title: Acquired radioresistance of human tumor cells by DNA-PK/AKT/GSK3beta-mediated cyclin D1 overexpression.
abstract: Recurrence is frequently associated with the acquisition of radioresistance by tumors and resulting failures in radiotherapy. We report, in this study, that long-term fractionated radiation (FR) exposures conferred radioresistance to the human tumor cells, HepG2 and HeLa with cyclin D1 overexpression. A positive feedback loop was responsible for the cyclin D1 overexpression in which constitutively active AKT was involved. AKT is known to inactivate glycogen synthase kinase-3beta (GSK3beta), which is essential for the proteasomal degradation of cyclin D1. The resulting cyclin D1 overexpression led to the forced progression of S-phase with the induction of DNA double strand breaks. Cyclin D1-dependent DNA damage activated DNA-dependent protein kinase (DNA-PK), which in turn activated AKT and inactivated GSK3beta, thus completing a positive feedback loop of cyclin D1 overproduction. Cyclin D1 overexpression led to the activation of DNA damage response (DDR) consisted of ataxia telangiectasia mutated (ATM)- and Chk1-dependent DNA damage checkpoint and homologous recombination repair (HRR). Long-term FR cells repaired radiation-induced DNA damage faster than non-FR cells. Thus, acquired radioresistance of long-term FR cells was the result of alterations in DDR mediated by cyclin D1 overexpression. Inhibition of the AKT/GSK3beta/cyclin D1/Cdk4 pathway by the AKT inhibitor, Cdk4 inhibitor or cyclin D1 targeting small interfering RNA (siRNA) suppressed the radioresistance. Present observations give a mechanistic insight for acquired radioresistance of tumor cells by cyclin D1 overexpression, and provide novel therapeutic targets for recurrent radioresistant tumors.
authors.affiliation: Department of Pathology, Institute of Development, Aging and Cancer, Tohoku University, Sendai, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Shimura
authors.forename: S
authors.initials: S
authors.lastname: Kakuda
authors.forename: Y
authors.initials: Y
authors.lastname: Ochiai
authors.forename: H
authors.initials: H
authors.lastname: Nakagawa
authors.forename: Y
authors.initials: Y
authors.lastname: Kuwahara
authors.forename: Y
authors.initials: Y
authors.lastname: Takai
authors.forename: J
authors.initials: J
authors.lastname: Kobayashi
authors.forename: K
authors.initials: K
authors.lastname: Komatsu
authors.forename: M
authors.initials: M
authors.lastname: Fukumoto
mesh_terms: D019938:Cyclin D1 / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D051358:Cyclin-Dependent Kinase 4 / Q000378:metabolism; D004249:DNA Damage; D004260:DNA Repair; D051747:DNA-Activated Protein Kinase / Q000378:metabolism*; D015536:Down-Regulation; D016193:G1 Phase / Q000502:physiology; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism*; D000071679:Glycogen Synthase Kinase 3 beta; D006367:HeLa Cells; D056945:Hep G2 Cells; D006801:Humans; D009369:Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology / Q000532:radiotherapy*; D051058:Oncogene Protein v-akt / Q000378:metabolism*; D011836:Radiation Tolerance; D016196:S Phase / Q000502:physiology; D015398:Signal Transduction
chemical_list: D019938:Cyclin D1; D051747:DNA-Activated Protein Kinase; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; D051058:Oncogene Protein v-akt; C495900:CDK4 protein, human; D051358:Cyclin-Dependent Kinase 4; D038362:Glycogen Synthase Kinase 3