Decreased efficiency of γ-ray-induced DNA double-strand break rejoining in malignant transformants of human bronchial epithelial cells generated by alpha-particle exposure

Abstract

Purpose : To investigate the cytogenetic changes and DNA double-strand break (DSB) rejoining of transformed cell lines generated from human bronchial epithelial cells by α -particle exposure. Materials and methods : Transformed cell lines were derived from the HPV 18-immortalized human bronchial epithelial cell line BEP2D generated by 1.5 Gy of α -particles emitted by a 238 Pu source. Two cell lines, BERP35T1 and BERP35T4, were investigated. Karyotypes were analyzed by trypsin/Giemsa banding. Cell survival was estimated by colony assay. PFGE was used to detect the DNA DSB. mRNA expression was analyzed by RT-PCR. Results : Abnormal chromosomes 2 and 12 with elongated long arm and deletions of chromosomes 2, 12, 13 and 17 were observed in the transformed cell lines. BERP35T4 showed a much higher proportion of polyploid cells (40.5%) compared with parental BEP2D cells and the BERP35T1 cell line (5%). BERP35T1 and BERP35T4 showed a markedly lower capacity for rejoining of γ-ray-induced DNA DSB and increased radio-sensitivity compared with parental BEP2D cells. The analysis of mRNA levels revealed a 2.5- to 6.5-fold down-regulated expression of the DNA repair genes XRCC-2, XRCC-3 and Ku80 in BERP35T1 and BERP35T4 cells. Conclusion : The karyotypic changes of chromosomes 2, 12, 13 and 17 and the deficiency of DSB rejoining could be related to the malignant transformation processing of BEP2D cells initiated by α -particle exposure.