title: The neurofibromatosis type 1 tumor suppressor controls cell growth by regulating signal transducer and activator of transcription-3 activity in vitro and in vivo.
abstract: Neurofibromatosis type 1 (NF1) is a common cancer predisposition syndrome in which affected individuals develop benign and malignant nerve tumors. The NF1 gene product neurofibromin negatively regulates Ras and mammalian target of rapamycin (mTOR) signaling, prompting clinical trials to evaluate the ability of Ras and mTOR pathway inhibitors to arrest NF1-associated tumor growth. To discover other downstream targets of neurofibromin, we performed an unbiased cell-based high-throughput chemical library screen using NF1-deficient malignant peripheral nerve sheath tumor (MPNST) cells. We identified the natural product, cucurbitacin-I (JSI-124), which inhibited NF1-deficient cell growth by inducing apoptosis. We further showed that signal transducer and activator of transcription-3 (STAT3), the target of cucurbitacin-I inhibition, was hyperactivated in NF1-deficient primary astrocytes and neural stem cells, mouse glioma cells, and human MPNST cells through Ser(727) phosphorylation, leading to increased cyclin D1 expression. STAT3 was regulated in NF1-deficient cells of murine and human origin in a TORC1- and Rac1-dependent manner. Finally, cucurbitacin-I inhibited the growth of NF1-deficient MPNST cells in vivo. In summary, we used a chemical genetics approach to reveal STAT3 as a novel neurofibromin/mTOR pathway signaling molecule, define its action and regulation, and establish STAT3 as a tractable target for future NF1-associated cancer therapy studies.
authors.affiliation: Department of Neurology, Mallinckrodt Institute of Radiology, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
authors.forename: Sutapa
authors.initials: S
authors.lastname: Banerjee
authors.forename: Jonathan N
authors.initials: JN
authors.lastname: Byrd
authors.forename: Scott M
authors.initials: SM
authors.lastname: Gianino
authors.forename: Scott E
authors.initials: SE
authors.lastname: Harpstrite
authors.forename: Fausto J
authors.initials: FJ
authors.lastname: Rodriguez
authors.forename: Robert G
authors.initials: RG
authors.lastname: Tuskan
authors.forename: Karlyne M
authors.initials: KM
authors.lastname: Reilly
authors.forename: David R
authors.initials: DR
authors.lastname: Piwnica-Worms
authors.forename: David H
authors.initials: DH
authors.lastname: Gutmann
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D002867:Chromones / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects; D016147:Genes, Tumor Suppressor / Q000502:physiology; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D008297:Male; D051379:Mice; D008819:Mice, Nude; D008822:Mice, Transgenic; D009025:Morpholines / Q000494:pharmacology; D025542:Neurofibromin 1 / Q000235:genetics / Q000502:physiology*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D050796:STAT3 Transcription Factor / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics; D058570:TOR Serine-Threonine Kinases; D014315:Triterpenes / Q000494:pharmacology; D023041:Xenograft Model Antitumor Assays
chemical_list: D002867:Chromones; D004791:Enzyme Inhibitors; D047908:Intracellular Signaling Peptides and Proteins; D009025:Morpholines; D025542:Neurofibromin 1; D050796:STAT3 Transcription Factor; D014315:Triterpenes; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C546842:MTOR protein, human; C546843:mTOR protein, mouse; D017346:Protein Serine-Threonine Kinases; D058570:TOR Serine-Threonine Kinases; C038106:cucurbitacin I