BRCA1 transcriptional activity is enhanced by interactions between its AD1 domain and AhR.
OBJECTIVE
We previously reported that BRCA1 interacts with aryl hydrocarbon receptor nuclear translocator (ARNT) and that this interaction affects TCDD-induced CYP1A1 gene expression (Kang et al., J Biol Chem 281:14654-14662, 2006). In this study we continue this investigation and begin to define the significance of this interaction for the regulation of stress-induced transcription.


METHODS
Immunoprecipitations (IPs), western blot (WB) analysis, GST pull-down assays and promoter reporter assays were used to investigate whether the aryl hydrocarbon receptor (AhR) can regulate transcription that is dependent on the activation domain 1 (AD1) domain of BRCA1.


RESULTS
We show that AhR, a transcription factor, can bind specifically to AD1 in the C-terminal region of BRCA1 and affect BRCA1's ability to regulate transcription activity. We found that xenobiotics that positively and negatively affect AhR's activity as a transcription factor (e.g., dioxin and alpha-naphthoflavone, respectively), have similar effects on AhR's ability to affect AD1-domain-dependent transcription. These physical and functional AhR-AD1 interactions may require the coiled-coil motif in AD1 because point-mutations in this motif reduce these interactions.


CONCLUSIONS
Xenobiotic-activated AhR can function in two ways, as a component of the AhR/ARNT transcription factor and a regulator of AD1-dependent transcription. Consequently, BRCA1 has two distinct mechanisms for sensing xenobiotics and regulating AhR-dependent stress responses to these xenobiotics. We speculate that the normal functioning of this interaction could play a role in BRCA1's tumor suppressing ability.
Kang
Hyo Jin
HJ
Department of Oncology, Lombardi Comprehensive Cancer Center, Georgetown University, 3970 Reservoir Road, NW, Washington, DC 20057, USA.
Kim
Hee Jeong
HJ
Cho
Chi-Heum
CH
Hu
Yanfen
Y
Li
Rong
R
Bae
Insoo
I
D019313:BRCA1 Protein / Q000737:chemistry* / Q000494:pharmacology; D001571:Benzoflavones / Q000494:pharmacology; D001667:Binding, Competitive; D045744:Cell Line, Tumor / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects / Q000502:physiology*; D017930:Genes, Reporter; D006801:Humans; D009363:Neoplasm Proteins / Q000737:chemistry* / Q000494:pharmacology; D000072317:Polychlorinated Dibenzodioxins / Q000494:pharmacology; D011485:Protein Binding; D025941:Protein Interaction Mapping; D017434:Protein Structure, Tertiary; D016755:Proto-Oncogene Proteins c-jun / Q000378:metabolism; D018336:Receptors, Aryl Hydrocarbon / Q000737:chemistry* / Q000187:drug effects; D014158:Transcription, Genetic / Q000187:drug effects / Q000502:physiology*
D019313:BRCA1 Protein; C492913:BRCA1 protein, human; D001571:Benzoflavones; D009363:Neoplasm Proteins; D000072317:Polychlorinated Dibenzodioxins; D016755:Proto-Oncogene Proteins c-jun; D018336:Receptors, Aryl Hydrocarbon; C011512:alpha-naphthoflavone