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Oncogene (2003) 22, 40074016
& 2003 Nature Publishing Group All rights reserved 0950-9232/03 $25.00www.nature.com/oncEstrogen receptor-a regulates the degradation of insulin receptor substrates
1 and 2 in breast cancer cellsCatia Morelli1,2, Cecilia Garofalo1,2, Monica Bartucci1,2 and Eva Surmacz*,11Kimmel Cancer Center, Thomas Jefferson University, Philadelphia, PA 19107, USA; 2Postgraduate School in Clinical Pathology,
Faculty of Pharmacy, University of Calabria, ItalyIn breast cancer cells, 17-b-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)-a affects IRS
molecules post-transcriptionally. We used ER-a-negative
MDA-MB-231 breast cancer cells and MDA-MB-231
cells with re-expressed ER-a. 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-a in MDA-MB-231 cells
correlated with enhanced stability of IRS molecules. This
effect coincided with signicantly reduced ubiquitination
of IRS-1 and IRS-2, but did not involve increased IRS-1
and IRS-2 transcription. The interference of ER-a with
IRS-1 and IRS-2 turnover could rely on the competition
for common degradation pathways, as in MDA-MB-231/
ER cells, ER-a processing was blocked by proteasome and
calpain inhibitors. Notably, a fraction of the cytosolic ER-
a 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.Oncogene (2003) 22, 40074016. doi:10.1038/sj.onc.1206436Keywords: estrogen receptor; insulin receptor substrate;
proteasome degradation; cell survival; breast cancerIntroductionInsulin receptor substrates (IRS) 1 and 2, members
of the IRS family of signaling molecules, are major
signaling intermediates of the insulin and insulinlike growth factor I (IGF-I) receptors (IR and IGFIR). In addition, IRS-1 and IRS-2 transmit signals
of many other receptors (e.g., prolactin, growth
hormone, several interleukins, and interferons, a6b4
integrins) (Yenush and White, 1997; Aguirre and
White, 2000; Burks and White, 2001; Shaw, 2001). In
response to ligand binding, IRS substrates are tyrosine
phosphorylated, which results in sequestration of
multiple effector molecules and stimulation of
different signaling pathways (Yenush and White, 1997;