Hydroxyurea reduces DNA replication by nucleotide deprivation, whereas UV damage generates DNA photoproducts that directly block replication fork progression. We show that the low fidelity class Y polymerase Pol η is recruited to proliferating cell nuclear antigen at replication forks both by hydroxyurea and UV light. Under nucleotide deprivation, Pol η allows cells to accumulate at the G1/S boundary by facilitating slow S-phase progression and promotes apoptosis. Normal cells consequently enter apoptosis at a faster rate than Pol η-deficient cells. Coincident with hydroxyurea-induced S-phase delay, Pol η-deficient cells undergo more replication fork breakage and accumulate more foci of the Mre11/Rad50/Nbs1 complex and phosphorylated histone H2AX. We conclude that under conditions of nucleotide deprivation, Pol η is required for S-phase progression but is proapoptotic. However, as Pol η is reported to require higher nucleotide concentrations than class B replicative polymerases, its recruitment by hydroxyurea requires it to function under suboptimal conditions. Our results suggest that hydroxyurea-induced apoptosis occurs at the G1/S boundary and that initiation of the S-phase requires greater nucleotide concentrations than does S-phase progression.
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The work described here was supported by an NIEHS Grant 1 RO1 ES 8061 and an NINDS Grant 5R01NS052781 (to JEC) and American Cancer Society RSG-00-036-04-CNE (to CLL). We are also grateful to the XP Society, Poughkeepsie, NY, for their continued support and encouragement to one of us (JEC). Dr D Karentz conducted this work while on sabbatical with additional support from the Lily Drake Cancer Research Fund from the University of San Francisco. We are also grateful to the Molecular Diagnostics Core, UCSF Cancer Center for assistance in immunofluorescence.
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de Feraudy, S., Limoli, C., Giedzinski, E. et al. Pol η is required for DNA replication during nucleotide deprivation by hydroxyurea. Oncogene 26, 5713–5721 (2007). https://doi.org/10.1038/sj.onc.1210385
- Pol η
- H2AX, hydroxyurea