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Mutat Res. 2008 Apr 2;640(1-2):1-7. doi: 10.1016/j.mrfmmm.2007.11.010. Epub 2007 Dec 17.

Resistance to ultraviolet-induced apoptosis in DNA repair deficient growth arrested human fibroblasts is not related to recovery from RNA transcription blockage.

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Department of Microbiology, Institute of Biomedical Sciences, Universidade de São Paulo, Av. Prof. Lineu Prestes 1374, 05508-900 São Paulo, Brazil.


The impact of ultraviolet (UV-C) photoproducts on apoptosis induction was investigated in growth arrested (confluent) and proliferating human primary fibroblasts. Confluent fibroblasts were more resistant to UV-C-induced apoptosis than proliferating cells, and this was observed for normal human cells and for cells from patients with Cockayne and trichothiodystrophy syndromes, deficient in transcription coupled repair. This resistance was sustained for at least seven days and was not due to DNA repair efficiency, as the removal of CPDs in the genome was similar under both growth conditions. There was no correlation between reduced apoptosis and RNA synthesis recovery. Following UV-C treatment, proliferating and confluent fibroblasts showed a similar level of RNA synthesis inhibition and recovery from transcription blockage. These results support the hypothesis that the decrease of DNA replication, in growth arrested cells, protects cell from UV-C-induced apoptosis, even in the presence of DNA lesions.

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