Long-term estradiol deprivation in breast cancer cells up-regulates growth factor signaling and enhances estrogen sensitivity
Autor: | J. Lawrence, Wei Yue, Richard J. Santen, Masamura A, Berstein L, Zhang Z, Rakesh Kumar, Robert X.-D. Song, Jeng Mh |
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Rok vydání: | 2005 |
Předmět: |
Cancer Research
medicine.medical_specialty Src Homology 2 Domain-Containing Transforming Protein 1 medicine.drug_class Endocrinology Diabetes and Metabolism medicine.medical_treatment Breast Neoplasms Biology Phosphatidylinositol 3-Kinases Endocrinology Epidermal growth factor Internal medicine medicine Tumor Cells Cultured Humans RNA Small Interfering Growth Substances PI3K/AKT/mTOR pathway Adaptor Proteins Signal Transducing Cell Proliferation Mitogen-Activated Protein Kinase Kinases Estradiol Kinase Cell growth Growth factor TOR Serine-Threonine Kinases Estrogen Receptor alpha Signal transducing adaptor protein Cell biology Up-Regulation Oncology Shc Signaling Adaptor Proteins Estrogen Drug Resistance Neoplasm Female Protein Kinases hormones hormone substitutes and hormone antagonists Signal Transduction |
Zdroj: | Endocrine-related cancer. 12 |
ISSN: | 1351-0088 |
Popis: | Deprivation of estrogen causes breast tumors in women to adapt and develop enhanced sensitivity to this steroid. Accordingly, women relapsing after treatment with oophorectomy, which substantially lowers estradiol for a prolonged period, respond secondarily to aromatase inhibitors with tumor regression. We have utilized in vitro and in vivo model systems to examine the biologic processes whereby long-term estradiol deprivation (LTED) causes cells to adapt and develop hypersensitivity to estradiol. Several mechanisms are associated with this response, including up-regulation of estrogen receptor-α (ERα) and the MAP kinase, phosphoinositol 3 kinase (PI3-K) and mammalian target of rapamycin (mTOR) growth factor pathways. ERα is four- to tenfold up-regulated and co-opts a classical growth factor pathway using Shc, Grb-2 and Sos. This induces rapid non-genomic effects which are enhanced in LTED cells. The molecules involved in the non-genomic signaling process have been identified. Estradiol binds to cell membrane-associated ERα, which physically associates with the adaptor protein Shc, and induces its phosphorylation. In turn, Shc binds Grb-2 and Sos, which result in the rapid activation of MAP kinase. These non-genomic effects of estradiol produce biologic effects as evidenced by Elk-1 activation and by morphologic changes in cell membranes. Additional effects include activation of the PI3-K and mTOR pathways through estradiol-induced binding of ERα to the IGF-I and epidermal growth factor receptors. A major question is how ERα locates in the plasma membrane since it does not contain an inherent membrane localization signal. We have provided evidence that the IGF-I receptor serves as an anchor for ERα in the plasma membrane. Estradiol causes phosphorylation of the adaptor protein, Shc and the IGF-I receptor itself. Shc, after binding to ERα, serves as the ‘bus’ which carries ERα to Shc-binding sites on the activated IGF-I receptors. Use of small inhibitor (si) RNA methodology to knockdown Shc allows the conclusion that Shc is needed for ERα to localize in the plasma membrane. In order to abrogate growth factor-induced hypersensitivity, we have utilized a drug, farnesylthiosalicylic acid, which blocks the binding of GTP-Ras to its membrane acceptor protein, galectin 1, and reduces the activation of MAP kinase. We have also shown that this drug is a potent inhibitor of mTOR as an additional mechanism of inhibition of cell proliferation. The concept of ‘adaptive hypersensitivity’ and the mechanisms responsible for this phenomenon have important clinical implications. The efficacy of aromatase inhibitors in patients relapsing on tamoxifen could be explained by this mechanism and inhibitors of growth factor pathways should reverse the hypersensitivity phenomenon and result in prolongation of the efficacy of hormonal therapy for breast cancer. |
Databáze: | OpenAIRE |
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