Insulin-like growth factor 1 attenuates antiestrogen- and antiprogestin-induced apoptosis in ER+ breast cancer cells by MEK1 regulation of the BH3-only pro-apoptotic protein Bim

• Published in: Breast cancer research : BCR 2012-03, Vol.14 (2), p.R52-R52, Article R52
• Main Authors: Periyasamy-Thandavan, Sudharsan, Takhar, Suchreet, Singer, Adam, Dohn, Michael Robert, Jackson, William Hutch, Welborn, April Eve, LeRoith, Derek, Marrero, Mario, Thangaraju, Muthusamy, Huang, Shuang, Schoenlein, Patricia Veronica
• Format: Article
• Language: English
• Subjects: Analysis; Apoptosis; Apoptosis - drug effects; Apoptosis Regulatory Proteins - metabolism; Bcl-2-Like Protein 11; Breast cancer; Breast Neoplasms - drug therapy; Breast Neoplasms - metabolism; Breast Neoplasms - pathology; Cancer cells; Cancer treatment; Care and treatment; Cell Line, Tumor; Enzyme Inhibitors - pharmacology; Enzymes; Estrogen Antagonists - pharmacology; Estrogen Receptor Modulators - pharmacology; Estrogens; Female; Health aspects; Hormone Antagonists - pharmacology; Humans; Insulin-Like Growth Factor I - metabolism; Insulin-Like Growth Factor I - pharmacology; Keratin; MAP Kinase Kinase 1 - antagonists & inhibitors; MAP Kinase Kinase 1 - genetics; MAP Kinase Kinase 1 - metabolism; Membrane Proteins - metabolism; Mifepristone - pharmacology; Monosaccharides; Oxidative Stress - drug effects; Phosphorylation - drug effects; Proto-Oncogene Proteins - metabolism; Reactive Oxygen Species - metabolism; Receptors, Estrogen - metabolism; Tamoxifen - analogs & derivatives; Tamoxifen - pharmacology
• ISSN: 1465-542X; 1465-5411; 1465-542X
• DOI: 10.1186/bcr3153

In this pre-clinical in vitro study conducted in estrogen receptor positive (ER+) breast cancer cells, we have characterized the effects of insulin-like growth factor I (IGF-1) on the cytostatic and cytotoxic action of antiestrogen treatment when used as a single agent or in combination with the antiprogestin mifepristone (MIF). Our goal was to identify new molecular targets to improve the efficacy of hormonal therapy in breast cancer patients that have a poor response to hormonal therapy, in part, due to high circulating levels of unbound insulinIGF-1. IGF-1-mediated effects on cytostasis and apoptotic cell death were determined with cell counts conducted in the presence and absence of trypan blue; enzyme-linked immunosorbent assays to determine the intracellular levels of cleaved cytokeratin 18, a marker of epithelial cancer cell apoptosis; and immunoblot analysis to determine the levels of cleaved poly-ADP ribose polymerase (PARP) and lamin A that result from caspase-dependent apoptosis. Cytotoxicity was further characterized by determination of the levels of reactive oxygen species (ROS) and the percent of mitochondrial membrane depolarization in cell populations treated with the different hormones in the presence and absence of IGF-1. Small molecule inhibitors of the dual-specificity protein kinase MEK1, MEK1 siRNA, Bim siRNA, and vectors overexpressing MEK1 wild type and mutant, dominant negative cDNA were used to identify key IGF-1 downstream prosurvival effectors. IGF-1, at physiologically relevant levels, blocked the cytotoxic action(s) of the antiestrogens 4-hydroxytamoxifen (4-OHT) and tamoxifen (TAM) when used as single agents or in combination with the antiprogestin MIF. The antiapoptotic action of IGF-1 was mediated primarily through the action of MEK1. MEK1 expression reduced the levels of ROS and mitochondrial membrane depolarization induced by the hormonal treatments via a mechanism that involved the phosphorylation and proteasomal turnover of the proapoptotic BH3-only Bcl-2 family member Bim. Importantly, small-molecule inhibitors of MEK1 circumvented the prosurvival action of IGF-1 by restoring Bim to levels that more effectively mediated apoptosis in ER+ breast cancer cells. his study provides strong support for the use of MEK1 inhibitors in combination with hormonal therapy to effectively affect cytostasis and activate a Bim-dependent apoptotic pathway in ER+ breast cancer cells. We discuss that MEK1 blockade may be a particularly effe