.

Molecular and Cellular Biology, July 2005, p. 5317-5328, Vol. 25, No. 13
0022-538X/05/$08.00+0     doi:10.1128/MCB.25.13.5317-5328.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.



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