Specific reduction of insulin receptor substrate 1 (IRS-1) expression in MCF7 cells by RNA interference

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IRS-1 is a major downstream signaling protein for Insulin Receptor (IR) and Insulin-Like Growth Factor Receptor (IGF1-R). IRS-1 conveys the signals from these receptors to the PI3K and MAPK (via SHP2 and Grb2) pathways. In breast cancer, IRS-1 overexpression has been associated with tumor development, hormone-independence and antiestrogen-resistance. These effects have been attributed to increased activity of IRS-1 and potentiation of its downstream signaling to Akt. In MCF-7 breast cancer cells, overexpression of IRS-1 has been shown to reduce estrogen requirements and counteract apoptotic effects of anti-tumor drugs. The aim of this study was to design anti-IRS-1 compounds inhibiting breast cancer cell growth and survival. We tested siRNAs against four different regions of IRS-1 mRNA. Effects of these reagents on IRS-1 protein levels have been studied by Western blot. After four days of treatment two of the siRNAs at a concentration of 100nM produced ∼2-fold decrease in IRS-1 protein expression that was associated with significantly decreased cell survival. The effects of these reagents are now being tested by quantitative real time PCR (QRT-PCR), transcription profiling, and apoptotic assays. Supported by DOE ER63055 and DOD DAMD17-99-1-9407.