title: Estrogen receptor-alpha regulates the degradation of insulin receptor substrates 1 and 2 in breast cancer cells.
abstract: In breast cancer cells, 17-beta-estradiol (E2) upregulates the expression of insulin receptor substrate 1 (IRS-1), a molecule transmitting insulin-like growth factor-I (IGF-I) signals through the PI-3K/Akt survival pathways. The stimulation of IRS-1 by E2 has been documented on the transcriptional level. Here we studied whether the expression of estrogen receptor (ER)-alpha affects IRS molecules post-transcriptionally. We used ER-alpha-negative MDA-MB-231 breast cancer cells and MDA-MB-231 cells with re-expressed ER-alpha. In MDA-MB-231 cells cultured under serum-free conditions, IRS-1 and IRS-2 were degraded through the 26S proteasome and calpain pathways. Re-expression of ER-alpha in MDA-MB-231 cells correlated with enhanced stability of IRS molecules. This effect coincided with significantly reduced ubiquitination of IRS-1 and IRS-2, but did not involve increased IRS-1 and IRS-2 transcription. The interference of ER-alpha with IRS-1 and IRS-2 turnover could rely on the competition for common degradation pathways, as in MDA-MB-231/ER cells, ER-alpha processing was blocked by proteasome and calpain inhibitors. Notably, a fraction of the cytosolic ER-alpha colocalized and coprecipitated with IRS-1 and IRS-2, indicating a possible common destination for these proteins. The stabilization of IRS-1 in MDA-MB-231/ER cells was paralleled by the upregulation of the IRS-1/Akt/GSK-3 pathway and improved survival in the presence of IGF-I, whereas IRS-2 was not involved in IGF-I signaling.
authors.affiliation: Kimmel Cancer Center, Thomas Jefferson University, Philadelphia, PA 19107, USA.
authors.forename: Catia
authors.initials: C
authors.lastname: Morelli
authors.forename: Cecilia
authors.initials: C
authors.lastname: Garofalo
authors.forename: Monica
authors.initials: M
authors.lastname: Bartucci
authors.forename: Eva
authors.initials: E
authors.lastname: Surmacz
mesh_terms: D015153:Blotting, Western; D001943:Breast Neoplasms / Q000378:metabolism*; D002455:Cell Division; D002470:Cell Survival; D003546:Cysteine Endopeptidases / Q000378:metabolism; D004721:Endoplasmic Reticulum; D047628:Estrogen Receptor alpha; D006801:Humans; D055504:Insulin Receptor Substrate Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008024:Ligands; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D009097:Multienzyme Complexes / Q000378:metabolism; D010447:Peptide Hydrolases / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism*; D011233:Precipitin Tests; D046988:Proteasome Endopeptidase Complex; D011960:Receptors, Estrogen / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D013997:Time Factors; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured; D025801:Ubiquitin / Q000378:metabolism
chemical_list: D047628:Estrogen Receptor alpha; C526292:IRS1 protein, human; C526297:IRS2 protein, human; D055504:Insulin Receptor Substrate Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008024:Ligands; D009097:Multienzyme Complexes; D010750:Phosphoproteins; D011960:Receptors, Estrogen; D025801:Ubiquitin; D010447:Peptide Hydrolases; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease