title: Estrogen-induced activation of mammalian target of rapamycin is mediated via tuberin and the small GTPase Ras homologue enriched in brain.
abstract: Inhibitors of the mammalian target of rapamycin (mTOR) are currently in clinical trials for the treatment of breast cancer. The mechanisms through which mTOR are activated in breast cancer and the relationship of mTOR activation to steroid hormones, such as estrogen, that are known to influence breast cancer pathogenesis, are not yet understood. Using MCF-7 cells as a model, we found that 17-beta estradiol (E(2)) rapidly increased the phosphorylation of downstream targets of mTOR: p70 ribosomal protein S6 kinase, ribosomal protein S6, and eukaryotic initiation factor 4E-binding protein 1. The phosphoinositide-3-kinase inhibitor, wortmannin, and the mTOR inhibitor, rapamycin, blocked E(2)-induced activation of p70 ribosomal protein S6 kinase. We hypothesized that tuberin and the small GTPase Ras homologue enriched in brain (Rheb), regulators of the mTOR pathway, mediate E(2)-induced activation of mTOR. Consistent with this hypothesis, E(2) rapidly (within 5 minutes) stimulated tuberin phosphorylation at T1462, a site at which Akt phosphorylates and inactivates tuberin. E(2) also rapidly decreased the inactive, GDP-bound form of Rheb. Finally, we found that small interfering RNA down-regulation of endogenous Rheb blocked the E(2)-stimulated proliferation of MCF-7 cells, demonstrating that Rheb is a key determinant of E(2)-dependent cell growth. Taken together, these data reveal that the TSC/Rheb/mTOR pathway plays a critical role in the regulation of E(2)-induced proliferation, and highlight Rheb as a novel molecular target for breast cancer therapy.
authors.affiliation: Department of Medical Oncology, Fox Chase Cancer Center, Philadelphia, PA 19111, USA.
authors.forename: Jane
authors.initials: J
authors.lastname: Yu
authors.forename: Elizabeth Petri
authors.initials: EP
authors.lastname: Henske
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D000230:Adenocarcinoma / Q000378:metabolism* / Q000473:pathology; D001943:Breast Neoplasms / Q000378:metabolism* / Q000473:pathology; D018797:Cell Cycle Proteins; D002455:Cell Division / Q000187:drug effects; D045744:Cell Line, Tumor / Q000187:drug effects; D004958:Estradiol / Q000494:pharmacology; D004967:Estrogens; D005260:Female; D006801:Humans; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D020559:Monomeric GTP-Binding Proteins / Q000037:antagonists & inhibitors / Q000502:physiology*; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors / Q000502:physiology; D009376:Neoplasms, Hormone-Dependent / Q000378:metabolism* / Q000473:pathology; D009479:Neuropeptides / Q000037:antagonists & inhibitors / Q000502:physiology*; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D011494:Protein Kinases / Q000502:physiology*; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D034741:RNA, Small Interfering / Q000494:pharmacology; D000076205:Ras Homolog Enriched in Brain Protein; D019893:Ribosomal Protein S6 Kinases / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D058570:TOR Serine-Threonine Kinases; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins / Q000502:physiology*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D018797:Cell Cycle Proteins; C087000:EIF4EBP1 protein, human; D004967:Estrogens; D009363:Neoplasm Proteins; D009479:Neuropeptides; D010750:Phosphoproteins; C490211:RHEB protein, human; D034741:RNA, Small Interfering; D000076205:Ras Homolog Enriched in Brain Protein; C000624653:TSC2 protein, human; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins; D004958:Estradiol; D011494:Protein Kinases; C546842:MTOR protein, human; C494918:AKT1 protein, human; D051057:Proto-Oncogene Proteins c-akt; D019893:Ribosomal Protein S6 Kinases; D058570:TOR Serine-Threonine Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020559:Monomeric GTP-Binding Proteins