Abstract
Lymphangioleiomyomatosis (LAM), a rare pulmonary disorder, manifests as an abnormal neoplastic growth of smooth muscle-like cells within the lungs. Mutational inactivation of tumor suppressor tuberous sclerosis complex 2 (TSC2) in LAM constitutively activates the mammalian target of rapamycin (mTOR)/p70 S6 kinase 1 (S6K1) signaling pathway and promotes neoplastic growth of LAM cells. In many cell types, type I interferon β (IFNβ) inhibits proliferation and induces apoptosis through signal transducers and activators of transcription (STAT)-dependent and STAT-independent signaling pathways, one of which is the mTOR/S6K1 signaling pathway. Our study shows that IFNβ is expressed in LAM tissues and LAM-derived cell cultures; however, IFNβ attenuates LAM-derived cell proliferation only at high concentrations, 100 and 1000 U/ml (IC50 value for IFNβ is 20 U/ml compared with 1 U/ml for normal human mesenchymal cells, human bronchus fibroblasts and human airway smooth muscle cells). Likewise, IFNβ only attenuates proliferation of smooth muscle TSC2-null ELT3 cells. Analysis of IFNβ signaling in LAM cells showed expression of IFNβ receptor α (IFNβRα) and IFNβRβ, activation and nuclear translocation of STAT1, and phosphorylation of STAT3 and p38 mitogen-activated protein kinase (MAPK), but IFNβ had little effect on S6K1 activity. However, the re-expression of TSC2 or inhibition of mTOR/S6K1 with rapamycin (sirolimus) augmented antiproliferative effects of IFNβ in LAM and TSC2-null ELT3 cells. Our study demonstrates that IFNβ-dependent activation of STATs and p38 MAPK is not sufficient to fully inhibit proliferation of cells with TSC2 dysfunction and that TSC2-dependent inhibition of mTOR/S6K1 cooperates with IFNβ in inhibiting human LAM and TSC2-null ELT3 cell proliferation.
Footnotes
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This work was supported by National Institutes of Health grants 2R01-HL071106 (to V.P.K.), HL55301 (to R.A.P.), HL64063 (to R.A.P.), by National Institute of Environmental Health Sciences grant ES0135080 (to R.A.P. and V.P.K.), and by The LAM Foundation (to V.P.K. and E.A.G.).
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R.A.P. and V.P.K. contributed equally to this work.
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ABBREVIATIONS: LAM, lymphangioleiomyomatosis; TSC, tuberous sclerosis complex; mTOR, mammalian target of rapamycin; STAT, signal transducer and activator of transcription; MAPK, mitogen-activated protein kinase; HBF, human bronchus fibroblast; BrdU, 5-bromo-2′-deoxyuridine; PDGF, platelet-derived growth factor; SM, smooth muscle; GFP, green fluorescent protein; IFN, interferon; IFNβR, interferon β receptor; FITC, fluorescein isothiocyanate; RT-PCR, reverse-transcriptase polymerase chain reaction; TUNEL, terminal deoxynucleotidyl transferase dUTP nick-end labeling; HASM, human airway smooth muscle; pEGFP, plasmid encoding for enhanced green fluorescent protein; ANOVA, analysis of variance; S6K1, p70 S6 kinase 1; JAK, Janus tyrosine kinase; RAPA, rapamycin; SB203580, 4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)-1H-imidazole.
- Received August 17, 2007.
- Accepted December 18, 2007.
- The American Society for Pharmacology and Experimental Therapeutics
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