RNAi-mediated silencing of insulin receptor substrate 1 (IRS-1) enhances tamoxifen-induced cell death in MCF-7 breast cancer cells - RNAi

RNAi-mediated silencing of insulin receptor substrate 1 (IRS-1) enhances tamoxifen-induced cell death in MCF-7 breast cancer cells
26 January 2006
Gregory Cesarone , Cecilia Garofalo , Marc T. Abrams , Olga Igoucheva , Vitali Alexeev , Kyonggeun Yoon , Eva Surmacz, Eric Wickstrom
Journal of Cellular Biochemistry
Article
RNAi-mediated silencing of insulin receptor substrate 1 (IRS-1) enhances tamoxifen-induced cell death in MCF-7 breast cancer cells
Gregory Cesarone 1, Cecilia Garofalo 2 4, Marc T. Abrams 1, Olga Igoucheva 3, Vitali Alexeev 3, Kyonggeun Yoon 1 3, Eva Surmacz 2 4, Eric Wickstrom 1 2 *
1Department of Biochemistry and Molecular Biology, Thomas Jefferson University, Philadelphia, Pennsylvania 19107
2Kimmel Cancer Center, Thomas Jefferson University, Philadelphia, Pennsylvania 19107
3Department of Dermatology and Cutaneous Biology, Thomas Jefferson University, Philadelphia, Pennsylvania 19107
4Sbarro Institute for Cancer Research and Molecular Medicine, Center for Biotechnology, Temple University, Philadelphia, Pennsylvania 19122

email: Eric Wickstrom (eric@tesla.jci.tju.edu)
*Correspondence to Eric Wickstrom, Department of Biochemistry and Molecular Biology, Thomas Jefferson University, Philadelphia, Pennsylvania 19107.
Funded by:
DOE; Grant Number: ER63055
DOD; Grant Number: DAMD-17-03-1-0655
NIH; Grant Number: AR049229
Keywords
apoptosis ? IRS-1 ? signaling ? siRNA ? tamoxifen
Abstract
Insulin receptor substrate 1 (IRS-1) is a major downstream signaling protein for insulin and insulin-like growth factor I (IGF-I) receptors, conveying signals to PI-3K/Akt and ERK1/2 pathways. In breast cancer, IRS-1 overexpression has been associated with tumor development, hormone-independence and antiestrogen-resistance. In part, these effects are related to potentiation of IRS-1/PI-3K/Akt signaling. In estrogen sensitive breast cancer cell lines, tamoxifen treatment reduces IRS-1 expression and function; consequently, inhibiting IRS-1/PI-3K signaling. We tested whether anti-IRS1 siRNA could inhibit growth and survival of estrogen-sensitive MCF-7 breast cancer cells, when used alone or in combination with TAM. Our results indicated: (a) out of four tested anti-IRS1 siRNAs, two siRNAs reduced IRS-1 protein by approximately three-fold in both growing and IGF-I-stimulated cells without affecting a closely related protein, IRS-2; (b) these effects paralleled IRS1 mRNA downregulation by approximately three-fold, measured by quantitative real time-polymerase chain reaction; (c) action of anti-IRS1 siRNAs induced the apoptotic response, observed by altered mitochondrial membrane potential coupled with downregulation of NF-B target Bcl-xL and reduced cell viability; (d) anti-IRS1 siRNA treatment enhanced the cytotoxic effects of TAM by 20%. In summary, anti-IRS1 RNAi strategy could become a potent tool to induce breast cancer cell death, especially if combined with standard TAM therapy. J. Cell. Biochem. 98: 440-450, 2006.
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