Estrogen receptor-alpha regulates the degradation of insulin receptor substrates 1 and 2 in breast cancer cells

Oncogene. 2003 Jun 26;22(26):4007-16. doi: 10.1038/sj.onc.1206436.


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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Blotting, Western
  • Breast Neoplasms / metabolism*
  • Cell Division
  • Cell Survival
  • Cysteine Endopeptidases / metabolism
  • Endoplasmic Reticulum
  • Estrogen Receptor alpha
  • Humans
  • Insulin Receptor Substrate Proteins
  • Intracellular Signaling Peptides and Proteins
  • Ligands
  • Microscopy, Confocal
  • Microscopy, Fluorescence
  • Multienzyme Complexes / metabolism
  • Peptide Hydrolases / metabolism
  • Phosphoproteins / metabolism*
  • Precipitin Tests
  • Proteasome Endopeptidase Complex
  • Receptors, Estrogen / metabolism*
  • Reverse Transcriptase Polymerase Chain Reaction
  • Signal Transduction
  • Time Factors
  • Transcription, Genetic
  • Tumor Cells, Cultured
  • Ubiquitin / metabolism


  • Estrogen Receptor alpha
  • IRS1 protein, human
  • IRS2 protein, human
  • Insulin Receptor Substrate Proteins
  • Intracellular Signaling Peptides and Proteins
  • Ligands
  • Multienzyme Complexes
  • Phosphoproteins
  • Receptors, Estrogen
  • Ubiquitin
  • Peptide Hydrolases
  • Cysteine Endopeptidases
  • Proteasome Endopeptidase Complex
  • ATP dependent 26S protease