Abstract #4818: IGF-II leads to estrogen receptor phosphorylation via IGF-IR and IR activity

Abstract

Estrogen receptor negative (ER-) tumors are more common in African American (AA) women, when compared to Caucasian women (C). These aggressive tumors are more common at every age and stage of breast cancer and are responsible for the survival disparity observed among AA patients. Thus, our laboratory is investigating how IGF-II activates estrogen receptors without the requirement of estrogen in breast cancer cells derived from breast tumors from AA patients and compared to cells derived from C patients. IGF-II is a fetal growth factor regulated by estrogen that promotes proliferation, prevent apoptosis and regulate energy production by signaling through the IGF-I (IGF-IR) and the Insulin Receptors (IR). We previously demonstrated that IGF-II expression in MCF-7 cells promoted tumor growth and metastasis in nude and SCID mice without estrogen treatment. We also demonstrated that IGF-II activated \#8220;estrogen-regulated genes\#8221; in breast cancer cells grown in serum-free media to promote survival and to prevent mitochondrial membrane depolarization. Our hypothesis is that IGF-II mediates estrogen actions in these cells by phosphorylating/activating ER-\#913; and ER- \#914; to promote estrogen independent growth and control mitochondrial and nuclear function to provide energy and cell survival proteins. In our present study we used two ATCC designated ER- breast cancer cell lines: (CRL-2335) a cell line derived from a tumor obtained from an AA (ER-/PR-) and a cell line from C (HS578t) ER-/PR-. We evaluated the phosphorylation and subcellular localization of ER-\#913; and ER-\#914; using Real-time Polymerase Chain Reaction (RT-PCR) and western blot (WB) analysis. The effects of IGF-II on breast cancer cell survival and proliferation were analyzed using MTT assay. The ability of IGF-II to phosphorylate ER-\#913; and ER- \#914; through the IGF-IR and IR was analyzed using IR and IGF-IR siRNA. Since both cell lines secrete high levels of IGF-II, we also used IGF-II siRNA to evaluate the \#8220;basal phosphorylation\#8221; levels of ER-\#913; and ER- \#914;. Our results show that breast cancer cells designated \#8220;ER-\#913; negative\#8221; express significant levels of ER-\#913; and ER- \#914; in the plasma membrane and in the mitochondria. Furthermore, ER-\#913; and ER-\#914; are phosphorylated and translocate within cell compartments when treated with IGF-II. Inhibition of IGF-II by siRNA significantly reduced the \#8220;basal phosphorylation\#8221; of ER- \#913; and ER- \#914;. Thus, our study demonstrates that IGF-II binding to the IGF-IR and IR leads to the phosphorylation of ER- \#913; and ER- \#914;. Since ER- tumors from AA patients express significantly higher levels of IGF-II, our data supports our hypothesis that IGF-II contributes to the survival disparity observed among AA. This may lead to new treatments to reduce the mortality rates and eliminate the survival disparity observed among AA breast cancer patients.

Citation Information: In: Proc Am Assoc Cancer Res; 2009 Apr 18-22; Denver, CO. Philadelphia (PA): AACR; 2009. Abstract nr 4818.