Evidence that camptothecin-induced aberrations in the G2 phase of cell cycle of Chinese hamster ovary (CHO) cell lines is associated with transcription
Author(s)
Date Issued
2000
Type
article
Volume
452
Issue
2
Start Page
189
End Page
195
Abstract
It is widely accepted that camptothecin (CPT) is an S-dependent genotoxin. In this study, we aimed to elucidate the 'puzzling' induction of chromosomal damage by CPT in the G2 phase of CHO cells, where no DNA synthesis is expected, focusing the attention on the possible role of the ongoing RNA synthesis, supposed to cause the conversion of CPT-single stranded cleavage complexes spaced closely on opposite DNA strands into DNA double strand breaks (DSB's) by the action of traversing RNA polymerase. CHO AA8 and its parental mutant EM9 cell lines were pre-treated with α-amanitin, which prevents transcription to pre-m-RNA and challenged cells with CPT for the last hour in culture to evaluate whether G2-CPT-induced aberrations would have been reduced or abolished in the absence of RNA synthesis compared with G2-CPT treatment alone. The results obtained indicated a marked and significant reduction of aberration yields, to almost the control values (α- amanitin alone) when inhibition of RNA synthesis was substantial (3 h total α-amanitin). Partial inhibition of RNA synthesis (2 h total α-amanitin) slightly reduced the CPT-induced aberrations yield only at the high dose- level employed of CPT (20 mM). This finding strongly supports the hypothesis that CPT-single stranded cleavages complexes spaced closely on opposite DNA strands are converted into DNA double strand breaks by the action of traversing RNA polymerase. (C) 2000 Elsevier Science B.V.