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 2

Different components of the proximal portion of the IGF-1 signaling pathway are activated in pre- and postpubertal Tg mammary glands.

Options: View larger image (or click on image) Download as PowerPoint
Different components of the proximal portion of the IGF-1 signaling path...
(A) Western blot analyses show increased tyrosine phosphorylation of IGF-1R (β-subunit), IRS-1, and Shc in mammary gland extracts from prepubertal Tg mice compared with age-matched WT mice. (B) Western blots of mammary extracts, immunoprecipitated with either anti–IGF-1R or anti–IRS-1, showing increased formation of the IGF-1R/IRS-1 complex in prepubertal Tg compared with WT glands. The total IGF-1R and IRS-1 loading controls for these lanes are shown in the corresponding lanes in A. (C) Western blot analyses reveal increased tyrosine phosphorylation of IGF-1R and Shc, but not IRS-1, in glands from postpubertal Tg compared with WT mice. (D) IGF-1R/IRS-1 complex formation is not increased in postpubertal Tg compared with WT glands. The total IGF-1R and IRS-1 loading controls are shown in the corresponding lanes in C. Each lane represents pooled glands from 4–6 mice of the same age and genotype. Representative Western blots from 3 different pools per genotype/age are shown. Graphs present mean ± SD of densitometric analysis of blots from 5–6 different pools/lanes of each genotype and age. *P < 0.05 versus age-matched WT mice, as determined by Student’s t test.