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Persistent DNA damage inhibits S-phase and G2 progression, and results in apoptosis
D K Orren1, L N Petersen, V A Bohr
1Laboratory of Molecular Genetics, National Institute on Aging, National Institutes of Health, Baltimore, Maryland 21224, USA.
Abstract:
We used genetically related Chinese hamster ovary cell lines proficient or deficient in DNA repair to determine the direct role of UV-induced DNA photoproducts in inhibition of DNA replication and in induction of G2 arrest and apoptosis. UV irradiation of S-phase-synchronized cells causes delays in completion of the S-phase sometimes followed by an extended G2 arrest and apoptosis. The effects of UV irradiation during the S-phase on subsequent cell cycle progression are magnified in repair-deficient cells, indicating that these effects are initiated by persistent DNA damage and not by direct UV activation of signal transduction pathways. Moreover, among the lesions introduced by UV irradiation, persistence of (6-4) photoproducts inhibits DNA synthesis much more than persistence of cyclobutane pyrimidine dimers (which appear to be efficiently bypassed by the DNA replication apparatus). Apoptosis begins approximately 24 h after UV irradiation of S-phase-synchronized cells, occurs to a greater extent in repair-deficient cells, and correlates well with the inability to escape from an extended late S-phase-G2 arrest. We also find that nucleotide excision repair activity (including its coupling to transcription) is similar in the S-phase to what we have previously measured in G1 and G2.
Insights
UV-induced DNA damage directly inhibits DNA replication and cell cycle progression. Repair-deficient cells show magnified effects, highlighting persistent DNA photoproducts
Area of Science:
- Molecular Biology
- Cell Biology
- Genetics
Background:
- DNA damage response is crucial for maintaining genomic integrity.
- UV radiation induces photoproducts that can impede cellular processes.
- Cell cycle checkpoints, including G2 arrest, are activated in response to DNA damage.
Purpose of the Study:
- To elucidate the direct role of UV-induced DNA photoproducts in inhibiting DNA replication.
- To investigate the induction of G2 arrest and apoptosis by UV damage.
- To compare the effects of different photoproducts on DNA synthesis.
Main Methods:
- Utilized Chinese hamster ovary (CHO) cell lines proficient and deficient in DNA repair.
- Synchronized cells to the S-phase before UV irradiation.
- Monitored cell cycle progression, DNA replication, G2 arrest, and apoptosis post-irradiation.
Main Results:
- UV irradiation of S-phase cells caused S-phase delays, G2 arrest, and apoptosis.
- Repair-deficient cells exhibited magnified effects, confirming DNA damage as the initiator.
- Persistence of (6-4) photoproducts significantly inhibited DNA synthesis more than cyclobutane pyrimidine dimers.
- Apoptosis correlated with an inability to exit an extended late S-phase-G2 arrest.
- Nucleotide excision repair activity was consistent across cell cycle phases.
Conclusions:
- Persistent UV-induced DNA photoproducts directly inhibit DNA replication and trigger cell cycle arrest and apoptosis.
- The severity of UV-induced effects is amplified in DNA repair-deficient cells.
- (6-4) photoproducts are more detrimental to DNA synthesis than cyclobutane pyrimidine dimers.