title: ERK/GSK3β/Snail signaling mediates radiation-induced alveolar epithelial-to-mesenchymal transition.
abstract: Radiotherapy is one of the major treatment regimes for thoracic malignancies, but can lead to severe lung complications including pneumonitis and fibrosis. Recent studies suggest that epithelial-to-mesenchymal transition (EMT) plays an important role in tissue injury leading to organ fibrosis. To investigate whether radiation can induce EMT in lung epithelial cells and also to understand the potential mechanism(s) associated with this change, rat alveolar type II lung epithelial RLE-6TN cells were irradiated with 8 Gy of (137)Cs γ-rays. Western blot and immunofluorescence analyses revealed a time-dependent decrease in E-cadherin with a concomitant increase in α-smooth muscle actin (α-SMA) and vimentin after radiation, suggesting that the epithelial cells acquired a mesenchymal-like morphology. Protein levels and nuclear translocation of Snail, the key inducer of EMT, were significantly elevated in the irradiated cells. Radiation also induced a time-dependent inactivation of glycogen synthase kinase-3β (GSK3β), an endogenous inhibitor of Snail. A marked increase in phosphorylation of ERK1/2, but not JNK or p38, was observed in irradiated RLE-6TN cells. Silencing ERK1/2 using siRNAs and the MEK/ERK inhibitor U0126 attenuated the radiation-induced phosphorylation of GSK3β and altered the protein levels of Snail, α-SMA, and E-cadherin in RLE-6TN cells. Preincubating RLE-6TN cells with N-acetylcysteine, an antioxidant, abolished the radiation-induced phosphorylation of ERK and altered protein levels of Snail, E-cadherin, and α-SMA. These findings reveal, for the first time, that radiation-induced EMT in alveolar type II epithelial cells is mediated by the ERK/GSK3β/Snail pathway.
authors.affiliation: Department of Radiation Oncology, Wake Forest School of Medicine, Winston-Salem, NC 27157, USA.
authors.forename: Devipriya
authors.initials: D
authors.lastname: Nagarajan
authors.forename: Tahira
authors.initials: T
authors.lastname: Melo
authors.forename: Zhiyong
authors.initials: Z
authors.lastname: Deng
authors.forename: Celine
authors.initials: C
authors.lastname: Almeida
authors.forename: Weiling
authors.initials: W
authors.lastname: Zhao
mesh_terms: D000111:Acetylcysteine / Q000494:pharmacology; D000199:Actins / Q000378:metabolism; D000818:Animals; D015415:Biomarkers / Q000378:metabolism; D002070:Butadienes / Q000494:pharmacology; D015820:Cadherins / Q000378:metabolism; D002460:Cell Line; D058750:Epithelial-Mesenchymal Transition / Q000187:drug effects / Q000528:radiation effects; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism*; D000071679:Glycogen Synthase Kinase 3 beta; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000528:radiation effects; D009570:Nitriles / Q000494:pharmacology; D011650:Pulmonary Alveoli / Q000473:pathology; D017564:Radiation Pneumonitis / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D011839:Radiation, Ionizing; D011878:Radiotherapy / Q000009:adverse effects; D051381:Rats; D020545:Respiratory Mucosa / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology / Q000528:radiation effects; D000071250:Snail Family Transcription Factors; D014157:Transcription Factors / Q000378:metabolism
chemical_list: C541116:ACTA2 protein, human; D000199:Actins; D015415:Biomarkers; D002070:Butadienes; D015820:Cadherins; D009570:Nitriles; C000604450:Snai2 protein, rat; D000071250:Snail Family Transcription Factors; D014157:Transcription Factors; C113580:U 0126; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; C000605508:Gsk3b protein, rat; D038362:Glycogen Synthase Kinase 3; D000111:Acetylcysteine