Transcription coupled repair deficiency results in increased chromosomal aberrations and apoptotic death in the UV61 cell line, the Chinese hamster homologue of Cockayne's syndrome B

Transcription coupled repair (TCR), a special sub-pathway of nucleotide exc ision repair (NER), removes transcription blocking lesions rapidly from the transcribing strand of active genes. In this study, we have evaluated the importance of the TCR pathway in the induction of chromosomal aberrations a nd apoptosis in isogenic Chinese hamster cell lines, which differ in TCR ef ficiency. AA8 is the parental cell line, which is proficient in the genome overall repair of UV-C radiation induced 6-4 photoproducts (6-4 PP) and the repair of cyclobutane pyrimidine dimer (CPD) from the transcribing strand of active genes. UV61 cells (hamster homologue of human Cockayne's syndrome (CS) group B cells) originally isolated from AA8, exhibit proficient repai r of 6-4 PP but are deficient in CPD removal by the TCR pathway. Upon UV-C irradiation of cells in GI-phase, UV61 showed a dramatic increase in apopto tic response as compared to AA8 cells. Abolition of TCR by treatment with a lpha -amanitin (an inhibitor of RNA polymerase II) in AA8 cells also result ed in an elevated apoptotic response Like that observed in UV61 cells treat ed with UV alone. This suggests that the lack of TCR is largely responsible for increased apoptotic response in UV61 cells. Furthermore, the chromosom al aberrations and sister chromatid exchange (SCE) induced by UV were also found to be higher in UV61 cells than in TCR proficient AA8 cells. This stu dy shows that the increased chromosomal aberrations and apoptotic death in UV61 cells is due to their inability to remove CPD from the transcribing st rand of active genes and suggests a protective role for TCR in the preventi on of both chromosomal aberrations and apoptosis induced by DNA damage. Fur thermore, flow cytometry analysis and time-course appearance of apoptotic c ells suggest that the conversion of UV-DNA damage into chromosomal aberrati ons precedes and determines the apoptotic process. (C) 2001 Elsevier Scienc e B.V. All rights reserved.