title: RNAi-mediated silencing of insulin receptor substrate 1 (IRS-1) enhances tamoxifen-induced cell death in MCF-7 breast cancer cells.
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-kappaB target Bcl-xL and reduced cell viability; (d) anti-IRS1 siRNA treatment enhanced the cytotoxic effects of TAM by approximately 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.
authors.affiliation: Department of Biochemistry and Molecular Biology, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA.
authors.forename: Gregory
authors.initials: G
authors.lastname: Cesarone
authors.forename: Cecilia
authors.initials: C
authors.lastname: Garofalo
authors.forename: Marc T
authors.initials: MT
authors.lastname: Abrams
authors.forename: Olga
authors.initials: O
authors.lastname: Igoucheva
authors.forename: Vitali
authors.initials: V
authors.lastname: Alexeev
authors.forename: Kyonggeun
authors.initials: K
authors.lastname: Yoon
authors.forename: Eva
authors.initials: E
authors.lastname: Surmacz
authors.forename: Eric
authors.initials: E
authors.lastname: Wickstrom
mesh_terms: D001943:Breast Neoplasms / Q000188:drug therapy / Q000378:metabolism*; D016923:Cell Death / Q000187:drug effects*; D005260:Female; D006801:Humans; D055504:Insulin Receptor Substrate Proteins; D010750:Phosphoproteins / Q000737:chemistry / Q000494:pharmacology*; D010766:Phosphorylation / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics* / Q000494:pharmacology*; D011960:Receptors, Estrogen / Q000037:antagonists & inhibitors; D015398:Signal Transduction / Q000187:drug effects*; D013629:Tamoxifen / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
chemical_list: C526292:IRS1 protein, human; D055504:Insulin Receptor Substrate Proteins; D010750:Phosphoproteins; D034741:RNA, Small Interfering; D011960:Receptors, Estrogen; D013629:Tamoxifen; D017346:Protein Serine-Threonine Kinases