© 2007 European Society for Medical Oncology
breast and ovarian cancer |
The estrogen receptor 
:insulin receptor substrate 1 complex in breast cancer: structure–function relationships
1 Dipartimento Farmaco Biologico, University of Calabria, Arcavacata di Rende, Cosenza
2 Section of Medical Oncology, Department of Surgical and Oncology, Università di Palermo, Palermo, Italy
3 Department of Neuroscience, Temple University School of Medicine, Philadelphia, PA, USA
4 Institut National de la Sante et de la Recherche Medicale, Unite Hormones et Cancer, Montpellier, France
5 Dipartimento di Biologia Cellulare, University of Calabria, Arcavacata di Rende Cosenza, Italy
6 Sbarro Institute for Cancer Research and Molecular Medicine, Temple University, Philadelphia, PA, USA
* Correspondence to: Dr D. Sisci, Dipartimento Farmaco Biologico, University of Calabria, 87100 Arcavacata di Rende, Cosenza, Italy. Tel: +39-0984-496211; Fax: +39-0984-496203; E-mail: dsisci{at}unical.it
Background: Insulin receptor substrate 1 (IRS-1) is a signaling molecule that exerts a key role in mediating cross talk between estrogen receptor 
(ER) and insulin-like growth factor 1 (IGF-1) in breast cancer cells. Previously, we demonstrated that a fraction of IRS-1 binds ER, translocates to the nucleus, and modulates ER-dependent transcription at estrogen response elements (ERE). Here, we studied structure–function relationships of the ER:IRS-1 complex under IGF-1 and/or estradiol (E2) stimulation.
Materials and methods: ER and IRS-1 deletion mutants were used to analyze structural and functional ER/IRS-1 interactions. IRS-1 binding to ERE and IRS-1 role in ER-dependent ERE transcription was examined by chromatin immunoprecipitation and gene reporter analysis, respectively. The requirement for IRS-1 in ER function was tested with RNAi technology.
Results: Nuclear translocation of IRS-1 was induced by E2, IGF-1, and a combination of both stimuli. ER/IRS-1 binding was direct and involved the activation function-1 (AF-1)/DNA binding domain (DBD) region of ER and two discrete regions of IRS-1 (the N-terminal pleckstrin homology domain and a region within the C-terminus). IRS-1 knock down abrogated IGF-1-dependent transcriptional activity of unliganded ER, but induced the activity of liganded ER.
Conclusions: ER/IRS-1 interactions are direct and involve the ER AF-1/DBD domain and IRS-1 domains mapping within N- and C-terminus. IRS-1 may act as a repressor of liganded ER and coactivator of unliganded ER.
Key words: estrogen receptor alpha (ERa), Insulin receptor substrate 1 (IRS-1), breast cancer
These authors contributed equally to this work.