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

Cancer Res. 2001 Aug 1;61(15):5771-7.


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.

Publication types

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

MeSH terms

  • Breast Neoplasms / metabolism*
  • Breast Neoplasms / pathology
  • Cell Division / physiology
  • Cyclin D1 / biosynthesis
  • Estradiol / pharmacology*
  • Estrogen Receptor alpha
  • Hemagglutinins / genetics
  • Humans
  • Insulin Receptor Substrate Proteins
  • Insulin-Like Growth Factor I / pharmacology*
  • Phosphoproteins / biosynthesis
  • Phosphoproteins / metabolism
  • Phosphoproteins / physiology*
  • Phosphorylation / drug effects
  • Receptor, IGF Type 1 / biosynthesis
  • Receptor, IGF Type 1 / physiology*
  • Receptors, Estrogen / biosynthesis
  • Receptors, Estrogen / genetics
  • Receptors, Estrogen / physiology*
  • Signal Transduction / physiology*
  • Transfection
  • Tumor Cells, Cultured


  • Estrogen Receptor alpha
  • Hemagglutinins
  • IRS1 protein, human
  • Insulin Receptor Substrate Proteins
  • Phosphoproteins
  • Receptors, Estrogen
  • Cyclin D1
  • Estradiol
  • Insulin-Like Growth Factor I
  • Receptor, IGF Type 1