title: Signal transducer and activator of transcription 3 is required for abnormal proliferation and survival of TSC2-deficient cells: relevance to pulmonary lymphangioleiomyomatosis.
abstract: Tumor suppressor complex TSC1/TSC2 represents a key negative regulator of mammalian target of rapamycin (mTOR)-S6 kinase 1 signaling. Mutational inactivation of TSC1 or TSC2, linked to a rare lung disease, lymphangioleiomyomatosis (LAM), manifests as neoplastic growth of smooth-muscle (SM)-like cells and cystic destruction of the lungs that induces loss of pulmonary function. However, the precise mechanisms of abnormal cell growth in LAM remain uncertain. Here, we demonstrate increased signal transducer and activator of transcription (STAT) 3 expression, phosphorylation, and nuclear localization in SM-like cells in LAM lungs and in TSC2-null xenographic tumors. Treatment of TSC2-null tumors with mTOR inhibitor rapamycin attenuated STAT3 expression and phosphorylation. Increased STAT3 level and activation were also observed in LAM-dissociated (LAMD) cell cultures compared with normal human bronchus fibroblasts (HBFs) from LAM patients. Although interferon (IFN)-gamma inhibited proliferation of HBFs, IFN-gamma treatment had little effect on proliferation of LAMD and TSC2-null cells. Re-expression of TSC2 or treatment with rapamycin inhibited IFN-gamma-induced STAT3 phosphorylation and synergized with IFN-gamma in inhibiting TSC2-null and LAMD cell proliferation. Reduction of STAT3 protein levels or activity using specific small interfering RNA or inhibitory peptide, respectively, decreased proliferation and induced apoptosis in TSC2-null and LAMD cells and sensitized cells to growth-inhibitory and proapoptotic effects of IFN-gamma. Collectively, our data demonstrate that STAT3 activation is required for proliferation and survival of cells with TSC2 dysfunction, that STAT3 impedes growth-inhibitory and proapoptotic effects of IFN-gamma, and that TSC2- and rapamycin-dependent inhibition of STAT3 restores antiproliferative effects of IFN-gamma. Thus, STAT3 may provide a novel therapeutic target for diseases associated with TSC1/TSC2 dysfunction.
authors: Pulmonary, Allergy, and Critical Care Division, Airways Biology Initiative, Department of Medicine, University of Pennsylvania, TRL, Room 1214, 125 South 31st St., Philadelphia, PA 19104, USA. goncharo@mail.med.upenn.edu
authors: Elena A
authors: EA
authors: Goncharova
authors: Dmitry A
authors: DA
authors: Goncharov
authors: Gautam
authors: G
authors: Damera
authors: Omar
authors: O
authors: Tliba
authors: Yassine
authors: Y
authors: Amrani
authors: Reynold A
authors: RA
authors: Panettieri
authors: Vera P
authors: VP
authors: Krymskaya
mesh_terms: D049109:Cell Proliferation; D002470:Cell Survival / Q000502:physiology*; D002478:Cells, Cultured; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D008171:Lung Diseases / Q000473:pathology* / Q000503:physiopathology; D008203:Lymphangiomyoma / Q000473:pathology* / Q000503:physiopathology; D010766:Phosphorylation; D011494:Protein Kinases / Q000187:drug effects; D012129:Respiratory Function Tests; D050796:STAT3 Transcription Factor / Q000235:genetics / Q000502:physiology*; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000502:physiology*
chemical_list: D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; C000624653:TSC2 protein, human; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins; D011494:Protein Kinases; C546842:MTOR protein, human; D058570:TOR Serine-Threonine Kinases; D020123:Sirolimus