Developmental stage determines estrogen receptor alpha expression and non-genomic mechanisms that control IGF-1 signaling and mammary proliferation in mice
Jie Tian, … , Claudio J. Conti, Robin Fuchs-Young
Jie Tian, … , Claudio J. Conti, Robin Fuchs-Young
Published December 19, 2011
Citation Information: J Clin Invest. 2012;122(1):192-204. https://doi.org/10.1172/JCI42204.
View: Text | PDF
Research Article Oncology

Developmental stage determines estrogen receptor alpha expression and non-genomic mechanisms that control IGF-1 signaling and mammary proliferation in mice

Abstract

Insulin like growth factor–1 (IGF-1) stimulates increased proliferation and survival of mammary epithelial cells and also promotes mammary tumorigenesis. To study the effects of IGF-1 on the mammary gland in vivo, we used BK5.IGF-1 transgenic (Tg) mice. In these mice, IGF-1 overexpression is controlled by the bovine keratin 5 promoter and recapitulates the paracrine exposure of breast epithelium to stromal IGF-1 that is seen in women. Studies have shown that BK5.IGF-1 Tg mice are more susceptible to mammary tumorigenesis than wild-type littermates. Investigation of the mechanisms underlying increased mammary cancer risk, reported here, revealed that IGF-1 preferentially activated the PI3K/Akt pathway in glands from prepubertal Tg mice, resulting in increased cyclin D1 expression and hyperplasia. However, in glands from postpubertal Tg mice, a pathway switch occurred and activation of the Ras/Raf/MAPK pathway predominated, without increased cyclin D1 expression or proliferation. We further showed that in prepubertal Tg glands, signaling was mediated by formation of an ERα/IRS-1 complex, which activated IRS-1 and directed signaling via the PI3K/Akt pathway. Conversely, in postpubertal Tg glands, reduced ERα expression failed to stimulate formation of the ERα/IRS-1 complex, allowing signaling to proceed via the alternate Ras/Raf/MAPK pathway. These in vivo data demonstrate that changes in ERα expression at different stages of development direct IGF-1 signaling and the resulting tissue responses. As ERα levels are elevated during the prepubertal and postmenopausal stages, these may represent windows of susceptibility during which increased IGF-1 exposure maximally enhances breast cancer risk.

Authors

Jie Tian, Thomas R. Berton, Stephanie H. Shirley, Isabel Lambertz, Irma B. Gimenez-Conti, John DiGiovanni, Kenneth S. Korach, Claudio J. Conti, Robin Fuchs-Young

×

Figure 4

Expression of ERα in NMuMG cells induces a switch in the IGF-1–initiated signaling pathway that affects cyclin D1 expression.

Options: View larger image (or click on image) Download as PowerPoint
Expression of ERα in NMuMG cells induces a switch in the IGF-1–initiated...
Treatment of NMuMG cells with either IGF-1 or vehicle, and transfection with a functional ERα expression vector (pRSV-ERα) or the empty (control) vector (pGL2 basic), as described in Methods. (A) Western blot analysis shows that treatment with IGF-1 following transfection with pRSV-ERα results in increased phosphorylation of Akt and reduced phosphorylation of Erk1/2. *P < 0.05 versus untreated control cells in SFM; #P < 0.05 versus IGF-1–treated cells without transfected vector (SFM) or transfected with pGL2 basic (control) vector, as determined by ANOVA and Student’s t test. (B) Time course of the effects of IGF-1 treatment and transfection of ERα on cyclin D1 expression and Akt phosphorylation. Western blot analysis of cell extracts shows that treatment with 40 ng/ml IGF-1 and pRSV-ERα significantly increases cyclin D1 expression and phosphorylation of Akt by 6 hours. Graphs represent mean ± SD of densitometric analysis of 3 independent Western blot experiments. A representative Western blot is shown. *P < 0.05 versus 0 hours, as determined by ANOVA and Student’s t test.