Impairment of nucleotide excision repair by apoptosis in UV-irradiated mouse cells.
We investigated the relationship between nucleotide excision repair (NER) activity and apoptosis in UV-irradiated cells. Mouse erythroleukemia (MEL) and lymphoma (GRSL) cells exhibited enhanced sensitivity to the cytotoxic effects of UV radiation compared to hamster cell lines, although normal UV-induced hprt mutation frequencies were found. Determination of UV-induced repair replication revealed a limited capacity of MEL and GRSL cells to perform NER consistent with poor removal of cyclobutane pyrimidine dimers and pyrimidine 6-4 pyrimidone photoproducts from transcriptionally active genes during the first 8 h after UV exposure. However, both cyclobutane pyrimidine dimers and pyrimidine 6-4 pyrimidone photoproducts appeared to be processed to almost normal level 24 h after UV treatment. In parallel, we observed that the UV-irradiated MEL and GRSL cells suffered from severe DNA fragmentation particularly 24 h after UV exposure. Taken together, these data indicate a reduced repair of UV-induced photolesions in apoptotic cells, already established at the early onset of apoptosis. To test whether inhibition of repair in cells was due to inactivation of NER or to apoptosis-induced chromatin degradation, we performed in vitro excision assays using extracts from UV-irradiated MEL cells. These experiments showed that the NER capacity during early apoptosis was intact, indicating that slow removal of UV-induced photolesions in apoptotic cells is due to substrate modification (presumably degradation of chromatin) rather than direct inhibition of factors involved in NER.
Vreeswijk
M P
MP
Medical Genetics Centre-Department of Radiation Genetics and Chemical Mutagenesis, Leiden University, The Netherlands.
Westland
B E
BE
Hess
M T
MT
Naegeli
H
H
Vrieling
H
H
van Zeeland
A A
AA
Mullenders
L H
LH
D000818:Animals; D002459:Cell Fusion; D002470:Cell Survival / Q000528:radiation effects; D006224:Cricetinae; D004249:DNA Damage / Q000528:radiation effects*; D053938:DNA Fragmentation; D004260:DNA Repair; D004261:DNA Replication; D004273:DNA, Neoplasm / Q000528:radiation effects*; D004255:Deoxyribodipyrimidine Photo-Lyase / Q000378:metabolism; D006801:Humans; D004915:Leukemia, Erythroblastic, Acute / Q000235:genetics* / Q000378:metabolism / Q000532:radiotherapy; D008223:Lymphoma / Q000235:genetics* / Q000378:metabolism / Q000532:radiotherapy; D051379:Mice; D011740:Pyrimidine Dimers / Q000378:metabolism; D014407:Tumor Cells, Cultured / Q000528:radiation effects; D014466:Ultraviolet Rays
D004273:DNA, Neoplasm; D011740:Pyrimidine Dimers; C098727:pyrimidine(6-4)pyrimidone photolyase; D004255:Deoxyribodipyrimidine Photo-Lyase