Re-expression of estrogen receptor alpha in estrogen receptor alpha-negative MCF-7 cells restores both estrogen and insulin-like growth factor-mediated signaling and growth.
Estrogen can increase insulin-like growth factor-I receptor (IGF-IR) and insulin receptor substrate-1 (IRS-1) expression, two key components of IGF-I-mediated signaling. The result is sensitization of breast cancer cells to IGF-I and synergistic growth in the presence of estrogen and IGF-I. We hypothesized that loss of estrogen receptor alpha (ERalpha) would result in reduced IGF-mediated signaling and growth. To test this hypothesis, we examined IGF-I effects in MCF-7 breast cancer cell sublines that have been selected for loss of ERalpha (C4 and C4-12 cells are ERalpha-negative) by long-term estrogen withdrawal. C4 and C4-12 cells had reduced IGF-IR and IRS-1 mRNA and protein expression (compared with MCF-7 cells) that was not inducible by estrogen. Furthermore, C4 and C4-12 cells showed reduced IGF-I signaling and failed to show any growth response to either estrogen or IGF-I. To prove that loss of IGF and estrogen-mediated signaling and growth was a consequence of loss of ERalpha, we re-expressed ERalpha in C4-12 cells by stable transfection with HA-tagged ERalpha. Three independent C4-12 ERalpha-HA clones expressed a functional ERalpha that (a) was down-regulated by estrogen, (b) conferred estrogen-induction of cyclin D1 expression, and (c) caused estrogen-mediated increase in the number of cells in S phase. All of the effects were completely blocked by antiestrogens. Interestingly, ERalpha-HA expression in C4-12 cells did not restore estrogen induction of progesterone receptor expression. However, ERalpha-positive C4-12 cells now exhibited estrogen-induction of IGF-IR and IRS-1 levels and responded mitogenically to both estrogen and IGF-I. These data show that ERalpha is a critical requirement for IGF signaling, and to our knowledge this is the first report of functional ERalpha expression that confers estrogen-mediated growth of an ER-negative breast cancer cell line.
Oesterreich
S
S
Breast Center, Department of Medicine, Baylor College of Medicine, Houston, TX 77030, USA.
Zhang
P
P
Guler
R L
RL
Sun
X
X
Curran
E M
EM
Welshons
W V
WV
Osborne
C K
CK
Lee
A V
AV
D001943:Breast Neoplasms / Q000378:metabolism* / Q000473:pathology; D002455:Cell Division / Q000502:physiology; D019938:Cyclin D1 / Q000096:biosynthesis; D004958:Estradiol / Q000494:pharmacology*; D047628:Estrogen Receptor alpha; D006388:Hemagglutinins / Q000235:genetics; D006801:Humans; D055504:Insulin Receptor Substrate Proteins; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D010750:Phosphoproteins / Q000096:biosynthesis / Q000378:metabolism / Q000502:physiology*; D010766:Phosphorylation / Q000187:drug effects; D017526:Receptor, IGF Type 1 / Q000096:biosynthesis / Q000502:physiology*; D011960:Receptors, Estrogen / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology*; D014162:Transfection; D014407:Tumor Cells, Cultured
D047628:Estrogen Receptor alpha; D006388:Hemagglutinins; C526292:IRS1 protein, human; D055504:Insulin Receptor Substrate Proteins; D010750:Phosphoproteins; D011960:Receptors, Estrogen; D019938:Cyclin D1; D004958:Estradiol; D007334:Insulin-Like Growth Factor I; D017526:Receptor, IGF Type 1