title: Hypoxia sustains glioblastoma radioresistance through ERKs/DNA-PKcs/HIF-1α functional interplay.
abstract: The molecular mechanisms by which glioblastoma multiforme (GBM) refracts and becomes resistant to radiotherapy treatment remains largely unknown. This radioresistance is partly due to the presence of hypoxic regions, which are frequently found in GBM tumors. We investigated the radiosensitizing effects of MEK/ERK inhibition on GBM cell lines under hypoxic conditions. Four human GBM cell lines, T98G, U87MG, U138MG and U251MG were treated with the MEK/ERK inhibitor U0126, the HIF-1α inhibitor FM19G11 or γ-irradiation either alone or in combination under hypoxic conditions. Immunoblot analysis of specific proteins was performed in order to define their anti‑oncogenic or radiosensitizing roles in the different experimental conditions. MEK/ERK inhibition by U0126 reverted the transformed phenotype and significantly enhanced the radiosensitivity of T98G, U87MG, U138MG cells but not of the U251MG cell line under hypoxic conditions. U0126 and ERK silencing by siRNA reduced the levels of DNA protein kinase catalytic subunit (DNA-PKcs), Ku70 and K80 proteins and clearly reduced HIF-1α activity and protein expression. Furthermore, DNA-PKcs siRNA-mediated silencing counteracted HIF-1α activity and downregulated protein expression suggesting that ERKs, DNA-PKcs and HIF-1α cooperate in radioprotection of GBM cells. Of note, HIF-1α inhibition under hypoxic conditions drastically radiosensitized all cell lines used. MEK/ERK signal transduction pathway, through the sustained expression of DNA-PKcs, positively regulates HIF-1α protein expression and activity, preserving GBM radioresistance in hypoxic condition.
authors.affiliation: Department of Biotechnological and Applied Clinical Sciences, University of L'Aquila, I-67100 L'Aquila, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Marampon
authors.affiliation: Department of Biotechnological and Applied Clinical Sciences, University of L'Aquila, I-67100 L'Aquila, Italy.
authors.forename: Giovanni Luca
authors.initials: GL
authors.lastname: Gravina
authors.affiliation: Department of Biotechnological and Applied Clinical Sciences, University of L'Aquila, I-67100 L'Aquila, Italy.
authors.forename: Bianca Maria
authors.initials: BM
authors.lastname: Zani
authors.affiliation: LIPOGEN LLC, Mount Laurel, NJ 08054, USA.
authors.forename: Vladimir M
authors.initials: VM
authors.lastname: Popov
authors.affiliation: Department of Biotechnological and Applied Clinical Sciences, Division of Radiotherapy and Radiobiology Laboratory, San Salvatore Hospital, University of L'Aquila, I-67100 L'Aquila, Italy.
authors.forename: Amato
authors.initials: A
authors.lastname: Fratticci
authors.affiliation: Department of Biotechnological and Applied Clinical Sciences, Division of Radiotherapy and Radiobiology Laboratory, San Salvatore Hospital, University of L'Aquila, I-67100 L'Aquila, Italy.
authors.forename: Manuela
authors.initials: M
authors.lastname: Cerasani
authors.affiliation: Department of Biotechnological and Applied Clinical Sciences, Division of Radiotherapy and Radiobiology Laboratory, San Salvatore Hospital, University of L'Aquila, I-67100 L'Aquila, Italy.
authors.forename: Daniela
authors.initials: D
authors.lastname: Di Genova
authors.affiliation: Department of Biotechnological and Applied Clinical Sciences, Division of Radiotherapy and Radiobiology Laboratory, San Salvatore Hospital, University of L'Aquila, I-67100 L'Aquila, Italy.
authors.forename: Marta
authors.initials: M
authors.lastname: Mancini
authors.affiliation: Department of Biotechnological and Applied Clinical Sciences, University of L'Aquila, I-67100 L'Aquila, Italy.
authors.forename: Carmela
authors.initials: C
authors.lastname: Ciccarelli
authors.affiliation: Medical Oncology, San Salvatore Hospital, University of L'Aquila, I-67100 L'Aquila, Italy.
authors.forename: Corrado
authors.initials: C
authors.lastname: Ficorella
authors.affiliation: Department of Biotechnological and Applied Clinical Sciences, University of L'Aquila, I-67100 L'Aquila, Italy.
authors.forename: Ernesto
authors.initials: E
authors.lastname: Di Cesare
authors.affiliation: Department of Biotechnological and Applied Clinical Sciences, Division of Radiotherapy and Radiobiology Laboratory, San Salvatore Hospital, University of L'Aquila, I-67100 L'Aquila, Italy.
authors.forename: Claudio
authors.initials: C
authors.lastname: Festuccia
mesh_terms: D001549:Benzamides / Q000494:pharmacology; D002070:Butadienes / Q000494:pharmacology*; D015687:Cell Hypoxia / Q000187:drug effects / Q000235:genetics / Q000528:radiation effects; D045744:Cell Line, Tumor; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects / Q000528:radiation effects; D005909:Glioblastoma / Q000188:drug therapy / Q000473:pathology* / Q000532:radiotherapy; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000528:radiation effects; D009570:Nitriles / Q000494:pharmacology*; D010100:Oxygen / Q000378:metabolism*; D011836:Radiation Tolerance / Q000187:drug effects / Q000235:genetics*
chemical_list: D001549:Benzamides; D002070:Butadienes; D004791:Enzyme Inhibitors; C555528:FM19G11; C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D009570:Nitriles; C113580:U 0126; D010100:Oxygen