The estrogen receptor alpha:insulin receptor substrate 1 complex in breast cancer: structure-function relationships.
BACKGROUND
Insulin receptor substrate 1 (IRS-1) is a signaling molecule that exerts a key role in mediating cross talk between estrogen receptor alpha (ERalpha) and insulin-like growth factor 1 (IGF-1) in breast cancer cells. Previously, we demonstrated that a fraction of IRS-1 binds ERalpha, translocates to the nucleus, and modulates ERalpha-dependent transcription at estrogen response elements (ERE). Here, we studied structure-function relationships of the ERalpha:IRS-1 complex under IGF-1 and/or estradiol (E2) stimulation.


METHODS
ERalpha and IRS-1 deletion mutants were used to analyze structural and functional ERalpha/IRS-1 interactions. IRS-1 binding to ERE and IRS-1 role in ERalpha-dependent ERE transcription was examined by chromatin immunoprecipitation and gene reporter analysis, respectively. The requirement for IRS-1 in ERalpha function was tested with RNAi technology.


RESULTS
Nuclear translocation of IRS-1 was induced by E2, IGF-1, and a combination of both stimuli. ERalpha/IRS-1 binding was direct and involved the activation function-1 (AF-1)/DNA binding domain (DBD) region of ERalpha 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 ERalpha, but induced the activity of liganded ERalpha.


CONCLUSIONS
ERalpha/IRS-1 interactions are direct and involve the ERalpha AF-1/DBD domain and IRS-1 domains mapping within N- and C-terminus. IRS-1 may act as a repressor of liganded ERalpha and coactivator of unliganded ERalpha.
Sisci
D
D
Dipartimento Farmaco Biologico, University of Calabria, Arcavacata di Rende, Cosenza. dsisci@unical.it
Morelli
C
C
Cascio
S
S
Lanzino
M
M
Garofalo
C
C
Reiss
K
K
Garcia
M
M
Russo
A
A
Andò
S
S
Surmacz
E
E
D021581:Active Transport, Cell Nucleus / Q000235:genetics; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D004958:Estradiol / Q000502:physiology; D047628:Estrogen Receptor alpha / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D005260:Female; D006801:Humans; D055504:Insulin Receptor Substrate Proteins; D007334:Insulin-Like Growth Factor I / Q000502:physiology; D010446:Peptide Fragments / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D010750:Phosphoproteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D011485:Protein Binding / Q000235:genetics; D017434:Protein Structure, Tertiary / Q000235:genetics; D011972:Receptor, Insulin / Q000502:physiology; D017471:Receptors, Interferon / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D012097:Repressor Proteins / Q000502:physiology; D013329:Structure-Activity Relationship
D047628:Estrogen Receptor alpha; C086185:IFNGR2 protein, human; C526292:IRS1 protein, human; D055504:Insulin Receptor Substrate Proteins; D010446:Peptide Fragments; D010750:Phosphoproteins; D017471:Receptors, Interferon; D012097:Repressor Proteins; D004958:Estradiol; D007334:Insulin-Like Growth Factor I; D011972:Receptor, Insulin