Abnormal retention of X-irradiated ataxia-telangiectasia fibroblasts in G2 phase of the cell cycle: cellular RNA content, chromatin stability and the effects of 3-aminobenzamide.

We have addressed three aspects of the abnormal sensitivity of SV40 transformed ataxia-telangiectasia (A-T) fibroblasts to X-irradiation, namely: (a) the radiogenic perturbations in cell-cycle traverse analysed by flow cytometry; (b) the involvement of 3-aminobenzamide-sensitive processes in cellular recovery in terms of viability and release from G2 + M phase delay; and (c) the functional and structural integrity of cells delayed in G2 + M phase using acridine orange as a probe for cellular RNA content and chromatin structure. We report that A-T cells show a dose-dependent and survival-related abnormal retention in G2 + M phase due to the lack of a recovery process, despite the capacity of such cells to synthesize ribosomal RNA and maintain the structural integrity of chromatin. Evidence is presented that the recovery process is dependent upon poly(ADP ribosyl)ation activity in both normal and A-T cells except that in the latter cell type recovery potential is rapidly saturated in terms of X-ray dose.