title: Radioresistance in a human laryngeal squamous cell carcinoma cell line is associated with DNA methylation changes and topoisomerase II α.
abstract: Accumulating evidence suggests that changes in methylation patterns may help mediate the sensitivity or resistance of cancer cells to ionizing radiation. The present study provides evidence for the involvement of radioresistance-induced DNA methylation changes in tumor radioresistance. We established radioresistant laryngeal cancer cells via long-term fractionated irradiation, and examined differences in DNA methylation between control and radioresistant laryngeal cancer cells. Interestingly, we found that the promoter-CpG islands of 5 previously identified radioresistance-related genes (TOPO2A, PLXDC2, ETNK2, GFI1, and IL12B) were significantly altered in the radioresistant laryngeal cancer cells. Furthermore, the demethylation of these gene promoters with a DNA methyltransferase inhibitor (5-aza-2'-deoxycytidine) increased their transcription levels. Treatment with 5-aza-2'-deoxycytidine also sensitized the radioresistant laryngeal cancer cells to irradiation, indicating that changes in DNA methylation contributed to their radioresistance. Of the tested genes, the expression and activity levels of TOPO2A were tightly associated with the radioresistant phenotype in our system, suggesting that the hypermethylation of TOPO2A might be involved in this radioresistance. Collectively, our data suggest that radiation-induced epigenetic changes can modulate the radioresistance of laryngeal cancer cells, and thus may prove useful as prognostic indicators for radiotherapy.
authors.affiliation: a Division of Radiation Cancer Research; Korea Institute of Radiological & Medical Sciences ; Seoul , Korea.
authors.forename: Jae-Sung
authors.initials: JS
authors.lastname: Kim
authors.forename: Sun Young
authors.initials: SY
authors.lastname: Kim
authors.forename: Minyoung
authors.initials: M
authors.lastname: Lee
authors.forename: Sung Hyun
authors.initials: SH
authors.lastname: Kim
authors.forename: Sang-Man
authors.initials: SM
authors.lastname: Kim
authors.forename: Eun Ju
authors.initials: EJ
authors.lastname: Kim
mesh_terms: D000951:Antigens, Neoplasm / Q000235:genetics*; D001374:Azacitidine / Q000031:analogs & derivatives / Q000494:pharmacology; D002294:Carcinoma, Squamous Cell / Q000188:drug therapy / Q000235:genetics*; D045744:Cell Line, Tumor; D018899:CpG Islands / Q000187:drug effects / Q000235:genetics; D019175:DNA Methylation / Q000187:drug effects / Q000235:genetics*; D004250:DNA Topoisomerases, Type II / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000235:genetics*; D000077209:Decitabine; D044127:Epigenesis, Genetic / Q000187:drug effects / Q000235:genetics; D006258:Head and Neck Neoplasms / Q000188:drug therapy / Q000235:genetics*; D006801:Humans; D007822:Laryngeal Neoplasms / Q000188:drug therapy / Q000235:genetics*; D011401:Promoter Regions, Genetic / Q000187:drug effects / Q000235:genetics; D011836:Radiation Tolerance / Q000187:drug effects / Q000235:genetics*; D000077195:Squamous Cell Carcinoma of Head and Neck; D014158:Transcription, Genetic / Q000187:drug effects / Q000235:genetics
chemical_list: D000951:Antigens, Neoplasm; D004268:DNA-Binding Proteins; D000077209:Decitabine; D004250:DNA Topoisomerases, Type II; D001374:Azacitidine
keywords: 5-Aza, 5-aza-2′-deoxycytidine; BSA, Bovine Serum Albumin; DNMT, DNA methyltransferases; HRP, Horseradish peroxidase; Hep-2, Human laryngeal squamous cell carcinoma; Human laryngeal squamous cell carcinoma; Methylation; PI, Propidium iodide; Pyrosequencing; RR-Hep-2, Radioresistant Hep-2; RT-PCR, Reverse Transcription-polymerase Chain Reaction; Radioresistance; TOPO2A; TOPO2A, Topoisomerase II α